WATER QUALITY ASSESSMENT FOR SUSTAINABLE AGRICULTURE
(Tully-Murray Rivers Catchment Area and Granite Creek on the Atherton Tablelands)
February 2004
ACTFR Report No. 03/18
Natural Resource Management Board (Wet Tropics) Inc., Innisfail
Project No. 2012015
Prepared by John Faithful and Wendy Finlayson*
Australian Centre for Tropical Freshwater Research
James Cook University
Townsville Qld 4811
Phone: (07) 47814262
Fax: (07) 47815589
Email: [email protected]
*Cardwell Shire Catchment Management
P.O. Box 929
Tully Qld 4854
Phone: (07) 40665594
Fax: (07) 4066 5594
Email: [email protected]
NRM Wet Tropics Sustainable Agriculture – ACTFR Report No. 03/18, February 2004
ACKNOWLEDGEMENTS
THE AUTHORS WISH TO ACKNOWLEDGE THE FOLLOWING GROUPS AND INDIVIDUALS FOR THEIR
INVOLVEMENT AND INPUT INTO THIS PROJECT:
NRM WET TROPICS, PARTICULARLY BRAD DORRINGTON AND DIANA O’DONNELL
PROJECT TECHNICAL COMMITTEE
ALAN HOOPER
ALAN MITCHELL
DAVID HAYNES
DAVID HINE
JON BRODIE
DON POLLOCK
JOHN ARMOUR
JOHN REGHANZANI
LEX COGLE
SIMON O’DONNELL
TULLY-MURRAY RIVERS CATCHMENT
THE LANDHOLDERS
GRANITE CREEK CATCHMENT
JOHN ARMOUR
LEX COGLE
TRACY WHITING
V. RASIAH
HELEN ADAMS
JANE GREER
MARK KEATING
MIKE DWYER
THE LANDHOLDERS
ACTFR LAB STAFF
Australian Centre for Tropical Freshwater Research
JENNY COOK
SARAH THORNTON
VIVIEN DANIS
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EXECUTIVE SUMMARY
This report summarizes the findings of a relatively intensive survey of paddock scale farm runoff after rain
events in tropical north Queensland. The study is considered unique and assesses the runoff from banana and
cane paddocks, in watersheds within two distinct regions of north Queensland, i.e. the Tully-Murray Rivers
catchment and the Granite Creek catchment south-west of Mareeba on the Atherton Tablelands (including an
urban drainage site in Mareeba).
The project concept was initiated in February 2001, with NRM Wet Tropics leading the consultation between a
number of landholder groups, specific interest groups (e.g. SUNFISH), wet tropics catchment groups, and
federal and state government departments. The project was conceived by the Tully banana growers local
producer association which expressed a strong interest in determining the extent of nutrient and sediment
losses from their farms during wet seasons. The banana farmers provided financial support and submitted a
successful proposal for funding to the Banana Sectional Group of the QFVG, which was later incorporated into
an NRM Board proposal for NHT funding.
Infrastructure works commenced in late 2001, but were not completed until late 2002. Water quality sampling
began in the 2002/2003 wet season in the Tully-Murray Rivers and Granite Creek catchments and included.
The 2002/2003 wet season was a very poor wet season, with both the Tully-Murray and Mareeba region only
receiving 67% of their annual average rainfall.
There were three levels of farm investigation: primary sites with crump weirs installed to allow for continuous
monitoring of discharge and meteorological data; secondary sites that were manually gauged and sampled less
regularly than the primary sites, and; random sites that were sampled opportunistically.
The level of investigation was considered insufficient to provide some of the outcomes that were proposed for
this report because of the poor wet season and the lack of any detailed site specific runoff data (i.e. nutrient and
flux concentrations from each farm, which could have been used to provide specific management advice to
individual farms). Nevertheless, one of the notable outcomes from the project was the development of on-farm
infrastructure and a community-minded water quality awareness that will allow for the continuation of this
kind of monitoring to better gauge the effectiveness of land management practices in reducing nutrient and soil
losses from agricultural landuses.
The concentrations of nitrogen, phosphorus and TSS encountered in this study were often very high in
comparison to those that are expected for a tropical stream or river, especially during drainage events resulting
from high rainfall periods, and as such may be are typical of runoff from some intensive agricultural landuse
activities.
Banana Farms
The TSS and TP concentrations in the paddock drainage from the banana farms were high. Concentrations
ranged from 7 to 7250mg/L (median 37mg/L) and 21 to 5000µg P/L (median 240µg P/L) respectively.
Nitrogen concentrations were also considered high ranging from 1200 to 21000µg N/L (median 2500µg N/L),
with nitrate (150 to 19500µg N/L, median 1610µg N/L) being the most dominant N form. High nutrient and
solids concentrations were associated with peak discharge events. The lower median concentrations reflected
the dominance of sampling on the falling stage of the storm event hydrograph, i.e. after peak runoff had passed
through the drainage channel.
BOD was detected and concentrations were higher than that for the cane farms, although values fell below
concentrations reported for other farm studies (e.g. Pearson et al. In Review). The occurrence of BOD in the
runoff was attributed to the small drainage paddocks and the higher mass of organic material (trash) around the
crops, and possibly from sap derived from the banana plants that may be washed into the runoff via stem flow
during rainfall events.
Consideration of crop management strategies, such as ensuring row direction (with respect to slope) was
appropriate and vegetating the crop inter-rows to allow grasses and various weeds to grow, would seem
essential to minimise sediment, and therefore, TP loss to the drains and ultimately receiving waters.
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Cane Farms
The cane farm paddocks did not have the high range of TSS or P concentrations in drainage waters as noted for
the banana farms. This was considered primarily due to a general lack of slope of the paddocks, a greater
‘canopy’ coverage minimizing soil exposure (particularly in the time of the year that the study was focused)
and because fertilisation is generally occurs once a year during the dry season. However, runoff data revealed
that nitrogen was lost in much more significant concentrations than that reported for the banana farms, and
comprised mostly nitrate. The total P concentration range was 20 to 1400µg P/L (median 60µg P/L), 1 to
1840mg/L (median 15mg/L) for TSS, and 100 to 15000µg N/L (median 3900µg N/L) for TN, with 100 to
13000µg N/L (median 3200µg N/L) for nitrate.
Nutrient and sediment concentration peaks in the channel flow occurred during the peak drainage periods after
storm rainfall events.
As observed for the banana farms, nitrate was very prominent in paddock runoff to the drain in the latter stages
of a storm hydrograph due primarily to the amount of nitrate available in the soil and sub-surface groundwater,
which is characteristic of the Wet Tropics soils under cane and banana farms.
Urban Lakes
The urban lakes data from the Bicentennial Lakes in Mareeba were considered useful in that they provided a
measure of comparison with the farm runoff data. Their catchment source was from Basalt Creek in the
Granite Creek catchment with additional urban stormwater inputs during storm events. The nutrient and TSS
concentrations were indicative of a small receiving waterway that was notionally impounded with exerted a
high degree of dilution through its catchment in contrast to being a source, e.g. the farm paddocks (TP range
10 to 600µg P/L (median 40µg P/L), TSS range 1 to 323mg/L (median 10mg/L), TN range 300 to 1800µg N/L
(median 500µg N/L) and nitrate range 10 to 390µg N/L (median 100µg N/L)). Unfortunately there was no
gauging information to put the water quality data into a flow perspective.
Nutrient and Sediment Flux
The more intensive sampling of the paddock drain from Banana Farm 2148 provided the best estimate of
nutrient and sediment loss from a single intense rainfall period for the project. Between April 18 and April 30,
estimated fluxes of nitrogen (9.2kg N per hectare), phosphorus (0.80 kg P per hectare) and suspended solids
(126 kg per hectare) were transported from the study paddock, calculated from flow-weighted mean
concentration data. If the single fertiliser application prior to the event is considered, then the estimated
nitrogen loss during the late April storm event equated to 21% of that preceding application. The lack of any
perceived exhaustion of nitrate during this event suggests that a considerable surplus of nitrate existed in the
soil.
The rapid exhaustion of TP, FRP and TSS in the runoff through the event indicated that there was either a
finite supply of these resources or that these elements were only mobilized from the soils during specific event
rainfall intensities and runoff velocities. High rainfall intensity and the resultant effects of rainfall on the soil
surface provided the energy to entrain and mobilize the surface sediment, which resulted in elevated P and TSS
in paddock runoff (and was exacerbated by higher paddock slopes). Like N, FRP was applied as a fertilizer
through fertigation at a rate of 0.65kg per hectare, and by spreader at a rate of 7.77kg P per hectare. For the
single event of the size experienced over April 19 to May 5, it can be estimated that the estimated P loss during
the late April storm represented 10% of the prior application.
However, the estimates for TN, TP and TSS may be considered a gross underestimate if losses are much more
significant in the rising stage and hydrograph peaks of the large storm events. As the rising stage of the
hydrograph was not sampled, even higher concentrations of N, P and TSS may have occurred, which also
would result in an underestimation of the flux of nutrients and sediment from the farm.
This project has given rise to infrastructure that is in now place, especially in the context of the primary sites,
which can be utilised in the future. Out of this project, specific recommendations for future direction are
provided that should only add value to the results from this single year study:
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NRM Wet Tropics Sustainable Agriculture – ACTFR Report No. 03/18, February 2004
o
Maintain the monitoring through another two wet seasons (at least), to cover the very dry
monsoon season experienced in 2002/2003. The study period was one of the driest wet seasons
on record, and any data collected in such a period is likely to be considered anomalous or extreme
until it can be compared with a longer term data set.
o
Focus on specific storm events at the primary sites, intensively sampling through the storm
hydrograph, to reliably determine nutrient and TSS fluxes from the farm paddocks. The
implementation of autosamplers, or rising stage samplers, is crucial in the capture of the rising
and event peak stages of the hydrograph that will provide more accurate load measurements.
This improved data set will allow for more rigorous data analysis correlating nutrient and TSS
losses with soil types, fertiliser type and application rates, watershed slope, farm history, etc.
o
There is a requirement to increase the level of monitoring in the Granite Creek region, which will
also be serviced by a better wet season. Although rainfall is lower on the Tablelands, it is still
imperative that structures (e.g. autosamplers, landholder catchment co-ordinators) and monitoring
strategies are in place to reliably collect samples in both the primary and secondary sites.
It is also considered a requirement that flow gauging systems be installed to the urban lakes
systems so that load estimates can be determined for comparison with the farm paddocks (at least
at the outfall point). The catchment area for the lakes is considerably larger than that for the farm
paddocks used in this study, but nevertheless that data will provide an estimate of nutrient and
TSS flux in wet tropics urban runoff.
o
Investigate the possibility that the primary site farms consider utilising other similar paddocks that
can be used for different management strategies (e.g. different fertiliser application rates,
application strategies) that can be compared with respect to nutrient and TSS concentration (and
loads) in event runoff and productivity.
o
Implement a groundwater-monitoring component so that an assessment of the sub-surface source
of nutrients can be taken into account in the loss of nutrients from the farm paddock and allow for
the measurement of a water balance. If further study requires a thorough estimate nutrient
balance for the paddock to be undertaken, then measurement of N-volatilisation will be necessary.
o
Consider additional landuse types in the monitoring program, such as cattle grazing (beef and
dairy), forestry, and other horticulture crops (e.g. pineapple, paw-paws, etc.).
o
As banana and cane agriculture utilise biocides to control weeds and pests, then it is necessary to
monitor for these compounds to determine whether they are being lost from the farm paddock,
and if so, how much is lost in storm event runoff. Pesticide and herbicide residues are reaching
downstream and marine environments and are becoming more of a national issue, with many
current environmental monitoring programs detecting various biocides of interest (e.g. diuron,
atrazine, etc. in cane production, and gromoxone, fusilade and diathene, etc. in banana
production) in the sediments of floodplain waterways and river mouths.
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ACRONYMS AND GLOSSARY OF TERMS
ACTFR
Australian Centre for Tropical Freshwater Research
AMTD
Adopted Middle Thread Distance. The distance in kilometers from the most downstream
point of a particular water course.
ANZECC and ARMCANZ
Australian and New Zealand Environment and Conservation Council
BOD
Biochemical Oxygen Demand
BoM
Bureau of Meteorology
BRICMA
Barron River Integrated Catchment Management Association
cumec
cubic metres per second (a cubic metre is equivalent to one thousand litres)
FRP
Filterable Reactive Phosphorus, sometimes simply referred to as orthophosphate or
phosphate
kg
kilogram
L
litre
m
metre
mg
milligram (one-thousandth of a gram)
mL
millilitre (one thousandth of a litre)
ML
megalitre (one million litres)
mm
millimetre (one-tenth of a centimetre)
N
Nitrogen
NH3
Ammonia
NOX
Oxidised inorganic forms of nitrogen (the sum of nitrate and nitrite; used primarily
because nitrite does not generally comprise a significant concentration in comparison to
nitrate)
NR&M
Queensland Department of Natural Resources and Mines
NRM Wet Tropics
Natural Resources Management Board (Wet Tropics) Inc.
P
Phosphorus
QFVG
Queensland Fruit and Vegetable Growers
TSS
Total suspended solids
µg
microgram (one-millionth of a gram)
µm
micron (one-millionth of a metre)
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µS/cm
micro-Siemens per centimetre, a unit measure for conductivity (a measure of the water’s
ability to conduct an electrical current, where conductance increases with the amount of
dissolved salts in the water)
Adsorption
The attachment, or attraction, of ions or compounds to the surface of a solid, namely in
this context, a soil particle
Available Nutrient The amount of nutrient in the soil that can be taken up by a plants. In the case of this
study available nutrients are nitrate, nitrite and ammonia (nitrogen source) and
filterable reactive phosphorus (sometimes referred to as orthophosphate)
(phosphorus source)
Catchment
The total area, or portion of that area, drained by a river or other waterbody
Denitrification The biochemical formation of gaseous nitrogen and or oxides of nitrogen from nitrate or
nitrite by some bacteria during anaerobic respiration. This process only occurs in
anaerobic or hypoxic conditions, i.e. when oxygen supply is limited as in a waterlogged
soil.
Ecosystem
A community of organisms and their physical environment that interact as an ecological
unit
Flux
In the context of this report, it is defined as the amount of material (e.g. N, P, and TSS)
that has been carried in a discharge over a given period of time.
Hydrograph
A particular flow event, i.e. relating flow volume per unit time.
Hypoxic
Refers to an aquatic environment that is low in oxygen, but not anaerobic or anoxic.
Median
Middle value in a data set, where exactly half of the data set will have greater values than
that quantity. In contrast to the mean or average value of the data set, the median is used
where the data set is not normally distributed, i.e. non-parametric.
Nitrification
The biochemical oxidation of ammonia to nitrate and then to nitrite by certain bacteria.
This process is strictly aerobic, or requires the presence of an oxygenated environment.
Respiration
A heterotrophic metabolism that utilises oxygen for substrate oxidation, i.e. a metabolic
process that consumes oxygen from the water body.
Watershed
An area or a region that is bordered by a divide and from which water drains to a
particular watercourse or body of water.
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TABLE OF CONTENTS
1.
INTRODUCTION ....................................................................................................................... 1
1.1
2.
BACKGROUND ................................................................................................................................ 1
LOCATION ................................................................................................................................. 3
2.1
3.
FARM SITE SELECTION................................................................................................................... 7
METHODS................................................................................................................................... 8
3.1
3.2
3.3
3.4
4.
CLIMATE ........................................................................................................................................ 8
FLOW GAUGING AND RAINFALL DATA LOGGING ......................................................................... 9
SAMPLING AND SAMPLE PRE-TREATMENT.................................................................................... 9
SAMPLE ANALYSES ...................................................................................................................... 12
RESULTS AND DISCUSSION................................................................................................ 12
4.1
4.2
4.3
4.4
5
PHYSICO-CHEMICAL INDICATORS ............................................................................................... 13
BIOCHEMICAL OXYGEN DEMAND ............................................................................................... 18
TOTALS SUSPENDED SOLIDS ........................................................................................................ 19
NUTRIENTS ................................................................................................................................... 22
FOCUS ON A MAJOR EVENT .............................................................................................. 27
5.1
ESTIMATE OF NUTRIENT AND SOLIDS FLUX FROM BANANA FARM NO. 2148 ............................ 29
6
WATER QUALITY DATA COMPARISON ......................................................................... 31
7.
FERTILISER USAGE .............................................................................................................. 33
8.
CONCLUSION .......................................................................................................................... 35
8.1
8.2
8.3
8.4
BANANA FARMS........................................................................................................................... 36
CANE FARMS ................................................................................................................................ 37
URBAN LAKES.............................................................................................................................. 37
NUTRIENT AND SEDIMENT FLUX ................................................................................................. 37
9.
RECOMMENDATIONS .......................................................................................................... 38
10.
REFERENCES .......................................................................................................................... 40
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1.
INTRODUCTION
This report summarizes the findings of a relatively intensive survey of paddock scale farm runoff after
rain events in tropical north Queensland. The study is considered unique and assesses the runoff from
banana and cane paddocks, in watersheds within two distinct regions of north Queensland, i.e. the TullyMurray Rivers catchment and the Granite Creek catchment south-west of Mareeba on the Atherton
Tablelands (including an urban drainage site in Mareeba).
A number of studies have been conducted in north Queensland measuring nutrient and sediment export
from agricultural watersheds on a catchment scale (e.g. Cogle et al. In Reviewa; Bramley and Roth 2002;
Johnson et al. 2001; Cogle et al. 2000; Bramley and Muller 1999; Hunter and Walton 1997; Hunter 1996;
Hunter et al. 1996), a sub-catchment scale (e.g. Pearson et al. In Review) and farm scale (e.g. Cogle et al.
In Reviewb; Hunter and Armour 2001, Moody et al. 1996; Prove and Hicks 1991; Prove 1988). Their
conclusions have established that intensive agricultural landuse activities, such as cropping and grazing,
result in elevated nutrient and sediment discharges to receiving waters. The level of impact to receiving
waters in the tropics is governed by the climatic variability encountered along the north Queensland coast,
the definitive wet and dry seasonality of the tropics and the intensity, timing and reliability of wet season
rainfall, geology and soil type, topography and vegetation cover.
With the co-operation of a number of growers, Cardwell Shire Catchment Centre, the Barron River
Integrated Catchment Management Centre and NR&M (Mareeba and Innisfail) staff, banana and cane
farms were utilised to provide a basis for comparison within and between catchments. The study was
conducted in the 2002/03 wet season with sampling primarily occurring during rainfall and corresponding
runoff events in the drainage channels downslope of the study paddocks. There were three levels of farm
investigation: primary sites with crump weirs installed to allow for continuous monitoring of discharge
and meteorological data; secondary sites that were manually gauged and sampled less regularly than the
primary sites, and; random sites that were sampled opportunistically.
The project was only established as a one-year pilot project but was considered to be an initial step
towards the development of a cost effective, regional water quality monitoring system based upon
landholders self-assessment of key parameters identified.
1.1
Background
The project concept was initiated in February 2001, with NRM Wet Tropics leading the consultation
between a number of landholder groups, specific interest groups (e.g. SUNFISH), wet tropics catchment
groups, and federal and state government departments. The project was conceived by the Tully banana
growers local producer association which expressed a strong interest in determining the extent of nutrient
and sediment losses from their farms during wet seasons. This followed community presentations by
Alan Mitchell (AIMS) and Nicola Wright (DNRM Waterwatch) that illustrated an increase in nutrient
levels in Wet Tropics waterways between 1997 and 2001. The banana farmers were very willing to
finance such a project and submitted a successful proposal for funding to the Banana Sectional Group of
the QFVG, which was later incorporated into the NRM Board proposal for NHT funding.
One of the driving issues behind the development of this project focused on the effects of land based
human activities on the quality of riverine discharge to the Great Barrier Reef Lagoon, which has a direct
link to the natural resource management in the Wet Tropics Region. The long-term objective of the
project was to develop a network of strategically placed sites across the Wet Tropics Region that would
allow efficient, cost-effective and continuous monitoring of key water quality indicators. This monitoring
was expected to produce scientifically accurate data to document the effects of catchment activities and
landuse in different regions of the Wet Tropics. In line with the NRM Board’s policy of community
involvement, major stakeholder groups were invited to be involved in the design and operations of the
project. Primary production groups, particularly banana and sugar cane growers, and broad-acre mixed
farming groups were involved, which also included their active participation in the monitoring and
sampling, and the provision of information enabling an evaluation of their farm practices.
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The proposal submitted to NHT in February 2001 sought funding to conduct a literature review, establish
drainage and gauging infrastructure at farms in the Wet Tropics, provide training for catchment coordinators and land-holders in the focus catchments, and provide for the analyses of samples collected
from the farms.
A system of rigorous on-farm water quality monitoring by landholders and catchment co-ordinators in
conjunction with storm events was utilised to determine the effect on water quality of various human
activities, particularly primary industries and certain farm management practices. Four landuse activities
were studied: bananas (Tully-Murray and Granite Creek), sugar cane (Tully-Murray and Granite Creek),
mixed agriculture (Granite Creek) and urban development (Granite Creek), with sites established within
each activity area. The focus was the water quality of drainage derived from specific farm paddocks, i.e.
small areas of the farm to establish specific nutrient and sediment losses during rainfall events.
Landholders and catchment co-ordinators were trained in water quality monitoring and sample collection
to ensure that any data generated was of a reliable quality.
The information provided by the results of this project could then lead to an evaluation and improvement
of farming practices, and a review of industry codes of practice. As industry groups and landholders
provided the impetus for this project and were involved in its development and implementation, there was
a high likelihood that results would lead to on-ground changes in farm management. Farm inputs data
were made available for inclusion in the data analysis.
The aims of this project were:
1.
To review all relevant completed monitoring and research and baseline data.
2.
Establish long-term water quality monitoring sites at banana, cane, and mixed cropping farms.
3.
Facilitate a skilled technical approach to water quality monitoring using community group
members, including training catchment co-ordinators and landholders in accurate and efficient
water quality monitoring and assessment techniques.
4.
Determine the effect of various landuse activities on water quality discharges from a farm
paddock, i.e. assess the status of water quality on a seasonal basis coinciding with crop
management events.
5.
Present the results of any research and monitoring in a clear and precise format, which has
relevance and meaning to the land based stakeholders involved.
6.
Provide feedback to primary producers, industry, and other land, water and vegetation managers
on performance of best practices.
Approval for the project was granted in October 2001, well after the planned commencement date for the
project, which had been listed as July 2001. The lateness of notification meant that it was not possible for
the infrastructure to be established before the 2001/02 wet season.
A technical and operational steering committee was established in November 2001 to facilitate the project
development and requested a project extension to allow for the twelve-month study period to be July
2002 to June 2003. The committees convened separately, or together, when required, with all parties
committed to giving this project a high priority in their individual work plans. The technical advisory
committee also established the general plan for the project, which was to take a three-tiered structure
approach incorporating different levels of landholder and farm involvement. Primary sites were to have
gauged weir structures and data logging systems (which included rainfall) that would be installed by
NR&M, secondary sites that would have flow structures with gauging boards and random sites that would
generally be restricted to drainage channels. The level of effort required by the landholders would be
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associated with their farm status, whereby primary sites would be intensively monitored and random sites
limited to occasional or opportunistic sampling. Prior to the 2002 wet season, ACTFR and the Tully
Catchment Co-ordinator, developed training programs for the catchment groups in the Tully-Murray
Rivers and Granite Creek regions, as well as field data sheets, sampling procedures, landholder diary
sheets and information folders for the landholders. NRM Wet Tropics developed nomination forms for
landholder property inclusion in the project and Landholder Agreements (contracts) that ensured the
landholders anonymity (landholder agreements were only necessary for the Tully-Murray catchment
farms).
Site selections were finalised in August 2002. Weir infrastructure was finalised at all sites by March
2003, but most sites were able to collect samples in the first rainfall event in late January as the wet
season began late. Presentations of the data were conducted on three occasions: March 26, April 9, and
September 26, 2003 to the technical advisory committee and the landholders. Individual landholder
reports were presented to the landholders on September 26, 2003.
2.
LOCATION
The two study catchments are located in the Wet Tropics on the north-east coast of Queensland, Australia
(Figure 2.1).
The Tully River is a component of the Tully-Murray Rivers Catchment Area (Figure 2.2) and covers an
area of approximately 1683km2 (Brodie et al. 2001). The Tully River is Australia’s least variable river
with respect to annual discharge, making it relatively unique to Australian river systems renown for their
extreme variability (Mitchell et al. 2001). The Tully River originates in the Cardwell Range, much of
which is in the Wet Tropics World Heritage Area (65%). Within the Tully River Catchment
approximately 15% is under sugar cane agriculture, 1.5% under horticulture (of which the largest
component is banana farming) and 19% under grazing land (Brodie et al. 2001). Sugar cane agriculture
dominates the floodplain, but in recent years banana agriculture has expanded throughout the floodplain.
Mean annual rainfall within the catchment is 2855mm, with mean annual runoff of 1954mm/m2 and mean
annual discharge of 3.3km3 (3.3 x 106ML). Issues specific to this catchment are that of erosion, which is
driven by the high propensity of flooding, particularly with respect to overbank flows in the middle and
lower reaches (Brodie et al. 2001). There has been significant alteration to the hydrological regime in the
floodplain and pesticides and high nutrients loads (particularly nitrate) are evident in the lower reaches of
the catchment (Brodie et al. 2001).
The Murray River catchment has an area of 1107km2 and also originates in the Cardwell Range. Almost
half its area comprises grazing (520km2) and the other half, Wet Tropics World Heritage Area (518km2)
(Brodie et al. 2001). Other landuses included ~60km2 cane farming and less than 10km2 of horticulture,
although increases in cane and horticulture areas within the catchment since 2000 are likely. Mean
annual rainfall is 2098mm, which is very similar to the Tully River catchment, although the mean annual
runoff of 958mm/m2 and discharge of 1.1km3 are approximately half and a third, respectively, of that of
the Tully River. Four sites (three cane and one banana farm) were located within the lower Murray River
catchment.
The Granite Creek catchment (Figure 2.3) is located as a western tributary of the Barron River catchment.
The area of the Barron catchment is 2902km2, of which the Granite Creek catchment is 188km2 (Cogle et
al. 2000). Granite Creek is in the distinct Atherton Tablelands portion of the Barron River catchment,
and has its confluence with the Barron River at the township of Mareeba. The Granite Creek catchment is
moderately developed with respect to urbanisation (2%), agriculture (23%, comprised of irrigated mixed
cropping such as sugarcane and horticulture) and grazing (6.3%). The amount of forested area
encompasses 47.9% of the catchment. The mean annual rainfall for Mareeba is 910mm, which is less
than half that for the Tully-Murray Rivers catchment.
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There is a water supply reservoir (Lake Tinaroo) that provides a drinking water supply, but is
predominantly an irrigation supply, especially for the mixed cropping on the Tablelands (such as the
farms within the Granite Creek catchment).
The study utilised the Bicentennial Lakes system (Mareeba) to provide an indication of the water quality
of a series of urban lakes. These lakes are fed by the Basalt Creek catchment and eventually discharge
into Granite Creek. The lakes system are comprised of a series of three small lagoons, and the sites were
located on stormwater drains (predominantly urban runoff) at one entry point feeding into the Lakes
(Costin Street) and at the exit point (Keeble Street). No flow gauging facilities are located on the lakes,
which made it impossible to determine inflow and outflow volumes during the study.
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Figure 2.1 A map of the north east coast of Queensland, Australia, showing the locations of the major
river catchments. Of particular note are the Tully-Murray Rivers catchment (shaded in blue)
and the Barron River catchment (shaded in yellow) in which Granite Creek is a sub-system
(Map source: Cardwell Shire Catchment Centre 2003).
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Figure 2.2 A cadastral map of the Tully-Murray Rivers Catchment area showing the variety of landuses
within the catchment and the regions where the farms utilised in this study were located
(denoted by the red circles). Individual farms locations could not be provided due to the
landholder confidentiality agreement. State Forest is coloured light green and agricultural
zones light yellow (Map source: Cardwell Shire Catchment Centre 2003).
TULLY
Hull River
Tully River
N
Murray River
0
2.5
5
kilometres
Figure 2.2 A map of the Granite Creek catchment showing the location of the banana farm (site 1), cane
farm (sites 2 and 3) and the Bicentennial Lakes (sites 4 and 5) used in this study. The
landholders did not enter into a confidentiality agreement having been previously involved
with research programs with NR&M (Mareeba) staff (Map source: BRICMA, 2004).
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2.1
Farm Site Selection
Site locations within the Tully-Murray Rivers catchment have not been provided because landholders
entered into confidentiality agreements assuring their anonymity. As a consequence water quality data is
grouped into landuse type and catchment region for assessment in this report.
Once farms were nominated in the Tully-Murray Rivers catchment, the Tully catchment co-ordinator
(Wendy Finlayson) and NR&M hydrographer (Alan Hooper) visited the sites taking site photographs and
gathering additional information. On the basis of these site visits and general paddock characteristics
(e.g. the proportion of drainage that may be allocated to the paddock, access, potential for infrastructure
installation, etc.) the sites were either selected or rejected. Farm status (e.g. primary, secondary or
random) was applied on the basis of the value of the farm paddock to the project and the commitment of
the landholder to conduct sampling during rainfall events. Of the sixteen sites selected in the TullyMurray Rivers catchment, four sites were located within the Murray River catchment, and twelve sites
within the Tully River catchment.
The number of sites in the Granite Creek catchment region was limited to four. These comprised a cane
farm (a secondary site), banana farm (a primary site) and two urban sites located within the Bicentennial
Lakes system in Mareeba. Like the agriculture sites, the lakes system (an impoundment comprised of
three linked storage lagoons) was located within the Granite Creek catchment. It is estimated that
approximately one megalitre moves through the lakes on a daily basis (NR&M Mareeba, pers. comm.,
2003) sourced primarily from irrigation supply derived from Tinaroo Dam for the farms of the
surrounding agricultural region and catchment runoff.
It was a requirement of the landholders’ selection into the project that they provided a thorough
description of their sites. For the Tully-Murray Rivers catchment landholders, this requirement was an
element of the participation agreement that they entered into. Each landholder was required to provide an
accurate estimate of paddock area, slope, soil type, and information regarding specific recent paddock
history and fertiliser application data. This information is provided in Table 2.1. Note that specific
nitrogen and phosphorus sources are provided in Table 2.1 rather than the generic fertiliser brand names
(these sources are listed in the individual farmer reports). In the case of the Tully-Murray Rivers
catchment sites, aerial photographs obtained from MapInfo held by the Cardwell Shire Catchment
Management Centre were used to illustrate the paddock, land contour and soil characteristics.
Additional information for each of the specific farms is contained in the individual landholder reports.
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Table 2.1
A list of the cane and banana farms from the Tully-Murray Rivers and Granite Creek
catchment areas and their allocated farm status, survey paddock area (ha), estimated
catchment slope, predominant soil type (with other evident soils listed in brackets) and
predominant forms of nitrogen and phosphorus in the fertiliser applications to the paddock.
Farm Status
Area
(ha)
Estimated
Catchment
Slope (%)
0204
Primary
13.5
<5
Warrami, Hillview Fine
Variant, Thorpe, Feluga Red
Variant, Malbon and Hewitt
Ammonia, nitrate and
phosphate
0227
Random
19
<5
Thorpe, Malbon and Hewitt
Unlisted N source, No P
0827
Random
92
<5
Coom (Thorpe and Tully)
Urea, ammonia and phosphate
(incl. mill mud)
1205
Random
19.1
<5
Warrami (Bulgun)
Urea, ammonia and phosphate
1505
Random
18.5
<5
Tully
Not provided
2020
Secondary
13.6
<5
Tully and Mossman
Urea, ammonia and phosphate
Sturiale
Secondary
15 - 20
<5
Arriga
Urea, ammonia and phosphate
Banana
0247
Random
5/6
<5
Mossman
Unlisted N and P source
0307
Secondary
10
<5
Thorpe and SC
Nitrate, ammonia and
phosphate
0923
Random
7.2
<5
Mossman and Tully
Ammonia and phosphate, and
other unlisted N and P sources
0948
Random
8
<5
Mossman and Tully
Urea, ammonia and nitrate
1530
Random
3.7
<5
Coom and Tully
Urea, nitrate, ammonia and
phosphate
1551
Random
1.6
20
Dingo and Utchee
Nitrate and ammonia, but no P
1609
Primary
2.8
<5
Mossman and Innisfail
Urea and ammonia, but no P
2050
Secondary
1/2
30
Galmara and MH
Unlisted N and P source
2119
Random
6.4
10
Jarra
Urea, ammonia, nitrate, and
phosphate (incl. molasses)
2148
Primary
2
30
Dingo
Nitrate, ammonia and
phosphate
TF1
Primary
12
<5
Walkamin Ferrosol (Red
basaltic)
Not provided
Urban
Costin
Random
n/a
n/a
n/a
n/a
Keeble
Random
n/a
n/a
n/a
n/a
Site ID
Soil Type
(as per Cannon et al. 1992)
Primary Fertiliser
Nutrients
Cane
3.
METHODS
3.1
Climate
The wet season rainfall data for the study period for the Tully-Murray Rivers catchment area and
Mareeba (representing the Granite Creek catchment area) indicated that the twelve month period between
July 2002 and June 2003 was very dry in comparison with annual expectations. Plots of monthly rainfall
data for the period July 2002 to June 2003 with average monthly rainfall data for central locations (e.g.
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Tully and Mareeba) in both study regions are presented in Figures 3.1 and 3.2. In both cases, the sum of
the monthly rainfall for this period was 66.7% of the expected average rainfall total.
3.2
Flow Gauging and Rainfall Data Logging
Flow gauging was conducted at each primary and secondary site, using various techniques. Flow data
loggers were provided at the primary sites, whereas gauging boards were used to provide information on
channel flow whilst sampling at the secondary sites.
Information pertaining to the gauging structures for each of the primary sites is provided in the individual
landholder reports. Flow data collated during this study are also listed in each of the landholder reports.
Summary flow data collected from each of the primary sites is shown in Figure 3.3. Despite obvious
spatial differences, channel flow responses across each of the primary sites coincided across the sites and
catchments.
A list of the gauged flow volumes through the primary sites over the course of the sampling period is
shown in Table 3.1.
Table 3.1
Discharge data for each of the flow structures installed at the primary cane and banana sites
in Tully-Murray Rivers catchment area and Granite Creek during the study period.
Farm Label
Plot Area
(ha)
Period of Flow
Gauging
Discharge
Volume (ML)
0307 – Banana (Tully)
1609 – Banana (Tully)
2148 – Banana (Tully)
0204 – Cane (Tully)
TF1 – Banana (Tablelands)
~10
2.8
2
13.5
12
29-03-03 – 30-04-03
12-01-03 – 27-05-03
27-11-02 – 30-04-03
11-01-03 – 30-04-03
22-12-02 – 07-05-03
23.7
9.3
8.1
53.3
1.04*
* Discharge data gaps were present between 23-12-02 and 02-01-03, and between 3-01-03 and 14-01-03;
therefore discharge volumes are considered to be an underestimate of total discharge.
Rainfall data for each of the primary sites is provided in each of the specific farm reports. There was
good correlation between the gauged rainfall data collected at the weir sites and that collected
individually by the landholders.
3.3
Sampling and Sample Pre-Treatment
The landholders, catchment co-ordinators and NR&M staff were trained in sampling techniques during a
field workshops held in Tully (October 21, 2001) and at Mareeba (October 24, 2001), with supplemental
notes provided to the landholders in a project package (Appendix A).
Each landholder (or catchment co-ordinator in certain circumstances) collected water samples during
rainfall events that resulted in weir overflow or baseflow conditions. The primary sites in each activity
area were subject to more comprehensive sampling on a regular and events-based regime, while the
secondary and random sites were subject to less frequently sampling. Catchment co-ordinators and
landholders were requested to monitor water quality and collect samples during specific weather and farm
management events, such as ‘first flush’ runoff after heavy rainfall, cultivation, fertiliser application,
harvesting, etc.
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Figure 3.1 Monthly rainfall data for Tully (Tully Post Office, BoM Station No. 032070) for July 2002
to June 2003. Included in the graph are average monthly rainfall totals (red stalks) for that
station (collected since 1983).
800
Total Monthly Rainfall (mm)
700
600
500
400
300
200
100
0
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
July 2002 to June 2003
Tully RF
Figure 3.2 Monthly rainfall data for Mareeba (Mareeba Post Office, BoM Station No. 0031039) for July
2002 to June 2003. Included in the graph are average monthly rainfall totals (red stalks) for
that station (collected since 1952).
Total Monthly Rainfall (mm)
300
250
200
150
100
50
0
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
July 2002 to June 2003
Mareeba RF
Portable field meters (WTW Portable 340i, Weilheim, Germany) were purchased for the project so that
physico-chemical water quality (pH, dissolved oxygen, temperature and conductivity) measurements of
the drainage flow could be collected during sampling at the primary and secondary sites. The Tully
Catchment Co-Ordinator retained one of the field meters and was able to collect physico-chemical data
during sample collection she undertook. Two additional meters were provided for the use of the primary
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site landholders and were rotated amongst the landholders on a regular basis. The meters were calibrated
prior to, and immediately after, delivery to a landholder by the catchment co-ordinator utilising
methodology and QA strategies provided by ACTFR.
Figure 3.3 Gauged flow data for the primary banana and cane sites in the Tully-Murray Rivers and
Granite Creek catchments.
0.35
Banana - Tablelands
Banana - Tully - 2148
Banana - Tully - 1609
Banana - Tully - 0307
Cane - Tully - 0204
0.30
Flow (cumec)
0.25
0.20
0.15
0.10
0.05
0.00
01 Dec 02
01 Jan 03
01 Feb 03
01 Mar 03
01 Apr 03
01 May 03
01 Jun 03
Date
Samples collected by the landholders in the Tully-Murray Rivers catchment area were returned to the
Catchment Co-ordinator who filtered the samples for total suspended solids (TSS), froze the filter
membranes and nutrient samples, and in the case of biochemical oxygen demand (BOD), returned the
samples to the ACTFR Water Quality Laboratory at James Cook University, Townsville, within 24 hours.
TSS filter membranes and frozen nutrient samples were batched and transported to the ACTFR lab in
regular submissions. The methodology for TSS filtration provided to the Catchment Co-ordinator is
provided in Appendix A.
The Granite Creek drainage samples were collected from the landholders by DNR (Mareeba) staff.
Samples for TSS were analysed directly by DNR, and nutrients samples were immediately frozen,
batched and transported to the ACTFR lab in several submissions. The urban sites were sampled by DNR
staff. Samples for BOD analyses were not collected from the Tablelands sites due to the difficulty in
returning samples to ACTFR within the time constraints for this particular analysis (i.e. within a
maximum of 24 hours of sample collection).
Quality assurance for field measurements and sample integrity was undertaken by ACTFR staff on two
occasions during the study period. ACTFR staff monitored the sample collection and physico-chemical
measurement process undertaken by landholders and the Tully Catchment Co-ordinator to ensure that
appropriate procedures were being adhered to for reliable water sample collection and field measurements
of physico-chemical parameters. Duplicate samples were also collected on these occasions and for all
parameters the results correlated within acceptable levels (i.e. the variability of results for the replicates
was less than 10%).
It should be noted that, as relatively few heavy rainfall events resulting in channel flow occurred prior to
mid-February 2003 and poor collection rates were noted in the heavier late-February rainfall events, a
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request to the landholders was made during the mid-project presentation (in March 2003) that where
possible, more intensive monitoring efforts should be undertaken by the landholders during the next
heavy rainfall period. It was also stressed that if the intensive sampling was carried out, an estimation of
nutrient and TSS loads could be determined for the resulting drainage runoff
3.4
Sample Analyses
Samples for TSS analyses were collected in 1L polypropylene bottles and aliquots filtered through preweighed Whatman GF/C filters (nominal pore size 1.2µm). TSS analyses undertaken by DNR (Mareeba)
staff followed the same procedure as that utilised by ACTFR. Samples for total nitrogen and phosphorus
analyses were collected in 100mL polyethylene bottles and frozen immediately. Samples aliquots for
total filterable nitrogen and phosphorus, ammonia, nitrate, nitrite and filterable reactive phosphorus (FRP)
were filtered through pre-rinsed Sartorius MiniSart filter modules (0.45µm pore size) into 10mL Sarstedt
polypropylene vials and frozen immediately. Samples for BOD were collected in 1L clean polypropylene
bottles and stored on ice.
TSS filter membranes were oven dried at 103-105°C for 24 hours and re-weighed to determine the dry
TSS weight. Samples for total and total filterable nitrogen and phosphorus were digested using an
alkaline persulfate technique and the resulting solution simultaneously analysed for nitrate and FRP by
segmented flow autoanalysis using an ALPKEM Flow Solution II. The analyses for nitrate, nitrite,
ammonia and FRP were also conducted using standard segmented flow auto-analysis techniques (APHA
1998, ACTFR In Prep.). Particulate nutrient concentrations were estimated by the subtraction of the total
filterable nutrient concentration from the total nutrient concentration. Filterable organic nutrient
concentrations were estimated by subtracting the filterable inorganic nutrient concentration from the total
filterable concentration. BOD analyses were conducted as per the standard method described in APHA
(1998).
4.
RESULTS AND DISCUSSION
The analytical results from this survey are provided on a catchment basis for banana and cane (and the
urban lakes sites) for each environmental indicator.
The complete data set is provided in Appendix B.
Summary data are presented in the form of boxplots to provide an indication of the data range of each
indicator for the sites surveyed in this project and to provide a basis of comparison between landuse. This
form of graphical representation provides a statistical summary of the data for each environmental
indicator.
The boxplot (sometimes referred to as a box and whisker plot) comprise a box and two whiskers (an
upward and downward whisker). The box represents the middle 50% data set with a line within the box
that refers to the median value (half the data values are higher than this value, and half the values are
lower than this value). The lines extending from the box show the highest and lowest values that are not
considered as extreme values with respect to the data set. Values outside of the whiskers are referred to
as outliers, with circular symbols representing data that occur between 1.5 and 3 box lengths from the
upper and lower whisker end value, and star symbols representing values greater than 3 box lengths away
from the upper and lower whisker end values. A summary diagram of a boxplot is provided in Appendix
C.
It was difficult to segregate the data on the basis of hydrographic state (i.e. its flow state, discussed in
more detail in Section 5), which can be described as the rising stage, event peak, falling stage or
subsequent baseflow. This segregation is considered necessary to ascertain the periods within the
hydrographic state that are likely to provide the greatest nutrient and TSS supply. The lack of appreciable
rainfall over the 2002/03 wet season meant that the number of samples collected during this survey was
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much lower than expected, particularly for the Tully-Murray Rivers catchment. Additionally, the
sampling process was limited by the low number of rising stage and peak event samples being collected
on site, due to the difficulty in obtaining such samples because of the generally immediate flow response
and the speed at which flow moves from the rising stage to post-event peak phase in wet season storm
events.
4.1
Physico-Chemical Water Quality Indicators
In general, the physico-chemical measurements were not collected during each sampling occurrence (51
and 53% of the samples had corresponding pH and conductivity values, respectively, but only 43 and
44% of the samples had corresponding dissolved oxygen and temperature data, respectively). This was
due to the limited availability of field meters during sample collection. The Granite Creek catchment
samples (predominantly the urban lakes samples) were best represented for pH and conductivity data (70
and 63%, respectively), but dissolved oxygen and temperature were poorly sampled (10% of the samples
had corresponding data for dissolved oxygen and temperature).
4.1.1
pH
The distribution of pH data collected in this survey is presented in Figure 4.1. It is important to note that
the measurements were derived from spot sampling techniques carried out at different stages of the flow
hydrograph, and as such may only serve to provide an indication of the pH range encountered in paddock
drainage channel flows.
Figure 4.1 A boxplot illustrating the distribution of pH in each landuse activity at the Tully-Murray
Rivers catchment area and Tablelands sites.
10.0
9.0
pH
8.0
7.0
6.0
Region
5.0
Tully
4.0
N=
Tablelands
23
9
Cane
36
1
Banana
18
Urban
Site Type
The data indicates that drainage from the cane paddocks was generally more acidic (i.e. values below 7)
than that from the banana paddocks. Urban flow through the lagoons in Mareeba was generally above
neutral (e.g. pH 7) with an upward outlier of 9.04 (possibly influenced by algal photosynthesis, and a
downward outlier of pH 6.06 (possibly linked to recent stormwater inflow).
Acidic drainage from cane lands after storm rainfall is not unexpected. Cane lands on floodplains in
north Queensland have been known to intersect acid sulphate or potential acid sulphate soils and as a
consequence stormwater flows, particularly in falling stages of the hydrograph, can fall to acidic levels.
The extent of this occurrence within the farms utilised in this study is not fully known. Occurrences of
low pH and decreasing pH with the falling hydrograph stage in the Tully River have previously been
reported (QDNRM Water Monitoring Group 2000).
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There is often some conjecture of the origin of low pH values in Wet Tropics waterbodies; one potential
source is rainwater itself. After the initial phase of initial overland and subsurface flow in response to a
storm event, there is a marked reduction in conductivity after the first flush due to the rapid exhaustion of
available soil-bound ions that can be leached from the soil surface. Drainage flow is then considered
reflective of rainwater quality, which is slightly acidic (~pH 5.5) due to its naturally low conductivity, and
therefore low buffering capacity, and relatively high proportion of dissolved carbon dioxide (which
produces carbonic acid). If the soil potential for acid sulphate is unknown, then a simple acidity test of
the drainage water should determine whether the low pH is related to natural runoff comprising high
runoff inputs or from influence with soils having acid sulphate potential.
pH values lower than 3.5 in water ways have been linked to a range of adverse ecological effects
(Rayment 2002), but only one site reported pH values below 5 during this study (Farm 0204, a primary
site). The low pH values at this site may indicate an acid sulphate influence on runoff waters. More
detailed pH data on a farm basis are listed in Figures 4.2 and 4.3. Although secondary and random sites
were poorly represented with respect to the number of samples, one cane site (0204) and one banana site
(2148) in the Tully-Murray Rivers catchment had pH values for the drainage flow that were much lower
than measured at the other farms in the study.
Figures 4.2 and 4.3
Boxplots showing the data range for pH values for the Tully-Murray Rivers
catchment banana and cane farms. Note the differing pH range between the two
comparison graphs.
Tully/Murray Rivers Catchments - Cane
7.0
6.5
pH
6.0
5.5
5.0
4.5
4.0
N=
12
1
5
2
3
0204
0227
0827
1205
2020
Farm Label
Tully/Murray Rivers Catchments - Banana
8.0
7.5
7.0
pH
6.5
6.0
5.5
5.0
4.5
N=
2
2
1
14
1
16
0247
0307
0923
1609
2119
2148
Farm Label
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The range of pH values determined at the Bicentennial Lakes is also shown in Figure 4.1. These values
were typical of pH that might be expected for a flow-modified (impounded) water body. In general, pH
variability was low, with the median concentration just above neutral. The lakes reduce flow rates from
Basalt Creek as they enter the impoundment, which is then supplemented by urban stormwater inputs.
When flows are reduced, in-stream chemical and biological processes tend to exert a greater influence on
water quality, such as nitrification, denitrification, thermal and oxic stratification, photosynthesis
(phytoplankton and submerged aquatic plants), respiration, etc. The pH outliers indicate periods of high
flow (slightly acidic – e.g. fresh water supply from the headwaters of Basalt Creek) and low/no flow (high
pH – greater than 9, which would tend to suggest that there was high phytoplankton photosynthetic
activity).
4.1.2
Conductivity
Conductivity values measured at the sites were considered representative of surface and sub-surface
drainage from the farm paddocks. The range of data collected from the Tully-Murray Rivers catchment
sites for both cane and banana farms were similar and encompassed the range of hydrographic conditions
experienced at the sites (Fig. 4.4). Cane farm paddock drainage from the Granite Creek catchment had an
upper conductivity range three times that reported for the cane farms in the Tully-Murray Rivers
catchment area. An explanation for this difference may be linked to a greater amount of soil solutes in
the Granite Creek region due to the drier climate where there is less chance of the solutes being flushed
from the soil due to lower intensity rainfall events. There is data available from the Herbert River
catchment (Pearson et al. In Review) that suggests cane areas contribute more salt to drainage flow, and
ultimately to receiving waters. The Tully-Murray Rivers catchment is relatively smaller in area and
rainfall is more consistent on an annual basis in comparison to the Herbert River catchment. As a
consequence it would be expected that the hydro-geomorphic characteristics would imply that relative
solute concentrations would be lower in the Tully-Murray Rivers region and that dilution factors in the
receiving waters would be more significant.
Figure 4.4 A boxplot illustrating the distribution of conductivity (µS/cm) of drainage from each landuse
activity in the Tully-Murray Rivers and Tablelands sites.
1000
Conductivity (µS/cm)
800
600
400
Region
200
Tully
Tablelands
0
N=
22
8
Cane
42
1
Banana
16
Urban
Site Type
Within the wet tropics, conductivity values in stream and river flow are generally low, regardless of flow
condition. On the small paddock areas, it is generally accepted that initial surface or sub-surface flow
generated by storm inputs will be high in solutes, which will reduce significantly over a short period of
time (generally through the course of the storm hydrograph) as the solutes are exhausted. This is
discussed in more detail in Section 5, which examines a storm hydrograph from a primary banana site.
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The conductivity data from the urban lakes sites were more consistent, which is characteristic of a system
that has a short residence time, but generally well mixed. Differentiation between the minimum and
maximum values does indicate inflow values evident during more extreme inflow events (~50µS/cm) and
those during low to no flow periods when conductivity values (~150µS/cm) tend to be similar to the
irrigation supply that is the lakes’ primary source.
4.1.3
Dissolved Oxygen
Dissolved oxygen is one of the most significant water quality indicators in the tropics, especially in
waterways receiving runoff from agricultural or urban landuses. It has been determined for the Herbert
River catchment that dissolved oxygen concentrations in pristine sites rarely exceed 80% saturation and
can at times fall to levels that can be stressful to aquatic organisms (Pearson et al. In Review). Receiving
waters are almost always flowing in the Tully-Murray Rivers catchment area, and are therefore often well
oxygenated by virtue of natural channel turbulence. Data illustrated in QNDRM Water Monitoring
Group (2000) shows that daytime spot dissolved oxygen measurements collected at AMTD 17.5km and
71km did not fall below 6mg/L (equivalent to 73% saturation at 25°C). However, runoff, particularly that
which occurs in the early phases of a storm hydrograph, are often characterized as having a significant
amount of organic material in the washload, which can exert a significant oxygen demand in receiving
waters, especially when flow is reduced, i.e. when flows enter lagoons or stream discharge diminishes
allowing in-stream processes more time to act on the compounds carried in stream. The oxygen demand
in waterways is exerted by biological decomposers, i.e. bacteria that consume oxygen as they degrade the
organic material. Additionally, as surface runoff declines, but sub-surface runoff continues, it is not
uncommon for sub-surface flow to be low in dissolved oxygen.
The data shown in Figure 4.5 illustrates the variability of dissolved oxygen concentrations that are likely
to be found through the various phases of a storm hydrograph within the different landuses. This data set
comprises spot measurements from early in the morning to late in the afternoon over a variety of different
flow stages. This does make the data difficult to interpret, and although there was a larger amount of data
from the Tully-Murray Rivers catchment sites than the Granite Creek sites, it does appear obvious that in
a comparison of the two landuse types, that the runoff from the banana farms was slightly less
oxygenated. This could be due to a number of reasons:
•
A higher organic load in the drainage runoff, and/or a
•
Greater oxygen demand at the soil surface and sub-surface.
Figure 4.5 A boxplot illustrating the variability of day-time oxygen concentrations (% saturation) of
drainage from each landuse type in the Tully-Murray Rivers catchment and Tablelands sites.
180
Dissolved Oxygen (% Sat)
160
140
120
100
80
60
40
Region
20
Tully
Tablelands
0
N=
22
2
Cane
40
1
Banana
4
Urban
Site Type
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With respect to drainage entering a receiving water body, the issue for aquatic ecosystem health,
regardless of the oxygen status of the drainage, is whether the receiving water can re-oxygenate the
generally low oxygenated inputs (i.e. through mixing with greater volumes of higher oxygenated
confluent stream flow) reducing the likely impacts upon the receiving environment. In most cases where
drainage flow is directed into rivers or streams, its confluence with more oxygenated water results in reaeration and volumetric dilution of the drainage inflow. Drainage flow into lagoons or streams that are
comprised of a number of deep reaches (where flows rates markedly decrease), suggests that there are
likely to be potential impacts on the receiving waters around the zone of inflow.
High oxygen concentrations (greater than 100%, i.e. oxygen saturation conditions) were detected on
occasions in cane and banana drainage channels during the study. In these circumstances measurements
were taken in a channel that was not flowing, and where prolific algal masses were observed. In these
conditions, the high oxygen concentrations are likely to be a result of algal photosynthesis. Submergent
plants and algae therefore supplement water oxygen concentrations, which in water bodies that have good
light quality and ready nutrient supplies, can sometimes reach 200% saturation.
As noted for pH and conductivity, a low number of dissolved oxygen concentration measurements were
collected from the urban lakes in Mareeba. However, despite the low number of measurements, the
variability between the measurements over the study period was low (values ranged between 70 and 80%
saturation). The timing of the sampling was not listed, but with only four readings that could be
converted to % saturation, the relative consistency of the data indicated that during these monitoring
periods the water was subject to some oxygen demand (e.g. respiration processes dominated over oxygen
supplementation processes, i.e. re-aeration or photosynthesis). As stated for the paddock measurements,
the interpretation of dissolved oxygen data from these types of water bodies is fraught with difficulty
because of the many different processes that either influence dissolved oxygen, or are influenced by
dissolved oxygen concentrations.
The interpretation of spot measurements of dissolved oxygen is often confounded because a large number
of influences affect its concentration within water. Some of the elements that need to be considered when
assessing any dissolved oxygen data, particularly in regard to drainage flow and/or receiving waters are
listed below:
•
The concentration of oxygen in water is temperature dependent, i.e. the colder the water the
higher the amount of oxygen that can be dissolved in the water. Water that possesses the
maximum amount of oxygen that can be dissolved is saturated (e.g. 100% saturation). Daily
temperature fluctuations (e.g. warmer during the day and cooler at night) also result in oxygen
concentration cycling on a daily basis (i.e. diel cycling).
Oxygen has a lower solubility in warmer water, which means that less oxygen needs to be
dissolved in water to achieve 100% saturation (e.g. for a water with a conductivity of 200µS/cm,
the 100% saturation concentration is 9.09mg/L @ 20°C and 6.94mg/L @ 35°C).
•
Water column oxygen concentration can significantly change through the course of a daily
period. Dissolved oxygen, and pH, increases during the course of a day are due to aquatic plant
photosynthesis (and the associated carbon uptake and oxygen evolution by the plants). The
extent of dissolved oxygen concentration change depends on the abundance and type of aquatic
plants in the water column, the quality of light, the ambient temperature, and the influence of
respiration activity. The warmest time of the day, i.e. mid-afternoon, is generally when
photosynthetic rates are expected to be at their highest, and therefore dissolved oxygen
concentrations, and pH, is expected to reach their maximum. When night falls, photosynthesis
naturally ceases, dissolved oxygen concentrations decline and pH gradually returns to
background levels.
•
In contrast to the plants ability to produce oxygen in sunlight conditions, plants, animals and
bacteria consume oxygen through respiration and decomposition processes all of the time.
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Oxygen consumption processes are temperature and biomass dependent. The balance between
respiration and photosynthetic processes can sometimes be used to characterize a waterbody.
Tropical waters experience high temperatures and therefore high respiration potential. Drainage
flows move through the drainage channels quickly and although the channels might have a high
biomass of plants, there is little potential for re-oxygenation via photosynthesis (unless the
drainage water is pooled behind a weir or other obstruction) so therefore oxygenation by air
exchange facilitated by turbulence is the only means of re-aeration. As much of the drainage
water during the falling hydrograph stage is derived from sub-surface drainage flow and therefore
generally oxygen poor, drainage waters flowing through relatively laminar channels are more
commonly oxygen deficient (i.e. less than 100%)
4.2
Biochemical Oxygen Demand
Samples for BOD were only collected from the Tully-Murray Rivers catchment sites, and then only
during the early stages of the wet season. As illustrated in Figure 4.6, BOD results above a reporting
limit of 2mg/L were detected from both cane and banana paddocks. However, a larger BOD range was
reported in the banana paddock drainage.
The main contributors of BOD in agricultural runoff are the readily decomposable and biologically active
constituents of particulate matter and soluble substances in runoff generated from the paddock by storms.
Some examples of these materials includes particulate matter comprising plant detritus and woody debris,
soil material, insoluble organic salts (e.g. humic acids) and microbial flora, and solutes such as plant
sugar, proteins, lipids, and intermediate degradation products such as alcohols, organic acids and other
decomposition products (e.g. humates).
Figure 4.6 Boxplot illustrating BOD in drainage runoff from banana and cane paddocks in the TullyMurray Rivers catchment area only.
Tully/Murray Rivers Catchments
Biochemical Oxygen Demand (mg/L)
10
8
6
4
2
N=
20
23
Cane
Banana
Farm Type
Cane farm runoff has been characterized as providing BOD-laden discharge to receiving waters (Bohl et
al. 2002, Rayment and Bohl 2002, Pearson et al. In Review), but the extent of BOD concentration is
regionally and seasonally dependent. Bohl et al. (2002) showed that BOD concentrations in drill drainage
could reach 300mg/L in farms in the Herbert and Burdekin catchments, primarily as a result of sugar
compound accumulation after the harvesting process and the crystallization of sugars in the following dry
and hot conditions often encountered after harvesting in the dry tropical regions. The impact of high
BOD runoff on receiving waters is also dependent on the amount of dilution the runoff mixes with in the
receiving waters.
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Within the Tully-Murray Rivers catchment, which is generally a wetter environment, it might be
anticipated that decomposition processes at the soil surface may preclude the accumulation of sugars after
harvesting, but it is important to note that the timing of this study coincided with the growing phase of
cane, so it is not surprising that little BOD was detected in the cane paddock drainage.
The higher BOD concentrations in banana paddock drainage is an interesting issue, and could be
reflective of the amount of organic trash (from weed slashing, etc.) or even banana sap that might make
its way to the drainage channel via paddock runoff and stem flow during storm events. The maximum
BOD of 8.5mg/L is considered high in comparison to that expected in the wet tropics streams or rivers,
but is likely to be subject to considerable dilution in receiving waters. However, the range of
concentrations encountered does suggest that the fate of trash from these banana farms (especially those
on steeper slopes) and their likely role as a BOD source may require further management consideration.
Pristine wet tropics stream waters generally have BOD values less than 2mg/L. Cane runoff in the
Herbert River study (Pearson et al. In Review) reported BOD values up to 20mg/L, with the elevated
values obtained during events and during the falling stage of the hydrograph, when large amounts of onfarm inputs were present in the drainage. In comparison, despite no BOD samples collected from the
urban lakes in Mareeba, Novotny and Olem (1994) list event median BOD concentrations of 9mg/L (the
90th percentile being 15mg/L).
4.3
Totals Suspended Solids
TSS or suspended particulate material is solid material that is suspended in the water column that has
been entrained in runoff and ultimately made its way into the drainage channel. Storm events in the wet
tropics are generally intense high-energy events that are capable of transporting high concentrations of
soil particles, as well as organic trash, via paddock runoff. Drainage channel flow resulting from these
storm events can sustain TSS in suspension until it reaches receiving waters.
TSS comprises an inorganic and organic fraction. The inorganic fraction comprises soil material, such as
clays and silts, nominally up to 63µm in diameter, that are easy to entrain yet small enough to stay in
suspension for long periods even when the water moves into low flow environments, i.e. the drainage
channel in the falling stage of a hydrograph or a pooled water body such as a in-stream lagoon. The
organic fractions generally comprises plant debris or organic trash that collects on the farm paddock, i.e.
after harvesting or routine slashing to limit weed growth around bananas for instance. The importance of
such potentially fine TSS is that they are very mobile and that they have a high propensity for sorbing
many types of water quality contaminants (i.e. phosphorus, trace metals, pesticides and organic nitrogen).
Figures 4.7 and 4.8 illustrate the distribution of TSS for each landuse within the two study catchments.
Specific farm data are shown in Figures 4.9 and 4.10. There are a number of significant points that can be
made with respect to the data:
•
TSS concentrations from the banana paddocks were generally higher (with a much greater
variability) than that for cane and the urban sites,
•
Despite a lower number of samples, the Granite Creek farm paddock sites had higher TSS
concentrations than sites in Tully-Murray Rivers catchment area (difficult to interpret fully given
the low number of samples and the single site for each landuse),
•
The urban sites had a variable TSS concentration range, with a median concentration of
approximately 10mg/L, and
•
High TSS concentrations corresponded with early phases of the storm hydrograph within the
drainage channels.
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Figures 4.7 and 4.8 Boxplots illustrating the range of total suspended solids (mg/L) concentrations in
drainage runoff from banana, cane paddocks and urban sites in the Tully-Murray
Rivers and Tablelands sites. Figure 4.8 has a maximum TSS concentration of
500mg/L.
Total Suspended Solids (mg/L)
8000
6000
4000
2000
Region
Tully
0
N=
Tablelands
42
11
82
Cane
3
Banana
26
Urban
Site Type
Total Suspended Solids (mg/L)
500
400
300
200
Region
100
Tully
Tablelands
0
N=
42
11
Cane
82
3
Banana
26
Urban
Site Type
The higher TSS concentrations in drainage from the banana paddocks are most likely a function of the
inter-row structure and the requirement for a minimum inter-crop distance between plants. Bananas can
also be grown on steeper slopes, which increase the potential for erosion. Comparisons between sites,
regardless of paddock slope, particularly the secondary and random sites, are difficult because samples
were not collected around the rising stage or peak events and runoff characteristics will be different
between the watersheds of each farm. The rising stage and event peak periods of flow response to storm
events is the period when TSS transport will be at a maximum. The Granite Creek banana sites had
elevated TSS concentrations (2680 to 3900mg/L), but the data were based on samples collected from only
the one site immediately after storm-induced channel flow.
Banana Farm 2148 had one of the steeper paddock slopes of farms used in this study, as well as having
some areas of the homestead and dirt access roads within the paddock watershed, but returned some of
the lowest TSS concentrations. The samples were also collected over a wider range of the flow event
hydrograph and therefore data best represented the distribution of TSS for drainage from the paddock in
this farm. It should be noted that as the rising stage of the hydrograph was not sampled to the same extent
as the falling stage, so it is very likely that TSS concentrations may have been significantly higher then
the maximum value obtained around the event peak. Nevertheless, it may be considered that one of the
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reasons for the lower TSS concentrations in the drainage runoff was the vegetated inter-rows, which
minimized the amount of bare soil open to rain impact and soil mobilization.
Figures 4.9 and 4.10
Boxplots showing site specific total suspended solids concentrations (mg/L) for
the banana and cane farms in the Tully-Murray Rivers catchment area. Note the
difference in concentration range between the two graphs. Farm No. 2020 has an
outlier of ~1850mg/L, which is not shown in Figure 4.10.
Tully/Murray Rivers Catchments - Banana
Total Suspended Solids (mg/L)
8000
6000
4000
2000
0
N=
8
6
2
2
2
3
16
5
3
35
0247
0307
0923
0948
1530
1551
1609
2050
2119
2148
Farm Label
Tully/Murray Rivers Catchments - Cane
Total Suspended Solids (mg/L)
600
500
400
300
200
100
0
N=
1
12
6
8
1
3
1
10
0152
0204
0227
0827
1001
1205
1505
2020
Farm Label
There were occurrences of access roads, homesteads and other ground uses within the area that were
within the watershed of some of the study catchments. These areas were mostly unsealed and were
considered a likely source of TSS. In many cases, particularly Banana Farms 2148 and 2050, it was very
likely that these areas may have been a significant source of the TSS in the drainage flow. This would
need to be considered in further investigations.
The distribution of TSS data for the urban lakes in Mareeba fell within the range normally expected for
waterways in the wet tropics (median 10mg/L), with considerably higher values obtained during inflows
associated with periods of rainfall. Novotny and Olem (1994) reported an event median TSS
concentration of 100mg/L (and a 90th percentile of 300mg/L) – this was for direct runoff as opposed to an
impounded creek flow that receives direct stormwater inputs.
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High TSS concentrations influence receiving waters because they can cause direct ecological effects to
biota (free swimming or benthic), reduce water clarity, exert an oxygen demand, carry sorbed
contaminants and/or result in sediment deposition of waterways (e.g. particularly water course lagoons).
Therefore banana farms that had median TSS concentrations in excess of 200mg/L need to address the
paddock’s soil stability by reviewing the integrity of the inter-row areas, and consider implementing a
vegetating or trash-covering strategy to reduce their soil loss. In the event of high soil dispersibilty then
consideration should also be given to establishing downstream lagoons to collect drainage water, which
will also act as a sediment trap (similar to that at Farms 2148 and 1505). This initiative has its own
issues, as in many cases the lagoons become storages of nutrient- and organic-rich water, which could
cause problems to receiving waters; but, on the other hand is very useful in that it can be an alternative
dry season irrigation supply.
The high TSS concentration upper range (506mg/L) observed at Cane Farm 0827 correlated with samples
that were collected during high flows. The flow with respect to the storm flow hydrograph was not
known, suggesting that even higher concentrations may have been encountered if sampling coincided
with the rising stage or peak of the flow event.
4.4
Nutrients
The concentration of nitrogen discharged in the runoff from agricultural landuse activities, especially in
highly bioavailable-dissolved forms (such as ammonia, nitrite and nitrate), can be very high.
Concentrations of phosphorus, on the other hand, are generally less extreme, but are linked to TSS
concentrations and are significantly higher than concentrations in tropical watercourses.
Nutrients in soils are generally orders of magnitude higher than they are in water. When fertilisation is
factored into the equation, then soil nutrient concentrations can then become that much higher. In natural
soil conditions, nutrients are associated with the soil matter, bound to the soil particles. Freely available
filterable (in some literature this is referred to as ‘dissolved’) forms of nutrients are generally only
available in the vicinity of the root zone of plants growing in the soil, but depending on the type of
fertilisers applied to the soil can be prevalent in the soil surface. Therefore the amounts of nutrients that
result in plant productivity are based entirely on the availability of nutrients in contact with the root zone.
In contrast natural aquatic environments maintain a significantly lower proportion of nutrients to sustain
their algal biomass. Slight shifts in nutrient availability can have significant effects on the aquatic
biomass and productivity of the aquatic system (mainly because agricultural soils tend to have a large
amount of available dissolved nutrients whereas natural waters have extremely low nutrient
concentrations comprised predominantly of organic forms of nutrients). Stormwater runoff is the
principle mode of export (loss) of soil nutrients to receiving waters, and this form of nutrient enrichment
will almost always result in an aquatic response, which is generally a loss of water quality (algal blooms,
greater diel oxygen cycling, etc.). With respect to the landholders, fertiliser application to ensure crop
viability and productivity means capital investment, therefore it is in the landholders best interests to
consider implementing strategies that reduce the loss of nutrients from the paddocks.
A conceptual model of the fate of nutrients (and TSS) on the farm paddock is provided in Figure 4.11.
4.4.1
Nitrogen
The distribution of nitrogen in the runoff from the farm paddocks and urban sites are shown in Figures
4.12 (total nitrogen), 4.13 (nitrate and nitrite) and 4.14 (ammonia). The high concentrations of nitrogen
measured in the drainage from the cane and banana farms in this study were not unexpected. In general
the following was evident:
•
The range of nitrogen concentrations was 100 to 21,000µg N/L.
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•
Nitrogen loss in runoff from the cane farms was generally higher than that from the banana
farms; however, the highest individual value was from a banana farm. Despite the lower number
of data from the Granite Creek, the level of difference in N runoff between banana and cane
farms in Tully-Murray Rivers and Granite Creek catchments was similar.
•
The nitrogen concentration range in the urban sites was considerably lower than found in the
agricultural paddock runoff. The Keeble Street drain had lower nitrogen concentrations than
Costin Street, indicating different source inputs and chemical processes (biological and
biochemical) within the lagoons.
Figure 4.11
A conceptual model of nutrient and soil/sediment runoff from a farm paddock.
Precipitation
Precipitation
Fertiliser
Plant Uptake
Volatilisation
N
Permeable
Surface Soil
Surface Runoff
TSS/P/N
Impermeable
NOx/NH3
Sub-Surface Runoff
Drainage
Channel
NOx/NH3
Sub-Surface
Soil
Into water
courses
downstream of
surface drain
•
Within the farm paddocks, high nitrogen concentrations were associated with early hydrograph
periods, i.e. around the event peaks, but as sampling more frequently occurred on the falling stage
of the events, it was very likely that higher nitrogen concentrations would have occurred in the
drainage.
•
In the majority of cases, for both landuse types, NOX (or nitrate plus nitrite) comprised a
significant proportion of the total nitrogen concentration. Data from the early storm hydrograph
periods indicated that particulate organic nitrogen comprised a higher proportion of the TN,
which shifted to nitrate in the latter stages of the hydrograph due to amount of nitrate available in
the soil and sub-surface groundwater. The high nitrate in the groundwater is a characteristic of
the Wet Tropics regions under cane and banana farms (Rasiah et al. 2003).
Flows during the early stages of a storm hydrograph are attributed primarily to surface runoff.
Within these paddock studies, once rainfall ceases, surface flow drops off rapidly whilst subsurface flow continues and constitutes a high proportion of drainage inputs to the drainage
Australian Centre for Tropical Freshwater Research
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channel. As time progresses a shift from shallow sub-surface soil layers through to deeper soil
profiles proceeds until all drainage flow ceases. As nitrate occurs in most deep soil profiles in the
wet tropics under these farms, sub-surface drainage comprised very high proportions of nitrate.
Figure 4.12 A boxplot illustrating the distribution of total nitrogen (µg N/L) in the drainage runoff from
various sites in the Tully-Murray Rivers and Tablelands sites.
25000
Total Nitrogen (µg N/L)
20000
15000
10000
Region
5000
Tully
0
N=
Tablelands
42
11
83
Cane
3
Banana
26
Urban
Site Type
•
Ammonia concentrations were small with respect to the total nitrogen concentration in the runoff
of each landuse category. Median concentration data from the Granite Creek farms, and overall
data range, were higher than the found for the Tully-Murray Rivers catchment data, but this data
set was poorly represented due to the lower number of samples.
Figure 4.13 A boxplot illustrating the distribution of nitrate and nitrite (µg N/L) in the drainage runoff
from various sites in the Tully-Murray Rivers and Tablelands sites.
Oxidised Nitrogen (µg N/L)
20000
15000
10000
5000
Region
Tully
0
N=
Tablelands
43
11
Cane
75
3
Banana
26
Urban
Site Type
There was a general predominance in the use of urea- and ammonia-based fertilisers by
landholders in this study, especially for the cane paddocks (Table 2.1). Nevertheless, the lack of
any appreciable amounts of ammonia in the drainage water was indicative of the high level of
nitrate in the sub-surface groundwater and predominance of soil nitrification processes (favoured
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as a result of the prolonged dry periods experienced by the farms in both study regions where any
nitrogen-based fertilisers would oxidise to nitrate). In waterlogged conditions, soils can become
hypoxic, and the conversion of ammonia to nitrate is inhibited resulting in a much larger
proportion of ammonia in runoff.
It is considered possible that ammonia would comprise a higher proportion of the N in drainage
runoff during a better wet season, when the soil surface would be expected to be much wetter and
anaerobic. This would facilitate some decomposition processes and ensure any resultant
ammonia would not be nitrified to nitrate.
Figure 4.14
A boxplot illustrating the distribution of ammonia (µg N/L) in the drainage runoff from
various sites in the Tully-Murray Rivers and Tableland sites.
2500
Ammonia (µg N/L)
2000
1500
1000
Region
500
Tully
0
N=
Tablelands
43
11
Cane
75
3
Banana
26
Urban
Site Type
Sugarcane cultivation is the major use of fertiliser in the GBR catchment (Brodie 2002), primarily
because it is the most significant agricultural activity (apart from grazing) in Queensland. Nitrogen in
runoff from the farm paddocks is directly associated with fertiliser activity, both on a recent and historic
basis. The obvious mobile, more bioavailable forms of nitrogen evident in the runoff, is also reflected in
the elevated nutrient concentrations found in the receiving streams and rivers, with the specific example
of a small trend of increased nitrate concentrations reported in the Tully River (Mitchell et al. 2000).
Although receiving water concentrations of nitrogen are often orders of magnitude lower than that found
in the farm runoff, Tully River nitrate concentrations have been found to have increased slightly over a
thirteen year period (1988 to 2000).
4.4.2
Phosphorus
Phosphorus is predominantly bound to soil particles, and as a consequence exhibits very similar responses
to runoff that are characterized by TSS. Generally, the greater the soil mobility, the greater the propensity
for phosphorus efflux from the farm paddocks. Phosphorus concentrations do not tend to reach the level
of concentrations found for nitrogen, but unlike nitrogen accumulates in aquatic ecosystems because there
are no biological/biochemical processes that are capable of permanently removing it (as is found with
nitrogen, e.g. under denitrifying conditions nitrate is converted to a gaseous form, i.e. nitrogen (N2) or
nitrous oxide (N2O), which can transfer out of the water to the atmosphere). Sediment can accumulate
phosphorus in concentrations several orders of magnitude greater than the overlying water, and under low
oxygen conditions can release phosphorus as FRP (a bioavailable form of phosphorus) back into the water
column, which can influence the overlying waterbody by providing a highly bioavailable nutrient.
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A high ratio of reactive bioavailable phosphorus (e.g. filterable reactive phosphorus or FRP) to total
phosphorus in runoff generally indicates a high level of P-fertiliser application to the paddock. Within
streams, a high level of FRP can indicate that it is enriched by fertiliser inputs, or that the water body is
stratified and that the bottom waters are severely hypoxic or anoxic (these concentrations are found close
to the bottom of the water column, near P-rich sediment that has accumulated over time from each
successive runoff event.
The distribution of phosphorus concentrations in the drainage runoff from the sites in the Tully-Murray
Rivers and Granite Creek catchments are shown in Figures 4.15 and 4.16 (total phosphorus), and 4.17
(FRP). From the data collected in this study, the following is evident:
Figures 4.15
Boxplots illustrating the distribution of total phosphorus (µg P/L) in the drainage runoff
from various sites in the Tully-Murray Rivers and Tablelands sites.
6000
Total Phosphorus (µg P/L)
5000
4000
3000
2000
Region
1000
Tully
0
Tablelands
N=
42
11
82
Cane
3
Banana
26
Urban
Site Type
Figure 4.16
A higher resolution boxplot illustrating the distribution of total phosphorus (µg P/L) in
the drainage runoff from various sites in the Tully-Murray Rivers and Tableland sites.
Total Phosphorus (µg P/L)
2000
1500
1000
500
Region
Tully
Tablelands
0
N=
42
11
Cane
82
3
Banana
26
Urban
Site Type
•
Runoff generated from the banana paddocks contained much higher concentrations of phosphorus
than the runoff from cane paddocks. This trend was obvious in the two study catchments.
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•
FRP concentrations varied between the banana and cane farms and represented between 10 and
40% of the total phosphorus. The distribution of FRP was most variable in the banana farms in
the Tully-Murray Rivers catchment, and believed to be a function of differences between each
paddock, such as fertiliser type and application strategies, paddock slope and TSS efflux.
Figure 4.17
A boxplot illustrating the distribution of filterable reactive phosphorus (µg P/L) in the
drainage runoff from various sites in the Tully-Murray Rivers and Tableland sites.
Filterable Reactive P (µg P/L)
800
600
400
200
Region
Tully
0
N=
Tablelands
43
11
Cane
75
3
Banana
26
Urban
Site Type
5
FOCUS ON A MAJOR EVENT
During the study, one banana farm landholder intensively sampled over a major storm event, which
commenced on April 19, 2003. This data is presented in detail in Farm Report 2148. The landholder
took samples in varying intervals between April 19 and May 6, 2003. Despite missing the rising stage of
the resulting drainage flow hydrograph at the beginning of the storm event, the monitoring and sampling
through this kind of event was extremely useful in that it provided a very clear picture of the influence of
a single pronounced rainfall event on the export of nutrients and TSS from a farm paddock in a wet
season that was considered relatively dry. The data collected is summarized as follows:
°
Conductivity values remained relatively consistent through the hydrograph.
°
pH values decreased through the hydrograph. pH depressions did not necessarily reflect
potential acid soils runoff, as reductions of up to one pH unit have been observed in high
rainfall event stormwater drainage flows in a tropical watershed (Elsenbeer et al. 1994). In
situations where rainfall is persistent and the soils become saturated, overflows predominate
and the drainage quality is more likely to be analogous to rainwater characteristics (e.g. low
ionic strength, slightly acidic, etc.).
°
Dissolved oxygen concentrations were low, decreasing with the progression of the
hydrograph indicating the increasing influence of sub-surface drainage.
°
TN concentrations diminished relatively slowly through the hydrograph, while nitrate +
nitrite (NOX) concentrations increased, particularly with respect to its proportion of the TN.
The relative consistency of TN concentrations through the hydrograph suggested that there
was a surplus of TN in the paddock (more than likely available from fertilizer application
and sub-surface nitrate).
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°
The much stronger diminution of TP through the hydrograph suggested that it was reduced to
exhaustion in the region of the soil layer influenced by rainfall and resultant runoff.
Phosphorus application via MAP fertilizer is a much smaller application in comparison to
nitrate (as KNO3) and was therefore unlikely to be in surplus. As P is more directly
associated with TSS, P transport diminished with overland flow and was not as significantly
transported in sub-surface drainage. It is important to note that there is a strong likelihood
that the bulk of the particulate (PP) (and TSS) is likely to be lost in the very early stages of
the event (i.e. the rising stage of the storm hydrograph).
°
TP concentrations mirrored those of TSS throughout the hydrograph. Nevertheless, TSS
concentrations were considered relatively low for agricultural runoff, suggesting that the
initial storm flow may have carried the bulk of any TSS (and TP) export.
The results fell within the expectations of nutrient and TSS responses to storm events at the paddock
scale. Figure 5.1 shows a diagrammatic representation of these responses with the progress of a storm
hydrograph. As a consequence of the sampling design, and the speed of the rising stage of a storm
hydrograph, it is very likely that the peak concentrations of P and TSS were missed. Nevertheless, some
samples were associated around the peak flow, so some indications of peak concentrations were provided.
The storm hydrograph can be broken into specific components. These are:
1. Baseflow
•
This may not exist within a drainage channel unless wet season rainfall is constant and that
surface and/or sub-surface input are persistent between storm events.
•
Nutrient and TSS inputs to the drainage channel are negligible, especially in comparison to storm
flows.
•
Water residence time is higher within drainage channel, particularly if impounded behind the
weir structure, allowing for some nutrient assimilation and TSS settlement.
2. Rising Stage
•
Brief and episodic, with rainfall intensity and duration governing the amount of influence on the
soil surface.
•
This stage is responsible for the vast majority of the total nutrient (especially P) and sediment loss
to the drainage channel.
•
Drainage flow also high enough to entrain settled TSS.
3. Falling Stage
•
More prolonged than event flows, but still considered episodic in nature, particularly in small
paddock runoff where small variations in rainfall intensity can produce a series a mini-event
stages.
•
Dominated by sub-surface gradient flow, which is likely to be comprised of a significant
proportion of nitrate (and also nitrite, and ammonia depending on soil redox potential).
•
TSS tends to settle out.
Intensive sampling of storm flow events was not conducted at any of the other primary sites. This was
unfortunate, as this type of investigation is considered necessary to fully address the issues that the project
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NRM Wet Tropics Sustainable Agriculture – ACTFR Report No. 03/18, February 2004
was ultimately trying to achieve, i.e. the assessment of different land management techniques with respect
to determining their influence on paddock losses of nutrients and sediment.
Figure 5.1 A diagrammatic illustration of likely nutrient and TSS concentration responses in drainage
flow initiated during a storm hydrograph.
Storm Hydrograph
Event Peak
Just prior to the event peak,
it is expected that a very
significant proportion of the
TP and TSS would have
been exported
Rising
Stage
Falling Stage
Baseflow
5.1
Estimate of Nutrient and Solids Flux from Banana Farm No. 2148
Between April 18 and April 30, an estimate of the flux of nitrogen, phosphorus and suspended solids
transported from the paddock on Banana Farm 2148 was calculated using flow-weighted mean
concentrations. These values were derived by dividing the total concentration load for each parameter
(e.g. nutrient and TSS) by the total drainage volume for the event period. It is assumed that nutrients and
TSS losses were derived from only the banana paddock within the watershed. Some of the factors taken
into account for the load estimates are listed below:
Watershed Area: 2 hectares, but calculations based on 1.5 hectares (taking into account that
the farm paddock represented ~75% of the watershed).
Rainfall:
523mm, which is equivalent to a potential precipitation volume of
7.85ML (i.e. 1.5ha x 523mm x 10,000)
Discharge:
5.411 x 106L or 5.411ML, which approximates 69% of the precipitation
volume meaning that 31% of the rainfall was most likely accounted for in
the sub-surface environment with some proportion trapped in the plant
mass or lost via evaporation
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TN, NOX and NH3
TN flux = 5.411 x 106 x 2.56 (TN Event Mean Concentration) = 13.85 x 106 mg N, which is
equivalent to 9.23kg N per hectare
NOX flux = 5.411 x 106 x 1.75 = 9.47 x 106 mg N, which is equivalent to 6.31kg N per hectare
NH3 flux = 5.411 x 106 x 0.061 = 0.33 x 106 mg N, which is equivalent to 0.22kg N per hectare
In terms of the event, the NOX flux comprised approximately two-thirds of the TN flux.
1. TP and FRP
TP flux = 5.411 x 106 x 0.223 = 1.20 x 106 mg P, which is equivalent to 0.80kg P per hectare
FRP flux = 5.411 x 106 x 0.101 = 0.54 x 106 mg P, which is equivalent to 0.36kg P per hectare
In terms of this specific event, PP flux comprised just over half of the TP export, with FRP
comprising the other half.
2. TSS
TSS flux = 5.411 x 106 x 35 = 189 x 106 mg TSS, which is equivalent to 126kg per hectare
These export values are based on a single storm event over the course of 12 days. To place these
estimates derived from a small event into some form of perspective, data from Hunter et al. (2001) show
that annual banana farm export estimates from the Johnstone River catchment are in the order of 42 kg N
per hectare, 6.8 kg P per hectare and 4000 kg TSS per hectare. Rainfall intensities and runoff
characteristics are very variable, and wet seasons comprise a variety of these events, with differences
expected in event duration, intensity and recurrence, as well as between catchments.
Over the period of study, there were three distinct fertilizer applications that added 16.2kg P and 114kg N
per hectare to the study paddock. Using the flux estimates determined from the single, intensively
sampled storm event in the late April rainfall event (resulting in 5,411ML discharge), it can be concluded
that for such an event approximately 8% of the total nitrogen (predominantly nitrate) from the three
applications was lost via runoff generated from this one event. If only the one fertiliser application
immediately prior to the event is considered, then the estimated loss from that single fertilisation
occurrence increases to 21%. The lack of any perceived exhaustion of nitrate in this event suggests that a
considerable surplus of nitrate exists in the soil. The source of particulate/organic nitrogen is unknown,
but there is likely to be a proportion directly associated with the most recent fertilizer application, plant
matter, and a proportion associated with previous fertilizer applications.
The rapid exhaustion of TP, FRP and TSS in the runoff through the event indicated that there was a finite
supply of these resources or that mobilization occurred above specific rainfall intensity thresholds, which
only occur for specific periods in the storm event. Rainfall intensity and the resultant effects of rainfall
on the soil surface provided the energy to entrain and mobilize the surface soils. This action resulted in
elevated P and TSS in initial paddock runoff, which was exacerbated by higher farm slopes. Like N, FRP
was applied as a fertilizer through fertigation at a rate of 0.65kg per hectare, and by spreader at a rate of
15.5kg P per hectare (i.e. from two applications of 7.77kg P per hectare). For the single event of the size
experienced over April 19 to May 5, it can be concluded that approximately 5% of phosphorus (applied in
the one fertigation and two summer blends) was lost in the resultant runoff – a similar proportion to
nitrate and ammonia. As for N, if only the summer blend application is considered, then the estimated P
loss during the late April storm event increases to 10%. The source of particulate/organic phosphorus is
not clearly defined, but it is expected that a proportion will be associated with the most recent fertilizer
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NRM Wet Tropics Sustainable Agriculture – ACTFR Report No. 03/18, February 2004
application, some from previous applications and a ‘natural’ soil/clay component (although this is likely
to be negligible).
However, the estimates for TN, TP and TSS may be considered a gross underestimate if losses are much
more significant in the rising stage and hydrograph peaks of the large storm events. As the rising stage of
the hydrograph was not sampled, even higher concentrations of N, P and TSS may have occurred, which
also would result in an underestimation of the flux of nutrients and sediment from the farm. Additionally,
the event hydrograph was very ‘flashy’ comprised of many mini-event flows reflecting the small
watershed and the immediate runoff responses to the variable rainfall intensities, and the paddock’s
hydrologic characteristics. The occurrence of a number of rising stages associated with these mini-event
flows could indicate a potential for a series of high concentration runoff events from the paddock that
were unable to be accounted for in the nutrient and sediment flux estimates.
Similarly, it should be noted that an estimate of nitrogen and phosphorus loss from the two small
preceding rainfall events (January 25 and February 28) could not be determined due to the low number of
samples collected through the course of the event, and the relatively short event periods.
From the data derived from that single storm event, and the resultant discharge where nitrogen
concentrations began to diminish (although marginally), it may therefore be theorized that if a number of
like-sized events occur in relatively close proximity soil-nitrogen concentrations may eventually be
leached to very low concentrations in the farm paddock (depending on the groundwater nitrate
concentration). This flux estimation did not take into account the growing phase of the banana crop and
the plants potential uptake, or volatilization (loss to the atmosphere).
6
WATER QUALITY DATA COMPARISON
It is difficult to draw direct comparisons between the results determined in this study and streams and
rivers in the Wet Tropics. Although samples have been predominantly taken during events that have
resulted in the drain flowing, the differences in watershed area land uses, the timing of the sampling with
respect to the hydrograph and hydrological differences make comparisons difficult.
Summary data (range and medians) for sugarcane, banana and urban sites surveyed in this report are
listed in Table 6.1, as well as concentration ranges of TSS, nitrogen and phosphorus and BOD in relevant
rivers and drainage waters in NE tropical Australia. Concentration data incorporate all site levels (e.g.
primary, secondary and random), but do not differentiate between paddock area and event size.
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NRM Wet Tropics Sustainable Agriculture – ACTFR Report No. 03/18, February 2004
Table 6.1
Concentration ranges of TSS, nitrogen and phosphorus and BOD in relevant rivers and
drainage waters in NE tropical Australia. Data collated from this study (highlighted in
yellow) only includes cropping and cane farm data from the Tully-Murray Rivers and
Granite Creek catchments, and urban data from the Bicentennial Lakes system in Mareeba.
TSS
TN
NO3
NH3
TP
FRP
BOD5
(mg/L)
(µg N/L)
(µg N/L)
(µg N/L)
(µg P/L)
(µg P/L)
(mg/L)
Cogle et al. (2000)
<1 – 1800
12 – 12700
1 - 2700
1 – 4850
Median
11
282
32
14
Mitchell et al.
(1997)
50 - 400
500 - 1600
Johnstone
Hunter et al.
(1996) and Hunter
and Walton (1997)
100 1300
140 (median)
15 - 30
Tully
Mitchell and
Furnas (1997) and
Mitchell et al.
(2001)
50 - 450
100 - 750
96 (max)
Brodie (2002)
60 - 500
1700 8500
0.3 – 118
4 - 500
300 - 6500
300 11000
Source
Reference
WATERWAYS
Granite Ck
Herbert
50 – 400 (DINs)
5–
33500
5
40 - 200
1 – 463
11
5 - 25
CANE
General
Herbert Ambient
Storm Event
This NRM
Study
Pearson et al. (In
Review)
100 15000
3900
210 1900
2 - 2500
10 - 10000
<1 1200
30 1000
100 - 13000
3 - 2300
3200
40
150 - 19500
7 - 550
1610
50
20 1800
90 - 420
20 1400
60
6- 330
2 - 270
<2 - 20
<2 - 12
1 - 60
<2 –
4.5
Range
1 - 1840
Median
15
Range
7 - 7250
Median
37
1200 21000
2500
Stormwater
Brodie (2002)
50 - 650
500 - 5800
This NRM
Study
Range
1 - 323
300 - 1800
10 - 390
3 - 100
10 - 600
2 – 110
Median
10
500
100
10
40
12
Brodie (2002)
50 - 100
100 - 4000
100 1000
Brodie (2002)
300
120
20
2
50000
45000
20000
4000
10000
9000
7000
600
Storm Event
4
CROPPING
This NRM
Study
Storm Event
21 5000
240
2 - 700
<2 –
8.5
81
URBAN
Storm Event
AQUACULTUR
E
SEWAGE
Raw
Primary
Secondary
Tertiary
Australian Centre for Tropical Freshwater Research
100 1500
300
200
15
2
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NRM Wet Tropics Sustainable Agriculture – ACTFR Report No. 03/18, February 2004
Table 6.2 Default ANZECC and ARMCANZ (2000) water quality trigger values for 95% protection of
slightly modified tropical upland aquatic ecosystems
Ecosystem
Type
Upland
River
7.
pH
Conductivity
(µS/cm)
Dissolved
Oxygen
(% Sat)
TP
(µg P/L)
FRP
(µg P/L)
TN
(µg N/L)
NOX
(µg N/L)
NH3
(µg N/L)
6.0 – 7.5
20 - 250
90 -120
10
5
150
30
6
FERTILISER USAGE
The fertiliser application rates differed markedly between the two crop types and within similar landuses
(Tables 7.1 and 7.2). Cane paddocks are characteristically fertilised in the October period after the
harvesting period, and rarely have any additional applications through the growing phase. Banana
paddocks are fertilized over a number of periods, due primarily to the fact that banana crops are
sustainable and productive over a much greater period of time. Multiple fertilisations to banana crops
maintain crop integrity and fruit productivity. Cane farms were primarily fertilised by spreader
techniques and banana farms by fertigation.
Comparisons between the two crops are difficult given the different requirements of banana and sugar
cane crops, but more importantly, the application data for bananas only encompasses six months (in most
cases), whereas the single application for cane farms encompasses an annual application cycle. The
fertiliser information provided by the landholders is considered reliable, with most landholders returning
detailed land holder diaries to the catchment co-ordinator.
Table 7.1
A summary of fertiliser application (nitrogen and phosphorus) for each cane farm in the
study (where data was made available).
Farm No.
2020 – a
2020 – b
2020 – c
1505
1205 - a
1205 - b
827
227
0204 – a
0204 – b
Tablelands
Block
Area
(hectare)
4.8
2.9
6
18.5
7.5
9.2
92
19
3.5
10.2
Start
Period
End
Period
Nitrogen
(kg N per
hectare)
Phosphorus
(kg P per
hectare)
-
Oct-02
Oct-02
Oct-02
Oct-02
Oct-02
Oct-02
Oct-02
Jun-02
Nov-02
Jun-02
156
156
122
64.2
106
46.9*
290
53
150
283
13.6
13.6
52.4
52.4
39.3
13.0*
0
58.8
0
20
Average
143
26
* Site area of 92ha comprised of a number of blocks, so application rate averaged over the blocks
– additionally mill mud application to three blocks that comprise 17ha not taken into account.
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Modern fertiliser application rates recommended for cane in Queensland fall between 150 and 200 kg N
per hectare per year. The average value for the farms in this study was 143 kg N per hectare, with a range
of 47 to 290 kg N per hectare. The average N application complies with the reported application rate for
the Cairns – Babinda – Innisfail – Tully region of 147 kg N per hectare in Simpson et al. (2001). The
source of N used on each cane farm varied from urea to mill mud, including readily soluble and highly
bioavailable forms of fertiliser composites. From the landholder records, ammonia and urea were the
primary sources of nitrogen applied to the paddocks (Table 2.1). The variation in application rates is
considered to be due to a number of factors, such as soil texture, soil pH and crop cycle.
The range of P applications to the farm paddocks varied from nil recorded to 59 kg P per hectare, with an
average of 26 kg P per hectare. This average value is slightly lower than the average of 33 kg P per
hectare listed in Simpson et al. (2001), which falls within the range listed in Pulsford (1991) of 25 kg P
per hectare per year for ratoon cane and 50 kg P per hectare per year for plant cane. Like N, P application
was via a variety of P sources, but mainly as bioavailable form of P (i.e. phosphate).
Table 7.2
A summary of fertiliser application (nitrogen and phosphorus) for each banana farm in the
study (where data was made available).
Farm No.
Block
Area
(hectare)
Start
Period
End
Period
Nitrogen
(kg N per
hectare)
Phosphorus
(kg P per
hectare)
2148
1551
1530
0948 – a
0948 – b
923
2119
1609
247
2050
307
TF1
2
1.6
3.7
4.5
3.5
7.2
6.4
2.8
5.5
1.5
10
12
May-02
Feb-03
Dec-02
Nov-02
Nov-02
Jan-03
Dec-02
Jan-03
Jan-03
Jan-03
Feb-03
-
Apr-03
Mar-03
May-03
Apr-03
Apr-03
Jun-03
Jun-03
Mar-03
Jun-03
Jul-03
May-03
-
304
102
162
193
183
104
70.1
112
153
109
41.6
-
27.9
0
49.4
66.7
68.6
28.1
104
0
46
32.1
21
-
Average
139
40
The fertiliser data for the banana farms in this study are restricted to the Tully-Murray Rivers farms, and
like cane, were very variable. These application rates are likely to represent up to half the fertiliser
amounts applied to the crop in a year. Adjustments need to be made to compare these amounts with
values quoted in the literature for annual applications.
Nitrogen application to banana plantations is quoted as an average of circa 500 kg/ha N per year (Armour
and Daniells 2002, Prasertsak et al. 2001). By current standards this figure seems high. The average
figure noted in the farms surveyed is 280 kg/ha N (adjusted for 12 months, i.e. 139 x 2 = ~280). We also
noted that nitrogen application for banana farming is highly variable, incorporating variations in the
timing and frequency of applications, soil type, and on the choice of the fertilizer product. The
landholder records showed that a variety of nitrogen forms (e.g. nitrate, ammonia and urea) were utilised
as nitrogen sources to the banana paddock (Table 2.1).
Benchmark research has demonstrated that in some areas a plant crop can be grown on 100 kg/ha N per
year, and a ratoon crop on 150 to 300 kg /ha N per year (Armour and Daniells 2002). The survey data in
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Table 7.2 would need to be interpreted with the crop class in mind, as the derived annual mean of 280
kg/ha N sits in the upper range of the fertilizer requirement suggested by this work.
Attention is also drawn to the fact that groundwater in cane and banana growing areas often have shown
elevated nitrate levels (Rasiah et al. 2003, Armour and Daniells 2002, Hunter and Armour 2001, Rasiah
and Armour 2001) suspected to be an artifact of long-term fertilizer use. These findings suggest that not
all applied fertilizer is going into crop production.
Phosphorus fertilizer application to tropical banana crops is not extensively covered in the literature.
Rasiah and Armour (2001) cite applications of 80 kg/ha P per year. However, reference to industry
literature provided through fertilizer companies maintain usual applications of circa 40 kg/ha P per year.
Like the cane farms, the banana landholders documented that phosphorus was applied in primarily readily
bioavailable forms of P (i.e. phosphate).
Survey data from this study show a mean of 80 kg/ha P per year (Table 7.2). It is usual for phosphorus to
be applied once or twice a year. One application is typical after the bulk of the wet season has passed,
and a second application is often made in the spring season. Typically, the majority of phosphorus is
applied to the plant crop and usually incorporated deep into the plant bed before planting.
Recent studies (Armour and Daniells 2002) have suggested that 19 kg/ha P per year for the life of the
plant may be all that is required. In some cases they note that ratoon crops may require up to 47 kg/ha P
per year. This finding asserts that phosphorus requirements of banana crops are much lower than the
current rates of application undertaken by many farms.
In this report we would like to reinforce the opportunity to refine fertilizer practices for banana growing,
avoiding the potential for over-fertilizing and reduce the chances for excess nutrient runoff in water
discharge from banana farms. While bananas are fertilized frequently, this means that the application of
small amounts of nutrient, usually by fertigation through sprinkler irrigation, has the potential to deliver
the crops nutrient requirements efficiently. However, ideal application rates for crop nutrition will remain
difficult with variation in soil type and aspect across farms and catchments. Attention by farmers and
agronomists will potentially deliver economic benefits if fertilizer usage can be made more efficient
(wastage reduced) and delivery of excess nutrient to water ways or ground water can be avoided.
8.
CONCLUSION
This study provides unique information detailing the amount of nutrients and sediments that exist in
runoff draining specific paddocks on banana and cane farms, with an urban lagoon system investigated
for comparison. Nitrogen and phosphorus are the primary nutrients considered of high interest in relation
to water quality. Nitrogen is most often present in the soils of agricultural lands in nitrate form, which is
highly susceptible to leaching and off-farm transport in surface runoff. Phosphorus is the key to plant
growth stimulation and is generally present as native P in north Queensland soils; however this native P
may not be directly available for plant uptake. Soil P (native or applied) is not generally lost via leaching,
but via surface runoff as soluble (bioavailable) P and particulate P, as it is most commonly associated
with suspended sediment.
We note in this report that the study period was unseasonally dry, with well below average rainfall. We
acknowledge that the prevailing dry conditions would mean that nutrient accumulation has occurred over
a longer period. Runoff water in the first rainfall events conceivably carries higher nutrient loadings than
would normally be expected from these same farmlands. This affects the interpretation of these water
quality data, in that we are unsure of the baseline for data interpretation. However, it must also be
acknowledged that the total loading of the farmland system over a full season of growth will be similar to
the amounts indicated by the landholder diary (Tables 7.1 and 7.2) and that any amount of excess nutrient
is still likely to be carried into the water system at some stage. Future interpretation of similar data
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demands consideration of the amount of rainfall to induce runoff, compared with the periodicity of prior
rainfall events.
The level of investigation was considered insufficient to provide some of the outcomes that were
proposed for this report because of the poor wet season and the lack of any detailed site specific runoff
data (i.e. nutrient and flux concentrations from each farm, which could have been used to provide specific
management advice to individual farms). Nevertheless, one of the notable outcomes from the project was
the development of on-farm infrastructure and a community-minded water quality awareness that will
allow for the continuation of this kind of monitoring testing the effectiveness of land management
practices. The concentrations of nitrogen, phosphorus and TSS encountered in this study were often very
high in comparison to those that are expected for a tropical stream or river, especially during drainage
events resulting from high rainfall periods, and as such may be are typical of runoff from some intensive
agricultural landuse activities.
A primary benefit of this study that should not be overlooked is the community involvement in both the
establishment and support of the project, as well as the time that has been allocated by the farmer in
training, consultation and conducting the field component of this project. It is a considerable undertaking
with respect to time requirements, but the integrated approach from the farmer, catchment co-ordination
and technical support has been a successful exercise. There are a number of similar programs that have
been developed in the past few years, or are in the process of being established, in north Queensland (e.g.
the Burdekin Dry Tropics (Faithful 2002a) and the Whitsunday Rivers (Faithful 2002b)). Community
involvement with such programs is perceived as essential for conservation and landuse management
(Williams 2002).
8.1
Banana Farms
The TSS and TP concentrations in the paddock drainage from the banana farms were high, especially in
the early stages of a rainfall event hydrograph.
Consideration of specific crop management strategies, such as reducing fertiliser application rates
(especially P), ensuring appropriate row direction and configuration (with respect to slope) and vegetating
the crop inter-rows to allow grasses and various weeds to grow, would seem essential to minimise
sediment, and therefore, TP loss to the drains and ultimately receiving waters.
Groundcover has the potential to reduce sheet erosion and rain impact mobilization, and the regular
slashing of inter-row vegetation should promote plant productivity and available nutrient uptake (there is,
however, little experimental data to validate this suggestion). The presence of an associated root mass
from the additional inter-row vegetation would also increase the amount of bioavailable nutrients (e.g.
FRP) through biochemical transformation of organic and particulate nutrients sources in the soil surface
that may become available to the crop or be taken up by the grasses. Routine slashing should be
minimized so that wheel track rutting of the inter-rows does not become a significant issue and develop
into runoff routes that will be prone to higher rates of erosion. Inter-row vegetation is considered even
more important on the higher slope farms because the ground cover will minimise erosion potential, as
well as reduce nutrient losses. As the crop canopy develops, shading should restrict excessive inter-row
weed growth.
Nitrogen concentrations were also high and dominated by nitrate. Management strategies to minimise
nitrate losses during drainage flow is more difficult due to the high levels of nitrate stored in the subsurface soil matrix and groundwater in the wet tropics agricultural regions. There is some level of
consideration being given to groundwater re-use as a nitrogen source, but this is untested and presents a
series of issues that need to be better understood.
BOD concentrations were higher than that for the cane farms, although values fell below concentrations
reported for other farm studies (e.g. Pearson et al. In Review). This was attributed to the small drainage
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paddocks and the higher mass of organic material (trash) around the crops and to sap from the plants that
may be washed into the runoff via stem flow during rainfall events.
8.2
Cane Farms
Cane farms do not lose as much TSS or P as the banana farms, due primarily to a general lack of slope on
the blocks, the greater ‘canopy’ coverage minimizing soil exposure (particularly in the time of the year
that the study was focused) and because fertilisation occurs in the dry season. The aerial coverage of the
plant (plant density) significantly reduces the amount of direct rain contact with the soil on the paddock
(dependent on the age of the plant), and wet seasonal rainfall influences (which will be more significant
with higher rainfall intensity) are therefore generally limited to the period when the plant is growing.
Trash blanketing is an effective practice for reducing the nutrient and sediment losses in the post-harvest
period. This practice occurs in the majority of farms in the Wet Tropics. However, plant cane is different
farming technique to ratoon cropping, and this practice is recognised as a separate issue which requires
more consideration with respect to a nutrient and soil losses.
Runoff data in this study revealed that nitrogen is lost in significant concentrations, particularly as nitrate,
due mostly to the historic use of nitrogen based fertilisers (both nitrate, ammonia and urea forms) on soils
that are capable of oxidizing the urea and ammonia-based fertilisers to nitrate. Nitrate is particularly
soluble and moves through the soil profile and adsorbs to soil particles as an anion, only to be remobilised with each successive infiltration or saturation. With wet season rainfall, the soil water
movement, via saturation to runoff and horizontal movement, nitrate transport to the paddock drain is
currently a common feature in the wet tropics floodplain agricultural regions.
Like the banana farms, strategies such as the reduction of fertiliser application rates, vegetating headlands
and drainage channels and the potential re-use of groundwater as a possible nitrogen source, have to be
considered if the problem of high sub-surface nitrate is to be addressed.
8.3
Urban Lakes
The urban lakes data was considered useful in that it provided a measure of comparison to the farm runoff
data. Its source was from the Granite Creek catchment with urban stormwater supplementation, and the
nutrient and TSS concentrations were indicative of that. Unfortunately there was no gauging information
to put the data into a flow perspective. There was the additional influence of the lakes reducing drainage
flow from Basalt Creek, which would have exerted a significant influence on water moving into the lakes
(slowing the flow down and allowing in-lake water quality processes to occur).
8.4
Nutrient and Sediment Flux
Estimates of nutrient and sediment flux (export) from the paddock are required to determine the actual
losses of nutrients and sediment during storm events. These data suggest that storm event runoff can
transport significant amounts of nutrients and sediment in just a single event, so wet season losses can be
substantial.
The intensive sampling that occurred at Banana Farm 2148 provided the best estimate of nutrient and
sediment loss from a single intense rainfall period. Despite the acknowledgeable effort by the landholder
to acquire these samples, the rising stage at the beginning of the event was not sampled, which meant that
flux estimates were likely to be underestimated as P and TSS concentrations in runoff are at their highest
concentrations immediately prior to the event peak. It is considered that intensive sampling exercises
through specific rainfall events are required at each primary farm site to provide any reliable assessment
of these losses. The use of rising stage samplers or more appropriately, autosamplers, will provide a
greater level of sample collection through a hydrograph which will lead towards more comprehensive
flux estimates. One of the noticeable points in the drainage hydrograph was the distinct peakiness or
‘flashy’ response of the hydrograph through the event, suggesting that for such a relatively small
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NRM Wet Tropics Sustainable Agriculture – ACTFR Report No. 03/18, February 2004
catchment area, the hydrograph was comprised of many small events, which was a function of the highly
variable rainfall intensity and paddock runoff characteristics. These will all have implications in the
estimation of flux concentrations, which highlights the point that autosamplers, or similar types of
sampling devices, are essential in these studies to target specific flow samples that can be utilised to
accurately measure flux concentrations.
It is recognized that it is difficult to draw direct comparisons between landuse activities, and between
farms, due to the preliminary nature of the project, and also because of the lack of capture of a significant
number of rising stage and event peak hydrograph samples.
9.
RECOMMENDATIONS
This project has given rise to infrastructure that is now in place, especially in the context of the primary
sites, which can be utilised in future investigations. Out of this project, specific recommendations for
future direction are provided that should only add value to the results from this single year study:
o
Maintain the monitoring through another two wet seasons (at least), to cover the very dry
monsoon season experienced in 2002/2003. The study period was one of the driest wet
seasons on record, and any data collected in such a period is likely to be considered
anomalous or extreme until it can be compared with a longer term data set.
o
Focus on specific storm events at the primary sites, intensively sampling through the storm
hydrograph, to reliably determine nutrient and TSS fluxes from the farm paddocks. The
implementation of autosamplers, or rising stage samplers, is crucial in the capture of the
rising and event peak stages of the hydrograph that will provide more accurate load
measurements.
This improved data set will allow for more rigorous data analysis correlating nutrient and
TSS losses with soil types, fertiliser type and application rates, watershed slope, farm history,
etc.
o
There is a requirement to increase the level of monitoring in the Granite Creek region, which
will also be serviced by a better wet season. Although rainfall is lower on the Tablelands, it
is still imperative that structures (e.g. autosamplers, landholder catchment co-ordinators) and
monitoring strategies are in place to reliably collect samples in both the primary and
secondary sites.
It is also considered a requirement that flow gauging systems be installed to the urban lakes
systems so that load estimates can be determined for comparison with the farm paddocks (at
least at the outfall point). The catchment area for the lakes is considerably larger than that for
the farm paddocks used in this study, but nevertheless that data will provide an estimate of
nutrient and TSS flux in wet tropics urban runoff.
o
Investigate the possibility that the primary site farms consider utilising other similar paddocks
that can be used for different management strategies (e.g. different fertiliser application rates,
application strategies) that can be compared with respect to nutrient and TSS concentration
(and loads) in event runoff and productivity.
o
Implement a groundwater-monitoring component so that an assessment of the sub-surface
source of nutrients can be taken into account in the loss of nutrients from the farm paddock
and allow for the measurement of a water balance. If further study requires a thorough
estimate nutrient balance for the paddock to be undertaken, then measurement of Nvolatilisation will be necessary.
Australian Centre for Tropical Freshwater Research
Page 38
NRM Wet Tropics Sustainable Agriculture – ACTFR Report No. 03/18, February 2004
o
Consider additional landuse types in the monitoring program, such as cattle grazing (beef and
dairy), forestry, and other horticulture crops (e.g. pineapple, paw-paws, etc.).
o
As banana and cane agriculture utilise biocides to control weeds and pests, then it is
necessary to monitor for these compounds to determine whether they are being lost from the
farm paddock, and if so, how much is lost in storm event runoff. Pesticide and herbicide
residues are reaching downstream and marine environments and are becoming more of a
national issue, with many current environmental monitoring programs detecting various
biocides of interest (e.g. diuron, atrazine, etc. in cane production, and gromoxone, fusilade
and diathene, etc. in banana production) in the sediments of floodplain waterways and river
mouths.
Australian Centre for Tropical Freshwater Research
Page 39
NRM Wet Tropics Sustainable Agriculture – ACTFR Report No. 03/18, February 2004
10.
REFERENCES
ANZECC and ARMCANZ (2000) Australian and New Zealand Guidelines for Fresh and Marine Water
Quality. National Water Quality Management Strategy, Canberra.
APHA (1998) Standard Methods for the Examination of Water and Wastewaters. 20th Edition. American
Public Health Association, American Water Works Association and Water Environment
Federation. Washington, USA.
Armour, J.D. and J.W. Daniells (2002) Banana Nutrition in North Queensland. Project No. FR95013.
Queensland Department of Natural Resources and Mines, Mareeba.
Bohl, H.P., Bonnett, G.D., Fanning, D.J., Rayment, G.E. and A.B. Davidson (2002) Biological
oxygen demand and sugars in irrigation water runoff from sugar cane fields. Proceedings of the
24th Australian Society of Sugar Cane Technologists Technology of the Future, 29 April – 2 May,
2002, Cairns.
Bramley, R.G. and D.E. Muller (1999) Water Quality in the Lower Herbert River – The CSIRO
Dataset. CSIRO Land and Water Technical Report 16/99. CSIRO, Canberra.
Bramley, R.G. and C. Roth (2002) Land-use effects on water quality in an intensively managed
catchment in the Australian humid tropics. Marine and Freshwater Research. 53(5): 931-940.
Brodie, J. (2002) The Effects of Landuse on Water Quality in Australian North-Eastern Catchments and
Coastal Waterways. ACTFR Report No. 02/07 to NRM Wet Tropics as a component of Project
No. 2012015.
Brodie, J., Furnas, M., Ghonim, S., Haynes, D., Mitchell, A., Morris, S., Waterhouse, J., Audis, D.,
Lowe, D. and M. Ryan (2001) Great Barrier Reef Catchment Water Quality Action Plan: A
Report to Ministerial Council on Targets for Pollution Loads. Parts 1, 2 and 3. Great Barrier
Reef Marine Park Authority, Townsville.
Cannon, M.G., Smith, C.D. and G.G. Murtha (1992) Soils of the Cardwell-Tully Area, North
Queensland. CSIRO Division of Soils. Division Report No. 115. CSIRO Australia.
Cogle, A.L., Langford, P.A., Kistle, S.E., Ryan, T.J., McDougall, A.E., Russell, D.J. and E. Best
(2000) Natural Resources of the Barron River Catchment 2: Water Quality, Land Use and Land
Management Interactions. Information Series QI00033, Queensland Department of Primary
Industries, Brisbane, Queensland.
Cogle, A.L., Langford, P.A., Russell, D.J., and M. A. Keating (In Reviewa) Sediment and nutrient
movement in a tropical catchment with multiple landuse. In: Protecting the Values of Rivers,
Wetlands and the Reef. Dawson, N., Brodie, J., Rayment G. and C. Porter (Eds). Papers and
Presentations from the Conference on Sustaining our Aquatic Environments – Implementing
Solutions, Townsville, 20-23rd November, 2001.
Cogle, A.L., Keating, M.A., Langford, P.A., Gunton, J. and I.S. Webb (In Reviewb) Runoff, soil loss
and nutrient transport from cropping systems on red ferrosols in tropical northern Australia.
Submitted to Aust. J. Soil Res.
Elsenbeer, H., West, A. and M. Bonell (1994) Hydrologic pathways and stormflow hydrochemistry at
South Creek, northeast Queensland. J. Hydrol. 162: 1-21.
Australian Centre for Tropical Freshwater Research
Page 40
NRM Wet Tropics Sustainable Agriculture – ACTFR Report No. 03/18, February 2004
Faithful, J.W. (2002a) Water Quality in the Townsville/Burdekin Dry Tropics Region. Surface Water
Quality and 2002 Post-Wet Season Sediment Quality. ACTFR Report No. 02/12 to Conservation
Volunteers Australia. National Heritage Trust Project No. 2002153.
Faithful, J.W. (2002b) Water Quality in the Whitsunday Rivers Catchments – Surface Water Quality –
December 2000 to August 2002. ACTFR Report No. 02/13 for the Whitsunday Rivers Integrated
Catchment Association. A Coast and Clean Seas Project.
Garside, A.L., Bell, M.J., Cunningham, G., Berthelsen, J. and N. Halpin (1997) Rotation and
fumigation effects on the growth and yield of sugarcane. Proceedings Australian Society of Sugar
Cane Technologists. 21: 69-78.
Hunter, H.M. and J.D. Armour (2001) Offsite movement of nutrients: contrasting issues at three
Australian study sites. In: Proceedings of the Offsite Movement of Agrochemicals in Tropical
Sugarcane Production Workshop, Bundaberg, May 8-9, 2001. ACIAR Project No. 9446.
Hunter, H.M. and R.S. Walton (1997) From Land to River to Reef Lagoon. Land Use Impacts on
Water Quality in the Johnstone Catchment. Queensland Department of Natural Resources,
Brisbane, 10pp.
Hunter, H.M., Walton, R.S. and D.J. Russell (1996) Contemporary water quality in the Johnstone
River catchment. In: Downstream Effects of Land Use, Hunter, H.M., Eyles, A.G. and G.E.
Rayment (Eds). Queensland Department of Natural Resources, Brisbane, pp. 339-345.
Johnson, A.K.L., Bramley, R.G. and C. Roth (2001) Land cover and water quality in river catchments
of the Great Barrier Reef Marine Park. In: Oceanographic Processes of Coral Reefs: Physical
and Biological Links in the Great Barrier Reef, Wolanski, E. (Ed). CRC Press, Boca Raton, pp.
19-37.
Mitchell, A. W., Reghenzani, J.R. and M.J. Furnas (2001) Nitrogen levels in the Tully River - a longterm view. Water Science and Technology. 43(9): 99-105.
Mitchell, A. W., Bramley, R.G.V. and A.K.L. Johnson (1997) Export of nutrients and suspended
sediment during a cyclone-mediated flood event in the Herbert River catchment, Australia.
Marine and Freshwater Research 48(1): 79-88.
Mitchell, A. W. and M. J. Furnas (1997) Terrestrial inputs of nutrients and suspended sediments to the
GBR lagoon. The Great Barrier Reef; Science, Use and Management, James Cook University,
Townsville, CRC Reef Research Centre, James Cook University.
Moody, P.W., Reghanzani, J.R., Armour, J.D., Prove, B.G. and T.J. McShane (1996) Nutrient
balances and transport at farm scale – Johnstone River catchment. In: Downstream Effects of
Land Use, Hunter, H.M., Eyles, A.G. and G.E. Rayment (Eds). Queensland Department of
Natural Resources, Brisbane, pp. 347-351.
Novotny, V. and H. Olem (1994) Water Quality: Prevention, Identification and Management of Diffuse
Pollution. Van Nostrand Reinhold, New York.
Pearson, R.G., Butler, B.M. and M. Crossland (in review) Effects of Cane-Field Drainage on the
Ecology of Tropical Waterways. ACTFR Report No. 03/04 for the Sugar Research and
Development Corporation.
Prasertsak, P., Freney, J.R., Saffigna, P.G., Denmead, O.T. and B.G. Prove (2001) Fate of urea
nitrogen applied to a banana crop in the wet tropics of Queensland. Nutrient Cycling in
Agroecosystems. 59: 65-73.
Australian Centre for Tropical Freshwater Research
Page 41
NRM Wet Tropics Sustainable Agriculture – ACTFR Report No. 03/18, February 2004
Prove, B.G. (1988) Soil erosion research in cane fields on the wet tropical coast of north-east
Queensland. In: Workshop on Nutrients in the Great Barrier Reef Region, Baldwin, C.L. (Ed).
Great Barrier Reef Marine Pak Authority, Townsville, pp. 30-32.
Prove, B.G. and W.S. Hicks (1991) Soil and nutrient movements from rural lands of north Queensland.
In: Landuse Patterns and Nutrient Loading of the Great Barrier Reef Region, Yellowlees, D.
(Ed). James Cook University of North Queensland, Townsville, pp. 67-76.
Pulsford, J.S. (1991) Historical inputs of fertiliser nutrients on to agricultural lands of coastal north
Queensland. In: Land Use Patterns and Nutrient Loading of the Great Barrier Reef Region,
Yellowlees, D. (Ed). James Cook University, Townsville, Queensland.
Rasiah, V. and J.D. Armour (2001) Nitrate accumulation under cropping in the ferrosols of far north
Queensland wet tropics. Aust. J. Soil Res. 39: 329-341.
Rasiah, V., Armour, J.D., Yamamoto, T., Mahendrarajah, S. and D.H. Heiner (2003) Nitrate
dynamics in shallow groundwater and the potential for transport to off-site water bodies. Water,
Air, and Soil Pollution. 147: 183-202.
Rayment, G.E. (2002) Landuse and Surface Water Quality in Sugar Catchments. Exposure Draft, CRC
Sustainable Sugar Production and Department of Natural Resources and Mines, Brisbane,
Queensland.
Rayment, G.E. and H.P. Bohl (2002) Dissolved oxygen in waterways of sugar catchments. In:
Managing soils, nutrients and the environment for sustainable sugar production. CRC Short
Course, 12-13 February 2002, CRC Sugar, James Cook University, Townsville, Queensland.
Simpson, B.W., Ruddle, L.J., Packett, R. and G. Frazer (2001) Minimising the risk of pesticide runoff
– what are the options? Proceedings of the Australian Society of Sugar Cane Technologists. 23:
64-69.
Thompson, G.D. (1990) Report on Burning and Trashing. South African Sugar Experimental Station
Internal Report, November 1990.
Williams, W.D. (2002) Community participation in conserving and managing inland waters. Aquatic
Conservation: Marine and Freshwater Ecosystems. 12: 315-326.
Australian Centre for Tropical Freshwater Research
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NRM Wet Tropics Sustainable Agriculture – ACTFR Report No. 03/18, February 2004
Appendix A
I.
Landholder Diary Forms
II.
Field Data Sheet
III.
Water Sampling Procedures
IV.
Sample Filtration for Total Suspended Solids Analysis
V.
Summary Review of Monitoring Parameters
Australian Centre for Tropical Freshwater Research
Page A - 1
NRM Wet Tropics – Water Quality Assessment for Sustainable Agriculture – ACTFR Supplement, September 2002
Water Quality Assessment
for
Sustainable Agriculture
Natural Resource Management Board
(Wet Tropics) Inc.
At the Leading Edge of Integrated Natural Resource Management
Farm
Activities
Diary
Landholder Number:___________
Australian Centre for Tropical Freshwater Research
Page LD - 1
NRM Wet Tropics – Water Quality Assessment for Sustainable Agriculture – ACTFR Supplement, September 2002
1. Rainfall Records for 2002/2003
Date
October
Day
November
Day
December
Day
January
Day
February
Day
March
Day
1
T
F
S
W
S
S
T
2
W
S
M
T
S
S
W
3
T
S
T
F
M
M
T
4
F
M
W
S
T
T
F
5
S
T
T
S
W
W
S
6
S
W
F
M
T
T
S
7
M
T
S
T
F
F
M
8
T
F
S
W
S
S
T
9
W
S
M
T
S
S
W
10
T
S
T
F
M
M
T
11
F
M
W
S
T
T
F
12
S
T
T
S
W
W
S
13
S
W
F
M
T
T
S
14
M
T
S
T
F
F
M
15
T
F
S
W
S
S
T
16
W
S
M
T
S
S
W
17
T
S
T
F
M
M
T
18
F
M
W
S
T
T
F
19
S
T
T
S
W
W
S
20
S
W
F
M
T
T
S
21
M
T
S
T
F
F
M
22
T
F
S
W
S
S
T
23
W
S
M
T
S
S
W
24
T
S
T
F
M
M
T
25
F
M
W
S
T
T
F
26
S
T
T
S
W
W
S
27
S
W
F
M
T
T
S
28
M
T
S
T
F
F
M
29
T
F
S
W
S
T
30
W
S
M
T
S
W
31
T
T
F
M
Australian Centre for Tropical Freshwater Research
April
Page LD - 2
NRM Wet Tropics – Water Quality Assessment for Sustainable Agriculture – ACTFR Supplement, September 2002
2. Block/Site History for sub catchment
Crop
(Bananas
or Cane)
Block No.
Date
Planted
Australian Centre for Tropical Freshwater Research
Crop
Age
Area of
crop in subcatchment
(estimate)
Special
practices
Previous
fertilizer to
October 2002
Cultural practices
Page LD - 3
Last crop and when
ploughed out
NRM Wet Tropics – Water Quality Assessment for Sustainable Agriculture – ACTFR Supplement, September 2002
3. Landholder Activities in sub-catchment
Date
Activity
Block
Quantity/Product
Name/Number
Australian Centre for Tropical Freshwater Research
Application Method
Page LD - 4
Notes
NRM Wet Tropics – Water Quality Assessment for Sustainable Agriculture – ACTFR Supplement, September 2002
Farm Plan – Information to be collected if possible
Map (supplied by CSCMA)
On this map locate infrastructure, slope/topography(contour lines), vegetation patches,
irrigation practices, waste disposal, drainage layout (drain lines).
Define the monitoring catchment.
Another map for soil types for the defined catchment area – locating any compaction
areas, soil structure, difficult soil management areas.
History:
Crop rotations:
Soil management (ie cover crops):
Soil pest control (eg nematodes, grubs):
Acid soils:
Drainage:
Design of Drains eg. spoon, rectangular, V drain, deep or shallow:
Drain condition:
Erosion?:
Vegetation:
Management, cleaning;
Erosion:
Areas (indicate on map)
Reduction Methods:
• Physical soil conservation – structures designed; not designed
• Sediment retention dams – designed; not designed
• Biological control methods – eg. Cover cropping, trees, vegetation in drains
• Other:
Nutrient & Fertiliser use:
History of Soil Test Results:
Crop Yields:
Nutrient Deficiencies:
Remedial Methods for deficiencies:
Storage of Fertiliser – reference to map
Hygiene – where spreaders are filled from eg bag lifter in paddock or at shed etc.
Disposal of waste materials:
Tillage of Practices:
Majority of zonal tillage (i.e. cane) or full cultivation.
Australian Centre for Tropical Freshwater Research
Page LD - 5
NRM Wet Tropics – Field Datasheets 2002/2003
Site Identifier:
__________________
Date:
Gauge Height / Water Depth (m): ___________________
Time: Start________
FIELD OBSERVATIONS
__ __ / __ __ / __ __ __ __
Finish: ________
DETAILS
Weather Conditions (in past 24 hours)
Fine
Cloud cover
1/8
Cloudy
2/8
Wind conditions
No breeze
Wind direction
N
Site position
3/8
S
E
W
5/8
No flow
Channel condition =
Fully Vegetated
Channel Cross-Section Estimates
Depth (m)
Slight flow
Heavy Rain
6/8
7/8
Windy
NW
SW
SE
Fully Shaded
Moderate flow
Partly vegetated ___ %
8/8
Very windy
NE
Partly Shaded = ___ %
Water flow
Presence of nuisance organisms
4/8
Slight breeze
Full Sun
Water colour, appearance
Raining
Fast flow
No Vegetation
Width (m)
Clear
Opaque
Dirty
Muddy
Macrophytes
Phytoplankton
Algal mats
Other ________
Presence of oily film on surface or on shoreline?
YES
NO
Presence of floating debris?
YES
NO
Presence of odour or frothing?
YES
NO
Other observations (eg. Flora, Fauna….)
WATER SAMPLES
Water quality samples taken? (circle)
BOTTLES
1 x 1 Litre
for TSS
1 x 100mL
for TNTP
3 x 10mL
for DINS - FILTERED
1 x 500ml
for BOD
Sample Identification No.:
FIELD MEASUREMENTS:
Field Equipment (Hydrolab / WTW / Other)
RESULTS
Calibration Date: ____________
Probe(s) Depth (m)
pH
Electrical Conductivity (µS/cm)
DO2 (mg/L)
DO2 (% sat)
Temperature (° C)
Issue #1 October 1, 2002 – The Australian Centre for Tropical Freshwater Research Wet Tropics datasheets.doc
NRM Wet Tropics – Water Quality Assessment for Sustainable Agriculture – ACTFR, October 2002
Water Sampling Procedures
1.
Total Suspended Solids (TSS) - One 1L plastic bottle
•
Rinse bottle out three (3) times with water to be sampled.
•
Discard rinse water away from sampling area.
•
Fill to overflowing and seal.
•
Do not leave an air gap.
•
Once sample is taken it should be kept in the dark (i.e. in a refrigerator or in an esky on ice
until collected by the project officer).
•
Please identify and date each sample, and record on the field data sheet.
Filtration should occur within 24 hours of sample collection
2.
Total Nitrogen and Total Phosphorus (TNTP) - One 100mL plastic bottle
•
Fill bottle with water to be sampled.
•
DO NOT RINSE sample bottles.
•
DO NOT OVERFILL sample bottles.
•
Please leave an air gap to prevent bottle splitting when frozen.
•
If possible, freeze the samples before collection by the project officer.
•
Otherwise store in the dark as soon as possible (i.e. in a refrigerator or in an esky on ice) until
collected by the project officer.
•
Please identify and date each sample, and record on the field data sheet.
To minimise contamination please keep fingers away from all tops and lids
3.
Dissolved Inorganic Nitrogen (DINs – Ammonia, Nitrate/Nitrite, FRP) - Three 10mL plastic
vials
SAMPLES NEED TO BE FILTERED
•
DO NOT RINSE sample vials.
•
Firstly, rinse out syringe three (3) times with the water to be sampled.
•
Discard rinse water away from sampling area.
•
Fill the syringe with 50mL of sample. To avoid possible contamination when syringing, leave
an air gap between the plastic syringe plunger and sample water (~ 5-10ml air pocket).
Australian Centre for Tropical Freshwater Research
Sampling Instructions – Issue #1
Page SI - 1
NRM Wet Tropics – Water Quality Assessment for Sustainable Agriculture – ACTFR, October 2002
•
Secondly, pass 10 to 20mL of sample through the filter with sample to prime the filter paper.
•
Finally, collect the filtered sample in the three (3) plastic vials to the 10ml line.
•
Filters may be re-used within the same sampling site. They must be detached from the syringe
before re-filling the syringe.
•
However, use a new filter for each new site.
•
DO NOT OVERFILL sample vials.
•
Please leave an air gap to prevent vial splitting when frozen.
•
If possible, freeze the samples before collection by the project officer.
•
Otherwise store cold in the dark as soon as possible (i.e. a refrigerator or in an esky on ice).
•
Please identify and date each sample, and record on the field data sheet.
To minimise contamination please keep fingers away from all tops and lids
4.
5-Day Biological Oxygen Demand (BOD5) - One 1L plastic bottle
•
Rinse bottle out three (3) times with water to be sampled.
•
Discard rinse water away from sampling area.
•
Fill to overflowing and seal.
•
It is important that all air is excluded, DO NOT leave an air gap.
•
Check for air bubbles by inverting the container. Refill if there any bubbles are present.
•
If possible, seal sample bottle underwater to exclude all air bubbles from container.
•
Alternatively, squeeze sample bottle to overflowing then seal.
•
Once the sample is taken, it should be stored in the dark on ice.
•
Please identify and date each sample, and record on the field data sheet.
For this analysis special consideration is required because analysis should occur within 24 hours of
sampling. The lab should receive the BOD samples between Wednesday and Friday.
Australian Centre for Tropical Freshwater Research
Sampling Instructions – Issue #1
Page SI - 2
NRM Wet Tropics – Water Quality Assessment for Sustainable Agriculture – ACTFR, September 2002
Sample Filtration for Total Suspended Solids Analysis
1
2.
3
Prepare Venturi Pump and Filtration Manifold
•
Connect Venturi pump and hoses to an appropriate tap fitting.
•
Wash all parts of filtering apparatus with distilled water (or Reverse Osmosis (RO) treated
water) before use.
•
Take appropriate number of pre-weighed Whatman GF/C filter papers from the desiccator
box.
•
Record the lid number for the selected filter paper with the corresponding sample ID on the
TSS log sheets.
•
Position the pre-weighed filter paper in the centre of the filtering unit, wrinkled side up.
•
To aid in positioning the paper, moisten the filter paper with a small volume of distilled
water, and then screw on sample container firmly.
•
Be careful not to screw the container on too tight as this usually tears the edges producing a
gap where the sample is likely to leak.
•
Test that there are no holes in the filter paper by turning on the tap and adding some distilled
water to the sample container and filter through. .
Sample Preparation:
•
The samples should have been stored cold and in the dark prior to analysis. Filtration should
also occur within 24 hours of sample collection. Keeping the samples between 0 and 4 °C up
to the time of analysis minimizes decomposition of solids.
•
Non-representative particulates, such as leaves, twigs, insect etc. should be removed from the
sample.
•
Ensure sample is well mixed prior to addition to the sample container.
•
Turn off the tap to the venturi pump before adding sample.
•
Add aliquots of well-mixed sample (100 to 250mL), noting the volume.
Filtering Procedure
•
Record the Sample ID and filter lid number used on the TSS log sheet.
•
Filter as much sample as possible and when filtering is complete record the total volume
filtered on the TSS log sheet.
•
If the sample is high in solids, the filter can clog and the time to process can become lengthy.
•
Therefore, if the sample takes longer than 10min to filter, discard the filter and re-sample.
Australian Centre for Tropical Freshwater Research
Filtration Methodology, Issue #1
Page FM - 1
NRM Wet Tropics – Water Quality Assessment for Sustainable Agriculture – ACTFR, September 2002
•
•
Use a new filter, shake the sample again and pour in a smaller aliquot.
Repeat the sample if it is evident that the sample has leaked, or if the filter paper has been
compromised in any way.
Upon the completion of filtering, please note:
•
Fresh water samples
Once you have completed filtering sample, rinse the sides of the container and the filter paper
with RO.
•
Salt water samples
Once you have completed filtering sample, it is important to rinse the sides of the container
and the filter paper thoroughly with RO, approx. 250ml, as salt crystals drying on the filter
paper can grossly over estimate the mass of suspended solids. Continue suction for 3min after
filtration is complete.
•
After filtering, with the pump still operating, carefully unscrew the sample container so as not
to tear the filter paper.
Place the Whatman GF/C filter back on the corresponding plastic lid and place back into a drying
container. The samples should be returned to the ACTFR laboratory in batches or as required.
Australian Centre for Tropical Freshwater Research
Filtration Methodology, Issue #1
Page FM - 2
NRM Wet Tropics – Water Quality for Sustainable Agriculture – ACTFR Supplement, September 2002
Summary Review of Water Quality Parameters
1
Physico-Chemical Parameters
1.1
pH
pH and pH-buffering capacity are vital properties of water because they virtually affect all chemical and
biochemical reactions. pH is a measure of the amount of hydrogen ions in the water and is measured on a
scale of 1 to 14 and indicates the acidic or alkaline (basic) character of a solution. A value of 7 is neutral;
values from 1-7 are acidic with 1 being the most acidic and values from 7-14 are alkaline with 14 being the
most alkaline.
Pure water normally contains intermediate concentrations of hydrogen ions and is said to be neutral
(neither acidic nor alkaline). Most natural waters will have ambient pH values between 6 and 9, with
values falling outside of this range a result of other factors such as high humic acid (from large amounts
of leaf litter), mine tailings, very high stormwater inputs reducing the pH to less than 6, or high levels of
plant photosynthesis that can elevate pH as high as 11.
The ability of water to resist pH changes with the influence of weak acids or alkalis is called the water’s
buffering capacity. The alkaline buffering capacity is referred to as its alkalinity and in natural freshwater
systems is due mainly to the presence of bicarbonate leached from the soils in rainwater runoff. Carbon
dioxide from the air constantly dissolves in water or rainwater to form weak carbonic acid, hence rain
water or pristine rainforest stream water tends to be mildly acidic (~5).
pH is very important to biological processes. Plants and algae can alter the pH of water. Strong cycling of
pH during temporal scales indicates vigorous growth rates and/or very large quantities of plants and algae.
Green algae can raise the pH of freshwater to 8.3, but are unable to photosynthesis above that level. Bluegreen algae and other aquatic plants are able to photosynthesize at pH values much greater than 8.3. In this
case, the presence of pH values above 8.3 can indicate the presence of significant populations of blue-green
algae.
Low pH values invariably cause concern amongst environmental managers. However, there are
obviously circumstances where low pH values occur naturally and are not necessarily bad. Merely taking
pH readings does not enable us to distinguish these natural conditions especially in Melaleuca wetlands,
from problems such as ASS runoff. It is merely an indicator and further investigation is required to
determine the type of acids present.
pH changes can influence other elements such as nutrients and trace metals, either making them available
or not, or increasing toxicity to some degree. Like dissolved oxygen and temperature, pH may cycle on a
daily basis depending on plant influences. Therefore noting the timing of sampling is very important.
For our type of monitoring, knowing the daily range of pH is particularly relevant.
1.2
Dissolved Oxygen
Dissolved oxygen is probably the single most important water quality parameter despite being not being
very soluble in water. Most aquatic organisms acquire oxygen directly from the water rather than
breathing air at the surface, and additionally oxygen is crucial to various reactions such as photosynthesis
and respiration, and affects the solubility of contaminants such as metals and speciation availability of
metals.
Oxygen concentrations refer to the actual amount of oxygen in the water, which is expressed as either
milligrams per litre of water (mg/L) or as parts per million (ppm), which is essentially the same
measurement. Oxygen saturation is the amount of oxygen in the water compared to the amount of
oxygen that body of water is able to hold and is expressed as a percentage (%). Oxygen saturation of
water varies with temperature with warmer water not able to hold as much oxygen as cold water. Both
oxygen concentration and oxygen saturation are important parameters and both should be measured in the
Australian Centre for Tropical Freshwater Research
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NRM Wet Tropics – Water Quality for Sustainable Agriculture – ACTFR Supplement, September 2002
field, as they provide different information about the same indicator. All reasonable quality oxygen
meters should provide both measurements; however, if only one measurement is feasible then it is more
pertinent to measure saturation as this is more directly relevant to aquatic organisms.
There is a constant exchange of oxygen between the water surface and the air. When a balance exists
between air and water, then the water is said to be saturated with oxygen and the dissolved oxygen
concentration will be 100% saturation. The actual concentration of oxygen in this saturated condition is
dependant on temperature, salinity and atmospheric pressure. In environmental conditions parts of the
water column are not freely exposed to air and depending on biotic circumstances may be oxygen
deficient (hypoxic if deficient or anoxic if oxygen depleted) or over saturated. During the day plants will
produce photosynthetic oxygen, which can supplement the water column oxygen levels exceeding the
theoretical maximum level that water can sustain – in some cases greater than 200% saturation. Such a
result actually tells us a fair bit about the biological processes operating in waterholes that can achieve
such high levels of oxygen.
It is generally accepted that once dissolved oxygen levels decline below 4mg/L, then mortality of less
tolerant aquatic biota will result although data supporting this assumption is very scant. Sub-lethal effects
on aquatic biota, such as activity levels, may be affected long before this level is actually reached. There
is a wide range of oxygen tolerance among species but very little hard data has been derived. The current
nationally accepted recommended guideline (ANZECC 2000) for dissolved oxygen levels in tropical river
systems is 90 to 110% saturation. It may not be unusual to find healthy ecosystems with lower maxima
(i.e. 60% saturation) for certain periods of the year.
Measures of dissolved oxygen are not important just because they are highly relevant to environmental
processes and the survival of aquatic biota, but also because they integrate the effects of a variety of
processes within the water. Dissolved oxygen is thus a very important indicator variable as it
demonstrates whether the processes operating within a waterbody have changed. For instance, if
increased nutrient levels are determined for a waterbody in a monitoring program, these may not be
indicative of a change in ecological processes. However, the oxygen measurements will allow for a
assessment as to whether increased nutrients levels have led to changes in oxygen production and cycling,
i.e. whether the increased nutrient levels recorded have actually had any affect on biological process
within the waterbody (or if the nutrient levels have changed because processes within the waterbody have
changed).
Oxygen concentrations in water are able to tell us immediately about the apparent health of the waterway.
However, as with pH, it is not uncommon in these coastal waters for dissolved oxygen to cycle over a
wide daily range, particularly in warmer months. The data gives us an insight into a measure of organic
production and decomposition and forms the basis of evaluating primary productivity. As with pH, the
sampling time is critical and spot measurements are not useful unless some indication of the daily range is
included.
Generally, we find that oxygen levels are lowest in the early morning because of respiration processes,
such as biotic oxygen consumption, microbial reduction of organic material and plant respiration activity.
As the sun rises providing light, plants and phytoplankton begin to photosynthesize which results in
increased water column oxygen levels. Oxygen levels generally reach a maximum level about midafternoon. As the sun goes down, photosynthesis decreases and respiration processes predominate,
resulting in a decline in oxygen levels. This increase and decrease of oxygen concentrations over the
course of a single day is called diel cycling. In strongly flowing waters the turbulence generated by the
water flow over the streambed (higher turbulence occurs if flow is over a steeper gradient and the stream
bed is rocky) aerates the water through exchange with the atmosphere, thus creating good oxygenation
and reducing the extent of diel cycling.
1.3
Temperature
As with the prior two parameters, temperature is also extremely important in aquatic ecosystems, as
various biological and chemical processes are temperature limited. As the temperature of a water body
Australian Centre for Tropical Freshwater Research
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NRM Wet Tropics – Water Quality for Sustainable Agriculture – ACTFR Supplement, September 2002
increases, the rate of chemical reactions increases, the evaporation and volatilisation of chemical
substances increases, but conversely the solubility of gases such as oxygen decreases (i.e. the water
cannot hold as much dissolved oxygen). In warmer waters the respiration rate of aquatic organisms
increases, as does the decomposition of organic matter, both of which consume oxygen, which as just
stated, is less available as water temperature increases. A 10-degree change in water temperature doubles
the respiration rate. Thus a wetland at 40 degrees would have 4 times the dissolved oxygen consumption
than a 20-degree wetland of similar characteristics. Growth rates of bacteria and phytoplankton also
increases significantly, leading to algal blooms if other conditions such as nutrient levels and light
availability are suitable.
Temperature affects all kinds of physical, chemical and biological processes. Many waterbodies,
especially deeper ones, usually experience thermal stratification with warmer water overlying cooler
water. Such stratification has significant bearing on the aquatic fauna. Water bodies undergo seasonal
and daily changes in temperature.
Temperature is usually the easiest field parameter to measure but will not tell you much about the health
of an aquatic system without knowing anything about the other parameters.
1.4
Conductivity
Conductivity is a measure of the ability of water to conduct electrical current, where conductance
increases with increasing total salts concentration in the water. It is measured in microsiemens per
centimetre (µS/cm) and is affected by the electrical charge of the dissolved solids, usually salts, within
water. Conductivity is sometimes confused with salinity, but it is important to recognize that the two are
specific measurements of ionic strength in freshwaters and marine waters respectively.
In freshwater science, salinity is an ill-defined term that is used colloquially in reference to the
concentration of salts. A more specific term for freshwaters is total dissolved or soluble salts (TDS)
measured in mg/L and most water quality standards are expressed as TDS, not salinity. Most freshwater
systems have conductivity values between 10 and 1,000µS/cm, which can equate to approximately 5 to
~700mg TDS/L (most concentrations for calculating total dissolved salts from freshwater conductivities
are derived empirically from freshwater data).
In marine science salinity is a very specific (and a complicated) technical definition. It was once
measured in parts per thousand (ppt or o/oo) but is now measured on a unitless scale where standard
seawater is 35. Salinity assumes that the ionic composition (major salts composition) is diluted seawater.
Conductivity is more stable than temperature, dissolved oxygen or pH. It is only subject to rapid changes
when there are new inputs of water such as stormwater influx (denoted by a sharp decline) or as a dry
season progresses (steady increases due to evapo-concentration) or increased effects of groundwater,
which generally has higher conductivity that fresh surface waters. Conductivity generally increases the
further downstream you go along a river, but significant discontinuities in this gradient can occur at points
of confluence with other tributaries and groundwater springs, etc.
2
Chemical/Biological Parameters
2.1
Chlorophyll a/Phaeophytin
Chlorophyll is an indirect measure of the amount of planktonic algae present in the water column, as well
as the trophic status of the waterbody. In clear waters, phytoplankton can dominate the suspended
material in the water column and therefore the chlorophyll concentration can provide an indirect measure
of total suspended solids. The same processes that affect algae and aquatic macrophytes will affect
phytoplankton, and therefore chlorophyll concentrations (i.e. temperature, light and nutrients). However,
although phytoplankton requires light to survive, chlorophyll measurements can still be very high in
turbid environments, as some species can make good use of the limited light available at the water
Australian Centre for Tropical Freshwater Research
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NRM Wet Tropics – Water Quality for Sustainable Agriculture – ACTFR Supplement, September 2002
surface. In still, turbid environments, species are favoured that can alter their buoyancy to stay near the
surface where light is more available. Most species of green algae cannot do this, they simply sink slowly
through the water column unless there are water currents available to keep them suspended; hence they
have less access to light. However, diatoms and blue-green algae can alter their position in the water
column (through flagella and vacuoles) and can be favoured in turbid environments by accessing the light
very close to the surface without competition from green algae.
Because turbid environments favour plankton/algal species that can alter their position in the water
column, chlorophyll measurements at such sites vary depending on the time of day and the depth
sampled. Values will be high near the surface in the morning as the algae access the light near the
surface. As the day progresses and sunlight gets stronger, they occupy lower positions in the water
column. In clear waters, the chlorophyll is more evenly distributed throughout the water column as light
penetration is strong and it is dominated by green algae, which cannot control their position in the water
column. In such cases, depth-integrated samples may be appropriate to provide an average chlorophyll
level for the water column.
Chlorophyll is a surrogate measure of algal biomass but does not necessarily reflect algal turnover rates.
Phaeophytin can also be measured in conjunction with chlorophyll to indicate turnover rates.
Phaeophytin is a measure of the degradation products of chlorophyll and a high level of phaeophytin and
low level of chlorophyll can indicate a high turnover or that an algal bloom has recently subsided.
One of the disadvantages of the use of chlorophyll a as a productivity indicator is that it underestimates
productivity in wetlands and streams that are small or poorly mixed where productivity is derived from
other sources. This is particularly evident in north Queensland where productivity can be heterogeneous,
autotrophic, benthic, planktonic, macrophytic, littoral or riparian. In situations where the primary
productivity is not phytoplanktonic, then reported chlorophyll concentrations will be exceptionally
difficult to interpret.
2.2
Total Suspended Solids
Total suspended solids (TSS) are a direct measure of the amount of suspended particulate material
(organic or inorganic) in the water column. They comprise silts and clays, organic detritus, microbes or
plankton and generally refer to material that is suspended in the water column and which does not float on
the surface. Due to settling properties, suspended particulate material in calm waters is generally much
smaller than SPM in flowing waters. The quantities of fine sediment transported in a watercourse are
often referred to as the washload. In north Queensland, measures of TSS in an aquatic environment often
indicate a level of disturbance in the catchment feeding the stream or in situ, within the stream. This is
probably valid only for the brief periods when there is surface runoff present in watercourses. For the
majority of time the water in streams originates from subsurface sources (soil through flow, groundwater
springs, etc.). Therefore, most of the time TSS are an indicator of more localized in-stream effects; some
natural, wind induced resuspension, bioturbation (e.g. water birds, macroinvertebrates, etc.), and some
anthropogenic, such as livestock and feral animal impacts, and human effluents.
2.3
Nutrients
There are two nutrients of major interest, nitrogen and phosphorus. These nutrients are among the most
well-known water quality parameters associated with polluted waters. In moderate concentrations, they
are essential to biological processes. High nutrient levels affect many processes, but are primarily renown
for increasing algal productivity (measured by chlorophyll levels), which in turn increases the degree of
oxygen and pH cycling and the level of oxygen consumption by microbes and planktonic animals that
feed on the organic matter produced by algae. As a consequence permanent or periodical low oxygen
levels are eventually experienced in nutrient enriched waters. This process is termed eutrophication.
Nutrients are usually measured in both the dissolved and total (including suspended) forms.
Australian Centre for Tropical Freshwater Research
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NRM Wet Tropics – Water Quality for Sustainable Agriculture – ACTFR Supplement, September 2002
2.3.1
Nitrogen
Nitrogen exists in organic and inorganic forms. The nitrogen cycle is quite complex and involves
biological and non-biological transformations. The non-biological processes include volatilisation
(gaseous loss to the atmosphere), sorption (attachment to sediment) and sedimentation. The biological
transformations include assimilation of inorganic forms (e.g. ammonia and nitrate) by plants and
microbes to form organic forms (e.g. amino acids), reduction by micro-organisms of nitrogen to ammonia
and organic nitrogen, oxidation of ammonia to nitrite and nitrate (nitrification), bacterial reduction of
nitrate to nitrous oxide and nitrogen under anoxic conditions (denitrification) and ammonification of
organic nitrogen to ammonia during decomposition of organic matter.
Ammonia
Ammonia (NH4) occurs naturally as a result of the decomposition of nitrogenous organic and inorganic
matter, from excretion by animals, the microbial reduction of nitrogen and atmospheric exchange. It may
of course, also be introduced from artificial sources such as industrial and urban waste, fertilizer use etc.
It is found in its highest concentration in wastewater discharges and is often present in significant
concentration in stratified anoxic water layers, particularly in tropical impoundments. There is some
work in the US that is indicating high atmospheric ammonia in agricultural regions that are utilizing high
amounts of ammonia fertilizer.
Ammonia is the nitrogen form that is most readily used by aquatic plants. At high concentrations and at
certain pH levels, ammonia is extremely toxic to biota.
Nitrate and Nitrite
Nitrate (NO3) and nitrite (NO2) combined together are referred to as the inorganic forms of oxidised
nitrogen.
Nitrate is the most commonly measured form of nitrogen. Nitrate occurs naturally in groundwaters from
soil leaching and along with conductivity, can be used as an indicator of groundwater inputs to surface
water. Like ammonia it may be sourced from industrial waste and from fertilizers, and is a by-product of
oxidation treatment ponds and secondary water treatment processes. Biologically nitrate is often reduced
to nitrite by denitrification, usually under anaerobic conditions. However, in the presence of oxygen,
nitrite can be oxidised to nitrate via nitrification processes. Nitrate and nitrite can be combined together
as oxidisable nitrogen.
2.3.2
Phosphorus
Phosphorus is an essential nutrient for living organisms. It is often considered to be the most limiting
nutrient for algal growth and therefore controls primary productivity in many waters and is widely
implicated in eutrophication when in excess. Phosphorus generally occurs in very low concentrations
within the natural environment and is rapidly taken up by plants.
Phosphorus usually occurs as dissolved orthophosphates. Principal natural sources of phosphorus are
weathering of phosphate-bearing rocks and decomposition of organic matter. There are numerous
artificial sources including fertilizer, detergents, wastewater, industrial effluent and animal excreta (cows,
sheep). In addition, because phosphorus sorbs very strongly to sediment, accelerated land erosion
increases phosphorus inputs to waterways. Phosphorus generally occurs in very low concentrations and
is rapidly taken up by plants. It is a very important component of the biological cycle and undergoes a
complex array of changes in form, thus making its pathways through an aquatic ecosystem difficult to
determine and model.
Australian Centre for Tropical Freshwater Research
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NRM Wet Tropics – Water Quality for Sustainable Agriculture – ACTFR Supplement, September 2002
Filterable Reactive Phosphorus (FRP)
FRP is the most readily available form of phosphorus that is utilized by aquatic plants. FRP is sometimes
referred to as orthophosphate, but it is important to note that in an analytical context FRP includes fine
colloids and organic phosphorus compounds that can pass through 0.45µm filters.
2.4.
Biochemical Oxygen Demand (BOD)
This parameter refers to an analytical procedure that estimates the amount of oxygen required for aerobic
microbes to decompose organic matter in a water body.
It is a traditional analytical test that was developed as an inexpensive means of estimating the
concentrations of organic carbon in sewage.
It has been utilised for environmental assessments; however, it should be noted that there are limitations
when applying this test to the natural environment, particularly when the composition and bioavailability
of organic matter varies enormously with location and over time. Other limitations include that organic
matter is not evenly distributed through the water column, other chemical oxidation processes are not
accounted for that may occur as a result of reduced inorganic chemicals in the water (i.e. high
concentrations of reduced iron), and varying oxygen concentrations and temperature in the water at the
time of sampling will determine whether organic matter persists or is decomposed very rapidly (BOD
results are determined from constant temperature and oxygen sufficient environments and need to be
interpreted carefully).
Both biochemical and chemical oxidation reactions take place in the aquatic environment, but the main
reactions in natural waters are biochemical. In terms of oxygen demand, the most important type of
biochemical reaction is the oxidation of organic material. In this case the reduced carbon in the organic
material is oxidised to carbon dioxide, through the metabolic action of microorganisms, principally
bacteria. The BOD test mimics the oxygen demand by providing nutrient and bacteria to utilise the
organic material present in a water sample. The decrease in oxygen concentration of the water sample
over a five-day period provides an estimate of the biochemical oxygen demand of the water at the time of
sample collection.
Essentially the BOD result correlates with the organic content of water and theoretically provides a
measure of the amount of oxygen required for the carbonaceous oxidation of a non-specific mixture of
chemical species, which includes both soluble and non-soluble organic compounds.
Australian Centre for Tropical Freshwater Research
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Appendix B
Complete Water Quality Dataset
Australian Centre for Tropical Freshwater Research
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NRM Wet Tropics Sustainable Agriculture Project - ACTFR Report No. 03/18, December 2003
Conductivity
(µS/cm)
Dissolved
Dissolved
Oxygen (mg/L) Oxygen (% Sat)
Temperature
(°C)
Site Label
Location
Site Type
Status
Date and Time
pH
0204
0204
0204
0204
0204
0204
0204
0204
0204
0204
0204
0204
0204
2020
2020
2020
2020
2020
2020
2020
2020
2020
2020
0827
0827
0827
0827
0827
0827
0827
0827
1505
0152
1001
0227
0227
0227
0227
0227
0227
1205
1205
1205
1609
1609
1609
1609
1609
1609
1609
1609
1609
1609
1609
1609
1609
1609
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
27/01/2003 08:10
18/02/2003 16:15
19/02/2003 06:15
21/02/2003 07:00
26/02/2003 17:15
27/02/2003 06:30
31/03/2003 08:00
07/04/2003 07:45
14/04/2003 13:50
20/04/2003 07:15
20/04/2003 13:45
20/04/2003 17:25
24/04/2003 08:15
26/01/2003 09:18
26/01/2003 12:00
26/01/2003 15:45
25/02/2003 15:50
13/03/2003 11:45
14/03/2003 10:45
15/03/2003 12:00
19/04/2003 16:00
20/04/2003 08:30
23/04/2003 08:30
25/01/2003 10:40
26/01/2003 07:45
26/01/2003 13:13
27/01/2003 08:40
18/02/2003 15:55
19/02/2003 08:25
13/03/2003 17:00
20/03/2003 09:50
13/03/2003 14:00
13/03/2003 14:35
13/03/2003 15:08
27/01/2003 08:30
14/03/2003 14:00
19/04/2003 09:00
23/04/2003 08:30
24/04/2003 07:00
07/05/2003 07:30
18/02/2003 17:45
19/02/2003 07:45
26/02/2003 18:00
12/01/2003 03:07
17/01/2003 17:45
25/01/2003 12:16
25/01/2003 17:55
25/01/2003 18:18
25/01/2003 18:40
25/01/2003 19:03
25/01/2003 19:25
25/01/2003 19:43
25/01/2003 20:20
25/01/2003 20:57
25/01/2003 21:20
26/01/2003 10:40
26/01/2003 16:58
5.34
4.67
4.61
4.54
4.81
4.40
5.46
5.61
6.50
4.67
4.60
4.58
166
168
175
169
59
158
54
52
48
83
92
8.61
7.99
8.41
8.05
6.74
8.00
8.87
7.96
11.83
5.86
7.50
102.4
100.8
102.6
100.0
91.6
100.1
104.8
96.0
163.9
70.0
87.5
24.00
27.00
24.50
26.50
27.20
27.00
24.50
24.70
31.60
24.20
26.20
26.20
5.26
162
6.51
81.1
24.60
6.17
5.57
145
88
4.98
7.15
51.4
63.8
14.10
9.00
6.08
50
6.95
74.2
24.90
5.61
5.60
5.42
6.35
80
108
62
75
5.56
3.46
5.50
3.18
72.5
41.9
68.4
39.5
29.10
25.80
26.30
25.80
5.20
47
5.04
58.3
21.40
5.69
5.50
6.95
7.30
7.00
82
70
108
221
105
111
60
69
67
77
45
71
85
71
193
308
8.50
7.94
5.40
5.80
5.07
4.40
7.10
101.8
98.4
68.0
71.0
67.2
57.0
87.0
23.90
26.50
6.40
6.30
6.70
5.70
5.10
79.0
77.3
84.0
71.0
64.0
5.70
5.10
68.3
66.0
6.80
6.90
7.00
6.80
6.80
6.61
6.40
26.30
27.50
28.30
26.00
26.00
25.70
25.60
24.70
24.60
24.70
24.50
25.00
26.40
Total
Total
Filterable Ammonia (µg
Nitrogen (µg
N/L)
Nitrogen (µg
N/L)
N/L)
10790
15480
14240
13090
5760
11800
1870
1350
584
5700
6510
Nitrate +
Nitrite (µg
N/L)
Total
Phosphorus
(µg P/L)
50
49
23
21
138
20
18
23
17
51
26
Total
Filterable
Phosphorus
(µg P/L)
Filterable
Reactive
Phosphorus
(µg P/L)
14
27
23
15
37
17
10
14
9
14
8
93
13
50
57
44
14
61
39
18
10
66
33
44
14
9
9
11
21
20
15
15
13
15
4
18
8
4
2
4
42
26
31
13
7
2
2
23
1
1
2
2
6
2
7
1
43
43
32
5
48
24
8
42
49
24
29
7
5
2
2
2
2
2
3
5
2
3
4
4
1
1
2
16
1
16
677
631
506
371
614
600
488
369
3.0
85.3
43.7
59.3
1840
61.2
25.8
16.5
21.8
15.8
14.5
129
384
86.5
22.8
506
53.0
68.8
6.8
31.4
38.8
14.0
2.0
8.2
6.9
1.4
4.6
9.0
50.0
10.8
92.5
383
201
318
127
2020
437
435
456
Total
Suspended
Solids (mg/L)
10700
14700
13630
12170
4700
10570
1200
1280
579
5460
6130
5770
3570
11470
11960
12490
793
3840
4270
3730
1400
1260
1030
1460
5660
12200
10700
4510
5840
1650
233
6660
1620
914
3160
471
3540
789
738
527
7980
1360
2750
120
2110
520
260
496
188
5
13
3
48
25
41
15
88
73
52
3
9
5
6
12
6
17
36
330
2250
633
66
70
30
5
16
20
20
417
36
914
117
122
14
148
47
141
9703
11682
13181
12581
3891
9941
1613
1123
320
4941
6021
5170
3232
11418
11787
11678
552
3523
4032
3363
1233
1032
872
1048
5227
9737
9450
4186
5612
1363
40
6133
1293
630
2727
134
2422
416
526
388
7267
1876
2316
4530
1400
1120
710
118
13
16
19
2521
609
340
364
630
10
299
50
134
91
81
1430
182
133
283
101
130
76
209
264
80
50
354
86
130
30
86
87
43
22
40
59
43
7
35
87
36
166
1260
996
974
853
2880
2680
1220
2670
1160
1340
660
611
752
25
11
7
192
168
151
1730
1260
1040
427
542
689
398
393
642
1040
304
215
6040
10300
5920
9800
17
37
5317
8781
307
374
288
351
281
314
32.5
9.8
3710
11610
12920
13410
2650
4150
4480
4550
1650
1420
1140
1980
6330
12590
11310
5550
6450
2090
270
7230
1980
961
3260
542
3640
988
817
853
8300
1520
2850
2060
5170
2060
1770
4340
4430
1800
1.6
6.8
1.0
1.0
155
0.6
1.3
1.5
1.7
13.8
2.7
Biochemical
Oxygen
Demand
(mg/L)
2.0
2.0
2.0
2.0
3.4
2.0
2.0
2.3
2.0
4.5
2.0
2.0
2.0
2.0
2.0
2.1
2.0
2.7
2.0
4.1
7.3
2.0
Page B - 2
NRM Wet Tropics Sustainable Agriculture Project - ACTFR Report No. 03/18, December 2003
Site Label
Location
Site Type
Status
Date and Time
pH
Conductivity
(µS/cm)
1609
1609
1609
1609
1609
1609
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2148
2050
2050
2050
2050
2050
0247
0247
0247
0247
0247
0247
0247
0247
0307
0307
0307
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Primary
Secondary
Secondary
Secondary
Secondary
Secondary
Random
Random
Random
Random
Random
Random
Random
Random
Secondary
Secondary
Secondary
26/01/2003 17:55
18/02/2003 14:52
12/03/2003 18:40
13/03/2003 09:11
22/04/2003 15:00
05/05/2003 17:00
25/01/2003 22:50
26/01/2003 00:10
26/01/2003 08:45
27/02/2003 16:00
13/03/2003 15:05
14/03/2003 11:20
18/04/2003 11:54
19/04/2003 08:00
19/04/2003 12:30
19/04/2003 17:45
20/04/2003 09:05
20/04/2003 13:00
20/04/2003 13:10
20/04/2003 18:30
21/04/2003 09:45
21/04/2003 18:30
22/04/2003 06:50
22/04/2003 16:30
23/04/2003 06:50
23/04/2003 16:00
24/04/2003 06:40
24/04/2003 15:50
25/04/2003 08:45
26/04/2003 06:20
28/04/2003 17:15
30/04/2003 17:30
30/04/2003 17:50
01/05/2003 05:25
04/05/2003 11:28
05/05/2003 10:40
05/05/2003 15:25
05/05/2003 18:30
06/05/2003 06:55
06/05/2003 15:50
06/05/2003 16:14
23/04/2003 11:30
23/04/2003 15:00
24/04/2003 06:30
24/04/2003 13:00
25/04/2003 07:00
25/01/2003 21:35
26/01/2003 09:00
17/02/2003 14:15
13/03/2003 08:41
13/03/2003 13:37
19/04/2003 07:00
19/04/2003 11:35
20/04/2003 11:10
27/02/2003 16:15
14/03/2003 15:30
22/04/2003 12:05
5.00
7.13
7.00
7.03
201
82
135
75
5.70
5.40
6.70
6.14
72.0
72.1
79.0
72.5
25.40
29.40
23.90
23.80
133
119
177
75
106
85
120
137
6.60
5.77
3.30
6.35
1.78
4.05
8.81
78.7
68.4
39.1
80.5
22.8
40.1
102.1
5.05
56.9
24.20
23.90
23.80
27.40
24.60
14.40
22.60
22.30
23.10
6.77
6.08
5.77
6.60
6.33
6.40
Dissolved
Dissolved
Oxygen (mg/L) Oxygen (% Sat)
Temperature
(°C)
5.92
282
3.20
30.2
24.30
5.83
131
2.81
33.9
24.80
5.89
5.96
125
141
2.48
1.32
27.2
16.2
25.20
23.70
5.79
5.95
6.97
5.98
114
117
97
118
1.59
1.67
9.80
2.68
18.8
19.8
124.5
36.1
25.20
25.50
28.30
25.70
6.53
5.94
99
127
5.20
2.20
68.2
18.2
25.10
23.60
6.91
6.98
119
84
4.74
5.27
55.6
65.5
23.10
25.90
7.13
6.56
159
115
4.94
5.89
64.8
72.4
28.40
25.00
Total
Total
Filterable Ammonia (µg
Nitrogen (µg
N/L)
Nitrogen (µg
N/L)
N/L)
2440
1280
1270
6370
2270
4160
3460
4250
2420
1570
1660
4673
2252
2400
3100
2070
4120
673
2520
3460
2360
3220
2610
2860
3190
2930
3230
2100
2460
2550
2120
630
2010
1530
1310
1810
1600
1730
695
2380
3030
3010
2500
2150
1590
2220
5780
5760
1410
956
2450
2060
2540
7840
3120
9400
Nitrate +
Nitrite (µg
N/L)
Total
Phosphorus
(µg P/L)
1520
55
784
151
1120
650
553
233
861
149
290
590
404
477
158
127
359
51
90
48
118
61
45
37
53
37
42
27
37
37
22
19
28
35
81
212
286
59
21
24
102
160
92
90
194
1330
674
2520
569
625
1500
1130
828
619
235
155
1280
919
749
6247
50
558
16
43
378
78
383
4714
3120
2820
256
106
1986
1964
1590
1490
1630
3250
2230
1860
2530
1680
2070
492
2050
3210
1490
2580
2280
2830
2900
2460
2990
1840
2390
2500
2020
590
1890
995
1040
1150
941
1730
534
1960
2840
2310
2430
1790
1120
1040
47
91
92
246
86
107
73
40
33
119
37
40
36
36
35
54
43
54
60
51
61
69
65
9
55
87
82
78
177
95
96
70
72
162
95
130
71
15
753
932
1286
2447
2128
1392
2170
1359
1787
228
2196
2942
1442
2202
2188
2610
2656
1852
2799
1808
2218
1630
1808
352
1828
961
805
677
736
1581
274
1115
2238
1756
1771
1392
544
719
4390
582
473
1670
1140
2240
6490
2870
9030
27
50
17
99
72
45
121
20
36
4399
191
136
873
503
1684
5620
2450
8198
Total
Filterable
Phosphorus
(µg P/L)
Filterable
Reactive
Phosphorus
(µg P/L)
410
15
265
126
252
6
242
105
546
306
476
279
306
74
70
229
271
194
94
106
86
5
67
38
76
41
33
28
27
28
15
17
18
6
7
7
11
6
57
55
79
22
5
7
72
66
78
19
90
334
270
31
48
212
270
176
85
87
76
3
64
30
74
38
27
24
19
24
9
10
5
3
5
6
2
3
14
34
81
5
2
3
63
33
51
11
70
318
411
198
225
762
652
536
323
191
115
374
180
199
725
451
522
283
167
99
Total
Suspended
Solids (mg/L)
678
238
194
3.2
842
111
70.1
22.0
398
31.9
90.5
174
31.8
96.0
20.4
16.1
25.3
23.2
6.7
2.8
19.5
3.1
3.0
4.6
3.2
4.0
4.9
6.4
5.7
6.5
8.1
5.2
6.4
10.4
15.7
59.0
76.0
15.0
4.2
5.1
2.8
19.6
4.5
5.0
5.9
500
195
885
210
213
68.8
302
99.4
662
13.7
5.2
Biochemical
Oxygen
Demand
(mg/L)
4.3
3.0
4.6
2.4
2.0
4.1
2.0
2.0
5.5
2.1
7.1
Page B - 3
NRM Wet Tropics Sustainable Agriculture Project - ACTFR Report No. 03/18, December 2003
Site Label
Location
Site Type
Status
Date and Time
0307
0307
0307
0923
0923
1530
1530
0948
0948
1551
1551
1551
2119
2119
2119
Costin
Costin
Costin
Costin
Costin
Costin
Costin
Costin
Costin
Costin
Costin
Costin
Costin
Keeble
Keeble
Keeble
Keeble
Keeble
Keeble
Keeble
Keeble
Keeble
Keeble
Keeble
Keeble
Keeble
Sturiale
Sturiale
Sturiale
Sturiale
Sturiale
Sturiale
Sturiale
Sturiale
Sturiale
Stur Pipe
Stur Pipe
Howes
Howes
Howes
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tully
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Tablelands
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Banana
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Urban
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Cane
Banana
Banana
Banana
Secondary
Secondary
Secondary
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Random
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Secondary
Primary
Primary
Primary
23/04/2003 12:00
23/04/2003 17:45
24/04/2003 09:20
26/01/2003 10:00
27/02/2003 16:10
18/02/2003 13:20
19/02/2003 07:45
18/02/2003 13:05
19/02/2003 11:25
26/08/2003 18:00
12/03/2003 17:30
26/01/2003 15:00
13/03/2003 14:30
20/04/2003 10:30
02/12/2002 01:12
07/01/2003 12:00
21/01/2003 12:00
28/01/2003 12:00
05/02/2003 12:00
09/02/2003 12:00
20/02/2003 12:14
25/02/2003 12:00
26/02/2003 12:00
27/02/2003 04:48
27/02/2003 10:48
28/02/2003 12:00
04/03/2003 07:12
02/12/2002 10.30
07/01/2003 12:00
21/01/2003 12:00
28/01/2003 12:00
05/02/2003 12:00
09/02/2003 12:00
20/02/2003 14.35
25/02/2003 12:00
25/02/2003 12:00
27/02/2003 10.40
27/02/2003 16.00
28/02/2003 12:00
04/03/2003 15.40
15/11/2002 12:00
02/12/2002 10.57
26/01/2003 12:00
26/01/2003 12:00
05/02/2003 12:00
12/02/2003 12:00
12/02/2003 12:00
27/02/2003 12:00
27/02/2003 15.15
05/02/2003 12:00
27/02/2003 11.13
23/12/2002 12:00
27/02/2003 12:00
27/02/2003 14.30
pH
Conductivity
(µS/cm)
Dissolved
Dissolved
Oxygen (mg/L) Oxygen (% Sat)
Temperature
(°C)
7.01
297
5.27
73.0
24.30
7.42
56
4.94
60.2
24.90
6.06
6.16
7.12
6.93
7.77
137
147
99
7.15
127
7.33
7.12
96
107
7.42
7.27
7.02
128
112
9.04
7.16
7.15
122
94
91
7.43
93
6.84
6.90
54
67
7.04
7.22
969
106
6.46
6.24
6.35
8.54
6.52
6.47
7.09
412
410
116
564
565
398
8.81
27.10
7.88
7.19
125
387
8.26
33.60
27.00
7.47
46
6.78
25.20
28.30
6.66
6.31
26.10
25.90
5.70
5.68
5.70
25.50
26.20
7.04
33.70
Total
Total
Filterable Ammonia (µg
Nitrogen (µg
N/L)
Nitrogen (µg
N/L)
N/L)
9400
3830
10660
10890
5530
12830
20850
2290
3240
3190
4922
7130
8170
726
4980
156
253
277
380
377
272
319
251
259
371
710
306
289
387
366
305
519
540
585
330
356
677
606
1060
898
1570
5420
3980
2940
3080
480
9570
9430
1400
12060
750
1830
4390
2030
1620
Nitrate +
Nitrite (µg
N/L)
Total
Phosphorus
(µg P/L)
Total
Filterable
Phosphorus
(µg P/L)
Filterable
Reactive
Phosphorus
(µg P/L)
8520
3450
10190
10630
1380
3200
20480
1040
1390
71
68
58
37
33
170
53
47
66
6341
2573
10183
9553
800
1347
19445
476
680
119
278
99
301
234
5120
121
1160
1520
434
887
67
194
75
223
170
688
79
255
287
61
177
67
219
142
632
72
218
252
7730
371
4750
154
210
185
283
373
264
196
238
235
331
403
269
282
329
295
246
275
446
452
298
239
526
428
485
726
637
4620
3040
2900
3030
389
9400
9050
1350
10800
582
1580
2020
908
658
170
11
126
6.0
7.3
61
11
15
7.5
23
4.4
8.8
8.5
8.6
5.1
9.4
32
5.2
7.6
43
39
29
3.1
5.3
46
25
28
49
82
342
376
137
128
29
1090
1200
13
277
46
9.9
439
76
49
7699
64
4256
23
55
123
30
36
59
17
88
17
79
70
99
91
28
12
3
27
16
114
73
10
204
23
175
341
164
4111
2282
2534
2484
153
7217
7426
1035
8807
75
1002
1323
705
503
21
133
54
9.2
14
23
39
25
23
39
19
20
61
176
25
23
40
48
28
92
98
147
22
57
173
164
386
173
605
43
54
68
60
51
80
83
140
97
65
59
1340
853
782
8
25
25
8.2
13
13
18
15
17
22
15
16
56
103
20
18
25
27
15
26
66
85
17
27
116
146
125
108
186
34
37
27
26
32
38
39
104
38
41
40
74
54
56
4
14
20
7.4
9.5
7.5
8.2
8.3
9.6
14
8.6
7.5
48
79
12
10
19
21
7.4
17
48
70
1.9
13
98
98
110
85
171
16
19
21
22
21
33
32
100
20
27
20
72
36
41
Total
Suspended
Solids (mg/L)
1.6
7.4
4.0
103
2760
7250
51.0
1060
1000
231
1546
2070
7.0
105
60.6
7.0
8.0
9.0
4.0
19.0
103
6.0
4.0
3.0
6.0
90.0
2.0
323
10.0
11.0
1.0
33.0
39.0
38.0
3.0
7.0
56.0
42.0
252.0
33.0
14.0
9.0
7.0
107
104
48.0
78.0
79.0
37.0
106
63.0
28.0
3900
2885
2681
Biochemical
Oxygen
Demand
(mg/L)
2.1
7.9
8.5
2.0
4.3
5.9
5.0
6.6
2.0
2.2
Page B - 4
Appendix C
A diagram illustrating the features of a boxplot graph, listing the median, 25th and 75%ile data and other
features such as outliers.
Values more than 3 box-lengths from 75th percentile (extremes)
Values more than 1.5 box-lengths from 75th percentile (outliers)
Largest observed value that isn’t an outlier (90th percentile)
75th PERCENTILE
50% of cases have
values within the box
MEDIAN
25th PERCENTILE
Smallest observed value that isn’t an outlier 10th percentile)
Values more than 1.5 box-lengths from 25th percentile (outliers)
Values more than 3 box-lengths from 25th percentile (extremes)
Australian Centre for Tropical Freshwater Research
Page C - 1