Effects of agricultural practices on the water quality
of the Scott River: with focus on primary production
Artemis Kitsios
Honours Thesis: Bachelor of Environmental Engineering
Supervisor: Dr Anas Ghadouani
Effects of Agricultural practices on the water quality of the Scott River
Abstract
The Scott Coastal Plain lies at the base of the Blackwood catchment, stretching 70km along
the south coast of Western Australia and 20km inland. In 2001 the Department of Agriculture
developed a strategy for a sustainable future for this region, in terms of intensifying and
varying agricultural land use. This study aims to predict the effects that future land uses will
have on the environmental water quality of the Scott River. Nutrient and primary production
data from sites along the Scott River were analysed, with the data from each site representing
the response of the river from land use of a sub catchment. Variations were studied during
different stages of the year. The aims of the study were to correlate observed total nitrogen to
total phosphorous ratios (TN:TP) in the Scott River with land use from the catchment, find a
relationship between TN:TP and production and determine if the production rates were
adversely affecting the water quality. Particular attention was placed on the occurrence of
cyanobacteria, which pose a threat to both ecosystem and human health.
The large proportion of land use dedicated to animal agriculture was reflected in the low
TN:TP observed in the Scott River. These conditions promoted production only on some
occasions. Further investigation revealed that the water temperatures and the nitrogen and
phosphorous concentrations were limiting growth. High TN:TP ratios were correlated with
low productivity. Cyanobacteria were never present among high TN:TP and did appear at low
TN:TP but dominated rarely. Further investigation showed that cyanobacteria at upstream
sites during spring and winter appeared during nutrient limiting conditions. There were
increased concentrations of cyanobacteria observed during summer. The dominant
phytoplankton groups changed with the seasons. During summer, cyanobacteria, diatom and
dinoflagellate counts dominated, as did diatoms and chrysophytes in autumn. During winter,
production was dominated by green algae and dinoflagellates and in spring, phytoplankton
groups were equally dominant.
Although the greatest concentrations of nutrients were exported into the river during winter, at
this time of the year, the water temperature was too cold to promote excessive growth of
phytoplankton and therefore did not have a great impact on the water quality of the Scott
River. Nutrient concentrations were lower in the summer period yet this did not prevent
similar concentrations of phytoplankton from appearing in the Scott River. The warmer
conditions did promote a larger concentration of cyanobacteria, which is a concern for the
health of the river as some species of cyanobacteria can be toxic even at low concentrations.
I
Effects of Agricultural practices on the water quality of the Scott River
Acknowledgements
The writing of this thesis was a challenging learning experience and there are many people I
would like to thank for helping me complete it. I would like to thank everyone at the Centre
for Water Research including students, administrative staff, computer support staff and
lecturers for making the time spent in the building a unique and enjoyable experience. Special
thanks also to Anas Ghadouani for supervising me throughout the project and encouraging me
to arrive at my own questions and answers.
I would like to thank the Department of Environment, particularly Rosemary Learch for her
assistance in gathering a great deal of data and other information for me to use in this study. I
would also like to thank Kate Bilinska for assisting with the site investigation of the Scott
River and the surrounding land uses. Finally, a sincere thankyou to my friends and family for
all their support throughout the year.
II
Effects of Agricultural practices on the water quality of the Scott River
Table of Contents
ABSTRACT ...................................................................................................................................... I
ACKNOWLEDGEMENTS .............................................................................................................II
TABLE OF CONTENTS............................................................................................................... III
LIST OF FIGURES ....................................................................................................................... IV
LIST OF TABLES ...........................................................................................................................V
GLOSSARY ................................................................................................................................... VI
1
INTRODUCTION ...................................................................................................................1
2
LITERATURE REVIEW AND BACKGROUND ..................................................................2
2.1
2.2
2.3
2.4
2.5
3
3.1
3.2
3.3
4
4.1
4.2
4.3
4.4
4.5
4.6
5
5.1
5.2
5.3
5.4
5.5
WATER QUALITY ...................................................................................................................2
NUTRIENT ENRICHMENT ........................................................................................................8
AGRICULTURE: A DIFFUSE SOURCE OF NUTRIENTS ...............................................................11
RIVERINE RESPONSES TO LAND USE .....................................................................................15
SITE DESCRIPTION ...............................................................................................................24
APPROACH ..........................................................................................................................31
SITE INVESTIGATION ............................................................................................................31
DATA COLLECTION ..............................................................................................................31
DATA MANIPULATION..........................................................................................................33
RESULTS ..............................................................................................................................35
LAND USE ...........................................................................................................................35
TN:TP IN THE SCOTT RIVER .................................................................................................37
LIMITATIONS .......................................................................................................................39
CYANOBACTERIA .................................................................................................................42
PHYTOPLANKTON GROUPS ...................................................................................................45
NUTRIENT VARIATIONS ........................................................................................................48
DISCUSSION.........................................................................................................................49
LAND USE ...........................................................................................................................49
SEASONAL VARIATIONS ON NUTRIENT SUPPLY .....................................................................50
LIMITATIONS TO PRODUCTION ..............................................................................................51
CYANOBACTERIA .................................................................................................................52
PHYTOPLANKTON GROUP SUCCESSION .................................................................................56
6
CONCLUSIONS....................................................................................................................58
7
RECOMMENDATIONS .......................................................................................................59
8
REFERENCES ......................................................................................................................60
9
APPENDICES........................................................................................................................65
9.1
9.2
9.3
9.4
9.5
9.6
9.7
APPENDIX 1: NUTRIENTS, CYANOPHYTA AND PHYTOPLANKTON RAW DATA. ..........................65
APPENDIX 2: DISSOLVED OXYGEN CONCENTRATIONS AT SRF01............................................66
APPENDIX 3: SALINITY VARIATIONS AT SRF01 .....................................................................67
APPENDIX 4: TURBIDITY VALUES AT SCOTT RIVER SITES .......................................................68
APPENDIX 5: COLOUR VALUES AT SCOTT RIVER SITES...........................................................69
APPENDIX 6: DISSOLVED ORGANIC CARBON CONCENTRATIONS AT SITE SRF01 ......................70
APPENDIX 7: TOTAL NITROGEN AND TOTAL PHOSPHOROUS CONCENTRATIONS AT SITE SRF01 71
III
Effects of Agricultural practices on the water quality of the Scott River
List of figures
Figure 2-2: Catchment scale (Blackwood Basin Group 2001) and the Local scale...................4
Figure 2-3: Producers within the aquatic ecosystem. ...............................................................5
Figure 2-4: Trophic dynamics .................................................................................................6
Figure 2-5: Water usage and wastes........................................................................................7
Figure 2-6: Row cropping and animal agriculture .................................................................11
Figure 2-7: Agricultural land use and corresponding nitrogen requirements ..........................12
Figure 2-8: Method of predicting cyanobacteria blooms (Elser 1999) ...................................19
Figure 2-9: The Blackwood Catchment (Read & Bessen 2003).............................................26
Figure 2-10: Scott River and surrounding aquatic systems ....................................................29
Figure 2-11: Pelican, Hardy Inlet ..........................................................................................30
Figure 3-1: Sampling locations .............................................................................................31
Figure 4-1: Land use in the Scott Catchment (WRC 2002)....................................................35
Figure 4-2: Comparison of TN:TP at Scott River sites in 2000 and 2001 ..............................37
Figure 4-3: Snapshot of phytoplankton group composition and the corresponding TN:TP ratio.
.............................................................................................................................................38
Figure 4-4: Scatter graph of TN:TP against cell counts of phytoplankton at all Scott River
sites 2000-2001 ....................................................................................................................38
Figure 4-5: Phosphorous concentrations and the corresponding phytoplankton cell counts
separated by sampling sites...................................................................................................39
Figure 4-6: Nitrogen concentrations and the corresponding phytoplankton cell counts
separated by sampling sites...................................................................................................40
Figure 4-7: Phytoplankton cell concentrations at Scott River sites 2000-2001 as a function of
in situ temperature. ...............................................................................................................41
Figure 4-8: Percentage of cyanophyta dominance as a function of TN:TP. Comparison of
Scott River data (without SRF01) with published data from Smith, 1983. .............................42
Figure 4-9: Scatter graph of Cyanophyta cell counts and TN. Vertical line at 1.0 mg/L of TN
.............................................................................................................................................43
Figure 4-10: Scatter graph of Cyanophyta cell counts and TP. Vertical line at 0.15mg/L of TP
.............................................................................................................................................43
Figure 4-11: Cyanophyta dominance separated by nutrient conditions. .................................44
Figure 4-12: Spring phytoplankton group patterns at site 609026, 2000 ................................45
Figure 4-13: Winter phytoplankton group patterns................................................................46
Figure 4-14: Seasonal variation in phytoplankton populations at SRF01 in 2001...................47
Figure 4-15: Surface samples of Total phosphorous and total nitrogen concentrations at
SRF01 in 2001......................................................................................................................48
Figure 5-1: Monthly rainfall and TN concentrations at 609002, 2000....................................49
Figure 5-2: Colour of Scott River..........................................................................................52
Figure 5-3: TN and TP loading at 609002 in 2000. ...............................................................54
Figure 5-4: Phytoplankton groups at 609002 in 2000. ...........................................................55
IV
Effects of Agricultural practices on the water quality of the Scott River
List of Tables
Table 2-1: Pollutant type and effect on water quality ..............................................................8
Table 2-2: Nutrient Inputs, Outputs and Losses of Dairy, Piggery and Horticultural land use 13
Table 2-3: Agricultural activities ..........................................................................................14
Table 2-4: Phylum and Features of Phytoplankton................................................................17
Table 2-5: Name and type of benthic algae ...........................................................................20
Table 2-6: Correlations of Environmental Variables with Zooplankton communities ............21
Table 2-7: Saprobic zones.....................................................................................................23
Table 2-8: Characteristics of drift .........................................................................................23
Table 2-9: Characteristics and affected length of Western Australian Rivers.........................25
Table 2-10: Proposed water quality targets for Scott River....................................................30
Table 3-1: Physical variables ................................................................................................32
Table 4-1: Land uses in each sub catchment of the Scott Coastal Plain..................................36
Table 4-2: Nutrient concentrations varying with depth..........................................................48
Table 5-1: In situ water temperature range and corresponding maximum cyanophyta
concentrations ......................................................................................................................53
Table 5-2: Dominance of phytoplankton groups during.........................................................53
Table 5-3: Environmental variables and cyanophyta concentrations......................................54
V
Effects of Agricultural practices on the water quality of the Scott River
Glossary
AEL
Australian Environmental Laboratories
AGAL
Australian Government Analytical Laboratories
cropping
land use relating to the cultivation of crops
cyanobacteria
Also known as blue-green algae, some species release toxins
dairying
land use relating to the production of milk and milk products from cows
estuary
section of water where a river meets the ocean, causing riverine
currents to interact with the tide
eutrophication
process where a water body becomes enriched in nutrients which causes
excessive growth of aquatic plants
fertiliser
material used to enrich soil
horticulture
land use where fruit, vegetables and/ or flowers are grown
in situ
refers to measurements carried out at the sampling site
lentic
Relating to still waters, such as lakes and ponds
light limitation
The condition where phytoplankton growth is restricted by low light
levels.
lithified
turned to stone
livestock grazing
land use where cattle/sheep feed on grass
lotic
Relating to moving water, such as rivers
mucilage
gummy substance found in plants
nutrient limitation
the condition where phytoplankton growth is restricted due to a lack of
nutrients
nutrient ratios
The ratio of two nutrients
pesticide
chemical substance used for destroying insect and plant pests
regulate buoyancy
a method used by cyanobacteria to control their position in the water
column
stagnant
not moving or flowing
stoichiometry
The quantitative relationship between two or more substances
TN
Total nitrogen, includes both dissolved and particulate nitrogen.
TP
Total phosphorous, includes both dissolved and particulate phosphorous
turbidity
A measure of the living and non-living particles in water bodies which
reduce the clarity of water and limit light penetration
VI
Effects of Agricultural practices on the water quality of the Scott River
1 Introduction
Water quality is a subject of topical discussion and describes the health of a water body
according to the intended use. Many reports have detailed the importance of water quality in
terms of aesthetics, drinking water, recreation and environmental quality. It is well
documented that changes in land use can result in changes in water quality due to nutrient and
pollutant fluxes. The purpose of this study is to determine the effect of agricultural land use
on the water quality of the Scott River.
Agricultural land use includes land used for cultivating soil, producing crops and raising
livestock. Such land uses are a diffuse source of nitrogen and phosphorous to receiving water
bodies. This is a problem because along with light, nitrogen and phosphorous limit growth of
primary producers, with phosphorous being particularly limiting in freshwater ecosystems.
Increases in these nutrients alter the growth and structure of these organisms. The loading of
nutrients entering the river is important as high loads lead to eutrophication, increased
production rates and a decline in water quality. The ratio of these nutrients is also important.
Low ratios of nitrogen to phosphorous have been shown to promote the dominance of
cyanobacteria, which is toxic to human and ecosystem health.
The Scott River is one of a few rivers in Western Australia still of high quality. Land use in
this region is expected to intensify, which may pose a threat to the environmental quality of
the Scott River. The region is one of high rainfall and low soil retention, producing high
nutrient export rates to the environment in comparison to nearby regions. Biological growth
in the river is also believed to be limited by light and increases in nutrients may therefore not
effect biological growth to a large extent. The purpose of this study is to predict the response
of the river from agricultural land use activities so that responses to land use changes can be
predicted.
This thesis is comprised of numerous chapters. Chapter 2 consists of a literature review
encompassing all relevant topics within this study and also describes the study site. The
approach undertaken in this study is described in Chapter 3 and the results detailed in Chapter
4. A discussion outlining the land use of the catchment, the nutrients observed in the river and
the growth of phytoplankton can be seen in Chapter 5. Conclusions and recommendations for
further work are outlined in Chapters 6 and 7 respectively.
1
Effects of Agricultural practices on the water quality of the Scott River
2 Literature review and Background
In order to understand the way in which agricultural activities can impact receiving water
bodies, a literature review has been conducted encompassing all relevant topics. Firstly, an
introduction into water quality, its definitions and its controls is detailed in Chapter 2.1.
Chapter 2.2 details the role that nutrient enrichment has on water quality and Chapter 2.3
describes the way in which agricultural activities have become a source of nutrients. The
response of river systems to such nutrients are detailed in Chapter 2.4 and Chapter 2.5 gives a
description of the study site.
2.1 Water Quality
Water quality has been defined as the physical, chemical and biological characteristics of a
water body, dependent on its intended use (USGS 2002; VDEQ 2004). In simpler terms, it is
a description of the health of a water body, assessed by the chemical, biological and physical
characteristics of the water.
Water has many uses, each requiring a specific health, or standard. These standards are met
by achieving the water quality targets set in guidelines. The majority of guidelines are based
on three standards which relate to drinking water quality, recreational quality and
environmental quality. Standards also exist for industrial use, stock source water and
irrigation. Assessing water quality can therefore determine if a specific use for the water is
appropriate. It can also record the improvement or deterioration of a water body over time.
Drinking water requires the highest standard for use, while standards for recreational use vary
according to the contact associated with the water body. The natural environment requires a
specific water quality, termed environmental water quality, which will be the focus of this
thesis. Environmental water quality varies naturally, however human impacts can cause the
environmental water quality to change dramatically (Department of Environment and
Heritage 2000). A variety of human activities affect the natural environment.
2
Effects of Agricultural practices on the water quality of the Scott River
2.1.1 Aquatic Ecosystems
A water body is a sensitive ecosystem, its quality influenced by the climate, the land use
within the associated catchment, neighbouring ecosystems, biological activity and physical
properties. It is both a habitat and a nutrient source for aquatic organisms. A water body
interacts with the atmosphere, the sediments and nearby water bodies. Consequently aquatic
populations exist in the water column, on and in the sediments, may migrate to different
depths of the water, be transported downstream or relocate upstream. These populations all
rely on the health of the ecosystem to provide them with their needs for growth and survival.
The health of aquatic ecosystems is impacted by physical and chemical stressors, such as
nutrients, turbidity and salinity, as well as toxicants (Department of Environment and
Heritage 2000). In particular, it is large increases away from the natural variation of such
stressors which causes environmental damage (Edgar & Nicholls 2003).
2.1.2 Controls on Water Quality
Water quality is controlled by spatial and temporal characteristics. The spatial scales that
influence water quality include the regional, catchment, and local scales. Temporal
characteristics relate to those which vary with time and may reflect the seasonality of the
system. Nearby ecosystems are also influential in controlling water quality.
The regional scale determines climate, which influences rainfall, solar radiation, evaporation
rates and their temporal variations. Rainfall influences water quality due to its impurities and
its correlation with discharge into the water body. Discharge is also dependent on the soil and
topography of the catchment. Climate determines the seasonal variations of flow and storm
flow, which largely control nutrient transport (Pionke et al. 1999).
At the catchment scale, the quality of the rain water that falls on the catchment is altered by
its interactions with the soil, vegetation, geology and any impervious substances (Gower
1980). During this process various impurities may become dissolved in the water via
chemical processes, including heavy metals, toxins or nutrients. This water may infiltrate the
land, perhaps enter groundwater stores or runoff and enter surface water stores. Point source
waste discharges from surrounding land use also enter water stores and influence water
quality. Particulates can also be transported from the catchment to the water body. Organic
particles in the water column originate from plant matter as well as dead or decaying aquatic
3
Effects of Agricultural practices on the water quality of the Scott River
life (Hemond & Fechner-Levy 2000). Nutrients which are added to the soil in farming
practises may also enter the water body by runoff (AGWEST 1998).
Figure 2-1: Catchment scale (Blackwood Basin Group 2001) and the Local scale
On a local scale, the biological activity and the physical and chemical properties of the water
body influence its water quality. The hydrodynamic and light conditions are influential in
nutrient availability and the control of biological growth. During heating of a water body,
water density changes. The warmer, lighter water floats on top of the cooler, heavier water,
creating a density gradient, leading to stratification. During such conditions, the bottom
waters can become anoxic due to its isolation from an oxygen source. Consequently, nutrients
are released from the sediments, and are made available for biological growth. Suspended
sediments can also reach the bottom of a water body by the process of settling. The organic
matter present in the sediments can promote growth of oxygen consuming micro-organisms
which can lead to anoxic conditions (Hemond & Fechner-Levy 2000). Salinity also
influences water quality. Oxygen is less soluble in saline water and chemical species have an
increased strength (Hemond & Fechner-Levy 2000). The meeting of saline waters with
freshwaters result in flocculation which increases the flux of sediments settling to the bottom
waters.
The water quality of water bodies is affected by neighbouring ecosystems. The water quality
of reservoirs, lakes, springs, rivers and estuaries is largely determined by the quality of
upstream and groundwater inflows. Conversely, water from rivers, lakes and reservoirs may
seep into the ground, affecting ground water quality. Wetlands often border rivers and lakes
(Hemond & Fechner-Levy 2000), enabling an exchange between the ecosystems. Estuaries
influence the chemistry and biology of the adjoining water body due to their characteristically
nutrient rich waters (Hemond & Fechner-Levy 2000), the influence of both marine and
catchment processes (Smith et al. 2001) and the intrusion of the salt wedge, causing
4
Effects of Agricultural practices on the water quality of the Scott River
stratification. Stratification is reported as a mechanism in controlling phytoplankton primary
production (Twomey & John 2001).
2.1.3 Primary Production
The aquatic ecosystem begins with the producers, which influence the trophic dynamics of
the entire food chain. The producers take up nutrients within the water body, the sediments or
fix them from the atmosphere, as shown in Figure 2-2. Arrows represent uptake of nutrients.
Producers include phytoplankton, benthic algae or nutrient fixing bacteria. The growth and
survival of phytoplankton and benthic algae is limited by light and nutrients, particularly
phosphorus and nitrogen. The competition for light and nutrients between other producers as
well as the predation by consumers also influence the growth and survival of primary
producers.
Nutrients
N fixers
Nutrients
Nutrients
Phytoplankton
Nutrients
Benthic algae
Nutrients
Figure 2-2: Producers within the aquatic ecosystem.
Light is a limiting factor in primary production as phytoplankton cells require light in order to
photosynthesise. Growth rates of phytoplankton have been directly related to light intensity
(Holmes 2000) as photosynthesis can only occur if the light intensity reaching the
phytoplankton cell is sufficient (SAHFOS 2004). When light is not limiting production, it is
the availability of nutrients that is most influential.
Prior to human settlement and agricultural development, productivity in aquatic ecosystems
was limited by nitrogen or phosphorus (Environment Canada 2001). Nitrogen became
5
Effects of Agricultural practices on the water quality of the Scott River
available only once it was fixed from the atmosphere and phosphorous became available once
weathered from rock (Environment Canada 2001). Phosphorus is reported as being the
limiting nutrient to phytoplankton growth in freshwater systems (Rabalais 2002; Creswell et
al. 2001) while nitrogen is limiting in marine systems (Creswell et al. 2001; Anonymous
2003) and some inland waters (Edgar & Nicholls 2003; Fellows 2003). In estuarine to coastal
areas, many nutrient limitations occur along the salinity gradient, including nitrogen,
phosphorous and silicon (Rabalais 2002). In recent times nitrogen and phosphorous have
become more readily available due to increased outputs into the environment from fertilisers
and atmospheric emissions. Effects of such increases include accelerated eutrophication of
surface waters and increases in the frequency of toxic algal blooms (Environment Canada
2001).
Primary producers including benthic algae and phytoplankton compete for nutrients and light
(Kahlert & Pettersson 2002). A large phytoplankton community can prevent the light from
penetrating to the benthic communities, however some benthic species can migrate into the
water column to access light. Nutrient fixing cyanobacteria can fix nutrients directly from the
atmosphere and can therefore dominate production when conditions prevent other primary
producers from doing so. Primary consumers are those species which feed on the producers,
having some control on the producer population. Primary consumers include zooplankton,
crustaceans and invertebrates. Secondary consumers (fish) feed on the primary consumers.
Trophic dynamics are illustrated in Figure 2-3. Red arrows indicate nutrient recycling.
fish
Bacteria
POM
zooplankton
DOM
phytoplankton
crustaceans
small
invertebrates
Benthic algae
Figure 2-3: Trophic dynamics
6
Effects of Agricultural practices on the water quality of the Scott River
2.1.4 Water Uses and Wastes
Settlements were traditionally positioned in areas with accessible drinking water of the
highest quality and quantity (Gower 1980), to provide the settled population with a stable
water supply. The extraction of water and discharge of wastes has had an adverse impact on
water quality. Today, land use changes including agricultural intensification, urbanisation and
industrialisation impose a stress upon aquatic systems. Water is extracted as a source and
wastes are discharged into the water bodies as diffuse sources (agriculture) or point sources
(industrial and urban wastes), as illustrated in Figure 2-4. Point sources directly discharge
into surface waters, whereas diffuse sources are transported in different pathways (Deumlich
& Völker 2003). Such wastes pollute water ways (Department of Environment and Heritage
2000) and can have detrimental effects upon the aquatic life.
Drinking
water
Urban
areas
Aquatic systems
Irrigation
Agriculture
Agricultural
wastewater
Urban
wastewater
Industrial
water
Industrial
wastewater
Industry
Figure 2-4: Water usage and wastes
2.1.5 Impacts of Wastes
Land uses are responsible for a variety of waste substances found in rivers. These pollutants
include nutrients, chemicals, pathogens and toxins, each detrimental to the health of aquatic
organisms. Organic pollutants are detrimental to ecosystem health as they are toxic and can
cause bioaccumulation up the food chain. Sediments smother plants and animals of the
benthos and restrict light penetration due to reduced clarity (Water and Rivers Commission
1997). Chemicals and heavy metals can also be found within the sediments or the water
column, capable of causing illness and death of aquatic organisms. Pathogens are micro7
Effects of Agricultural practices on the water quality of the Scott River
organisms typically found in waste from wastewater effluent, however are also found in
agricultural wastes. Waterborne pathogens are a threat to aquatic ecosystems (Environment
Canada 2001) as ingestion of pathogen contaminated water can result in illness and disease of
plants and animals (Water and Rivers Commission 1997). Biotoxins are those released by
living organisms such as cyanobacteria, dinoflagellates or diatoms (Water and Rivers
Commission 1997). Toxic species pose a threat at cell counts as low as 5 cells/mL (Water and
Rivers Commission 1997). Increased nutrient loads are detrimental to aquatic organisms as
this can lead to eutrophication and reduced oxygen levels. A summary of pollutant type and
its effect on water quality is detailed in Table 2-1.
Table 2-1: Pollutant type and effect on water quality
Pollutant
Nutrients
Toxins
Pathogens
Physical
pollutants
2.2
Examples
Effect
Nitrogen*
Eutrophication, algal blooms, reduced O2 levels
Phosphorous*
causing fish kills
Pesticides*
Bioaccumulation; deaths, defects or illness of
Heavy metals*
plants and animals
Bacteria*
Disease in plants, animals and humans
Viruses
Sediment*
Reduce water clarity & restrict light availability
Salt*, litter
* Pollutants from agricultural land uses
Nutrient Enrichment
Nutrient enrichment can alter the water quality of a water body. Both the loading of nutrients
into a water body, as well as the stoichiometry of the nutrients are influential. Three sources
of nutrient enrichment include atmospheric deposition of nitrogen, industrial and domestic
discharges of phosphorous and agricultural intensification producing increased losses of both
nitrogen and phosphorous (Edwards et al. 2000). High nutrient loads are detrimental to water
quality as this can lead to nutrient enrichment, or ‘eutrophication’. The ratio of nutrients
affects the growth and structure of the primary production community.
2.2.1 Nutrient Load
The magnitudes of nutrient loads are dependant on both nutrient concentration and flow rate.
The concentrations of nitrogen and phosphorous vary differently in time and space,
8
Effects of Agricultural practices on the water quality of the Scott River
influenced by land use and upstream concentrations. Areas of intense land use will have high
rates of nutrient loss to the environment, as nutrients which fail to be taken up by the soil will
be lost through leaching and runoff (Neville & Weaver 2003) and enter groundwater or
surface water stores. Phosphorous export is concentrated in time, space, and by flow
component while nitrate-N is more dispersed (Pionke et al. 1999).
Flow rates have a large effect on nutrient transport as they can vary by orders of magnitude,
whereas the nutrient concentrations vary by small percentages (Pionke et al. 1999). For a
given nutrient concentration, higher flow rates produce higher nutrient loading. The increased
water velocity means that the nutrients can be diluted and dispersed downstream at a quicker
pace. Storm flows are responsible for increased phosphorous loadings, creating a random
nature of the phosphorous temporal scale (Stalnacke et al. 2003).
2.2.2 Eutrophication
An increase in nitrogen or phosphorous concentrations can lead to eutrophication (Dassenakis
et al. 1998), which refers to the process of nutrient enrichment in a water body causing
excessive growth of aquatic plants (USGS 1998). This growth is often too large for the
consumer population to control. Algal blooms occur as a result, adversely affecting the entire
ecosystem. For moderate to large sized algal cells (diameter > 15-20 microns), a
phytoplankton concentration greater than 15,000 cells/mL is considered a bloom (Water and
Rivers Commission 1998). For small cells (diameter < 1-5 microns), discolouration occurs at
concentrations of 100,000 cells/mL and is considered a bloom (Water and Rivers
Commission 1998). During bloom conditions oxygen levels become depleted, no longer
accessible to fish species. The depletion of oxygen also causes anoxic conditions to occur.
Such conditions result in the release of nutrients from the sediments, providing additional
nutrients for growth.
2.2.3 Stoichiometry
The stoichiometry of nutrients within a water body influences the growth rate and the
composition of the phytoplankton community. The optimal molar ratio for phytoplankton
growth is C:H:O:N:P = 106:263:110:16:1, also referred to as the Redfield ratio. The ratios
9
Effects of Agricultural practices on the water quality of the Scott River
most commonly studied is that of C:N:P, and at times simply N:P. When dealing with N:P
the optimal growth rate for phytoplankton is 16:1. Any deviations from this ratio are capable
of affecting phytoplankton biomass, species composition, food web dynamics (DEPA 2004)
and consequently water quality.
A topical debate is whether or not low TN:TP ratios promote a dominance of cyanobacteria,
which has been described as a major risk to human and ecosystem health (Downing et al.
2001). Many have shown that a low N:P promotes a dominance of cyanobacteria (Smith
1983; Schindler 1978) yet others believe that this hypothesis is flawed (Downing et al. 2001;
Scheffer et al. 1997).
Low N:P has been reported to indicating nitrogen limitation (Temponeras et al. 2000; DEPA
2004). Under certain conditions some cyanobacteria can fix atmospheric nitrogen (Scheffer et
al. 1997; Ahn et al. 2002). This fact leads to the idea of cyanobacteria dominating in low
TN:TP, because other phytoplankton groups would be N limited (Smith 1983). Ahn and
others (2002) report that cyanobacteria dominate at low TN:TP because their optimum
TN:TP is lower than that of other algae. Smith (1983) states that cyanobacteria blooms occur
at TN:TP below 29:1 and are rare above this figure.
In many cases, a low TN:TP is not correlated with a dominance of cyanobacteria. Downing
and others (2001) suggest that cyanobacteria blooms are more strongly correlated with
variations in TP, TN, or standing algae. In a study by Jensen and others (1994) regarding 210
Danish shallow lakes, no relationship was found between cyanobacteria abundance and
nitrogen availability (Scheffer et al. 1997). There is the possibility that correlations aiming at
cyanobacteria versus TN:TP can be due to either an increase in phosphorous or a decrease in
nitrogen. Ferber and others (2004) suggest that the low TN:TP ratio is only one characteristic
that can promote cyanobacteria dominance, with other possibilities including migration to
benthic ammonium sources and the use of dissolved organic nitrogen (Ferber et al. 2004).
10
Effects of Agricultural practices on the water quality of the Scott River
2.3 Agriculture: A Diffuse Source of Nutrients
Agricultural activities are a source of nutrients to both freshwater and marine ecosystems
(Arbuckle & Downing 2001), the concentrations of which have been strongly correlated to
the percentage of agricultural land in its catchment (Stalnacke et al. 2003; Edwards et al.
2000). Agricultural land use includes land used for cultivating soil, producing crops and
raising livestock and does not include timber harvesting activities. Examples of agricultural
land use are displayed in Figure 2-5. Pesticide and fertiliser runoff are examples of diffuse
nutrient sources from agricultural land use (Hemond & Fechner-Levy 2000). Agricultural
intensification has had great impacts upon the water quality of receiving water bodies
(Gilvear et al. 2002). As a result, many studies have tried to understand the controls on
nutrients from such activities entering water stores.
Traditional mixed farming agriculture involved the recycling of nutrients. Agricultural
technologies have now developed such that operations are specialised concerning either
livestock or intensive cropping. This means that more manure is wasted and more fertiliser is
required, which increases loss rates to the environment. Nitrogen levels of Latvian rivers in
agricultural areas displayed this trend. The nitrogen levels of the rivers increased with
increased use of nitrogen fertilisers and intensification of animal production (Stalnacke et al.
2003).
Figure 2-5: Row cropping and animal agriculture
11
Effects of Agricultural practices on the water quality of the Scott River
Stalnacke and others (2003) identified four controls on the magnitude and temporal
variability of nutrient concentrations in agriculturally dominated rivers. These included
farming practices, the soil nutrient pool, hydrological pathways, temporal variability in flow
conditions as well as in-stream, riverine, and lake retention.
Scrimgeour and Kendall (2002) conducted a study regarding the impacts of agricultural land
uses on streams. A variety of treatments were applied including early season livestock
grazing (June–August), late season livestock grazing (August–September), all season grazing
(June–September), and a livestock absent treatment as a control. Their results found that the
concentration of total phosphorus was significantly higher in the all-season livestock grazing
than that in the livestock-absent control, and the early season and late season grazing
treatments. As a result of this study, five processes were outlined by which livestock grazing
can increase concentrations of N and P entering water courses:
1) increasing N and P inputs to stream channels, riparian zones and shallow groundwater
from voided wastes;
2) mobilizing N and P in stream sediments and stream banks;
3) increasing the tendency of overland flow during precipitation events;
4) decreasing denitrification rates within the riparian zone;
5) reducing uptake by riparian vegetation.
Arbuckle and Downing (2001) suggest that in agricultural regions, the ratio of nitrogen to
phosphorous (N:P ratio) in aquatic systems is correlated with the N:P fluxes from agricultural
land use. Land uses including livestock grazing, cropping, horticulture and dairying discharge
nitrogen and phosphorous into rivers in specific ratios. As shown in Figure 2-6, horticultural
land use (right) require more nitrogen than land used for livestock (left).
Figure 2-6: Agricultural land use and corresponding nitrogen requirements
Source Department of Agriculture, 2004
12
Effects of Agricultural practices on the water quality of the Scott River
Arbuckle and Downing (2001) found that N:P was over 50 where over 90% of the lake’s
catchment was dedicated to row crop agriculture, as this land use often involves low
amendments of phosphorous and the use of nitrogenous fertilizers (anhydrous ammonia,
ammonium nitrate, liquid nitrogen). In the same study, the lakes which drained pasture lands
(animal agriculture), were shown to have low N:P ratios as losses from animal feeding and
pasture operations are P-enriched, (Arbuckle & Downing 2001).
A study carried out by Neville and Weaver (2003) detailed a nutrient budget for three
different types of agricultural land use. Inputs into the farm included fertiliser, feed, animals,
nutrient fixation, rainfall and wastes while outputs from the farm included products sold such
as cheese, milk, animals and vegetables. The nutrient losses to the environment were
calculated by subtracting the outputs from the inputs. The details are shown in Table 2-2. In
terms of dairy, piggery and horticultural land use, the N:P ratio input to the farm is very
similar to the N:P ratio of the losses. Animal agriculture displays a low N:P ratio, similar to
that predicted by Arbuckle and Downing (2001). Horticulture also has a low ratio, which is
the opposite of what was stated in the same study. This may be due to the lower percentage of
land dedicated to horticulture in the study by Neville and Weaver and also because the N:P
varies within the catchment on each sampling day (Edwards et al. 2000).
Table 2-2: Nutrient Inputs, Outputs and Losses of Dairy, Piggery and Horticultural land use
Dairy
Piggery
Horticulture
P inputs (kg / ha)
28.7
81.5
65.0
N inputs (kg / ha)
137
409.0
380.7
N:P input (kg / ha)
4.8
5.0
5.8
P outputs (kg / ha)
5.3
21.9
11.5
N outputs (kg / ha)
27.1
118.5
59.7
P losses (kg / ha)
23.5
59.6
54.6
N losses (kg / ha)
110.6
290.5
321.0
N:P losses (kg / ha)
4.7
4.9
5.9
13
Effects of Agricultural practices on the water quality of the Scott River
In summary, Table 2-3 identifies various agricultural activities and their characteristics
relating to the nutrient concentrations observed in the receiving water bodies.
Table 2-3: Agricultural activities
Activity
Effect
Mixed farming
Recycling livestock manure for crop fertiliser minimises
nutrient wastes
Fertiliser application
Increased nitrogen levels (Stalnacke et al., 2003)
Cattle breeding
Increases suspended sediments and nutrients (De billy, 1999)
particularly nitrogen (Stalnacke et al., 2003)
Pasture
Low N:P ratios (Arbuckle and Downing, 2001)
Dairy
Increase in nutrients and organic load (DoE, 2004)
Row cropping
High N:P ratios (Arbuckle and Downing, 2001)
14
Effects of Agricultural practices on the water quality of the Scott River
2.4 Riverine Responses to Land Use
The impact of nutrient enrichment on river systems is complex (Edwards et al. 2000). Studies
completed on issues mentioned in previous chapters have mainly focused on lakes and
reservoirs. Although rivers are susceptible to similar problems, the application of this
knowledge to riverine systems may have differing results as rivers are dominated by fluvial
processes rather than limnotic ones. Water quality in rivers has been directly correlated with
population density and intensity of human activity (Gilvear et al. 2002) as rivers are also
susceptible to diffuse and point source pollution. Characteristics including advective
transport, high input rates and upstream-downstream gradients (Wiley & Seelbach 1997)
make their response to change different than other aquatic systems.
2.4.1 Transport
Once pollutants have been discharged into the river system either by point or diffuse sources,
they are then transported downstream. Materials inclusive of sediment, nutrients, dissolved
gases, pollutants and organisms are transported through advective means (Wiley & Seelbach
1997). Contaminants in rivers can travel long distances (Gower 1980) as transport rates are
high and directional, whereas in other aquatic ecosystems they are multi-directional, slow and
diffusive (Wiley & Seelbach 1997). They are also diluted and dispersed downstream
(Hemond & Fechner-Levy 2000). Suspended sediment transport is more significant in river
systems (Hemond & Fechner-Levy 2000) and has been shown to decrease in concentration
with an increase in flow rate (Dassenakis et al. 1998).
2.4.2 Sensitivity and Resilience
Rivers are sensitive ecosystems; however they are capable of self cleansing. Their small
volume and high input rates give them a characteristically high turnover rate, making them
both more sensitive to change yet more resilient to this change (Wiley & Seelbach 1997). If
the pollutant inputs are too severe, this may cause a decline in river water quality. The natural
process of self purification involves re-aeration, oxygenation of organic waste, production of
CO2, and the supply of oxygen by algal photosynthesis (Hino 1994). Rivers and streams have
a limited capacity of self cleansing (Gower 1980). For example, rivers have received
15
Effects of Agricultural practices on the water quality of the Scott River
effluents from cities, industries and agriculture without dilution (Prat & Munne 2000) and
this may be too poisonous to the river system. Small river ecosystems are more fragile than
larger ones and require careful management (Dassenakis et al. 1998).
2.4.3 Stratification
During high flow rates, river systems have shorter residence times. During such conditions,
the water body is not stationary long enough for stratification to develop. During low flow
rates, water can become stagnant. Combined with high solar radiation rates, rivers have been
known to stratify. These conditions contribute to a degraded water quality (Bormans &
Webster 1997), through the growth of cyanobacteria and the development of anoxic
conditions.
2.4.4 Biological Responses
Hydrology influences the ecology of rivers (Gilvear et al. 2002; Lloyd et al. 2003), with small
changes in river flow capable of causing large ecological responses (Lloyd et al. 2003). Flows
assist in providing a range of in-stream habitat for many organisms at differing stages of their
life cycle (Gilvear et al. 2002). As rivers flow downstream, biological material accumulates,
causing an upstream-downstream gradient and pattern of biological communities (Wiley &
Seelbach 1997). Any changes to the hydrology of the river system will cause an ecological
response, however there will be a lag time before this response is detected (Lloyd et al.
2003).
2.4.5 Phytoplankton
In large rivers phytoplankton abundance is influenced by turbulence, flow rates, turbidity,
temperature, and residence times (Thoms et al. 2000). During periods of reduced flow
velocities and high temperatures, the biomass, abundance and species richness of
phytoplankton communities have been shown to increase (Piirsoo 2001). Due to the
correlation with these seasonally driven variables, phytoplankton groups dominate at
different times of the year. A succession of phytoplankton groups is seen as the seasons
progress. In some systems flow rates and salinity are more important in regulating
16
Effects of Agricultural practices on the water quality of the Scott River
phytoplankton succession rather than nutrients (Chan & Hamilton 2001). Characteristics of
various phytoplankton groups are summarised in Table 2-4.
Table 2-4: Phylum and Features of Phytoplankton
Name
Phylum
Features
* Green algae
Chlorophyta
•
photosynthetic
•
fix C from atmosphere
•
freshwater
•
photosynthetic and heterotrophic
•
marine and freshwater
•
require Si for scales and spine
•
photosynthetic and heterotrophic
•
oceanic environments
•
Some toxic to fish and shellfish
•
Coccolithophorids contain calcite plates
•
Require Si for cell walls
•
Some are toxic
•
Grow under range of flow rates, dominate at high flows
•
Radial or bilateral symmetry
•
Photosynthetic
•
freshwater, marine waters, damp soil, tree trunks
Euglenophyta
•
photosynthetic and heterotrophic
Dinophyta
•
most photosynthetic, some predatory
•
low growth rates, occur during low flow rates
•
important part of shellfish diet
*Golden
Chrysophyta
flagellates
* Haptophytes
* Diatoms
``Yellow-green
Prymnesiophyta
Bacillariophyta
Xanthophyta
algae
*Euglenoid
flagellates
*Dinoflagellates
*Cryptomonads
Cryptophyta
•
photosynthetic and heterotrophic
Blue-green algae
Cyanophyta
•
regulate buoyancy
•
fix N from atmosphere
Sources: *(Knox et al. 1994); ``(Berkeley University 2001)
2.4.6 Cyanobacteria
Cyanobacteria have characteristics different to phytoplankton groups. Their populations are
controlled by different forces, which therefore enable the populations to thrive in a variety of
conditions. Cyanobacteria are harmful to the ecosystem in small concentrations as some are
capable of producing harmful toxins.
17
Effects of Agricultural practices on the water quality of the Scott River
The ability of cyanobacteria to fix and store nutrients and regulate buoyancy equips them
with an advantage over other phytoplankton groups. Some cyanobacteria are able to fix
nitrogen from the atmosphere (Holmes 2000). Phosphorus is therefore regarded as the
limiting nutrient for growth because if nitrogen is limiting it can be fixed (Maier & Dandy
1997). Cyanobacteria can also store enough phosphorous for two to four cell divisions (WHO
1999), reducing the impact of any phosphorous limitations. Smith (1983) also states that
cyanobacteria are better nitrogen and poorer phosphorous competitors than other groups of
algae, however Tonno (2004) suggests that this is only a general trend for nitrogen fixing
forms. Many planktonic forms of cyanobacteria contain gas vacuoles, which are aggregates
of gas filled vesicles (WHO 1999). The gas is lighter than water, enabling the cyanobacteria
to become buoyant.
As detailed in Chapter 2.2.3 low N:P ratios are associated with cyanobacteria blooms
(Arbuckle & Downing 2001). A wide range of other physical and chemical properties also
favour their growth. Water high in nitrogen, phosphates, carbonates and organic matter
stimulates growth (Main 2004), yet they can also out compete other phytoplankton groups
under nitrogen or phosphorous limiting conditions (WHO 1999).
High pH favours
cyanobacteria domination as the bicarbonate ion can be used as a carbon source (Shapiro
1984).
Low flow conditions favour their growth (Bormans & Webster 1997; Maier & Dandy 1997;
Knox et al. 1994) as their slow growth rate requires long retention times (WHO 1999). Light
is also a factor, affected by radiation, colour and turbidity (Maier & Dandy 1997). Under
eutrophic conditions, turbidity is high and light availability is low. Cyanobacteria grow best
in these conditions (WHO 1999), as they can regulate buoyancy to achieve the desired light
(Environment Canada 2001).
Population sizes of cyanobacteria are affected by growth and decomposition rates, grazing
rates, and imports and exports of the algae (Maier & Dandy 1997). Cyanobacteria have slow
growth rates when compared to other phytoplankton groups (WHO 1999). The optimum
temperature for growth is 25°C, higher than for diatoms and chlorophyta (WHO 1999). The
ability to regulate buoyancy prevents losses via sedimentation processes and decreases loss
rates (WHO 1999). Cyanobacteria are not grazed as much as other phytoplankton, however
their population sizes are controlled by the detrimental effects from viruses and bacteria
(WHO 1999).
18
Effects of Agricultural practices on the water quality of the Scott River
Bloom conditions have been reported to depend on increased nutrient inputs and temperature
(Temponeras et al. 2000) as well as a decrease in N:P (Pliński & Jóźwiak 1999) occurring in
lakes, reservoirs and slow moving rivers (Environment Canada 2001). Elser (1999) describes
the occurrence of cyanobacteria blooms with the aid of a hierarchal decision tree. As shown
in Figure 2-7, the blooms depend on the high nutrient loading, low N:P loading, favourable
light & hydrodynamic conditions, and finally predation.
Figure 2-7: Method of predicting cyanobacteria blooms (Elser 1999)
Not all cyanobacteria blooms are toxic, however those that are produce toxins, which are
capable of causing illness and death in both animals and humans who drink the water (Knox
et al. 1994). At concentrations greater than 15 000 cells/mL, water is unsafe for people to
drink and at concentrations between 500 – 2 000 cells/mL, action is taken by water managers
(Water and Rivers Commission 1997). The cyanobacteria Anabaena circinalis produces
neurotoxins, Paralytic Shellfish Poisons (PSPs). The PSPs can become accumulated up the
food chain via mussels and if ingested in large amounts can kill stock animals (Thoms et al.
2000).
19
Effects of Agricultural practices on the water quality of the Scott River
2.4.7 Benthic Algae
Benthic algae grow attached to the sediments, plants and snags (Thoms et al. 2000). They
exist in loose aggregations, mucilaginous films or lithified crusts (Davis 2003) and are
distributed patchily in the horizontal scale (Kahlert & Pettersson 2002). The name and type of
benthic algae are detailed in Table 2-5. Nutrients from the sediments are of great importance
for benthic algae. Benthic algae, particularly within thick mats, find it difficult to access
nutrients from the water column and also must compete for these nutrients with
phytoplankton (Kahlert & Pettersson 2002). Living substrates, such as macrophytes or
mussels, excrete nutrients and are an important nutrient sources for the benthic algae (Kahlert
& Pettersson 2002). One may assume that the importance of this nutrient supply would
decrease as water bodies become more eutrophic; however this is not always the case.
Kahlert & Pettersson (2002) suggest that it is internal processes within the benthic microbial
mat that regulate nutrient status.
Table 2-5: Name and type of benthic algae
Name
Type
diatoms
microscopic, single celled
cyanobacteria
filamentous
chlorophytes
multi-cellular
The growth of benthic algae is limited by light and nutrients. Increased turbidity levels can
lead to a loss of benthic algae, however some benthic micro algae species can migrate into
the water column in order to gain light. Production tends to increase from upstream to
downstream, but is limited by erosion (Angelier 2003). Flow rates are also important, with
many freshwater benthic algae species prefering lotic environments rather than lentic ones
(Wilkie & Mulbry 2002).
Agricultural activities can increase the biomass of benthic algae (Scrimgeour & Kendall
2002). A study by Wilkie and Mulbry (2001) investigated the growth of benthic algae as an
option for effluent reuse and measured production rates in response to different effluents and
loading rates. Results found that despite these differences, the production rates remained the
same. Nitrogen uptake rates increased with increased concentrations of the effluent.
20
Effects of Agricultural practices on the water quality of the Scott River
2.4.8 Zooplankton
Zooplankton feed on phytoplankton. In freshwater river ecosystems, the zooplankton species
which dominate are those of the rotifers, bosminids and young copepods (Kobayashi et al.
1998). Zooplankton increase in abundance in downstream sites (Kim & Joo 2000; Kobayashi
et al. 1998) and are affected by flow rates and salinities.
River flow has a large effect on zooplankton communities. Evidence suggests that in the
middle reaches of large rivers, the high flushing rates reduce reproduction rates and reduce
zooplankton abundance (Kim & Joo 2000). During high flows, the zooplankton abundance is
generally low, however at this time species upstream are moved downstream (Kobayashi et
al. 1998). Zooplankton abundance has been correlated with many environmental variables,
their relationships detailed in Table 2-6.
Table 2-6: Correlations of Environmental Variables with Zooplankton communities
Variables
Rivers (General)
Hawkesbury-Nepean River
Temperature
Positive
Positive
Chlorophyll a
Positive
Positive
Turbidity
Either
Positive
River flow rate
Negative
Negative
Conductivity
Negative
Positive
Source: Kobayashi et al., 1998
Riverine species are known to be displaced by saline species, near the river mouth and in
estuaries (Kobayashi et al. 1998), and may develop lotic type species during low flow
conditions. Rotifers, cladocerans, nauplii and copepods increased in abundance towards the
mouth of the Nakdong River during the period 1995 – 1997 (Kim & Joo 2000). It is
suspected that the estuary at the base of this river provides an optimal habitat for zooplankton
(Kim & Joo 2000).
2.4.9 Benthic Invertebrates
The growth of benthic organisms is limited by water depth, turbidity, insolation and current
(Angelier 2003). Benthic communities are often responsible for uptake of nutrients or sinking
21
Effects of Agricultural practices on the water quality of the Scott River
phytoplankton not taken up by zooplankton. They have also been used as a method of
determining water quality due to their diversity of forms and responses to environmental
stresses (Usseglio-Polateraa & Beisel 2002).
Water levels have a significant role in determining benthic development. During low water
levels, plankton is limited in growth and as a result, the invertebrate species with rapid
growth rates are favoured (Angelier 2003). The water level also determines the significance
of the hyporheic zone (HZ), which is the area between the surface stream and groundwater
(Boulton et al. 1998). If the water table drops, the HZ is recharged from surface waters. When
the water table rises, the HZ is recharged from groundwater. Benthic organisms of temporary
streams often use the HZ as a refuge during dry seasons (Angelier 2003). The water level of a
river also has a large role in determining the distribution of benthic organisms. During
periods of high water, reduced benthic activity occurs as organisms take shelter from the
currents, while the occurrence of floods may lead to a temporary increase in drift (Angelier
2003). During low waters, the individual behaviour of benthic species determines their
distribution.
An increase in nutrients causes benthic invertebrates to appear in reduced diversity and
altered abundance (Environment Canada 2001) and their distribution is determined by the
location of the nutrients. The availability of nutrients is affected by additional parameters.
Phosphorus concentrations, for example, in interstitial water are affected by oxygen
distribution and loss (Boulton et al. 1998). This is known to cause a change in redox
conditions, causing phosphorous to be released from bound iron or manganese (Boulton et al.
1998).
Sediment deposits may alter the distribution of benthic organisms, through replacing diverse
river habitats with uniform sand beds (Edgar & Nicholls 2003). Turbidity may arise due to
the presence of sediments and tannins within the water. As a result, productivity is reduced
due to the prevention of light penetration (Edgar & Nicholls 2003).
The current acts as an organising factor. It influences erosion as well as the transport and
redistribution of benthic organisms (Angelier 2003). In steep areas, microhabitats are likely
as the current will flow in many directions. In smaller sloped areas, the current mainly flows
in one direction and the microhabitats will be larger and of a different type (Angelier 2003).
Organisms of the benthos can stay within their habitat despite the influence of the current
22
Effects of Agricultural practices on the water quality of the Scott River
forcing them downstream. This is due to mechanisms of adhering to the substrate, high
reproductive rates and a flying phase of their life cycle allowing for recolonising (Angelier
2003). Benthic invertebrates are distributed according to saprobic zones, detailed in Table
2-7.
Table 2-7: Saprobic zones
Zone
Characteristics
Polysaprobic
Detritivores feed on organic matter, low oxygen concentrations are
tolerable. These include Oligochaeta Tubificidae, Diptera Eristales
larvae, Chironomus thumniplumosus
Mesoprobic
Oxygen concentrations increase, crustracea, Hirudinea, Sialis larvae
and Tanytarsus appear
Oligosaprobic
original settlement
Source: Angelier, 2003
Drift is a large method of distribution of benthos. The size of the drift is a function of the
current, however this does not indicate the structure of the benthic community (Angelier
2003). Increased runoff resulting from cleared land would increase the maximum flows
through the river. Therefore, drift is a mechanism which may be altered as a result of land use
change. A variety of benthic organisms drift in different ways, at different times and to
different extents as detailed in Table 2-8. Small, heavy or substrate adhering benthic
organisms drift to a small extent (Angelier 2003).
Table 2-8: Characteristics of drift
Drift type
Characteristics
Current speed
1
Organisms are transported as inert drift and return to the >19cm/s
bottom by chance.
2
Drift distance is reduced and the percentage of 10 - 12 cm/s
organisms returned to the bottom is high.
3
Drift distance is short, returning to the bottom is high
and successive drifts occur.
23
Effects of Agricultural practices on the water quality of the Scott River
2.5 Site Description
2.5.1 Australian Waters
Australia is surrounded by water from the Indian, Pacific and Southern Oceans and the
Timor, Arafura and Coral Seas. Inland, there exist lakes, reservoirs, rivers, wetlands and
estuaries, yet Australia is the driest inhabited continent (AWA 2003). Rainfall is variable in
time and space, making management of water difficult (AWA 2003) and contributing to a
dependence on limited water resources (ATSE 2004). A variety of land uses require this
water and their wastes have contributed to a degradation of water quality.
In Australia, both saline and freshwater water bodies occur. The effects of salinity have
induced saline conditions in many naturally fresh water bodies. Another characteristically
Australian water body is that of the estuary, where the salt water from the ocean is mixed
with the freshwater of inland waterways. Approximately 28% of Australian estuaries are
either moderately or severely modified (Smith et al. 2001).
Australian waterways often have problems associated with eutrophication and resulting algal
blooms. Australian waters contain high levels of suspended particles, which limit light
penetration (Lawrence et al. 2000). The light is therefore only available to the algae within
the euphotic zone (Lawrence et al. 2000). During summer in temperate areas of Australia,
mixing in water bodies is low, preventing many phytoplankton groups from reaching the
euphotic zone. During these conditions, cyanobacteria can dominate as they regulate
buoyancy to reach the euphotic zone.
2.5.2 WA Waterways
The climatic patterns of Western Australia vary across the state and contribute to the variety
of waterways found in the state (Water and Rivers Commission 2004). There is a
characteristically ‘summer’ rainfall pattern in the North of the state (Norris et al. 2001)
responsible for the hot and dry conditions found in the Pilbara and Gascoyne regions and
intense rainfall during cyclones (Water and Rivers Commission 2004). Towards the south,
‘winter’ rainfall patterns combine with a Mediterranean climate (Norris et al. 2001)
producing wet winters and long dry summers (Water and Rivers Commission 2004). In the
24
Effects of Agricultural practices on the water quality of the Scott River
remaining regions ‘extreme variations’ in seasonal and annual rainfall occur (Norris et al.
2001). In many areas annual evaporation exceeds annual rainfall.
Many Western Australian waterways have been impacted by land use activities (Water and
Rivers Commission 2004). Approximately 27% of river length in Western Australia was
assessed during the National Land and Water Resources Audit. Table 2-9 details the results
from this assessment. It listed land use changes an issue of concern, as well as the high levels
of total phosphorus and suspended sediment. Habitats were substantially altered, believed to
be due to the condition of the river bed and changes to riparian vegetation (Norris et al.
2001).
Table 2-9: Characteristics and affected length of Western Australian Rivers
Characteristic
Percentage of assessed
River length
Damaged biological communities
36%
Lost species (inferred)
20 - 50%
Disturbed catchments
76%
Classified as degraded
90%
Moderately modified
78%
Substantially modified
14%
Altered habitat
66%
Altered nutrient and sediment loads
95%
Moderate to high P loads
64%
Elevated loads of suspended sediment
55%
Numerous studies have been carried out on the Peel Harvey area and the Swan river estuary,
both of which have been impacted by land use changes. 100 years of clearing for farming and
development within the Peel Harvey catchment resulted in algal blooms (Everall Consulting
Biologist 2002). Over 35 species of blue-green algae have been found in the Peel-Harvey
estuarine system (Water and Rivers Commission 1999).
The Swan–Canning Estuary is suffering from anthropogenic stressors due to agricultural and
rural development (Thompson 2001). The water quality and biodiversity of this system has
been reduced by the influx of nutrients and nutrient rich sediments from such land uses. The
25
Effects of Agricultural practices on the water quality of the Scott River
nutrient loads into the estuary determine the frequency, extent and type of algal blooms. In
the 2001-2002 sampling period, the phytoplankton bloom criterion of 20 000 cells/mL was
exceeded in 36 out of 52 sampling occasions. Diatoms reached 340 000 cells/mL at Ron
Courtney Island during this time. The annual winter nutrient load fuels spring phytoplankton
blooms in the lower estuary and the late spring - early summer algal blooms in the upper
estuary (Swan River Trust 2002). Late summer algal blooms are influenced by these earlier
blooms and summer rainfall patterns (Swan River Trust 2002). These water quality declines
have lead to a loss of habitat and biodiversity (Storrie & Thomson-Dans 2000).
2.5.3 Blackwood Catchment
The Blackwood Catchment is approximately 20 461 km2 (Hunt 2003), illustrated in Figure
2-8. It is comprised of 18 local councils and 143 sub-catchment groups, with a population of
approximately 35 000 (Ecker & Chadwick 2001). The town of Augusta is situated near the
Hardy Inlet, with approximately fourteen other towns distributed among the catchment.
Hydrology within the Blackwood Catchment is dominated by the Blackwood River, the Scott
River and the Hardy Inlet, which links the riverine freshwaters with the saline ocean waters.
Rainfall in this area is approximately 1000mm per year.
Figure 2-8: The Blackwood Catchment (Read & Bessen 2003)
2.5.4 Scott Coastal Plain
The Scott Coastal Plain exists in the south of the Blackwood catchment, stretching 70km
along the south coast of Western Australia and 20km inland (Department of Agriculture
2001). The Scott Coastal Plain has an area of 105 000 ha, 42 900 ha of which is private
26
Effects of Agricultural practices on the water quality of the Scott River
freehold land. Three sub catchments (Sc) exist in the Scott coastal plain; Sc1, Sc2 and Sc3.
The plain has been described as low-lying and swampy, with much of the land in the west
cleared for agriculture (WAPC 2004).
Soils in the Scott Coastal Plain have been described as deep dry sands (WAPC 2004) and
poorly drained deep loose sands (Water and Rivers Commission 2002). Closer to the river
they are described as ‘winter waterlogged sandy duplex soils’ (WAPC 2004). The soil profile
of the superficial formation is mainly saturated, however unsaturated sediment exists below
the elevated coastal dunes (Baddock 1995). The soils of the catchment require the addition of
lime to raise the pH, in order to grow pasture and crops (AMRSC 2001), and also have a low
retention of nutrients.
Historically, annual rainfall has been documented at 1400mm and the shortest dry season
documented at four months (Jarvis 1986). Additional records show annual rainfall to be
approximately 1000mm, mainly falling between the months of May to October (Baddock
1995; Water and Rivers Commission 2002). Potential evaporation has been estimated at
approximately 1100mm (Baddock 1995; Water and Rivers Commission 2002). The
groundwater of the Scott Coastal Plain flows downwards and southwards, and leaks into
nearby wetlands and watercourses (Baddock 1995).
2.5.5 Land Use on the Scott Coastal Plain
Augusta was explored in 1834 and was pastoral until 1840 (Jarvis 1986). Europeans began
settlement in 1860 with the introduction of cattle runs (Department of Agriculture 2001).
During 1920 additional permanent European settlement occurred (Department of Agriculture
2001). Early land use in the Scott Coastal Plain included dairy pastoral farming, fruit and
potato farms, beef, sheep and pig farms. Saw mills, tobacco farms, tree plantations and
mining are examples of later land uses.
A great deal of land was cleared for agricultural purposes between 1900 and 1930. Potato
growing was significant during the 1930’s and by 1939 there was intensive pastoral farming
of dairy cattle near Augusta (Jarvis 1986). A saw mill was operating in 1959, 150 tobacco
farms were in existence in the Augusta-Margaret river area in 1960, however none remained
by the mid 1960’s (Jarvis 1986). During the 1960’s conditional purchase blocks were cleared.
27
Effects of Agricultural practices on the water quality of the Scott River
This land was predominantly used for dairy in the west of the Scott Coastal Plain and grazing
in the east (Department of Agriculture 2001). Horticulture, tree plantations, and mining
became a common land use during the 1990’s (Department of Agriculture 2001). At this
time, grazing became an unviable option and as a result dairying spread east and blue gum
plantations began (Department of Agriculture 2001). Mining also emerged with sites at
Beenup and Jandardup. Mineral sands reserves are still in existence and may be developed
further in the future (Department of Agriculture 2001).
Additional land use changes are occurring in the Scott Coastal Plain. In June 2001, the
Department of Agriculture, Western Australia published a strategy for sustainable
development of the Scott Coastal Plain, in terms of varying and intensifying agricultural land
use. The Scott Coastal Plain has characteristics favourable for agricultural development that
other areas cannot provide. The area has very high growth potential for dairy farming on
irrigated pastures (Primary Consulting Services 2003); whilst climate, groundwater and lot
sizes provide ideal conditions for mechanised horticultural production (Department of
Agriculture 2001).
North of the Scott River, the new strategy seeks to continue and enhance intensive and
extensive agriculture on freehold land (AMRSC 2001) implemented with appropriate land
management practices (Department of Agriculture 2001). Such land uses include crop
growing (horticulture and timber) and animal husbandry (dairying and grazing). South of the
Scott River, the strategy seeks to zone this area ‘Rural Landscape and Conservation’ in order
to protect the fragile environment and varied landscapes (Department of Agriculture 2001).
Increasing the use of the land for agricultural purposes will also promote further changes.
One or two townsites may be built, creating increased vehicles on roads and greater power
demands. Tourist development is also predicted to increase (Department of Agriculture
2001).
During 2001, between 400 to 600 hectares of land was developed for irrigated agriculture, to
farm potatoes, carrot, sweet corn and onions (Department of Agriculture 2001). In 2003, the
Scott Coastal Plain was reported as having 300 ha dedicated to vegetable production
(Economics Consulting Services 2003). The large scale, centre pivot irrigation systems
established in the Scott River area are also enabling increased pasture production (Primary
Consulting Services 2003).
28
Effects of Agricultural practices on the water quality of the Scott River
2.5.6 Scott River
The Scott River is highly valued, as of yet it is relatively un-impacted from anthropogenic
influences and is in good condition. It also has aboriginal significance, as it is a site of
aboriginal art (Jarvis 1986). Changes in land use of the Scott Coastal Plain are a concern for
the health of the Scott River. Its connection with other aquatic ecosystems makes
maintenance of its quality an important issue in many areas.
Flows from the Scott River discharge to the Hardy inlet and the Blackwood River. It joins the
Blackwood River north and south of Molloy Island (Hunt 2003). The Scott River is tidal for
approximately 8km, fresh upstream of this point (Department of Agriculture 2001) and
surrounded by the Scott River wetland system. The Scott River is placed within a
topographically low area, where artesian flows have been observed (Baddock 1995). The
aquatic systems are illustrated in Figure 2-9.
Blackwood River
Scott River
Molloy
Island
Figure 2-9: Scott River and surrounding aquatic systems
A problem associated with the proposed land use changes are the increased amounts of
nutrients entering the river. The Scott River is naturally adapted to nutrient poor conditions
(Department of Agriculture 2001) and any increase in nutrients may have detrimental effects
upon the aquatic life in the river. The nutrient concentrations within the Scott River often
exceed ANZECC guidelines. Dissolved inorganic nitrogen is above national standards,
however elevated levels of nitrogen within the Scott River are believed to be natural
(Department of Agriculture 2001). Despite concerning nutrient levels, physical symptoms of
29
Effects of Agricultural practices on the water quality of the Scott River
eutrophication are only evident on occasion (Department of Agriculture 2001). Table 2-10
below shows the proposed water quality targets for the Scott River.
Table 2-10: Proposed water quality targets for Scott River
Parameters
Target
Units
FRP
0.059
mg/L
NH3
0.037
mg/L
DIN
0.6
mg/L
Turbidity
8.1
NTU
Colour
220
Gilvin 440
Source: Department of Agriculture
In 1997 the Scott River contributed 40% of phosphorous and 30% of nitrogen to Hardy Inlet
(Department of Agriculture 2001). In periods of low flows, the inlet is impacted further, as
there is no flushing mechanism to remove the nutrients. The health of this system is important
as it supports a unique higher order ecosystem of birds, ducks, pelicans, and dolphins and is
connected to the southern ocean.
Figure 2-10: Pelican, Hardy Inlet
30
Effects of Agricultural practices on the water quality of the Scott River
3 Approach
In order to determine the relationship between agricultural land use of the Scott Coastal Plain
and water quality of the Scott River, a specific approach was taken. Firstly, land use
information and water quality data was collected. This was then analysed to see how
agricultural land use influenced the nutrient concentrations observed in the river at different
times of the year. The initial focus of this study was the influence of nutrient ratios (TN:TP)
in promoting production and cyanobacteria dominance, however an additional focus was
adopted, being the effects of increased nutrients, particularly phosphorous, in promoting
phytoplankton growth.
3.1 Site Investigation
Evidence of land use practices were detailed within one sub catchment, Sc1 along Scott River
Road. A visual examination of the Scott River at Brennan’s Bridge was also carried out.
Surrounding aquatic ecosystems were also investigated, including the Blackwood River,
Hardy Inlet and the Southern Ocean.
3.2 Data Collection
Water chemistry, physical and biological data was collected from the Water and Rivers
Commission. The sites used in this study were 609026 (yellow), 609002 (pink), 6091051
(blue) and SRF01 (orange) as indicated in Figure 3-1. Methods the Water and Rivers
Commission used for collecting the data are outlined below.
Figure 3-1: Sampling locations
31
Effects of Agricultural practices on the water quality of the Scott River
3.2.1 Phytoplankton
All phytoplankton samples from 609002, 6091051 and 609026 were grab samples. All
phytoplankton samples taken from site SRF01 were integrated throughout the water column,
with the use of either an integrated hose/pipe with an internal diameter of 25mm or a hose
with a diameter of 20mm. Phytoplankton samples were analysed by the use of a Sedgwick
Rafter cell and microscope by the Phytoplankton Ecology Unit (PEU).
3.2.2 Nutrients
Nutrient data from 609002, 6091051 and 609026 were collected as Grab samples from the
surface and analysed for total nitrogen, total phosphorous, TKN, nitrate, nitrite and filterable
reactive phosphate at AGAL. Nutrient samples from SRF01 were taken from varied depths
and were analysed at AEL for total nitrogen and total phosphorous.
3.2.3 Physicals
The physical variables and their measuring devices are recorded in Table 3-1. All readings
were taken in situ.
Table 3-1: Physical variables
Variable
Units
Measurement device(s)
Sites
Temperature
°C
Hydrolab Data Sonde 4 Series
All
Hydrolab H20
WTW conductivity meter.
Dissolved
mg/L
Hydrolab Data Sonde 4 Series
oxygen
%
Hydrolab H20
Turbidity
NTU
Hydrolab Data Sonde 4 Series
All
All
Hydrolab H20
Salinity
mg/L
Hydrolab Data Sonde 4
609026, 609002, 6091051
Hydrolab Data Sonde 3
SRF01
32
Effects of Agricultural practices on the water quality of the Scott River
3.3 Data Manipulation
The equations used to manipulate the raw data to that used in the results are outlined below.
3.3.1 Nutrient Ratios
TN : TP =
TN
TP
TN:TP = Nitrogen to Phosphorous ratio
TN
= concentration of total nitrogen in mg/L
TP
= concentration of total phosphorous in mg/L
3.3.2 Nutrient Loadings
Ln = C n × Q
Ln
= Nutrient loading of nutrient n
Cn
= Concentration of nutrient n
Q
= flow rate
n
= nutrient
3.3.3 Percentage of Phytoplankton Group Dominance
%i =
xi
× 100
xT
% i = percentage dominance of phytoplankton group i
xi = cells/mL of phytoplankton group i
xT = cells/mL of all phytoplankton groups
i
= phytoplankton group
33
Effects of Agricultural practices on the water quality of the Scott River
3.3.4 % Land Use Estimations
%i =
Ni
× 100
NT
% i = percentage of land dedicated to land use type i
N i = number of sections of sub catchment dedicated to land use type i
N T = total number of sections of sub catchment
i
= land use type
34
Effects of Agricultural practices on the water quality of the Scott River
4 Results
4.1 Land Use
Figure 4-1, illustrated below, details the land use of the Scott Coastal Plain, as at 2001. South
of the Scott River in Sc1, land use is dominated by conservation and natural environments,
with a small amount of grazing and improved pastures. North of the river, land use is
dominated by grazing, with a lesser amount of dairy and mining. Land use within sub
catchment Sc2, north of the Scott River is dominated by ‘grazing and improved pastures’.
Seasonal horticulture, dairying, cropping and plantation forestry are also present. Further
north above the river, the catchment is largely composed of conservation areas and natural
environments. South of the river exist small areas of grazing and improved pasture. A large
proportion of the sub catchment Sc3 is of natural or conserved environments. The remaining
land use is dominated by grazing and to a lesser extent seasonal horticulture and plantation
forestry. Mining and cropping are also present in the catchment.
Figure 4-1: Land use in the Scott Catchment (WRC 2002)
35
Effects of Agricultural practices on the water quality of the Scott River
The relative proportion of each type of land use in each sub catchment was calculated (see
section 3.3.4). The approximate values are detailed in Table 4-1. Over 50% of each sub
catchment is dedicated to conservation and natural environments. The next highest
percentage of land use is grazing and improved pastures, varying between 20 – 33% between
sub catchments.
Table 4-1: Land uses in each sub catchment of the Scott Coastal Plain
Sub catchment 1
Conservation
environments
and
natural 55%
Sub catchment 2
Sub catchment 3
51%
65%
Grazing and improved pastures
33%
31%
20%
Dairy
6%
3%
0%
Seasonal horticulture
0%
9%
6%
Cropping
0%
3%
0.4%
Mining
3%
0%
0.4%
As described in Chapter 2.3, animal agriculture tends to export a low ratio of TN:TP to the
environment. There is a significant amount of land dedicated to animal agriculture in each of
the sub catchments of the Scott Coastal Plain. As a result, this low ratio may be mirrored in
the TN:TP measured in the Scott River. These ratios are investigated in the next chapter.
36
Effects of Agricultural practices on the water quality of the Scott River
4.2 TN:TP in the Scott River
Figure 4-2 details a comparison of the TN:TP ratio at three sites along the Scott River in 2000
and 2001. During the majority of sampling dates, the TN:TP ratio is below 20. The sites
609002 and 6091051 display similar trends throughout the entire sampling period. A peak in
TN:TP is seen in June during both years at two sites: 609002 and 6091051. The other site,
609026 remains at a low TN:TP. This discrepancy was analysed to see if it the ratios had any
effect on production in the Scott River.
TN:TP ratio
50
6091051
609002
609026
N:P
40
30
20
10
0
May-00
Jun-00
Jul-00
Aug-00
Sep-00
Oct-00
Date of sample
TN:TP ratio
70
6091051
60
609002
609026
N:P
50
40
30
20
10
0
Jun-01
Jul-01
Aug-01
Sep-01
Oct-01
Nov-01
Date of sample
Figure 4-2: Comparison of TN:TP at Scott River sites in 2000 and 2001
The nutrient ratios observed in the Scott River on June 5, 2001 were analysed along with the
phytoplankton communities in the river on the same date. This date was one where the
37
Effects of Agricultural practices on the water quality of the Scott River
TN:TP ratio was high at sites 609002 and 6091051 but low at 609026. Figure 4-3, below,
details the phytoplankton group cell concentrations and the corresponding TN:TP ratio. There
is a large increase in the chlorophyta, diatom and euglenophyta populations and a decrease in
the cryptophyte population at 609026. This graph clearly shows that there are lower cell
concentrations at high TN:TP and higher cell concentrations at lower TN:TP.
Phytoplankton community composition and N:P
5/6/2001
1000
60
900
58
5
609002
609026
800
cells/mL
700
600
500
400
300
200
100
0
6091051
Chlorophyta
Diatoms
Cryptophyta
Euglenophyta
Figure 4-3: Snapshot of phytoplankton group composition and the corresponding TN:TP ratio.
This trend did not occur during all sampling dates. As shown in Figure 4-4 a decrease in cell
counts is observed at high TN:TP but a variation in cell counts is observed at lower TN:TP.
The vertical dashed line represents a TN:TP of 23, above which the cell counts are low. This
variation was further investigated to see if it was phosphorous or nitrogen concentrations that
were influencing production rates or any other factors.
phytoplankton (cells/mL)
4000
3500
3000
2500
2000
1500
1000
500
0
0
20
40
60
TN:TP
Figure 4-4: Scatter graph of TN:TP against cell counts of phytoplankton at all Scott River sites 2000-2001
38
Effects of Agricultural practices on the water quality of the Scott River
4.3 Limitations
4.3.1 Phosphorous Limitations
Figure 4-5 details the concentrations of phosphorous and the corresponding concentrations of
phytoplankton cells at each site along the Scott River. The highest phosphorous
concentrations exist at site 609026, which also displays high concentrations of
phytoplankton. Both lower phosphorous and phytoplankton concentrations are observed at
sites 609002 and 6091051. Despite low phosphorous concentrations at site SRF01 there are
large concentrations of phytoplankton. Eliminating data from the SRF01 sampling site, a
weak positive trend between cell counts and total phosphorous concentrations can be
observed.
4000
3500
609026
609002
6091051
SRF01
cells/mL
3000
2500
2000
1500
1000
500
0
0.0
0.2
0.4
0.6
0.8
1.0
TP (mg/L)
Figure 4-5: Phosphorous concentrations and the corresponding phytoplankton cell counts separated by
sampling sites
39
Effects of Agricultural practices on the water quality of the Scott River
4.3.2 Nitrogen Limitations
A similar trend is observed between phytoplankton cell concentrations and total nitrogen
concentrations. Figure 4-6 shows that higher concentrations of total nitrogen are observed at
site 609026, which corresponds to an increase in phytoplankton cell concentrations. The total
nitrogen concentrations at sites 609002 and 6091051 are generally lower than at 609026,
corresponding with a lower phytoplankton cell concentration. Despite low total nitrogen
concentration at SRF01 high phytoplankton cell concentrations are observed.
4000
3500
cells/mL
3000
6091051
2500
609026
2000
609002
1500
SRF01
1000
500
0
0.0
1.0
2.0
3.0
4.0
5.0
TN(mg/L)
Figure 4-6: Nitrogen concentrations and the corresponding phytoplankton cell counts separated by
sampling sites.
40
Effects of Agricultural practices on the water quality of the Scott River
4.3.3 Temperature Limitations
A weak positive trend between phytoplankton concentrations and in situ water temperature
can be observed in Figure 4-7. Data at SRF01 was taken during summer and is both higher in
temperature and cell concentrations. Data from the other sites were taken during winter and
spring and have lower temperatures and generally lower cell concentrations.
In situ water temperature and phytoplankton cell
concentrations at Scott River sites 2000-2001
cells/mL
3000
2500
2000
6091051
1500
1000
609026
609002
SRF01
500
0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
temperature ('C)
Figure 4-7: Phytoplankton cell concentrations at Scott River sites 2000-2001 as a function of in situ
temperature.
41
Effects of Agricultural practices on the water quality of the Scott River
4.4 Cyanobacteria
As detailed in chapter 2.2.3, the dominance of cyanobacteria has been correlated with a low
TN:TP ratio in the water body from which it grows. Figure 4-8 displays a scatter graph of
Cyanophyta against TN:TP in order to show this correlation with data from the Scott River.
Data from three Scott River sites (6091051, 609002, 609026) was plotted in comparison to
data taken from Smith (1983). The fourth Scott River site, SRF01 was not included in this
analysis as the data at this site was not taken at the same times as the other sites. Its proximity
to the salt wedge also did not make it ideal to be used in freshwater analysis. The Scott River
data fits the predictions by Smith, with dominance of cyanophyta rare at TN:TP above 29 but
dominating on some occasions below this figure. One detail that is different in the two data
sets is that the cyanophyta from the Scott River do not dominate at a percentage greater than
30%.
% cyanophyta
100
80
Lakes worldwide (Smith 1983)
Scott River sites
60
40
20
0
0
20
40
60
80
100
120
TN:TP
Figure 4-8: Percentage of cyanophyta dominance as a function of TN:TP. Comparison of Scott River
data (without SRF01) with published data from Smith, 1983.
Due to the fact that cyanophyta were only dominating on some occasions when the TN:TP
ratio was below 29, this implies that there must be other factors controlling their dominance.
In order to investigate this further, cyanophyta cell counts were plotted against both TN and
TP concentrations. It appeared that the cyanophyta were increasing in concentration during
nutrient limiting conditions. At total nitrogen concentrations below 1.0 mg/L, cyanophyta
42
Effects of Agricultural practices on the water quality of the Scott River
concentrations ranged from 0 – 250 cells /mL and above 1.0 mg/L they were not observed. A
similar case occurs for total phosphorous concentrations. Above 0.15 mg/L of TP, no
cyanophyta are observed and below 0.15 mg/L concentrations range from 0 – 250 cells/mL.
Cyanophyta (group) (cells/mL)
These trends are displayed in Figure 4-9 and Figure 4-10 respectively.
250
200
150
100
50
0
0.0
1.0
2.0
3.0
4.0
5.0
TN (mg/L)
Cyanophyta (group) (cells/mL)
Figure 4-9: Scatter graph of Cyanophyta cell counts and TN. Vertical line at 1.0 mg/L of TN
250
200
150
100
50
0
0.0
0.2
0.4
0.6
0.8
1.0
TP (mg/L)
Figure 4-10: Scatter graph of Cyanophyta cell counts and TP. Vertical line at 0.15mg/L of TP
Although there is an evident trend that cyanobacteria are higher in concentration during lower
nutrient conditions, on some occasions cyanobacteria were not observed. Due to this, further
investigation was done to see if a combination of nitrogen and phosphorous limiting
conditions prompted the growth of cyanobacteria.
43
Effects of Agricultural practices on the water quality of the Scott River
Figure 4-11 below describes the domination of cyanophyta and the corresponding nutrient
conditions. The condition entitled ‘both’ refers to both nitrogen and phosphorous being
limiting. During such conditions, total nitrogen concentrations are below 1.0 mg/L and total
phosphorous concentrations are below 0.15 mg/L. The condition ‘none’ refers to neither
nitrogen nor phosphorous being in short supply. During these conditions, concentrations of
total nitrogen are greater than 1.0mg/L and total phosphorous concentrations are greater than
0.15mg/L. The other condition, ‘TP<0.15’ refers to only total phosphorous being limiting and
total nitrogen not limiting. The reverse of this condition (total nitrogen limiting only) never
occurred and has therefore not been included. The highest extent of cyanophyta dominance
occurs when both total nitrogen and total phosphorous are limiting (the condition ‘both’).
During the other conditions, cyanobacteria were never recorded.
Nutrient conditions and cyanophyta dominance
100
both: TN < 1; TP < 0.15
% dominance
80
TP < 0.15
none: TN > 1; TP > 0.15
60
40
20
0
0
10
20
30
40
50
60
N:P
Figure 4-11: Cyanophyta dominance separated by nutrient conditions.
44
70
Effects of Agricultural practices on the water quality of the Scott River
4.5 Phytoplankton Groups
Phytoplankton data was taken at sites 609026, 609002 and 6091051 during the same
sampling dates. Phytoplankton groups at site 609026 were typically of higher concentration
and similar composition to the other sites and have therefore been used to represent the
phytoplankton groups of all upstream sites.
4.5.1 Spring
As illustrated in Figure 4-12, September through to November of 2000 saw mainly
dominance of chlorophyta and diatoms and to a lesser extent cryptophyta and cyanophyta.
The phytoplankton groups euglenophyta and dinophyta were also observed. Four samples
were taken: September 8, September 20, October 20 and November 2. The two September
samples were of similar composition, with the latter sample revealing a larger abundance of
all phytoplankton groups apart from the euglenophyta group which decreased slightly. The
October 20 sample was of a lower abundance than the September 20 sample. Lower
concentrations of cyanophyta, diatoms and chlorophyta occurred but increases in
chrysophyta, euglenophyta and dinophyta were observed. The November sample was higher
in abundance than the October sample, with increases in all phytoplankton groups apart from
the chrysophyta group which decreased slightly and the cyanophyta group which was not
observed at all.
Phytoplankton composition 609026
900.000
800.000
700.000
cells/mL
600.000
500.000
400.000
300.000
200.000
100.000
0.000
08-Sep-00
20-Sep-00
20-Oct-00
Chlorophyta (group)
Chrysophyta
Cryptophyta
Diatoms (group)
Dinophyta
Euglenophyta
02-Nov-00
Cyanophyta (group)
Figure 4-12: Spring phytoplankton group patterns at site 609026, 2000
45
Effects of Agricultural practices on the water quality of the Scott River
4.5.2 Winter
As illustrated in Figure 4-13, June through to August of 2001 saw dominance of chlorophyta
and diatoms and to a lesser extent cryptophyta, crysophyta and euglenophyta. Five samples
were taken: June 5th, June 18th, July 3rd, July 17th and August 14th. There is a significant
change in phytoplankton abundance and composition from the June 5th sample to the June
18th sample. There is a decrease in chlorophyta abundance and an increase in euglenophyta,
diatom and cryptophyta abundance. There also emerge small counts of dinophyta as well as a
significant population of chrysophyta. The July 3rd sample is similar in composition to the
June 18 sample but smaller in abundance. The concentrations of each of the phytoplankton
groups decrease apart from the chlorophyta which increase slightly. The July 17th sample has
a smaller abundance than the previous sample however the composition is very similar. There
is more of an even distribution of phytoplankton groups on this occasion. The August 14
sample is higher in abundance than the previous two samples, with chlorophyta dominating.
The composition is similar to that of the first sample (June 5th).
Phytoplankton composition 609026
3500.000
3000.000
cells/mL
2500.000
2000.000
1500.000
1000.000
500.000
0.000
05-Jun-01
18-Jun-01
03-Jul-01
Chlorophyta (group)
Chrysophyta
Cryptophyta
Diatoms (group)
Dinophyta
Euglenophyta
17-Jul-01
Figure 4-13: Winter phytoplankton group patterns
46
14-Aug-01
Cyanophyta (group)
Effects of Agricultural practices on the water quality of the Scott River
4.5.3 Seasonal Variations
Samples were taken sporadically throughout the year at one site, SRF01, giving a snapshot
into the phytoplankton groups during different seasons. Figure 4-14 details the seasonal
variations of phytoplankton group abundance at SRF01 in 2001. There exists a dominance of
green algae in January and diatoms in March. Dinoflagellates dominated in late June and
early July, while diatoms dominate in mid July. A large concentration of cyanophyta is
observed in December, at 1000 cell/mL.
The phytoplankton groups present at this site are different to those observed at the other sites
during similar parts of the year. For example in June and July of 2001, there was a significant
population of chlorophyta and the group dinophyta was rare. At this site, however, the
dinophyta are dominating and the chlorophyta are rare.
2001 Phytoplankton populations SRF01
4000
cells/mL
3000
2000
1000
0
19/01/01
Chlorophyta (group)
28/03/01
Cryptophyta
20/06/01
04/07/01
Cyanophyta (group)
18/07/01
Diatoms (group)
17/12/01
Dinophyta
Figure 4-14: Seasonal variation in phytoplankton populations at SRF01 in 2001
47
Effects of Agricultural practices on the water quality of the Scott River
4.6 Nutrient Variations
Given that it has been established that cyanobacteria occur during nutrient limiting conditions
and phytoplankton counts generally increase with nutrient increases, it is necessary to
understand how the nutrients in the Scott River vary with the seasons. Nutrient data from
upstream sites (609026, 609002, and 6091051) was only available during winter and spring.
Year long data was available at site SRF01 during 2001. The total nitrogen and total
phosphorous concentrations at SRF01 are displayed in Figure 4-15. Nutrient concentrations
are highest in June and July (TN max: 2 mg/L; TP max: 0.23 mg/L), decrease in August and
September and increase again in October (TN max: 1.1 mg/L; TP max: 0.15 mg/L). Lower
concentrations are observed in the summer months.
0.25
2.5
TP
TN
0.15
2
1.5
0.1
1
0.05
TN (mg/L)
TP (mg/L)
0.2
0.5
0
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Figure 4-15: Surface samples of Total phosphorous and total nitrogen concentrations at SRF01 in 2001.
Samples were taken from SRF01 at varied depths. On some occasions there are more
nutrients in the surface waters and on other occasions there is no difference. These
concentrations are detailed in Table 4-2. Variations with both depth and date can be seen in
Appendix 7.
Table 4-2: Nutrient concentrations varying with depth
Date
19/1/2004
4/7/2001
Depth
TN
TP
(m)
(mg/L)
(mg/L)
0
0.38
0.03
0.9
0.38
0.02
0
1.8
0.16
1.2
0.95
0.03
48
Effects of Agricultural practices on the water quality of the Scott River
5 Discussion
5.1 Land Use
The high proportion of land dedicated to animal agriculture was reflected in the low TN:TP
ratio (below 20) observed in the Scott River. At times the TN:TP ratio observed in the river
was higher, greater than 50. This peak can be attributed to high concentrations of nitrogen,
possibly due to the application of fertilisers being high in nitrogen. Another potential source
is clover grass pastures. Clovers fix nitrogen and in areas of sandy or permeable soils. They
can release nitrate, which may enter the water table (Anonymous 2002) and consequently, the
Scott River. Another potential source of nitrogen may be from forestry practises, as fertiliser
trials are occurring in the Scott Coastal Plain. Another source has been speculated as being
rainfall. Other evidence suggests that the high nitrogen levels are in fact natural (Department
of Agriculture 2001).
Monthly rainfall and average monthly total nitrogen concentrations are shown in Figure 5-1.
On some occasions, an increase in rainfall is matched with an increase in TN concentrations.
This is particularly evident from May to June. The decline in rainfall from July until
December is only partially matched with a decline in total nitrogen concentrations. This
suggests that the nitrogen source is most probably not rainfall but the increased rainfall rates
are contributing to an increase in total nitrogen concentrations by immobilising the nutrient
from the catchment.
300
1.8
rainfall
TN
200
1.2
150
100
0.6
50
0
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 5-1: Monthly rainfall and TN concentrations at 609002, 2000.
49
TN (mg/L)
Rainfall (mm)
250
Effects of Agricultural practices on the water quality of the Scott River
It has been suggested that intensive land uses in high rainfall areas contribute large amounts
of nutrients to the environment (Water and Rivers Commission 2002). This suggests that
during high rainfall periods, nutrient loss from these practises is higher, which explains the
increase in both TN and rainfall from May to June.
5.2 Seasonal Variations on Nutrient Supply
Nutrient data is available at upstream sites (609002, 609026, and 6091051) from May until
November, and at sporadic intervals year round at SRF01. At upstream sites, peaks in
nutrient concentrations are observed in the winter months (June, July and August), which are
detailed in Appendix 1. This is possibly due to higher rainfall, causing increases in nutrients
entering the river, particularly high phosphorous concentrations at site 609026. There also
appears to be a drain entering the river originating from Milyeannup Coast Road, which may
be responsible for the high phosphorous concentrations. Concentrations of nutrients are still
fairly high during low rainfall and low flow rates. This suggests that nutrient transport is also
via groundwater processes. The proximity of the Scott River wetland system also supports
this theory.
Due to low rainfall and flow rates rainfall in summer, the majority of nutrient supply at
SRF01 would not be through surface water flow. Nutrient supply at this site in summer may
be from groundwater, sediment nutrient release or possibly the estuary. Nutrient release from
the sediment usually occurs during anoxic conditions. During summer, the dissolved oxygen
at this site is well saturated, indicating that this would not be the case (see Appendix 2).
High salinities have been observed at this site from January through to May. This may be due
to higher evaporation rates at this time of the year, creating a more saline environment or the
salt wedge from the estuary creeping up the river Salinity variations can be viewed in
Appendix 3. If the latter is the case then nutrient supply to the Scott River may be from the
estuary. The most probable nutrient source during the summer is that of groundwater. The
typically low transport rate of groundwater (Hemond & Fechner-Levy 2000) may be
responsible for the nutrient concentrations during low rainfall periods.
50
Effects of Agricultural practices on the water quality of the Scott River
5.3 Limitations to Production
From the results presented in Figure 4-3 and Figure 4-4, it can be seen that there is a
relationship between the ratio of TN:TP and phytoplankton cell concentrations. At high
ratios, above 50, there is little production (< 300 cells/mL) and at low ratios there is a variety
of cell counts, ranging from less than 200 cells/mL to over 3500 cells/mL. The ratio of
nutrients is not the only relationship with production.
There appears to be a phosphorous and nitrogen limitation in the upstream sights, however
once separated by site it is only really 609026 that exhibits high production at high
concentrations of phosphorous (max: 0.91 mg/L) and nitrogen (max: 4.3 mg/L). At sites
609002 and 6091051, concentrations of nitrogen and phosphorous are not as high (TP max:
0.26 mg/L; TN max: 2.4 mg/L) but at times still above guideline levels yet low cell counts
occur (< 800 cells/mL). At lower concentrations (TP < 0.2 mg/L; TN <1.5 mg/L), cell counts
at SRF01 were often above 1000 cells/mL, reaching 3500 cells/mL on one occasion. The
small cell counts at 609002 and 6091051 can be attributed to other limitations in growth such
light or temperature limitation or alternatively grazing by zooplankton.
It is likely that there is increased zooplankton grazing at these sites as zooplankton tend to
increase in abundance as you move downstream a river system, hence explaining the lower
cell concentrations at these sites. Samples at these sites were also taken during low in situ
water temperatures of 10 – 20°C, also contributing to the low cell concentrations. At similar
temperatures, site 609026 also exhibited low cell concentrations, however at times this was
not the case.
Low nutrient concentrations were observed at SRF01, yet high phytoplankton cell
concentrations were observed. Low nutrient concentrations may suggest entire nutrient
consumption rather than a lack of nutrients. Therefore low nutrients and high phytoplankton
counts suggest that either phytoplankton are fixing nutrients during nutrient poor conditions
or they are using all the nutrients available to them. There would also expect to be more
grazing pressure at this site, however this does not seem to be the case. If this site is higher in
salinity then perhaps the conditions at this site are not ideal for the zooplankton being
transported from upstream.
51
Effects of Agricultural practices on the water quality of the Scott River
As shown in Appendix 4, turbidity values during the 2000-2001 sampling period are very low
with average levels at 10.1 NTU. A maximum level of 78.3 NTU was observed at site
6091051 in June of 2001. The low turbidity values indicate that there are not many particles
in the water and that nutrient input through soil erosion would therefore be minimal. This also
coincides with the Department of Agriculture, Western Australia (2001) in saying that the
majority of nutrients were in solution. Colour information was not measured at upstream sites
in 2000-2001. As shown in Appendix 5, historical data shows that high colour values have
been observed, upwards of 100 Hu. The colour of the Scott River can be seen in Figure 5-2.
Due to the high historical colour values and the colour of the river itself, it is possible that the
colour of the Scott River is contributing to light limitation.
Figure 5-2: Colour of Scott River
5.4 Cyanobacteria
The occurrence of cyanobacteria was influenced by the ratio of TN:TP. When this ratio was
greater than 50, no cyanobacteria were present, and at ratios below this, cyanobacteria were
present. At the high TN:TP nitrogen was not limiting. During such conditions cyanobacteria
do not have any advantage over the other phytoplankton groups because nitrogen is not
limiting their growth. This trend was illustrated in Chapter 4.4, Figure 4-11. When total
nitrogen is greater than 1.0 mg/L, no cyanobacteria are ever recorded. Once at or below 1.0
mg/L cyanobacteria are observed. The low nitrogen conditions may trigger growth of
cyanobacteria as it can out-compete other types of phytoplankton.
52
Effects of Agricultural practices on the water quality of the Scott River
Factors also contributing to cyanobacteria growth include physical properties such as
temperature and flow rate, chemical properties such as dissolved oxygen and pH, as well as
biological properties such as dominance of other aquatic life. No relationship was found
between cyanobacteria concentrations and secchi depth, total suspended solids, or turbidity.
At higher temperatures, cyanobacteria reached greater concentrations, as their optimal growth
rate is 25°C. This trend is displayed in Table 5-1.
Table 5-1: In situ water temperature range and corresponding maximum cyanobacteria concentrations
Temperature range
(°C)
10-15
15-20
25-30
Max concentration
(cells/mL)
235
99
1047
During periods where cyanobacteria were not present, other phytoplankton groups dominated
production, as shown in Table 5-2. This may mean that the dominance of other groups
prevents cyanobacteria growth, which is possible since cyanobacteria are poorer phosphorous
competitors (Smith 1983). It may also mean that other conditions such as temperature and
flow rate were not optimal for growth.
Table 5-2: Dominance of phytoplankton groups during
periods of zero cyanobacteria cells counts at SRF01
Collected
Date
Phytoplankton
group
Dominance
(%)
23/02/2000
Diatoms
95.112
08/03/2000
Diatoms
97.151
04/05/2000
Chrysophyta
62.642
16/05/2000
Chrysophyta
58.755
06/06/2000
Cryptophyta
40.049
19/01/2001
Chlorophyta
39.56
28/03/2001
Diatoms
82.521
20/06/2001
Dinophyta
81.95
04/07/2001
Dinophyta
93.292
18/07/2001
Diatoms
66.206
53
Effects of Agricultural practices on the water quality of the Scott River
A process for predicting cyanobacteria blooms proposed by Elser (1999) for freshwater lakes
and was displayed in chapter 2.4.6, Figure 2-7. In order for there to be a cyanobacteria bloom
there must firstly be a high nutrient loading, this loading must have a low TN:TP, there must
be the ‘correct’ hydrodynamic and light conditions and finally the grazing pressure must be
minimal. This process was looked at for one site, 609002 during spring as this was the only
site with flow data and biological data. As indicated in Figure 5-3, there exist high nutrient
loads during September and Table 5-3 shows that the TN:TP ratio was low at this time.
TN and TP loading at 609002
2500
kgP/day
kg/day
2000
kgN/day
1500
1000
500
2-Nov
19-Oct
5-Oct
21-Sep
7-Sep
24-Aug
10-Aug
27-Jul
13-Jul
29-Jun
15-Jun
1-Jun
18-May
0
Figure 5-3: TN and TP loading at 609002 in 2000.
Table 5-3: Environmental variables and cyanobacteria concentrations
Date
Cyanobacteria
Flow
(cells/mL)
(m3/s)
8/9/2000
33
24.3
20/9/2000
28
5/10/2000
N:P N loading P loading
Temp
DO
(°C)
(%)
(kg/day)
(kg /day)
9.1
2099.5
230.9
4.6
6.8
271.6
39.9
13.6
84.9
12
1.5
7.3
101.8
14.0
17.0
71.5
20/10/2000
70
0.6
8.5
38.4
4.5
16.4
56.1
2/11/2000
0
0.22
6.7
13.9
2.1
82.4
42
The ideal hydrodynamic conditions are those during low flow periods and high temperatures.
The cell concentrations of cyanobacteria at this site are very low, ranging from 12 – 70
cells/mL, indicating non-bloom conditions. This can be attributed to ‘incorrect’
54
Effects of Agricultural practices on the water quality of the Scott River
hydrodynamic conditions such as high flow rates and low temperatures, as displayed in Table
5-3. It can also be attributed to a dominance of other phytoplankton groups, as shown in
Figure 5-4.
2000 Phytoplankton Species at 609002
900.000
800.000
700.000
cells/mL
600.000
500.000
400.000
300.000
200.000
100.000
0.000
08-Sep-00
20-Sep-00
05-Oct-00
Chlorophyta (group) (cells/mL)
Chrysophyta (cells/mL)
Cyanophyta (group) (cells/mL)
Diatoms (group) (cells/mL)
20-Oct-00
02-Nov-00
Cryptophyta (cells/mL)
Figure 5-4: Phytoplankton groups at 609002 in 2000.
Generally, high nutrient loads enter the Scott River from, June until September due to the
increased rainfall. The increased rainfall causes increases in flow rates, which are not ideal
for growth of cyanobacteria. The water temperature at this time is also very cold, with an
average of 15°, 10° lower than the optimum temperature for cyanobacteria growth. Due to
this we would expect to never see blooms of cyanobacteria during the winter months.
Providing sufficient nutrients from groundwater flows in summer, the warmer summer
temperatures and low flow conditions may be ideal conditions for cyanobacteria growth.
This was the case at site SRF01 in December 2001. High concentrations of cyanobacteria
were observed when average water temperature was 25° and nutrient conditions were low
however (TN=0.4mg/L and TP = 0.03 mg/L). This may be because they were used up in
growth, or nutrients were fixed from the atmosphere or the sediments. It is also possible that
nutrients were stored within the cyanobacteria cells, enabling growth during nutrient limiting
conditions. The high concentrations of cyanobacteria and low nutrient concentrations at this
time of the year suggest there is sufficient nutrient sources to not limit growth of
cyanobacteria.
55
Effects of Agricultural practices on the water quality of the Scott River
5.5 Phytoplankton Group Succession
5.5.1 Site 609026
Phytoplankton group composition was similar at sites 609026, 609002 and 6091051. The
abundance of phytoplankton was far greater at 609026. This is possibly due to the higher
phosphorous concentrations observed at this site and therefore represents the site under most
influence from agricultural practises.
Winter
The dominance of green algae can be attributed to the freshwater conditions of the river
(Chan & Hamilton 2001) at this time of the year, while the dominance of diatoms can be
attributed to its ability to grow at high flow rates (Angelier 2003). Cryptophyta can develop at
cold periods (SWCSMH 2004), explaining their dominance in winter.
Spring
The dominance of diatoms can be explained by their ability to grow at a variety of flow rates
(Chan & Hamilton 2001). The lower concentration of cryptophyta can be attributed to
warmer temperatures. This may also be responsible for the increased concentration of
chlorophyta as they develop at times of low waters, higher temperatures and longer transit
times (Angelier 2003). Cyanophyta were observed, but did not dominate the phytoplankton
groups. Their low dominance can be explained with the water temperature being below its
optimal for growth at this time of the year.
5.5.2 Site SRF01
Dominance of green algae in January can be attributed to the warmer water temperatures.
This was also a period of low dissolved organic carbon concentrations (see Appendix 6).
Green algae have an advantage over other phytoplankton groups under such conditions as
they can fix carbon from the atmosphere. The low nutrient conditions during late June and
early July may be responsible for the dominance of dinoflagellates as their motility enables
them to overcome nutrient limiting conditions (Twomey & John 2001).
56
Effects of Agricultural practices on the water quality of the Scott River
The dominance of diatoms in mid July can be attributed to their ability to withstand high flow
rates and to migrate vertically through the water column. At this time, nutrient concentrations
were high in the deeper waters (see Appendix 7) and perhaps the motile ability of the diatoms
enabled them to capitalize on these nutrient conditions. A large concentration of cyanophyta
is observed in December, possibly due to increases in water temperature.
57
Effects of Agricultural practices on the water quality of the Scott River
6 Conclusions
Agricultural practises in the Scott Coastal Plain are only impacting the water quality of the
Scott River at certain times of the year. The majority of nutrient transport occurs during
winter however cold water temperatures are preventing excessive growth of phytoplankton.
The warmer temperatures in the summer are enabling higher concentrations of cyanobacteria
to occur.
The majority of nutrient transport occurs in the winter months, influenced largely by surface
water flow. Nutrient concentrations at 609026 are higher than at 609002 and 6091051,
possibly due to nutrient sources being supplemented from a drain coming off the main road.
During the winter months, the temperature of the water is too cool to promote excessive algal
growth and as a result the nutrients alone are not increasing phytoplankton production. Only
the upstream site at Milyeannup, 609026, exhibited abnormally high increases in
phytoplankton (over 2000 cells/mL) which may be due to the higher nutrient concentrations
and / or a decreased pressure of zooplankton grazing.
Although nutrient concentrations in the river are high in winter and spring, cell counts were
never at bloom levels, indicating no signs of eutrophication. Reasons for the low cell counts
include cold water temperatures, as well as the possibility of light limitations and
zooplankton grazing. Low stoichiometry coincided with the occurrence of cyanobacteria. At
TN:TP >50 there were no cyanobacteria recorded and at TN:TP < 20 cyanobacteria were
observed on some occasions however concentrations were low. This is still significant as
certain species are toxic at concentrations as low as 5 cells/mL.
Nutrient concentrations were also fairly high during low rainfall periods, indicating
groundwater as a nutrient source. During summer these nutrient concentrations and warmer
water temperatures were ideal conditions for increased phytoplankton cell concentrations as
observed at site SRF01. During this time cyanobacteria concentrations were higher due to
warmer conditions and perhaps lower flow rates but did not occur at low TN:TP. There may
be a shift to benthic dominated algal production at upstream sites in the summer due to the
lower water level, however if the river is dry this would not be the case.
58
Effects of Agricultural practices on the water quality of the Scott River
7 Recommendations
This study aims to look at the effects from agricultural activities. The nutrient load was
highest at site 609026 however it is possible that the nutrient sources were originating from
other land uses. It is therefore recommended that the possible point source at site 609026 is
investigated.
There were higher phytoplankton concentrations measured at 609026 than the other upstream
sites. This could be attributed to the higher nutrients but it could also be due to a lack of
grazing by zooplankton. It is therefore recommended that a measure of zooplankton is
recorded at each site.
The growth of phytoplankton was limited in the winter months by the cold temperature of the
Scott River. During summer the river has been recorded as dry but at other times it is flowing
slowly. There may be a shift in primary production in summer from phytoplankton to benthic
algae due to the lower water levels. It is therefore recommended that the upstream sites
should be sampled in summer for nutrients, benthic algae and phytoplankton.
59
Effects of Agricultural practices on the water quality of the Scott River
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64
Effects of Agricultural practices on the water quality of the Scott River
9 Appendices
9.1 Appendix 1: Nutrients, cyanophyta and phytoplankton raw data.
Site #
Sampling date
TN
(mg/L)
TP
(mg/L)
Cyanophyta (group)
(cells/mL)
Phytoplankton
(cells/mL)
6091051
08/09/2000
0.920
0.094
102.000
464.000
20/09/2000
0.720
0.093
12.000
118.000
05/10/2000
0.810
0.093
10.000
176.000
20/10/2000
0.750
0.079
0.000
147.000
02/11/2000
1.000
0.120
0.000
362.000
05/06/2001
2.400
0.040
0.000
121.000
18/06/2001
2.100
0.240
0.000
485.000
03/07/2001
2.000
0.110
0.000
301.000
17/07/2001
2.100
0.260
0.000
191.000
14/08/2001
2.000
0.190
0.000
722.000
08/09/2000
0.880
0.150
79.000
293.000
20/09/2000
0.690
0.052
235.000
853.000
20/10/2000
0.700
0.047
43.000
506.000
02/11/2000
0.840
0.065
0.000
720.000
05/06/2001
3.800
0.800
0.000
841.000
18/06/2001
4.300
0.910
0.000
3099.000
03/07/2001
3.600
0.760
0.000
1156.000
17/07/2001
3.200
0.530
0.000
446.000
14/08/2001
2.700
0.450
0.000
2211.000
08/09/2000
1.000
0.110
33.000
142.000
20/09/2000
0.680
0.100
28.000
704.000
05/10/2000
0.800
0.110
12.000
341.000
20/10/2000
0.760
0.089
70.000
670.000
02/11/2000
0.740
0.110
0.000
863.000
05/06/2001
1.100
0.019
0.000
212.000
18/06/2001
1.800
0.260
0.000
640.000
03/07/2001
1.600
0.150
0.000
206.000
14/08/2001
1.800
0.210
0.000
262.000
609026
609002
65
Effects of Agricultural practices on the water quality of the Scott River
9.2 Appendix 2: Dissolved oxygen concentrations at SRF01
Sample date
Depth
(m)
O - DO
(%)
O - DO (in situ)
(mg/L)
17/12/2001
0
106.2
8.04
17/12/2001
0.5
105.1
7.94
17/12/2001
1
104.3
7.9
66
Effects of Agricultural practices on the water quality of the Scott River
9.3 Appendix 3: Salinity variations at SRF01
The figure below shows that the salinity at SRF01 varies significantly throughout the seasons.
Low salinity is observed from July through to October and increases from November until
January. Salinity remains high until April where it starts to decrease.
Salinity variations at SRF01;
aggregation of 5 years of data
30000
salinity (mg/L)
25000
20000
15000
10000
5000
0
Sept Oct
Nov Dec
Jan
Feb Mar April May June July
Seasonal salinity changes at SRF01
67
Effects of Agricultural practices on the water quality of the Scott River
9.4 Appendix 4: Turbidity values at Scott River sites
6091051
609002
Collected Date
Turbidity (NTU)
Collected Date
Turbidity (NTU)
08/09/2000
5.600
08/09/2000
3.100
20/09/2000
7.700
20/09/2000
8.500
05/10/2000
8.900
05/10/2000
11.500
20/10/2000
3.920
20/10/2000
3.700
05/06/2001
10.100
05/06/2001
3.700
03/07/2001
4.760
03/07/2001
3.180
17/07/2001
3.400
14/08/2001
5.900
14/08/2001
4.900
609026
SRF01
Collected Date
Turbidity (NTU)
Collected Date
Turbidity (NTU)
08/09/2000
0.100
28/01/2000
9.133
20/09/2000
3.900
23/02/2000
5.150
20/10/2000
5.140
17/12/2001
4.600
05/06/2001
15.400
03/07/2001
6.520
17/07/2001
4.200
14/08/2001
3.900
68
Effects of Agricultural practices on the water quality of the Scott River
9.5 Appendix 5: Colour values at Scott River sites
Site 6091051
Site 609002
Collected Date
Colour (true)
(Hu)
Collected Date
Colour (true)
(Hu)
13/07/1982
170.000
10/02/1982
7.000
19/07/1982
165.000
09/03/1982
5.000
28/07/1982
160.000
02/06/1982
35.000
05/08/1982
160.000
09/07/1982
160.000
10/08/1982
160.000
09/07/1982
180.000
16/08/1982
160.000
13/07/1982
170.000
28/08/1982
140.000
13/07/1982
195.000
07/09/1982
150.000
26/08/1982
165.000
16/09/1982
105.000
16/09/1982
95.000
18/09/1982
150.000
06/10/1982
140.000
27/09/1982
170.000
06/10/1982
130.000
02/10/1982
165.000
15/11/1982
130.000
06/10/1982
160.000
15/11/1982
110.000
09/10/1982
160.000
30/12/1982
12.000
15/10/1982
170.000
22/10/1982
160.000
31/10/1982
140.000
06/11/1982
150.000
13/11/1982
150.000
15/11/1982
150.000
15/11/1982
100.000
01/12/1982
100.000
08/12/1982
60.000
30/12/1982
90.000
69
Effects of Agricultural practices on the water quality of the Scott River
9.6 Appendix 6: Dissolved organic carbon concentrations at site SRF01
Sample date
Depth
(m)
C (sol org)
(Baddock)
(mg/L)
19/01/2001
0
5
19/01/2001
0.9
4.8
28/03/2001
0
7.9
28/03/2001
0.5
7.7
20/06/2001
0
23
20/06/2001
1.2
4.2
4/07/2001
0
36
4/07/2001
1.2
17
18/07/2001
0
31
18/07/2001
1.5
26
1/08/2001
0
12
1/08/2001
1
8
10/10/2001
0
29
10/10/2001
1.2
28
17/12/2001
0
8
17/12/2001
1
8.4
24/10/2001
0
52
24/10/2001
1.3
30
70
Effects of Agricultural practices on the water quality of the Scott River
9.7 Appendix 7: Total nitrogen and total phosphorous concentrations at site
SRF01
Sampling dates are along the x axis, represented by month number (for example January is
represented by 1). Depth is along the y axis, with 0 being the surface of the river.
Concentrations are illustrated with the colour bar. Dark red represents high concentrations of
nutrients and purple low concentrations. Dots represent sampling times and depths.
71