Nutrients in Marine and Estuarine Environments
edited by
Phillip R. Cosser
Australia: State of the Environment
Technical Paper Series (Estuaries and the Sea)
Environment Australia, part of the Department of the Environment
Commonwealth of Australia 1997
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Cataloguing-in-publication data:
Nutrients in marine and estuarine environments / edited by
Phillip Cosser.
53 p. 29.7 x 21 cm. – (Australia: State of the environment technical
paper series (Estuaries and the sea))
Bibliography: pp. 23–27, 43–44, 53.
ISBN 0 642 25276 9
1. Nutrient pollution of water-Australia. 2. Marine
pollution-Australia. 3. Coastal zone management-Australia. I. Cosser,
Phillip. II. Australia. Dept. of the Environment. III. Series.
557.727’0994-dc21
For bibliographic purposes, this paper may be cited as:
Cosser, P.R. 1997, ed. Nutrients in marine and estuarine environments, State of the Environment
Technical Paper Series (Estuaries and the Sea), Department of the Environment, Canberra.
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Contents
Page
Preface
4
Introduction to case studies— Phillip R. Cosser
5
Case study 1: Nutrients in the Great Barrier Reef Region
Jon Brodie
7
Case study 2: Recent changes to the Tuggerah Lakes system as a
result of increasing human pressures
Andrew D. Kennedy
29
Case study 3: Impact of nutrient-rich sewage discharged to
near-shore waters on the Sunshine Coast,
Queensland
Phillip R. Cosser
45
3
Preface
Australia: State of the Environment 1996 (the first ever independent
and comprehensive assessment of the state of Australia’s
environment) was presented to the Commonwealth Environment
Minister in 1996. This landmark report, which draws upon the
expertise of a broad section of the Australian scientific and technical
community, was prepared by seven expert reference groups working
under the broad direction of an independent State of the Environment
Advisory Council. While preparing the report, the former
Department of the Environment, Sport and Territories, on behalf of
the reference groups, commissioned a number of specialist technical
papers. These have been refereed and are being published as the
State of the Environment Technical Paper Series. Reflecting the
theme chapters of the report, the papers relate to human settlements,
biodiversity, the atmosphere, land resources, inland waters, estuaries
and the sea, and natural and cultural heritage. The topics covered
range from air and water quality to seagrasses and historic
shipwrecks.
4
Introduction to case studies
Phillip R. Cosser
Effective management of the cumulative and chronic
effects of the range of pollutants entering the waters
of the coastal zone is widely acknowledged as being
one of the major environmental management
challenges facing Australia. Pollutants enter coastal
zone waters from a variety of sources. Virtually all
economic sectors contribute directly or indirectly to
the pollutant load. Given the diversity of polluting
sources, and the inherent difficulties in identifying
cause and effect relationships, it is extremely difficult
to develop effective management strategies to protect
estuarine and marine waters from the adverse impacts
of pollution.
In recognition of the importance of water pollution in
any assessment of the state of the coastal zone
environment, the Marine and Estuarine Reference
Group, formed to assist in preparing Australia: State
of the Environment 1996, has attempted to identify
some of the major water pollution issues currently
threatening near-shore waters. One of the most
significant water pollution issues, in terms of both the
area affected and the potential impact, is nutrient
enrichment. Accordingly, the former Department of
the Environment, Sport and Territories, on behalf of
the Reference Group, commissioned several
technical papers to briefly review different aspects of
the nutrient enrichment problem within the context of
the Organisation for Economic Cooperation and
Development (OECD) Pressure-State-Response
model which was used in a modified form as the basis
for Australia: State of Environment 1996.
These reviews focus on quite different case studies to
highlight the complexity and diversity of issues
surrounding the nutrient problem. The case studies
are as follows:
difficulties in dealing with the issue on such a large
scale.
Case study 2: Tuggerah Lakes, New South
Wales
This study examines the impact of catchment
development on the nutrient regime of an
estuarine lake system.
Case study 3: Moffat Heads, Queensland
This study details the impact of a single,
nutrient-rich effluent outfall on the algal
community of an intertidal rock platform.
Nutrients, principally nitrogen and phosphorus, are of
particular significance for water quality and
productivity of marine and estuarine environments,
firstly, because of their fundamental role in the
functioning of biological systems and, secondly,
because their concentrations and bioavailability are
susceptible to human manipulation. The nutrient
regime of coastal and estuarine waters is therefore of
considerable significance to the state of Australia’s
coastal environments.
The growth of marine plants such as macroalgae and
phytoplankton is regulated primarily by temperature,
light regime and the availability of certain nutrients,
principally carbon, nitrogen, phosphorus and a
number of trace elements. Plant growth can be
summarised by the following generalised and
simplified equation:
!
! ! !
Case study 1: The Great Barrier Reef Region
This study examines a regional scale marine
nutrient enrichment problem, and highlights the
multiple sources of nutrient inputs and the
The availability of these essential nutrients is
therefore critical to sustaining plant growth. Should
the availability of one or more be limited, growth can
be constrained. In the marine environment, where
5
temperature and light regimes are suitable, the rate of
growth of phytoplankton and macroalgae is often
limited by the availability of nitrogen (N). However,
in some circumstances, phosphorus (P) may be the
limiting nutrient, while in others various
combinations of simultaneous or alternating N or P
limitation have been reported. The N:P ratio of the
water can also influence growth, with a particular
ratio favouring some species while constraining
others.
The naturally low nutrient concentrations in most of
Australia’s shallow marine waters is often one of the
major factors limiting marine plant growth. Under
circumstances where either N or P is limiting, the
subsequent addition of the nutrient and elevation in
concentrations of bioavailable N and/or P in the water
column may stimulate plant growth. The term
‘eutrophication’ describes the process whereby
primary productivity is enhanced as a result of an
increase in the availability of nutrients. Eutrophic
waters typically support a high standing stock of
either phytoplankton or attached algae.
As a result of rapid and extensive post-war
agricultural development together with increasing
urbanisation of coastal zone land, nutrient loads
entering estuarine and coastal waters have increased
markedly in recent decades. On a national scale,
nutrients originating from diffuse catchment sources
and entering marine waters through river discharge
represent by far the major nutrient source, accounting
for an estimated 85 per cent of total nutrient loading
in coastal zone waters. Land clearing, grazing and the
use of agricultural fertilisers are recognised as being
the primary causes of increased catchment nutrient
export. However, in view of the coastal distribution of
Australia’s population, domestic sewage and
industrial effluents can account for a significant
proportion of nutrient inputs in the vicinity of major
urban centres.
This increase in both diffuse-source and point-source
nutrient loading to shallow, and often poorly flushed
coastal waters has resulted in the development of
eutrophic conditions in many instances. While algal
blooms are a natural phenomenon and were reported
by the first Europeans to explore Australia’s coastline,
they appear more common and affect more
embayments and estuaries today than several decades
ago.
Increased algal growth in the Peel–Harvey estuary,
6
Western Australia, was first noticed in the 1960s,
becoming progressively worse during the 1970s and
early 1980s. In Cockburn Sound (WA) urban and
industrial development of the adjacent coast during
the late 1950s and increasing inputs of nutrient rich
industrial and domestic wastewater during the 1960s
resulted in a 97% loss of seagrass beds by 1978, a total
loss of some 3300 hectares.
By the 1970s more and more embayments and coastal
lakes were exhibiting symptoms of nutrient
enrichment. Significant algal blooms or other
nutrient-related problems have now been reported in
waters along the east coast of Australia, from
Townsville to Adelaide and in the south-west of
Western Australia. Some of the more notable
examples include: Gulf St Vincent; Westernport Bay;
Botany Bay; Moreton Bay; Tuggerah Lakes; Lake
Illawarra, Lake Macquarie; Narrabeen Lagoon;
Orielton Lagoon; Gippsland Lakes; Cockburn Sound;
Wilson Inlet; Peel Inlet; Harvey estuary; Hawkesbury
estuary; Georges estuary; Derwent estuary; Swan
estuary; Huon estuary; and Princess Royal Harbour.
Non-estuarine coastal waters have also experienced
significant algal blooms. In January 1993 widespread
red algal blooms were observed off the Sydney coast
extending from Wollongong to the Hawkesbury
estuary. Extensive algal blooms, particularly those
formed by the cyanophyt Trichodesmium, are also
commonly reported in the Great Barrier Reef Lagoon
between Bundaberg and Cairns, although it remains a
matter of contention as to whether the frequency and
extent of such blooms have increased in recent years.
A number of factors determine the biological
significance of nutrient inputs. These include the
absolute amount or nutrients entering the system, the
temporal distribution of input, areal loading
characteristics and the form of the nutrient. Nutrient
input associated with river runoff is typically episodic
and quantitatively significant, while the consequent
loading per unit area in coastal zone waters is
relatively low. Conversely, loading associated with
point-source discharges is continuous, quantitatively
less significant relative to total system loading, while
areal loading may be high in limited areas. Clearly, the
biological significance, fate and potential impacts of
nutrients originating from the different sources differ.
The case studies reported herein demonstrate the
different impacts of nutrients entering coastal waters
in different circumstances.
Case study 1: Nutrients in the Great Barrier Reef Region
Contents
1
2
Page
Introduction
9
1.1
1.2
1.3
1.4
9
9
9
9
Statistics
Habitats
System functions
Resources and use
Pressures
10
2.1
10
Terrestrial runoff
3
Sources
10
4
Potential effects
17
4.1
4.2
17
17
5
6
Nutrients
Sediment
State
18
5.1
5.2
5.3
18
18
20
Global condition of coral reefs
Evidence of effects on the Great Barrier Reef
Monitoring
Responses
21
Abbreviations
22
References
23
List of Figures
Figure 1:
Figure 2:
Figure 3:
Figure 4:
Figure 5:
Figure 6:
Figure 7:
Increasing tourist numbers on the Great Barrier Reef
Nitrogen and phosphorus from terrestrial sources
Nutrient inputs to the central Great Barrier Reef
Sediment exports: Contributions from each land use category
Annual fertilizer use in Atherton Shire
Growth in fertilizer use
Flood plumes in the Great Barrier Reef Marine Park, 1st and
2nd Febuary 1994
Figure 8: Observed movement of eastern edge of Fitzroy River flood plume during
January 1991
Figure 9: Stone Island reef before 1920 and in 1994
Figure 10: Seasonal variation in diatoms, 1928 and 1992
Figure 11: Historical variation in per cent void space in coral from Green Island
10
11
12
13
14
14
15
16
18
19
20
List of Tables
Table 1: Soil loss from various land use types
12
7
8
Case study 1: Nutrients in the Great Barrier Reef Region
Jon Brodie, Great Barrier Reef Marine Park Authority, Townsville.
1
Introduction
1.1 Statistics
The Great Barrier Reef (GBR) system covers an area
of about 350 000 sq km on the north–eastern
Australian continental shelf. It is a long, narrow reef
system stretching 2000 km from 10.5S at Cape York
to 24.5S near Bundaberg. It ranges in width from
50 km in the north to 200 km in the south. The system
consists of approximately 3000 reefs, on which about
350 species of hard coral are found along with
1500 species of fish, 240 species of seabirds and at
least 4000 species of mollusc. Our knowledge of the
taxonomy and distribution of the lesser known groups
of invertebrates such as echinoderms and worms is
still very limited. In a recent study, 134 species of
marine flatworms, over 90 per cent of which were
new species, were recorded from two adjacent reefs
(Heron Island and One Tree Island Reefs) effectively
increasing by a factor of 10 the total number of species
of this Order known from the whole GBR (Newman
& Cannon 1994).
1.2 Habitats
Generally, the range of habitats found on the GBR is
relatively uniform from north to south but varies
across the continental shelf (Hopley 1982). Inshore,
the coastline is dominated by mangroves
(3900 sq km) (Robertson & Lee–Long 1991)
interspersed with areas of low energy sandy beaches
and limited lengths of rocky shoreline. Immediately
offshore, shallow seagrass beds are common,
covering an area of 4300 sq km (Lee Long et al.
1993); in the north, large areas of deepwater (>10 m)
seagrass are found further offshore. The GBR lagoon
floor is dominated by soft-bottomed communities of
algae, sponges, bryozoans and echinoderms
interspersed with bare sand. In the north, extensive
Halimeda sp. algal beds occupy the deeper offshore
waters, sustained by nutrient-rich water upwelling
from the Coral Sea (Drew & Abel 1988).
The coral reefs of the GBR consist of two main types:
fringing reefs (∼ 760 reefs) which occur inshore
around the continental islands; and those of the main
barrier reef (∼ 2200 reefs) which occupy a band on the
outer edge of the continental shelf. The main reef does
not form a continuous barrier but consists of
individual reefs separated by inter-reefal waters.
1.3 System functions
Coral reefs are generally considered to do best in low
nutrient conditions. Nutrient sources to the GBR
include the surface waters of the Coral Sea
(nutrient-poor), upwelling Coral Sea deep water
(nutrient-rich), terrestrial runoff and atmospheric
inputs, including nitrogen fixation by cyanobacteria
(Furnas et al. 1995). Flushing of the GBR lagoon is
limited by the enclosure formed by the main reef.
Residence times in the lagoon, while not precisely
known, may be prolonged (Wolanski 1994).
1.4 Resources and use
The major uses occurring in the GBR region are
tourism, recreation, fishing and shipping. The region
also has primary natural environment values and
Aboriginal cultural values.
Tourism is the boom industry of the region. Following
a forty fold increase in the number of tourists visiting
the area between 1946 and 1980, significant growth
has continued. In the last decade visitor nights have
doubled (Driml 1994) (Figure 1). In addition, with the
introduction of high speed ferries, large numbers of
tourists are now able to visit even outer-shelf reefs,
with some reefs now receiving more than 500 visitors
per day.
9
Traditional fishing by indigenous people is confined
to areas close to Aboriginal communities. Traditional
hunting and fishing are permitted in all zones of the
Great Barrier Reef Marine Park (GBRMP) except
Preservation Zones. Given that turtles and dugongs
are hunted, yet are recognized as threatened species
in GBR waters, some concern has been expressed
about management of traditional hunting.
Million visitor nights
25
20
15
10
5
91–92
90–91
89–90
88–89
87–88
86–87
85–86
84–85
0
Year
Figure 1: Increasing tourist numbers on the
Great Barrier Reef
Source: Driml 1994
Note: Visitor nights for Great Barrier Reef and mainland.
Shipping is a major activity, with over 2000 ships per
year passing through the area (Driml 1994). A number
of substantial bulk carrier ports occur within the
region, shipping coal, alumina and sugar. The
discharge of shipping ballast water, collected at other
ports, is recognised as a potential mechanism by
which undesirable species could be introduced to the
GBR. However, no undesirable introductions have
yet been detected in the GBR region. Risk assessment
and management options are now being studied as a
response to this potential problem.
The principal commercial fisheries of the GBR are the
prawn and scallop trawl fisheries. Other commercial
fisheries include line fishing for reef and pelagic
stocks, crabbing and inshore net fisheries.
Recreational fisheries for bottom and pelagic stocks
are also important as are the traditional fisheries of
Aboriginal and Torres Strait Islanders. Fish stocks in
the GBR are small when compared to temperate
offshore fisheries. The total value of primary landings
in the commercial fisheries in the area was
$128 million in 1991 (Driml 1994).
The reef-fish line fishery includes both commercial
and recreational components, with the main target
being the larger species such as coral trout and
snapper. There are about 300 commercial operators,
24 000 recreational boats and more than 150 charter
boats.
10
2
Pressures
2.1 Terrestrial runoff
There is growing realization that the declining quality
of terrestrial runoff may be one of the most significant
anthropogenic threats to the GBR region (Baldwin
1990; Yellowlees 1991; Bell 1991; Brodie 1995a).
Catchments in north and central Queensland have
been extensively modified since European settlement
as a result of forestry, urbanization and
agriculture–particularly sugar cane cultivation and
grazing. Recognition of the potential impact of land
degradation on downstream waters occurred some
time ago (Douglas 1967), as did recognition of the
potential impacts on the GBR (Bennell 1979).
Scientific debate continues as to the severity of the
problem (Bell & Gabric 1991; Kinsey 1991a),
although there is general agreement as to the need for
clarification of the scale of the problem.
3
Sources
Recent studies using catchment models and existing
data have attempted to quantify the principal sources
of sediment and nutrients discharged to coastal waters
of Queensland (Moss et al. 1992). The report
estimates that 15 million tonnes of sediment,
77 000 tonnes of nitrogen and 11 000 tonnes of
phosphorus are discharged annually to the coastal
waters of the GBR by mainland rivers. Other
significant findings are that grazing lands contribute
approximately 80 per cent of nutrients, areas under
sugarcane 15 per cent, and sewage discharges
approximately 1 per cent of the overall flux (Figure 2).
The latter however, can be significant at local scales
due to their concentrated form and chronic daily
delivery mode.
Urban
(0.6%)
Pristine
(5.7%)
Urban
(0.4%)
Cropping
(15.7%)
Pristine
(5.7%)
Cropping
(16.4%)
Grazing
(78.0%)
Grazing
(78.0%)
Nitrogen
Phosphorus
Figure 2: Nitrogen and phosphorus from terrestrial sources
Source: Moss et al. 1992.
It is estimated that sediment and nutrient delivery to
the GBR from terrestrial discharge has increased by
four times since European settlement, (i.e. in the last
140 years). More detailed studies of sediment export
on individual catchments have found similar
increases. Goulay and Hacker (1986) estimated that
the yield from the Pioneer River catchment had risen
from 80 000 to 140 000 tonnes per year in
pre-European times to 300 000 tonnes per year now,
a two to fourfold increase. A doubling of sediment
yield from the Barron River was estimated by Bird
(1973). The large changes in sediment yield
associated with land use changes in north Queensland
have also been documented in detail by Pringle
(1986).
Furnas et al. (1995) attempted to quantify all sources
of nutrient input to the central GBR, showing that 39
per cent of all nitrogen and 52 per cent of phosphorus
originated from river inputs, while sewage discharges
accounted for 2.3 per cent and 7.7 per cent for N and
P respectively (Figure 3). However, given the limited
availability of data on loads carried during periods of
high river flow, riverine input may be underestimated.
In view of the relative contribution of riverine inputs
together with the postulated increase in such inputs,
the available data suggest that total nutrient input to
the GBR has risen by about 30 per cent in the past 140
years. However, the increase in the inshore part of the
GBR lagoon (i.e. in depths less than 20 metres and less
than 20 km from the coast) is probably much greater
as this section holds only 5 per cent of the volume of
the lagoon but receives the full impact of the increased
river and coastal inputs.
Nutrients lost from grazing lands are largely those
nutrients naturally present in the soil, as distinct from
added fertilizer. The principal cause of this loss is the
removal of the natural vegetation (Beckman 1991)
and overgrazing (Gardner et al. 1988), both of which
increase the soil’s susceptibility to erosion. In the case
of sugarcane cultivation, both natural soil nutrients
and added fertilizer are lost, with fertilizer addition
and loss far more important than in the grazing
situation (Prove & Hicks 1991).
Studies in the Johnstone River system show that,
while agricultural activity has had a noticeable
influence on the nutrient content of riverine and
estuarine sediments, the effect is local and does not
extend far across the GBR shelf (Pailles et al. 1993).
Phosphorus present in the sediments examined is also
apparently not readily desorbable into the water
column (Pailles & Moody 1992).
11
Trichodesmium
nitrogen fixation
(25%)
Rainfall
(11%)
Sewage
(2%)
Sewage
(8%)
Rivers
(39%)
Upwelling
(29%)
Reefal
nitrogen
fixation
(8%)
Rainfall
(15%)
Rivers
(52%)
Upwelling
(10%)
Phosphorus
Nitrogen
Figure 3: Nutrient inputs to the central Great Barrier Reef
Source: Furnas et al. 1995
Moss et al. (1992) identified the principal sources of
riverine sediment from coastal catchments (Figure 4).
As with nutrients, grazing lands are the major source,
with cropping and urban lands contributing
significant, but smaller, amounts. Even at low runoff
levels, grazing lands can lose large amounts of
sediment in comparison with natural or plantation
forest and woodlands. Table 1 shows some measured
values of the comparative losses (Dunne 1979)
highlighting the large losses per hectare potentially
associated with cropping (sugarcane, pineapples) and
urban development.
Much of the fourfold increase in sediment and
nutrient export from coastal catchments has occurred
in the last forty years. During this period, fertiliser use
increased dramatically in all major catchments. In
addition, deforestation continued on a massive scale
as a result of land development programs such as the
Brigalow scheme (Fitzroy and adjacent catchments),
which resulted in the destruction of three million
hectares of Brigalow woodland between 1960 and
1975. Increased erosion on the resulting grazing
lands, exacerbated by droughts and seasonal
overgrazing, is the cause of the large increases in
sediment and nutrient input to coastal waters. Sewage
discharges, associated with a growing population,
have also contributed to the overall accelerated rise in
nutrient inputs.
12
Table 1: Soil loss from various land use types
Land Use
Soil loss
tonnes/hectare/
year
Paddock scale
Undisturbed rainforest (NEQ)
4.8
Selectively logged rainforest
10.9
Cleared rainforest in first year
59.6
Sugarcane
– Johnstone R.
Burnt (conventional cultivation)
Zero tillage, 0% trash
Zero tillage, 50% trash
Zero tillage, 100% trash
– Pioneer R.
Burnt (conventional cultivation)
1501
15
10
5
56–390
City average (Victoria)
200
City construction sites
400
Gravelled roads
140–250
Pineapple farms (SEQueensland)
0.1–105
Catchment scale
Rainforest
0.2–0.3
Woodland/grassland
0.5–1.4
Cleared catchment
20–30
Source: Dunne 1979.
1. Average given, range is 70 to 500 t/ha/yr.
Catchment area boundary
North-East Cape York
Mossman-Daintree
Barron
Pristine
Grazing
Cropping
Urban
North-East Cape York
Mulgrave-Russell
Mossman-Daintree
Johnstone
Barron
Tully-Murray
Mulgrave-Russell
Johnstone
Herbert
Tully-Murray
Herbert
Ross-Black
Ross-Black
Burdekin-Haughton
Burdekin-Haughton
Don
Don
Proserpine
Proserpine
Pioneer-O’Connell
Pioneer-O’Connell
Shoalwater Bay-Sarina
Shoalwater Bay-Sarina
Fitzroy
Curtis Coast
Curtis Coast
Burnett-Kolan
Fitzroy
Burnett-Kolan
Mary
Sunshine Coast
Mary
Brisbane
Sunshine Coast
Gold Coast-Beaudesert
Brisbane
0 0.5 1 1.5 2 2.5 3
Tonnes of sediment/yr
(millions)
Gold Coast-Beaudesert
Figure 4: Sediment exports: Contributions from each land use category
Scource: Moss et al. 1992
13
that up to 50 per cent of applied nitrogen fertilizer can
be lost to drainage and runoff. For phosphorus, losses
are smaller though significant (Prove & Moody
1994). The increased use of fertilizers and the
resultant loss of residual nutrients in river runoff is
thought to have caused elevated nutrient
concentrations in off-shore waters (Rasmussen &
Cuff 1990).
4000
Tonnes
3000
2000
1000
0
1950
1960
1970
Year
1980
1990
Figure 5: Annual fertilizer use in Atherton Shire
Source: Based on Australian Bureau of Statistics data: Totals
of all types, from Valentine 1988.
Fertilizer use in the Barron River area (Atherton
Shire), increased from 144 tonnes in 1960 to about
3000 tonnes at present (Valentine 1988) (Figure 5).
An increase of similar magnitude has occurred for the
whole GBR coast (Pulsford 1996) (Figure 6). Studies
in the Johnstone River catchment have demonstrated
Prawn farming is an expanding industry along the
GBR coast and prawn farm effluents may be a
considerable source of nutrients. At present, the
amounts of nutrients involved are small with only
potential risks, but as acreages increase some of the
associated eutrophication problems seen overseas
may begin to occur.
While sand and silt sized sediment fractions may be
redeposited within catchments, most of the fine clay
fraction is transported to the river mouth. Material
redeposited within the catchment during low flow
events may also be resuspended and transported to the
coastal zone during major flood events associated
with cyclonic rains. These major events are
responsible for almost all the transport of material
from catchments to the coastal zone. This can be seen
clearly from the work of Cosser (1989) on the South
Pine River in south-east Queensland, where 86
per cent of phosphorus flux occurred during periods
of stormflow (2.8 per cent of the time).
100
90
Tonnes (1000)
80
70
Nitrogenous fertiliser use
60
50
40
Phosphatic fertiliser use
30
20
10
0
1910
1920
1930
1940
1950
Year
1960
1970
1980
1990
Figure 6: Growth in fertilizer use
Note: Historical fertiliser use in coastal Queensland river catchments adjacent to the Great Barrier Reef Marine Park
Source: Pulsford 1996.
14
The great majority of the total phosphorus load
(77 per cent) was associated with particulate material
as opposed to being in solution. Similar data has been
presented for the Johnstone River in north
Queensland (Furnas & Mitchell 1991; Hunter 1995).
Intense rainfall associated with cyclones Winifred
(1987), Joy (1991) and Sadie (1994) caused massive
river flows, with plumes which intruded far into the
GBR lagoon (Figure 7).
Figure 7: Flood plumes in the Great Barrier Reef Marine Park, 1st and 2nd Febuary 1994
15
King and Wolanski (1991) have shown, by modelling,
that river plumes are normally constrained close to the
coast by hydrodynamic conditions generated by the
prevailing south-east wind regime, but under other
wind conditions river plumes can reach the outer reef
(Brodie & Mitchell 1992; Preker 1992). The
combined plume from a number of north Queensland
rivers during the Cyclone Sadie rain of 1994 extended
between Townsville and Port Douglas and up to
100 km offshore (Figure 7), crossing many of the
mid-shelf reefs (Brodie 1995b). The Fitzroy River
Plume, during the Cyclone Joy floods of 1991,
reached the Capricorn–Bunker group of reefs on
23rd January, 1991, 200 km from the mouth of the
river (Figure 8).
Opinions about the dispersion of material carried in
terrestrial runoff differ (Wolanski et al. 1986; Johnson
& Carter 1988; Gagan et al. 1987, 1990). Most
terrestrial sediment deposited on the floor of the GBR
lagoon does so in a band within 15 km of the coast
(Belperio 1983). Some studies suggest that
terrigenous input reaches only halfway across the
shelf while others have found terrigenous marker
chemicals extending to the edge of the shelf break. In
general, there does appear to be an inner reefal area
dominated by terrestrial sediment and an outer area
dominated by carbonate sediment (Johnson & Carter
1988; Wolanski & van Senden 1983).
Nutrients such as phosphate associated with the
sediment may travel much further offshore than the
sediment itself. This occurs as the phosphate desorbs
off the sediment particles in the estuarine mixing
process, and is then in solution and able to move
greater distances (Brodie & Mitchell 1992).
Shelf sediments may act as large nutrient sinks that,
under suitable conditions, may release stored
nutrients back into the water column (Ullman &
Sandstrom 1987; Chongprasith 1992). It is known that
nutrient pulses from resuspension of bottom
sediments during moderate south-easterly winds can
occur (Walker & O’Donnell 1981) and during
cyclonic wind events the large pulses of nutrients
released into the water have caused extensive
phytoplankton blooms (Furnas 1989).
N
0
5
10
Kilometers
North
Keppel
Island
18–1–91
Yeppoon
Barren Island
Great
Keppel
Island
23.1.91
Emu Park
12–1–91
Keppel
Bay
19–1–91
North West
Island
Capricorn
Bunker
Group
Hummocky Island
Heron Island
Fitzroy River
Curtis Island
The Narrows
Figure 8: Observed movement of eastern edge of Fitzroy River flood plume during January 1991
16
4
Potential effects
4.1 Nutrients
The effects of nutrient enhancement on coral reefs are
now fairly well known (Kinsey 1991b), with the
largest ’natural experiment’ having occurred in
Kaneohe Bay, Hawaii. In this large, partially enclosed
bay with an extensive barrier reef system, treated
sewage effluents were discharged from the late 1940s
until 1977. Extensive reef degradation occurred, with
areas nearest the outfalls becoming dominated by
filter-feeding organisms, while in areas some distance
away coral was replaced by algal communities (Smith
et al. 1981). Since discharge ceased in 1978, the coral
communities have made a slow, although by no means
complete recovery (Maragos et al. 1985).
Excess nutrients can have a number of effects on coral
and reef systems. Under conditions of nutrient
enrichment, phytoplankton density can increase,
leading to a decrease in water clarity and reduced light
penetration. This, in turn, can reduce the growth rate
of deeper water corals. The increased phytoplankton
crop also encourages the growth of filter-feeding
organisms such as sponges, tube worms and barnacles
which compete for space with coral. As many of these
organisms bore into the reef structure, enhanced reef
bioerosion may occur leading to the loss of reef
structural integrity. In addition, nutrients enhance the
growth of turf and macroalgae which overgrow the
coral.
Elevated phosphorus concentrations can also reduce
coral density, and so weaken the coral skeleton, thus
making the colony more susceptible to storm damage
(Rasmussen & Cuff 1990). A general reduction in
calcification of the reef system also occurs (Kinsey &
Davis 1979).
Details of the effects of nutrients on coral reef
communities in the absence of phytoplankton effects
are being determined in the ENCORE experiment on
the southern Great Barrier Reef. In this study small
patch reefs are being fertilized with nitrogen and
phosphorus additions to assess the individual and
combined impacts on a variety of reef organisms of
this nutrient enrichment (Steven & Larkum 1993).
However, the experiment will not provide data
relating to the longer term impacts of nutrient
enrichment on phytoplankton. Neither does it closely
resemble the ‘usual’ conditions associated with
anthropogenic nutrient enrichment (riverine and
sewage input) in that under such conditions N and P
inputs are accompanied by many trace elements and
an array of organic compounds. Such substances may
interact with N and P and may also affect reef
organisms directly, making it difficult to extrapolate
the results to other reef systems.
A postulated secondary effect of increased
phytoplankton abundance is the increased survival of
crown-of-thorns starfish larvae arising from
increased food availability. The population of the
starfish (Acanthaster planci) has exploded in waves
of outbreaks on Indo-Pacific coral reefs since the
mid-1960s (Birkeland & Lucas 1990). This
coral-eating echinoderm has devastated reefs in many
parts of the western Pacific region and many
anthropogenic causes have been invoked to explain
the outbreaks. The two most enduring have been
overfishing of predators (fish or the triton shell)
(Lassig & Engelhardt 1994) and enhanced survival of
the larval stage of the animal (Brodie 1992; Birkeland
& Lucas 1990) due to phytoplankton blooms
associated with elevated nutrient levels. Despite
many years of research, a conclusive answer as to
whether the outbreaks are caused or enhanced by
human activity has not emerged.
4.2 Sediment
Increased sediment loads lead to muddier systems
with less light for bottom communities and
disturbance to bottom fauna due to siltation. In north
Queensland both the Pioneer River (Goulay & Hacker
1986) and the Johnstone River (Arakel et al. 1989)
have dramatically increased sedimentation in recent
years due to changed land management practices in
their catchments. Other rivers can be expected to be
in a similar condition but have not been studied.
Mangroves, which grow in muddy environments,
may actually increase in area with increased sediment
deposition and this appears to be the case in Cockle
Bay, Magnetic Island, where the area of mangrove has
expanded at the expense of beach and seagrass areas
(Alan Mitchell, pers. comm.). However, in areas with
severely increased suspended sediments, mangroves
may also be damaged and lost.
Seagrasses are more susceptible to sedimentation
than mangroves, suffering as a result of both light
reduction and direct smothering (Robertson &
17
Lee–Long 1991). In recent times large areas of
seagrass meadow have been lost in muddy flood
events, such as the 100 000 hectares lost in Hervey
Bay in 1992.
Coral reefs may be severely effected by even
moderate increases in sedimentation and turbidity
but, paradoxically, some corals thrive in the quite
muddy conditions found on inshore reefs such as
Virago Shoals and Middle Reef in Cleveland Bay and
at Cape Tribulation. This depends on their tolerance
for low light conditions and their sediment rejection
and removal mechanisms (Stafford–Smith &
Ormond 1992). There is considerable anecdotal
evidence that reefs, particularly inshore fringing
reefs, are now muddier and have less coral but more
algal cover. For example, accounts suggest coral reef
flats on Magnetic Island formerly had far higher coral
abundance than at present. Similar stories can be
documented about other inshore fringing reefs (e.g.
those in the Whitsunday and Palm Island groups).
The reef slope communities seem to be in better
shape, perhaps implicating sedimentation as the
cause of coral loss on the flats. The anecdotal
evidence for loss of coral cover on many inshore reef
flats is partially supported by historical photographs
from early this century showing better coral cover
than now exists at some locations (Figure 9). Other
locations show no change in coral cover.
5.2 Evidence of effects on the Great
Barrier Reef
As research and monitoring programs have
progressed in recent years evidence of the scale and
nature of eutrophication/sedimentation problems in
the GBR has emerged. Anecdotal accounts suggest
that reef water is now more turbid and the reefs,
particularly inshore fringing reefs, have more algae
and less coral cover than in the period remembered
before 1970. With a lack of good long-term
monitoring records to support this evidence the
GBRMPA has been collecting historical photographs
of reefs (generally reef flats exposed at low tide) for
comparison with current conditions. The
comparisons appear to show that far less branching
coral cover is now present on some fringing reef flats
than in periods before 1920 (Figure 9) while other
reef flats show no change.
Many corals and coral reef systems seem to be able
to exist successfully in relatively turbid
environments. The reefs of the Cape Tribulation
mainland shore north of the Daintree River exist in a
highly turbid water and large increases in turbidity
associated with a poorly constructed, dirt coastal road
appear to have had minimal impact on the reefs
(Craik & Dutton 1987; Fisk & Harriot 1989).
5 State
5.1 Global condition of coral reefs
Many coral reefs around the world are now in an
alarming state of decline due to terrestrial runoff of
sediments and nutrients together with other factors
such as overfishing and destructive fishing
(Wilkinson 1994). Deforestation, agriculture on steep
slopes and sewage discharges are causative factors
often implicated.
18
Figure 9: Stone Island reef before 1920 (above)
and in 1994 (below)
Evidence of eutrophication in the phytoplankton
record is unclear. No long-term records of
phytoplankton biomass in the GBR lagoon exist. The
existing records, particularly the data from the British
Museum Great Barrier Reef Expedition in the Low
Isles region of 1928–1930 (Orr 1933; Marshall 1933)
and Revelante & Gilmartin’s (1982) work in the late
1970s off Townsville, have been used as a
comparative record by some researchers. Studies
which have repeated measurements of phytoplankton
composition and abundance performed in 1928–29 in
a single area near Low Isles have found significant
differences and the claim has been made that the
differences show the system to be in a higher nutrient
condition than at that time (Bell & Elemetri 1993).
Results for diatom concentrations (Figure 10) show
higher levels in 1992 than in 1928–29. Results from
broad-scale phytoplankton surveys in the GBR on the
other hand show biomass and species composition
consistent with an unimpacted system (Furnas 1991;
Liston et al. 1992).
50 000
Total diatoms 1992
Number of diatoms
40 000
30 000
Total diatoms
1928/29
20 000
10 000
0
J
F M A M J J A S O N D
Months
J
Figure 10: Seasonal variation in diatoms, 1928
and 1992
Note: Comparison of 1992 seasonal variation of total diatoms
at 3 Miles East station–Low Isles with that measured in
1928–29.
Source: Bell & Elmetri 1992
Coral growth leaves a record in the coral skeleton of
growth characteristics in the year of deposition.
Corals may attain ages of several hundred years and
thus interpretation of environmental conditions
affecting growth over this period is potentially
available from coral cores (Isdale 1984). Evidence
from coral cores from the Queensland coast suggest
that coral growth conditions did change significantly
in recent times, and that this can be correlated with
landuse changes on the adjacent coast (Rasmussen et
al. 1994).
Some problems still remain in separating an
anthropogenically sourced signal in the coral skeleton
from signals due to natural variability in
environmental conditions. However, evidence of
deteriorating water quality is increasing. Studies off
Cairns, of the ‘void space’ (the proportion of holes in
the coral) in growth rings, suggest that significant
changes in water quality occurred starting about fifty
years ago. These changes adversely affected the
growth of the coral and have been correlated with land
use changes on the adjacent Barron River catchment
(Rasmussen et al. 1994). Graphs of void space versus
years in a core from Green Island demonstrate the
effect (Figure 11).
In some limited areas of the GBR region evidence of
eutrophication is indisputable. Large increases in the
area of seagrass beds around Green Island, a
mid-shelf reef, are associated with the prolonged
discharge of untreated sewage from the island and the
retention of the diluted discharge in the vicinity of the
island (van Woesik 1989). Sediments in the vicinity of
the actively expanding seagrass areas have high
nutrient concentrations and the seagrass is growing in
reefal environments where seagrass does not grow on
other GBR midshelf reefs. Similarly, Trinity Inlet,
next to Cairns city, and subject to prolonged sewage
discharge into confined waters is now known to be
eutrophic with continuous and periodically intense
phytoplankton blooms. Discharge of sewage given
secondary treatment at the Hayman Island Resort in
the Whitsunday Islands caused localized effects on
the adjacent coral reef (Steven & van Woesik 1990),
including reduced species diversity, lower coral
cover, suppressed coral recruitment and greater
turnover of species. The outfall is now rarely used as
effluent is used for resort gardens irrigation.
19
% void space
73
71
69
67
65
63
61
59
57
55
53
51
49
47
45
43
1878
Pre-1958
Sample mean 1 std. dev
Post-1958
Sample mean 1 std. dev
1887
1896
1805
1914
1923
1932
1941
1950
1959
1968
1977
1986
Year
Figure 11: Historical variation in per cent void space in coral from Green Island
Note: The graph indicates an increase in void space in the past 50 years.
While localized areas are known to suffer adverse
impacts as a result on nutrient enrichment, the impact
of nutrients on the GBR ecosystem at the regional
scale remains largely a matter of conjecture.
Monitoring programs currently in place have been
unable to clearly demonstrate either a changing trend
in the nutrient status of reef waters or adverse impacts
attributable to nutrient enrichment. In view of the
natural temporal and spatial variability of nutrient
concentrations in reef waters, identifying trends or
changing conditions is extremely difficult.
5.3 Monitoring
Measurement of water quality parameters in the GBR
region has a long history, with significant data from as
far back as the British Museum Great Barrier Reef
Royal Expedition of 1929/1930 (Orr 1933). However,
continuous, reliable data sets have been collected only
in the past 15 years, by the CSIRO and then the
Australian Institute of Marine Science (AIMS). Large
data sets of oceanographic parameters, nutrients and
chlorophyll are available from the work of Andrews
and co-workers in the early years of the 1980’s (e.g.
Andrews 1983; Revelante & Gilmartin 1982) and
then from the AIMS Biological Oceanography Group
from the mid-80’s to the present (e.g. Furnas 1991,
Furnas et al. 1992). Satellite remote-sense monitoring
20
of chlorophyll and turbidity using the Coastal Zone
Colour Scanner has been attempted (Gabric et al.
1990), but considerable difficulties in the
interpretation of the data and the loss of the platform
in the mid-1980s have prevented continued use.
Monitoring of benthic community condition started
with broad scale surveys of crown of thorns and gross
coral cover in the mid-1980s, and has now progressed
(since 1991) to more detailed annual surveys of coral
cover and composition on a large number of reefs
(approximately 150). Monitoring also encompasses
regular surveys of turtle, dugong and seabird
numbers, long-term sea temperature monitoring and
irregular surveys of pesticides and heavy metals in
biota. Good, long-term records of catches and catch
per unit effort for the major fisheries does not exist but
more comprehensive monitoring was introduced in
1990.
The significance of the available water quality data
has been debated in recent years (Bell & Gabric 1991,
Kinsey, 1991a, Barnes & Lough 1991, Brodie 1991).
The data do not demonstrate that the GBR lagoon is
nutrient enriched or that productivity has increased in
recent decades, although they do indicate that this is
a priority area for monitoring. The GBRMPA and
AIMS have both, in cooperation, begun extensive
monitoring programs of both water quality and
benthic community condition to resolve questions as
to the present status of the GBR as well as to monitor
trends (Brodie & Furnas 1994). In November 1992, a
long-term water quality monitoring program
commenced to monitor the nutrient status of the GBR
(Brodie & Furnas 1994). The objectives of the
monitoring program are as follows:
to detect long-term trends in nutrient status of the
GBR lagoon
to detect and quantify regional differences in
nutrient status and correlate these with nutrient
input in those areas
to quantify cross shelf differences in nutrient
status and correlate these to nutrient input
information
to monitor the effectiveness of programs to reduce
the terrestrial input of nutrients on the nutrient
status of Park waters.
The program uses chlorophyll concentration as a
measure of phytoplankton abundance, which itself is
an integrating indicator of nutrient availability
(Brodie & Furnas 1994).
Twenty-two stations in four latitudinal transects are
sampled on a monthly basis while five more stations
in one transect are sampled weekly. A further hundred
stations spread over the whole GBR are sampled once
or twice a year. Sampling is carried out by a group of
organizations: the Australian Institute of Marine
Science (AIMS), Reef Biosearch, Queensland
Department of Environment and the Lizard Island
Research Station and the Heron Island Research
Station.
Preliminary analysis of the first year’s chlorophyll
data reveals the effect of the unusually dry conditions
of 1993, which resulted in no significant river
discharge events (Brodie et al. 1995). Chlorophyll
concentrations across most cross-shelf transects were
higher at inshore stations. This is consistent with
previous research and reflects the higher nutrient
status of inshore waters due to terrestrial discharge
and bottom resuspension (Walker & O’Donnell 1981,
Furnas 1991). Chlorophyll concentrations were
higher during the wet/summer season reflecting
some, if minor, river discharge and higher
temperatures in this period. There was little difference
between bottom and surface values but where
differences did occur the bottom values were
generally higher. This is consistent with earlier work
(Wolanski et al. 1981, Walker & O’Donnell 1981) and
has been explained on the basis of both Coral Sea
upwelling of nutrient rich water affecting outer shelf
bottom waters and also sediment resuspension
enriching bottom waters with nutrients. No latitudinal
trends in the chlorophyll concentrations were
observed.
6
Responses
From the above synopsis of the status of our
knowledge of the threat to water quality in the GBR,
a number of key issues can be identified:
beef grazing on the large, dry catchments adjacent
to the Marine Park (in particular the Burdekin and
Fitzroy) has involved extensive tree clearance and
over-grazing. As a result, widespread soil erosion
and the export of the eroded material, with
associated nutrients, has occurred
cropping, particularly for sugarcane, on numerous
wet catchments has involved intensive fertilizer
use as well as substantial soil erosion. As a result,
large amounts of nutrients and sediment have been
discharged into rivers and into the GBR
discharge of sewage effluent associated with the
increasing population on the GBR coast, is a
significant local problem in some areas
diffuse urban runoff from the major coastal cities
is a significant, but very localized, problem
discharge of nutrient-rich effluent from coastal
prawn farms is increasing with the development of
the aquaculture industry.
Management changes in some industries in recent
years have the potential to reduce nutrient runoff. The
most notable example is green cane harvesting and
trash blanketing in sugarcane cultivation, both of
which may reduce soil erosion and phosphorus loss
(Prove & Hicks 1991; Kuhn 1990). In the case of
sewage discharges, the present policy of the
GBRMPA, for tertiary treatment (nutrient removal) or
land irrigation of sewage effluent within the Great
Barrier Reef Marine Park and increasing use of
sewage effluent for irrigation on the mainland, has led
to some reduction in direct fluxes to coastal zone
waters. (Brodie 1991, 1995c).
The options allowed under the tertiary treatment
policy are tertiary treatment (nutrient reduction)
21
followed by marine discharge, or land reuse of
secondary or tertiary effluent with minimal marine
discharge. The policy has an implementation period
up to January 1996, when all outfalls in the Park
should meet the standard. As no mainland outfalls
enter the Park the policy only affects island resorts at
present but any future mainland outfall discharging
directly into the Park would also be required to
comply with the policy.
The management of water quality in the Great Barrier
Reef Marine Park involves policy decisions,
cooperative
arrangements
with
Queensland
Government departments to reduce pollutant inputs
(such as those now being pursued with the
Department of Primary Industries), case by case
management of activities such as dredging and spoil
dumping, and enforcement of Australian government
acts such as those regulating the dumping of
substances from ships (Woodley 1989). The
GBRMPA’s preferred approach for mainland (city)
sewage discharges is that maximum reuse and
minimum marine discharge be adopted. This advice is
provided to local governments as comment on various
strategic and town plans and as a public position when
this is required. The GBRMPA also provides
comments on regional strategic and town plans and
promotes the ‘policy’ of the adoption of urban
development practices which minimize sediment
runoff. This may be elaborated to provide suggestions
such as minimum vegetation removal and disturbance
and the use of sediment traps.
At a larger scale, it is hoped to reduce agricultural
sources of sediment and nutrients through an
Integrated Catchment Management (ICM) program
(QDPI 1993)–the principal tool of the Queensland
Government for reduction of catchment based
pollutant discharge to the coastal zone. One objective
of the program is to have ICM implemented in all
coastal catchments in the plan by the year 2000. The
recently enacted Environmental Protection Act also
has the capacity to regulate diffuse nutrient sources.
22
With coordination through the ICM process, better
land management methods such as: stubble retention
on cropping lands; retention and rehabilitation of
riparian zones and wetlands; vegetation management
on grazing lands; and better fertilizer application
technology will achieve the desired reductions in
inputs. Factors such as green cane harvesting/trash
blanketing in sugar cane cultivation can affect losses
per hectare within a single land use type. In sugar cane
cultivation areas north of Townsville this practice is
common (greater than 75 per cent use) while south of
Townsville usage averages less than 25 per cent.
To further unify the management of the GBR region
a 25 year Strategic Plan for the Great Barrier Reef
World Heritage Area was developed (GBRMPA
1994). This binds Australian, Queensland and local
government agencies, industries and community
groups to a set of management objectives for the area.
The Plan was developed in a consultative fashion with
all these groups and they have agreed to support and
implement its provisions.
The reduction in nutrient fluxes from coastal
catchments into the Great Barrier Reef Marine Park is
seen as the most important water quality issue by the
GBRMPA, and the monitoring and modelling of such
fluxes and the associated nutrient budgets is a priority
activity.
Abbreviations
ABS
Australian Bureau of Statistics
AIMS
Australian Institute of Marine Science
GBR
Great Barrier Reef
GBRMPA Great Barrier Reef Marine Park
Authority
ICM
Integrated Catchment Management
N
Nitrogen
P
Phosphorus
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27
28
Case study 2: Recent changes to the Tuggerah Lakes
system as a result of increasing human pressures
Contents
Page
1
Introduction
31
2
Pressures on the Tuggerah Lakes
32
2.1
2.2
2.3
2.4
32
33
33
33
3
4
5
Human population growth
Changes in land use
Munmorah Power Station
Commercial and recreational fishing
State of the Tuggerah Lakes
35
3.1
3.2
3.3
3.4
3.5
3.6
3.7
35
36
36
37
37
39
39
Lake substrata
Water quality
Water temperature
Plant distributions
Benthic communities
Pelagic communities
Fisheries
Response by the Wyong Shire Council
40
4.1
4.2
4.3
41
41
42
Reducing nutrient inputs
Removing nutrients already present
Increasing tidal exchange
Conclusion
References
42
43
List of Figures
Figure 1: List of Tables
Table 1: Nutrient sources for the Tuggerah Lakes
Table 2: Nutrient reservoirs in the Tuggerah Lakes
Table 3: Seasonal and total changes in the area (hectares) of seagrasses in the
Tuggerah Lakes system during the period 1980–1985
Table 4: Sequence of events leading to deterioration of Tuggerah Lakes
environment
34
35
38
40
29
30
Case study 2: Recent changes to the Tuggerah Lakes system as a result of
increasing human pressures
Andrew D. Kennedy, CSIRO Marine Laboratories, Perth.
1
Introduction
Lake
Munmorah
The Tuggerah Lakes system (33°17’S, 151°30’W) in
New South Wales consists of three interconnected
water bodies: Lake Tuggerah, Lake Budgewoi, and
Lake Munmorah. These are brackish-water barrier
lagoons formed by the historical establishment of a
dune complex along their seaward margin. The lakes
have a total surface area of 77 sq km2, a water volume
of approximately 123 × 106 m3, and are characterised
by a shallow mean depth of 1.6 m. The catchment of
the Tuggerah Lakes covers an area of approximately
670 sq km. Freshwater flows into the lakes primarily
through the Wyong River and Ourimbah and Wallarah
Creeks, and the lakes discharge into the Pacific Ocean
via a narrow channel called ‘The Entrance’ on the
eastern side of the southernmost lake (Figure 1).
The Tuggerah Lakes support a diversity of aquatic
organisms. Three species of seagrass occur,
Halophila ovalis, Zostera capricorni and Ruppia
megacarpa, together with a range of macroalgae,
including species such as Chaetomorpha,
Cladophora,
Enteromorpha,
Rhizocarpium,
Gracilaria and Dictyota. Aquatic fauna includes
prawns, worms, bryozoa, jellyfish, snails, shellfish
and finfish. The main commercial and recreational
finfish species caught in the lakes include bream
(Acanthopagrus australis), sea mullet (Mugil
cephalus), luderick (Girella tricuspidata), and
Australian anchovy (Engraulis australis), while the
main shellfish species are greasyback prawn
(Metapenaeus bennettae), king prawn (M. plebejus),
and school prawn (M. macleayi).
Munmorah
Power Station
Wallarah
Creek
Lake
Budgewoi
Wyong River
N
Lake
Tuggerah
Ourimbah
Creek
The Entrance
0
km
5
Figure 1: Map of the Tuggerah Lakes system
showing main freshwater tributaries, the
Entrance, and the site of the Munmorah Power
Station
31
2
Pressures on the Tuggerah Lakes
instead the ‘extreme’ events experienced only once or
twice per century.
It is important to first set anthropogenic impacts on the
Tuggerah Lakes against a background of natural
spatial and temporal variation. The lakes have never
been a static system; indeed, prior to the deposition of
sand-dunes along its eastern boundary, the entire lake
basin would have been an estuary connected to the
sea. During recent years, extreme weather events are
likely to have played an important a role in structuring
the lakes’ biota. For example, severe winds and
flooding in June 1974 caused the local extinction of
Halophila, uprooting of Zostera and Ruppia, and
substantial fish mortality in Lake Munmorah. A
number of benthic invertebrates, including the
bivalve Theora fragilis, disappeared from mud
habitats (Powis 1975). Subsequently, during the late
1970s, a prolonged drought reduced the freshwater
inflow to the lakes with concomitant effects on the
biota. Such natural variation exerts a major impact on
the lakes’ ecology and may disguise or counteract
anthropogenic pressures.
The Tuggerah Lakes are an important aesthetic,
recreational and fishing resource, and a significant
component of Australian heritage. Local people
exploit the lakes for food and leisure and a substantial
tourist industry has developed. Despite these
recognised values, the lakes have recently come
under increasing pressure from human activities. The
expanding population, reflected in agricultural,
urban, and industrial development, has placed
significant pressures on the lakes ecology. Erosion
products, sewage and other pollutants pose a
considerable challenge to the lakes sustainable
management.
Potentially of greater significance than human
impacts alone is the threat of cumulative
anthropogenic effects in concert with natural
pressures. During heavy rains, major inflows can
surcharge the lakes to a significant height above sea
level and lead to very significant flushing, with
salinities reduced to below 5ppt. Conversely, during
periods of drought, the lakes can become hypersaline
with salt concentrations rising above 45ppt (35 per
cent above sea water). In the latter situation, the
anthropogenic evaporation caused by the discharge of
heated water from the Munmorah Power Station into
Lake Budgewoi may further increase salinity to above
the threshold at which mortality of the lake’s biota
occurs. This, together with nutrient release from the
highly enriched sediments, may result in very atypical
conditions for the biota. In such a situation it is not the
‘normal’ conditions that control the lakes’ biota, but
32
2.1 Human population growth
The Tuggerah Lakes are situated in one of the most
rapidly developing sectors of the New South Wales
coast. The residential population of the Wyong Shire,
which in 1954 numbered only 13 097, had by 1989
increased to approximately 96 000. Of this
population, approximately 22 000 live within the
catchments of Lake Budgewoi and Lake Munmorah.
The present rate of population growth is estimated at
7–8 per cent per year.
Tourism is a major source of visitors to the area.
During the 1992/93 period, 1 025 000 visits were
made to the combined Gosford and Wyong Shires,
representing an 11.8 per cent increase over the
917 000 visits received in 1991/92. The majority
(93.1 per cent) of visits were by residents of Sydney
and country areas of NSW, with 6.9 per cent of visitors
coming from interstate, mostly Victoria and
Queensland. The 25 to 39 year age category was best
represented (33.6 per cent of total visits) with females
accounting for a greater proportion (57.4 per cent)
than males. The most common month to return from
visits to the area was January (NSW Tourism
Commission 1994).
2.2 Changes in land use
The major pressure influencing the environmental
quality of the Tuggerah Lakes is nutrient input from
the catchment (Kinhill 1991b, Thresher et al. 1993).
Freshwater flowing into the lakes via the Wyong
River and Ourimbah and Wallarah Creeks, together
with groundwater, carry nutrients into the lakes.
These nutrients originate from erosion products,
sewage and plant fertilisers. Further nutrients are
added as urban wastes and airborne particulates from
populated areas and as sawdust and ash from the
Munmorah Power Station. Although there are no
systematic data on the integrated nutrient load from
the 670 sq km catchment (Table 1), it has been
suggested that 33, 10 and 22 tonnes of phosphorus (P)
are added each year to Lake Tuggerah, Budgewoi and
Munmorah respectively (Batley et al. 1990). As early
as 1970, it was suggested that such inputs were
causing eutrophication of the lake system (Higginson
1970).
Two major pressures have contributed to the lakes
nutrient status. The first is the displacement of native
habitats by agriculture with concomitant loss of top
soil and fertilisers. Large areas of the natural
vegetation of eucalypt forest, heathland and swamp
have been cleared to make way for citrus orchards and
cattle farms. Sheet erosion affects 19 per cent of the
catchment land surface, and its occurrence correlates
closely with the distribution of cleared land. Erosion
products enter the lakes mainly during floods
(Higginson 1970). Total nutrient inputs from the
Wyong, Ourimbah and Wallarah catchments
(sediment plus fertilisers) have been estimated at 30
and 170 tonnes of P and N per year respectively
(Batley et al. 1990).
The second major cause of the increase in nutrients is
the escalating number of industrial and residential
properties in the area. Waste products from urban
developments enter the lake system in the form of
detergents, sewage and household chemicals via an
expanding network of drains and storm water
channels. Judell et al. (1987) recorded high
concentrations of nutrients
nitrogen (N) 1100–3200 g per litre
nitrate 120–740 g per litre
phosphate (P) 26–14 600 g per litre
in storm water channels at Taylor’s Point, Rotary Park
and San Remo. Jones (1983) suggested that high
nitrate and ammonia concentrations (553 and
75 g/L) in Jilliby Creek and Wyong River originated
from urban Wyong. Armstrong (1985) reported that
quantities of nitrate and phosphate flowing into Lake
Tuggerah from the Toukley Sewage Treatment Works
varied between 1.415–1.004 kg N per day and
0.018–0.05 kg P per day during wet and dry weather
respectively, yielding annual inputs of 145 kg N per
year and 14 kg P per year.
2.3 Munmorah Power Station
The Munmorah Power Station on the shore of Lake
Budgewoi is the single most important point-source of
anthropogenic pollutants to the Tuggerah Lakes
system. The facility exerts a range of pressures,
including raising water temperature, releasing
chlorine and heavy metals, entraining biota, and
altering the hydrodynamic environment of the lakes.
Of the power station’s various effects upon the lake
environment, those caused by elevated water
temperature are perhaps the most significant. The
considerable heat load on the upper lakes causes a
significant impact upon organisms and ecosystem
processes and these are believed to have caused
substantial ecological impacts within 1 kilometer of
the outfall canal (Thresher et al. 1993). The power
station may also have more broad-ranging effects on
Lake Munmorah and Lake Budgewoi, although this
could not be determined from the available data
(Thresher et al. 1993).
2.4 Commercial and recreational
fishing
Fish populations in the Tuggerah Lakes are a valuable
living resource. Both finfish and shellfish are
exploited, and this represents a pressure on the lakes
ecology. Between 170 and 1000 anglers fish on the
lakes each day (Henry & Virgona 1980). Commercial
fishing also plays a traditional role in the Tuggerah
lakes and dates back to before records began: in 1883
there were already 40 commercial fishing licences in
circulation while almost one hundred years later, in
1980, 130 licences had been issued and three fishing
cooperatives had been established (Henry & Virgona
1980).
33
Table 1: Nutrient sources for the Tuggerah Lakes
Sources
Munmorah + Budgewoi
Tuggerah
Combined lakes
P
N
P
N
P
N
L. Munmorah 1954
*
*
*
*
0.1
*
Budgewoi
*
*
*
*
*
*
Gorokan
*
*
*
*
*
*
Toukley
*
*
*
*
*
*
Berkley Vale
*
*
*
*
*
*
Berkley Vale 1986
0.2
*
*
*
0.5
*
Long Jetty
*
*
*
*
*
*
The Entrance 1989
*
*
*
*
0.8
*
*
0.023
*
*
*
*
1974 flood
*
2.1
*
*
*
*
1974
*
*
*
1.0
*
*
1974 flood
*
*
0.17
1.8
*
*
1974
*
*
0.09
1.4
*
*
1974 flood
*
*
0.09
0.9
*
*
Wyong + Ourimbah 1988
*
11.7
7.0
*
*
*
Tumbi Umbi Creek
*
*
*
*
*
*
Salt Water Creek
*
*
*
*
*
*
Colongra Siphon
*
*
*
*
*
*
The Pacific Ocean
*
*
3.0
*
*
*
GroundWater
*
*
*
*
*
*
Sewage outfall (Toukley) 1985
*
*
0.014
0.145
*
*
Power station sewage
0.12
110.0
*
*
*
*
Power station screens
0.012
*
*
*
*
*
Power station sawdust
0.008
0.250
*
*
*
*
Power station ash
2.0
*
*
*
*
*
Urban Sites
Catchment/Rivers
Wallarah
Wyong
Ourimbah
1974
Point Sources
Source: Batley et al 1990
All figures are in Tonnes per year.
Missing data (*).
P = Phosphorus, N = Nitrogen.
It is not known whether the present level of fishing
activity poses a threat to the sustainability of the
Tuggerah Lakes’ biotic resources. Population
estimates do not exist for any of the resident fish
species. It has been noted that 64 per cent of the bream
34
caught by recreational anglers are undersized and
immature (Thresher et al. 1993). This tendency is a
cause for concern since removing a proportion of the
population before it matures may negatively affect
numbers in the next generation.
3
State of the Tuggerah Lakes
To understand the impact of human activities on the
ecology of the Tuggerah Lakes it is first necessary to
appreciate the special characteristics of their
hydrological and sedimentary environments. The
lakes shallow depth, narrow outlet to the ocean, and
dynamic sediment-water interface pose unique
difficulties to their effective management. The
sediments sequester a substantial reservoir of
nutrients (Table 2) that may be released and cycled
through the lake system under appropriate
environmental conditions; generally this occurs when
the oxidised microzone on the bottom surface is
broken down by bioturbation, wind-driven
turbulence, and other mixing processes (Armstrong
1984). Furthermore, the narrow channel at ‘The
Entrance’ means that the interchange of nutrient-rich
water between the lakes and the sea is limited: tidal
exchange in Tuggerah Lake is approximately 1 per
cent of its total volume (Batley et al. 1990). Thus, only
a small proportion of the materials that enter the lakes
ever get washed out again. Nutrients, heavy metals,
and other pollutants slowly accumulate in the lake
basins, primarily in the sediments.
In the following assessment of the state of the
Tuggerah Lakes, data from a variety of published and
unpublished sources have been used to estimate the
anthropogenic impacts. However, biological
communities undergo natural episodic changes in
population size and structure and, in the absence of
control data from before the impacts began, it is
difficult to detect genuine long-term trends or to
separate
anthropogenic
perturbations
from
background variability. As a result, despite the
availability of considerable amounts of recent data,
the reliability of much of their interpretation is low.
The following discussion should thus be considered
with appropriate caution.
3.1 Lake substrata
During the last 30 years, many of the inshore areas of
the Tuggerah Lakes have been affected by the
deposition of 5 to 8 centimetres of fine mud
(Higginson 1970; Armstrong 1984). This deposit,
which is believed to be derived from a combination of
catchment input of suspended solids and macrophyte
decomposition, covers extensive stretches of
shoreline that, prior to 1960, were clean sand. The
mud is rich in nutrients (2 to 6 per cent organic
content—Batley et al. 1990) and supports rapid
growth of dense seagrass meadows (especially
Ruppia) and macroalgal stands. Its high ammonia
concentration (mean approximately 16.4 mg/kg)
implies
strong
anaerobic
processes
and
eutrophication.
Table 2: Nutrient reservoirs in the Tuggerah Lakes
P
N
Years
56 × 103
200 × 103
1987
Water2
0.27
0.45
1973–79
ECNSW 1980
SIROMATH 1982
Seagrass3
2.7
30.0
1980–85
King & Hodgson 1986
King & Barclay 1986
Macroalgae4
0.7
11.0
Phytoplankton 5
1.6
10.0
Flood 1974
70.0
317.0
1986–87
Sediments1
Mud6
Source
Cheng 1987a
ECNSW 1988
Cheng 1987c
ECNSW 1980
Cheng 1987a
Wilson & King 1988
Source: Batley et al. 1990
All figures are Tonnes
1. Entries calculated for basin sediments at 85% of the lake area, for 20 cm sediments with mean values of 0.2% N and 0.6% P.
2. The entries are calculated from the common mean given of by SIROMATH (1982).
3. Calculated from dry weight data by King & Barclay (1986) and King & Hodgson (1986) and also mean values for Zostera
determined by Atkinson & Smith (1983).
4. Calculated from data by Cheng (1987) and Wilson & King (1988).
5. Calculated from ECNSW nitrate data and Redfield ratio, 1974 flood period. Blooms for the 1980s were probably similar.
6 Calculated for a 50 m wide deposit 5 cm thick around the perimeter of the lakes.
35
The concentrations of other pollutants in the lake
sediments have also increased in recent years.
Elemental analysis reveals enrichments of zinc, lead,
copper, and antimony, particularly in Lake
Munmorah and Lake Budgewoi. Heavy metals now
reach values of 130 g/g for zinc, 60 g/g for copper
and lead, and 365 g/g for chromium. Other heavy
metals detected in the lake sediments include
cadmium, mercury and nickel (Marshman 1988 &
1989).
Potentially of greater concern than heavy metals, but
less well understood, is the possible occurrence of
trihalomethanes in the lake sediments. These
compounds are formed by the combination of
chlorine with organic materials and are extremely
toxic, particularly to benthic organisms likely to
suffer high exposure (Cooper 1989).
3.2 Water quality
The primary nutrients controlling the eutrophic status
of the Tuggerah Lakes are nitrogen and phosphorus.
It is thus pertinent to consider the concentrations of
these elements in the lakes and how they have
changed with time.
Concentrations of nitrate-N in the lakes increased
between 1973 and 1979 but have declined since 1981
(Dunsmuir 1982; Kinhill 1991a). During this period,
concentrations ranged from 0 to 70 g/L in the
surface waters and from 0 to 80 g/L in the bottom
waters (Thresher et al. 1993). Significantly more
nitrate-N was present in the two northern lakes
(annual mean of 16.12 g/L) than in Lake Tuggerah
(annual mean of 12.06 g/L) between 1973 and 1979,
but the concentrations are now about the same.
Concentrations of orthophosphate (the only inorganic
form of phosphorus readily available for algal
growth) vary from 0 to 20 g/L, with the highest
concentrations in the bottom water of Lake Tuggerah.
Orthophosphate concentrations recorded in the 1960s
were reportedly higher than present-day values
(Higginson 1970), but are believed to have increased
in the bottom waters of Lake Munmorah and Lake
Budgewoi since 1982 (Kinhill 1991a).
The concentrations of nutrients in the water column
are controlled to a significant extent by fluxes from
the underlying sediments. The surficial substrata of
the Tuggerah Lakes support a high density of
microorganisms which play an important role in
36
nutrient cycling. Cheng (1987b) calculated that the
rate of release of phosphate from sediment samples
collected around Long Jetty could account for
substantial
crops
of
Chaetomorpha
and
Enteromorpha. Total P fluxes from the sediment of
Lake Munmorah have been estimated to lie in the
range 7 to 78 tonnes P per year.
The levels of heavy metals measured in the outfall
water from the Munmorah Power Station approach
levels reported to be acutely toxic to marine
invertebrates. Batley and Brockbank (1992) recorded
that samples of Lake Munmorah water exceeded the
acceptable criterion for copper in marine and
estuarine waters on 4 out of 7 sampling occasions.
The turbidity of the Tuggerah Lakes increased over
the period 1963 to the present (Batley et al. 1990). The
increased turbidity may be related to nutrient inputs
during that period, fuelling plankton and algal growth,
and possibly is exacerbated by currents and
turbulence around the power station. Turbidity is
highest around the power station outfall (mean Secchi
depth of 0.89 ± 0.03 metres compared with 1.09 ±
0.03 metres elsewhere in the lakes (Dunsmuir 1982).
3.3 Water temperature
The Munmorah Power Station exerts a significant
effect on water temperature in the two northernmost
lakes. Lake Budgewoi, into which the cooling water
flows, is the warmest lake in the system. Surveys of
surface water temperature reveal that, on an area
basis, approximately 51.8 per cent of Lake Budgewoi
is subjected to a temperature rise greater than 2C,
while 6.9 per cent is subjected to a rise greater than
7C (Thresher et al. 1993). In addition, Lake
Munmorah is 0.75C warmer than Lake Tuggerah
(Dunsmuir 1982), indicating that the thermal plume
does not fully dissipate before being recirculated
through the power station.
The waste heat emitted by the power station is
responsible for two types of biological impact. First,
the increase in temperature may cause direct mortality
to macrophytes and benthos, particularly during the
summer. Enzyme systems become denatured at high
temperatures leading to the collapse of metabolic
processes and ultimately death. The absence of the
seagrasses Zostera capricorni and Ruppia megacarpa
along the northern shore of Lake Budgewoi is likely
to be one manifestation of this effect (Thresher et al.
1993). The second consequence of the increased heat
load, likely to affect a wider area, is an acceleration of
physiological processes, including photosynthesis
and respiration, and of ecological processes, such as
nutrient mineralisation and decomposition. These
respond to each 10C rise with a 2 to 4 times increase
in rate.
3.4 Plant distributions
Changes in the distribution and abundance of
macrophytes may occur in response to changes in the
ambient environment. Accordingly, macrophytes can
be used as indicators of changing conditions. Nutrient
enrichment may have either positive or negative
effects on seagrass and other macrophytes. Under
circumstances of elevated concentrations of nutrients
in the water column, the growth of epiphytic algae
growing on the leaves of macrophytes may be
enhanced, thus adversely affecting macrophyte
growth. Conversely, if sediments become enriched,
the availability of nutrients to rooted macrophytes is
increased and therefore growth may be stimulated.
Although statistically rigorous data from which to
detect changes are lacking for the Tuggerah Lakes,
there is a general consensus that over the last 30 years
the distribution of both seagrasses and macroalgae
has changed, with the greatest variations coinciding
with the period of greatest human development of the
catchment (Batley et al. 1990) (see Table 3). The
Wyong Shire Council suggests that the area of plant
growth in the lakes has increased from 300 to
400 hectares in the 1950s to more than 1500 hectares
in the 1980s. Though there is some uncertainty about
the reliability of earlier data describing macrophyte
distribution. Certainly, the abundance of the seagrass
Ruppia megacarpa is increasing in both Lakes
Budgewoi and Munmorah while its distribution,
which formerly occupied the centre of the lakes, is
now focused on the margins. These changes are
believed to have been caused by the increased
turbidity in the lakes and by the deposition of silt in
shallower regions. Furthermore, there has been a
marked increase in the amount of macroalgae in
near-shore waters since the early 1980s so that, in
some places, they now constitute the bulk of the plant
material (Batley et al. 1990).
In addition to the value of macrophytes as indicators
of environmental change, changes in the distribution
and abundance of seagrasses and algae exert a direct
impact on the economic value of the lakes. Aquatic
weeds clog fishing lines, foul propellers, block
waterways, and make walking across the lake
shallows both difficult and hazardous. Several of the
macroalgae
species
(notably
species
of
Chaetomorpha, Cladophora, Enteromorpha, and
Rhizoclonium) are not attached to the lake bottom and
so are susceptible to being blown by the wind into
dense accumulations where they can cause problems
for recreational users of the lakes. Furthermore,
blankets of macroalgae can smother seagrass beds,
leading to decay and the removal of oxygen from the
water and the release of hydrogen sulphide from the
sediments. Seagrasses themselves modify water
currents and mixing processes, and it has been
suggested that in the Tuggerah Lakes they impede the
exchange of inshore and mid-lake waters (Batley et al.
1990).
3.5 Benthic communities
Benthic communities play an important functional
role in the Tuggerah Lakes. They provide food for fish
and through bioturbation increase water flow through
the sediments. Nutrients are released and oxygen is
gained by sediments through their burrowing
activities.
Powis (1975) classified the dominant Tuggerah Lakes
benthic communities as a function of substratum type.
Associations ranged from ‘weed in muddy sand’
(dominated by Owenia fusiformis), to ‘weed on mud’
or ‘mud near weed’ (associated with Macoma
deltoidalis), to ‘mud only’ (associated with Theora
fragilis), to ‘sand’ or ‘weed on sand’ (without a
dominant organism). The controlling role played by
substrata in the distribution of these associations
makes it inevitable that any change in the mud or sand
content of the lakes will exert a concomitant effect
upon their benthic fauna. The recent deposition of fine
silt in shallow areas is of great significance in this
respect.
37
Table 3: Seasonal and total changes in the area (hectares) of seagrasses in the Tuggerah Lakes system
during the period 1980–1985
Season and year
Seagrass location and type
Winter 80 Summer 81 Winter 81 Summer 82 Summer 83 Summer 84 Summer 85
Combined Lakes
Zostera
1092
866
1596
1285
1669
1461
1226
Halophila
410
914
1098
971
1336
751
1040
Ruppia
252
176
313
220
273
501
824
1434
1313
1760
1419
1864
1628
1911
731
560
1105
893
1312
1027
958
67
605
716
453
815
377
643
Ruppia
250
176
312
171
273
375
548
Total
993
976
1206
904
1312
1143
1269
Zostera
286
217
361
212
275
321
119
Halophila
255
219
220
294
396
262
249
2
*
1
33
*
98
222
305
228
382
300
419
343
403
Zostera
75
89
130
180
82
113
149
Halophila
88
90
161
224
125
112
148
*
*
*
16
*
28
54
136
109
172
225
133
142
239
Total
Lake Tuggerah
Zostera
Halophila
Lake Budgewoi
Ruppia
Total
Lake Munmorah
Ruppia
Total
Adapted from Batley et al. 1990
Source: King & Hodgson 1986.
Two specific anthropogenic affects on benthic
organisms are worth noting. The first concerns the
mussel Xenostrobus securis whose occurrence has
increased in recent years. It is thought that the
increased turbidity, circulation and temperature
caused by the Munmorah Power Station have
triggered the population growth of this important
fouling organism, which now has a lake-wide
distribution. The second specific effect on the lakes’
38
benthos concerns the distribution of prawns which has
been perturbed by the reversal of flow between Lake
Budgewoi and Lake Munmorah. The strength of the
current in the channel separating these two lakes
means that king and school prawns are no longer able
to migrate out to sea to spawn. As a result, prawns in
Lake Munmorah are both larger and more abundant
than those elsewhere in the lake system, and a fishery
has been created where none existed before.
3.6 Pelagic communities
The only extensive surveys of phytoplankton
populations in the Tuggerah Lakes have been carried
out by Hodgson (1979) and Watson (1983). Watson
(1983) found an increased phytoplankton biomass in
Lake Munmorah and Lake Budgewoi compared to
Tuggerah Lakes, and compared to the 1974/75 data
(Hodgson 1979). This led Batley et al. (1990) to
suggest that eutrophication processes were
responsible. However, Thresher et al. (1993) point out
that there is little data on which to base this
conclusion; the changes may reflect ambient weather
conditions or some other limiting factor. Watson
recorded 145 taxa belonging to 75 genera, with
greater diversity in Lake Munmorah and Lake
Budgewoi than in Lake Tuggerah, suggesting that
greater water mixing and sediment disturbance occur
in these lakes, potentially a result of the power
station’s outflow. However, an alternative
explanation is that the relationship reflects the
shallow depth of the upper two lakes.
Zooplankton populations in the Tuggerah Lakes
include a variety of Crustacea (primarily copepods)
together with the larvae of benthic organisms such as
barnacles, decapods and bivalves (Smith 1971).
Monthly plankton samples collected by Pacific Power
during the period 1973–1982 showed seasonal
cycling in abundances, probably controlled by the
supply of nutrients from the catchment with
physiological limits set by temperature. No long term
data set for population changes is available from
which to detect anthropogenic impacts.
One significant change in a pelagic species within the
lakes is the almost complete disappearance of the
brackish water scyphozoan jellyfish Catostylus
mosaicus. This animal was once so abundant as to
interfere with recreational and commercial users of
the lakes (Pulley 1971). At one stage, swarms of the
jellyfish blocked inflow screens to the power station,
and so interfered with power production. However,
since the early 1970s, its abundance has declined
(J. Bell, pers. comm., quoted in Batley et al. 1990).
Thresher et al. (1993) suggest that this population
reduction may be an indirect effect of the heat
released from the Munmorah Power Station: the
warmer water reduces the abundance of the plankton
species Sulcanus and Gladioferams which together
may constitute a significant component of Catostylus’
diet.
3.7 Fisheries
Total fish catches within the Tuggerah Lakes
increased significantly between 1946 and 1984
(Thresher et al. 1993). However, this increase cannot
be interpreted as a change in the total fish stocks
within the lakes. Fluctuations in the number of
licensed fishermen working in any one year, together
with improvements in equipment technology, mean
that the recorded increase is not a valid reflection of
changes in fish populations. For this purpose, the
parameter ‘fish caught per unit effort’ (CPUE) should
be used. Approximate figures of 7.5 kg/hour for
commercial fishermen and 0.043 kg/hour for
recreational fishermen have been quoted (Henry &
Virgona 1980) but no data for changes in CPUE with
time are available. Furthermore, no CPUE values for
shellfish collection have been published. Clearly,
adequate information from which to detect changes in
Tuggerah Lakes fish populations does not exist.
The partitioning of total commercial fish catch
between different species is reported to have changed
markedly in recent years. Sea mullet (Mugil cephalus)
has increased as a proportion of the catch, while
luderick (Girella tricuspidata) has fluctuated from 10
tonnes caught in 1956 to 140 tonnes in 1966 and back
to 10 tonnes in 1980 (Henry & Virgona 1980; Virgona
& Henry 1987). Greasyback prawns (Metapenaeus
bennettae) apparently declined in abundance in Lake
Tuggerah between 1951 and 1958 and were caught in
Lakes Budgewoi and Munmorah only prior to 1958.
It has been suggested that the recreational fishery in
the Tuggerah Lakes has been enhanced by the
Munmorah Power Station (Thresher et al. 1993). The
warmer temperature, increased currents, and supply
of food from algae and mussels on the canal walls
attract fish which, in turn, attract anglers. In winter,
the outlet canal is used by 80 per cent of recreational
fishermen, with 32 per cent of the total annual amateur
catch being attributable to the power station’s
presence (Henry 1983). This ‘positive’ anthropogenic
effect needs to be considered when evaluating the
overall impact of human activities on the lakes.
39
4
Response by the Wyong Shire
Council
Concern for the state of the Tuggerah Lakes
environment was first expressed in 1970.
Accumulations of black mud on previously clean
sandy beaches had by then caught the public’s
attention and had begun to detract from the tourist and
real estate potential of the region. The need to
maintain acceptable water quality, areas of weed-free
foreshores for bathing, and a viable recreational
fishing resource inspired responsive action by the
local authorities (Table 4).
A fortunate coincidence of legislative geography
meant that the catchment area of the Tuggerah Lakes
conformed closely with the boundary of the Wyong
Shire Council (WSC). Responsibility for the
management of the catchment thus belonged largely
to a single local government management agency.
This situation has simplified the planning and
implementation of control measures, and has allowed
steps to be taken to minimise the negative
anthropogenic impacts on the lakes through the
adoption of a ‘total catchment management strategy’.
In 1985, the WSC announced the start of the
‘Tuggerah Lakes Restoration Programme’ (TLRP).
This $12 million project aims to undo the damage
caused by many years of environmentally detrimental
practices. The TLRP is coordinated by a committee
consisting of representatives of WSC, the NSW
Environmental Protection Agency, the Department of
Conservation and Land Management (CALM), the
Public Works Department (PWD), Pacific Power, and
the local community. The Committee reports to a
NSW Ministerial Task Force.
Table 4: Sequence of events leading to deterioration of Tuggerah Lakes environment
Sequence of deterioration
Process of recovery
Before human development: clean lake
Shallow lake requiring
restoration
Urbanisation, industry, agriculture in the
catchment
Construction of sediment traps
and nutrient filters
Sediment inflow causes shallowing
Nutrient inflow causes algal blooms
Inshore removal of aquatic
plants and silt
Excess seagrass/algae accumulations
Beachcleaning
Seagrass/algae die and are washed onto
foreshores causing unpleasant smell and black
ooze layer on lake bed
Dredging to deepen channels
Results in reduced sediment and
nutrient input
Results in less rotting seagrass
and algae
Results in less material to decay
on foreshores
Results in improved circulation
and tidal flushing
Limited tidal exchange results in poor flushing
Attractive waters and foreshores, improved amenities,
ecologically sound environment
for marine and birdlife
Shallow lake requiring restoration
Source: Wyong Shire Council
40
The TLRP has identified three priorities for controlled
intervention to improve the environmental quality of
the lakes:
a reduction in the quantity of sediment and
nutrients entering the lakes system
the removal of nutrients and plant material already
present in the lake basins
engineering measures to increase the rate of tidal
exchange between the lakes and the ocean,
thereby facilitating mixing processes and flushing
of nutrients out to sea. The steps taken to
implement these objectives are described below.
4.1 Reducing nutrient inputs
The nutrient status of the Tuggerah Lakes has already
been described. Anthropogenic inputs result from
three main sources:
erosion products and fertilisers from cleared land
sewage input
industrial and household wastes. To minimise the
magnitude of these sources, a diverse range of
control measures has been implemented including
changes in the reticulation of sewage, installation
of storm water treatment zones, erosion controls
on new developments, and better planning of land
use.
To reduce the input of erosion products to the
Tuggerah Lakes the first urban Soil Conservation
Project Area (SCPA) in NSW has been created within
the WSCs boundaries. This provides information on
natural resources in the area (including soil types,
land capability, and erosion hazards) to all residents,
builders, developers, and government agencies
operating in the catchment. Examples of
SCPA-encouraged land-use practices include:
cultivating with the land contour and only on
slopes ≤ 5°
revegetating exposed areas and retaining tree
cover
establishing wind breaks and providing vegetation
strips above cultivated areas to reduce run-off
installing silt dams to collect run-off. Farmers are
being encouraged to use fertilisers and pesticides
conservatively, to select non-residual compounds
in preference to long-lasting ones, and to store
such chemicals more than 100 metres away from
water courses. Further clearance of natural
vegetation is controlled, and new developments
must meet strict planning criteria. Roads are
undergoing a programme of shoulder sealing and
grassing of verges to reduce the leaching of road
base and vehicle pollutants. Combined, these
measures have lowered erosion and the input of
nutrients from the surrounding land, particularly
during periods of flooding.
Steps to reduce sewage input to the Tuggerah Lakes
have relied largely on modernisation of the sewerage
system. Before 1973, the only residential areas to be
connected to sewage systems were the settlements at
Wyong and The Entrance. Houses in the remainder of
the lakes catchment relied on septic tanks that leached
nutrients into the soil. Recently, there has been a
considerable expansion of the sewage network so that
there are now three council-owned sewage treatment
plants to which almost all settlements on the shores of
the lakes are connected. Four privately-owned plants
service the Wyong Abattoir, the Wolloo Caravan
Park, the Lakeland Caravan Park and the Munmorah
Power Station. From 1988, the Council diverted all
sewage products away from Wyong Creek to an ocean
outfall at Norah Head, bypassing the Tuggerah Lakes
completely. In addition, sewage from the Munmorah
Power Station’s 600 employees is no longer
discharged into its effluent outlet canal.
Industrial and household waste products entering the
lakes have been reduced by a variety of methods.
Around 210 stormwater drains and minor pipe outlets
have been modified by the addition of sediment
trapping pits and by the planting of ‘mini-wetlands’
that remove up to 50 or 60 per cent of nitrates together
with a substantial proportion of the incoming
sediment (WSC 1990). Gross pollutant traps,
incorporating a sediment pit, energy dissipation
structure, and a trash rack, have been installed in 33
major rivers and streams flowing into the lakes, and
these are dredged and cleaned every 3 to 6 months
according to rainfall patterns.
4.2 Removing nutrients already
present
As previously discussed, a substantial reservoir of
nutrients had already accumulated in the lakes’
sediments. This accumulation buffers any reduction
of nutrient inflow (Cheng 1987a; 1987b). Fewer
nutrients entering the lakes in drain water and sewage
may thus have no net effect on their concentration in
the water column. To combat this problem, the WSC
has initiated an extensive programme of seagrass,
41
algae and mud removal from sites around the
Tuggerah Lakes. An estimated 56 km of foreshore has
been demarcated for dredging. This action is intended
to improve water circulation, control noxious smells,
and revitalise the beaches around the lakes, and is also
intended to slow the eutrophication process.
Two dredging techniques have been tested by WSC.
The first, called ‘wet dredging’, relies on the simple
method of skimming mud and weeds off the lake
bottom and transporting them ashore for subsequent
disposal on land. Although effective, this method is
both time-consuming and expensive and is potentially
only a short-term solution. The second technique,
called ‘dry dredging’, involves the building of walls
of mud and fabric around affected foreshore areas; the
water inshore from the walls is then pumped out and
the sediments are left to dry. Bulldozers then excavate
the sediment and bury it on the foreshore beneath a
permanent earth layer. The mud-and-fabric walls are
collapsed, allowing water to cover the excavated area,
and clean sand is pumped ashore to cover the dried
mud and weeds and to provide an aesthetically
acceptable finish. According to WSC, up to 30 metres
of lake shallows may be reclaimed at a time by this
process and the resulting foreshore is ideal for
childrens’ recreational activities.
An advantage of the ‘dry dredging’ technique is that
it allows the foreshore of the lake to be contoured to
reduce disruptions to longshore circulation, thereby
minimising weed and silt trapping areas. Landscaping
and planting of grasses on the adjacent land provides
a buffer zone between the lake and nearby urban
development.
4.3 Increasing tidal exchange
A major geomorphological feature contributing to the
eutrophication of the Tuggerah Lakes is the restricted
outlet to the Pacific Ocean. The small width and
shallow depth of this channel cause low rates of
flushing between the lakes and the sea, with
correspondingly few opportunities for the loss of
nutrients from the system. On nine occasions during
the last 100 years, the channel has closed completely
(Batley et al. 1990).
To counteract this constraint, the WSC and the NSW
Public Works Department have undertaken to
restructure the boating channel and sand banks at The
Entrance to increase the volume of water exchange.
42
Instead of building permanent structures of steel and
cement, a ‘soft engineering’ approach has been
adopted: a purpose-built dredge is being used to
continually move sediment to broaden and deepen the
channels. This also benefits navigation and is likely to
increase the opportunities for fish migration. Spoil
from the dredging operation is used to create
additional foreshore reserves at Picnic Point and
North Entrance. The soft engineering approach has
the additional advantage of permitting natural
scouring and flushing of the channel after heavy
rainfall to proceed unhindered.
5
Conclusion
In attempting to evaluate the present state of the
Tuggerah Lakes and to assess the significance of the
changes detected in their environment, it is pertinent
to consider the management objectives for the region.
Specific end uses influence the ‘acceptability’ of the
lakes condition (Thresher et al. 1993). If it is required
that the lakes be managed for their ecological
attributes and biodiversity, then any changes to the
‘natural state’ may be viewed as detrimental.
Conversely, if the lakes are being managed to provide
a multiple-use resource, satisfying fishing, recreation,
and industrial objectives, then changes in the stocks of
non-commercial biota may be less important. The
clearest example of this conflict involves changes in
the macrophyte distribution around the lakes: the
abundance of these plants has recently increased to
such an extent that the Wyong Shire Council,
concerned for the tourist potential of the area, has
taken steps to solve the perceived problem. However,
these ‘weeds’ provide sediment stability and support
food chains upon which the ecology of the lakes
depend. Thus the Council’s response, large-scale
dredging, may satisfy one objective at the expense of
another, causing more problems than it solves.
The maintenance of a multiple-use lakes system that
includes recreational bathing and fishing will
probably be the most demanding management
objective facing the WSC. Many years of almost
uncontrolled nutrient inputs to the lakes has resulted
in the accumulation of vast amounts of nutrient rich
sediments. The restoration management of the lakes
for recreational purposes alone is costing many
millions of dollars ($12m for one program alone). The
achievement of multiple-use objectives for the lakes
would be better served by the earlier adoption of
environmentally sensitive planning strategies and
waste minimisation techniques. Now that these
approaches are being introduced by WSC, formal
procedures to track their effectiveness are required.
These should monitor the key elements of the lakes
system (such as the macroalgae and seagrass
distribution, fish composition and production, etc.) to
ensure that nutrient input management controls and
the TLRP are achieving their intended goals. In this
respect, the national State of the Environment
reporting approach (using the Pressure, State and
Response model) could be implemented at a local
level to track local changes in the environment and
demonstrate the cost-effectiveness of introducing
such measures.
References
Armstrong, D. 1984, Water quality and
sedimentation of the Tuggerah Lakes system,
Entrance, Wyong Shire Council Health and
Building Department, pp. 1–88.
Armstrong, D. 1985, The effects of sewage effluent
ponding and soil infiltration upon nutrient levels
and bacterial populations, final year report,
Hawkesbury Agriculture College of Advanced
Education.
Atkinson, M. J. & Smith, S. C. 1983, ‘C:N:P ratios
of benthic marine plants’, Limnology and
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Batley, G., Body, N., Cook, B., Dibb, L., Fleming,
P.M., Skyring, G., Boon, P., Mitchell, D. &
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NSW, 41 pp.
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Council.
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dibenzo-p-dioxins and polychlorinated
dibenzofurans on aquatic organisms’, Aquatic
Sciences, vol. 1, pp. 227–242.
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Tuggerah Lakes, Book 1: report by SIROMATH,
SIROMATH Pty Ltd, Sydney, pp. 1–70.
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lists, 1973–1976 and 1976–1979, Electricity
Commission of New South Wales internal data.
ECNSW 1988, Interim assessment of trace element
concentrations in waters and sediments of
Tuggerah Lakes, Electricity Commission of New
South Wales Report No. PD 009/89.
Henry, G.W. & Virgona, J.L. 1980, The impact of
the Munmorah Power Station on the recreational
and commercial finfish fisheries of Tuggerah
Lakes, New South Wales State Fisheries report
for Pacific Power, Sydney, pp. 1–31.
Higginson, F.R. 1970, ‘Ecological effects of
pollution in Tuggerah Lakes’, Proceedings of the
Ecological Society of Australia, vol. 5,
pp. 143–152.
Hodgson, B.R. 1979, The hydrology and
zooplankton ecology of Lake Macquarie and the
Tuggerah Lakes, New South Wales, thesis,
University of NSW, Sydney.
Jones, R.J. 1983, Wyong River water quality
survey–a study of physical, chemical and
biological levels in the river, report to Wyong
Shire Council.
Judell, Platt, Thomas and Associates Pty Ltd. 1987,
Water samples from Tuggerah Lakes, Laboratory
report no. 8712020 prepared for the Electricity
Commission of New South Wales.
43
Kinhill, 1991a, Tuggerah Lakes Part A: Statistical
analysis of water quality data 1973–1988,
Kinhill Engineers Pty Ltd, W.A. August 1991
(Report to Pacific Power).
Pulley, K. 1971, A study of the hydrology of Lake
Macquarie and the Tuggerah Lakes in NSW and
the occurrence of Scyphomedusae in their
waters, University of NSW, Sydney, p. 79.
Kinhill, 1991b, Tuggerah Lakes Part B: Water
quality assessment, Kinhill Engineers Pty Ltd,
WA. August 1991 (Report to Pacific Power).
SIROMATH Pty Ltd 1982, Time series analysis of
Tuggerah Lake: Physical and chemical data,
Project No. N82/86, report to Electricity
Commission of New South Wales.
King, R.J. & Barclay, J.B. 1986, ‘Aquatic
angiosperms in coastal saline lagoons of New
South Wales. III. Quantitative assessment of
Zostera capricornii, Proceedings of the Linnear
Society of NSW, vol. 109, pp. 41–50.
King, R.J. & Hodgson, B.R. 1986, ‘Aquatic
angiosperms in coastal saline lagoons of New
South Wales III. Quantitative assessment of
Zostera capricorni., Proceedings of the Linnean
Society of NSW, vol. 109, pp. 51–60.
Marshman, N.A. 1988, Interim assessment of trace
element concentrations in waters and sediments
of the Tuggerah Lakes, Pacific Power planning
and development group, Sydney, NSW,
pp. 1–32.
Marshman, N.A. 1989, Trace element and ash
content of Tuggerah Lakes sediment cores,
Pacific Power, Sydney, NSW, pp. 1–20.
New South Wales Tourist Commission 1994,
Tourism trends in New South Wales
1991/92–1992/93, report prepared by the
National Centre for Studies of Travel and
Tourism, Brisbane, NSW Tourist Commission,
Sydney.
Powis, B. J. 1975, The benthic fauna of the
Tuggerah Lakes, University of NSW, Sydney,
p. 143.
44
Smith, P. 1971, The seasonal abundance of
planktonic larvae and temperature tolerance of
some planktonic organisms in two NSW coastal
lakes (Lake Macquarie and Lake Munmorah),
University of NSW thesis, Sydney.
Thresher, A., Ward, T. & Crossland, C. 1993, An
assessment of the impacts of Munmorah Power
Station on the fauna of Tuggerah Lakes, a report
to Pacific Power from CSIRO, 69 pp.
Virgona, J.L. & Henry, G.W. 1987, Investigations
into the commercial and recreational fisheries of
Lake Macquarie and Tuggerah Lakes, Fisheries
Research Institute report for Pacific Power,
Sydney, 42 pp.
Watson, L. 1983, Phytoplankton studies in the
Tuggerah Lakes, University of NSW, Sydney,
p. 58.
Wilson, N.C. & King, R.J. 1988, Studies on
macroalgae in the Tuggerah Lakes with
particular reference to the effects of heated
water discharged from Munmorah Power
Station, report for Electricity Commission of
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Wyong Shire Council (WSC) 1990, Tuggerah Lakes
Restoration Programme, Internal Report.
Case study 3: Impact of nutrient-rich sewage
discharged to the near-shore waters on the Sunshine
Coast, Queensland
Contents
Page
Introduction
47
1
Pressures
47
2
State
48
2.1
2.2
2.3
48
49
49
3
Effluent plume circulation
Water quality
Intertidal algal community
Responses
References
52
53
List of Figures
Figure 1: Location of transects and effluent plume circulation
48
List of Tables
Table 1: Abundance-dominance scores for algal species by transect
50
45
46
Case study 3: Impact of nutrient-rich sewage discharged to
near-shore waters on the Sunshine Coast, Queensland
Phillip R. Cosser, Department of Environment, PO Box 155, Brisbane, Albert Street,
Queensland.
Introduction
With the majority of Australia’s population living
close to the coast, the discharge of nutrient enriched
sewage effluent to estuarine and near-shore coastal
waters is a common occurrence. As a simple and
comparatively cheap method of effluent disposal,
coastal discharge is a favoured option. With
increasing population growth and urbanisation the
volume of domestic and industrial effluent discharged
to coastal environments continues to grow.
The discharge of sewage effluent to the near-shore
environment constitutes a type of environmental
disturbance, a disturbance to the ambient physical and
chemical regime with concomitant effects on the
biota. The potential impact on marine ecosystems of
such effluent disposal practices has been recognised
for many years. A number of studies have
documented the environmental impacts of such
discharges in the waters of Victoria, South Australia
and New South Wales (Borowitzka 1972; Axelrad
et al. 1981; Neverauskas 1985; Neverauskas 1987;
Walters et al. 1986; Brown et al. 1990). In some cases
however, the study area is also subject to other
disturbing influences, making it difficult to
distinguish the impact of the sewage effluent from
other factors.
In 1984/85 a study was undertaken to determine the
impact of sewage effluent discharged to shallow
near-shore waters on Queensland’s Sunshine Coast
(Cosser & Moss 1986; Craswell & Miller 1986). In the
absence of any local industrial discharges it was
possible to examine the impact of the sewage effluent
on the intertidal zone in the absence of other
complicating factors. The only other potentially
significant source of nutrients was a small creek
located behind the beach which did not flow, except
under conditions of high rainfall (several times per
year) when it would breach the hind dunes and flow
across the beach. Accordingly, nutrient input would
have been highly episodic and infrequent.
The subject of the study was the Caloundra sewage
treatment plant outfall located at Moffat Head,
Caloundra, south-east Queensland (Figure 1).
1
Pressures
Caloundra is a coastal holiday resort town located
approximately 100 kilometres north of Brisbane. In
1986 it had a permanent population of approximately
20 000, increasing to some 40 000 during peak
holiday periods. The area is experiencing rapid
development and associated population growth. The
permanent population is expected to reach 50 000 by
the year 2000.
Given its resort status, wastewater is almost entirely
of domestic origin. The sewage treatment plant was
originally designed to service 12 000 persons and
provided primary treatment followed by chlorination.
In 1976 the plant was augmented to service 32 000
persons to provide secondary treatment with
chlorination.
The outfall was a 540 millimetre diameter pipe
located just 10 metres off-shore from the intertidal
rock platform at a depth of 1.4 metres below mean
spring low water. The outfall was originally designed
to extend some 180 metres off-shore, but due to
construction difficulties it was terminated just beyond
the intertidal platform.
Effluent monitoring results for the period 1977/1985
indicate a mean effluent total nitrogen concentration
of 31.3 mg/L and a mean total phosphorus
concentration of 6.0 mg/L. For a connected
population of 20 000 persons this represents a daily
inflow of 150 kilograms of nitrogen and
28.8 kilograms of phosphorus. At full capacity, and
47
during holiday periods, the nutrient load discharged to
near-shore waters would increase further.
(rhodamine WT) added to the effluent. The dye
plume, tracked by aerial photography and water
monitoring, provided a clearly visible indication as to
where the effluent was being dispersed.
Moffat Head and the adjoining Moffat Beach are
popular surfing, fishing and bathing areas.
Accordingly, given the proximity of the sewage
outfall to bathers, concern had been expressed about
the microbiological safety of the water. With an
increasing population being serviced by the outfall,
the pollutant pressure on both the intertidal ecosystem
and the bathing beach was growing.
2
After emergence from the outfall, the dye plume
moved onshore and tracked westwards along the
shoreline moving in the breaker zone (Figure 1). The
dye then moved beyond the rock platform and north
onto Moffat Beach, again moving along the shoreline.
Within one hour of release, the dye had travelled the
full 800 metres length of Moffat Beach, discolouring
the entire shoreline. The dye plume then moved
eastwards back through the surf zone and offshore in
a band some 70 metres wide. Once beyond Moffat
Head, the plume turned south, moving parallel to the
coast.
State
2.1 Effluent plume circulation
The circulation pattern of the effluent plume off
Moffat Head was determined by monitoring dye
Rocky
foreshore
N
Transect 5
Moffat Beach
Tooway
Creek
0
Effluent plume
circulation
100
200
Metres
Transect 2
Outfall
Transect 1
Moffat Head
Caloundra
Transect 3
Rocky
foreshore
Figure 1: Location of transects and effluent plume circulation.
Transect 4 as located several kiolmetres away at point Cartwright and is not shown
48
300
Theoretical considerations suggest that currents
within the bay would be dominated by wave
generated currents which will cause a longshore
current west along Moffat Head towards Moffat
Beach (Craswell & Miller 1986). When this current
becomes non-uniform due to the combined effects of
breaker gradients, a rip current is formed by currents
within the surf zone flowing from regions of high to
low breaker height and then seaward and flowing
through the breakers to disperse offshore from the surf
zone (Gourlay & Apelt 1978). Gourlay (1964)
observed such a rip current circulation in physical
model studies of Moffat Beach, and the results of this
dye release confirm the existence of these current
patterns.
The circulation of the bay thus indicates that at least
under certain tidal conditions the popular bathing
beach is severely contaminated with sewage effluent.
2.2 Water quality
Microbiological water quality, determined by
monitoring the enteric bacterium Escherichia coli,
was frequently poor throughout the bay and around
Moffat Head. Sampling stations monitored along the
shoreline of Moffat Beach did not meet the
recommended criteria for primary contact recreation
(bathing and surfing) (Queensland Water Quality
Council Standard). The elevated counts of E. coli
indicated a level of faecal contamination which was
unfit for bathing purposes. Monitoring at different
stages in the tidal cycle indicated that tidal state was
not an important factor determining the dispersion of
the effluent plume, as the results of E. coli monitoring
were similar on both the flood and the ebb tide.
Monitoring of nitrogen (as ammonia, oxidised
nitrogen and organic nitrogen) and phosphorus in bay
waters indicated elevated concentrations to the west
of the rock platform and along Moffat Beach,
decreasing with distance northwards. Concentrations
further offshore in the bay were consistent with
background levels measured in unpolluted areas
(unpublished data of the Queensland Water Quality
Council). Nutrient concentrations were thus elevated
only along the shoreline, returning to background
levels once the effluent plume was dispersed in deeper
offshore waters.
Offshore phytoplankton levels (measured as
chlorophyll a) were consistent with those typical of
off-shore waters, with peak levels of only 1.4
micrograms per litre. It would appear that the offshore
dispersion of the effluent plume prevents the localised
build-up of elevated nutrient concentrations and the
development of a phytoplankton standing crop.
Localised, off-shore algal blooms have not been
reported and as such it would appear that offshore
blooms were not an impact associated with the outfall.
2.3 Intertidal algal community
This study focused attention on the impact of the
discharge on the intertidal epilithic algal community.
Attached algae are immobile and therefore tend to
integrate the effects of long term exposure to adverse
conditions. As important autotrophs, epilithic algae
influence community productivity and trophic
structure, and therefore changes within the algal
community may cause changes to the entire intertidal
community. For these reasons, examination of the
algal flora can provide considerable information
about the severity of disturbance to near-shore
ecosystems.
The growth rate, species diversity (species richness)
and species abundance of epilithic algae were
measured at intervals along five transects running
through the intertidal zone from high water to low
water. Three transects were located on the rock
platform of Moffat Head:
near the outfall (T1),
220 m west (T2)
220 m east (T3)
several kilometres north along the coast (T4)
at the northern end of Moffat Beach (T5)
The transects (T4) and (T5) were also monitored for
purposes of comparison. Transects were selected for
their similarly with respect to aspect, height,
substratum type and slope.
The intertidal zone is typically subjected to a range of
conditions and considerable extremes as a result of the
tidal cycle. The differential tolerance of species to
such conditions results in the characteristic vertical
zonation of the intertidal algal community. Species
diversity was found to increase with increasing depth
below high water on all transects (see Table 1),
reflecting the gradient of decreasing environmental
stress.
49
Table 1: Abundance-dominance scores for algal species by transect
TRANSECT
Level
TRANSECT 1
TRANSECT 2
TRANSECT3
TRANSECT 4
TRANSECT 5
1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7
CYANOPHYTA
Entophysalis deusta
Microcoleus lyngbyaceus
5 3 2 1 1 1 1 3 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 1 2 2 1 2 4 5 3 3
3 2 4 5 1 1 2 3 4 4
Schizothrix calcicola
1 1 1 1 1
Scytonema hofmaii
3
2 3 3 2
1
2 4 4 1
Oscillatoria lutea
1 1 1 1 2 2 2
2 3 3 2
1 1 1 1 1
1 1 1
1
Calothrix crustacea
1
1 1 1 1 1 2 1 1 1
2 3 3 2
3 3 3 3 2 1
Oscillatoria lyngbyaceus
1 2
1 1
1
Kythurhrix maculans
1 1
2 2 2 1 1
1 4 4 4 4 4 3 2
CHLOROPHYTA
Ulva sp.
Enteromorpha clathrata
1 5 2 1
1 2 1
5 2
Chaetomorpha sp. (1)
1 2 4 4 3
1 2 1 1
2 1
1
Chaetomorpha sp. (2)
2 2 2 2
Cladorphora sp.
1
1
1 1
1 1
1
1 1
1
1
2 1
RHODOPHYTA
Corallina officinalis
Pterocladia sp.
Gelidium pusillum
1 3
1 1 3
1
1
1
1 1 1 2
1
1
Centroceras clavulatum
Lithothamnion sp.
1
1 1 2 1
1
1
1
1
1
1
1
1
Bangia sp.
1 1
Falkenbergia hillebrandii
1
Polysiphonia scopularum
1 1 1
1
Jania adhaerans
1
1
Audouinella sp.
1 1
1 1
1
PHAEOPHYTA
Bachelotia fulvescens
Mesopora schmidtii
Herposiphonia tenella
Spacelaria sp.
2 1 1 1
2 1 1 1
2 1
1 2 1
5 4 5
2 2 3 3
1 1 1
1
1 1 1 1
1 1
1 1
Spacelaria tribuloides
1
Spyridia filamentosa
1
Ralfsia sp.
1
Ectocarpus mitchellae
1 1
2 2 2
1
1 1
2 2 3 4
Notes: Levels represent 0.15 m vertical height increments, with Level 1 being the most seaward.
Abundance-dominance score: As a number of species were frequently present in the one sample, accurate estimates of cover were
not possible, and as such species were assigned a numerical abundance dominance score as follows:
5. the species accounts for 75–100% of the algal biomass and/or substrate cover within the quadrat
4. 50–75%
3. 25–50%
2. 5–25%
1. less than 5%.
50
The total number of species recorded from each
transect differed between transects. Diversity was
lowest on T1 (10 species), followed by T2 (13
species). Transects T3, T4 and T5 recorded 21, 21 and
17 species respectively. The decrease in diversity in
the outfall area was most evident towards the high
water end of the transect. A total of 15 species
recorded from reference transects T4 and T5 were not
recorded on transects T1 or T2, while one species
(Ulva sp.) was prolific only in the outfall area (T1) and
was not recorded from reference transects. Littler and
Murray (1975) found the diversity of intertidal
macroalgae to be considerably lower in a sewage
affected area.
The species composition and relative abundance of
the four major algal taxa, Cyanophyta (blue-green
algae), Chlorophyta (green algae), Rhodophyta (red
algae) and Phaeophyta (brown algae), differed
between transects. Blue-green algae dominated the
upper levels of all transects, indicating considerable
tolerance to the physically harsh environment of the
upper intertidal zone. However, four of the total of
eight blue-green algal species recorded were not
recorded from T1.
The Rhodophyta and Phaeophyta were well
represented in terms of both diversity of species and
relative abundance at lower levels on transects T3, T4
and T5, whereas the diversity and abundance of green
algae were low. Conversely, the most abundant
species on T1 and T2 were the green algae Ulva sp.
and Enteromorpha clathrata, while the diversity of
red and brown algae was low. Transects T1 and T2
recorded only three species of red algae and two
species of brown algae, compared to 5 to 7 species of
red and 4 to 6 species of brown algae on other
transects.
The Rhodophyta and Phaeophyta appear particularly
sensitive to organic pollution, declining in both
numbers of species and relative abundance at sites
affected by the effluent. In particular, Ralfsia sp. and
Mesopora schmidtii were major constituents of the
lower intertidal algal flora on transects T3, T4 and T5,
whereas Ralfsia sp. was absent from T1 and T2 and M.
schmidtii was only a minor component on T2. The
differential sensitivity of the different algal taxa to
pollution has also been recorded by Borowitzka
(1972) on the Sydney coast.
The most abundant species of the lower intertidal
zone of T1 and T2, Ulva sp. and Enteromorpha
clathrata, were observed to form a luxuriant turf over
the rock platform in the vicinity of the outfall and
extending to T2. The response of these species to
elevated nutrient concentrations is well documented.
Ho (1975) reported increased growth of Ulva sp. to be
a reliable indicator of elevated ammonia nitrogen
levels. Walker and Ormond (1982) and Fitzgerald
(1978) both report luxuriant growth of Ulva sp. and
Enteromorpha sp. in areas enriched by nutrients. In
addition to the increased dominance of these species
in the region affected by the outfall plume, their
growth rates were also measurably higher in the
enriched zone. Growth rate, measured by weighing
algal biomass growing on glass and aluminium plates
anchored to the substratum for several weeks, was
positively correlated with nutrient concentration.
On the basis of the available data, the elimination of
selected taxa and changes in species dominance in the
impacted area is considered to result from the
differential response of algal species to the presence
of elevated concentrations of growth stimulating
nutrients.
Some form of differential selection of algal species,
due either to the influence of substances which
selectively inhibit colonisation or a competitive
growth advantage, is indicated in the recolonisation
succession of substrata cleared of all algae. (Quadrats
on the different transects were scrubbed with a wire
brush and sodium hypochlorite and then observed for
several months as the algae recolonised.) Initial
colonisation of all cleared quadrats was by Ulva sp.
and E. clathrata. However, after one month
Ectocarpus sp. had also established as a significant
species at reference quadrats, whereas Ulva sp. and E.
clathrata remained the only species recorded from
near the outfall. These data suggest that the growth of
Ectocarpus sp. may have been inhibited near the
outfall. Littler and Murray (1975) concluded from
their work that environmental stress in the outfall area
selects against all but the most tolerant and rapidly
colonising organisms. Borowitzka (1972) observed
that whereas at cleared reference sites a diverse
community of red and brown algae eventually
developed (12 months) following initial colonisation
by Ulva and Enteromorpha, at locations near to
sewage outfalls additional species did not colonise.
Inhibition of colonisation was indicated, with the
51
possible synergistic effect of reduced competitive
ability resulting from growth stimulation of Ulva and
Enteromorpha.
Major changes to the diversity of the algal flora, the
relative abundance of different taxa and the
productivity of the intertidal algal community were
identified in the zone of influence of the effluent
plume. Such significant changes undoubtedly have
concomitant effects on the diversity and abundance of
invertebrate organisms associated with the algal
community. The changes induced by exposure to the
various constituents of sewage effluent, including
nutrients, can be viewed as being detrimental to some
species and beneficial to others.
The discharge of sewage effluent clearly altered the
ecology of the intertidal algal community. When
compared to reference transects, this change may be
viewed as being an adverse change as a result of
pollution. Further, as a result of the possible presence
of pathogenic organisms asociated with the effluent,
the discharge clearly presented a health risk to persons
swimming in the in-shore waters of Moffat Beach.
3
Responses
The initial response to what was perceived to be a
pollution problem arising from the inappropriate
placement of a sewage outfall was this detailed study.
While a problem was perceived to have developed
due to the location of the outfall, the extent and
severity of the perceived problem were not known.
The first response from the government was thus to
initiate a detailed study of the outfall area with a view
to clarifying just what the magnitude of the problem
was, recognising that with a growing population any
existing problem would just get worse.
52
Following analysis of the study data, which did indeed
indicate adverse impacts on local water quality, a
series of alternative disposal options were developed.
These included:
continued disposal through the existing outfall
continued disposal off Moffat Head from a new,
off-shore outfall
continued disposal of some portion of the effluent
through the existing outfall and transfer the
remaining effluent to a new ocean outfall
(Kawana) located 6 kilometres further north and
discharging 800 metres off-shore
close the existing outfall and transfer all effluent to
the new Kawana outfall.
Other options, including land disposal, were also
considered, but rejected for various reasons before
detailed analysis.
With a view to selecting the most suitable disposal
strategy for the long term, the decision to close the
existing outfall and transfer all effluent to the Kawana
outfall was taken. Any option involving continued
discharge at Moffat Head was considered
unacceptable due to a potential health risk to bathers.
The impact of the discharge on the intertidal
community, while acknowledged as being an adverse
impact, was not instrumental in the decision.
The outfall was subsequently closed and all effluent
pumped north to Kawana for disposal 800 metres
off-shore. The response to a pollution problem
created by inappropriate disposal practices in the
1960s was therefore to move the outfall further
off-shore where deep water dilution would
significantly reduce the dangers of pollution to
humans.
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J., Brown, V., Edwards, R. & Hickman, N.J.
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on the biota of port Philip Bay, Victoria,
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53