Lake Monger – An Introduction to the Ecology

This article is taken from my Ph.D. Thesis – Lund, M.A. (1992) Aspects of the ecology of a degraded Perth wetland (Lake Monger, Western Australia) and implications for biomanipulation and other restoration techniques. Ph.D. Thesis, Murdoch University, Western Australia.

This article describes the location, history, physical, chemical and biotic factors of Lake Monger. The lake is a large urban wetland with high aesthetic and recreational values (Figure 2.1) (Middle, 1988), but poor water quality resulting from the effects of urbanisation. These effects have included physical modification, removal of fringing vegetation, introduction of exotic biota, artificial regulation of water levels, pesticide treatments and nutrient enrichment. This has led to problems with nuisance midges (Chironomidae) (Davis et al., 1988), algal odour (Aplin, 1977), botulism outbreaks (Grubb, 1964; McRoberts, 1989), fish kills (Grubb, 1964; Bekle, 1981) and algal (Cyanobacteria) blooms. The severely degraded state but high social value of the lake make it ideal for future restoration. The degradation of lakes reduces the overall complexity of processes within them allowing them to be more easily interpreted. This knowledge can then be applied to more complex and natural systems (Harris, 1969).

Figure 2.1 (Click to enlarge)

Location

The lake (32o4’S 115o20’E) lies approximately 4 – 5 km from central Perth on the Swan Coastal Plain (Figures 2.2 and 2.3). Perth, with a population of approximately 1 million is the state capital of Western Australia. The Swan Coastal Plain is bordered by the Indian Ocean to the west, the Darling Scarp to the east, and extends approximately 100 km to the north and south of Perth (Seddon, 1972).

Figure 2.2 (Click to enlarge) Figure 2.3 (Click to enlarge) Aerial Photograph supplied by DOLA

At Perth, the plain is approximately 30 km wide and is formed from sediments, unlike the igneous and metamorphic nature of the scarp. The plain is divisible into a series of systems that run parallel to the scarp. These are, from west to east; the aeolian Quindalup dunes, Spearwood dunes, Bassendean dunes and the alluvial Pinjarra plain and the Ridge Hill Shelf which make up the lateritic foothills of the scarp (Figure 2.4) (Seddon, 1972).

Figure 2.4 (Click to enlarge)

Lake Monger lies in the Spearwood dune system which is younger than the Bassendean dunes, but still of Pleistocene origin. This system has, as a result, typically higher hills and more fertile soils than the Bassendean dunes or the much younger Quindalup dunes. Rainwater permeating through ridges in the dune, leaches calcium carbonate which re-solidifies in the centre of the ridge as limestone (Seddon, 1972). Between the limestone ridges are chains of lakes, which are “expressions of the unconfined aquifer above the ground surface and water levels vary in sympathy with the elevation of the water table” (Cargeeg et al., 1987). Lake Monger used to be part of a series of freshwater wetlands running northwards from the Swan River (Bekle, 1981). European settlement has led to the majority of these wetlands being drained. Indeed, central Perth is built on several drained wetlands (Figure 2.5). Riggert (1966) calculated that by 1964, 49% of wetlands on the coastal plain between the outer suburbs of Perth had been drained, filled or cleared. A recent estimate by Godfrey (1989) puts the loss at 80%.

Figure 2.5 (Click to enlarge)

Climate

Perth has a Mediterranean-type climate, with hot dry summers and cool wet winters (Cargeeg et al.,1987). Rainfall between May and October accounts for about 90% of the total rainfall (Cargeeg et al., 1987). The annual average rainfall is 870 mm and Class A pan evaporation is 1819 mm (Cargeeg et al., 1987). Evaporation exceeds precipitation in all months except between May and August. Annual rainfall is variable from year to year, with extended periods of above or below average being common (e.g. between 1971 and 1987 only 4 years had average or above rainfall) (Cargeeg et al., 1987). Average air temperatures, rainfall and evaporation are shown in Figure 2.6.

Figure 2.6 (Click to enlarge)

History

Perth was first settled by Europeans in 1829, although the area had been inhabited by aborigines for over forty thousand years (Spillman, 1985). A timeline of the history of Lake Monger is presented in Table 2.1.

  Table 2.1 (Click to enlarge)

The lake first came to prominence as the site of a minor skirmish between soldiers and aborigines in 1830 (Miller, 1980). By 1832, the lands around the lake had been subdivided into eight lots; a southern one of 80 ha was owned by J.H. Monger. The name of the lake was eventually changed from Triangle Lake to Lake Monger after this early settler (Metcalfe, 1988). In the 1880’s several of the lots were subdivided for housing and by 1902 a board from the Municipal Council of Leederville had been appointed to manage the lake (Metcalfe, 1988). In 1909, the Mounts Bay Drain was completed connecting the lake and the Swan River and this allowed the water level to be regulated (Bekle, 1981; Metcalfe, 1988). In 1917, the lake came under the control of Perth City Council (Metcalfe, 1988). The lake and surrounding area was used by aborigines as a camp, providing food from abundant waterfowl and from the surrounding rushes. Aborigines called the lake Galup and were still camping in the area up to the 1920’s (Metcalfe, 1988). The lake has significance to Aborigines, who are likely to oppose any further physical disturbance of the lake. In the 1920’s the lakes southern shore was developed with a kiosk, bathing sheds (west side), boat house and a T-shaped jetty (Metcalfe, 1988). The lake was used for yachting, swimming, fishing and as a picnic spot, with areas of the lake being dredged to improve yachting (Miller, 1976). During the 1930’s much of the fringing vegetation was removed and replaced with lawns, as part of the reclamation of the eastern swamp land. Reclamation was assisted by the dumping of rubbish (including raw sewage from nightsoil collectors) and dredging silt (Perth City Council, 1960) from the lake. By 1936 the effects of this began to be noticed with the first reports of nuisance midges (Bekle, 1981). The Depression saw the popularity of swimming and yachting peak, but the death of a youth in 1939 lead to boating being forbidden and swimming being discouraged. Between 1950 and 1964, a 1.8 m deep sanitary landfill (domestic waste only) reclaimed 97 ha of wetland area. This was covered by 60 cm of soil as part of a lake beautification project in the north and north-eastern parts of the lake (Slattery, 1963). A comprehensive plan for the lake was drawn up in 1959, this saw the provision of land destined to become the Mitchell Freeway (built in 1970’s) (Metcalfe, 1988). In 1912, the lake had an area of 111 ha, but by 1968 when sanitary landfill ceased, this had been reduced to 70 ha, its present size (Miller, 1980). An island was created during the 1960’s in the south-western corner as a bird refuge (Van Delft, 1988).

The lake is presently used extensively for recreation and is a major tourist attraction. Indeed, Middle (1988) suggested that in excess of 12 000 visitors per week visit the lake. He also found the most important activities were connected with birds (watching, feeding, photographing) and exercise.

Physical Features

The lake lies within a public park of 110 ha and has an area of 70 ha, within which is a small 1.3 ha island (Arnold, 1990). The lake originally used to dry up to a small pool during the summer (Metcalfe, 1988). The Mounts Bay drain has, since its completion, been used to regulate water depth in winter and in recent years the Perth City Council have maintained summer water levels by adding bore water. In 1909, the water depth varied from 1 to 4.27 m (Metcalfe, 1988). In the summers of 1955 – 57 the maximum water depth recorded was 2.44 m near the landfill site but the rest of the lake was approximately 0.9 m deep. In winter, depths rose 0.5 m until further increase was controlled by the overflow drain (Edward, 1964). In 1847, the water level was 13.3 m AHD (Australian Height Datum – height above sea level) (Bekle, 1981) and Arnold (1990) records maximum water levels of 13.43 m in 1976 and a minimum of 12.39 in 1972. At present the sediment surface is calculated to be 11.7 m AHD. It is likely that the height of the lake bed has risen since European settlement, although dredging will have temporarily deepened some areas.

An east-west bottom profile in Lund et al., (1991) shows that the only significant changes in depth occur near drain outlets and within 5 m from the shore. They also found that organic matter levels in the sediment followed a similar pattern with an average of 37.0 ± 2.4% dry wt. across the lake bottom. However within 5 m of the shore, organic matter levels drop to 1.4 ± 0.2% dry wt. as the sediment changes to sand. Edward (1964) found the lake sediment to be up to 3 m deep, consisting of three strata. The top layer (< 0.28 m) is very fine and flocculent and up to 22 – 58% water (Perth City Council, unpublished data). The solid material appears to be mainly Chironomidae faecal pellets, and both algal and animal remains (Edward, 1964). In 1847 the lake bed was described as being too dense to use waders in (Bekle, 1981) presumably due to its softness. At present the lake bed is too soft to wade through. The middle stratum is an approximately 0.3 m thick layer of coarse fibrous material which appears to be the remains of water hyacinth, and below this is a peat-like layer (Edward, 1964). The top layer has a neutral pH, while the other strata are slightly acidic.

Vertebrates

Fish

Miller (1980) describes the fish population of the lake in 1912 as containing English perch (Perca fluviatilis L.), tench (Tinca tinca L.) and carp (Cyprinus carpio L.). By the 1930’s bream (probably Silver Perch, Terapon bidyanus (Mitchell), see Scott, 1962) was also present (Bekle, 1981). The original native fish population of the lake is unknown but may have been been limited to gobies (Pseudogobius olorum (Sauvage)) which survived in small pools when the lake virtually dried during summer. Edward (1964) records the presence of P. olorum (Glossogobius suppositus (sic)), Goldfish (Carassius sp) and the mosquitofish Gambusia holbrooki (Girard) (G. affinis (sic); see Lloyd and Tomasov, 1985; Wooten et al., 1988). Carp and then mosquitofish were introduced to control mosquitoes (Mees, 1977; Bekle, 1981). Mosquitofish are now possibly the most abundant fish in the south-west of Western Australia (Morrissey, 1978). Goldfish are believed to be unwanted aquarium fish (see Balla et al., 1985). Bream, tench and perch were probably introduced for improved fishing (Morrissey, 1978). At present, the lake contains P. fluviatilis (A. Pinder, pers. comm.), G. holbrooki, common carp (C. carpio) and Goldfish (Carassius auratus L.).

Birds

The birds commonly found on Lake Monger are given in Table 2.2. Bekle (1984) believed that many of the waterfowl roosted in Herdsman Lake as opposed to Lake Monger but commuted to the lake for feeding. Many waterfowl also nest in Herdsman Lake but when Herdsman begins to dry walk their young to the permanent waters of Lake Monger (Bekle, 1984). Feeding the swans and ducks has become a popular tradition amongst both tourists and locals; an estimated 50 loaves of bread are fed to the birds each day. This excessive feeding is believed to contribute towards the prevalence of avian botulism in the summer months (Grubb, 1964; McRoberts, 1989; see Eccher, 1991). Although it is possible that some of the deaths attributed to botulism may be the effects of algal toxicity.

Table 2.2 (Click to enlarge)

Amphibians and Reptiles

Edward (1964) lists some common amphibia and reptilia found at the lake (Table 2.3). The lake still supports a large population of Western long-necked tortoises (Chelodina oblonga), the biology of which has been studied by Porter et al. (1987) (cited in Main Roads Department, 1989). The tortoises were found to be significant predators of Chironomidae, ingesting an estimated total of 1000 kg of larvae per month.

Table 2.3 (Click to enlarge)

Macroinvertebrates

Edward (1964) lists some of the more common species of macroinvertebrates found within the lake during the 1950s. However it was not until 1985 that the first detailed study of macroinvertebrates was undertaken by Davis and Rolls (1987) and Rolls (1989). They recorded a total of 40 species. The lake was sampled on 3 occasions between 1989 – 90, and a total of 35 species were recorded (Davis et al., 1992). A list of the species recorded in each study is given in Table 2.4.

Table 2.4 (Click to enlarge)

The zooplankton of the lake has not been studied in any detail, although the Water Authority (W.A.) has counted zooplankton identified only to family level on several occasions between 1989 – 90. In November 1990, zooplankton identified to subfamily level were collected using activity traps as opposed to plankton tows (Trayler, 1991).

Vegetation

In the 1890s, introduced couch grass (Agropyron sp) had become established around the lake, probably from a nearby orphanage (Spillman, 1985). At this time the lake was described as being surrounded by large clumps of rushes and large trees (Spillman, 1985). The large trees were probably a mixture of Melaleuca rhaphiophylla (Swamp Paperbark), Eucalyptus rudis (Flooded Gum), Banksia littoralis (Swamp Banksia) and the common rush Typha orientalis Presl (Bekle, 1981; Bekle, 1984). In the 1920s and 30s much of this vegetation was removed and lawns were planted. In the 1950s Edward (1964) describes the water as having a brown colour, which is commonly associated with the presence of fringing vegetation (Wrigley et al., 1988). Edward (1964) and Harris (1969) describe the lake in the 1950s and 60s as having thick growths of Typha domingensis Pers (T. angustifolia (sic)) and Schoenoplectus validus Love (Scirpus lacustris (sic)) around the shore except at the northern tip and the southern shore. Edward (1964) also found the emergent Polygonum
minus Huds. In 1970s, Gordon (1975) recorded the fringing vegetation as T. domingensis (T. angustifolia (sic)) and S. validus. Davis and Rolls (1987) recorded the emergent macrophytes T. orientalis and S. validus (Baumea
articulata (sic)). In this study, S. validus and T. orientalis were the dominant emergent macrophytes, Polygonum decipiens R. Br. was present in low numbers. None of the paperbarks or banksias remain around the lake and stands of Agropyron sp and T. orientalis form the bulk of the fringing vegetation especially on the eastern side.

Water hyacinth (Eichhornia crassipes Solms) was introduced into the lake, prior to 1920 (Miller, 1976) and had by 1940s covered almost 3/4 of the water (Edward, 1964). Between 1950 – 1952, aerial spraying with 2, 4D herbicide eliminated most of the hyacinth, banksias, paperbarks and reeds (Perth City Council, unpublished data). Edward (1964) recorded a small number of water hyacinth plants between 1955 – 57 but none remain now. He also found the floating macrophyte Spirodella oligorrhiza Hegelm. Harris (1969) found the submerged macrophyte Potamogeton pectinatus L. and noted that the sediments were covered at various times of year by the algae Cladophora sp and Spirogyra sp. Lund et al. (1991) also recorded Cladophora sp. and in this study dense stands of Oedogonium sp were noted in spring. In this study, a few plants of Potamogeton crispus L. were collected in November 1988. The current distribution of vegetation around the lake is shown in Figure 2.7.

Figure 2.7 (Click to enlarge)

Algae

The algal composition of Lake Monger is presented in Table 2.5. Edward (1964) only noted some of the more common forms between 1955 – 57, but Harris (1969) made a detailed study of phytoplankton ecology between 1968 – 69 and recorded 29 species. At this time Perth City Council tried unsuccessfully to control blooms of Anabaena spiroides Klebahn using copper sulphate (15 000 kg were added in February 1969) (Harris, 1969). Gordon et al. (1981) recorded 43 species in 1975, but unfortunately only listed the most common ones (Gordon, 1975; Finlayson, 1975). Aplin (1977) only recorded counts for three species in a 1975 study of algal odour; no odours were noted during the study. Davis et al. (1992) conducted algal counts on several occasions between 1989 – 90, but recorded relatively few species. Several general trends emerge from all the studies; the Cyanobacteria (especially Microcystis aeruguinosa Kutz) are dominant in summer, with green algae becoming dominant during winter. All studies have reported substantial improvements in water quality during winter.

Table 2.5 (Click to enlarge)

Nutrient and Water Balance

No nutrient or water balance has been determined for the lake. Twenty-three drains enter the lake. Three are Main Roads Department drains from the freeway and one is a Water Authority of Western Australia (WAWA) drain. The remainder are Perth City Council drains (Figure 2.8). Only one drain carries water from the lake, the Mounts Bay drain (controlled by WAWA). The total catchment of the lake is 597.8 ha, covering mainly residential areas. Water enters the lake from three sources, surface runoff through the drains, rainfall and from groundwater, and leaves via groundwater, evaporation and through the Mounts Bay drain.

Figure 2.8 (Click to enlarge)

Groundwater is the hardest component to quantify. Bayley et al. (1989) for North Lake (Western Australia) (area 27 ha, depth, 2 – 3 m) found that groundwater contributed 29% of the water, 20% of total phosphorus and 26% of total nitrogen input into the lake between 1987 – 88. Groundwater outflow accounted for only 17% of the water output. This was approximately half the input water volume and carried half the input phosphorus load and double the nitrogen load. The remainder of the input was made up by surface inputs. A similar pattern was also found for the water balance of Lake Joondalup (Western Australia) (Congdon,1985). It appears likely that the water balance of Lake Monger is similar to these two lakes as they are all situated on the same soil type and have similar origins. In summer, the groundwater in the sediments of Lake Monger had higher concentrations of phosphate and ammonia, and lower concentrations of nitrate, sulphate, chloride, sodium, calcium and magnesium than the lake water (Davis et al., 1991). These findings were believed to be typical of anoxic waters with some leachate contamination. The groundwater flows in a south westerly direction across the lake (Figure 2.9). It is therefore, likely that groundwater is adding to the nutrient loading of the lake, bringing in leachate from the sanitary landfill and nutrients from the urban catchment. It is also likely that only a small proportion of the nutrient load entering the lake is lost through groundwater outflow, although a larger proportion may be lost through the outflow drain. Considering the large numbers of drains entering the lake, the greatest contribution to both the nutrient load and water inflow probably occurs through the drains.

Figure 2.9 (Click to enlarge)

Surface runoff from surrounding urban areas and the freeway was believed to have polluted the lake sediments with lead (Lund et al., 1991) and nutrients (Davis and Rolls, 1987; Metcalfe, 1988). The source of nutrients appears to be applications of fertilizer to domestic and park gardens (Metcalfe, 1988). Since 1988, changes have been made to the fertilizing regime used by Perth City Council on the park lawns. This was done to reduce pollution from this source (Table 2.6). The sandy soils around the lake have a very low capacity to retain nutrients (Alexander, 1988) and therefore much of the fertilizer will enter the lake through the groundwater or surface runoff. Water quality data for the lake have been reported in Edward (1964), Harris (1969), Aplin (1977), Gordon et al. (1981) (taken from Gordon (1975) and Finlayson (1975)), Davis and Rolls (1987), Rolls (1989), Davis et al. (1988), Davis et al. (1991a), Pinder et al. (1991) and Davis et al. (1992).

Table 2.6 (Click to enlarge)

Urban lakes of Perth (Western Australia): A history of degradation and loss

The original article was published by Mark Lund in the June 1995 Issue of Lakeline Magazine Vol 15(2) pg 24 (ISSN 0743-7978) and has been modified slightly for inclusion here.


“At home [the U.K. presumably], a lake is known only as a sheet of water which seldom or ever dried up, and it is naturally associated in one’s mind with pleasant and picturesque scenery, but here it is quite different … there is an air of desolation about these lakes which strikes the spectator at once … It is complete still life without one point of interest in it, as far as striking scenery goes, and totally different from anything I ever saw outside Australia.”

These sentiments were expressed in a 1847 Perth newspaper. Similar attitudes have largely been responsible for the loss and degradation of the urban wetlands of Perth from its foundation until recently.

TRADITIONAL AND EUROPEAN WETLAND MANAGERS

Aborigines have occupied the region around Perth for about 38, 000 years. They made extensive use of the wetlands as sources of water and food (fish, waterfowl, turtles, frogs and edible aquatic plants). Aboriginal people are believed to have managed and possibly modified the wetlands by selective burning of fringing vegetation to increase productivity.

The British founded the Swan River Colony (later to be renamed Perth) in 1829 on a site surrounded by wetlands, adjacent to the Swan River. As Perth expanded, wetlands were drained for housing and market gardens, as it was quickly realised that the lakes were too shallow to provide useful sources of drinking water. Therefore, some were subdivided into lots, some were drained for market gardens, some used for recreation, and others used for road reserve. Interestingly, on many occasions settlers misjudged their ability to drain the wetlands and initially flooding was a serious problem. Within 16 years of settlement, six wetlands, representing approximately 50-70 ha of open water, were drained and built over. The low perceived value of wetlands has meant that reclamation of wetlands for urban development continues to the present day.

Perth is the capital city of the State of Western Australia and currently boasts a population of over one million. Perth has a ‘Mediterranean’ climate with hot, dry summers and cool, wet winters. The city lies on the Swan Coastal Plain (SCP), a series of parallel sand dunes which are bordered by the Indian Ocean to the west, the Darling Scarp to the east and extend approximately 100 km north and south of Perth. In the depressions between the dunes, the water table becomes exposed, forming chains of wetlands. As the wetlands are largely surface expressions of the groundwater, they generally have no surface inflows or outflows, although, in extremely wet years, there is evidence to suggest that groups of wetlands became linked. The seasonal changes that are experienced within the major groundwater aquifers have an important influence on the water levels of many of the wetlands.

This article will restrict itself to the Perth metropolitan area and the following types of wetland: lakes (permanent water), swamps (seasonal lakes, dry in summer) and floodplains (areas of flat land, seasonally inundated).

In few Australian cities has the ‘Australian Dream’ of a house on a quarter-acre block been so achievable as in Perth. Hence, the rate of urban expansion has been considerable with the city now covering around 2030 km2. Estimates of the area of wetlands lost from the SCP range from 60 to 80 percent. Unfortunately, the loss of wetlands per se represents only a portion of the problem, the other is the degradation of the remaining wetlands.

WETLAND USES

Health risks associated with high fecal coliforms and attempts to reduce disturbance to waterbirds stopped active recreation on the wetlands. Prior to this they had been used for swimming, boating, water skiing, diving, fishing and catching edible crayfish. Current use is restricted to passive recreation, BBQ’s, walking, bird watching, picnicking, bird feeding and so on. Lake Monger, a popular lake close to central Perth, was estimated to receive over 12,000 visitors per week.

CAUSES OF THE DEGRADATION

The sentiments expressed at the start of this article are prevalent even today. There is a strong perception that our natural wetlands are not as attractive as Northern Hemisphere lakes. This has fostered a mentality that the wetlands should be altered to ‘improve’ their appearance. These improvements include lawns to the lake edge, infilling of swampy areas, dredging (to increase depth) and removal of fringing vegetation. This is particularly so in newly developing suburbs, which are frequently populated by immigrants from the Northern Hemisphere who are often uncomfortable with the uniqueness of the Australian bush. Aside from ‘improvements’, the wetlands are also seen as convenient receiving environments for pollutant discharge, including stormwater.

Artificial maintenance of water level

The majority of wetlands are shallow (1 – 4 m deep) and seasonal. As dry wetlands are deemed unattractive, many now have water levels artificially controlled (with outlets to control winter flooding and the addition of bore (groundwater) water in summer). One of the arguments for this practice other than pure aesthetics, is that it provides a permanent water source for fauna. Countering this argument are that permanent flooding can lead to the death of fringing vegetation (in particular Melaleuca trees) and the majority of fauna has evolved to cope with seasonal drying.

Nutrient enrichment

Many of the wetlands are used for water compensation (directing stormwater drains into the wetland). Surface runoff on Perth’s sandy soils is normally very low, but the increase in hard surfaces (roads, roofs, etc.) through urbanization increases runoff significantly. Many wetlands are now experiencing unusually high water levels, as a result of urbanisation of their catchment. The stormwater that enters the lakes carries nutrients (from lawns and gardens) and pollutants (oil, pesticides etc) from the surrounding urban area. The groundwater also carries fertilisers from surrounding lawns into the lake. This input can be quite significant. When the lawns around Lake Monger ceased to be fertilized, the levels of total P dropped from around 800 ug/l to 150-250 ug/l. High nutrient loads and high summer temperatures (air temperatures vary between 30 and over 40 oC) can result in blue-green algal blooms (up to 700 ug/ l of chlorophyll a) of Anabaena and Microcystis. Associated with algal blooms are localised problems of avian botulism, fish kills, noxious smells, and nuisance levels of non-biting midges (Chironomidae). The latter has resulted in the regular spraying of some wetlands for the past 27 years with Temephos (Abate). Copper sulphate has been used occasionally to control algal blooms, with varying success.

Physical modifications

Physical modifications to the wetlands include some that are probably beneficial for urban lakes, such as the construction of islands (for waterbird habitat safe from predation by cats, rats and dogs), and the construction of walkways to provide access for bird watching and educational purposes. Other modifications are more detrimental and include the use of walls to replace the shoreline, dredging, mining (sand, peat or diatomaceous earth), use as a sanitary landfill, and infilling. Walls which form the shore of the lake result in a loss of habitat, especially for invertebrates, and are rarely necessary for other than aesthetic purposes. Mining can have three major influences; 1) the physical disruption to habitat, 2) reduction in pH through oxidation of iron sulphides, and 3) deepening of the lake, which can result in long periods where the lake is thermally stratified (the wetlands are normally too shallow for this). The use of wetlands as sanitary landfill sites was an occasional practice in the 1950-60s, and was usually described as a lake beautification project. Although the areas of the wetland which had been used for landfill were eventually capped with a layer of clay, they continue to be a source of nutrients and other pollutants to the remaining area of water.

Replacement of native plants with exotics

Other modifications that are also usually the result of ‘beautification’ schemes are the removal of fringing vegetation to provide householders with an uninterrupted vista of open water. Characteristically the fringing vegetation of the wetlands on the SCP was dominated by Paperbarks trees (Melaleuca sp), with occasionally bands of reeds (Typha, Schoenoplectus and Baumea). These plants are also believed to be at least partially responsible for highly colored (brown color or gilvin) waters in many wetlands. The color has been shown to limit algal growth, even at high nutrient levels, by either limiting light penetration or through binding micronutrients. In many areas, the native vegetation has been removed and replaced with lawns. The poor nutrient status and water holding capacity of the sandy soils means the lawns require high quantities of fertilizer and watering. Along with exotic grasses, many other plants have been introduced, including water hyacinth (Eichhornia crassipes), Salvinia (Salvinia molesta), several species of Cyperus (e.g. Papyrus), Willows and Para grass (Urochloa mutica). Both Salvinia and water hyacinth are controlled, as they have been declared noxious weeds. In the 1950s, water hyacinth covered Lake Monger and was eradicated with Hormex. In lakes with submerged macrophytes they are sometimes considered a problem where they break the surface and are considered unsightly.

Waterbirds

The feeding of waterbirds is a popular local tradition; in fact many people believe that the birds require this supplementary feeding for survival. It is extremely unlikely that this is, in fact, the case, and addition of large quantities of bread probably increases the risk of avian botulism. Council rangers tell stories of small truckloads of stale bread being dumped into wetlands, sometimes without the plastic wrap being removed. Some councils are now trying to discourage feeding with varied success. Councils have generally placed signs saying ‘Please do not feed the birds’ without providing any form of explanation as to why not, which I believe contributes to people ignoring the signs. Many degraded wetlands support large numbers of waterbirds; this doesn’t reflect the health of the wetland, but rather the fact that large numbers of birds commute from healthier lakes nearby to feed. The loss of wetland area is also likely to have concentrated birds around in those which remain.

Exotic waterbirds have been introduced to many wetlands, including domestic geese, muscovy and mallard ducks. Mallards, in particular, pose a major threat as they are capable of interbreeding with native ducks, producing fertile offspring.

Fish

The seasonal nature of the majority of wetlands has resulted in a very limited native fish fauna (only seven species). A variety of fish have been introduced into the wetlands for aesthetics (goldfish), fishing (prior to the 1980s) and mosquito control. Fish introduced for angling include common carp, redfin (English) perch, bream (probably Silver Perch; now extinct) and tench (now extinct). In 1934, the mosquitofish (Gambusia holbrooki) was introduced into Western Australia by an amateur fish breeder; they were later spread by Heath Authorities to control mosquitos. There is little evidence to suggest that mosquitoes were ever a serious problem prior to the introduction. Regardless of whether they control mosquitos (many researchers consider them relatively ineffective) or not, the fish prove a problem by consuming a wide range of invertebrate taxa. It has also been suggested that their aggressive behaviour may lead to the driving out of native species. At present, comparatively little is known about the effects of these introductions on wetland ecosystems. The introduction of these fish raises questions as to whether biomanipulation may be a useful restoration technique; in the studies I have undertaken this appears not to be the case.

LEGISLATIVE PROTECTION OF WETLANDS

Wetlands are either owned freehold by private landowners, local councils and government departments, or are on Crown Land which is often vested in a Government Department (e.g. Department of Conservation and Land Management). Legislative protection works through the three tiers of government (Commonwealth, State and Local) using a variety of Acts. The two most important are Ramsar wetlands (International treaty for the protection of migratory birds) and a State Environmental Protection Policy (EPP) (1992) which prohibits unauthorised filling, mining, drainage into or out of, and effluent discharge into lakes on the SCP that contained over 1000 m2 of water on 1st of December 1988. This date marks the start of summer when normally wetland levels would be at their highest. However, 1988 had a dry winter and, as a result of this and the fact that many wetlands fall under the minimum size, only 5.3 percent of the total wetland (using a very broad definition of wetland) area of the entire SCP was protected. The EPP was particularly important, as for the first time it allowed Government to regulate wetland damage on freehold land. Although many wetlands were overlooked, these policies are reviewed periodically and this problem may be addressed in the future.

MANAGEMENT AND RESTORATION

Aside from legislation, management of the wetlands is usually left to the agency responsible for the wetland. Management Plans have been written for many of the wetlands; however, few have really been acted on. Management as a whole, certainly at the local government level, is largely reactive. As a result, there have been few attempts at lake restoration. The approaches that have been tried are dosing with aluminium sulphate, dredging, and nutrient diversion. In only one case was a coordinated approach used to tackle the problem. This involved a study of North Lake, where a nutrient and water budget identified two drains as the main sources of nutrients. The most polluting drain was redirected, and the other drain was passed through an artificial wetland to reduce nutrient loads. After a shaky start, a monitoring program was established to determine the effectiveness of the restoration. Unfortunately, this type of restoration involving a detailed evaluation of the problem, followed by treatment and then monitoring to measure success, is atypical. The scenario normally followed one where the local residents complain, the agency responds by deciding to clean up the wetland, the agency determines the best method (how is often a mystery), and then it is implemented. If there are no further complaints it is deemed a success. Perhaps this is a cynical view of the process but, certainly from my perspective, this approach leads to a treatment of symptoms, not cause, wasted money (e.g. dredging where no attempt is made to control nutrient rich surface inflows), and a failure to build up detailed knowledge on restoration processes (i.e. everyone’s working in the dark).

An example of this is a study I was involved in at Jackadder Lake. This small lake was eutrophic, and had problems with algal blooms and nuisance midges during summer. In response to public concern, the agency responsible decided, rather than spraying the lake again, to try and fix the problem. Addition of aluminium sulphate was the chosen option. I became involved when I learned through the grapevine what was planned. The agency was contacted and agreed to conduct it as an experiment. Unfortunately, there was little opportunity to collect data from before the treatment, despite the fact that the addition was delayed from late spring to mid-summer (mainly for bureaucratic reasons). I monitored the lake for the next year. The exercise was to all intents and purposes a failure (despite some overly optimistic reports which were produced at the time). This I ascribe to one main cause, the major sources of nutrients were not determined prior to the addition. As a result, it is doubtful whether the addition of aluminium sulphate was the best strategy.

Another example involves water withdrawal; Perth on an annual basis obtains approximately 30 percent of its drinking water from groundwater. The groundwater comes from two aquifers located on either side of the Swan River. To protect these aquifers, overlying development has been minimized. As wetlands are reflections of the groundwater, any lowering of the groundwater will potentially impact wetlands. The Water Authority has developed complex models of groundwater movement to use as a basis for planning the best sites for withdrawal. Despite this, or because of it, a series of wells were placed near a chain of valuable wetlands to abstract about four million cubic meters per year (a very small amount). The models were used to plan where the wells could be sunk so as to minimize potential environmental impact. Yet it is obvious that for such a low yield of water, the potential environmental harm was not justifiable and the groundwater wells should have been relocated in a less sensitive area. Unconnected with this was a government decision to place a housing estate on the same aquifer (Jandakot Mound). To ensure the site would not flood, the water table was lowered through a system of drains. The drains linked into a chain of wetlands. This has led to excessive water levels in many of these wetlands.

Until such time as a structured approach to wetland restoration and management is taken by agencies, protection of Perth’s unique wetland systems will continue to be a hit and miss affair. A positive note is the publication of a series of detailed scientific reports on a variety of wetland issues by the Water Authority and Department of Environmental Protection. The first volume (listed below) of the series is written for managers. At the media launch of the first volume the State Minister for the Environment stated that the degradation of Perth’s wetlands was the result of ignorance and that the publishing of this book should rectified that problem. Let’s hope he was right.