Waterways of the Merri Catchment flowing slowly through emergent vegetation; and the lower 30% is a slow, non-uniformly flowing stream.
3.3.2 Summaries of the Significant Tributaries
This summary is based on the work of N.M. Craigie & Associates (Craigie, 1994). They divide each stream into a series of reaches based on generally similar features such as channel, bank and verge characteristics. This section deals with the channel origin and the flow character alone and lists the creeks as they join the Merri Creek from its headwaters to its mouth.
It is worth noting that N.M. Craigie & Associates acknowledge that the classification of the catchment in this manner is quite broad and can be refined by more detailed study. However, this is the best available work that covers the whole watershed.
Mittagong Creek
This creek is the northernmost headwaters of the Merri Creek system but joins Wallan Creek before the Merri Creek near the Hume Freeway. Craigie classed it as having only one reach. From its beginnings to its confluence with Wallan Creek, Mittagong Creek is 5 km long.
Although the channel is essentially natural in origin, there has been extensive modification to it. There are several large on-stream dams and the stream from William Street in Wallan to its confluence with Wallan Creek has been straightened somewhat.
The flow is generally negligible but there are disconnected but relatively permanent pools. The dams constructed obviously control the flow.
Wallan Creek
This creek in the headwaters of the Merri Catchment arises on the south side of Pretty Sally on the Great Dividing Range. It flows south then east through the township of Wallan into the Merri Creek near Wallan East, a total distance of nearly six kilometres. The creek has been divided into four reaches.
The uppermost reach, which has not been described by Craigie, flows through farmland and the urban fringe a distance of 1.2 km. It is likely that the form has not been altered much. The sections of the creek downstream of the township, 65% of the total length (5.35 km), have been substantially altered. These alterations include channel enlargement, installation of a low-flow pipe, channel straightening, channelisation and de-snagging.
The uppermost reach is characterised by a stream flowing slowly through emergent vegetation. The middle reach has not been classified as it has a low-flow pipe. The section from the Hume Freeway to the Merri Creek does not normally flow but has disconnected and semi-permanent pools.
Page 50 State of the Environment Report - Introduction
Strathaird Creek (Airfield Drain)
This creek has its origins in the hills to the west of Wallan, from which it flows southward until it reaches Rowe's Lane where it turns east and flows into the Merri Creek. The point at which it is joined by Taylor's Creek it is termed the Airfield Drain. Craigie divided the creek-drain system into two reaches and the total length of the system is approximately nine kilometres.
Of the total length of the system (8.6 km), 56% has been drastically modified to an unlined artificial drain while the upper 3.8 is in a close to natural state.
The flow regime of the upper part of the creek is likely to be discontinuous but relatively permanent pools with negligible flow. Downstream of Rowe's Lane the creek-drain system is characterised as a slow flowing stream filtered through emergent vegetation.
Taylor's Creek
Taylor's Creek arises on the southern side of Pretty Sally on the Great Dividing Range and flows southwards past Wallan before joining the east flowing Airfield Drain at Macsfield Road and then uniting with the Merri Creek at Herne's Swamp south of Wallan, total length of approximately eight kilometres. The creek has been divided into four reaches.
Of the total length of the creek to the Airfield Drain (5.6 km), 23% is highly modified (straightened and de-snagged), 14% has slightly less modification (de-snagging) and 63% is largely unmodified.
The flow character of each of the three reaches is slow and filtered through emergent vegetation.
Unnamed Western Tributary
This minor tributary drains a small area northeast of Mt Fraser. Although Craigie described the lower two kilometres only as one reach, the upper one kilometre of the stream appears (from the topographic map) to be in a largely natural state. The reach described by Craigie is an artificial unlined drain. Therefore 66% of the creek has been highly modified.
The flow in the lower section is slow and filtered by emergent vegetation.
Bald Hill Drain
This small tributary drains an area northeast of Bald Hill. Again Craigie has described the lower 1.5 km only (as one reach), although the drain begins another 2 km further upstream. The reach described by Craigie is a natural channel that has been extensively modified by straightening and de-snagging. It appears that the remainder could be classed similarly.
The flow has been characterised as slow and filtered through emergent vegetation.
Kalkallo Creek System
This system of drains and creeks draws water off the hills west of Beveridge flowing southward to join Merri Creek near Donnybrook Road. Five drains unite west of Kalkallo to
Page 51 Waterways of the Merri Catchment form Kalkallo Creek proper. Craigie has described three of these drains and termed them Kalkallo Creek West Leg, Kalkallo Creek Centre Leg and Kalkallo Creek East Leg.
The state of the channels of this drainage network is that nearly 36 km of channel length, 14.6 km (41%) is in nearly natural (with only slight modifications) whilst 20.7 km (59%) is unlined channel.
Except for the East Leg which flows only after rainfall, the flow character of all the streams is one of discontinuous but semi-permanent pools of water with negligible flow.
Malcolm Creek
This western tributary joins the Merri Creek a little north of Craigieburn. The creek has its headwaters in an area of open forest between Mickleham and Mt Ridley from which it flows southwards through open pasture until it reaches Craigieburn whereupon the creek turns eastward and flows into the Merri Creek a total distance of approximately 8.3 km. Craigie divided the creek into just two different reaches - that above the Hume Freeway and that below.
The two reaches are in a close to natural state with only minor de-snagging, however the lower reach has greater inputs of rubbish.
The whole of the stream flow is very slow to non-existent and is characterised by disconnected but relatively permanent pools.
Aitken Creek
Another western tributary, this creek joins the Merri Creek just south of Craigieburn. The headwaters of this creek are near the Old Sydney Road about 5 km west of Craigieburn from which it flows in a southeasterly direction through open pasture and then the township of Craigieburn until it joins the Merri Creek a total distance of approximately eight kilometres. Neil Craigie divided the creek into three reaches; that above the Craigieburn Golf Course, the section through the golf course and the section through the township to the Merri Creek.
As a percentage of the total, over 81% of the creek is kept in a nearly natural state and the character of the remainder, whilst extensively modified, is not completely destroyed.
From the headwaters to the golf course the flow is almost non-existent and is characterised by disconnected but relatively permanent pools. There are also many on-stream dams, which in times of storm activity must disrupt the natural flow of the creek. The flow through the golf course is slow and filtered through emergent vegetation. Through the township the flow is slow and non-uniform having runs, glides and pools.
Curly Sedge Creek
This medium-sized tributary arises northeast of Summer Hill and joins the Merri Creek near O'Hern's Road, a distance of around 7.5 km. Craigie has classed the whole creek as one reach. The creek is in a basically natural state with only minor de-snagging.
The natural flow of the creek is negligible with the stream consisting of discontinuous but relatively permanent pools.
Page 52 State of the Environment Report - Introduction
Campbellfield Creek
This small creek is a tributary of Merlynston Creek that runs parallel and adjacent to the Hume Highway. It begins at Mahoney's Road and enters Merlynston Creek in the Fawkner Crematorium, a length of 2.2 km.
Although Craigie has not examined this creek, it is apparent from the topographic maps that the section below the retarding basin to Box Tree Road (a distance of 0.5 km) has been straightened and is probably channelised.
It appears that the creek is an intermittent stream. Surrounding urban development has probably caused an increase in the flow during storm events.
Merlynston Creek
This creek is one of the western tributaries of the Merri Creek and has its headwaters a little north of Barry Road near the Upfield railway station. It flows southward for approximately seven kilometres through the suburbs of Broadmeadows and Glenroy and then through the Fawkner Crematorium, finally entering the Merri Creek two hundred metres above Coburg Lake. The creek has been radically altered by the industrial and urban development. Neil Craigie has divided the creek into five reaches.
Of the total length of the stream (some 6.75 km), 43% is either a pipeline or an open concrete channel and a further 27% has had major modifications. Only 30% of the stream remains relatively unmodified.
For the most part the flow in Merlynston Creek is either very slow or negligible. In the first unconcreted section (the second reach), the flow is almost non-existent, the stream characterised by discontinuous but permanent pools. The next two reaches are distinguished by slow but reasonably steady and uniformly flowing water. The lowest reach has not been classified as it is a pipe.
Edgar’s Creek
Edgar's Creek is the largest tributary of the Merri Creek, flowing from near Wollert on the eastern edge of the catchment through the suburbs of Epping, Thomastown and Reservoir to join the Merri Creek just below Coburg Lake, a distance of almost 17 kilometres. Neil Craigie has split the creek into ten different reaches.
The total length of the creek is 16.9 km, 11% of which is concrete lined. Another 34% of the channel is artificial but unlined. This leaves around 55% of the stream length in near original condition, however, these reaches are at the head and lower end of the stream and are separated by 7.6 km of artificial channel.
The uppermost reach is a mostly dry bed with the occasional semi-permanent pool. The second reach is characterised by a non-flowing stream of disconnected but relatively permanent pools. The section through Huskisson Avenue Reserve is a slow flowing stream
Page 53 Waterways of the Merri Catchment through emergent vegetation. The fourth reach is not classified being a concrete channel. The fifth reach is distinguished by a stream of slow and non-uniformly flowing water passing though runs, pools and glides. The sixth reach is not classified. The seventh reach is distinguished by a stream of slow and non-uniformly flowing water passing though runs, pools and glides. The eighth reach has not been classified. The ninth reach is classed as slow but reasonably uniform and steady flow. The final reach is characterised by fast but non-uniformly flowing water, passing through pools, glides, runs and rapids.
3.3.3 Wetlands
Wetlands are an important landform for both their capacity to temporarily store water “in- catchment” and as habitat for many species of plants and animals. Oates (1994) identifies a number of different types of wetland morphology, of which five are currently found, or were historically present, in the Merri Catchment. These types are: • floodplain/river flats • volcanic plains • alluvial fan/plains • foothills • along drainage lines
At present the main natural wetland area is Hernes Swamp near Wallan. This volcanic plains type used to be an area of approximately 1 km2 but this has been significantly reduced. The swamp at Beveridge (a volcanic plains/alluvial plains type) used to be approximately 1 km2 but is much less than this today. Wetlands along drainage lines are still found throughout the catchment, for example those along Aitken Creek, but they are disappearing due to increased channelisation. Restricted floodplain type wetlands still occur in various locations along the Merri Creek (eg. around Mahoneys Road).
A number of wetlands that were marked on a geological map of the catchment produced in the early 1970s by Earl (1974), but have since been drained. The swampy alluvial fan area around Wallan East used to be some 5-6 km2 but is no longer wetland. Maps show an area (1 x 0.5 km) two kilometres west of Hernes Swamp as a foothills type wetland but it does not appear on recent maps. An area (1.2 x 0.7 km) on the west bank of the Merri Creek between Merriang and Merri Creek Park was an example of the alluvial plains wetland. A swampy area (1 km2) north of Cooper Street was a volcanic plains wetland but is now the site of the Cooper Street Landfill. No doubt many other wetlands were found in both the urban and rural parts of the catchment and have long since disappeared.
The main wetlands that remain in the Merri Catchment (refer to Map 8 in Aquatic Ecology) are: • an unnamed swamp east of Dunlop factory at Campbellfield • Hernes Swamp (S4) • Beveridge Swamp (R6 on east side of Spring Street, Beveridge)
Page 54 State of the Environment Report - Introduction
3.3.4 Water Harvesting
Water harvesting is the extraction of water from a catchment for human uses, such as agriculture and industry. In the Yarra Catchment this has been split into two categories (c.f. Haydon, 1994); Major Diversions (e.g. the Water Storage Reservoirs) and Minor Diversions (eg. Private diverters). In the Merri Catchment there are no Major Diversions.
The Minor Diversions are attributed mainly to private diverters for irrigation or domestic use and as the data is not accurate its true impact has not been investigated. Private diverters are issued licences to extract water administered by Melbourne Water and the amounts allowable vary depending upon the area to be irrigated or the capacity of the licensee's storage. There is no actual measurement of this amount but past studies show that the amount allocated and the amount used is roughly the same. For the Merri Catchment the amount allocated 52 Megalitres (ML) per year.
Another form of harvesting exists for property owners who have waterways on their properties. This "Riparian Right" allows farmers to divert 2.2 ML/year of water for the whole catchment without need for a permit. There is no information as to how many owners exercise this right for the Merri Catchment.
The total extractable water in the catchment is 54.2 ML/year. Based on an average annual flow of 17000 ML, this is approximately 0.32% of the average total contribution of Merri Creek flow to the Yarra River. Whilst this appears to be very small, it could be significant to stream flows in the areas from where it is taken (mainly in the rural segment of the catchment). The allowable extractions also do not take into account periods of low flow in the creek and indeed may be exercised to their full extent during these times of drought, thus increasing pressures on the creek ecosystems.
3.3.5 Stormwater
Although stormwater runoff is a natural process, in the urban environment it is increased due to large areas of land being sealed and paved with an impervious layer that does not allow the ground to soak up excess runoff. Many studies, including Jovanovic (1986), have shown that the process of urbanisation decreases the amount of infiltration. The most obvious impact is an increase in the volume of stormwater entering the stormwater drainage system. The impact of this on the increase in volume on the creek system is best illustrated in Figure 1. This shows how the peak volume and velocity of water flowing in the creeks is raised with increasing urbanisation and how, generally, the peak flows are reached much earlier. Rankin (1994) outlines the process that occurs in the northern tributaries of the Yarra River suggesting that creeks such as the Merri Creek are more sensitive to rainfall with increased development and display an increased “peakiness” of water level, meaning that waterways rise more quickly to a high level - a level higher than pre-development flows - and maintain that level for a longer period.
Page 55 Waterways of the Merri Catchment
Figure 1 Runoff hydrographs for different percentages of urbanisation of a catchment (from Jovanovic, 1986).
The increased runoff in urban areas gives rise to the need for a stormwater drainage system. This extensive network of pipes and drains draws water from the roads and house roofs and directs it into the natural watercourses such as the Merri Creek. The responsibility for this network is currently split between Melbourne Water Corporation (main drains) and the local councils. The following is a list of the main drains that flow into the Merri Creek, their location is shown on Map 5.
• Alexandra Parade Main Drain • Chauvel Street Main Drain • Alexandra Parade Relief Main Drain • Merlynston Main Drain (see Merlynston Ck) • North Fitzroy Main Drain • South Street Main Drain • Lygon Street Main Drain • Middle Street Main Drain • Dover Street Main Drain • Fawkner East Drain • Green Street Main Drain • Campbellfield Creek Diversion Drain • Glenlyon Road Main Drain • Lynch Road Main Drain • Sumner Avenue Main Drain • Major Road Main Drain • Albert Street Main Drain • Fawkner North Drain • Preston Main Drain • Maffra Street Drain • The Avenue Main Drain • Somerset Road Drain • Spring Street Main Drain • Augusta Avenue Drain • Elizabeth Street Main Drain • Jesica Street Drain • Merrilands Drain • Ainslie Road Drain • Harding Street Main Drain
It should be noted that although this is the full list of main drains, there are also numerous smaller drains which carry water off each suburban street before feeding into the main drain system. These smaller street drains are the responsibility of the local councils. The increased runoff carries many sorts of pollutants into the waterways and the increased volume can also cause a loss of in-stream sediments due to erosion.
Page 56 State of the Environment Report - Introduction
Map 5 Drains to the urban waterways of the Merri Catchment
Page 57 Waterways of the Merri Catchment
3.3.6 Floods
One of the more important aspects of stream flow is flooding. Floods are important both in terms of their intimate association with the ecology of the waterways and in terms of impacts on human communities.
Floods and the Human Landscape
In May of 1974 the Merri Creek flooded. This event was, and still is, the worst of the 19 floods since records began in 1894 and caused serious damage to several hundred properties built on the lower Merri Creek floodplain (Earl, 1974). In their Merri Creek Plan, the MMBW (1987) mapped out the 1% (or 100 year) flood levels based on environmental conditions and data current for the mid 1980s and which are subject to change. The most important of these changes are new urban developments that are constantly going outward from the city. There can be little doubt that such urban expansion will, if certain measures are not taken, increase the risk of flood damage to those who live in the lower portions of the catchment. This very view was expressed after the 1974 floods (Earl, 1974).
Current Flood Control Mechanisms
Weirs and Retarding Basins are perhaps the most obvious means by which the management authorities have attempted to mitigate flood events. These are situated at:
• Weir at Coburg Lake: A structure that has no low-flow outlet and relies on the principle of flow in = flow out and the lake remains at a constant level. However, if the level should drop below the weir height (due to groundwater recharge in times of prolonged drought), no flow could be released downstream of the weir until the level recovered sufficiently.
• Weir at Edwardes Lake: A similar structure to that at Coburg Lake (with the same restrictions).
• Retarding Basins on Merlynston Creek: There are three of these structures on this creek designed to protect residents from flooding as the downstream portion is an enclosed drain.
Other dams on the minor tributaries include:
• Retarding basin on Campbellfield Creek • Dam on Strathaird Creek - 5.1 km upstream of confluence with Merri Creek. • Retarding basin on Kalkallo Creek Central Leg - 7 km upstream of confluence with Merri Creek. • Dam on Mittagong Creek - 2.8 km upstream of confluence with Merri Creek
There are also a number of small illegal dams on the creeks in the upper part of the catchment which will have some influence on flooding.
Page 58 State of the Environment Report - Introduction
Other engineered structures that control floods are levee banks on the Merri Creek between Normanby Avenue and Anderson’s Street, Sumner Avenue and Winifred Street. A retarding basin on the Merri Creek has been proposed at Campbellfield but has not been constructed to date.
Other methods engineers have used to reduce the impacts of floods are channel straightening, de-snagging and in some cases lining the channel with rocks or concrete. These all have the effect of removing water swiftly from one area but this can cause more flooding problems further downstream. The parts of the creeks with such works are outlined in more detail above.
In his report on the floods of May 1974, Earl (1974) acknowledges the role that wetlands play in flood prevention. He said then “...that if further relatively minor drainage works are undertaken to drain the natural rural swamps, flood flows downstream of these areas will increase greatly...” At the time the Shire of Whittlesea planned to establish a Drainage Trust to oversee the draining of rural lands. MMBW strongly opposed this for the reasons outlined above but it seems the draining has continued. Since 1974 the community has not experienced such a damaging flood and it is more than likely that if and when one occurs, the damage will be more extensive than that disaster.
3.3.7 Groundwater
Groundwater in the Yarra Catchment is important as it contributes about 50% of the total flow of the water into the Yarra River. Groundwater is also a significant source of water supply within the catchment with the annual licensed diversion to irrigators and others being around 7000 megalitres per year. Groundwater is a major source of soluble salt load carried by the river contributing somewhere between 50-80% of the total (Shugg & O’Rourke, 1994).
Groundwater catchment boundaries generally coincide with their surface counterparts, however aquifers may cross catchment boundaries. This means that activities in one catchment may affect the water quality and quantity in another.
The Department of Natural Resources and Environment monitors groundwater in the Merri Catchment and their results are outlined in the discussion of groundwater quality in Section 4.4.3.
Groundwater use
The authorised yield for the Merri Catchment is not specified but the amount from the "Basalt Plains" as the authors refer to it (which includes the Merri Creek) is 269 megalitres and there are 1027 registered bores in this region (Shugg & O’Rourke, 1994).
Groundwater Hydrology
Groundwater recharge on the basalt plains is around or below 10 mm per year (Shugg & O’Rourke, 1994). The fracture permeability throughout the basalt plains of the northern part
Page 59 Waterways of the Merri Catchment of the Yarra catchment is usually high and groundwater flow is likely to occur over large distances. Indications point to several local recharge areas which, if they inject saline waters into the aquifers, have the potential to produce augmented salinity concentrations (Thomas & Cummings, 1994).
3.4 Conclusions
Very little of the Merri Creek or its tributaries escape the affect of morphology and flow changes brought about by post-European settlement landuse practices. In the rural reaches these changes are most pronounced where the channel is least incised. In the headwaters, the swampy alluvial fan and the chain-of-ponds settings, agricultural practices have, in places, drastically altered stream form by channel straightening, drainage of wetlands and snag removal. Natural flows are reduced by both on- and off-stream dams.
The encroachment of urban development up the valley of the Merri Creek has brought with it the almost inevitable changes to morphology and flow. These are most severe in the long- established inner urban areas of Northcote and Brunswick. It is here that channel modifications, designed to limit the impacts of floods are most extensive. However, the problems which flooding causes to the people living near the creek are exacerbated by landuse practices further up the catchment such as paving and associated stormwater drainage, the channelisation of streams and drainage of in-catchment water storage wetlands.
The portion of the Merri Creek least altered by landuse changes since the arrival of Europeans is a stretch a few kilometres either side of Craigieburn. In these reaches, the incised valley protects the creek from destructive farming practices. Flows here are somewhat restricted by dams.
The understanding of groundwater, which is normally a significant contributor to streamflow, is very limited in this catchment. More work needs to be done to determine the effects of landuse practices on rates and volumes of discharge to the catchment streams.
Page 60 State of the Environment - Water Quality
Summary: Water Quality
Over the last twenty years there have been 11 studies examining water quality. Some of these have been one off “snapshots” while others have been over a period of a few years and still others are even longer term. Most of these investigations examine only physico-chemical aspects of water quality but four studies consider biological aspects (shown in Table 6). Much of the monitoring has taken place as a part of a larger sampling program for the Yarra Catchment, so the number of sites monitored in the Merri Catchment has been limited. As a result, there is a lack of data for tributaries of the Merri Creek. Edgars Creek has been the subject of some research but this amounts to, at most, two sites per study. Other tributaries receive no attention whatsoever.
Table 6 Overview of surveys examining water quality in the Merri Catchment. Study Type Date Location Type of # of parameter sites MMBW period Apr1971Mar.1984 Merri&Edgar physico-chemical 10 EPA longterm 1972-1981 Merri Creek physico-chemical 1,2 PIRG snapshot Dec. 1974-JanMerri Creek physico-chemical 13 1975 & biological Campbell period Nov. 1979-Ma Merri Creek physico-chemical 2 1980 & biological Mitchell & Clark snapshot March 1990 Merri &physico-chemical 12 Edgars & biological VWQMN longterm Jan. 1991- Merri Creek physico-chemical 2 Mitchell & Dunn snapshot 26-28October1992Merri&Edgar physico-chemical 10 Gaal period 1993-1994 Edwardes physico-chemical 1 Lake & biological Ellett & Kingsley snapshot 1994 Merri Creek physico-chemical 5 Roy snapshot April, August 199 Merri&Edgar physico-chemical 8,4 Melbourne Water snapshot Feb.-March 1995 Merri&Edgar biological 16
The Merri Creek
The studies of physico-chemical and biological parameters show broad changes down the length of the Merri Creek. These changes in water quality are indicative of changes in the surrounding land use over time and along the length of the waterways. In general, the level of alteration to the surrounding land reflects the level of degradation of the aquatic ecosystem, with the rural sections of the waterways being healthier than the industrial and urban sections. However, each broad land use has its own distinctive problems and these are described downstream along the creek. This is based on available monitoring information but it should be noted that other polluting substances such as surfactants, pesticides, petroleum products are potential problems based on current catchment activities, but they have not been recorded. The quality of the water is, in most cases, measured against SEPP guidelines, however where these standards are inadequate other more relevant guidelines are used (eg. ANZECC and Ontario guidelines).
Page 61 Waterways of the Merri Catchment
The rural section The main problem in the rural sector (ie from the headwaters to Craigieburn) is nutrient (and suspended solids) levels, the main source of which is runoff from agricultural land. Concentrations of nutrients measured occasionally fail the ANZECC guideline objectives.
Heavy metals are not generally a problem in this segment. However two recent studies have noted high levels (one of 27 ppm in sediments) of arsenic from Summerhill Road to Craigieburn (maybe from pesticides). Currently there are no objectives set for heavy metals in sediments. All studies of macroinvertebrate communities reveal good diversity and abundance indicative of fairly low pollution levels.
The industrial section Water declines in quality after the creek enters the industrial zone (from Craigieburn to Mahoneys Road). Poor water quality is evident in all studies of macroinvertebrates. Populations of these organisms experience a major decline between O’Herns and Mahoneys roads.
The upper portion of this section is dominated by treated effluent discharges from the Craigieburn Sewage Treatment Plant. Invariably the high concentrations of nutrients measured downstream of Craigieburn fail the ANZECC guideline objectives. Of particular concern is the jump in levels of reactive phosphorus at Craigieburn (up two orders of magnitude). More recent surveys show that suspended solids also have high levels from Craigieburn to O’Herns Road. Although the lack of data makes comparison difficult, results suggest levels exceed the SEPP objectives. Nutrient levels, after decreasing downstream of Craigieburn, rise again just below Cooper Street before again decreasing downstream.
A number of studies point out that heavy metals in the water column and in stream sediments increase markedly upon reaching the industrialised region. This is recognised as a potentially serious threat to the aquatic life of the creek. Of the two forms of contamination, it is thought that those in the sediments may offer the best means of gaining a long-term account of the importance of heavy metals in the creek.
The three studies that have tested the sediments show that concentrations of copper, lead and zinc (and to a lesser extent cadmium and chromium) increase by at least one order of magnitude around Barry Road in Campbellfield. These high levels decrease slightly on progression downstream but not very significantly. Inputs of heavy metals to stream sediments may be from historical effluent prior to sewer connection of this area, as well as the continued diffuse inputs from catchment activities via stormwater drains.
The residential section Some indicators show that the water quality improves in some parts of the residential area (downstream of Mahoneys Road), but generally it deteriorates further. Studies show that the macroinvertebrate community recovers downstream of Mahoneys Road indicating a slight improvement in overall water quality.
Nutrient levels (although they do not return to their pre-Craigieburn levels), salinity and suspended solids show some improvement. Heavy metals, on the other hand, generally maintain their high levels in sediments. Litter levels increase markedly downstream through
Page 62 State of the Environment - Water Quality the urban area. Dissolved oxygen levels display a deterioration downstream and are close to the limits below which aquatic fauna may not survive. This could be a result of organic pollution and high levels of algae.
Edgars Creek
Edgars Creek is the only other creek in the catchment that is monitored, and there have been a limited number of monitoring sites. The available data show that it generally shares the same problems as the Merri Creek, however it differs in some respects.
Levels of turbidity are generally lower in Edgars Creek as are levels of suspended solids and salinity. Nutrients do not display a consistent pattern downstream, but lower than the Merri Creek. Heavy metals are generally lower than those of the Merri Creek, however Mitchell & Dunn (1993) found the highest levels of metals in sediments for their whole study were on Edgars Creek at Mahoneys Road. Their study of heavy metals in the water column did not display these high levels. On a positive note, levels of dissolved oxygen are well in excess of those recommended by the SEPP and appear to have improved from 1990 (Mitchell & Clark, 1991) to 1992 (Mitchell & Dunn, 1993).
Conclusions
The water quality in the Merri Creek and Edgars Creek generally declines downstream along the waterways. Much of this decline is associated with changes in the surrounding landuse, from rural to urban. However, each landuse has its own particular problem.
In agricultural areas, high nutrient levels are a problem. From the industrial region, there is a rise in heavy metal pollution. The main problems in the urban area are the result of inadequate sewage disposal and diffuse source pollution via the stormwater drainage system.
Page 63 Waterways of the Merri Catchment
Page 64 State of the Environment - Water Quality
4. Water Quality
4.1 Introduction
The quality of the water in which plants and animals live is of vital importance for their survival. Therefore it is important to consider water quality when assessing aquatic ecosystem health. A number of key indicators, such as dissolved oxygen or suspended solids, have traditionally been used to determine water quality. This section assesses past and present water quality based on the information available on various water quality indicators. This section then examines the polluting sources, both diffuse and point, to enable appropriate management of the degradation.
4.1.1 Previous Work
This section is a review of the state of water quality based on a number of studies. It attempts to draw together all of the relevant pieces of work into one coherent document. What follows is a brief description of the scope of the important research efforts. The outline below highlights the great amount of information about water quality so one of the tasks of this section is to underline the most important aspects and the areas where the research fails in its efforts to pin-point the nature of the problem. The following list shows how water quality monitoring has moved away from using purely physico-chemical assessments to using biological monitoring as well.
The Public Interest Research Group (1975) study of December 1974 through to January 1975. This group sampled 10 sites along the Merri Creek from Craigieburn to Clifton Hill. They analysed the water for Biological Oxygen Demand (BOD), Dissolved Oxygen (DO) and acidity (as pH). They also collected aquatic fauna at 13 sites (see Section 5).
Environment Protection Authority (EPA, 1975, 1981, 1982, 1983a) long-term study from 1972 to 1981. These surveys sampled the Merri Creek at Heidelberg Road and Roseneath Street (1972-1974), Roseneath Street (1974-1975), Roseneath Street and St Georges Road (1976-1978), numerous sites on the Merri Creek and a number of tributaries (May-July 1977; May 1979-April 1981). Physico-chemical parameters measured include turbidity, suspended solids, pH, E. coli, heavy metals in the water (copper, zinc), DO, salinity (Total Dissolved Solids-TDS) and nutrients.
The Ministry of Conservation (Campbell, et al., 1982) study from November 1979 to October 1980. This group measured BOD, DO, nutrients, heavy metals (lead, zinc, copper, chromium and mercury) and benthic macroinvertebrates at two sites (Summerhill Road and Heidelberg Road) on the Merri Creek as part of a Yarra Catchment-wide project.
Melbourne & Metropolitan Board of Works (unpublished) study from April 1971 to March 1984. This agency conducted a six-site survey on the Merri Creek (simultaneously with the EPA) between Craigieburn and St Georges roads, on Edgars Creek at Boyne and Leamington streets and Mahoneys Road and at Merlynston Main Drain. Sample analysis was for nutrients (total phosphorus and nitrogen, orthophosphate and nitrate),
Page 65 Waterways of the Merri Catchment
Mitchell & Clark (1991) study in March 1990. This report is based on physico-chemical and biological monitoring from 10 sites on the Merri Creek between Beveridge and Heidelberg roads and on Edgars Creek at Broadhurst Avenue and Leamington Street. Samples were analysed for temperature, pH, salinity (Electrical Conductivity-E.C.), DO, BOD, suspended solids, nutrients (oxidised nitrogen, total kjeldahl nitrogen and reactive and total phosphorus), E. coli, heavy metals in water (arsenic, cadmium, chromium, copper, zinc, iron, lead, manganese and nickel), heavy metals in sediment (cadmium, chromium, copper, zinc, iron and lead) and surfactants. Macroinvertebrates and diatoms were the biological parameters measured.
Mitchell & Dunn (1993) study in October 1992. This survey over three weeks was carried out at eight sites on the Merri Creek (between Summerhill Road and Broadhurst Ave) and two sites on Edgars Creek (at Mahoneys Road and upstream of the Merri Creek confluence). Parameters measured include turbidity, suspended solids, nutrients (oxidised nitrogen, kjeldahl total nitrogen and reactive and total phosphorus), DO, pH, E.C. and heavy metals in water and sediment (arsenic, cadmium, chromium, copper, zinc and lead).
Victorian Water Quality Monitoring Network (Hunter & Zampatti, 1994a, 1994b) study since January 1991. This study measures physico-chemical aspects at two sites on the Merri Creek (Cooper Street and Roseneath St). Monitoring at Cooper Street recently stopped. They are measuring parameters such as temperature, pH, E.C., DO, turbidity, suspended solids and nutrients (oxidised nitrogen, total kjeldahl nitrogen and reactive and total phosphorus).
Gaal (1994) study of Edwardes Lake during 1993 and 1994. This study examined the physico-chemical parameters of Edwardes Lake such as turbidity and nutrients (total nitrogen and total phosphorus). Macroinvertebrates were the biological parameters measured.
Ellett & Kingsley (1994) study of 1994. This study examined the chemistry of a number of drains entering the Merri Creek between Barry and Mahoneys roads. Five sites were sampled and measurements taken for velocity, temperature, pH, E.C., total suspended solids, TDS, DO, chemical oxygen demand (COD), metals (chromium, zinc, copper, manganese iron) and nutrients.
Melbourne Water (unpublished) study from February to March 1995. This study, conducted in conjunction with a survey of Platypus numbers, sampled 15 locations on the Merri Creek and two on Edgars Creek (one site doubled up) for macroinvertebrates.
Victorian Water Quality Monitoring Network (VWQMN), 1995. Victorian Water Quality Monitoring Network Database, Water EcoScience. While not a study, water quality data for the Merri Creek from the VWQMN database has been analysed for use in this section.
Roy (1996) study in April and August 1995. This study assessed the level of heavy metals in sediments of Merri and Edgars creeks. In April, eight sites on the Merri Creek from Summerhill Road to Rushall Station along with one at Edgars Creek below the Epping Trade Waste disposal site were studied in the first stage. The second stage in August reduced the
Page 66 State of the Environment - Water Quality number of sites to four (all on the Merri Creek). Metals analysed include arsenic, chromium, cadmium, copper, lead, zinc, nickel and mercury. Selenium was added to the list for the second stage. Other parameters measured include DO, E.C., pH and temperature.
4.1.2 Scope of this section
This section seeks to establish the current state of knowledge of water quality of streams in the Merri Catchment. It reviews previous work in which physico-chemical and biological parameters were monitored and assessed in an attempt to determine what state the creek system is in, while being aware of the limitations of this information. It also includes results from specific studies undertaken for this report, to assess heavy metal contamination in creek sediments and the impact of landfill leachate on the Merri Creek.
4.2 ‘Natural’ states
To understand the level of degradation or the level of health of the aquatic environment of the Merri Creek, it is important to try to determine the 'natural’ state of the Merri Creek before human interference.
However, this is not an easy task. Much of the Merri Catchment lies in the Volcanic Plains Grasslands. This is prime grazing land and has been utilised from the earliest days of settlement. This land was so quickly and thoroughly used, that in 1916 it was written of the plains, north and west of Melbourne that '...it has been put so thoroughly to pastoral and agricultural uses that hardly any part now remains in the virgin state' (OCE, 1988). These settlers did not make many detailed accounts of the early state of this environment. If there were any records, they do not remain today.
As a result of such activities, it is difficult to determine the natural water quality of the Merri Creek. High levels of salinity in the Merri Creek may be a result of the clearing of vegetation within the catchment, or may be naturally high due to mineral deposits or a natural lack of vegetation with deep root systems. Determining the natural degree of vegetation cover in the area is also difficult. Since the catchment is part of the west Victorian Volcanic Plains morphology (Jenkin, 1988), it is likely that the degree of tree cover to begin with was small. In addition, aboriginal hunters may have played some part in the clearing of forest cover to open up areas for more accessible hunting. The extent of management undertaken by the aboriginal people before European settlement is often overlooked, especially when trying to predict so-called 'natural’ states.
Determining baseline levels of heavy metals in the sediments is also difficult to determine. It is possible that these baseline levels may be quite naturally high due to the large amount of volcanic activity in the region. An indication of background levels based on the Rock Shale Standard is in given in Appendix 7.
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4.3 Water quality parameters as indicators of stream health Traditionally, a number of physical, chemical and biological indicators are used to monitor the health of streams. These indicators are the basis of the monitoring programs beginning in the 1970s to ascertain the condition of the Merri Creek. The following section outlines these, and the reasons for using each as an indicator of stream health.
Box 9 Water Quality Indicators
One of the main means of measuring the health of aquatic ecosystems is the use of water quality indicators. These indicators may be divided into two broad categories, key indicators and secondary indicators.
Key indicators are most sensitive indicators for providing information on aquatic ecosystem health These include:
• Physical & chemical indicators • Biological indicators
Secondary indicators provide information relating to human activities which impact on the environment and provide clues to the state of the environment if key indicators are absent. Examples of secondary indicators include such things as:
• Indigenous vegetation cover • Land use • Sewage & waste discharges.
4.4 Existing states
A number of studies have analysed the water quality of the Merri Creek since the 1970s (outlined above), using physical, chemical and biological parameters. A brief summary of their specific aims and results is provided in Appendix 4. The following section is an overview of the state of the water quality in the Merri Creek.
4.4.1 Physical and chemical parameters
Physical and chemical tests are highly specific measurements of water quality. Their purpose is to determine the health of a stream based on the quantitative or qualitative measurement of a specific physical or chemical parameter of the water. For example, it is possible to measure the level of dissolved oxygen in the water, and use that information to determine if aquatic fauna can survive in the stream. Dissolved oxygen is essential for the for the respiration of aquatic organisms. If levels of dissolved oxygen are low, more sensitive species will not be able to survive and aquatic biodiversity will be diminished.
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Table 7 summarises the main purposes behind the use of a number of physical and chemical parameters that have been monitored in the Merri Catchment. However, there are limitations in their use, which has prompted the recent introduction of biological indicators. Table 13 evaluates the performance of the Merri Creek with respect to pollution issues against EPA State Environment Protection Policy guidelines.
Turbidity
Turbidity in the Merri Creek has been a consistent problem over the monitoring period. The Public Interest Research Group (PIRG, 1975) study noted high level of turbidity in 1974, as did the EPA 1974-75 study. More recently, data from the Victorian Water Quality Monitoring Network from 1992 to 1994 also recorded intermittently high levels. While turbidity levels are not always high, there are periods (often associated with high flow) when turbidity exceeds the level recommended by the EPA State Environment Protection Policy (SEPP). Mitchell & Dunn (1993) noted that turbidity increases downstream along the Merri Creek and is generally higher in the Merri Creek than in Edgars Creek.
A water quality study of Edwardes Lake (Gaal, 1994) found that the levels of turbidity in the lake may also be high from time to time. With the reduction of stream flow as Edgars Creek enters Edwardes Lake, the lake is acting as a sink for the fine suspended particles and is gradually becoming shallower requiring periodic dredging. An artificial wetland is being constructed directly upstream of the lake to act as a silt and litter trap. This will improve the water quality of Edwardes Lake for recreational activities.
Suspended Solids
Like turbidity, suspended solids have consistently been a problem in the Merri Catchment. EPA data from 1974-75 noted high levels of suspended solids, as did the data from 1976-78. This later report noted that there were significant peak loads during high flows, but that levels had decreased since the earlier study (EPA; 1975, 1982). This corresponded with the connection to sewer of previously unsewered areas. Mitchell & Clark (1991) noted increased suspended solid levels downstream of the Craigieburn Sewage Treatment Plant and again between Mahoneys Road and Broadhurst Avenue. This indicates that the sewage treatment plant and urban stormwater are causing an increase in suspended solids in the creek. The VWQMN data from Campbellfield and Fitzroy North from 1992-1995 indicated that levels of suspended solids are intermittently high in the creek, with the upstream site being in excess of the SEPP 90th percentile level.
Temperature
Based on recent cumulative water quality data from the Victorian Water Quality Monitoring Network, the temperature of the Merri Creek fluctuates seasonally from a minimum of about 8OC to a maximum of 24OC with a mean of 15.6OC at St Georges Road in Fitzroy and 5OC to 22OC with a mean of 13.5OC at Coopers Street in Somerton. Fluctuation may occur as a result of natural conditions or events such as the amount of shade or the climate. The major anthropogenic effect on water quality is likely to be from discharges of industrial cooling water or urban stormwater. The temperature of the water will have some effect on the suitability of the creek for certain aquatic fauna and flora. Temperature also affects other parameters. For example, cooler water is able to hold more dissolved oxygen, whereas
Page 69 Waterways of the Merri Catchment warmer water will increase the metabolic activity of certain aquatic organisms such as bacteria and algae, which in turn may affect levels of dissolved oxygen.
Salinity (Electrical Conductivity)
Salinity levels in the Merri Creek have generally been high. It is uncertain if these high levels are natural to some extent, or the result of anthropogenic impacts. Based on measurements of total dissolved solids, the EPA report noted significant salinity in the Merri Creek in 1976-78, and occasional failure to comply with the EPA SEPP in the 1979-81 data. More recently, the Victorian Water Quality Monitoring Network data (Hunter & Zampatti, 1994a; VWQMN, 1995) showed levels of salinity that often exceeded the EPA SEPP, particularly at Campbellfield where more of the flow originates from the groundwater. Mitchell & Dunn (1993) reported an increase in salinity downstream along the Merri Creek with highest levels between Barry Road and Mahoneys Road, and higher levels in the Merri Creek than in Edgars Creek.
Litter
According to community consultation, litter is one of the most serious problems facing the Merri Creek (Jan Bruce & Assoc. Pty Ltd, 1993). For aesthetic reasons, litter is one factor that may limit peoples' appreciation of the creek corridor and ultimately their level of commitment to its preservation and restoration.
An EPA report from 1979-1981 (EPA, 1981), noted that the Merri Creek fails to meet the EPA SEPP draft guidelines for litter.
A 1987 study "Litter Control in Urban Waterways" carried out a quantitative study of the litter problem in the Merri Creek, and is believed to be the first study of its type in Australia. It involved the identification of litter types and sources, assessment of a variety of simple litter trap devices and the development of recommendations arising from these investigations and associated recommendations. An analysis of the litter caught in the traps classified 66% as general plastics. Further classification of the trapped litter into 56 categories found that 59% of this litter was made up of 5 types of item; plastic bags, plastic sheeting and film, plastic confectionery and crisp wrappers, take away food containers and free distribution items. This study produced eleven recommendations and an action plan. While a number of the actions have been implemented, litter in the Merri Creek is still a major problem.
The Water Quality Concept Plan (Mitchell & Dunn, 1993) again noted that the Merri Creek "would be likely to fail the 'no visible floating matter' criteria for floatable matter". The great amount of litter remaining caught on riparian vegetation during periods of high flow is a problem that needs addressing, if creek restoration is to be realised.
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Table 7 Water Quality Parameters as Indicators a. Physical Parameters Parameter Indicator of Potential impact Possible cause
Suspended Plant Matter, sand, May smother benthic • Catchment erosion; Solids silt and clay. Is a organisms, plants, & • Inappropriate land measurement of fish, habitat, eggs, & use coupled with concentration or respiration. A inadequate stream- load, and doesn’t transport medium for side vegetation. indicate ‘cloudiness’. phosphorus and heavy metals. Turbidity Water ‘cloudiness’, Reduces light As above indicating the penetration & limits presence of photosynthesis. This suspended or limits animal food colloidal matter sources. Temperature Temperature Fauna and flora have • Seasonal fluctuations specific temperature fluctuations; tolerances. May • Stormwater; effect other • Industrial waste; parameters. eg • Sewage effluent. dissolved oxygen. Electrical Salinity Important • Clearing of trees; Conductivity determinant of fauna • Irrigation. and flora distribution. b. Chemical Parameters Parameter Indicator of: Potential impact Possible cause
Phosphorus Nutrients; Promotion of • Pastures of N-fixing Nitrogen Algal growth. excessive plant legumes; growth, leading to: • Fertilisers; • toxic algal • Treated sewage; blooms, making • Plant debris. water unsafe for human and animal consumption • alteration of the macroinvertebrate community structure. pH Acidity/alkalinity May alter toxicity of • Alkalinity-HCO3, other pollutants. ammonia (natural); eg acidity increases • Acid rain. metal toxicity
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E. coli Faecal Restrict use of water • Sewerage leaks and contamination; for recreation, due to overflows; Human pathogens. health risks. Increase • Diffuse source BOD and are harmful inputs of animal to aquatic life faeces. Biological oxygen required by Affects levels of • See causes for Oxygen biological processes dissolved oxygen nutrients and E. Demand (BOD) in water coli.
Heavy Metals Lead, zinc, copper, Occurs naturally but • Mining; arsenic, cadmium, high levels from • Industrial waste; chromium, mercury, human activities • Urban runoff; etc. accumulate over time • Sewage effluent. and are toxic to human and aquatic life Toxicant Summation of effects Toxicants present As above. Mixture Ratio of various toxicants together often have additive toxic effects
Dissolved Oxygen
Levels of dissolved oxygen in the creek are an area of possible concern. While recorded levels have generally been within the EPA SEPP recommended levels, there is some indication that this may not always be the case. Dissolved oxygen levels fluctuate throughout the day, with highest levels usually occurring in the afternoon and lowest levels occurring at night. Assuming that monitoring usually occurs during daylight hours, actual levels may fall below acceptable levels at night and therefore may not be sufficient for fish survival.
The PIRG study noted extremely low dissolved oxygen levels in the creek at Mahoneys Road in 1974. The EPA study from 1976-1978 (EPA 1982) recorded high levels in summer, indicating excessive algal photosynthesis. This indicates potentially low DO levels at night (when photosynthesis stops and algal respiration starts). Recently, Ellett & Kingsley (1994) noted occasionally low levels of dissolved oxygen in the creek at Campbellfield.
Edwardes Lake has levels of dissolved oxygen below SEPP recommended values, especially below a depth of 1.5 metres (Gaal, 1994). This is probably due to the low levels of oxygen in the water feeding the lake from Edgars Creek, and a high oxygen demand due to the lake's organic sediments and algal activity.
Nutrients
A high level of nutrients in the Merri Catchment is likely to be one of the most serious problems facing the aquatic health of the creek. The PIRG study in 1974 noted eutrophication at Craigieburn Road East. The EPA data consistently recorded high levels of nutrients in the creek. The 1976-1978 EPA study noted significant levels of nutrients, with high levels of phosphorus associated with the Somerset Road drain. For the 1979-1981 EPA
Page 72 State of the Environment - Water Quality study, the Merri Creek failed to comply with the EPA draft SEPP for phosphorus, nitrogen and macrophyte growth levels. More recently, Mitchell & Clark (1991) noted high levels of nutrients at all sites, both from chemical measurements and according to biological indicators (diatoms). Mitchell & Dunn (1993) indicated that the Craigieburn Sewage Treatment Plant was an important source of nutrient pollution of the Merri Creek, but that levels 'assimilated' to some degree further downstream. Levels again increased downstream of Ainslie Road drain and Central Creek, indicating these as potential sources. A study on levels of pollution in urban stormwater (Weeks, 1982) indicates that stormwater is a significant source of nutrient pollution. Ellett & Kingsley (1994) recorded high phosphorus levels, but noted a slight improvement since the 1990 data. However, care must be taken when making such comparisons given the different sampling times, techniques and sites. VWQMN data from the period 1992-1994 (Hunter & Zampatti, 1994a) indicated that total phosphorus levels at both the upstream and downstream sites, exceeded the Australian Water Quality Guidelines and the quantitative levels outlined in the new draft SEPP for the Yarra Catchment on all occasions. Likewise, the levels of nitrates from the upstream site (Campbellfield) exceed the new SEPP levels set for total nitrogen for 50% of the samples, whereas the downstream site (North Fitzroy) exceeds these levels on one occasion.
Toxic algal blooms are recognised as a problem in Edwardes Lake. In summer, the high nutrient levels and the right temperature and flow conditions provide favourable conditions for algal growth. The levels of total phosphorus and total nitrogen measured in a 1993/1994 study (Gaal, 1994) often were close to or exceeded the values at which eutrophication may be expected to occur. While drains within the lake are a source of nutrients, the major input appeared to be from Edgars Creek. High phosphorus levels were also recorded in the Lake sediments and may also be a potential source of nutrients to aquatic plants and algae. pH
Most studies of the Merri Creek have noted that the pH of the water is neutral to basic, and generally within the EPA SEPP acceptable levels. EPA data from 1973-1974 (EPA 1975) recorded pH levels of 5.0 (acidic) in June and July 1973, outside the now acceptable SEPP range of 5.5 - 9.5, and noted that pH levels were occasionally unacceptable. Mitchell & Dunn (1993) noted a pH of 9.3 (basic) in Edgars Creek in 1992, a level just within the EPA’s upper limit of 9.5. Acidity is an important factor affecting the mobility of heavy metals in stream sediments and changes to the pH could release contaminants into the water column.
BOD
BOD was not measured in all the monitoring studies in the Merri Catchment. The PIRG report recorded BOD levels in 1974 and recorded high levels at Craigieburn and very high levels at Mahoneys Road. At this time, the creek passed through several unsewered areas, and organic pollution (and therefore oxygen demanding substances) within the creek was high. The EPA data from 1976-1978 noted high levels of BOD from the Somerset Road drain, but also noted that levels of E. coli were acceptable. Recent reports (Mitchell & Dunn, 1993) note that organic pollution in the creek has decreased to some extent since the 1970s, possibly due to most of the catchment being connected to sewer. However, the problem still exists.
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Heavy Metals
Heavy metal contamination has been the subject of a detailed study as a part of this report. This section is therefore more detailed than for the other indicators of water quality.
Background: Heavy metals occur naturally in the environment, but high levels resulting from human activities are toxic to aquatic life. Monitoring heavy metals in the water may detect recent pollution events, but if sampling does not take place soon after the time of the polluting event, these high levels may not be detected. Heavy metals bind to fine particulate matter in the water and settle to the bottom of the stream, becoming incorporated in the stream sediment. Monitoring stream sediments therefore gives a more long term view of the levels of heavy metal pollution in the creek
Once bound in the stream sediments, the heavy metal contaminants may become less available to impact on aquatic life. However, there is a threat that these toxic metals may still have the potential to impact on the aquatic ecosystem by remobilisation into the water column in a number of physical, chemical and biological processes.
Metals in the water column: A number of surveys have recorded high levels of heavy metals in the waters of the Merri Creek. EPA data from 1979-1981 (EPA, 1981) noted that there was poor compliance with the toxicant mixture ratio (a measure of the cumulative effect of several heavy metals and other toxic pollutants), and high levels of zinc and copper. Campbell (1982) recorded high levels of lead, zinc, copper, chromium and mercury. More recently, Mitchell & Clark (1991) recorded high levels of arsenic, chromium, iron and zinc in the waters of the Merri Creek. Arsenic levels were much higher than had previously been recorded. Mitchell & Dunn (1993) noted high levels of chromium and zinc in the water column on the one sampling occasion.
Metals in sediment (past studies): Toxic heavy metal pollution of the sediments of the Merri Creek and Edgars Creek has only recently been recognised as a serious threat to the aquatic health of these waterways (Mitchell & Clark, 1991). Measurements of heavy metal contamination of the sediments of the Merri Creek undertaken by Mitchell & Clark (1991) noted a large increase in the level of heavy metals between O'Herns Road and Barry Road, at the point where the creek enters the industrial area. Levels of cadmium, zinc and copper increased seven to eightfold, whereas lead increased by a factor of twenty-six. The 1991 report noted that this increase in the level of heavy metals coincided with the major decline in the abundance and diversity of the macroinvertebrate community and concluded that the heavy metal contamination was having a substantial impact. Mitchell & Dunn (1993) noted high levels of arsenic in sediments in the rural segment at Summerhill Road, and high levels of copper, lead and zinc further downstream in an industrial area. This 1992 study also recorded moderate to high levels of heavy metal contamination in Edwardes Lake for copper, lead, zinc and chromium. Due to the higher levels recorded upstream of this lake, it appears that Edwardes Lake is acting as a sink for heavy metal pollution of Edgars Creek.
Metals in sediment (1995 study): To further investigate the impact of heavy metal contamination on the aquatic health of the Merri Creek, some sediment sampling was undertaken in April and August 1995 the results of which are included as part of this report (c.f. Roy, 1996). The aim of this research was to identify the nature of the metal-sediment interactions in the Merri Creek in order to predict the potential availability of the heavy
Page 74 State of the Environment - Water Quality metals to act as contaminants. The information in past studies has only given information on the total concentration of metal contaminants in sediments, which is usually an over- prediction of the availability of the contaminant. This study identified the relative association of the contaminant heavy metals to different phases of the creek sediments, thereby giving some indication of their bio-availability and the factors most likely to cause remobilisation of the heavy metal contaminants to the water column. The creek sediments are described in terms of the type association that binds the metals to the sedimentary particules. Four different phases are found; organic, exchangeable, reducible and residual.
This research consisted of three stages; the first of which involved an analysis of the total heavy metal concentrations in sediments at seven sites on the Merri Creek and one site on Edgars Creek. The second stage involved an analysis of the partitioning of heavy metals within different phases of sediment whilst the third stage examined one element in order to develop a model that broadly predicts the heavy metal availability in the Merri Creek.
The findings of this study agreed with those of Mitchell & Dunn (1993), showing that metal concentrations generally increase downstream along the Merri Creek, with major increases in concentrations being recorded at Barry Road (site APR4, Map 6), the results of which are listed in Appendix 5. A comparison of heavy metal concentrations at each site along the Merri Creek is presented in Figure 2.
At present there are no Australian criteria to determine the acceptable levels of heavy metals in the stream sediments to protect environmental values, hence it is difficult to assess the importance of this contamination. A number of Australian sediment assessment studies (including Sinclair Knight & Partners, 1991; Mitchell & Dunn, 1993) have used the Ontario Limit of Tolerance Levels as the comparison levels. The Ontario sediment guidelines are listed in Appendix 6 along with the levels indicated in Figure 2 (when Ontario levels are exceeded) as a means of assessing the severity of heavy metal contamination of the Merri Creek sediments.
While it is understood that these guidelines may not be directly applicable to Australian conditions, they are well in excess of the levels set in the other existing criteria listed in Appendix 6 and are, therefore, probably a fair estimate of levels at which serious impacts on ecosystem health may occur. Of course, it is possible that these metals may affect ecosystem health at far lower levels than this, and caution must be used in managing toxic contaminants.
Results from the April 1995 study add further support to the data collected previously and show the consistently high level of the heavy metal contamination of the streambed sediments over a number of years. The metals with high concentrations in this study are the same as those of the previous studies and the recorded levels are similar. Copper, lead, zinc, and to a lesser extent, chromium, are consistently high in all studies of metal contamination in the sediments of the Merri Creek. The contamination in Edgars Creek is less consistent but very little monitoring has been done there, so it is difficult to make such comparisons. Insufficient information exists to determine trends in heavy metal levels from recent studies. A long term monitoring program with consistent sites and methods will be required if this is to be known.
Of particular interest in the April 1995 study is the high levels of mercury in the creek sediments, in particular at Barry Road (Site APR4) and Broadhurst Avenue (Site APR5).
Page 75 Waterways of the Merri Catchment
Map 6 Sediment sampling sites 1995 heavy metal study.
Page 76 State of the Environment - Water Quality
Results from the sequential extraction analyses in August 1995 also noted high levels of mercury at Barry Road but levels at all other sites were below detection limits. The levels of mercury recorded at Barry Road in April and August were 2.9 and 18.3 mg/kg respectively. These are very much higher than the Ontario ‘severe effect’ level of 1.7 mg/kg. Barry Road was the site of severe increase in the levels of heavy metal contamination indicated in the 1990 and 1992 studies but neither of these studies analysed the sediments for mercury concentrations. The 1982 EPA study of the Merri Creek (along with other studies of urban waterways in Melbourne) indicated that mercury pollution was not a problem in these type of streams and so it was not monitored in the 1990 and 1992 studies (Mitchell P., pers. comm.). A more recent polluting event may be contributing to these high levels recorded by Roy (1996).
The second stage of the 1995 study involved a sequential extraction of the metals from the sediments sampled from four sites on the Merri Creek (Map 6). The sequential extraction technique gives some further insight into the bioavailability of the metal contaminants by using the sequential addition of specific reagents which are designed to selectively remove the metals bound to the different phases of the sediment. Each reagent theoretically removes metals from each of the sediment phases based on the type and strength of the interaction. The operationally-defined phases are exchangeable, reducible, organic and the tightly bound residual metal. The exchangeable phase represents those metals that are loosely bound to the sediment and in equilibrium with the water column. Changes in the concentration of metals in the water column will therefore affect the amount of uptake or remobilisation of metals from this phase. The reducible and organic phases of the sediment are approximately equal in their ability to bind heavy metals, but the strength of binding differs under varying environmental conditions. The metals associated with the reducible phase are most likely to be released if the redox potential is significantly reduced, such as when the dissolved oxygen content of the water/sediment is lowered to approximately <1mg/l. The metals associated with the organic phase are most likely to be released if the pH of the system is reduced. The metal bound in the residual phase are highly stable and unlikely to be remobilised under any environmental conditions likely to occur in the Merri Creek.
Sequential extraction results from the four sites sampled on the Merri Creek in August 1995 indicate that a number of the metals have considerable potential to be remobilised These results are listed in Appendix 8 and presented graphically in Appendix 9. The results for each element found in high concentrations in Merri Creek sediments (chromium, copper, lead, mercury and zinc) are discussed in detail below.
Chromium:The distribution of chromium was similar in the sediments from all four sites sampled. Approximately 50-70% was associated with the residual phase, 20-30% with the organic phase, and very little chromium associated with the exchangeable and reducible phases. Total chromium concentrations are fairly high in the Merri Creek sediments, and were above the Ontario ‘severe effect’ level in the 1992 study.
Copper: High levels of copper have been found in Merri Creek sediments in all studies. At the highly contaminated sites at Barry Road (AUG3) and Rushall Station (AUG4), there is an increase in the proportion of copper associated with the reducible and exchangeable phases compared to the less contaminated sites (AUG1, AUG2). Barry Road sediments had a total concentration of 135 mg/kg and 150 mg/kg recorded in August 1995 and April 1995 studies respectively. While the spatial variation in the sampling point may mean that these values are not significantly different, they both exceed the Ontario ‘severe
Page 77 Waterways of the Merri Catchment
Figure 2 Concentration of metal in sediments downstream along Merri Creek (April 1995)
8
( indicates Ontario 'severe' effect level)
7
Sum m erhill R oad (APR1)
6
O'Herns R oad (APR2)
5
C ooper Street (APR3)
4 Barry R oad (APR4)
Broadhurst Ave (APR5)
3
Coburg Lake (APR6)
Concentration (mg/
2 1.7
Rushall Station (APR7)
1
0 ArsenicCadmium M ercury
Sam ple site
350
( indicates Ontario 'severe effect' level )
300
Summerhill Road (APR1)
/
250 O'Herns Road (APR2)
210
Cooper Street (APR3)
200
Barry Road (APR4)
150
Broadhurst Ave (APR5)
110
Concentration (mg 100 Coburg Lake (APR6)
75
Rushall Station (APR7)
50
0 Chromium Copper Lead N ickel Sam ple site
1800 ( indicates Ontario 'severe effect' level )
1600
1400 Sum m erhill R oad (APR1)
1200 O'Herns R oad (APR2)
C ooper Street (APR3)
1000
Barry R oad (APR4)
820 mg/kg
800
Broadhurst Ave (APR5)
600 C oburg Lake (APR6)
Concentration (mg/
400 Rushall Station (APR7)
200
0 Zinc Sam ple site
Page 78 State of the Environment - Water Quality effect’ level of 110 mg/kg. At Barry Road, approximately 25% is associated with the exchangeable phase, 10% with the reducible phase, 35% with the organic phase and 30% with the residual phase. Further downstream at the Rushall station site there is a decrease in the total concentration to 130 mg/kg and 91 mg/kg recorded in August 1995 and April 1995 respectively. These are still in excess of or close to the Ontario limit but there is a decrease to approximately 5% and 10% associated with the exchangeable and reducible phases, and an increase to 50% associated with the organic phase. At these sites, a considerable amount (70%) of the total metal concentration is in a form (exchangeable, reducible and organic) which has the potential to be remobilised from the sediment. Waterway management agencies should ensure that the conditions which could cause this release, such as increased acidity or low dissolved oxygen levels in the water/sediment, are limited.
Mercury: Only Barry Road recorded concentrations above the analytical detection limits and is, therefore, the only site that can be realistically discussed. At Barry Road, total concentrations of 2.9 mg/kg and 12 mg/kg were recorded in April and August 1995 respectively, which exceed the Ontario guidelines of 1.7 mg/kg. Most of the mercury in this sediment is associated with the organic phase (approximately 70%) and residual phase (30%). Very little (<1%) of this element is associated with the exchangeable and reducible phases.
This high mercury level is of particular concern and needs to be investigated further. The behaviour of mercury in sediments is complex but it is known to bind effectively to sediment organic material rather than remain in the water column. The amount of mercury attached to organic sediment material increases with decreasing pH, whereas mercury associated with inorganic phases may be displaced by other cations at decreasing pH (Stein et al., 1995). Therefore, decreasing pH will increase the amount of mercury associated with the organics and decrease the amount associated with the inorganics. Methylmercury is the most biologically available and toxic form of mercury, and is formed in association with organic matter. While only a tiny percentage of mercury is methylated, a large proportion of this has been found in the biota (Stein et al., 1995). An analysis of the levels of mercury in the biota at Barry Road would provide some insight in to the impact of this metal on the aquatic biota in this region.
Lead: Lead contamination in the Merri Creek sediment was high, especially at the downstream sites. The distribution of lead was fairly similar at all four sites sampled. Approximately 20-30% is associated with the residual phase, 40% with the organic phase, 10-20 % with the reducible phase and <5% with the exchangeable phase. At the downstream, more polluted sites, more of the lead was associated with the reducible and exchangeable phases. This suggests that the more contaminated sediments have a higher proportion of lead in the fraction more easily mobilised to the water column, and hence have a greater bioavailablity.
Zinc: As with lead, zinc contamination in the Merri Creek sediment was high, especially at the downstream sites. There is a similar proportion of zinc associated with the residual phase (10%) and organic phase (5%) at all four sites sampled. Moving downstream, there is a progressive increase in total zinc levels in the sediments from 92 mg/kg at Summerhill Road (AUG1) to 1430 mg/kg at Rushall station (AUG4). Corresponding to this increase in zinc contamination is a progressive increase in the proportion of zinc associated with the exchangeable phase (from 25% to 40%) and a decrease in the proportion associated with the residual phase (from 35% to 10%) and is similar to the trend noted for lead. Levels of total zinc contamination in the August 1995 were also above the Ontario ‘severe effect’ limits. A large proportion of this contamination (40%) is associated with the easily
Page 79 Waterways of the Merri Catchment remobilised exchangeable phase. It could, therefore, be predicted that zinc in the Merri Creek sediment will be relatively easily remobilised, increasing its potential to affect the local biota. It will also be washed downstream over time, impacting on downstream aquatic communities. The Yarra River catchment (which includes the Merri catchment) carries an estimated 63 tonnes/year of zinc to Port Phillip Bay, and there is concern about the impact of this zinc on this almost enclosed marine environment (EPA, 1995).
The final stage of the project developed a predictive model to give more information on the association of zinc with the Merri Creek sediments sampled from Barry Road. Together with the results obtained from the sequential extraction technique, it was hoped that the results from the model would enable the prediction of the heavy metals availability within the aquatic environment of the Merri Creek. For more detail on the methods, refer to Roy, 1996.
The model results indicated that the Merri Creek sediments from Barry Road have three cation binding sites for metal adsorption but that their binding capacity is strongly influenced by pH. The graph representing the adsorption of zinc to the three sediment binding sites is presented in Appendix 10.
It is possible to draw some correlation between the information obtained from the model and the sequential extraction results. At pH 7.0, the model predicts that approximately 1300 - 1500 mg/kg of the zinc could be associated with the sediment under the experimental conditions adopted. In comparison, the sequential extraction of the Merri Creek sediment indicated that approximately 850 mg/kg (440 + 170 + 280 mg/kg) of zinc was associated with the sediment phases (exchangeable, reducible, organic) from which zinc could be expected to be remobilised by more acidic conditions. This suggests that the Barry Road sediment analysed in August 1995 has the capacity to adsorb almost twice as much zinc as it presently has associated with it.
By using the values obtained from the model, it would also be possible to predict the adsorption/desorption of zinc to the sediments from the water column at varying pH. This is an application of the predictive model that could be applied in future research to help determine the potential impact of the contaminated sediments in the Merri Creek.
Results from the 1995 research confirm that the levels of heavy metal contamination in the Merri Creek from the industrial zone to the confluence with the Yarra River are high and may be a significant cause of the decline in the macroinvertebrate species diversity and abundance. Metals of particular concern are copper, lead, mercury and zinc. Other water quality parameters, along with habitat, are also important for the maintenance of a rich aquatic fauna. This makes it is difficult to assess the degree to which heavy metal pollution is impacting on the aquatic ecosystem. However, while the sediments are acting as a storage site for heavy metal pollution, results indicate that most of the metals identified in the sediments of Merri Creek and Edgars Creek have the potential to be remobilised as a result of physical, chemical or biological changes in aquatic environment.
Surfactants
Measurements of surfactants in the Merri Catchment have not been recorded generally, however Mitchell & Clark (1991) noted that the levels of surfactants in the creek were above
Page 80 State of the Environment - Water Quality the threshold level, T, at all sites (T is used in the EPA SEPP to describe the level at which chronic sublethal effects on aquatic fauna may occur).
Other Toxicants The Guidelines for the protection of aquatic ecosystem (Appendix 11) indicate that there is a broad range of toxicants existing as a result of human activities that have the potential to impact on aquatic life. However, little monitoring has been undertaken to determine if these toxicants are present in the Merri Creek and its tributaries.
Catchment activities and circumstantial evidence suggest that several toxicants, such as hydrocarbons and pesticides, may exist in the waters and sediments of the Merri Creek. For example, the incomplete combustion of polyaromatic hydrocarbons (PAHs) in automobile engines releases these substances to the atmosphere, which is a significant route to the aquatic environment (ANZECC, 1992). PAHs may also reach the aquatic environment directly from crude oil and petroleum products. Oils can be seen on the surface of the water from time to time and physical disturbance of the sediments at a site such as Barry Road may release oil stored here to the water column. Stormwater drains continue to carry road runoff containing oils, petrol and heavy metals directly to the waterways, and there is little doubt that levels of these toxicants from this source are high, however, little work has been done to establish this.
Likewise, there has been no monitoring of the levels of pesticides in the waterways. Recent studies have shown the persistence of pesticides such as DDT and dieldrin in the waters of the rural Ovens and King rivers in northeast Victoria even though these chemicals were banned in 1987 (ANZECC, 1992). In 1991, Mitchell & Dunn (1993) recorded high levels of arsenic in the sediments of the Merri Creek in the agricultural area and noted that arsenic compounds are used as pesticides and in cattle and sheep dips. It may be that arsenic could be an indicator of pesticide use. Water and sediment monitoring are required to test the levels of these other toxicants.
4.4.2 Biological Parameters
Macroinvertebrates There has been relatively little use of macroinvertebrate sampling as a measure of biological indication of the health of the Merri Creek, however where it has been used it has been quite informative. The PIRG study undertook some biological monitoring in 1974 and noted a generally high diversity at the upper rural sites, before a large deterioration in the macroinvertebrate species abundance and diversity at Mahoneys Road. This species decline corresponded with a major deterioration in water quality as indicated by low dissolved oxygen, high BOD and eutrophication. The macroinvertebrate community recovered to some degree further downstream but never to the level before the creek entered the industrial and urban section.
Mitchell & Clark (1991) undertook a comprehensive macroinvertebrate study of the Merri Creek in 1990. Like the PIRG study, it noted a massive decline in the abundance and diversity of the macroinvertebrate community once the creek entered the industrial and urban section, with the major decline occurring between O'Herns Road and Barry Road. This corresponded with a measurable deterioration in water quality, especially with a significant increase in the level of heavy metal pollution within the water column and sediments.
Page 81 Waterways of the Merri Catchment
Downstream of Barry Road there was no apparent further decrease in the macroinvertebrate community that corresponded to further significant change in the water quality.
Sampling of the macroinvertebrates in Edgars Creek by Mitchell & Clark (1992) indicated that this creek was also in a poor condition but that its impact on the Merri Creek was minimal. Work to improve the aquatic ecosystem of the Merri Creek downstream of the confluence with Edgars Creek nonetheless requires improvement in the water quality of Edgars Creek as well as the middle sections of the Merri Creek.
Macroinvertebrates species recorded in Edwardes Lake by Gaal (1994) were generally pollution-tolerant forms able to survive conditions of high turbidity and low dissolved oxygen. Lower than expected numbers of chironomids and worms may be a reflection of the high levels of toxicants, such as heavy metals, in the sediments.
Diatoms
Mitchell & Clark (1991) also monitored benthic diatoms as a measure of water quality. This sampling, along with water quality sampling, indicated that the Merri Creek was neutral to basic, 'brackish' (with E.C. levels >1000 µS/cm), eutrophic throughout its length, and low- moderately organically polluted at the upper sites to moderately-highly organically polluted at the lower Merri Creek sites.
Page 82 State of the Environment - Water Quality
Box 10 Biological Indicators of Stream Health
Macroinvertebrates have often been used as biological indicators. Macroinvertebrates are a group of animals without backbones that can generally be viewed with the naked eye. The group includes insects, worms, snails, shrimps and water fleas to name a few. They are an important part of the food chain, feeding on plants and algae in the stream, and in turn being eaten by larger invertebrates. These larger invertebrates are food for fish, birds, Platypus, etc. (Melbourne Parks & Waterways, 1994). They are useful biological indicators because they live in the water for up to a year and can not easily escape pollution (as fish can). Different species also show a variation in their tolerance to pollution such that the relative abundance and diversity of species present points to the level of pollution.
Table 8 lists the macroinvertebrate groups and their level of tolerance to organic pollution (sewage and agricultural runoff). Note, groups may show a different tolerance to other types of pollution such as heavy metals, pesticides and sediment inputs. (Melbourne Parks & Waterways, 1994).
It is necessary to realise that pollution is not the only factor that affects the suitability of a stream for certain species. Factors such as habitat and the stage of a macroinvertebrate species life cycle may also play an important role in what will be detected. Riffles (where water flows rapidly) are colonised by organisms adapted to such conditions, whereas pools support a very different community. Generally, riffles contain a greater species diversity due to the greater variety of places for macroinvertebrates to live (Melbourne Parks & Waterways, 1994). Likewise, macroinvertebrate community structure will vary between sites in the cooler, more shallow and faster flowing upstream regions of the stream in comparison to the generally warmer, deeper and slower moving downstream regions.
In the Merri Catchment there is not such a wide distinction between sites upstream and those downstream with regard to flow rate, depth and temperature. However, there may nevertheless be significant variation along the stream. For example, in the rural reaches of the creek north of Summerhill Road the creek is shallow and flows rapidly over rocks before entering a wide deep pool. Variation in the type of macroinvertebrates found between these two sites would represent a difference in habitat or substratum rather than a difference in water quality over this short distance. Mitchell & Clark (1991) noted that difference in macroinvertebrate structure between Beveridge Road and Summerhill Road reflected more the difference in substratum and flow rate than a difference in water quality (Mitchell & Dunn, 1993). It is worth noting that this zone of riffle followed by a pool then a run may be a remnant of the chain-of-ponds description of the Merri Creek prior to much of the creek being channelised as a result of urbanisation.
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Table 8 Biological Indicators of Organic Pollution
Pollution Macroinvertebrate Scientific name Tolerance (Class & Order) Very Sensitive • Stonefly nymphs Insecta plecoptera good water quality • Caddisfly nymphs Insecta trichoptera
Sensitive • Mayfly nymphs Insecta ephemeroptera good-medium water quality • Elmids or riffle beetles Insecta coleopteron -family Elmidae
Medium tolerance • Dragonfly nymphs Insecta odonata less likely to occur when • Damsel-fly nymphs Insecta odonata poor water quality • Mites Arachnida Acarina • Yabbies Crustaceae decapoda -family Parastacidge • Shrimps -family Atyidae • Amphipods, Scuds or Crustacaea amphipoda Sideswimmers • Water Bugs Insecta hemiptera • Diving Beetles Insecta coelentera -family dytiscidae • Water scavenger beetles -family hydrophilidae • Whirligig beetles -family Gyrinidae • Water pennies -Psephenidae
Tolerant • Snails and limpets Gastropoda can live in poor quality • Bivalves and mussels Bivalvia water • Flatworms Turbellaria • Leeches Hirudinea
Very Tolerant • Chironomids Insecta diptera most abundant species in • Freshwater worms -family Chironomidae poor water quality Oligochaeta (Melbourne Parks & Waterways; 1994)
Note: For more information on the description and illustrations of these macroinvertebrates, refer to the publications Community StreamWatch - A Water Quality Monitoring Manual for Victoria published by Melbourne Parks and Waterways or Australian Freshwater Life :- the invertebrates of Australian inland waters by Williams (1980).
Page 84 State of the Environment - Water Quality
4.4.3 Groundwater quality
Groundwater quality is usually measured using chemical parameters. Like surface water testing, analysis of the water can be expensive if a broad range of parameters are desired. For this reason, parameters chosen are normally inexpensive to measure such as pH and E.C. with the addition of some other parameters such as metals and salts. The following section outlines the monitoring program in the Merri Catchment and the implications for surface water quality.
The chemical composition of the groundwater is important because it determines to a large extent the background chemistry of the stream waters in the Merri Catchment. The average chemical analyses from all 105 Rural Water Corporation bores in the catchment are listed in Table 9. Table 10 and Table 11 are summaries of parameters from bores in the northern part (around Wallan - 67 bores) and the middle part (around Campbellfield - 38 bores) respectively. Due to the rather clumped nature of bore locations, further reference to average values of parameters is skewed by the data generated and may not be fully representative.
One parameter of major concern throughout rural Victoria is salinity. Table 9 shows that the average concentration of Total Dissolved Solids for the whole catchment is 2811 ppm (equivalent to mg/L) and Electrical Conductivity is 4534 µS/cm and there appears to be a slight increase in concentration in the middle portion of the system (from 2775 ppm, 4630 µS/cm to 2846 ppm, 4437 µS/cm). These concentrations are well above those recommended by the SEPP for the water of the Merri Creek (<1000 ppm below Malcolm Creek and <500 ppm above).
At present it is unclear as to whether the current (relatively) high salinity levels measured in the Merri Creek reflect an increase in groundwater salinity due to changes in land use or that they represent a naturally high salinity in groundwater that has always been present in the stream. Thomas & Cummings (1994) rate the soil salinity (groundwater discharge sites) in the Merri Catchment as being high and suggest that the problem may be increasing. The YarraCare report on groundwater conditions in the Yarra Catchment (Shugg & O’Rourke, 1994) notes that along with salinity, the "Basalt Plains Catchments” also have the highest levels of nutrients in them and says that this may be due to local contamination. Though the paper does not specifically mention the Merri Creek, it points out that groundwater contributes between 50 and 80% of the total salt load reaching the Yarra River.
What data is available and where is it from?
The Department of Natural Resources and Environment monitors groundwater in the Merri Catchment. The bores that they use to accomplish this are situated in two main areas. In the northern portion there are 67 bores around Wallan and further south there are 38 bores on the outskirts of Melbourne between Broadmeadows and Craigieburn. The only bore in the inner urban area is a groundwater pollution monitoring bore at Field Street in Clifton Hill. These bores monitor water quality and groundwater levels and the information is available from the Groundwater Database (jointly managed by Sinclair Knight Merz and the Department of Natural Resources and Environment; Groundwater Management and Protection section).
Page 85 Waterways of the Merri Catchment
Parameter Average (mg/l)* pH 7.91 E.C. 4533.53 2- SiO3 37.79 TDS 2811.05 BiCarbonate as HCO3 4492.92 Carbonate alkalinity as 28.87 2- CO3 2- Sulphate as SO4 91.06 Chloride as Cl- 1163.30 Calcium 67.31 Magnesium 173.36 Potassium 18.80 Sodium 568.56 Iron: total 5.07
Table 9 A summary of the average chemistry from 105 bores in the Merri Catchment. (*) All values in mg/l except pH and electrical conductivity (in µS/cm)
Parameter Ave. (mg/l)* Parameter Ave. (mg/l)* pH 7.7 pH 8.13 E.C. 4630.03 E.C. 4437.03 2- 2- SiO3 35.13 SiO3 40.45 TDS 2775.5 TDS 2846.67 BiCarbonate as HCO3 374.09 BiCarbonate as HCO3 611.76 Carbonate alkalinity as 19.88 Carbonate alkalinity as 37.87 2- 2- CO3 CO3 2- 2- Sulphate as SO4 92.23 Sulphate as SO4 89.89 2- 2- Nitrate as NO3 10.0 Nitrate as NO3 20.45 Chloride as Cl- 1178.15 Chloride as Cl- 1148.45 Calcium 93.06 Calcium 41.56 Magnesium 189.35 Magnesium 157.37 Potassium 10.3 Potassium 27.29 Sodium 495.67 Sodium 641.46 Iron: total 3.87 Iron: total 6.27
Table 10 Table 11 A summary of the average chemistry A summary of the average chemistry from 67 bores in the upper portion of from 38 bores in the lower portion of the Merri Catchment. (*) All values in the Merri Catchment. (*) All values in mg/l except pH and electrical conductivity mg/l except pH and electrical conductivity (in µS/cm) (in µS/cm)
Page 86 State of the Environment - Water Quality
Leachate Contamination
Leachate from landfills is a potential source for heavy metal contamination of ground and surface water in the Merri Catchment (Mitchell & Clark, 1991). This has been the subject of a detailed study as a part of this report. Twenty six landfill sites have been identified to date (Finlay, 1996) in the urban section of the Merri Catchment, many of which are situated close to the banks of the Merri Creek (Map 7). Of these sites, seven are currently operating, 17 have been closed and one site is proposed. (shown in Table 12). Because most of these sites have been defunct for a number of years, operating practices were such that the content of the waste was not strictly controlled and measures to contain leachate leakage were limited or non-existent.
Furthermore, a number of exhausted quarries that are not confirmed as landfill sites have been identified. These sites (marked a to l on Map 7) are almost certainly filled with rubbish of some description.
The extent of this potential problem is not fully understood but the research into the former landfill at Cooper Street suggests that leachate from this landfill potentially contributes 0.23% of the copper, 0.34% of the nickel and 8.6% of the zinc to the waters of the Merri Creek at Cooper Street.
Page 87 Waterways of the Merri Catchment
Table 12 Landfill sites and reclaimed quarries and type of landfills in the urban portion of the Merri Catchment (from Finlay,1996). Known landfill sites No. Site Name Waste type Status Period of Capacity Host Operation (m3) lithology 1 Craigieburn Road, Craigieburn Putrescible, trade Operating 1974? - 400,000+ Basalt 2 Cooper St No.1, Epping Putrescible Closed 1984 - 1987 1,365,000 Basalt 3 Cooper St No.2, Epping Putrescible Operating 1991 - 2,000,000 Basalt 4 Cooper St No.3, Epping Putrescible Proposed n.a. Basalt 5 Memorial Ave, Epping Unknown Closed ?1970 - 1974 n.a. Basalt 6 Rufus St, Epping Unknown Closed n.a. n.a. Basalt 7 Cooper St, Epping Unknown Closed ? - 1972 - ? n.a. Basalt 8 Epping Waste Disposal Trade Operating 1985? - n.a. Basalt 9 Teal Cres., Epping Unknown Closed 1974 - 1978 250,000+ Basalt 10 Bolinda Ave, Broadmeadows Putrescible Operating 1992 - 3,200,000 Basalt, Tertiary sediments 11 Onslow Ave, Broadmeadows Putrescible, Closed 1980 - 1983 1,300,000 Basalt, industrial Tertiary sediments 12 Camp Road, Broadmeadows Unknown Closed - 1974 -1978 1,360,000+ n.a. 13 Camp Road south, Putrescible Closed 1984? <1,000,000 n.a. Broadmeadows 14 Zinnia St, Reservoir Unknown Closed 1966 - 1974 n.a. n.a. 15 Arunta St, later Reservoir Putrescible, Closed 1970 -1978 265,000+ n.a. Transfer Station commercial, liquid 16 Newlands Road, Coburg North Unknown Closed 1974 - 1978 n.a. Basalt 17 Trade Place, Coburg North Unknown Closed 1975 - 1977 270,000 Basalt 18 Thomas St, Preston Non-putrescible Closed - 1976 n.a. n.a. 19 Collins St, Preston Unknown Closed Unknown n.a. n.a. 20 Shower St, Preston Unknown Closed ?1966 - 1970 n.a. n.a. 21 Watt St, Thornbury Unknown Closed Unknown n.a. Basalt 22 Albion St, Brunswick Putrescible Closed 1976 - 1994 720,000 Basalt 23 Lee St, Brunswick Unknown Closed early 1970s n.a. Basalt 24 Whelan's Kartaway Non-putrescible Closed 1963 - 1993 1,400,000 Basalt 25 Clifton St, Northcote Non-putrescible Operating 1979 - 2,000,000 Silurian sediments 26 Field St, Collingwood Unknown Closed Unknown n.a. Basalt Reclaimed quarries, unconfirmed as landfill sites Depth (m) Volume approx. (m3) Location a Unrecorded Unknown Church St, Epping b Unrecorded Unknown Bellarine Dr, Epping c Unrecorded Unknown Emma Crt, Coburg North c Unrecorded Unknown Mathieson St, Coburg North c Unrecorded Unknown Anzac Ave., Coburg North d Unrecorded Unknown Tilly St, Coburg North e Unrecorded Unknown Mercy College, Carr St, Coburg North f 2.0 5,000 St Bernhards, Patterson St, Coburg g Unrecorded Unknown Veronica St, Northcote h Unrecorded Unknown Arthurton Road, Northcote h Unrecorded Unknown Woolhouse St, Northcote h Unrecorded Unknown Beavers Road, Northcote Unrecorded Unknown Roberts St, Brunswick Unrecorded Unknown Lee St, Brunswick Unrecorded Unknown Hamer St, Brunswick East 3.04 34,200 Elm Grove, Brunswick East Unrecorded Unknown Fleming Park, Brunswick East 4.57 17,150 Loyola Ave, Brunswick East k 3.66 13,600 Noel St, Brunswick East k 2.7 57,000 Cnr Glenlyon & Nicholson Sts, Brunswick East Unrecorded Unknown Balfe Park, Brunswick East Unrecorded Unknown Cnr Miller & Nicholson Sts, Brunswick East 3.04 4,500 Truscott St, Brunswick East Site numbers and letters correspond to those in Map 7. The letters for the unconfirmed sites are grouped together in Map 7.
Page 88 State of the Environment - Water Quality
Map 7 Location of landfills in the urban portion of the Merri Catchment.
Page 89 Waterways of the Merri Catchment
4.5 Conclusions
Major sources of pollutants
It is possible to draw some conclusions on the likely sources of pollution in the waterways of the Merri Catchment based on an assessment of key indicators of water quality. These are generally associated with the surrounding land use.
Sewage disposal
In the upper portion of the Merri Creek, the Craigieburn Sewage Treatment Plant is a major source of nutrient and suspended solid pollution. The level of phosphorus treatment at this plant was upgraded in 1994 to reduce the output concentration to 1 mg/L (Section 2.2.4). If compliance to this level of treatment is occurring, then it brings the concentration of the effluent within SEPP water quality objectives. It is therefore expected that the level of nutrients in the Merri Creek downstream of Craigieburn will have improved. However, a recent study (Merrick, unpublished) indicates that nutrient levels from the Craigieburn Sewage Treatment Plant are still a major concern (Section 2.2.4). The significant flow of effluent from the treatment plant relative to creek flows still makes it a major contributor to suspended solid and nutrient loads.
Improper or neglected methods of sewage disposal on unsewered properties may also lead to abnormal levels of nutrients and other contaminants in ground and surface waters. Leakage from unsewered properties contributing to the nutrient load is a problem in rural towns and the estates on the fringe of urban development.
Illegal connections of stormwater to sewerage causes sewage overflows. This is commonly associated with urban and industrial development and are obvious pollution sources.
Litter and waste disposal
Stormwater carries the bulk of the litter to the Merri Creek. This suggests improper or inadequate methods of collection and/or disposal of all sorts of litter and waste.
Accidental spills of commercial and industrial chemicals and waste present serious problems for the water quality in the Merri Creek. The implication of this is insufficient or inadequate preventative mechanisms.
Illegal rubbish dumping is also a problem in all sections of the creek. It encompasses things as diverse as organic waste to car bodies. Urban and industrial aspects of this problem are often mentioned and Barry Road appears to be of particular concern. However illegal dumping is a problem in the rural portion of the catchment too.
Contamination of ground and surface waters by landfill leachate is potentially serious. Investigations have revealed 26 such sources in close proximity to drainage lines.
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Agricultural practices
The amount of nutrients entering the creek by agricultural runoff is likely to contribute significantly to the pollution load in the upper reaches of the waterways of the Merri Catchment. Likewise, pesticides may also be polluting the creek in this manner.
The high salinity levels (which invariably exceed the SEPP objectives) are most likely a result of a high proportion of groundwater flowing into the stream. Whether these levels are natural or result from agricultural practices, such as land clearance, is not clear.
Stormwater and urban runoff
Drains (or the liquids that emerge from them) are the major pollution sources in the industrial and residential portions of the creek. The main drains of concern are: • Ainslie Road, Barry Road, Somerset, Road, Mahoneys Road drains. All are identified as causing heavy metal pollution problems • Campbellfield Creek Diversion and the Fawkner East drains have been suggested as sources of the high zinc concentrations at the Broadhurst Avenue site. • All other drains must contribute to the levels of nutrient, turbidity and toxins such as hydrocarbon bi-products, paint and rubber. The other significant drains are Merlynston Creek, Elizabeth Street, Preston, Sumner Avenue and Park Street main drains. • For a more detailed description of these drains with locations see Section 3.3.5. The drains are also one of the carriers to the creek of litter.
Edwardes Lake acts as a pollution sink, trapping contaminants such as nutrients, heavy metals, sediments and toxicants. Species that are most tolerant to pollution dominate the macroinvertebrates communities (Gaal, 1994). The lower than expected levels of the very tolerant Chironomids and worms is probably due to the very high levels of heavy metals (and other toxicants).
These issues are addressed in the Strategy for the Restoration of the Waterways of the Merri Catchment - Action Plan.
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Table 13 Evaluation of Pollution issues against SEPP objectives (adapted from Mitchell & Dunn, 1993)
Parameter Level of SEPP compliance
Dissolved Above SEPP objectives, but rocky nature of creek causes aeration. Oxygen Occasional extensive algal growth suggest low night-time O2 levels.
E. coli SEPP based on average of samples over a set time period and the monitoring of the Merri Creek has not been adequate and cannot be assessed. Single studies indicate levels greater than that for primary contact. Testing for coprostanol in the new SEPP will help determine the extent to which this is caused from sewer leaks or diffuse stormwater sources (pet faeces). pH Results of recent studies are within SEPP objectives and the range recommended to protect aquatic ecosystems.
Temperature Within acceptable range, but licensed discharges of heated water needs investigation.
Salinity Exceed SEPP objectives in rural and outer urban areas. The extent of naturally elevated groundwater levels needs investigation.
Turbidity Meets mean objective level, but not with 90 percentile.
Toxicants Only a small number (heavy metals) investigated in the Merri Creek Iron, chromium & arsenic exceeded SEPP objectives in 1990 sampling, but not in single sample study of 1992. No Australian criteria for metals in sediments, but 1995 data indicates that copper, lead, mercury and zinc levels in sediment are above the Ontario Severe Effect Levels. No information on levels of toxicants in edible fish and yabbies.
Nutrients SEPP levels are qualitative (levels which cause excessive growth). Indications are that these levels are not being met. P & N downstream of C.STP exceed ANZECC and new draft SEPP criteria. Inputs from industrial and urban stormwater are also a problem.
Suspended SEPP 90th percentile levels are being exceeded in the upstream reaches Solids of the Merri Creek, and are intermittently high at all sites. Craigieburn Sewage Treatment Plant and stormwater drains are contributing suspended solids to the waterways. Litter Merri Creek would fail the "no visible floating matter" criteria.
Page 92 Chapter 2 - State of the Environment - Aquatic Ecology
Summary: Aquatic Ecology Although the exact structure of the aquatic ecosystem prior to European settlement is not known, many sources indicate that the aquatic flora and fauna are considerably altered from that time. At the same time, we must recognise that an ecosystem is not static and that there is much that is still not known about the current state, such as knowledge of the in-stream aquatic plants. However, there is an abundance of recent work, summarised in Table 14, that gives much valuable information on the biological communities in the waterways of the Merri Catchment.
Table 14 Overview of flora and fauna surveys in the Merri Catchment Study Date Location Type of parameter # of sites PIRG Dec. 1974-Jan. Merri Creek aquatic fauna 13 1975 Campbell Nov. 1979-May Merri Creek macroinvertebrates 2 1980 ARI 1982-1990 Merri Creek fish n.a Mitchell & Clark March 1990 Merri & invertebrates 12 Edgars Schulz & Webster 1991 Merri fauna n.a waterways McMahon &1993 catchment- flora & fauna n.a Schulz wide Gaal 1993-1994 Edwardes invertebrates 1 Lake Craigie Feb.-March 1994 Major streams vegetation n.a. Melbourne Water Feb.-March 1995 Merri & platypus &16 Edgars invertebrates MCMC current catchment- vegetation n.a wide (n.a. means not applicable)
Details of the aquatic fauna, waterbird and amphibian populations of streams other than the Merri Creek is limited to two sites on Edgars Creek, as with the Water Quality section. Knowledge of flora, on the other hand, is a little more extensive. This summary gives an overview of the current state of the aquatic ecology of the Merri Catchment, based on the major flora and fauna types.
Streams The effects of human changes to the streams of the catchment, such as channelisation and flood mitigation have had major impacts on the aquatic ecosystem, for example by reducing the invertebrate community upon which many other species depend.
Wetlands Wetlands are vitally important in aquatic ecosystems, providing a valuable habitat for waterbirds, amphibians, reptiles and fish, as well as a unique array of wetland flora. However, no large unmodified wetlands exist in the Merri corridor as a consequence of the drainage of once extensive wetlands in the upper part of the catchment. Remnants of these wetlands remain, such as Hernes Swamp and Beveridge Swamp, but these are currently being drained.
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Riparian and Aquatic Vegetation The riparian zone is an important part of the aquatic ecosystem having a major influence on the structure of the aquatic biota. Several aquatic or semi-aquatic plant community types are approaching extinction in the Merri Catchment. These include Red Gum dominated plains grassland, floodplain grassland drainage-line complex, escarpment shrubland and grassy wetlands. Exotic plants, such as Willow and Gorse, dominate many parts of the waterways, particularly in urban areas. However, there are some areas of remnant vegetation. Extensive remnants of floodplain grassland exist in the northern section of the catchment. Community remnant of Regional and National significance exist in the middle sections of the catchment.
Micro-organisms Micro-organisms play a key role in ecosystem processes, but little information on them exists for the Merri Catchment. A study of Benthic Diatoms showed a decline in taxa on Merri Creek below the rural site at Summerhill Road before a partial recovery downstream of Bell Street.
Invertebrates The invertebrate community forms the basis of many food chains in the waterways of the Merri Catchment. They also are important processors of the leaf litter that enters the waterways. In degraded areas their numbers are depleted, and this influences their effectiveness at processing leaf-litter. Macroinvertebrates have been studied in a number of surveys in the Merri Catchment, both as an indicator of their health and distribution and as an indicator of ecosystem health. A 1991 study in the upper section of the Merri Creek identified a diverse macroinvertebrate community, with 39 discrete taxa being identified.
Reptiles and Amphibians Many reptiles and amphibians are restricted to the damp environment of watercourse and they are of great importance within the food chains of river and wetland communities. Several amphibians and reptiles found in the waterways of the Merri Catchment are listed as uncommon, rare or threatened, such as the Lowland Copperhead and Growling Grass Frog.
Fish The levels of native fish appear to be low in the waterways of the Merri Catchment. Remnant communities of Freshwater Blackfish still exist in the upper section of the catchment. Most native fish are migratory and barriers to fish movement, such as Coburg Lake weir and areas of poor water quality, prevent fish migration upstream. Exotic fish, such as Carp and Goldfish, are very common and dominate the waterways.
Waterbirds Loss of wetlands has lead to a decrease in waterbird diversity and abundance. However, several waterbird species of State and Regional significance, such as Rufous Night Heron, have been found in the Merri Catchment.
Aquatic Mammals The Water Rat and Platypus are the only two species associated with inland waters in Victoria. The Platypus is found in most of the larger tributaries of the Yarra Catchment, although not in high numbers in urban areas. However, a recent survey indicates that it is not resident in the Merri Catchment. The Water Rat is still common in the waterways of the Merri Catchment.
Conclusion There are broad changes, both natural and human-induced, in the stream ecology downstream along the waterways of the Merri Catchment. Loss of wetlands and riparian vegetation and channel modifications have caused major reductions in available habitat. Other issues include decrease of water quality, barriers to migration and competition from exotic species.
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However, areas of remnant flora and fauna of National and State significance remain, providing a basis on which to build an ecological restoration program for the waterways of the Merri Catchment.
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5. Aquatic Ecology
5.1 Introduction
The interdependent nature of ecosystems and the physical environment is long-established. Water quality, geomorphology and flow all influence habitat structure, and hence the structure of the aquatic biota. The aquatic biota, in particular the riparian (bank-side) vegetation, influences water quality and flow.
This section outlines the communities that inhabit the different geomorphological settings through which the creeks flow. It does this by examining the different components of the biota. It examines some of the many inter-relationships between the physical aspects of the creek and the structure of the biotic communities. Firstly the Pre-European state is considered, in as far as evidence is available, before turning to the present state.
5.1.1 Previous work
A number of different studies have been conducted on various aspects of the flora and fauna of the Merri Catchment and the principle investigations are outlined below. This review collates and summarises the relevant findings of this work.
Aquatic fauna
The Public Interest Research Group (1975) study of December 1974 through to January 1975. This group reported on the numbers of vertebrates and invertebrates found at sites along the Merri Creek (13) from Beveridge to Clifton Hill. The report also has a list of recorded bird sightings at Coburg Lake.
The Ministry of Conservation study(Campbell et al., 1982) from November 1979 to May 1980. This group studied benthic macroinvertebrates at two sites (Summerhill Road and Heidelberg Road) on the Merri Creek as part of a Yarra Catchment-wide project.
Arthur Rylah Institute (ARI, 1991) study of 1982 through to 1990. This group studied fish populations in the Merri Creek as part of an on-going but sporadic survey of freshwater fish in Victorian streams.
Mitchell & Clark (1991) study conducted in March 1990. This study examined the populations of macroinvertebrates and benthic diatoms as indicators of water quality. Ten sites on the Merri Creek and two sites on Edgars Creek were analysed.
Gaal (1994) study of Edwardes Lake during 1993 and 1994. This is an examination of the invertebrate community to determine what the impacts of water quality are on that community.
Melbourne Water (unpublished) study of January though March 1995. The Platypus survey group investigated the Merri Creek at 15 locations and Edgars Creek at two sites as part of a Yarra Catchment-wide study. Other species trapped in the process were also
Page 96 Chapter 2 - State of the Environment - Aquatic Ecology recorded. A qualitative survey of macroinvertebrates was carried out in conjunction with the Platypus survey.
Flora
Merri Creek Management Committee (Faithfull, current, unpublished). As part of the on-going revegetation work, this group is compiling a database of vegetation distribution in the Merri Catchment. To date most information is on the terrestrial vegetation.
N.M. Craigie & Associates (Craigie, 1994) study of February/March 1994. Craigie broadly surveyed the general floral characteristics of all the major streams in the Merri catchment as part of the “Inventory of waterways of the Yarra Catchment” study of the condition of streams. The survey outlines the state of the bank and verge vegetation only.
Todd, Carr & Race (1992). A study of the remnant indigenous vegetation in Northcote.
Broad Spectrum Surveys
Schulz & Webster (1991). This is a broad study of fish, reptile, amphibian and waterbird distribution in the Merri Catchment.
McMahon & Schulz (1993). This study, similar to the preceding one, is a review of the distribution of remaining indigenous vegetation, reptiles, amphibians and waterbirds (rare and/or restricted species only) in the Merri Catchment.
5.1.2 Scope of this section
For the purpose of this report only those animals and plants directly associated with standing or running water in the Merri Catchment have been included, as the aim of the present study is to restore the aquatic systems of the Merri Catchment. For some animal groups, in particular fish, it is clear which species can be considered “aquatic”. However, for most groups, such as reptiles, amphibians, mammals and birds, the division is less distinct. For these, an animal has been considered as “aquatic” if it is necessarily associated with standing water for at least part of its life-cycle. For example, in the case of mammals, only those species which habitually swim and feed within the creek, that is the Platypus and Water Rat, are included in this report. Mammals which may drink occasionally from the creek or wetlands, or that live in the riparian zone, such as foxes or possums are not included. This distinction may seem somewhat arbitrary but is necessary to deal with the vast amounts of data. For plants, both aquatic plants and riparian/floodplain plants are included. It was decided to include riparian and floodplain vegetation as they have such a major impact on the aquatic ecosystem.
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5.2 ‘Natural’ states
Little information is available on the condition of the ecology of the waterways of the Merri Catchment and their riparian vegetation prior to European settlement. It is known that the aboriginal inhabitants, the Wurundjeri people, actively managed the landscape using fire regimes for more than 40,000 years. The vegetation was most likely a patchwork of grasslands and River Red Gum forests. The thin line of River Red Gums that edges the creeks today is the remnant of a dense forest - in the early days of European settlement it was so thick that “residents along the Merri could become lost on their way to Melbourne” (PIRG, 1975).
We know that the Wurundjeri used the watercourses for many purposes, as a source for drinking water, and for its food supply, many kinds of fish, eels, freshwater mussels, yabbies and frogs. They utilised the waterbirds, and their eggs, along with aquatic plants such as water-ribbon, reeds and rushes. They also used the River Red Gum for the construction of shields and canoes (Wigney, 1994).
5.3 Existing states
The aquatic ecology of the waterways of the Merri Catchment has changed significantly since European settlement. The riparian vegetation of the waterways of the Merri Catchment is no longer the dense forest of the past. This loss has been a major effect, perhaps the major effect, on the aquatic ecology of the waterways; affecting the water quality, reducing habitat, reducing food availability to invertebrate community, and many other consequences. Loss of wetlands through drainage has also greatly affected the aquatic ecosystem, reducing the habitat available for waterbirds and amphibians, and breeding grounds for many native fish. Deterioration in water quality, and stream channelisation are also likely to have significantly reduced the aquatic biota.
However, the Merri Catchment today still has areas that are well worth preserving and restoring. A number of reaches in the upper parts of the catchment are considered by the Department of Natural Resources and Environment to be of National, State and Regional biological significance. Of National significance are the reaches of the Merri Creek in the Bald Hill region, and between Craigieburn Road and Cooper Street (Schulz and Webster, 1991) (See Map 8).
Recent studies give a good breadth of information on the state of the plants and animals living in and immediately adjacent to the Merri Creek and its tributaries and wetlands. This section firstly looks at the main types of aquatic habitat in the Merri Catchment, streams and wetlands. It then separates the biota into groups of riparian and aquatic vegetation, micro- organisms, invertebrates, fish, reptiles and amphibians, waterbirds and finally aquatic mammals. In each section the importance of the group in the ecosystem is considered, followed by an overview of its current status in the Merri Catchment.
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Map 8 Zoning of the Merri waterways according to the distribution of habitat, flora and fauna
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5.3.1 Streams
Many of the original streams of the Merri Catchment have been channelised, as described in Geomorphology and Flow. The effect of channelisation, and consequent loss of the pool and riffle structure, is to remove the total amount and the diversity of habitat available to the aquatic fauna, in particular invertebrates and fish.
In the original stream system there would have been many small tributaries verged by overhanging trees. The leaf litter they provided would have been a major source of food for the invertebrates, such as many caddis flies, that feed on large pieces of plant material, the “shredders”. These invertebrates form an important part of the food chain, being the prey, for example, of many fish species. In urban areas many of these small tributaries have been piped into drains (see section 3.3), drastically reducing the availability of leaf litter and hence altering the structure of the aquatic ecosystem.
The flood mitigation structures described in section 3.3 also have major impacts on the stream ecology, for example, they often create barriers to fish movement. Flooding is also an important process in promoting the breeding of fish, and is also important in the lifecycle of many other groups, both plants and animals.
5.3.2 Wetlands
The importance of wetlands in the ecosystem cannot be underestimated. They provide invaluable habitat for waterbirds, amphibians, reptiles and fish as well as a unique array of wetland flora. The widespread loss of wetlands is one of the great tragedies of Victoria’s natural heritage. Since European Settlement, over one third of Victorian wetland area has vanished (Oates, 1994). Of those lost, about half were freshwater meadows and marshes.
As described in section 3.3, much of the upper parts of the Merri Catchment would have originally been swamps and marshes, however, there are now no large unmodified wetlands remaining.
The result is a reduction in many species, for example there is now a reduced diversity and quantity of resident and breeding waterbirds. At the present time waterbirds are restricted to farm dams, seasonally inundated freshwater meadows, the major watercourses and drained large wetlands which hold water after periods of prolonged rainfall.
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