Threats to Freshwater Ecosystems

Threats to freshwater ecosystems Jon Nevill 28/10/00

Acknowledgments: Alena Glaister, Andrew Boulton, Angela Arthington, Chris Walsh, Frederick Bouckaert, George Wilson, Hugh Jones, Jim Puckridge, Margaret Brock, Robert Walsh, Stewart Blackhall., Stuart Blanch, Stuart McCallum, Susan Cunningham.

Australia is the world's driest inhabited continent (the driest being Antarctica), and rainfall over much of the land is highly variable. In the two centuries since European occupation, fresh water (both surface and ground) has often been a scarce commodity, and (generally speaking) supplies have been extensively harvested and allocated for human use. For example, if all existing water allocations in the Murray-Darling Basin (Australia's largest river basin) were implemented, 90% of the average natural stream flow would be diverted. The lower Murray now experiences drought level flows three years out of every four, compared to one in twenty years under natural circumstances (Commonwealth of Australia 1998:22).

In spite of gross over-allocation of the water resource, the Murray-Darling Basin Ministerial Council has had difficulty implementing a cap on water usage (Murray- Darling Basin Ministerial Council 1998; Murray-Darling Basin Commission 1998). The cap was set at 1994 extraction levels, and may not be sufficiently restrictive to protect the remaining biodiversity of many of the Basin's rivers and wetlands1. In the Queensland and Victorian sections of the basin, harvesting of surface flows with off- stream dams continues to be unregulated by State government (Jim Puckridge, pers.comm. 5/9/00).

Wetlands have been extensively drained, cleared and grazed for agriculture. Overall, around 50% of Australia’s wetlands have been converted to other uses (Commonwealth of Australia 1997:7). In other areas the situation is much worse: for example, less than 4% of wetlands in the south-east of South Australia remain, and about 1% in the Greater Adelaide Metropolitan Region. Many wetlands along the lower Murray River now have artificially maintained water levels (R Walsh, SA DEH pers. comm. 11/5/00). In New South Wales, the Macquarie Marshes, a hemispheric wetland reserve for waterbirds, is among many major wetlands to be seriously degraded (Kingsford 2000). Because wetlands store and slowly release water over time, their loss has further accentuated the highly variable natural flows in most rivers.

According to the 1996 State of the Environment Report (refer also to the Report's technical background papers) major problems affecting many remaining rivers, wetlands and aquifers of conservation value include (not in order of importance):  extraction of surface or groundwater flows;  alterations to flow volumes, timing, temperature and quality stemming from stream regulation and levee bank construction;  water pollution from agricultural, urban and industrial sources;  habitat degradation, including: (a) degradation of riparian vegetation by grazing and altered fire regimes, (b) weed infestation, (c) changed river morphology associated with erosion and sediment deposition, (d) recreational activity impacts, including destruction of vegetation, destructive litter such as nylon fishing lines, and poisoning of soils and biota with lead shot, (e) river de-snagging, and (f) drainage, infilling or channelisation for agricultural purposes  structures impeding the passage of fish on life-cycle journeys;  introduced aquatic pests species (including plants, animals and micro- organisms); and  disturbance of wildlife by recreational and urban encroachment, powerlines (causing birdstrike) and predation by feral animals such as cats, foxes and dogs; and  the direct and indirect effects of mining operations, including: (a) the mining of materials associated with water systems, such as peat, sphagnum moss, gold, certain gemstones, tin, sand or river gravel, (b) water pollution from soil disturbance, process waste or acid drainage, and (c) altered groundwater regimes resulting from mine dewatering or process water extraction.

Further information on these threats may be obtained from the wetland strategies developed by Western Australia, Victoria, New South Wales, Queensland, and the Northern Territory, and the draft wetland strategies now being developed by Tasmania and South Australia.

Prior to recent water reforms, groundwater and surface water flows were managed with little coordination, and the legacy of this mistake remains today. For example, until the new Water Management Act was passed by the Tasmanian government in 1999, groundwater and surface water flows (even when directly interlinked) were managed by different State government departments, under different pieces of legislation and policy, for different objectives and within different government programs. In some locations around Australia, groundwaters have been so heavily used that springs have dried up, along with their associated local ecosystems. Pollution with salt or chemical wastes, and changes to aquifer flow patterns, have destroyed or degraded substantial localised freshwater ecosystems (Bailey & James 1999).

Australia's National Strategy for the Conservation of Biological Diversity provided a strategic framework incorporating both systematic protection through reservation, as well as the use of "sympathetic management" in utilised ecosystems (Principle 8). Although terrestrial ecosystem reserves are now well advanced in many areas, freshwater and marine reserves have not received the same degree of attention.

Freshwater ecosystems in Australia have received considerable study. Comprehensive inventories of freshwater ecosystems, however, remain incomplete in all Australian States. Western Australia, Queensland, Victoria and New South Wales are all committed, in terms of policy statements, to the development of systems of representative freshwater reserves. Victoria, however, is the only State to fund a program to develop such a system. And even in this State, the program did not achieve its full objectives (Nevill, in prep.) and is in urgent need of revision.

Outstanding examples of sites which need urgent reservation to protect site-specific values are the artesian springs associated with the Great Artesian Basin (mound springs). These unique habitats contain a diverse endemic fauna (fishes, invertebrates). While some springs are now protected in South Australia, virtually none of those in Queensland are protected, including the group with the largest endemic fauna (Edgbaston Springs). Increasing evidence of extraordinary endemism in some groups (especially molluscs and crustaceans) shows that many taxa are confined to single streams or watersheds. (pers.comm. Winston Ponder, Australian Museum, 3/8/00). Reservation alone, of course, would be useless if developments in the region seriously deplete groundwater stocks and flows. The establishment of freshwater reserves needs to be accompanied by catchment and aquifer management programs.

An aquifer in Western Australia has the highest diversity of subterranean amphipods recorded anywhere in the world (Western Australian Museum, media release 29/8/2000), highlighting stygofauna as an area of conservation significance and concern. More general groundwater issues are discussed by Hatton & Evans 1997.

Improved catchment management is crucial to any program designed to protect freshwater biodiversity. The expansion of agriculture has been marked by extensive clearing of native vegetation, the construction of large numbers of small and medium sized dams, uncontrolled grazing of riparian vegetation, the draining of wetlands, the application of fertilisers, and the proliferation of pests such as carp, willows and water weeds. The cumulative effects of such incremental development have proved more difficult to manage than point-source industrial pollution. Very small levels of catchment urbanisation can have profound effects on instream biotic communities (Walsh, in press). Yet the Implementation Guideline published by the National Water Quality Management Strategy to guide catchment planning does not explicitly address the management of cumulative impacts, nor does it recommend the incorporation of biodiversity concerns into catchment planning. Indeed, the lack of comprehensive and accessible freshwater ecosystem inventories makes such incorporation difficult at this point in time.

The temporal and spatial mosaic of ecosystem types in the landscape are important for the protection of biodiversity. Freshwater biodiversity depends in part on the natural diversity of wetland types in the landscape, a pattern which is degraded by draining and damming and the replacement of a range of wetland types by a homogeneous landscape of farm dams (Margaret Brock, pers.comm. 4/9/00).

Unconstrained grazing and trampling by introduced herbivores continues to degrade riparian zones over 70% of the continent (Jim Puckridge, pers.comm. 5/9/00). Introduced pest fish, such as carp, plague minnow (Gambusia) and (dare I say it) trout have dominated ecosystems in many streams. Exotic riparian vegetation with seasonal leaf-falls (eg: willow) has choked rural streams across southern Australia (Boulton and Brock 1999).

Water pollution may be categorised into six broad classes:  sand and silt, which smother aquatic micro-habitats;  suspended solids, or other pollutants causing increased turbidity, which inhibit light penetration and thus aquatic photosynthesis;  salt, which causes direct toxicity, and alters ecosystems by favouring salt- adapted species;  nutrients, which alter ecosystem balances, and can result in algal blooms with toxic effects;  industrial and agricultural chemicals, such as pesticides, which can cause acute or chronic toxicity; and  acid resulting from the disturbance of acid-sulphate soils, reasonably common along flat low-lying coastal areas of NSW and southern Queensland. Australia does not suffer the acid precipitation problems of northern Europe and northern America.

The effects of large dams on biodiversity in rivers and floodplain wetlands are all too evident in south-eastern Australia (Kingsford 2000) and should serve as a benchmark for poor water management practices, to be avoided by future developments. Yet, despite the Council of Australian Governments water reform agenda with its attendant environmental flow requirements, major new dams and weirs are being proposed in Queensland, Western Australia and Tasmania. Urgent action to establish systems of representative freshwater reserves is needed in all Australian States. Action is also urgent with respect to the management of cumulative impacts of incremental water infrastructure development, and here ecosystem inventories and integrated catchment management can play crucial roles (Nevill, in prep).

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General references: see, for example, Australian State of the Environment reports (Commonwealth and State), the National Biodiversity Strategy, the Wetlands Policy of the Commonwealth of Australia, technical papers under-pinning these strategic documents, State wetland strategies and policies, and journals covering Australian freshwater ecosystem issues.

References referred to in the text: Agriculture and Resource Management Council of Australia and New Zealand / ANZECC (1998) Implementation guidelines: water quality and catchment management planning. Australian Government Publishing Service, Canberra. Bailey P and James K (1999) Riverine and wetland salinity impacts - assessment of research and development needs. Land and Water Resources Research and Development Corporation, Canberra. Boulton, Andrew J and Brock, Margaret A (1999) Australian freshwater ecology: processes and management. Gleneagles Publications; Glen Osmond SA. Commonwealth of Australia (1997) Wetlands policy of the Commonwealth of Australia. Environment Australia; Canberra. Commonwealth of Australia (1998) Australia’s national report to the Fourth Conference of the Parties to the Convention on Biological Diversity. Environment Australia; Canberra. http:www.biodiversity.environment.gov.au/biocon/natrep/ . Commonwealth of Australia (Council of Australian Governments) (1996) The national strategy for the conservation of Australia’s biological diversity; Commonwealth Department of the Environment, Sport and Territories; Canberra. Also available at http://www.erin.gov.au/net/biostrat.html Hatton, Tom & Evans, Richard (1997) Dependence of Ecosystems on Groundwater and its Significance to Australia. report to LWRRDC by CSIRO and Sinclair Knight Merz. Kingsford, R.T. (2000). Ecological impacts of dams, water diversions and river management on floodplain wetlands in Australia. Austral Ecology 25: 109-127. Murray-Darling Basin Commission (1988) Murray-Darling Basin Cap on Diversions 1997/98. MDBC; Canberra. Murray-Darling Basin Ministerial Council (1998) Review of Cap Implementation 1997/98; report of the Independent Audit Group. Murray-Darling Basin Commission; Canberra. Nevill, Jon (in preparation) Freshwater biodiversity: protecting freshwater ecosystems in the face of infrastructure developments. Draft available for comment on http://www.onlyoneplanet.com/freshwater_a.htm . State of the Environment Advisory Council (1996) State of the Environment Australia 1996. Australian Government Publishing Service, Canberra. Also available on www.ea.gov.au Walsh, C. J. (in press). Urban impacts on the ecology of receiving waters: a framework for assessment, conservation and restoration. Hydrobiologia. Endnotes: 1 According to Stuart Blanch (Inland Rivers Network) pers.comm. 6/9/00:  thermal pollution affects about 3000 km of the Murray-Darling Basin;  of the 26 native fish in the Basin, seven are listed by the IUCN as threatened;  three fish species have become extinct in the Murrumbidgee, with another handful threatened;  introduced carp comprise 80% of fish biomass in the Basin;