Inland Waters Theme Report
Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Jonas Ball, Sinclair Knight Merz Pty Limited, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06750 7
Aquatic ecosystems (continued)
Condition of aquatic ecosystems
Habitat and physical condition of inland waterways
Condition of riparian zones [IW Indicator 5.1]
The preservation of the riparian zone and its vegetation are critical to the long term sustainability of our catchments. For riparian zone management programs to be successful, it is necessary to gain an understanding of the current extent and condition of riparian zones. Data on the condition of riparian vegetation are only available for some river systems. In most cases, these data show widespread losses in and degradation of riparian vegetation.
Weeds now dominate the riparian zone of many inland waters. Only 48% of rivers and 34% of creeks surveyed between Gingin and Mandurah in Western Australia have more than half of their native fringing vegetation intact. Only 7.5% of wetlands in the same area have healthy fringing vegetation (DEP 1998).
Rubber vine, the most significant riparian weed species in Queensland, smothers native riparian vegetation causing habitat loss (Queensland EPA 1999). Introduced para grass in the Herbert River catchment in Queensland has spread from riparian zones to streams, choking watercourses (Queensland EPA 1999). This, in turn has affected natural stream processes and excluded native aquatic species.
Increased instream and dryland salinity has also affected riparian vegetation in some areas. In western Australia, 80% (by length) of stream fringing zones are seriously degraded by salinity in the cleared agricultural areas of the state (DEP 1998).
The Index of Stream Condition (ISC) is a protocol developed in Victoria for evaluating or benchmarking the general condition of streams and riparian zones by comparing them to their 'natural' state. It also can be used to provide a broad indication of the effectiveness of management and rehabilitation. Some Victorian catchments have been assessed using the ISC protocol and rated (see Table 33), with 10 indicating excellent condition and zero indicating highly disturbed condition. Ratings for Victorian catchments ranged from 3.5 (Portland Basin) to 7.1 (Mallee Basin).
| Index rating | Basin |
|---|---|
| 0 to 2 | None |
| 2 to 4 | Hopkins, Barwon, Corangamite, Portland |
| 4 to 6 | Ovens, Upper Murray, Kiewa, Broken, Goulburn, Campaspe, Loddon, Avoca, Wimmera, Snowy, Tambo, Mitchell, Thompson, Latrobe, South Gippsland, Maribyrnong, Werribee, Moorabool, Glenelg |
| 6 to 8 | Mallee, East Gippsland, Otway |
| 8 to 10 | None |
Four representative catchments were investigated further to highlight which pressures have the largest impact on stream-zone condition. Riparian areas that were intact over larger distances or areas were more likely to be in better condition. Structural intactness, exotic vegetation and the width of the streamside zone also had a strong influence on streamside condition.
Case study 10: Condition of riparian vegetation in selected Queensland catchments
The Condamine River catchment is located on the western slopes of the Great Dividing Range in southern Queensland, covering an area of 29 150 km2 and including Toowomba, Warwick, Millmerran, Pittsworth, Oakley, Dalby and Chinchilla (Queensland EPA 1999). The river is a major source of irrigation water for the Darling Downs area. The condition of the catchment is poor with exotic weed species occupying 37% of the catchment (Queensland EPA 1999) (see Table 34). Riparian areas in good condition were generally found in national parks and state forests. In rivers and streams that had been cleared of their riparian vegetation, 94% of river banks were eroding due to the loss of structural stability and the impacts of livestock (Queensland EPA 1999). The condition of aquatic vegetation was related to the width of the riparian zone, with areas of better condition in wider riparian zones.
| Catchment | Area of catchment drained (km2) |
Length of major streams (km) |
Stream length rating (%) | Surveyed sites with exotic species (%) |
||||
|---|---|---|---|---|---|---|---|---|
| Very poor | Poor | Moderate | Good | Very good | ||||
| Dawson River | 50 800 | 1 300 | 59 | 24 | 9 | 6 | 3 | 88 |
| Herbert River | 8 574 | 2 622 | 58 | 18 | 11 | 6 | 7 | 65 |
| Lockyer Creek | 2 971 | 1 089 | 41 | 34 | 9 | 8 | 8 | 89 |
| Mary River | 9 697 | 2 947 | 4 | 36 | 31 | 18 | 11 | 63 |
| Upper Condamine | 13 292 | 3 919 | 79 | 9 | 8 | 2 | 2 | 96 |
Source: Queensland EPA 1999.
Decline in wetland extent [IW Indicator 6.7]
Wetlands can be defined as:
areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt (Ramsar 2000).
In Australia, wetlands include ecosystems such as swamps, floodplain depressions, billabongs, marshes, ponds and mangroves (DCFL 1988: Boulton & Brock 1999). The key differences between wetlands include natural salinity and whether they hold permanent water. Because of the high seasonal and year-to-year variation in rainfall in many areas of Australia, many wetlands are temporary and dry out periodically. The permanency of wetlands is also influenced by topography and their association with groundwater and/or surface water systems. Wetlands are closely interconnected with both aquatic and terrestrial ecosystems and may also have a strong influence on these environments.
Wetlands are important in the Australian landscape. Some of their functions and effects are flood mitigation, erosion control, groundwater recharge and discharge, nutrient interception and modification, biomass export, provide habitat and food resources for plant and animal species and drought protection (Dugan 1988).
Wetland ecosystems are resilient to natural variability, but are extremely vulnerable to human intervention. Pressures on wetlands such as changes in natural flow regimes, vegetation clearing, salinisation and floodplain isolation have been discussed in detail in Pressures on aquatic ecosystems.
Australian wetlands have been declining at an alarming rate since European settlement (ANCA 1996). Australia: State of the Environment 1996 (State of the Environment Advisory Council 1996) highlighted losses in wetlands in New South Wales, Western Australia, South Australia and Tasmania. There is little additional information to report since 1996. In Queensland, the Johnstone, Moresby and Mulgrave-Russel river catchments have lost large areas of wetland between 1951-52 and 1992 (see Table 35).
| Catchment | Area of wetland 1951-52 (hectares) |
Area of wetland 1992 (hectares) |
Net change in area (hectares) |
Percentage change |
|---|---|---|---|---|
| Johnstone | ||||
| Melaleuca forests | 1 227 | 282 | -995 | -78 |
| Mixed melaleuca | 462 | 258 | -204 | -44 |
| Palm/pandanus | 439 | 160 | -279 | -64 |
| Freshwater swamps/reeds | 499 | 225 | -274 | -55 |
| Moresby | ||||
| Non-tidal | 3 363 | 1 175 | -2 188 | -65 |
| Mulgrave-Russell | ||||
| Melaleuca forests | 3 860 | 1 808 | -2 052 | -53 |
| Mixed melaleuca | 666 | 319 | -347 | -52 |
| Palm forest | 1 766 | 738 | -1 028 | -58 |
| Sedge swamps | 1 077 | 562 | -515 | -48 |
| Rainforest | 1 759 | 308 | -1 451 | -82 |
| TOTAL | 15 118 | 5 835 | -9 333 | -62 |
Source: Queensland EPA 1999.
Other states and territories including Western Australia, South Australia and the Northern Territory are under-represented by wetland surveys. This is currently being addressed by surveys of high value wetlands by Environment Australia (Environment Australia 2001). There is detailed information on the loss of wetland areas for the Chowilla floodplain (South Australia) and the Macquarie Marshes (New South Wales).
Case study 11: Macquarie Marshes
The Macquarie Marshes are located on the lower Macquarie River and represent an area of approximately 130 000-200 000 ha (Kingsford 2000; Wolfgang 1998). Grazing and irrigated agriculture are common activities in the wetland catchment. Part of the marshes are nature reserve (18 000 ha) that is listed under the Ramsar Convention (Kingsford 2000). The marshes contain a number of wetland types and their important ecological features include waterbird habitat, inland reed swamps and floodplain woodlands (Kingsford 2000).
Since the 1960s there has been a loss of over 50% of the original marshes area (Table 36) (Wolfgang 1998; Brereton 1994). These losses correspond to a decrease over the same period of 40-50% in the area inundated by large floods and have resulted in a decline in the waterbird population (Kingsford 2000).
The primary cause of wetland loss in the marshes is a 30% reduction in annual river flows since the construction of Burrendong Dam in the late 1960s (Kingsford 2000). Prolonged inundation and alienation of floodplain areas from the river by levees and erosion of river channels have also had significant impacts. There has also been some reclamation of the marshes for farming. The reduction in wetland area in the marshes has had additional downstream impacts including increasing salinity and erosion (Kingsford 2000; Wolfgang 1998; Brereton 1994). The management of the Macquarie Marshes is focused on achieving a sustainable balance between water supply for irrigation, erosion control and environmental values. Initiatives include the cap on diversions of unregulated flows at 50 000 ML/yr (Kingsford 2000).
| Habitat type | Percentage loss | Time period |
|---|---|---|
| River red gum | 50 | 44 years (1937-81) |
| Reed beds | 50 | 9 years (1963-72) |
| Water couch | 40 | 42 years (1949-91) |
Source: Brereton 1994.