Ecological processes and species populations

2011

 

The health of our inland water systems can be assessed according to the modification of the systems and the state and trends of their ecological processes, including habitat and biodiversity, and of native species populations.

State and trends of ecological processes

Stream and wetland condition monitoring is resource intensive. Most states do not undertake comprehensive monitoring of rivers; very little and limited monitoring is done by some states. Apart from Victoria, there is very little broad-scale monitoring of wetland condition in states and territories. The available national picture of ecological health is particularly fragmented—more so than for other dimensions of our inland water environments.

The stream habitats in more than half the nation’s river length were assessed in 2005 as being modified from pre-European conditions.23 Degradation of habitat was largely attributed to changes in sediment loads, which alter channel morphology, and to the loss of riparian vegetation (i.e. vegetation on riverbanks). Scores for habitat were lowest in New South Wales, South Australia and Western Australia, largely reflecting the conditions of the Murray–Darling, South-east Coast and South-west Coast drainage divisions, respectively.

Repeated sampling of stream macroinvertebrates at sites across Australia32 indicates no significant trends in condition at a national scale over the past 15 years (Table 4.4). Most sites (51%) are similar to the reference condition, while 40% of sites are significantly impaired. These results relate to the sites sampled during the 2003–10 assessment period in each state and territory; they do not reflect an even coverage of Australia’s rivers and wetlands, but rather a consistent set of sites monitored over time. Australia is currently developing and testing a more national and comprehensive approach for assessing river and wetland health (Box 4.4).

Table 4.4 Australian River Assessment System (AUSRIVAS) macroinvertebrate assessment at test sites for the 2001, 2006 and 2011 State of the Environment (SoE) reporting periods
There is no clear trend over time.
Period of assessment Number of sites (% assessed)
More biologically diverse than reference condition Similar to reference condition Significantly impaired Severely impaired Extremely impaired Total
2003–10 (SoE 2011) 97 (3) 1795 (51) 1403 (40) 213 (6) 18 (0.5) 3526
1990–2004 (SoE 2006) 195 (4) 2465 (52) 1556 (33) 433 (9) 56 (1) 4705
1994–99 (SoE 2001) 154 (5) 1702 (54) 963 (31) 254 (8) 39 (1) 3112

Box 4.4 National Framework for the Assessment of River and Wetland Health

Australia has no national-level program for monitoring and reporting on aquatic ecosystem condition. The National Framework for the Assessment of River and Wetland Health (FARWH) was developed in 2005 to provide nationally comparable data on river and wetland health in Australia. It establishes a national monitoring, assessment and reporting system for river and wetland health that will allow comparable assessments within and between jurisdictions for future national reporting. It is based on the premise that ecological integrity is represented by all the major components of the environment that constitute the ecosystem. These components may be reported separately and brought together to provide an overall assessment of river and wetland condition, which is comparable across jurisdictions. The framework has been trialled in six jurisdictions. Assessments of two contrasting catchments in Queensland (the Pioneer and the Burdekin) are compared below (Table A).

The Pioneer is a relatively small, heavily cropped catchment in the wet tropics, with a large dam and numerous weirs. The Burdekin is a very large, mainly grazed catchment in the dry tropics, with only one large dam. These systems differ in both their biogeography (combination of landscape features and species) and in the pressures on their ecosystems arising from water resource development, clearing, land use and pollution. Although the overall scores from the FARWH assessments of these two systems are similar (i.e. in the same ecological condition band), the degree of impairment of indicators differs. For example, the fringing zone, catchment and physical form in the Burdekin seem to be in poorer condition, but the aquatic biota, water quality and soils, and hydrology seem to be in better condition.

Table A Comparison of FARWH assessments for the Pioneer and Burdekin stormwater management authorities for 2008
Higher scores reflect conditions closer to an undisturbed condition.
Component Pioneer Burdekin
Fringing zone 0.61 0.56
Catchment disturbance 0.62 0.56
Aquatic biota 0.82 0.89
Water quality and soils 0.84 0.86
Hydrological disturbance 0.33 0.48
Physical form 0.96 0.86
Overall score 0.63 0.66

These health indicators should help with diagnosing pressures and identifying appropriate management actions. In the case of the Pioneer, this would mean improving the hydrology (i.e. providing more natural flows) through water resource planning and management, improving the fringing zone (riparian) vegetation and reducing catchment disturbance.

A synthesis report on the national set of trial evaluations of FARWH methodology is expected in late 2011 as part of the Waterlines series of publications from the National Water Commission. This approach holds promise for improved national-scale reporting on river and wetland condition in future State of the Environment reports.

Source: Senior et al.33

Of all the drainage divisions, the most widespread concerns are about the ecological state and trend of the Murray–Darling. An assessment in 200114 found that 40% of the river length assessed in the Murray–Darling was impaired, having lost a significant number of aquatic macroinvertebrate species expected to occur there, and 10% of the river length was severely impaired, having lost at least 50% of the aquatic macroinvertebrate species expected to occur. More than 95% of the river length assessed had an environmental condition that was degraded, and 30% was substantially modified from the original condition.

In the Queensland portion of the Murray–Darling drainage division, the condition of rivers and wetlands reported for 2007 was of concern.21 The majority of the Victorian catchments in the division had less than 30% of their stream length in good condition as reported in 2007, and large areas in the central and western regions had less than 10% in good condition.18 In the New South Wales portion of the division, 7 of the 25 native freshwater fish species found in lowland rivers were listed as threatened with extinction—almost double the number reported in 2006.19 Three freshwater invertebrates were listed as endangered species, and the status of many other species was of concern for conservation purposes. Three aquatic ecological communities were listed as endangered under the New South Wales Fisheries Management Act 1994. The health of rivers, streams and wetlands of the Murray River floodplain in South Australia is declining due to overextraction of water from the river system, increasing salt levels, drought and the nondelivery of environmental flows.20 The health of floodplain vegetation is also declining. Macroinvertebrate communities of the Murray River are stable and typical of a large, permanent, slow-flowing, regulated river. The biodiversity of native fish species is declining as a result of loss of habitat as wetlands dry due to drought and management actions.20

Assessments over the period 2004–076 reported on fish, macroinvertebrates and hydrology, which were chosen as criteria for their significance in river ecosystems, their sensitivities to interventions and their linkages to other features of river ecology. The assessments found the following:

  • Only the Paroo was in good ecosystem health. The Border Rivers and Condamine were in moderate health. Seven valleys were in poor health, and 13 were in very poor health.
  • Native fish populations had declined, particularly in the south. Many native fish species expected to occur in particular valleys were not recorded at all; overall, species were found in only 43% of valley zones where they were predicted to occur under reference conditions. Alien species rivalled or outnumbered native fish in 9 of 23 valleys; 10 alien species contributed 43% of abundance and 68% of biomass. Three alien species (common carp, gambusia and goldfish) were present in all rivers—carp alone were 58% of all fish biomass.
  • Most macroinvertebrate communities showed lower diversity than the reference condition.
  • One-third of sites fell short of the hydrology reference condition; these were mostly sites in the main channels of the division’s principal rivers.

The report on the reassessment of the Sustainable Rivers Audit for the Murray–Darling division for 2008–10 is anticipated in late 2011. Given that most of the data was collected during a drought, it is unlikely that the above results will have greatly improved.

The decline of ecosystems across the Murray–Darling as a result of diminished water flows has been documented in many areas of ecological science (Figure 4.10). Many of the wetlands of the northern part of the division (some of which are listed under the international Ramsar Convention) are highly degraded. About half of the river red gums (Eucalyptus camaldulensis) and river coobas (Acacia salicina) have died.34 The northern nature reserve of the Macquarie Marshes lost about three-quarters of the cumbungi (Typha spp.) and water couch (Paspalum distichum) over the 10 years to 2007.35 Three-quarters of the association between water couch and spike rush (Eleocharis obicis) and more than half of the marsh club-rush (Bolboschoenus spp.) were lost between 1996 and 2005.36

Impacts on waterbird and shorebird populations of loss of freshwater habitat due to abstractions and extended drought were evident by 2008. The annual survey of waterbird communities at the Living Murray icon sites37 in 2008 found a 48% decrease in bird numbers from the previous year. No waterbird breeding was recorded at the Lower Lakes, Coorong and Murray mouth, and only minimal breeding of white ibis and black swans occurred at Chowilla Floodplain and Lindsay–Wallpolla islands. The decline of inland wetlands was identified as a significant contributor to the drastic decline in shorebirds (73% and 81% declines for migratory and resident shorebirds, respectively) over the period 1983–2006.38

The floods in late 2010, following years of drought, were beneficial for floodplain forests, wetlands and rivers. The prolonged drought had led to a significant build-up of leaf litter on the floodplains, which in turn led to an extensive blackwater event. Blackwater events are a natural phenomenon associated with the rapid breakdown of accumulated leaf litter on the forest floor, which causes water discolouration. The breakdown of leaf litter plays an important ecological role in delivering nutrients back into the river system, thereby supporting the growth of many aquatic organisms. However, this process can result in very low dissolved oxygen levels, which can be severe enough to cause fish deaths. By mid-December 2010, a blackwater event extended across the Murray River in the Edward and Wakool river system and the Goulburn–Broken, Lower Darling anabranch and Loddon rivers. The Victorian Environment Protection Authority reported the death of hundreds of Murray cod later that month.

In the southern part of the South-east Coast division, less than 30% of stream length was found in good condition; only the catchments in eastern Gippsland had more than half their stream length in good condition.18 River health did not demonstrably change over the period 1999–2004. The condition of fish populations in coastal rivers in the northern part of the division was generally poor to moderate, while macroinvertebrate communities in most coastal river catchments were in fair to good condition.19

River health in the South Australian Gulf division, as indicated by macroinvertebrates, declined due to the effects of the prolonged drought. Wetland areas have been extensively modified, filled and drained since European settlement, and close to 90% of those in south-eastern South Australia have been lost. Along the Fleurieu Peninsula, approximately 30% of wetlands existing before European settlement remain, and just 1% of the original extent of wetlands remains in a pristine condition.20

Queensland lost more than 7000 hectares per year of wetlands from 1997 to 2003, mostly in the North-east Coast division. However, the river condition was good at almost 70% of sites monitored, based on macroinvertebrate communities. Northern regions tend to be in better condition than southern regions, with condition generally good in the wet tropics and the central region, and potentially of concern in south-east Queensland. Approximately 27% of the total length of streambank assessed for riparian vegetation condition was in poor condition (based on sampling in three catchments only). The number of native fish species across catchments remained the same as in 2003, but the number of exotic species increased by one in the Herbert, Mary and Warrego catchments. The major pressures on river condition were identified as changes in land-use and land-management practices, and changes to the natural flow regime. The Stream and Estuary Assessment Program report on the central freshwater biogeographic province of Queensland39 concluded that the overall river ecosystems in Central Province are in slightly disturbed condition (as measured by the ecological responses); the same study found that riparian condition was moderately disturbed, partly due to habitat removal and partly due to weeds.

Rivers and wetlands of the Gulf of Carpentaria division are in generally good condition.21

In Tasmania, an assessment of the ‘naturalness’ of inland waters of the Tasmania division17 found 114 175 kilometres (75%) of the state’s river length to be in near natural condition and 24 478 kilometres (16%) to be severely altered from the natural condition. Base levels of stream aquatic health were determined in 2003–04; approximately 49 of the 60 sites (82%) were in good condition (unimpaired), 10 sites (17%) were significantly impaired and 1 site (2%) was severely impaired. There was a small overall change in site condition between 2003–04 and 2005–06.

Assessment of lake naturalness in Tasmania indicated that 580 lakes (43%) are still in a natural or near-natural condition. However, only 6176 hectares (5%) of their total area has not been altered. Up to 110 274 hectares (81%) of the total lake area has been severely altered, and 20 591 hectares (15%) has been significantly altered. The discrepancy between the number and area of lakes altered is related to several large lakes that have been regulated and/or modified for hydro-electricity and/or abstraction.

More than half of Tasmania’s wetlands (12 171 hectares; 59%) and nearly three-quarters of their total area (153 604 hectares; 74%) are still in natural or near-natural condition, 7150 wetlands (35%) and 30 432 hectares (15%) of wetland area have been severely altered, and 1276 wetlands (6%) and 22 754 hectares (11%) of wetland area have been significantly altered.

A number of threatened species were associated with inland waters in Tasmania, including 14 species of freshwater plant, more than 30 riparian plant species and 76 species of freshwater fauna (including 12 native fish and 5 crayfish).

Only about 30% of Western Australia’s major rivers are in good condition, and most of these lie outside the South-west Coast division (Figure 4.11).40 Thirty-two per cent of major river basins (i.e. 12 of the 38 that are monitored) are in a largely unmodified state; most of these are in the North-western Plateau and Timor Sea divisions. Only 17% of remaining wetlands on the Swan Coastal Plain have high conservation significance, and wetland vegetation is being lost or degraded at the rate of more than 300 hectares per year. Information about the condition of other Western Australian wetlands is extremely limited.

The rivers and catchments of the Lake Eyre Basin are in generally good condition. In particular, the low level of hydrological modification means that critical aquatic ecosystem processes remain intact.41

State and trends of key species populations

The Eastern Australian Waterbird Survey provides the longest and largest-scale dataset on wetland extent and waterbird populations. The survey, which began in 1983, covers one-third of Australia on up to 2000 wetlands, using a consistent methodology. Data from the survey were used to evaluate the relationships between water availability and waterbird numbers for the 10 wetlands with highest waterbird numbers, plus the Macquarie Marshes.

Across the whole survey area, there was a significant decline in wetland extent over a 27-year period (1983–2010). Consistent decline below the long-term mean occurred after 1999, associated with the millennium drought and long-term effects of river regulation.

Waterbird abundance declined significantly over this period, with numbers dropping below the long-term mean in 1998 and remaining there (Figure 4.12). The number of breeding waterbirds and the number of breeding species also fell significantly.42 There was a clear relationship between the extent of wetlands and the abundance of waterbirds, demonstrating the importance of wetland areas. The relationship between the status of native species populations and the condition of rivers and wetlands, at a national scale, is not always so clear (Figures 4.13 and 4.14).

(2011). Inland water: Ecological processes and species populations. In: Australia state of the environment 2011, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/science/soe/2011-report/4-inland-water/2-state-and-trends/2-3-ecological-processes-species-populations, DOI 10.4226/94/58b656cfc28d1