Indicator description

Why is it indicative

What does the data show

Data

Related Indicators

Acknowledgment

Indicator description

Assemblages of macroinvertebrates at the river reach and basin scale, as assessed by AUSRIVAS (Australian River Assessment Scheme) sampling protocols and computer models and E-Ball models.

Why is it indicative

Similar to AUSRIVAS, this indicator assesses river condition in a manner that complements more traditional assessments of water quality by introducing an ecosystem perspective. Macroinvertebrate assemblages are considered to be good indicators of disturbance to rivers and their catchments. They are also components of, or critical to, the goods and services provided by healthy rivers that are valued by society. Catchment and habitat conditions are assessed in addition to macroinvertebrates to provide information about the causes of degradation, which can help to guide management decisions (Norris et al. 2001).

What does the data show

• ARC was conducted with a primary focus for reporting at the basin scale using different methods to those employed in the River Health (AUSRIVAS) indicator, and as a consequence there are some inconsistencies between the results of the separate assessments.
   
• In ARC biota assessments are broad scale and represent the average condition of the rivers and streams in a basin as assessed by sites sampled relative to minimally damaged reference sites (Norris et al. 2001). Therefore, any variation in river condition between seasons and habitats, which is noted to be of some import in Tasmania (see River Health indicator), is not distinguished.
   
• AUSRIVAS test sites are used in the ARC biota assessments, which may have introduced some bias towards poorer health than might have been assessed if sites had been chosen randomly across an entire basin.
   
• Data was not always consistently available, both spatially and temporally, for the environmental assessment, which limited the length of river that could be assessed and resulted in variations in the quality of measure for some sub-indices.
   
• River reaches and basins assessed across the state using ARC methods are generally in good condition based on their macroinvertebrate communities, but the environmental condition assessment demonstrates that more than half of the reaches and basins are degraded. Reasons for this discrepancy may include:
   
• macroinvertebrates may be insensitive to some environmental changes, including large-scale changes (e.g. changes in connectivity and catchment disturbance), and to changes in some riverine habitat components (e.g. changes in salinity);
   
• there may be lags between environmental degradation and biotic condition (e.g. nutrient or sediment loads to streams); or
   
• an environmental component that would explain a biotic response was not measured (e.g. a toxicant).
   
Where the two indices agree that neither the biota nor the riverine environment have been damaged, the management action adopted may be conservation or maintenance of the status quo. Similarly, where both indices suggest severe impact, the ecosystem is clearly damaged and action is required (Norris et al. 2001).
• The key issues affecting the rivers are associated with changes in land use, reduction in riparian vegetation and connectivity of the stream and elevated loads of total phosphorus and suspended solids.
   

Data

ARC is reported in two parts including the biota index and the environmental index. There are five basic indices that comprise the overall ARC, including:

• one for biotic condition - Aquatic Biota Index;
   


• one for catchment condition - Catchment Disturbance Sub-Index; and
   


• three for habitat condition - Nutrient and Suspended Sediment Load Sub-Index, Hydrological Disturbance Sub-Index and Habitat Sub-Index.
   

In the ARC procedure (available through the ANRA website) biotic index values for reaches are derived from the AUSRIVAS O/E FAMILIES values, and/or modeled E-Ball MO/E values. Where neither was available in a reach, no biotic index was recorded for that reach.

The overall biological assessment of Tasmanian rivers found that 76% of the river length assessed is in reference condition as noted in the table below. The remaining 24% of river length assessed, however, is impaired, with 20% significantly impaired.

The environmental assessment found that 63% of the river length assessed was modified (59% moderately modified and 4% substantially modified). Catchment disturbance, habitat and nutrient and suspended sediment loads contribute the most to this damage.

Over half of the river length assessed had disturbed catchments. This was particularly as a result of land use activities contaminating run-off to rivers, while disturbance from infrastructure was a minor contributor. More than 25% of the river length assessed had altered hydrological regimes. Eight to twelve per cent and six to fourteen per cent of the river length assessed in substantially modified and moderately modified condition, respectively, were being affected by changes to mean annual flow, flow duration and seasonal amplitude. However, only 23% of the total river length was assessed.

The physical habitat has been changed in over 40% of the river length assessed. This is in response to changes in connectivity and riparian vegetation at 33% and 22 % of the river length assessed, respectively. Twenty-two per cent of the river length assessed was severely modified, based on connectivity, indicating significant changes to the lateral and/or longitudinal connectivity in these areas.

Greater than 40% of the river length assessed in Tasmania had altered nutrient and suspended sediment loads with elevated loads of suspended solids and total phosphorus at 34% and 39% of the river length assessed, respectively.

The key issues affecting the rivers are associated with changes in land use, reduction in riparian vegetation and connectivity of the stream and elevated loads of total phosphorus and suspended solids (Norris et al. 2001).

Statewide river condition for biota and environment indices, and environment sub-indices.

	Total length of reach in each category and percentage of total				% of total with data
	Reference	Significantly Impaired	Severely Impaired	Extremely Impaired
Biota Index (Map)	4,248 76%	1,097 20%	142 3%	100 2%	100%
	Largely Unmodified	Moderately Modified	Substantially Modified	Severely Modified
Environment Index (Map)	2,028 37%	3,250 59%	194 4%	0 0%	98%
Catchment Disturbance	2,455 44%	2,918 52%	213 4%	0 0%	100%
Hydrology	951 73%	180 14%	152 12%	20 2%	23%
Habitat	3,296 59%	998 18%	1,177 21%	114 2%	100%
Nutrient and Suspended Load	3,233 59%	1,811 33%	429 8%	0 0%	98%

Values may not add up exactly as a result of rounding.

Source: Norris et al. 2001

Across the State, eight basins are largely unmodified and the biota are in reference condition, as shown in the table below. The environmental condition of nine basins are modified to some degree, while the biota in only four of these basins (Coal, Piper-Ringarooma, Derwent and Tamar) were rated as significantly impaired.

Summary results of river condition by basin

Basin	Environment Index	Biota Index
Arthur River	0.82	1
Coal River	0.44	0.78
Derwent River	0.64	0.79
East Coast	0.72	0.89
Flinders-Cape Barren Islands	Not assessed	Not assessed
Forth River	0.64	1
Gordon River	0.86	1
Huon River	0.85	1
King Island	Not assessed	Not assessed
King-Henty Rivers	0.82	0.95
Kingston Coast	0.79	0.89
Mersey River	0.63	0.97
Pieman River	0.82	0.85
Piper-Ringarooma Rivers	0.69	0.79
Rubicon River	0.63	0.85
Sandy Cape Coast	0.91	0.97
Smithton-Burnie Coast	0.68	0.99
South-west Coast	0.88	1
Tamar River	0.6	0.8

Index values given range between 0-1, and equate to river conditions described in Figure 36 within the Australian Catchment, River and Estuary Assessment 2002 Report

Source: Norris et al. 2001

Related Indicators

Acknowledgment

'Core Inland Waters and Wetlands Indicator' IW 13 (ANZECC 2000) adapted using: Norris et al. 2001.