Monitoring River Health Initiative Technical Report Number 8b
Simon Townsend - Northern Territory Department of Infrastructure, Planning and Environment
Department of the Environment and Heritage, 2003
ISBN 0 642 54969 9 ISSN 1447-1280
- Australia-Wide Assessment of River Health: Northern Territory Status Report and Commentary (2001) (PDF - 256 KB)
About the report
When the National River Health Program Monitoring River Health Initiative (MRHI) was initiated in 1994, the Northern Territory agency primarily responsible for water resource management was the Power and Water Authority. Ecological assessment and monitoring by the Authority focused on reservoirs supplying potable water. Negligible effort was directed to monitoring the river health. The participation of the Power and Water Authority in the MRHI prompted the agency to extend biological monitoring to the Territory rivers, and more specifically, to develop predictive models to contribute to the assessment of the river health. Owing largely to logistic and practical constraints, only the seasonally, seaward flowing rivers in the Top End of the Territory were included in the MRHI.
Flow regimes in the wet/dry tropics of the Top End are highly seasonal, with more than 95% of flow volume during the wet season. Most rivers and streams cease flowing during the dry season, though the timing is dependent on stream order, catchment hydrology, wet season rainfall and the depth of the groundwater table. In the dry season, seasonally flowing rivers reduce to either a series of permanent or temporary pools, or a dry riverbed. Some rivers, however, are perennial, being supplied by groundwater throughout the dry season; for example, the Daly, Katherine and Roper Rivers.
MRHI assessments during the wet season were both impracticable, for reasons of access and safety, and undesirable, owing to the frequency of storm runoff and flood events that modify the physical habitat and disturb the macroinvertebrate community. Consequently, samples were collected during the dry season. Early dry season sites were sampled between May and August, and late dry season sites between July and November. The overlap of the two sampling periods was due to differences between years in river access and river flow, and resource availability. At each site, edge and sand-bed habitats were sampled in accordance with the Territory's sampling protocol (Lloyd and Cook 1998).
The Northern Territory MRHI developed six predictive models. These models were derived from macroinvertebrate data and environmental variables at sites considered to be in reference condition. Macroinvertebrate samples were sorted in the laboratory. Models were produced for edge and sand bed habitats for the early and late dry season, and combined season data sets, for each habitat. The differences in the classification of the macroinvertebrate fauna groups for each model were small, with no clear geographic pattern between sites, or membership between years (Dostine 2001).