Macroinvertebrate and water quality responses to low flows in Tasmanian rivers

This report has been prepared for the National Water Commission as part of the Low Flow Ecological Response and Recovery Project, which seeks to examine low-flow ecological response thresholds and recovery trajectories.

To investigate ecological responses to low-flow conditions in riverine ecosystems in Tasmania, two case studies are presented. The first investigates aquatic macroinvertebrate communities in unregulated rivers in Tasmania with natural low-variability (LV) and high-variability (HV) flow regimes, and their responses to hydraulic variables during low-flow conditions over a four-year period (2007–10) is presented. This case study relied heavily on existing datasets from the Tasmanian Environmental Flows Project (TEFlows Project) that the Department of Primary Industries, Parks, Water and Environment (DPIPWE) completed recently. The second case study examines water quality (physico-chemical) monitoring data collected by DPIPWE in rivers with LV and HV flow regimes in Tasmania in relation to the effects of low-flow conditions. This case study used in situ measurements and continuously recorded physico-chemical data from rivers during periods including low-flow spells to examine physico-chemical responses to low-flow events and recovery trajectories in these variables following the resumption of moderate (or high) flows. Riverine monitoring programs that have recently been undertaken in Tasmania were also reviewed. Based on the findings of the two case studies, and knowledge gained from other recent studies in Tasmania, the effectiveness of these monitoring programs during low-flow conditions is briefly evaluated. We also outline the issues that should be considered if targeted low-flow monitoring programs are to be developed.