The shallow Tooms Lake dam was constructed in 1840 and supplies water for irrigation to much of the Tasmanian Midlands, via Tooms River. Although this river has been regulated for over 170 years, the invertebrate community remains depauperate and dominated by fly larvae, worms and snails, in contrast to the diverse fauna of the adjacent unregulated Macquarie River. In addition, the 2006-08 drought impacted more severely on the macroinvertebrate community of Tooms River, showing that the biota have less resilience to drought and potentially to climate change, than the biota of the highly variable-flow Macquarie River.
There is a tendency to consider that the benefits of dams outweigh the detriments, but little monitoring has been done to actually measure the impacts of small irrigation supply dams. Despite this, further irrigation projects are proposed for the central Midlands, with more dams and inter-catchment transfers of water to expand agricultural productivity and build resilience to drought and climate change for farmers.
The NCCARF ‘Joining the Dots’ project combined outputs from dynamically downscaled climate models with hydrological modelling and systematic biodiversity data as inputs to Bayesian Belief Networks (BBNs). The BBNs identified major impacts to Tasmanian freshwater biota from projected climate change. These impacts are predicted to be most severe in low rainfall regions which already have high demand for irrigation supply, such as the central Midlands.
Is this the future for freshwater biodiversity in southern Australia? A proliferation of dams to exacerbate the impacts of climate change?