6. 7. Assessment of ecosystem responses to in-channel environmental flow pulses The regulation of the world’s major river systems is a threat to global biodiversity (; ; ; ). Under natural flow regimes, riverine systems are a complex mosaic of habitats which vary across space and time with changes in water volume, velocity and flooding duration (; ; ). Periods of high flows (flood pulse) inundate river benches, fill back waters and small anabranches and raise ground water levels which can lead to the creation of groundwater ponds along river margins (; ). Likewise periods of low flow result in slow flowing or still water which can provide habitat for taxa sensitive to higher flow velocities (; ). Under river regulation, these periods of very high and very low flows are reduced with subsequent reductions in the availability of habitat types linked to these flow conditions (). Despite the threat presented by regulation, there are only a small number of empirical studies testing the mechanisms whereby changes to the river flow regimes drive changes in key population processes and ecological functions (; ). In the case of fish, changes in natural flooding regimes can lead to reduced recruitment success (), changes in movement patterns () and increased densities of exotic fish species (). Changes to aquatic macroinvertebrate communities (; ; ; ) and biofilm production () also occur following the simplification of flow regimes. The impacts of river regulation on other riverine taxa, such as frogs, are poorly understood. In recent years, growing awareness of the ecological impacts of river regulation has led to increased interest in managing flows and delivering environmental water to restore the ecological function of regulated river systems (; ; Poff 2009). In Australia over the past five to ten years there have been numerous examples of the delivery of environmental water to inundate wetlands, and in many cases
flows. Dissolved oxygen data from continuous loggers (to be presented in the final report) will provide more detail related to environmental watering and natural pulses. Weekly water samples collected during the natural flow events in March 2012 illustrate the progression of the associated blackwater event through all sites, with Little Merran Creek being the only system continuing to be affected by early April and all sites returning to normal levels by May 2012. There was no immediate response of frogs to the environmental watering in Colligen Creek in February 2011. The abundance of frogs in Colligen Creek did not change in response to the February environmental watering or during the unregulated high flows in March. In contrast the abundance of frogs increased in March and April in Yallakool, Wakool and Little Merran Creeks with the most notable increase occurring in Yallakool Creek. The frog community in Colligen Creek was different to that in the other three rivers. It is not clear whether this was influenced by the environmental watering in Colligen Creek or reflects specific geomorphic features of the study reach. A more comprehensive understanding of frog responses to environmental watering would be gained by increasing the number of sample reaches within each river in order to capture the full extent of geomorphic diversity within each river.