Human activities have significantly modified flow regimes worldwide through the consumptive use of water and climate change. The frequency of overbank flow events is one aspect of flow that has been particularly impacted. Water management has reduced the frequency of overbank flows while more variable rainfall patterns may mean dry periods are increasingly interspersed with extreme flooding events. However, the importance of these high-flow events for aquatic productivity and energy flows within riverine ecosystems is not well understood. Food webs can be used to capture and quantify species interactions, revealing whole ecosystem responses, rather than the typical approach of measuring individual species’ responses.
Working on Wiradjuri Country on the Calare (Lachlan River) NSW, this project quantified the influence of high and overbank flow on river food webs by measuring the abundance of basal resources and consumers and assessing their trophic interactions through the analysis of stable isotopes. The uncharacteristically high flows during sample collection provided a unique opportunity to quantify food web responses under prolonged overbank flows. Overall, our results indicated overbank flows produce booms of aquatic productivity. As the volume of water and the duration of floodplain inundation increased, we observed a surge in the biomass of basal resources such as detritus and algae. High abundances of decapods on the floodplain suggested this productivity was utilised by higher trophic levels. This suggests riverine productivity regimes will be modified by a more variable climate and this knowledge can be used to identify optimal environmental flow strategies to maintain food webs in the face of global change.