Assessing change in riverine organic matter dynamics in the Hunter River, NSW, over the last 200 years: Implications for stream restoration

Successful river rehabilitation requires the restoration of self-sustaining ecosystem functions. One key function is organic matter cycling, including the sources, transfers and sinks of organic matter as it moves from the catchment, across floodplains, down streams, and exchanges with groundwater in the hyporheic zone. River food webs may depend heavily on organic matter generated in-stream by microbial and algal biofilms whereas flow pulses may import leaf litter from the floodplain. Bars and riffles retain this organic matter while generating diverse microhabitats whose particular biogeochemical conditions favour different suites of microbes. Poor land management has deprived the Hunter River of geomorphic complexity at the broad scale of bars and riffles. This paper reviews historical changes to channel shape and vegetation regime in the Hunter River and the repercussions of these on organic matter dynamics over the last 200 years. We conclude that introduction of wood will partly restore conditions closer to those pre-European settlement and alter hyporheic processes but that organic matter dynamics may never be fully restored.