Investigating the ecological benefits of stormwater channel naturalisation in Sydney Harbour

<p dir="ltr">Urban stormwater delivers a range of pollutants to waterways via stormwater channels, traditionally constructed of impervious surfaces that prevent infiltration. Efforts to address this issue include naturalising stormwater channels, which involves the removal of concrete and revegetation of banks. This assists in filtering pollutants and provides habitat for benthic communities that increase oxygenation of sediments and may enhance resilience to disturbances. This study investigated the effect of channel naturalisation on sediment quality, benthic populations, and its potential ecological responses to rainfall events. Five stormwater channels (2 naturalised and 3 unmodified) were sampled in Sydney Harbour (Australia) during average conditions and periodically (2, 3 and 5 weeks) after a heavy rainfall event. We found channel naturalisation did not affect sediment quality, measured by the organic matter content, grain size and metal concentrations. Naturalisation slightly increased benthic infauna abundances, but overall biodiversity was extremely low, comprising of the macroinvertebrate families Nereididae and Chironomidae, and did not see any significant recovery after the rainfall event studied. While channel naturalisation has been linked to other benefits including improved aesthetics, this study provided limited evidence of ecological benefits with respect to increased infauna abundances and no evidence of faster recovery after major disturbance.</p>