Testing the waters: impacts of contaminants on ecosystem structure and function in urban waterways

Estuaries are diverse and productive ecosystems that are subject to high levels of disturbance from multiple human stressors. These ecosystems are exposed to multiple stressors such as legacy contaminants in sediments and... [ view full abstract ]

Estuaries are diverse and productive ecosystems that are subject to high levels of disturbance from multiple human stressors. These ecosystems are exposed to multiple stressors such as legacy contaminants in sediments and ongoing inputs of nutrients and metals via stormwater. Such anthropogenic modifications are likely to impact both ecosystem structure and function. However, most assessments of waterways only measure ecosystem structure and we are not yet able to predict anthropogenic effects on ecosystem function. We surveyed sediment communities at four locations with large stormwater drains in Sydney Harbour, Australia. Locations were either embayments and were poorly flushed or were open channels and were well flushed. Sediment was collected monthly for 6 months from 3 sites within each location at increasing distance from the stormwater drain (0, 200 and 1000 m). Next-generation sequencing was used to characterize the sediment microbial community together with traditional morphological identification of infauna. Sediment was subsampled for a range of sediment characteristics including metals, total organic carbon, total nitrogen and phosphate, and chlorophyll-a. Sediment cores were also collected to measure biogeochemical processes. Sediment microbial communities differed significantly between channels and embayments and shifted significantly with distance from drains, but only in channels. Community respiration rates decreased away from storm drains and lowest rates of primary production occurred during base flows (<5mm rainfall/day). Rarely have observations been collected of both structure and function in conjunction with ecological processes. The results have implications for future management practices in estuaries and increase our understanding of the relative impacts on benthic estuarine communities of stormwater run-off and contamination from industrial practices.