Functions of riparian forest in urban catchments: a case study from sub-tropical Brisbane, Australia

Abstract

Riparian forests are vital for maintaining healthy stream ecosystems; acting as buffers against nutrient and contaminant inputs, contributing energy subsidies and providing favorable instream habitat conditions. In urban catchments riparian forests are often degraded or cleared, removing the ecosystem functions the forest provides. Intact riparian forest along urban waterways, may mitigate some aspects of degradation associated with an urbanized catchment. In Bulimba Creek, an urbanized catchment in southeast Queensland, Australia, we investigated some ecosystem functions provided by riparian forest. We found that during baseflow periods a forested riparian corridor provided energy subsidies to the stream through litterfall and had a controlling influence on instream production through shading. Denitrification potential of benthic sediments increased with increasing levels of woody debris and organic matter, deposited from riparian vegetation. Denitrification was nitrate limited, indicating some potential to reduce nitrate loads in the stream. Riparian soils also showed moderate denitrification potential; which, through management strategies, could be utilized to reduce excess nitrate loads. These results suggest that riparian forests provide important functions for urban streams; highlighting the importance of conserving forest remnants in urban landscapes and the usefulness of replanting degraded riparian forest to enhance stream health and habitat condition.