Ecological assessment of streams

Project D210
Urbanization and the ecological function of streams

Project Objectives

Catchment managers, particularly in urban areas, aim to minimize the export of nutrients, especially nitrogen, from the land into streams, estuaries and coastal waters. Two aspects of urban land have been shown to result in increased loads of nutrients and other pollutants in streams:

• the proportion of the catchment covered by hard, constructed surfaces (imperviousness), and
• how well those hard surfaces are connected to the streams by stormwater pipes (connection).

These attributes also explain patterns of degradation to animal and plant communities in streams. However, the effects of catchment imperviousness and connection on the capacity of stream ecosystems to process nutrients (i.e. to convert dissolved nutrients into plant or animal tissue, to microbes, or in the case of nitrate, to nitrogen gas) have not been assessed.

Our primary aim was to determine the effects of these two key attributes of urban land use on nutrient transport and processing in streams. We also aimed to assess if the observed effects on nutrient processes are consistent with effects on more commonly used indicators of stream health (diatom and macroinvertebrate community composition).