The influence of urbanisation on macroinvertebrate biodiversity in constructed stormwater wetlands

The construction of wetlands in urban environments is primarily carried out to assist in the removal of contaminants fromwastewaters; however, thesewetlands have the added benefit of providing habitat for aquatic invertebrates, fish and waterbirds. Stormwater quantity and quality is directly related to impervious area (roads, sealed areas, roofs) in the catchment. As a consequence, it would be expected that impervious areawould be related to contaminant load and biodiversity in receivingwaters such as urbanwetlands. This study aimed to establish whether the degree of urbanisation and its associated changes to stormwater runoff affected macroinvertebrate richness and abundance within constructed wetlands. Urban wetlands in Melbourne's west and south east were sampled along a gradient of urbanisation. There was a significant negative relationship between total imperviousness (TI) and the abundance of aquatic invertebrates detected for sites in thewest, but not in the south east. However macroinvertebrate communities were relatively homogenous both within and between all studywetlands. Chironomidae (non-biting midges)was the most abundant family recorded at the majority of sites. Chironomids are able to tolerate a wide array of environmental conditions, including eutrophic and
anoxic conditions. Their prevalence suggests that water quality is impaired in these systems, regardless of degree of urbanisation, although the causal mechanism is unclear. These results show some dependency between receiving
wetland condition and the degree of urbanisation of the catchment, but suggest that other factors may be as important in determining the value of urban wetlands as habitat for wildlife.