Urban stormwater has been identified as a prime degrader of river health. And wetlands are commonly used to protect streams from the effects of urban runoff and to improve the state of the waterways in downstream reaches. We assessed changes in macroinvertebrate community along three urban streams, upstream and downstream of stormwater wetlands accounting for spatial autocorrelation.
Constructed wetlands are intended to improve water quality and ecological condition in the downstream reaches but we found no evidence of improvement in ecological condition downstream of the three wetlands we studied.
These constructed wetlands were not adequately designed for the quantity and quality of the runoff they receive. Wetlands with better design, coupled with dispersed stormwater features are likely to provide a better outcome for the stormwater treatment.
The role and benefit of constructed wetlands as a commonly used river health management option is not always clear. At least in some cases, they do not improve the ecological state of streams and may even contribute to its degradation.