Experimental approach for assessing how stormwater runoff affects macroinvertebrate communities in urban streams

Background/Question/Methods

Numerous studies have documented declines in the diversity and abundance of macroinvertebrate communities in urban watersheds. However, the extent to which these declines are caused by non-point source pollution as opposed to physical habitat factors remains unclear. We examined the effects of contaminants in urban stormwater on macroinvertebrate communities, specifically whether exposure to contaminated sediments alters macroinvertebrate drift behavior and survival. Using a custom built filtration system and experimental stream channels on a degraded stream in Seattle, WA, we exposed diverse macroinvertebrate communities (from an unimpacted stream) to either filtered (“clean”) or unfiltered (ambient) stream water for several three-week experiments.

Results/Conclusions

Analysis of chemistry samples indicated there were differences between treatments (e.g. reduction of polycyclic aromatic hydrocarbons and metals in filtered treatments relative to unfiltered treatments), and we observed differences in the drift behavior and survival for some sensitive macroinvertebrate taxa. Several mayfly genera in the Heptageniidae family were particularly sensitive to the unfiltered treatments, drifting out of the unfiltered channels at higher rates during rain events. Such reductions in sensitive invertebrates may help explain why communities in chronically-exposed urban watersheds are depauperate, and why species that rely on invertebrate production, such as endangered salmonids may be at risk as well.