Biomonitoring of wet-weather flow impacts on fine sediments in urban waters: Canadian and French experience

Benthic invertebrate assessments can be used to gauge the impact of urban wetweather flows in receiving waters. Experiences from Cemagref in France have shown that standardized benthic indices (e.g. Oligochaete Index of Sediment Bioindication IOBS) can be used to reliably determine the ecological status of urban streams and can be incorporated into the new European Water Framework Directive. The Canadian studies on streams and stormwater ponds using chemical analyses, benthic toxicity testing and benthic community structure comparisons have shown that toxicity was more likely to occur in deeper ponds where fine sediments from urban runoff accumulated. A more comprehensive evaluation of wet-weather flow impacts could be obtained by combining approaches from both countries.