In search of effective bioassessment of urban stormwater pond sediments: enhancing the ‘sediment quality triad’ approach with oligochaete metrics

Stormwater ponds have been widely used to control increased volumes and rates of surface runoff resulting from urbanization. As receiving waters, they are under the influence of intermittent pollution from urban wet-weather discharges. Meanwhile they offer new aquatic habitats balancing the transformation of initial ecosystems and their associated biodiversity. Bioassessment of stormwater facilities is therefore crucial to insure the preservation and rehabilitation of biodiversity in urban areas. Nonetheless, the application of traditional bioassessment methodologies such as the sediment quality triad (SQT), based on the comparisons with reference sites, is challenged by the artificial and atypical features of urban stormwater ponds. Our concern in finding a more specific and effective bioassessment methodology led us to consider associating the Oligochaete Index Methodology (OIM) with the SQT. This study shows that although some adjustments were needed, the OIM brought new and complementary information to the SQT assessment on the effects of contaminants and on the biological quality status of the sediment in a test urban stormwater pond.