Limitations of sediment quality surveys: a case study of an urban watershed in British Columbia, Canada

This case study of a 7200 ha. urban watershed illustrates the challenges involved in using sediment quality surveys to determine pollutant sources and trends. Trace metal and chlorinated hydrocarbon analyses were performed on sediment samples obtained from 33 stream, 24 street, and 1 lake (sediment core) locations. The stream and street sediment survey was initially conducted in 1973 and repeated in 1993. Consistent results across all sediment media indicate significant reductions in Pb, PCB, and DDT levels have occurred since the 1970's as a result of source controls. While streambed results indicate Hg and Mn levels have increased significantly since 1973, neither a spatial analysis of streambed results or a comparison to street concentrations indicate a source for the increase. A more detailed geo-chemical analysis and/or atmospheric contaminant survey may provide more conclusive source information.