Bacterial enzyme activity and metal speciation in urban river sediments

The effects of stormwater and combined sewer overflows on receiving waters were investigated using measurements of bacterial enzyme activity and metal speciation in the sediments of five urban rivers. Free flowing urban rivers had high enzyme activity and low metal concentration in sediments, indicating a lack of contribution by stormwater sediments. More stagnant urban rivers, which tended to trap sewer-discharged sediments, were characterised by inhibited enzyme activity and high ammonium acetate- and EDTA-extractable metal concentrations. Profiles along two urban rivers showed a direct inhibition of enzyme activity at sites of stormwater and industrial discharge. Deposited sewage, from combined sewer overflows, was indicated by highly elevated enzyme activity and metal concentrations. The results of this study demonstrate that the ecologically relevant enzyme activity measurement may be a useful complement to metal speciation analysis when investigating the effects of stormwater discharges on urban rivers.