In situ bioassessment of dredging and disposal activities in a contaminated ecosystem: Toronto Harbour

Toronto harbour received polluting discharges from the Don river, sewer outflows, industrial and municipal effluents as well as disturbance of the toxic sediments caused by dredging, dredge spoil disposal, navigation and recreational activities. Size-fractionated primary productivity studies involved experiments on the in situ impact of dredging (pre, during, post), and disposal (pre, post (10 or 60 minutes)) together with sediment elutriate bioassays and statistical evaluation. Results indicated that, due to interactions between nutrients and toxic contaminants, as well as to the variable sensitivity of natural phytoplankton size assemblages to bioavailable chemicals, microplankton/netplankton (greater than 20 um diameter) productivity was increased while ultraplankton (less than 20 um diameter) productivity was inhibited. The in situ environmental techniques as applied to Toronto harbour were effective, sensitive and rapid and had great potential for the assessment of the ecotoxicology of harbours and other polluted environments.