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

Abstract

The contamination of Toronto Harbour is a very serious problem. The major sources of pollution are the Don River and sewer outflows, as well as industrial, and municipal effluents. The problem is further compounded by perturbations of the toxic sediment caused by dredging, dredge-disposal, navigation, and recreational activities. The impact of contamination and nutrient enrichment was reflected in the sizefractionated primary productivity experiments. Generally, microplankton/netplankton (> 20 im) productivity was enhanced whereas ultraplankton (< 20 Jm) productivity was inhibited. These observations are attributable to interactions between ameliorating nutrients and toxic contaminants as well as to the differential sensitivity of natural phytoplankton size assemblages to the bioavailable chemical regime. In situ environmental techniques applied in Toronto Harbour were effective, sensitive, and rapid, and provided a better understanding of the impact of dredging/disposal activities under natural conditions. These techniques have great potential in the assessment of the ecotoxicology of harbours and other stressed environments.

Environmental studies on impacts of dredging

“…Sivadasan and Joseph [45], 1995 have opined that in estuarine waters the ratio of Chlorophyll c/Chlorophyll a is often an indication of the crop activities and also points to the environmental health under conditions of external stress. In situ bio assessment of dredging at Toronto harbour had approached the problem by considering the ratios of planktonic abundance in order to differentiate the relative effects of desilting [46]. During the dredging period (moderate to intensive) the values above unity is thence an IMPACTS OF DREDGING 715 indication of rather unhealthy crop as read for surface waters.…”

Environmental Screening Method for Dredging in Contaminated River

“…The reason for using historical dredging data lays in the fact that previous research indicates that concentration levels of metals in sediments increased after dredging. This means that contaminants dispersed by dredging are deposited back onto the new layer of sediments, exposed after excavation [14][15][16]. This creates a potential for future dredging to disperse the contaminants that have been re-deposited.…”