Two sulfur-mediated reactions are resulting in the eutrophication of Lake Biwa, Japan. The iron (II) phosphate mineral vivianite is dissolving in sulfide-enriched sediments that in places results in porewater concentrations of phosphate exceeding 3 mg l Ϫ1 . The dissolution of phosphate is evident in profiles of total phosphorus where zones of dissolution and a zone of precipitation in the most oxic surface sediments are visible. At times sulfate reduction in these surface sediments results in pH values as high as 9.9, which can dissolve phosphate adsorbed to iron (III). This release of phosphorus from sediments is at least partially responsible for the recent appearance of blue-green algal blooms.

An outbreak of avian botulism in Whitewater Lake, Manitoba, Canada was associated with reducing sediments. But any linkage between sediments and botulism was only indirect; Clostridium botulinum was not observed in the sediments. The source of the C. botulinum was unclear but carcasses that overwintered appeared to perpetuate the outbreak. The algal toxins anatoxin-a and ( ) microcystin-LR were present 17 ( mg/ L when many birds were moulting and unable to fly, likely making them more sensitive to botulism. The sediment anoxia released phosphorus into lakewater so that concentrations increased from about 73 to 470 mg/ L and enhanced growth of Microcystis and Aphanizomenon. Wind resuspension of sediments resulted in areas with more algal biomass and associated algal toxins. ᮊ

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Sediment treatment options include dredging, physical and chemical capping, and in situ sediment treatment. In our studies, in situ sediment treatment has been used to oxidize sediment sulphides, control eutrophication and bioremediate organic contaminants. Sediment contamination of various types was studied in 22 sites from six countries in North America, Europe and Asia. In Hong Kong, field testing of sediment treatment oxidized 99% of sulphide and controlled odours. In Lake Biwa, Japan, where excess nutrients in sediments enhanced growth of toxin producing algae, sediment treatment with calcium nitrate blocked growth of these algae. Oxidation of sulphide in Lake Biwa sediments precipitated > 80% of the porewater phosphorus. Oxidation of sulphides and addition of nutrients biodegraded more than half of the organic contaminants in Hamilton Harbour, Canada. The biotreatability of polynuclear aromatic hydrocarbons is very site specific and is faster in sites with higher concentrations of oil.

Many of the Great Lakes Areas of Concern include harbours and navigable channels that experience disturbance of bed sediment due to the passage of large ships. Sediment resuspension due to ship passage may impact efforts to restore habitat and remediate contaminated bed sediment through in situ treatment. To examine the impacts of ship passage, water column profiles of temperature, pH, turbidity and dissolved oxygen, as well as suspended sediment samples, were taken at varying distances behind ships entering an industrial slip area of the Hamilton Harbour Area of Concern during the summer of 1995. Weekly water column profiles and suspended sediment samples also were collected at three sites in the slip area and a harbour control site to characterize ambient water quality. Ship passage significantly increased turbidity above ambient levels due to sediment resuspension, although the increase was less in the deeper areas of the slip. Levels of turbidity and suspended sediment concentration associated with ship passage exceeded that recommended for a moderate level of fish habitat protection. In association with the increased turbidity, levels of dissolved oxygen declined and often were less than 5 and 6.5 mg L-1, the Canadian Water Quality Guideline for later life stage warm and cold water fisheries, respectively. Based on the sample data and in situ flume experiments, the estimated depth of bed erosion due to a ship passage ranged from 1 to 8 mm. The impacts of sediment disturbance due to a ship passage should be considered when selecting and designing appropriate sites and technologies for remediation.