The re-eutrophication of Lake Erie: Harmful algal blooms and hypoxia.

Lake Erie supplies drinking water to more than 11 million consumers, processes millions of gallons of wastewater, provides important species habitat and supports a substantial industrial sector, with >$50 billion annual income to tourism, recreational boating, shipping, fisheries, and other industries. These and other key ecosystem services are currently threatened by an excess supply of nutrients, manifested in particular by increases in the magnitude and extent of harmful planktonic and benthic algal blooms (HABs) and hypoxia. Widespread concern for this important international waterbody has been manifested in a strong focus of scientific and public material on the subject, and commitments for Canada-US remedial actions in recent agreements among Federal, Provincial and State agencies. This review provides a retrospective synthesis of past and current nutrient inputs, impairments by planktonic and benthic HABs and hypoxia, modelling and Best Management Practices in the Lake Erie basin. The results demonstrate that phosphorus reduction is of primary importance, but the effects of climate, nitrogen and other factors should also be considered in the context of adaptive management. Actions to reduce nutrient levels by targeted Best Management Practices will likely need to be tailored for soil types, topography, and farming practices.

Trends in spatial and temporal levels of persistent organic pollutants in Lake Erie sediments.

A Lake Erie sediment survey was conducted in 1997 to characterize spatial trends in contamination, and for comparison with a 1971 survey to assess any changes in environmental quality since the advent of measures to reduce contaminant sources. Contaminant data for some contaminant classes in 1971 was based on analysis of frozen archived samples, thereby allowing a direct comparison between surficial sediment contamination in 1971 and 1997 based on modern analytical methods. Lake-wide contaminant concentrations of polychlorinated biphenyls (PCBs) and organochlorine compounds including hexachlorobenzene and the DDT compounds in 1997 were substantially lower, compared to levels in samples collected in 1971. Lake-wide average sediment PCB levels were found to have decreased roughly 70% from 136 ng/g in 1971 to 43 ng/g in 1997. Similarly, reductions in other compound classes ranged from 40% to 80%. In 1997, some individual contaminants classes including PCBs exhibited a spatial trend toward increasing sediment contamination from the eastern basin to the western basin, and from the north-central basin to the south-central basin. Levels of organic contaminants in sediments in some areas of Lake Erie still exceeded the strictest Canadian Federal and Ontario Provincial guidelines. However, exceedances of guidelines describing contaminated environments in 1997 were predominantly restricted to the western basin and near-shore sites in the southern part of the central basin.