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Over the past several decades, reductions in phytoplankton stocks and increased water clarity in Lake Erie have resulted from phosphorus load abatement and the introduction of zebra (Dreissena polymorpha) and quagga mussels (D. bugensis). The relative impacts of these developments and their implications for lake management have remained difficult to delineate. To address this issue, we numerically model the complex biophysical interactions occurring in Lake Erie using a two-dimensional hydrodynamic and water quality model that is extended to include dreissenid mussel and zooplankton algorithms. The model reasonably simulates longitudinal trends in water quality as well as the dynamics of central basin hypoxia. Phosphorus is the limiting nutrient through the euphotic zone and its control decreases the algal growth rate and biomass (∼55–60%). Filter feeding by dreissenid mussels also decreases algal biomass (∼25–30%), simultaneously stimulating increased net algae growth through enhanced algal consumption and subsequent phosphorus recycling. Effective recycling implies that algae stocks are ultimately regulated by external phosphorus loads. Returning phosphorus loads to pre-abatement 1960s levels, in the presence of dreissenid mussels, results in a western basin algae concentration of ∼0.7 mg dry weight L-1 with a potential for nuisance algae growth. [ABSTRACT FROM AUTHOR]

The circulation and exchange processes during summer stratification were examined using time-series data of horizontal velocity, temperature, and dissolved oxygen profiles during 2004 and 2005 in the mid-central basin of Lake Erie. The current and temperature spectra showed a prominent peak at around 18 h, indicating the presence of clockwise rotating inertial waves. The mean bottom currents were strong (>0.1 m s-1) and flowed in opposite direction to winds because of the surface pressure gradient due to wind set-up. The general range of horizontal exchange coefficients in the central basin is 0.2-1.2 m² s-1. Vertical exchange coefficients varied from 1 x 10-5 to 1 x 10-4 m² s-1. The high values usually occurred in the surface layer because of surface winds. The source of turbulent energy is current shear due to near-inertial oscillations in and above the thermocline and shearing stress due to the effect of mean currents and wave-induced motions during energetic wind events at the lake bottom. During strong wind episodes significant wave-induced currents were observed close to the bottom. The short-term oxygen depletion rates varied considerably between +0.87 mg L-1 d-1 and -1.16 mg L-1 d-1 in 2004 mainly because of physical processes in the central basin. When the hypolimnion depth is sufficiently thick (4 m), shortterm changes in dissolved oxygen concentrations were partly due to vertical mixing and partly due to horizontal transport and mixing. [ABSTRACT FROM AUTHOR]

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 predominately restricted to the western basin and near-shore sites in the southern part of the central basin. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]