Dreissenid mussels have been exceptionally successful invaders in North American lakes and rivers, especially in the lower Laurentian Great Lakes. As benthic filter feeders capable of attaching to hard substrates, the magnitudes of their biomass and filtering activity in nearshore waters are without precedent. The dreissenid colonization has implications for the removal and fate of materials filtered from the water by the mussels and for the longer-term development of the nearshore benthic community and lake ecosystem. A conceptual model, the nearshore shunt, seeks to describe a fundamental redirection of nutrient and energy flow consequent to dreissenid establishment. The model explains some emergent problems in the Great Lakes, such as reemergence of Cladophora in some coastal zones while offshore P concentrations remain low, and highlights areas in need of more research. The source of particulate nutrient inputs to dreissenids and the fate of materials exported from the benthic community are critical to understanding the role of dreissenids in the lakes and assessing the applicability of current models for managing nutrients and fisheries. The nearshore shunt would require even more stringent P management for lakes strongly impacted by dreissenids to maintain nearshore water quality.Résumé : Les moules dreissenidées ont envahi avec un succès exceptionnel les lacs et rivières d'Amérique du Nord, et en particulier les Grands Lacs inférieurs. Des animaux benthiques se nourrissant par filtration et capables de se fixer à des substrats durs, ils ont atteint des biomasses et des niveaux d'activité de filtration sans précédent dans les eaux côtières. La colonisation des dreissenidés a des conséquences sur le retrait et le sort des matériaux filtrés de l'eau par les moules, ainsi que sur le développement à plus long terme de la communauté benthique près du rivage et sur l'écosystème lacustre. Un modèle conceptuel, la « déviation côtière », cherche à décrire l'altération fondamentale du cheminement des nutriments et du flux d'énergie depuis l'établissement des dreissenidés. Le modèle explique certains des problèmes qui surgissent dans les Grands Lacs, comme la ré-emergence de Cladophora dans certaines zones côtiè-res, bien que les concentrations de phosphore au large restent faibles et il identifie des domaines qui nécessitent des recherches supplémentaires. Une connaissance des sources des apports de particules nutritives pour les dreissenidés et du sort des matériaux exportés de la communauté benthique est essentielle pour comprendre le rôle des dreissenidés dans les lacs et pour évaluer l'applicabilité des modèles courants de gestion des nutriments et des pêches. La « dévia-tion côtière » exigerait une gestion encore plus rigoureuse du phosphore dans les lacs fortement affectés par les dreissenidés afin de maintenir la qualité de l'eau près du rivage.[Traduit par la Rédaction] Hecky et al. 1293

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Until recently, hypolimnion oxygen consumption was thought to be a way of comparing the productivity of lakes. This study shows that hypolimnion oxygen represents hypolimnion thickness and temperature as well as productivity. A relationship based on the multiplicative effects of chlorophyll (productivity), thickness, and temperature closely fits the observed oxygen depletion in the Laurentian Great Lakes and in many small lakes. Applied to Lake Erie, the relationship suggests that although a 50% decrease in productivity may result in higher oxygen concentrations, significant oxygen depletion would still occur. The use of oxygen concentrations, depletion rates, or areal deficits to compare the productivity of lakes is not justified without reference to hypolimnion thickness and temperature.Key words: lake, hypolimnion, oxygen, productivity, Lake Erie

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 × 10‐5 to 1 × 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.