Three dimensional hydrodynamic and ecological models for water quality problems in Lake Erie

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Billions of dollars have been spent on the control of nutrient loading to Lake Erie in the U.S. and Canada with the elimination of deep water hypoxia (low oxygen levels) in the central basin of the lake an important goal. In spite of improvements in chlorophyll and phosphorus levels in offshore lake waters, hypoxia appears to have worsened in recent years. There are several hypotheses for the cause of this, including changing climatic conditions, changes in nutrient input from rivers, and the effects of non-native mussels which invaded Lake Erie in the 1980s.Deep water hypoxia occurs in the lower layer of the lake, called the hypolimnion, which lies beneath a thin layer of rapid temperature change with depth called the metalimnion. The metalimnion represents a barrier for the downward flux of oxygen. In recent years it has become appreciated that breaking internal waves in the metalimnion are an important mechanism for this downward flux. This is one of several ways in which physical processes in the lake have an impact on biological and chemical processes.In this research data will be used to validate a lake-scale hydrodynamic-biogeochemical numerical model which will then be used to demonstrate the implications of current hypotheses and to explore the possible implications of future climate change scenarios. In order to elucidate the role of breaking internal waves in the thermocline a field program will be conducted to obtain data with high temporal and spatial resolution. This will be the first such study in Lake Erie. Physical, chemical and biological measurements will be made enabling links between various processes to be made and to establish their role in the formation of hypoxic water. Lake-scale and high-resolution numerical simulations will be undertaken to provide a fuller picture of these important processes. This research will result in a synthesized picture of the role of large and small scale processes in the formation of deep water hypoxia and provide useful tools for the future management of this important lake, tools which can also be applied to other lakes.