The seasonal depletion of oxygen (hypoxia) is a significant water quality issue in Chesapeake Bay. Billions of dollars have been spent on nutrient reduction with the goal of decreasing the extent and severity of summer hypoxia. However, assessing the effectiveness of these efforts is often confounded by the complexity and variability of the physical processes that control the distribution of dissolved oxygen in the Bay. The goal of this presentation is to assess the importance of the variations in physical forcing on modulating dissolved oxygen in Chesapeake Bay using a 3-D circulation model with an extremely simple formulation for oxygen dynamics. The model uses a depth-dependent oxygen utilization (respiration) that is constant in time and exchanges oxygen with the atmosphere via a surface flux. Despite the simplicity of the approach, this model can accurately simulate the observed seasonal cycle of hypoxia in the Bay. Further, because the biological utilization of oxygen is constant in time, the model effectively isolates the role of physical processes in modulating dissolved oxygen in this system. Model runs demonstrate that variations in wind speed and direction are the most important physical variables in controlling seasonal hypoxia. Secondardy effects are attributed to variations in water temperature. The model suggests that the magnitude of river discharge has little impact on the extent and severity of seasonal hypoxia in the Bay. Comparisons with historical data support the importance of wind forcing and suggest that long-term climate variability may play a key role in the interannual variability of hypoxia in Chesapeake Bay.

Dr. Malcolm Scully received a B.A. degree from the University of Virginia in 1993 and earned M.S. and Ph.D. degrees from the College of William and Mary, School for Marine Science in 2001 and 2005, respectively. He was a postdoctoral scholar at the Woods Hole Oceanographic Institution from 2005-07 and joined Old Dominion University as an assistant professor in 2008. Dr. Scully's research interests include estuarine dynamics, stratified turbulence, and cohesive sediment transport.

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