Physical and Biogeochemical Controls on Hypoxia in Green Bay

Session: 45. - Hypoxia: Causes, Impacts, and Management

J. Val Klump, School of Freshwater Sciences, [email protected]

Abstract

Eight years (2009-2017) of water column profile data show hypoxic conditions are common in the bottom waters of southern Green Bay, Lake Michigan during the summer.   While ultimately driven by nutrient loading from the watershed and the subsequent excessive algal production thus triggered, the formation and duration of hypoxia in Green Bay are largely controlled by coupled physical-biogeochemical processes that combine to produce conditions that lead to hypoxia.   Depleted oxygen concentrations (< 5 mg L^-1) affect nearly 70% of the stations sampled representing an area of ~500-600 km², although the impact of depleted oxygen on the benthos may be more extensive.  Variability in the extent and duration of hypoxia likely results from a combination of thermal stratification, oxygen consumption in deeper waters of the bay, and physical forcing mechanisms that drive cool, oxygen depleted, bottom waters on a southerly trajectory. Hypoxia would also appear to be sensitive to relatively small changes in these forces, particularly changes in organic carbon loading and in the duration of stratification.  Coupled biogeochemical/hydrodynamic models at present do not capture the spatial distribution of hypoxia very well, a consequence we believe results from inadequate parameterization of the respiration of fresh recently settled algal debris.  

1. Keyword
oxygen

2. Keyword
biogeochemistry

3. Keyword
Green Bay