CHRP - Green Bay Hypoxia: Biogeochemical Dynamics, Watershed Inputs and Climate Change
Green Bay, Lake Michigan while representing only ~7% of the surface area and ~1.4% of the volume of Lake Michigan, contains one-third of the watershed of the lake, and receives approximately one-third of the total nutrient loading to the Lake Michigan basin as a whole. With a history of hyper-eutrophic conditions dating back nearly a century, the southern portion of the bay behaves as an efficient nutrient and sediment trap, sequestering much of the annual carbon and nitrogen input within sediments that quickly become anaerobic. Hypoxia within lower Green Bay and the Fox River has been a problem for decades, and recent evidence suggests that hypoxia may be worsening, with the potential for “dead zones” and fish kills becoming both more frequent and more extensive.
Climate change projections: Climate change predictions for the Great Lakes region include warmer and more prolonged summers, increased precipitation and a higher frequency of extreme events. Higher temperatures increase organic matter decomposition rates, decrease oxygen solubility, and increase sediment oxygen consumption. Increases in precipitation may enhance nutrient inputs in the absence of mitigation strategies to limit non-point source runoff, prolonging or worsening hypereutrophy and hypoxia in the bay. Climate change may also trigger indirect consequences like those observed in the summer wind field, decreasing flushing of the bay and increasing the retention of labile organic matter.
Scientific objectives: 1) Develop a data set of the temporal and spatial distribution of oxygen concentrations in Green Bay that will allow modeling the principal features of summertime hypoxia. 2) Expand the current integrative watershed approach for quantifying inputs of nutrients and suspended sediments to the bay; and assess the efficacy of the implementation of land use best management practices throughout the watershed; 3) Develop and implement a high resolution 3-D coupled hydrodynamic and biogeochemical nutrient-oxygen model framework for the bay linked to the Princeton Ocean Model for Lake Michigan; and 4) Assess the impact of future regional climate change projections based upon the assimilation and downscaling of an ensemble of 14 GCM’s being conducted by the Wisconsin Initiative on Climate Change Impacts for both mid-century and late century scenarios.
Collaborations: This research is a collaboration among several university research groups within the University of Wisconsin System, including: UW-Milwaukee Great Lakes WATER Institute, UW-Green Bay, Dept of Natural and Applied Science, UW-Madison Center for Climatic Research, UW Sea Grant program; as well as other groups and stakeholders including: public sector utilities, e.g. the Green Bay Metropolitan Sewerage District; governmental agencies, including the Wisconsin Department of Natural Resources and the US EPA Region 5; and the Wisconsin Initiative on Climate Change Impacts. This research effort will employ analysis of historical data, empirical measures of oxygen dynamics, and high resolution models of both watershed inputs and in bay biogeochemisty and hydrodynamics.
Management use: Quantifying the link between nutrient inputs and hypoxia, and an assessment of the target levels of abatement needed to meet water quality goals, are essential outputs of this research. The potential impacts of climate change on the biogeochemical behavior of the bay and on future nutrient loading will alter key baseline drivers in this system, but to a yet unknown extent. Developing these linkages directly improves the capabilities of managers to devise more robust regulatory and non-regulatory mitigation strategies, defend those strategies to stakeholders, and more accurately estimate costs and benefits to water quality.