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Hypoxia in Green Bay, Wisconsin: Biogeochemical Dynamics, Watershed Inputs, and Climate Change

This project began in August 2010 and was completed in July 2014

Hypoxia conditions have plagued the lower part of Lake Michigan’s Green Bay and the Fox River for decades. We know nutrients are contributing to the problem, and we are developing a series of linked models that predict how changes in nutrients, runoff, oxygen levels, and watershed land use, as well as climate change, will affect the size and impact of the hypoxic zone. These tools will help managers estimate the costs and benefits of improving water quality in Green Bay.

Why We Care
Lake Michigan’s Green Bay represents 7 percent of the surface area and 1.4 percent of the volume of Lake Michigan, but it contains 33 percent of the watershed and receives 33 percent of the basin’s total nutrient load. With a 100-year history of high-nutrient pollution (causing eutrophia, low oxygen, fish kills, harmful algal blooms), the southern portion of the Green Bay behaves like a nutrient and sediment magnet. It captures much of the annual runoff of plant and animal particles and nitrogen in its sediments, which quickly become depleted of oxygen (hypoxic) from decay. Recent evidence suggests that hypoxia in the lower Green Bay and the Fox River areas may be worsening, along with a potential for more frequent and extensive dead zones and fish kills.

What We Are Doing
We are quantifying the linkage between nutrient inputs and hypoxia and developing an assessment of the target levels of abatement needed to meet water quality goals, providing an evaluation of the planning efforts thus promoting successful management. The modeling will allow assessment of potential impacts of climate change on the biogeochemical behavior of the bay and on future nutrient loading, which will improve the development of better and more cost-effective management strategies.

The overall objective of this project is to improve the means to develop successful regulatory and nonregulatory nutrient mitigation strategies, to demonstrate the usefulness and value of nutrient mitigation plans, and to accurately estimate the costs and benefits for improving water quality.

To achieve this objective, we will:

  1. Develop a data set of the times and locations of oxygen concentrations in Green Bay
  2. Expand the determination of inputs of nutrients and suspended sediments to the bay and assess the usefulness of land-use best management practices throughout the watershed
  3. Develop and implement a three-dimensional “coupled” water flow and nutrient-oxygen model framework
  4. Assess the impact of future regional climate change projections.

A longer term objective is that this analytical approach for evaluating watershed and best management practices will be expanded and allow remediation and protection from future degradation of the larger Fox-Wolf watershed (including urban areas) and other locations in the future.

This work is part of the Coastal Hypoxia Research Program (CHRP). The project team is led by Dr. J. Val Klump of the University of Wisconsin at Milwaukee Great Lakes WATER Institute with co-investigators from the Green Bay Metropolitan Sewerage District, Wisconsin Department of Natural Resources, and the University of Wisconsin campuses at Green Bay, Madison, and Milwaukee.

What We Are Finding
Remediation of oxygen-impaired waters in Green Bay will require a significant effort and cost for nutrient abatement and non-point source management throughout the watershed. Specific abatement targets are being developed and have been recommended by the federal (EPA), state, and regional planning efforts.

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