How Climate Change Impacts the Bay of Green Bay
Over the next few decades climate change will have very significant impacts on the Great Lakes. Particularly affected will be shallow bays, like Green Bay, that are freshwater estuaries. These estuaries are more sensitive to increases in temperature, precipitation, and runoff than other regions of the Great Lakes.
Green Bay is one of the largest freshwater estuaries in the world. The bay is characterized as an estuary because it functions as a nutrient trap and because of the thermal and chemical differences between the water of the bay tributaries as compared to Lake Michigan. The bay of Green Bay originates at the mouth of the Fox River, which is the largest tributary to Lake Michigan. Unfortunately, while representing only 7 percent of the surface area and 1.4 percent of the volume of Lake Michigan, the bay receives approximately one third of the total phosphorus loading within the Lake Michigan basin.
Approximately 70 percent of the phosphorus and suspended sediment load to the southern bay enters from the Fox River, including an estimated 330,000 tons of sediment and 1,210 tons of total phosphorus.
Agricultural activities, especially large dairy farms and CAFOs, spread liquefied phosphorus-rich manure onto fields that eventually migrates into streams and rivers that empty into the bay. Testing done on the bay tributaries shows average summer phosphorus levels twice to four times as high as what scientists say is acceptable. All this phosphorus contamination, that agricultural interests call “nutrient loading” when spreading manure on farm fields, leads to large algae blooms in the bay. Some of the algae produced in the bay are Cyanobacteria, better known as blue-green algae. You don’t want to swim or recreate in or around blue-green algae. It can produce skin rashes, severe gastric distress, and significant breathing problems in people, and it’s likely fatal to dogs that ingest it.
The large shallow basin of the bay would result in nutrient-rich waters even without the above-mentioned human activities. Green Bay and the lower Fox River, however, have been severely polluted since as early as 1925. Door County waters are impacted from the pollution from the Fox River and lower bay waters. Unfortunately, it seems that whatever is in the Fox River water is, although diluted, eventually coming to Door County.
The mixing processes in Green Bay are complex and driven by wind, lunar tide, and temperature differences. Warm water enters the bay in the south and cooler water enters from the north through Deaths Door and the Rock Island passages from Lake Michigan. This layered system operates somewhat like a conveyor belt, with warmer nutrient-laden surface water moving north on the east coast and cooler Lake Michigan water moving south on the west side. The bay has basically a counterclockwise circulation pattern.
The effects of climate change and a warming planet will also significantly impact bay waters in the future. Winter has been found to be the fastest warming season in the state.
Green Bay and Milwaukee have experienced two of the fastest warming winters of any major cities in America, with the average temperatures warming by 6 degrees Fahrenheit. Bay and lake water temperatures have also increased. One of the main factors affecting temperature increases in the bay is declining ice coverage. As the planet’s atmosphere warms, more moisture is being trapped in the air. The 8 greater humidity provides a buffer to cold fronts making deep freeze temperatures less frequent.
A warmer bay will be more hospitable to algae growth and, likely, other undesirable effects. In the short run, there is very little we can do to stop a planet from warming. We can, however, do something right now about the amount of phosphorus that’s being allowed to enter the bay. Agricultural interests cannot be exempted from responsibility relative to nutrient rich runoff that ends up in the bay. Why are we allowing CAFO expansion in Northeast Wisconsin when we are currently pouring tens of thousands of gallons of milk on the ground daily in this county? The bay is an invaluable asset, and it’s our responsibility to pass it on to future generations in good condition. Let’s all work to appreciate and protect the bay.
