Some 1.2 million pounds of phosphorus flow into Green Bay each year from the Fox River, according to Tracy Valenta, who worked as a water resources specialist for NEW Water, the metropolitan sewerage district in Green Bay, Wis. The bay, in Wisconsin on the western shore of Lake Michigan, also receives the equivalent of 27 dump truck loads of sediment each day.
The result is large, harmful algal blooms that sink to the bottom when they die. The decomposition process uses up so much oxygen that fish and invertebrates living in the deepest layer of water cannot survive. This “dead zone” can last for weeks—the longest recorded in Green Bay was 43 days—and extends more than 30 miles into the bay.
“We’ve had gobies that have been beaching themselves on the shores trying to escape the anoxic waters on two different occasions,” Valenta told Circle of Blue.
Stricter nutrient removal regulations could help reduce the blooms. Point source dischargers in the Lower Fox River Basin, which feeds Green Bay, must now comply with a total maximum daily load (TMDL) allocation for phosphorus and total suspended solids. The TMDL, a tool used by states and the U.S. EPA to bring water quality in line with the standards set forth by the Clean Water Act, sets limits on pollutants in water bodies that have been designated as “impaired.” The Fox River’s TMDL, approved in 2012, requires that phosphorus levels never exceed 0.1 milligram per liter in the main river channel, and 0.075 milligrams per liter in the river’s tributaries.
The goal of the TMDL is to reduce the nutrients flowing to Green Bay and thereby reduce the dead zone, which has been plaguing Green Bay since at least the 1920s. Valenta said that the sewerage district, like all other point source dischargers in the Fox River basin, will need to cut the phosphorus in its effluent—now at about 3 to 4 milligrams per liter—down to the new TMDL standards, a reduction equivalent to 30,000 pounds of phosphorus each year. It can choose to do so by either spending approximately $US 250 million to put in a tertiary treatment system at its wastewater facility, or working with landowners and farmers upstream to limit nonpoint sources of phosphorus.
“Basically it’s a back door approach to get us to go out and do nonpoint source reduction,” Valenta said. “In the end, it should be cheaper for us to go into the watershed and pay farmers to not spread manure on their land, or to take certain parcels out of production, or to put in bigger buffer strips. It should be cheaper for us to do that than it should be to put the $US 250 million in the ground.”