by Megan O’Shea

Excessive algae, a condition known as eutrophication, has been a problem that has plagued the Lower Fox River and Lower Green Bay for decades. Algal blooms are fueled by high concentrations of sediment and nutrients running off the land and into the water.

One approach to managing nutrient and sediment pollution is to determine the Total Maximum Daily Load (TMDL). The TMDL allocates the maximum amount of a pollutant that a body of water can receive without disrupting designated uses, like fishing and swimming. In the entire area that drains into the Lower Fox River, two tributaries—Plum Creek and nearby Kankapot Creek—contribute the highest amount of sediment and nutrients per acre to the Lower Fox River/Green Bay Area of Concern. In order to meet the goals of the Lower Fox River TMDL, phosphorus and sediment will have to be reduced by 59% and 55%, respectively.

 

Continuous Monitoring Buoy (photo credit: Todd Miller, UW-Milwaukee)

Estimates from modeling attribute nearly 87% of the annual loading of phosphorus and sediment to agricultural land in Plum Creek, whereas natural areas contribute 1%. Phosphorus and sediment from streambank erosion were not directly accounted for in the modeling; however, Outagamie County’s recent stream inventories of Plum Creek indicate that 24 of the 43 miles inventoried had actively eroding streambanks. Preliminary estimates are that these streambanks could be contributing 45% of the sediment annual loading measured at the USGS gage.

If stream processes are producing almost half of the annual loading of TSS, the proposed TMDL goal to reduce TSS by 55 percent will not be achievable through agricultural soil conservation practices alone. In order to better assess this potentially unaccounted for source, researchers from the U.S. Geological Survey will be collecting soil samples throughout the area that drains into Plum Creek. They will collect soil samples from a variety of land uses, including agricultural cropland and eroding streambanks. By using trace element analysis, they will be able to distinguish anthropogenic from natural sediment loading. They will also be able to identify stream reaches with gullying, bank, and channel erosion that may need to be ad-dressed through other soil and sediment conservation practices.

For more information about the project, please contact Megan O’Shea.

Article originally published in the Wisconsin Lakesider