Green Lake and its tributaries: Water quality and hydrology

Science Center Objects

Green Lake is the deepest natural inland lake in Wisconsin. Through time its water quality has degraded, with relatively high phosphorus concentrations and zones of hypoxia. This project is quantifying the water quality of the lake and its tributaries, and it will provide information to help guide efforts to improve the lake.

Map of Green Lake, Wisconsin and its watershed, with sampling data

Map of Green Lake, Wisconsin, and its watershed, with sampling data.

Green Lake is the deepest natural inland lake in Wisconsin. The lake’s watershed includes the cities of Ripon and Green Lake and is dominated by agriculture. The lake was oligotrophic with very good water quality in the early 1900s. But several factors have led to degradation in its water quality, including changes in land use and climate. These changes resulted in increased nutrient loading, which may have caused increased phosphorus concentrations and hypoxic conditions in both the metalimnion and hypolimnion of the lake.

Objectives

The goals of this study are to: 1) describe water quality in Green Lake, especially metalimnetic and hypolimnetic hypoxia; 2) describe what factors have caused the degradation in water quality using eutrophication models; 3) quantify how reductions in nutrient loading should improve the water quality of the lake (reductions in phosphorus, algae, and reduction in metalimnetic and hypolimnetic hypoxia) using the eutrophication models; and 4) provide information to help guide actions to reduce the nutrient loading, improve the water quality, and remove the lake from the State's impaired waters list.

Dissolved oxygen profiles in Green Lake, Wisconsin demonstrating metalimnetic and hypolimnetic hypoxia

Dissolved oxygen profiles in Green Lake, WI, demonstrating metalimnetic and hypolimnetic hypoxia in 2017.

Approach

Automated stream monitoring techniques are being used to collect streamflow, and phosphorus, nitrogen concentrations in four main tributaries to the lake. Phosphorus loading is being estimated with GCLAS. Standard limnological procedures are being used to monitor water quality in the lake. The Canfield Bachman eutrophication model is being used to determine load reductions needed to reduce the phosphorus concentrations in the lake. The hydrodynamic/water quality GLM/AED model is being used to describe the hydrodynamic, chemical, and biological processes that lead to the hypoxia, and what type of nutrient reductions are needed to reduce it.