Anvil Lake: Response of lake water quality to changes in nutrient loading, with special emphasis on the effects of changes in water level

Science Center Objects

Anvil Lake is a relatively shallow, high-quality lake whose water level has dropped dramatically in recent years, adversely affecting the recreational and aesthetic values of the lake. The USGS is developing detailed water and phosphorus budgets, determining groundwater contributions, modeling likely responses to changes in phosphorus loading, and assessing the effect of climate on water quality.

Aerial photo of Anvil Lake

Aerial photo of Anvil Lake.

Problem

Anvil Lake is a relatively shallow, high quality lake located in Vilas County, Wisconsin. In recent years, in addition to redevelopment in the watershed, Anvil Lake has experienced dramatic changes in water level, reaching its lowest elevation in the 75-year record (see Graph). Changes in water level have adversely affected the recreational and aesthetic values of the lake, and may have affected the water quality in the lake. This potential climatic effect on water level, in addition to potential continued redevelopment around the lake, may cause a degradation in the water quality of the lake.

 

Objectives

The objectives are to:

1.   develop a detailed water budget by measuring all major sources and estimating minor sources,

2.   determine groundwater contributing areas and flow paths into the lake,

3.   determine a detailed phosphorus budget by quantifying loading associated with each nutrient source,

4.   evaluate lake water quality relative to longer-term trends and to measured loading through the use of empirical and dynamic eutrophication models;

5.   use the eutrophication models to predict the likely response of Anvil Lake to changes in phosphorus loading associated with various lake-management actions, and

6.   relate historical lake water quality with precipitation records to assess the effect of climatic factors on lake water quality.

 

Changes in the water level of Anvil Lake from 1936 to 2010

Changes in the water level of Anvil Lake from 1936 to 2010.

Methodology

The study will consist of two years of data collection followed by data analysis and report preparation. Water quality will be monitored in the lake and water levels will be recorded. Sediment cores will be collected to estimate internal phosphorus loading, and analyzed by the Wisconsin DNR to describe historical changes in water quality. Piezometers will be installed around the lake to measure groundwater gradients and phosphorus concentrations to aid in developing a groundwater model for the area. The groundwater model will be used to help describe groundwater contributing areas and nutrient loading. These measured data, along with other estimates, will be used to develop complete hydrologic and phosphorus budgets for the lake. Concurrent water and phosphorus budgets and in-lake water-quality data will be used to calibrate lake eutrophication models, which will be used to estimate Anvil Lake's response to various climate and anthropogenic phosphorus-loading scenarios. Understanding these relationships is important for anticipating lake-system response to possible future climate and land use changes.