Little St. Germain Lake: Phosphorus loading, winter anoxia, and stage regulation

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Little St. Germain Lake, Wis., consists of four main basins separated by narrows. This study monitored lake water quality, identified phosphorus sources, determined spatial and temporal distribution of oxygen, evaluated the effectiveness of winter aeration systems, and modeled groundwater/lake-water interactions.

Map of Little St. Germain Lake, Wis., winter aerators, and sampling locations.

Map of Little St. Germain Lake, Wis., winter aerators, and sampling locations.

PROBLEM
Little St. Germain Lake consists of four main basins (East Bay, Upper East Bay, South Bay, and West Bay) separated by narrows. Muskellunge Creek, the lake’s only inlet stream, enters East Bay. A dam at the lake’s outlet is used to regulate lake stage and flow from South Bay. Hence, the net flow of water is from East Bay to South Bay. Summer water quality ranges from good to very good in the West Bay, fair to good in the South Bay, and poor to very poor in the East Bay, based on monitoring from 1992–1994. Dissolved oxygen was absent at the South Bay monitoring site in late winter each year from 1992–1994. The areal extent and cause of the oxygen problem was identified in studies from 1994–2000. The Lake District is considering various measures to improve lake water quality. These include aeration of Upper East and South Bays in winter and possible treatment of Muskellunge Creek water before it enters the lake.
 

OBJECTIVES
The primary objectives of this project are to:

  1. Continue the water-quality trend monitoring at sites in the four main basins of the lake
  2. Continue monitoring to determine water and phosphorus loading to the lake from Muskellunge Creek
  3. Identify sources of phosphorus to Muskellunge Creek
  4. Determine spatial and temporal distribution of oxygen in winter before and after installation of aeration systems
  5. Model ground-water/lake-water interaction and estimate loading of phosphorus to the lake from ground water
  6. Synthesize all data, new and old, to evaluate the effectiveness of aeration systems and refine lake water and phosphorus budgets
  7. Examine the potential effects of releasing water from the lake at different times of the year.
     
Graph showing changes in winter dissolved oxygen in Little St. Germain Lake, Wis., before using aeration

Graph showing the changes in winter dissolved oxygen concentrations throughout Little St. Germain Lake, Wis., under the ice prior to using aeration.

APPROACH
The lake’s water and phosphorus budgets will be defined to better resolution than in previous studies by quantifying ground-water inflow and outflow through modeling aided by data from piezometers installed around the lake’s perimeter. Determination of inflow to the lake from Muskellunge Creek will be improved by the operation of a continuous stage monitor. Measurements of flow and phosphorus concentration will be made at three locations along Muskellunge Creek to identify general source areas for phosphorus. Phosphorus loading from ground water will be based on data from sampled near-lake piezometers and inflow estimates generated by the ground-water model (GFLOW). Lake-water quality trend monitoring will continue at the four main basins of the lake. Measurements will be made to determine the spatial and temporal distribution of oxygen in winter before and after installation of aeration systems. All new and old data will be synthesized to evaluate the effectiveness of the aerations systems and to refine lake water and phosphorus budgets.