Big Green Lake Sediment Core Sampling (1999)

Questions often arise concerning how a lake’s water quality has changed through time as a result of watershed disturbances. Questions often asked are if the condition of the lake has changed, when did this occur, what were the causes, and what were the historical condition of the lake?  Paleoecology, or core sampling, offers a way to address these issues. In 1999, sediment cores were extracted from 4 sites throughout Green Lake.  The study concluded:

• Historically, phosphorus levels were highest in the eastern portion of the lake.  This was because most of the tributaries enter the lake there.
• Soil erosion in the watershed increased significantly beginning around 1930.  This was the result of increased mechanization of agriculture.
• Following World War II, the use of commercial fertilizers increased resulting in increased delivery of phosphorus to the lake.  This increased phosphorus happened despite a reduction in soil erosion in the watershed.
• The lake soon responded to increased phosphorus loading by experiencing an increase in algal levels.  This was most apparent in the eastern part of the lake.
• The highest phosphorus levels during the last 150 years occurred during the 1990’s.

View the complete study.

Photo Credit: Wisconsin DNR core sampling site study. Image of Green Lake and its watershed. The stars are core sampling sites. The two sites at either end are the main sites.

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