Analyzing Phosphorus Trends in Green Lake (2011)

Water quality has been officially monitored and regulated since the implementation of the Clean Water Act of 1972. One major parameter used to determine water quality is phosphorus concentration. Phosphorus is a nutrient required by organisms to survive. However, too much phosphorus can cause organisms within the lake to become over active, which can decrease the quality of the water. Pollution from sources, such as wastewater, agricultural runoff, and residential fertilizers, can increase levels of phosphorus (and other nutrients) within the lake.

2011 GLA intern, Kylie Ainsley, researched phosphorus concentration in Big Green Lake. Her analysis concluded that phosphorus has been slightly decreasing over the past two decades, with concentrations highest in the spring and summer months and lowest in the fall and winter months. The higher concentrations during the spring and summer are most likely the result of increased runoff due to snow melt, the rainy season, and crop planting. While best management practices implemented around the lake have been successful in at least maintaining water quality in the lake, many of Green Lake’s tributaries are listed as impaired waters due to excess sedimentation and nutrients. Read Kylie's full report.

In addition to further tributary analysis, other water quality parameters, such as Secchi depth, chlorophyll a, and dissolved oxygen, should also be assessed in future analyses to better characterize the overall water quality of the lake and how it has changed over time. Determining Total Maximum Daily Loads, or TMDL, for phosphorus would also help better understand how much phosphorus Big Green Lake could receive and still safely meet water quality standards.