Volunteer Lake Monitoring Program

Putting the Data to Work

The hard work of dedicated volunteers over the last twenty years has produced a wealth of information about water quality of the lakes in our region. One method used by Watershed Council staff to determine lake water quality is the calculation of the trophic status using Carlson's Trophic Status Index (TSI). This index utilizes Secchi disk depth recordings and chlorophyll-a measurements collected by volunteer monitors to calculate a lake score that ranges from 0-100. Lakes that score at the low end of the scale (TSI values ranging from 0-38), are considered to be oligotrophic with excellent water quality. A TSI score of 39-49 indicates a mesotrophic lake with good water quality and a TSI value of 50 or greater is considered to be a eutrophic lake with poor water quality.

Seasonal averages for Secchi disc depth and chlorophyll-a concentrations are used to calculate TSI values, but data spanning multiple years is preferable because of the great influence that environmental factors, such as weather, can have on index values. A summary of long-term TSI values for select lakes in our service area can be viewed in Table 2. Can you spot any trends in the TSI data?

Volunteer lake monitors are encouraged to participate in The Great North American Secchi Dip-In by sending in Secchi depth data for one sampling event in the summer. Coordinated by Professor Robert E. Carlson, Ph.D. in the Department of Biological Sciences at Kent State University, this program brings together transparency (Secchi depth) data collected by volunteer monitors from all over the U.S. and Canada. The data is used to assess transparency on lakes throughout the continent and evaluate trends. The trend that staff from both the Watershed Council and the Secchi Dip-In have noticed is that transparency is increasing in the lakes of the northern Lower Peninsula of Michigan. Although nothing is certain, this trend is likely due to the introduction and proliferation of zebra mussels.

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