The MiCorps Monitor: July 2009

Article 6:
Lake Water Quality Assessment (LWQA) Monitoring

In 1998, the MDEQ formed a partnership with the U.S. Geological Survey to continue the MDEQ’s Lake Water Quality Assessment (LWQA) monitoring program (view program fact sheet for more information). Under this program, surveys are conducted during spring turnover and summer stratification periods in Michigan’s public-access lakes. The purpose of the monitoring is to measure a variety of water quality parameters that indicate the condition and trophic status of the lake.

In February 2009, the leaders of this initiative released a report that summarized the monitoring results for the first five years of the monitoring program, 2001 through 2005. This short article summarizes their major findings. For the full report, please go to pubs.usgs.gov/sir/2008/5188/.

From 2001 through 2005, 433 lake basins from 364 lakes with public boat launches were sampled. Each year, lakes are randomly selected from watersheds corresponding with the five year DEQ watershed assessment cycle. Therefore, from 2001 to 2005, lakes for every major watershed in Michigan were sampled. The monitoring results indicated that 17% of Michigan lakes are oligotrophic, 53% are mesotrophic, 22% are eutrophic, and 4% are hypereutrophic.

This report determined that there were distinct patterns between the lakes’ nutrient status and Michigan’s five ecoregions (see figure below). Ecoregions are distinct geographic areas that have similar geology and vegetation. For example, the Northern Lakes and Forests and the Northern Central Hardwood Forests, which spread across the whole Upper Peninsula and the northern Lower Peninsula, are composed of about 28% oligotrophic lakes. The two regions contain about 85% of all of the lakes classified as oligotrophic across the state.

The three southern Michigan ecoregions (Huron/Erie Lake Plains, South Michigan Drift Plains, and Eastern Corn Belt Plains), in general, had more nutrients and higher specific conductance (which is indicative of the level of dissolved elements from the landscape such as chloride, sodium, magnesium, potassium, etc.) than the two northern ecoregions. As southern Michigan contains the vast majority of the state’s agricultural lands, this result is logical.

Comparisons with historical monitoring data indicate that 72% of the lakes sampled did not change trophic class, 18% decreased a partial or whole trophic class (indicating improved water clarity), and 11% increased a partial or whole trophic class (indicating decreased water clarity). None of the trophic evaluations increased or decreased more than one trophic class.

One interesting component of this program integrates data collected from remote sensing satellite imagery and transparency data collected by CLMP volunteers (view program fact sheet or the project webpage for more information). The two data pieces are used to build a regression model that predicts the water clarity for unsampled Michigan inland lakes. This is a great example of how effort put forth by CLMP volunteers can add to the greater statewide effort of keeping all of our lakes healthy.

For additional information on the MDEQ lake monitoring programs, visit the inland lake monitoring webpage.

The following lakes will be sampled under the LWQA program in 2009:

Author:
Paul Steen
MiCorps Staff
Huron River Watershed Council

MiCorps