New Lake Data: How are our lakes doing?
The Environmental Protection Agency (EPA) has completed a five year follow-up study of the National Lake Assessment that began in 2007. Data is available for the nation as a whole, but I will concentrate on lakes in the Upper Midwest: Minnesota, Michigan, and Wisconsin.
Key findings show that shorelines and shallow waters suffered the most stress, with inadequate shore habitat the most widespread stressor. Using the habitat measure, 40 percent of Minnesota and Michigan lakes were judged to be in poor condition.
Ironically, although lakes of the Upper Midwest are generally considered to be in better condition than lakes in other regions of the country, by this measure, Minnesota and Michigan lakes rank in poorer condition than the national average.
The study also assessed a lake’s:
- Biological health
- Nutrient conditions (relative amounts of phosphorus and chlorophyll)
- Recreational condition
How does one measure the biological health of a lake? EPA did it by examining the health of the lakes’ plankton community, a key element in the aquatic food chain. Phytoplankton is an assemblage of tiny plants and photosynthetic bacteria. Zooplankton are tiny animals such as water fleas and micro crustaceans and most are smaller than a tiny carrot seed. Both phytoplankton and zooplankton are moved more by wind and wave than by their own power and form the base of the aquatic food web.
Zebra mussels feed themselves by filtering large quantities of plankton, greatly reducing food supply for fish and other aquatic life.
EPA’s research revealed that 75 percent of Minnesota lakes have good biological health, as measured by plankton health. The remaining 25 percent of our lakes are poor to fair.
Look to the next post for recreational indicators of lake health.