The Minnesota Pollution Control Agency (MPCA) and several other groups collected data on chlorophyll a concentrations and several water quality parameters (TP, TN, and Secchi transparency) in 90 reference lakes between 1985 and 1987. Reference lakes were chosen to represent minimally impacted sites within each ecoregion. In addition to the reference lake database, MPCA examined a statewide database containing data collected by the same groups on approximately 1,400 lakes from 1977 to 1987.
Differences in morphology, chlorophyll a concentrations, TP, TN, and Secchi transparency were found among lakes in the four ecoregions in both studies. Box-and-whisker plots for chlorophyll a and water quality measurements in the reference lake study paralleled the morphological differences seen among the ecoregions. Results of the statewide database analysis showed the same trends.
The results of the two database analyses support the use of ecoregions in developing frameworks for data analysis, monitoring strategies, assessing use patterns, and developing phosphorus goals and criteria for lakes (USEPA 2000a).
Reference:
USEPA. 2000a. Nutrient Criteria Technical Guidance Manual: Lakes and Reservoirs. EPA-822-B-00-001. U.S. Environmental Protection Agency, Office of Water, Office of Science and Technology, Washington, DC. Accessed October 2016. https://nepis.epa.gov/Exe/ZyPDF.cgi/20003COV.PDF?Dockey=20003COV.PDF.