Monitoring water quality of inland lakes, Great Lakes Network, 2009 and 2010: Data summary report

Elias, Joan; Damstra, Richard

The Great Lakes Inventory and Monitoring Network monitored water quality of inland lakes at six national park units in 2009 and 2010: Voyageurs National Park (VOYA), Apostle Islands National Lakeshore (APIS), Isle Royale National Park (ISRO), Pictured Rocks National Lakeshore (PIRO), Indiana Dunes National Lakeshore (INDU), and Sleeping Bear Dunes National Lakeshore (SLBE). The primary objective of this monitoring program is to monitor water quality in order to describe the current status and to detect trends of common limnological parameters within sampled lakes. We hope to be able to provide early warnings of change, work with researchers to understand the causes of change, and provide interpretation of our results to park staff. Thirty-three index lakes were sampled during the open water season in 2009 and 2010. Field measurements included depth profiles of temperature, pH, specific conductance, and dissolved oxygen; water clarity; and water level relative to a benchmark. Water samples were collected for laboratory analyses of total phosphorus, total nitrogen, nitrate+nitrite-nitrogen, ammonium-nitrogen, dissolved silica, calcium, sodium, magnesium, potassium, sulfate, chloride, dissolved organic carbon, alkalinity, and chlorophyll-a. Results from 2009 and 2010 are compared across parks. For individual parks, results of some key parameters are compared across years since monitoring began. Results show that many lakes exceed the U.S. Environmental Protection Agency (USEPA) reference criteria for Secchi depth, pH, chlorophyll-a, total phosphorus, total nitrogen, and nitrate+nitrite-nitrogen for their ecoregion. The EPA’s criteria for defining what constitutes a reference condition are stringent, based on the 25th percentile of all sampled lakes in each EPA-defined ecoregion. Calculations of trophic state indices show most index lakes to be mesotrophic. Mean summer water levels remained constant or declined in most lakes since sampling began, though the influence of beaver activity over-rode the effects of precipitation in several lakes. Additional park-specific data and comments and recommendations relating to logistics are included. We expect monitoring to continue in 2011 at the same index lakes, with additional sites, visits, and parameters included as funding permits.

Monitoring water quality of inland lakes, Great Lakes Network, 2009 and 2010: Data summary report

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