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Water Quality of Inland Lakes

Importance
Inland lakes are important resources, with 129 named and several hundred unnamed lakes occurring across six of the nine Great Lakes Network (GLKN) parks. The preservation of water quality and quantity is of utmost importance to park managers, researchers, and the general public. Though water quality is generally good throughout GLKN inland lakes, threats exist from climate change, atmospheric deposition, urban and agricultural runoff, wastewater discharge, seepage from septic systems, recreational use, and exotic species. Because conditions can change quickly, it is important to detect change as early as possible, in order to maximize the potential for effective management actions. Park lakes are used extensively by visitors for fishing, boating, swimming, and other recreational activities. Changes in lakes serve as sentinels of change occurring in the atmosphere and in surrounding terrestrial systems.

Veg Monitoring
Lake Ahmik in Isle Royale National Park

Long-term Monitoring
The Great Lakes Network monitors 33 lakes, selected to span gradients of surface area, depth, visitor use, water chemistry, and spatial distribution within each park. Each lake is sampled at the deepest location three times annually during the open-water season. A multiprobe sonde is used to measure temperature, specific conductance, pH, and dissolved oxygen from the surface to the bottom at 1-m intervals. Clarity is measured with a Secchi disk or transparency tube. Water samples are collected with a 2-m integrating tube for laboratory analysis of alkalinity, dissolved organic carbon, calcium, potassium, sodium, magnesium, chloride, sulfate, total nitrogen, total phosphorus, nitrate+nitrite-nitrogen, ammonium-nitrogen, dissolved silica, and chlorophyll-a. Water level is measured relative to a permanent benchmark with a hand-held eye level and surveyors rod.

This monitoring is integrated with a protocol to monitor diatom remains in surface sediments. Diatoms are a class of algae with silica-based cell walls. When a diatom dies, the remains are preserved in lake sediments. Diatoms make excellent bioindicators because they are generally abundant in aquatic systems and respond rapidly to changes in their environment. Through monitoring water quality and diatoms together, we expect to be able to determine trends in lakes sooner and more accurately than by monitoring water quality alone.

For more detailed information, see the In-depth Information box below.

Network park units with Inland Lakes Water Quality monitoring
Apostle Islands NL	Pictured Rocks NL
Indiana Dunes NL	Sleeping Bear Dunes NL
Isle Royale NP	Voyageurs NP
NP = National Park; NL = National Lakeshore

In-depth Information:

Factsheets:
Executive Summaries:
Annual Reports:
Monitoring Protocols:	GLKN Inland Lakes Water Quality monitoring protocol - [2 MB PDF]
Contacts:	Joan Elias, joan_elias@nps.gov

Additional Water Quality Monitoring Publications

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