National Park Service

Great Lakes Network (GLKN)

Diatom Monitoring

GLKN biologists taking lake substrate core samples
GLKN biologists taking lake substrate core samples

GLKN Diatom Monitoring Brief

GLKN Diatom Monitoring Reports

GLKN Diatom Monitoring Protocol

For more information contact: David VanderMuelen

Importance

Diatoms are a class of algae that have cell walls made of silica. They are found throughout the water column of a lake or river, and when they die, their remains (portions of the cell walls called frustules) settle onto the bottom. Because of their high silica content, frustules are preserved in the bottom sediments like tiny bits of glass. As additional sediments accumulate on the lake or river bottom, they capture a chronological record of the diatom species present in the lake through time. Different species of diatoms can be determined by the unique patterns of their frustules. Because of their high silica content, frustules are preserved in the bottom sediments like tiny bits of glass. As sediment accumulates on the lake or river bottom, a chronological record of the diatom species present in the lake through time is maintained.

Because particular diatom species only exist under certain conditions, researchers can infer historic changes in water quality by looking at the diatom species present throughout a core of bottom sediments. Diatoms are sensitive to environmental changes, and the composition of diatom communities (presence and abundance of different species) will shift in response to such changes. Therefore, diatoms serve as powerful water quality indicators.

The Great Lakes Inventory and Monitoring Network, in partnership with researchers from the St. Croix Watershed Research Station, began monitoring diatoms in 2005. Researchers collected 'long cores' (1-2 m, or 3-6 ft) of lake and river bottom sediments to analyze diatom species composition and water quality conditions dating back to pre-Euro-American settlement. The Network collected the top few centimeters of bottom sediments ('surface sediments') from approximately 75 lakes to track more recent changes.

Long-term Monitoring

The long cores showed large and consistent changes across lakes around the time of Euro-American settlement. As settlement occurred in the late 1800s, increases in agriculture and logging caused changes in water quality, which led to changes in the diatom community. In general, the cores showed increases in sedimentation rates and inorganic content, likely a result of accelerated rates of erosion due to land clearance, changes in runoff, and possible changes in lake levels.

The long cores also showed a shift in diatom composition in the 1950s to the 2000s, with many lakes showing change in the 1970s to 1980s. These changes cannot be easily ascribed to known land use alterations, but may instead be related to climate change. Recent ecological modification linked to changing climate include shorter duration of ice cover, leading to earlier warming of surface water and longer growing seasons; and increased frequency or intensity of summer storms, which may increase the availability of nutrients when lake waters mix more frequently or nutrients are washed into the lakes from the surrounding landscape.

Collecting surface sediments is a method used to assess recent (approx. 3-5 yrs.) changes in diatom communities. Diatom monitoring occurs in the same lakes and at select river sites that are part of the Great Lakes Network's water quality monitoring program. Each lake is sampled for diatoms on a 3 to 5 year rotation. The surface sediment cores build on the historical profile defined by the long cores.

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Last Updated: December 30, 2016 Contact Webmaster