COOPERATIVE ECOSYSTEM STUDIES UNIT, NORTH ATLANTIC COAST CESU

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Atmospheric deposition of nitrogen (N) from fossil fuel combustion and agriculture is the largest source of nutrient input to high-elevation ecosystems in the Rocky Mountains. When atmospheric N deposition exceeds uptake by plant and microbial communities, the system becomes N saturated and nitrate is leached from soils into surface waters. This additional N causes a cascade of ecological effects in aquatic ecosystems including shifts in the nutrient status of lakes, increases in phytoplankton biomass, and changes in the diatom community structure. Data from Rocky Mountain National Park (ROMO) suggests some high-elevation lakes in the park are at an advanced stage of nitrogen saturation and that harmful effects on aquatic ecosystems are already occurring. To protect these resources, ROMO has proposed setting a critical load for nitrogen deposition, which is the level at which deposition causes some harmful effect. Establishment of critical loads will become increasingly important as policy makers consider options for reducing anthropogenic N emissions. The National Park Service has identified a need for information that will contribute towards establishment of scientifically based critical loads. Critical loads can be developed using different methods and may vary depending on the ecological response indicator of interest. This grant is available to investigate the use of lake diatoms as an ecological response indicator to excess nitrogen deposition. Research activities, to be conducted in collaboration with the USGS-CWSC, include establishment of a calibration dataset for sediment diatom assemblages in lakes in ROMO. This will provide information about how the current water quality of lakes affects diatom distribution within the park. Once established, the calibration dataset will be applied to historical sediment records to reconstruct baseline nutrient concentrations for these lakes. These research results can ultimately be used to estimate critical loads for the ecological impacts of atmospheric nitrogen deposition on high-elevation lakes in the Rocky Mountains region.

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