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Acadia National Park on Mount Desert Island, Maine is located downwind of the major population centers in northeastern United States. Air masses from Boston and other cities traversing the Gulf of Maine are intercepted by the prominent topography of Acadia. Three million visitors and several industrial point sources in the area each year create additional air pollution. As a result, surface waters and their watersheds at Acadia receive elevated atmospheric inputs of pollutants, with nitrogen one of the key issues of concern to the National Park Service. Nitrate concentrations in streams draining forests in the northeast are higher than in any other forested region in the U.S., and have increased by a factor of 3 to 4 since 1970. The USGS, in cooperation with the National Park Service and the University of Maine, are quantifying spatial and temporal trends in nitrogen loads in small watersheds on Mount Desert Island, Maine. The purpose of the project is to document spatial variability of nitrogen concentrations and loads as a function of recent fire history, and as a function of hydrogeologic and land-use settings, and determine N-loading to important estuaries on Mount Desert Island.
Recent evidence suggests that some estuaries in the Gulf of Maine region are becoming eutrophic in response to nitrogen loading from nonpoint sources. Acadia's Bass Harbor Marsh estuary appears to be eutrophying based on growth of dense macroalgae, shifts in benthic species dominance, and high inorganic nitrogen inputs from freshwater tributaries. Conversely, nutrient loading is low to Somes Sound, a fjord-type estuary on Mt. Desert Island partly bounded by the Park. Nutrients, chlorophyll, and dissolved oxygen all indicate a relatively healthy system. However, the potential for increases in non-point source nutrient loading is high because much of the Somes Sound watershed lies outside the protective boundaries of the Park and are subject to development.
A severe wildfire burned nearly one-third of the park in 1947. Thus, we have a natural experimental landscape in which to monitor nitrogen biogeochemistry. The contrasting site histories have caused significant differences in ecosystem properties. For example, burned watersheds have more hardwood forests and less organic matter in soils, in contrast to the unburned softwood forest with older (thicker), more acidic soil organic horizons. An underlying premise of the current project is that in the burn zone, the ecosystem pools of C and N were essentially lost in 1947.
Stream gage on Cadillac Mountain, Acadia National Park