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The U.S. Geological Survey Office of Water Quality’s Atmospheric Deposition Program has identified the need to assess and evaluate the effects of atmospheric deposition on aquatic and terrestrial ecosystems. This program supports the NADP/NTN network. The program recognizes the need to support analysis of this data in conjunction with additional data on water quality, soils, forest productivity, biology, and sediments to more comprehensively assess terrestrial and aquatic ecosystem health and future response to chronic atmospheric acidic deposition. Significant scientific and policy discussions are now underway to ascertain whether emission reductions to date resulting from implementation of the Clean Air Act have been sufficient to reduce adverse environmental effects. Recent legislation has been introduced calling for significant additional reductions for both sulfur dioxide and nitrogen oxide emissions. There is a need for research that addresses the scientific uncertainties of the links between emissions, deposition and ecosystem response.
The USGS is conducting a study of calcium depletion in forest ecosystems in the eastern U.S. The objective of the proposed research is to apply the NADP/NTN precipitation chemistry and other data on water quality, soils, forest productivity in a regional synthesis to determine current calcium status in selected Maine forest ecosystems.
Calcium cycling studies using NADP/NTN deposition data in conjunction with small watershed and plot studies have indicated a potential problem in forest nutrition and related adverse water-quality effects. Long-term monitoring of stream-water chemistry has revealed downward trends in calcium concentrations in several small streams in forested areas in the eastern U.S., including sites in Maine. Long-term monitoring of atmospheric deposition has indicated declining trends in calcium deposition in many areas in the eastern U.S. The problem of calcium depletion is related to calcium removal in forest harvesting, calcium leaching aggravated by acidic atmospheric deposition, recent declines in calcium deposition, and low calcium supplies in soils. Decline in Atlantic salmon in certain Maine coastal streams is also consistent with acidic deposition-induced base cation depletion and associated decreases in pH and increases in "biologically active" aluminum species.