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Input-Output Budgets of
Major Ions, Trace Elements,
and Mercury


Input-Output Budgets of Major Ions, Trace Elements,
and Mercury for a Forested Watershed in Western Maryland

This field study, sponsored by the Maryland Power Plant Research Program, was conducted to increase our understanding of the retention and movement of major ions and trace elements in forested watersheds. Atmospheric inputs (precipitation and throughfall) and stream water export of major ions, trace metals, and mercury from a completely forested watershed in western Maryland were measured from June 1996 through May 1997. Results were used to estimate major ion, trace metal, and mercury export; examine regional patterns in wet deposition and canopy-atmosphere interactions; and compute input-output budgets for HCWS.

Results indicate that HCWS: receives some of the highest atmospheric inputs of H +, NH4 +, NO3- and SO4 2- in the eastern U.S.; is a net sink for H +, NH4 +, NO3 - and K +; and is exhibiting signs of N saturation. A strong regional gradient in wet deposition of many trace elements was observed (e.g., wet deposition was highest in western Maryland, intermediate in central Maryland, and lowest near the East Coast). This pattern reflects both closer proximity to regional sources and higher precipitation rates in the Allegheny Plateau.

The forest canopy has little effect on the deposition of Al, As, and Pb; however, the canopy was a net source of Mn, Fe, Cu, Zn, and Se. Input-output budgets suggest that atmospheric inputs of Al equaled stream water outputs; 50-90% of the atmospheric inputs of Pb, As, and Se were retained in HCWS; 25% of the atmospheric inputs of Fe, Cu and Cr were retained; and HCWS is a net source of Zn, Ni and Cd. Wet deposition flux of Hg to western Maryland is similar to that of other rural sites in Maryland; variability between sites and years is largely a function of differences in rainfall amounts. The concentration of total Hg in precipitation did not correlate strongly with any other major ions or trace elements, suggesting that no particular source profile predominates. Comparable to other forested watersheds, the yield of Hg from the stream is low, suggesting a buildup of Hg in soils.

Above is the abstract. The abstract and executive summary are available on-line in pdf format (you will need the Adobe Acrobat reader to view it.)
The entire file (617 KB) is available on-line in zipped format (you will need WinZip or other extraction software to view it. Once unzipped, you will need the Adobe Acrobat reader to view it)


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This page was updated on March 30, 2001.