Technical Report NPS/NER/NRTR2007/080
Jeffrey S. Kahl1, Sarah J. Nelson
Senator George J. Mitchell
1 current address:
Center for the Environment
Ivan J. Fernandez
U.S. Department of the Interior
This project provided a continuation of the 1999-2005 record of major ion and Hg chemistry in throughfall and streamwater, and the hydrologic fluxes, for a pair of intensively studied watersheds at Acadia National Park. Research on selected landscape factors influencing the amount of chemical deposition in these watersheds indicated that canopy openness, vegetative cover composition, and elevation were the most important landscape variables for predictive modeling of major ion and Hg deposition. A notable exception was NO3, where landscape variables did little to help prediction of wet deposition. We used a regression tree model approach to predict atmospheric deposition of SO4 and Hg using these landscape factors. We surveyed streams across the Park, some of which had not been sampled since the 1980s, and coordinated key stream water quality data sets into a single database. Comparison of modeled deposition across the Park and streamwater survey data suggested that although the deposition of Hg and SO4 appeared to be controlled by the same landscape factors (vegetation structure and elevation), spatial patterns in streamwater chemistry for these two analytes were not the same. Streamwater SO4 appeared to generally follow deposition patterns. Streamwater Hg was highest in association with lowland and wetland landscape features. Another focus of this research was temporal patterns in atmospheric deposition, particularly for Hg. Research in other areas of the US had suggested that Hg deposition was minimal in winter, yet winter deposition of Hg using wet-only collectors was approximately one-quarter of annual wet deposition flux at Acadia. This places a greater emphasis on winter deposition monitoring in order to evaluate ecosystem exposure for Hg, although further research is necessary to understand Hg deposition in winter, such as losses via volatilization.
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