SCHROTH, Andrew ('98) & SUTTON, Brian ('98)
(Advisors: Richard April & Dianne Keller)
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A COMPARATIVE STUDY OF THE GEOCHEMISTRY OF TWO WESTERN ADIRONDACK WATERSHEDS
AFFECTED BY ACIDIC DEPOSITION
SCHROTH, Andrew ('98) & SUTTON, Brian ('98)
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Acidic precipitation, resulting from the release of sulfur dioxide
primarily by coal plants and nitrogen oxides from gas combustion, has become a
global pollution problem. The acidification of surface water can limit the
biodiversity of a lake community and cause deforestation. While acid rain is
falling throughout the entire eastern United States, only some regions are
considered acid sensitive. The Adirondack mountains of N.Y. state is an area
which receives highly acidic precipitation with a pH of around 4. However,
watersheds within the Adirondacks have shown varying acid neutralizing
capabilities due to differeces in their soil and bedrock mineralogy. The
intent of this study is to explain why the Windfall Pond watershed, located in
the Chain of Lakes region of the Adirondacks, effectively neutralizes acid
entering its system; while the adjacent Townsend pond watershed located in
the same region does not. To determine the factors controlling the acid neutralizing capacity of these two watersheds, water, bedrock and soil samples were taken from the study sites. Thin section analysis of the Windfall Pond watershed bedrock samples reveals the presence of five lithologies; two can be generally described as calcsilicates, one as a calcitic quartzite, and two are variations of granitic gneiss. Both the calcsilicates and the calcitic quartzite have the potential to neutralize acid fairly quickly due to the weatherability of minerals present in these lithologies. The bedrock samples from the Townsend Pond watershed, however, reveal only two types of granitic gneiss, both of which are dominated by fairly resistant minerals such as quartz and potassium feldspar. Due to the high resistance of these minerals to weathering bedrock from Townsend Pond has a low potential to neutralize acid deposition. Analyses of the soils show similar mineralogies for both watersheds. Bulk mineralogy is dominated by quartz and feldspars, and vermiculite and kaolinite are the dominant clays present. Although vermiculite has exchangeable base cations and therefore could play a role in acid neutralization, we feel that due to similarities in soil minerlogy and hydrological conditions within the two watersheds, soil characteristics cannot account for significant differences in ANC. Water chemistry analysis from Windfall Pond shows calcium as the major base cation. Water samples from two streams running over calcitic quartzite within the Windfall Pond watershed have higher Ca concentrations and higher alkalinity values than other streams, indicating the influence of this bedrock type. Townsend Pond water samples show consistently low alkalinity and pH values relative to Windfall Pond samples. A weathering experiment was performed to show how the geologic materials from the watershed react with sulfuric acid, a major component of acid deposition. Results show that the calcitic bedrock from the Windfall Pond watershed releases the most base cations and raises the pH and alkalinity of the solution most rapidly, while the granitic gneisses from Townsend Pond have only a minor effect on the solution. As a result it is concluded that the interaction of precipitation with bedrock, specifically calcitic quartzite, is the main cause of the high ANC of the Windfall Pond watershed relative to Townsend Pond. |
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http://departments.colgate.edu/geology/ |
