Monday, 10 July 2006

Spatial Variability of Pedogenic Reaction Rates in a Podzolized Watershed.

Blake Ketchum1, Susan Brantley1, and Alan Busacca2. (1) Center for Environmental Kinetic Analysis, 2217 EES Building, Penn State Univ, University Park, PA 16802, (2) Dept of Crops and Soils, Washington State Univ, PO Box 646420, Pullman, WA 99164-6420

Soil genesis in forested watersheds can be characterized by great spatial variability. In podzolic soils, eluvial tongues present changes in depth of the E horizon of as much as 20 centimeters in only a few centimeters of lateral distance, suggesting significant and highly localized variations in biogeochemical reaction rates. In order to quantify dissolution and precipitation reaction rates throughout a highly variable podzolized watershed, we conducted elemental mass balances on 15 pedons that were randomly distributed throughout a 0.64ha 0th-order watershed of Spodosols formed in 9,900 year-old incised glacial outwash in the Upper Peninsula of Michigan. Dissolution and precipitation rates were parsed from the bulk elemental data for each soil horizon using XRD mineralogy and sequential extractions to identify and quantify the residual materials and secondary precipitates in each horizon. We examined the spatial distribution of reaction rates at a variety of spatial scales: within each horizon, within the pedon, and throughout the watershed. Our results suggest close linkages between pedogenic reaction rates and soil hydrology: precipitation reaction rates were generally greater in drier landscape positions and dissolution reaction rates dominated in wetter landscape positions.

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