Influence of Topography on Soil Acidity and Hydrogen Ion Budgets in an Arctic Landscape

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>The mechanisms by which topography influences soil acidity and H.+ budgets along an elevation gradient in the Alaskan tundra will be studied. A central hypothesis of the proposal is that H.+ production and consumption in a tundra elevation gradient are regulated primarily by belowground chemical and microbial processes that depend on topographically induced variation in redox potentials. To examine the topographic variation in soil acidity and test the central hypothesis, six ecosystems along an elevation gradient of about 300m on the banks of the Sagavanirktok River, north of the Brooks Range, will be examined. Part of the study will be descriptive. Patterns of acidity will be determined by measuring free H.+, and titratable acidity, exchangeable cations, and the acid strength of the exchange complex. In addition, estimations will be made of the major components of H.+ budgets, including atmospheric inputs, internal ecosystem production and consumption, and export. The study will also include experimental manipulations to test the controls of H.+ production in three of the six ecosystems along the elevation gradient. A combination of standard methods will be used to measure the various components of the H.+ budget. Among these are: 1) denitrification by anaerobic laboratory assays using the acetylene block procedure; 2) nitrification by the buried bag procedure; and 3) plant ion balance by the biomass accumulation procedure. A H.+ budget serves to validate our understanding of biogeochemical cycling in an ecosystem. Better understanding of biogeochemical cycling in the tundra is needed for its wise management. Dr. Binkley is a productive researcher who has substantial experience in developing H.+ ion budgets. The institutional support available to him is very good.