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Landscape-level Biogeochemistry
One of the main ways in which environments interact at the landscape scale is through the fluxes of water by surface and subsurface pathways. Lakes, wetlands, and streams are abundant and diverse in the glacial landscape around KBS and represent an important resource. The central question we are addressing with our landscape biogeochemistry component is "How do current and future land use and landscape patterns affect the fluxes of water and nutrients from upland areas to lakes, streams and wetlands?" We are approaching this question on multiple fronts, including sustained sampling of local lakes, streams, and wetlands, as well as more specific lines of research that are briefly highlighted here. 
Nutrient retention by streams and wetlands: During the summer of 2005 we completed the third and final year of field experiments for the NSF-funded Lotic Intersite Nitrogen Experiment (LINX). Whole-stream stable isotope additions were employed to investigate nitrate removal by headwater streams in contrasting land uses (agricultural, urbanized, and forested)(Mulholland et al. 2004). This intersite comparison is yielding unprecedented insights into patterns and controls of nitrate interception in stream networks (Mulholland et al., in prep.). A new project investigates the role of impoundments along small watercourses, comparing them to free-flowing stream channels.
Linkages between N and S cycles: New research examines novel pathways of nitrogen transformation in aquatic sediments, including nitrate reduction by sulfur bacteria (Burgin and Hamilton 2007), building upon previous work (Whitmire and Hamilton 2005). This research is fundamental to understanding the fate of nitrate, much of which originates from agriculture, as it moves through landscape flow paths.
Liming and carbon sequestration: The biogeochemistry of soil solutions reveals the fate of carbon in lime that is typically applied to agricultural soils (Hamilton et al. in press). The counterintuitive conclusion is that as lime dissolves it sequesters CO2 as bicarbonate ions, which can then be transported to groundwater reservoirs with long residence times.
Evolution of chemical characteristics as water infiltrates soils: The work on the fate of lime carbon (see above), together with ongoing collaborations with geochemists at the University of Michigan (Jin et al. in prep.), is elucidating the major mineral weathering and microbial reactions in near-surface soils that determine the chemistry of groundwater, and how land use and agricultural practices affect these reactions.
Selected publications:
Burgin, A.J. and S.K. Hamilton. 2007. Have we overemphasized the role of denitrification in aquatic ecosystems? A review of nitrate removal pathways. Frontiers in Ecology and the Environment 5: 89-96.
Hamilton, S.K., A.L. Kurzman, C. Arango, L. Jin, and G.P. Robertson. Evidence for carbon sequestration by agricultural liming. Global Biogeochemical Cycles. In press.
Jin, L., L.M. Walter, and S.K. Hamilton. Seasonal variations of chemical weathering in soils developed on glacial drift in Michigan (USA). Chemical Geology. In review.
Mulholland, P.J., H.M. Valett, J.R. Webster, S.A. Thomas, L.N. Cooper, S.K. Hamilton, and B.J. Peterson. 2004. Stream denitrification and total nitrate uptake rates measured using a field 15N tracer addition approach. Limnology and Oceanography 49: 809-820.
Mulholland, P.J. and the LINX team. Nitrate concentration regulates denitrification and nitrogen removal in streams and stream networks. Science. In review.
Whitmire, S.L. and S.K. Hamilton. 2005. Rapid removal of nitrate and sulfate by freshwater wetland sediments. Journal of Environmental Quality 34: 2062-2071.