Whitmire, S.L. and S.K. Hamilton
Presented at the All Scientist Meeting (2002-10-04 )
Biogeochemical transformations in wetlands impact water quality and nutrient transport across landscapes as well as greenhouse gas fluxes. We explored the influence of anaerobic microbial respiration on wetland biogeochemistry in surficial sediments of six southwest Michigan wetlands in a glacial terrain, three of which were mainly groundwater-fed and three were mainly precipitation-fed. Water source for each site was verified from major solute composition. We measured ambient rates of denitrification, sulfate reduction, iron reduction, methanogenesis and acetate turnover, and performed in-situ push-pull experiments using local groundwater amended with bromide. Nitrate concentrations in porewaters were low at all sites, even though groundwater inputs are often elevated in nitrate. Despite the lack of actual denitrification, all six wetlands showed potential to rapidly remove nitrate, as indicated by denitrifying enzyme activity and in-site push-pull experiments. Iron (II) concentrations varied among the sites, but iron reduction was measurable mainly in precipitation-fed wetlands. Sulfate reduction rates were greater in groundwater-fed wetlands than precipitation-fed wetlands, resulting in removal of sulfate and some accumulation of hydrogen sulfide. Sulfate was taken up from injected groundwater only after nitrate was depleted. Methanogenesis was measurable in all wetlands, with no differences between wetlands with contrasting water sources, indicating that methanogenesis is important regardless of water source.
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