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Do groundwater inputs matter for wetland biogeochemical functions?
Whitmire, Stefanie1, Hamilton, Stephen 1, 1
ABSTRACT- Anaerobic microbial decomposition plays a central role in the biogeochemical functions of wetlands. Since wetlands are often situated at points of groundwater recharge and discharge these biogeochemical processes can affect downstream water quality. Four wetlands in southwest Michigan were selected to examine how anaerobic microbial processes influence their biogeochemistry. Two of the sites were mainly groundwater fed wetlands and the other two were mainly precipitation fed. Nitrate concentrations were low at all sites, even though groundwater inputs are often elevated in nitrate. Iron (II) varied among the sites, but iron reduction was measurable only in two wetlands and was not related to water source. Sulfate reduction rates were greater in the groundwater-fed wetlands than the precipitation-fed wetlands, resulting in removal of sulfate and some accumulation of hydrogen sulfide. Dissolved gases extracted from sediment porewater samples usually contained at least 50% methane, indicating that methanogenesis is important in all types of wetlands, although methane production rates were higher in precipitation-fed wetlands. Considering the equivalent carbon mineralization rates, sulfate reduction is relatively important in the groundwater-fed wetlands, while methanogenesis is important at all sites and dominates in the precipitation-fed wetlands. Iron reduction appears to play a relatively minor role.
KEY WORDS: biogeochemistry, anaerobic, decomposition