0516076 Role of microbial sulfur oxidation in nitrogen removal by wetlands and streams (S.K. Hamilton)
Excessive nitrogen (N) entering streams, often originating as nitrate from agricultural or urban areas, creates problems with water-quality and is a growing concern. Surface and groundwater flow through landscapes often passes through wetlands and headwater streams, where nitrate removal is typically observed. Further removal may occur in downstream impoundments and floodplains. The research proposed here was inspired by previous studies that showed that nitrate removal from freshwater sediments in Michigan coincided with sulfate production. Pilot research indicates that this is a biological process that could occur via sulfur (S) oxidation by bacteria that utilize nitrate as an oxidant in place of oxygen. The overarching hypothesis under investigation is that nitrate reduction linked to S oxidation is an important process in many freshwater sediments. Such sediments are not unusually high in S, which like nitrate has natural sources, but also is a ubiquitous pollutant. The importance of nitrate reduction by S oxidizers will be investigated across diverse wetlands, streams, and riverine reservoirs and floodplains in southwestern Michigan, and in headwater streams at several U.S. locations that are study sites for the Lotic Intersite N Experiment (LINX). The removal of N by wetlands and streams is of particular interest in agricultural landscapes because N export by rivers to coastal waters has been implicated in creating hypoxic zones (e.g., the Gulf of Mexico) and harmful algal blooms. Wetland and stream restoration for the purpose of N management should consider the possible linkage between microbial S and N transformations, which bears on the controls of N removal rates and the eventual fate of the N that is removed. Graduate student training is integral to this research, and the results will contribute to outreach and teaching activities.
