This research is designed to determine the effect of elevated nutrients on microbial function and diversity in streams. The overall objective is to evaluate the relationship between nutrient concentration and dissolved organic matter (DOM) cycling through field-based experimentation on nutrient-rich and nutrient-poor streams in watersheds of two major Mississippi River tributaries. Microbial activity on DOM exposed to solar radiation will be used to assess the ecological impact of nutrient concentration on ultraviolet light-mediated reactions in stream water. Stable isotope tagged nutrients will be used to determine their fate and participation in these reactions. Stable isotope tagged organic substrates will be used in field enclosures to track their use by microbes. These tagged compounds will be followed into microbial cell membrane fatty acid markers that are indicative of different stream microorganisms. This approach will provide a means to assess the stream microbial community, its role in DOM cycling, and the extent to which it can be altered by nutrient enrichment.
Nutrient enrichment, a common scenario resulting from nitrogen deposition, fertilization, and other land use changes, is the primary stressor in aquatic ecosystems. Dead zones occurring along coastlines worldwide are the result of nutrient enrichment derived from associated watersheds. Small streams are the primary location of nutrient processing within watersheds, and represent the first places where terrestrial nutrients enter the aquatic environment. Small streams also are heavily impacted by current land use trends. Microbial processing of nutrients in streams is governed by the availability of DOM. Changes in DOM composition resulting from nutrient-enrichment may alter microbial communities, thereby influencing the ability of streams to process watershed-deriveed nutrients. The proposed research will involve the training of students at various levels in stable isotope biogeochemistry and ecosystem science at an institution underrepresented in the research community, and serving a diverse population of students from largely rural backgrounds.
