Silvia E. Newell, Ph.D. (Advisor); Mark J. McCarthy, Ph.D. (Committee Member); Rebecca E. Teed, Ph.D. (Committee Member)
Master of Science (MS)
Excess loading of nitrogen (N) and phosphorus (P) is a serious global problem and has numerous negative impacts on water quality of aquatic ecosystems including eutrophication, harmful algal blooms, and hypoxia. Anthropogenic activities (such as the Haber-Bosch process, burning of fossil fuels, sewage treatment, and manure reuse) have led to excess N loading to aquatic systems. Sediment N dynamics were examined from Oct 2019 – Oct 2020 in an agricultural settling pond connected to a constructed wetland adjacent to an agricultural field. Intact sediment cores were amended with 15N for continuous-flow incubations to measure denitrification and N fixation rates, as well as net nutrient and oxygen fluxes. Net N2 consumption (N fixation > denitrification) was observed over most of the year, suggesting that pond sediments were a net N source. Denitrification was stimulated when 15N-nitrate was added, and net denitrification was observed following a N fertilizer application in May 2020. NOx entering the wetland and settling pond was rapidly transformed or assimilated. However, during winter and following fertilizer application, ambient NOx concentrations increased in the wetland, but remained lower in the settling pond, suggesting rapid N removal in the pond. Sediment oxygen demand and potential denitrification rates increased in warmer months, suggesting greater microbial activity and organic matter decomposition. Settling ponds in agricultural settings thus have the potential to supplement agricultural nutrient control practices. Further research should focus on understanding the frequency, timing, and amount of N loading that enters field-adjacent wetlands and ponds to determine if the sediments will consistently function as a net N sink and to maximize denitrification efficiency.
Department or Program
Department of Earth and Environmental Sciences
Year Degree Awarded
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