Control of Microbial Nitrous Oxide Production in Coastal Waters
Seed Grant 2016
Award Period: 2016-2018
Denitrification removes fixed nitrogen, which enters surface and ocean waters from agricultural activities,and thus reduces eutrophication by producing dinitrogen (N2) and nitrous oxide (N2O). N2O, produced by both natural microbial processes and internal combustion, is an ozone destroying agent and a potent greenhouse gas, so the ratio of N2O to N2 production determines the net environmental impact of denitrification. This ratio is highly unconstrained and the relative importance of several microbial pathways involved in N2O production and their control by environmental conditions is poorly known. In this research, the relationship between N2O production and fixed N concentrations will be quantified in order to understand the regulation of those pathways.
In summer of 2016, the first set of experiments were performed on a research cruise in the Chesapeake Bay. Samples were collected from the oxic/anoxic interface in the main stem of the Bay. Time course incubations were performed with isotope tracers and the samples were preserved and returned to the lab. All of the samples have been analyzed on the mass spec, and preliminary evaluation of the results is consistent with the initial hypothesis. The rate of N2O production from nitrate exceeds the rate of production of N2O from nitrite only at high ratios of nitrate to nitrite. A second expedition is planned for next spring in order to repeat the experiments and to obtain higher resolution in the time course experiments.
The main educational impact of this project so far is in research training: Yea-shine Lee, an undergraduate student who has not yet declared a major, worked in the laboratory on related research projects all summer, participated in the research cruise, and helped with the mass spec analysis of the incubation samples. Xin Sun, a first year graduate student at the time, participated in the cruise and helped with the incubations. She will further analyze particulate material samples that were collected in parallel with the incubations by nucleic acid sequencing to investigate the microbial assemblage responsible for the measured rates. This project will be part of her dissertation research. Qixing Ji has mentored both Lee and Sun, teaching them the laboratory and mass spec protocols for many different kinds of isotope analysis.
- Amal Jayakumar, Senior Research Specialist, Geosciences
- Xin Sun, GEO
- Qixing Ji (2012-2016), GEO
- Yea-Shine Lee, Class of 2019