Project: Anammox, denitrification and nitrogen fixation in the Black Sea

Anammox, denitrification and nitrogen fixation in the Black Sea

The goal of this research project is to understand the large variability in the chemical and microbial distributions related to nitrogen cycling in the suboxic zone of the Black Sea. The large temporal variability is best explained by changes by microbially mediated processes such as ANAMMOX and nitrification. Previous work has identified some of the bacteria present across the chemocline, but their metabolisms, activities, and relative contributions to the biogeochemical balance of nitrogen are still very poorly understood. This project will address not only the presence and absence of different types and abundances of microbial groups, but also their metabolic activity by testing two hypotheses. The first hypothesis is that the seasonal variability in the flux of particulate organic carbon causes variability in the relative importance of ANAMMOX and denitrification. The second hypothesis is that variability in the concentrations of N2 and Delta 15 N-N2 is determined by variability in the vertical flux of particulate organic nitrogen produced by nitrogen fixation in the euphotic zone. The principal investigators will address these hypotheses by conducting a time series of observations that consist of four short cruises (spring, fall, winter and summer) on a Russian research vessel to deep water stations in the Black Sea. During these cruises comprehensive hydrophysical, chemical and microbiological sampling, and measurements of the sinking flux of particulate organic carbon will be conducted. This new geochemical data will be used to expand on the investigators previous data sets by looking specifically at the variability in nitrogen species and isotope distributions and fluxes over the annual cycle. The specific focus of the biological work proposed here is to document not only changes in the microbial community, but to identify active growth and gene transcripts of specific groups of microbes. The study has ramifications beyond the Black Sea as the results will help us understand some of the controls on nitrogen cycling under low oxygen conditions in general. The ability to predict future change as a result of anthropogenic forcing requires that we understand the current dynamics in the nitrogen cycle. Suboxic and anaerobic environments are susceptible to anthropogenic forcing, and play an increasingly important role not only in enclosed basins but in areas of high productivity and economic importance, such as the Oregon and Washington coast. These results will also shed light on suboxic and anaerobic processes that have been important throughout Earth's history.

RELATED PUBLICATIONS:

Fuchsman, CA; Murray, JW; Konovalov, SK. "Concentration and natural stable isotope profiles of nitrogen species in the Black Sea," MARINE CHEMISTRY, v.111, 2008, p. 90-105. [View at Web of Science]

Konovalov, SK; Fuchsman, CA; Belokopitov, V; Murray, JW. "Modeling the distribution of nitrogen species and isotopes in the water column of the Black Sea," MARINE CHEMISTRY, v.111, 2008, p. 106-124. [View at Web of Science]