Nathaniel E. Ostrom
Ph.D., Memorial University of Newfoundland, 1992236C Natural Science Building
Office Telephone: 517-355-4661
Application of Stable Isotopes in Ecosystem Science
My research focuses on the application of stable isotopes and other approaches for understanding the biogeochemical cycling of carbon and nitrogen in a variety of ecosystems. Current research projects include:
1. Understanding novel nitrogen cycling pathways in Lake Vida, Antarctica
Lake Vida is a permanently icy covered lake located in the dry valleys of Antarctica. About five years ago, an expedition drilled through the 16 m of ice cover and sampled the brine located beneath the ice for the first time and found the presence of viable microbial mats even though the temperature of this body of water is 14°C below zero, lacks oxygen and receives no sunlight. The microbial community has been isolated from the surface for at least 2,000 years and the waters contain a very unusual distribuion of N containing compounds including levels of nitrite toxic to most microbes and the highest levels of nitrous oxide observed anywhere on Earth. The research team will return to Lake Vida this fall and my part of this project is to determine rates of nitrification, denitrification, anammox as well as the origins of nitrous oxide. Recent studies suggest that nitrous oxide in the nearby Don Juan Pond was derived from inorganic reactions but the presence of mats in Lake Vida suggest that it may be produced by microbial metabolic reactions. We will determine the abundance of the stable isotopes within nitrous oxide as an approach for resolving its origin. This research will help us understand how life functions within one of the coldest environments on Earth and has implications for how life may function elsewhere in our solar system.
2. The impact of the Deepwater Horizon oil spill on hypoxia in the northern Gulf of Mexico
In May and August of 2010 we participated in a research cruise to the northern Gulf of Mexico as part of a research team focused on the relationship between nitrogen cycling and the development of the low oxygen conditions west of the Mississippi River delta; a region known as the "dead zone". While the May research cruise was scheduled months in advance of the oil spill we realized that most of our study sites were located in close proximity to the Deepwater Horizon spill site that occurred one month earlier. Consequently, we requested and receive funding to address the affect of the oil spill on the development of hypoxia. We hypothesized that the oil spill will enhance hypoxia by (1) fostering respiration as the oil is degraded, (2) blocking sunlight and the production of oxygen by photosynthesis and (3) decreasing gas exchange across the air-water interface. The presence of even thin layers of hydrocarbons on the surface has been shown to decrease gas exchange markedly. The project will focus on measuring rates of primary production and respiration and the concentration and hydrocarbon composition of the surface micro-layer of the ocean. See an article I wrote on this topic in the Prairie Fire Newspaper (http://www.prairiefirenewspaper.com/2010/09/the-dead-zone).
3. Application of the isotopomers of nitrous oxide to evaluate the origins of this greenhouse gas
Nitrous oxide is a surprisingly complex molecule as it contains two elements with five naturally occurring stable isotopes (14-N, 15-N, 16-O, 17-O, and 18-O). Further, nitrous oxide is not a symmetrical molecule like carbon dioxide but rather is asymmetrical (N-N-O) which means that the two nitrogen atoms in nitrous oxide often contain different abundances of 15-N. We were one of the first research teams to pioneer the application of site specific isotope values to evaluate the microbial origins of this gas. We have applied this approach in a variety of ecosystems (Puerto Rico, New Mexico, and the Kellogg Biological Station in SW Michigan) and have found bacterial denitrification to be the primary source of nitrous oxide. This information provides an important foundation for how agricultural environments in particular may be managed to minimize fluxes of nitrous oxide to the atmosphere to help mitigate global warming.
4. Instrument development to enable real time and in situ stable isotope measurements
Our research team has worked extensively toward the goal of obtaining stable isotope data on greenhouse gases in the field environment rather than having to return samples to the laboratory. To this end we have collaborated with mechanical and electrical engineers to develop and instrument that can quantitatively trap trace gases for months at a time for later measurement. Further, we have collaborated with space scientists to develop a small energy efficient mass spectrometer that can be deployed in remote settings.
Applications of mass spectrometry for the real time and continuous monitoring of the abundance and isotopic composition of trace and abundant gases.
Ostrom N.E., A. Pitt, R.L. Sutka, P.H. Ostrom, A.S. Grandy, K.M. Huizinga, H. Gandhi, J.C. von Fischer and G.P. Robertson (2010) Isotopologue data reveal bacterial denitrification as the primary source of N2O during a high flux event following cultivation of a native temperate grassland. Soil Biology and Biochemistry. 42, 499-506
Opdyke, M., N.E. Ostrom and P.H. Ostrom (2009). Evidence for the predominance of denitrification as a source of N2O in temperate agricultural based on isotopologue measurements. Global Biogeochemical Cycles, 23, GB4018, doi:10.1029/2009GB003523.
Elsbury, K.E., A. Paytan, N.E. Ostrom, C. Kendall, M.B. Young, K. McLaughlin, M.E. Rollog, and S. Watson (2009) Using Oxygen Isotopes of Phosphate To Trace Phosphorus Sources and Cycling in Lake Erie. Environmental Science and Technology, DOI: 10.1021/es8034126
Leigh M.B., V.H. Pellizari, O. Uhlý´k, R. Sutka, J. Rodrigues, N.E. Ostrom, J. Zhou, and J.M. Tiedje (2007) Biphenyl-utilizing bacteria and their functional genes in a pine root zone contaminated with polychlorinated biphenyls (PCBs). International Society of Microbial Ecology Journal 1: 134-148
Sutka R.L., N.E. Ostrom, P.H. Ostrom, J.A. Breznak H. Gandhi, A. J. Pitt, F. Li. (2006) Distinguishing nitrous oxide production from nitrification, and denitrification on the basis of isotopomer abundances. Applied and Experimental Microbiology. 72. 638-644
Ostrom N.E., M.E. Russ, A. Field, L. Piwinski, M.R. Twiss, H. J. Carrick. (2005) Understanding the relationship between primary production and respiration in Lake Erie Based on oxygen isotope techniques, Journal of Great Lakes Research. 31:138-153