Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: September 2, 2010
Publication Date: July 4, 2011
Citation: Spokas, K.A. 2011. Stable Isotopes in Evaluation of Greenhouse Gas Emissions. In: Encyclopedia of Agrophysics. J. Glinski, J. Horabik, and J. Lipiec (Eds). Springer. Heidelberg, Germany. pp. 845-849. Technical Abstract: Isotopes offer a unique way to have natural tracers present in the ecosystem to track produced greenhouse gases (GHG) through multiple scales. Isotopes are simply atoms of the same element (same number of protons) with differing number of neutrons. This differing number of neutrons leads to differences in the atomic masses of the elements. For example, carbon-12 (12-C) and carbon-13 (13-C) are two naturally occurring isotopes of carbon, both have 6 protons except 12-C has 6 neutrons and 13-C has 7 neutrons. For many biological (e.g. microbial reactions, enzyme reactions, plant respiration, etc.) and abiotic processes (e.g. diffusion, solution equilibrium, etc.) there are differences in the rates of the processes for the different isotopes. This difference in the rates leads to differences in the distribution of the isotopes in the product compared to the reactant, which is referred to as fractionation. This is of particular importance in GHG research for variations in the isotopes of C, nitrogen (N) and oxygen (O). In general, although exceptions do exist, lighter isotopes react faster than heavier isotopes. This small difference in reaction rates (fractionation) between isotopes leads to differences in the isotopic signature of the products as compared to the reactants. However, this fractionation can be a function of several variables (e.g. microbial species, temperature, substrate availability, etc.). Provided this preference is known along with the reactant and product isotopic distribution, the relative contribution of different processes can be calculated from the changes in the isotopic distribution. This chapter briefly describes the current state of research in utilizing the isotopic signatures of GHGs for emission research.