HR: 0800h
AN: B31A-0067    [Abstracts]
TI: Mechanistic Representation of the N Isotope Composition of Pools and Fluxes in a Coupled Soil and Plant System: Model Development, Testing, and Application
AU: * Riley, W J
EM: wjriley@lbl.gov
AF: Earth Sciences Division, 90-1116 Lawrence Berkeley National Lab 1 Cyclotron Rd, Berkeley, CA 94720, United States
AU: Maggi, F
EM: fmaggi@berkeley.edu
AF: UC Berkeley, Berkeley Water Center 413 O'Brien Hall, Berkeley, CA 94720, United States
AU: Gu, C
EM: cgu@berkeley.edu
AF: UC Berkeley, Berkeley Water Center 413 O'Brien Hall, Berkeley, CA 94720, United States
AB: The composition and location of ¹⁵N atoms on N₂O molecules has been used to characterize soil biological N cycling, N₂O surface emissions, and N₂O atmospheric transport and fate. However, the complexity and interdependency of soil microbial processes (e.g., nitrification, denitrification, mineralization, decomposition), physical processes (e.g., soil moisture and temperature dynamics, aqueous and gaseous advection and diffusion), and abiotic chemical processes (e.g., dissolution and precipitation, pH buffering) makes interpretation of the isotopic composition of measured N₂O pools and surface fluxes very difficult. We report here on the development of a mechanistic model (TOUGHREACT-N) that attempts to account for these interactions and aids in the interpretation of ¹⁵N soil and plant measurements. The model accounts for the various N exchanges in nitrification, dentrification, decomposition, and mineralization; dynamics of several microbial populations; soil moisture and heat dynamics; multiple chemical reactions in solution and with the mineral phase; and exchanges with the overlying atmosphere. Interactions of soil N and water with plants are currently being implemented. We briefly describe the successful testing of TOUGHREACT-N in agricultural fields under a number of fertilizer and irrigation treatments. The model is then used to interpret the ¹⁵N composition of N pools and surface fluxes in published experiments. Our results indicate that the previously unaccounted transport and microbial processes substantially increase the uncertainty of source partitioning (e.g., between nitrification and denitrification). We also demonstrate several ways in which the model can be used to design sampling protocols to improve measurement interpretation.
DE: 0402 Agricultural systems
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0466 Modeling
DE: 0469 Nitrogen cycling
SC: Biogeosciences [B]
MN: 2007 Fall Meeting