Biogeochemical Modeling

AGS believes that process-oriented models are a critical component of land management and decision support tools for developing site-specific best management practices in agro-ecosystems. The process-oriented computer simulation model, Denitrification-Decomposition or DNDC, developed by Dr. Changsheng Li at the University of New Hampshire is based on the biogeochemical concepts for predicting soil carbon and nitrogen biogeochemistry (Li et al., 1992, 1996; Li 2000). DNDC was constructed with two components to reflect the two-level driving forces that control geochemical and/or biochemical processes related to carbon and nitrogen fluxes. The entire model forms a bridge between basic ecological drivers, management of agro-ecological systems, and water, C and N cycles (figure below). DNDC utilizes GIS databases with spatially and temporally differentiated information on climate, soil, vegetation and farming practices as parameters for supporting local, regional and national scale analyses.



The core of DNDC is a soil biogeochemical model, which can be linked to vegetation models to predict C sequestration and N cycling for different ecosystems. DNDC has been linked to a crop model (i.e., Crop-DNDC, Zhang et al. 2002) to simulate soil organic carbon (SOC) dynamics and emissions of dinitrogen (N2) and several trace gases including N 2O, nitric oxide (NO), ammonia (NH 3) and methane (CH 4) from both upland and wetland agricultural ecosystems. Linked to GIS databases, the model has been used to estimate C sequestration, nitrate production and emissions of N 2O, NO, CH 4 and NH 3 in agricultural lands in the U.S. and China. Li et al. (2001, 2002a,b) indicated soil N loss occurred in the U.S. and China through different paths: denitrification dominated soil N loss in the U.S., and NH 3 volatilization in China. This model has been independently tested by many researchers worldwide and now is utilized for national trace gas inventory studies in the U.S., Canada, the U.K., Germany, China, Japan, Thailand, Indonesia and Philippines. DNDC has also been linked to a forest physiological model (i.e., PnET developed by Aber and Federer 1992) to form a forest biogeochemical model, PnET-N-DNDC (Li et al. 2000). This model can predict C sequestration and trace gas emissions in temperate forest ecosystems, and is currently being utilized for a large-scale European project "Nitrogen oxides emissions from European forest ecosystems" (EU-granted, 2002-2005). Recently, DNDC ability to predict nitrate leaching from agro-ecosystems has been tested using water leaching fluxes and nitrate concentration data from a study in Iowa (Jaynes et al. 2001). Modeled water leaching rates compared favorably with field measured flux rates from 1996 through 1999 measured by Jaynes et al. (2001) (see Figure below). Modeled and field estimates of annual nitrogen leaching rates exhibited similar patterns and magnitudes (see insert) (Farahbakhshazad et al. 2004).

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