Modeling carbon and nitrogen biogeochemistry in forest ecosystems
A forest biogeochemical model, Forest-DNDC, was developed to quantify carbon sequestration in and trace gas emissions from forest ecosystems. Forest-DNDC was constructed by integrating two existing moels, PnET and DNDC, with several new features including nitrification, forest litter layer, soil freezing and thawing etc, PnET is a forest physiological model predicting forest photosynthesis, respiration, C allocation, and litter production. DNDC is a soil biogeochemical model predicting soil organic matter turnover, trace gas emissions and N leaching. The two models were linked to each other by exchanging information of litter production, plant demand for water and N, and availability of water and N in soil. Input parameters required by Forest-DNDC are daily meteorological data, forest type and age, soil properties, and forest management practices (e.g., harvest, thinning, fire, restoration, drainage, wetland restoration etc.). For wetland applications, observed or modeled water table data are required to drive the soil redox potential dynamics. Forest-DNDC runs at daily time step, and produces daily and annual results of forest growth, net ecosystems C exchange, fluxes of CO2, CH4, N2O, NO. N2, and NH3 emissions, and N leaching from the rooting zone. The modeled C and N fluxes can be compared with the observations gained with static chamber, automated chamber, Eddy tower facilities. Actually, Forest-DNDC has been tested against measured fluxes of CO2, CH4, N2O, and NO at about 20 forested sites in North America, Europe and Ocenia. Currently, Forest-DNDC is being linked to GIS databases and hydrological models for estimating environmental impacts of forest management in the U.S. and several European countries at regional scale. We also plan to test this integrated simulation system at a dozen research sites across China that were recently instrumented with eddy covariance flux measurements under the US-China Carbon Consortium (USCSS) framework.