Modelling a global biogeochemical nitrogen cycle in terrestrial ecosystems

Bl. Lin et al., Modelling a global biogeochemical nitrogen cycle in terrestrial ecosystems, ECOL MODEL, 135(1), 2000, pp. 89-110
Citations number
Categorie Soggetti
Journal title
ISSN journal
0304-3800 → ACNP
Year of publication
89 - 110
SICI code
An integrated global model developed mechanistically based on nitrogen tran sformation processes and nitrogen fluxes between the terrestrial biosphere and the atmosphere is described in this paper. This model was designed in c onjunction with our previous global carbon model on the compartments of veg etation and organic-soil, a third compartment, inorganic-soil, comprising a mmonium and nitrate was also incorporated. We divided the global terrestria l biosphere into 60156 grid cells, each cell being 0.5 degrees latitude by 0.5 degrees longitude in size, whereas we simplified the atmosphere by rega rding it as a well-mixed reservoir. Each grid cell was fixed as one of the five types of ecosystems: tropical forest, temperate forest, boreal forest, crops/grassland, or no vegetation (desert, ice). Geographical information system (GIS) data on climate, soils, and vegetation for each grid cell was used to drive the model in monthly time steps. Almost all of the key proces ses governing nitrogen cycling in the natural ecosystem were defined based on their respective mechanisms and specific relationships to environmental factors, then integrated into a highly aggregated dynamic model. Parameters required by the model were derived from published information or determine d by model calibrations such as curve fitting. Our model-based estimate of potential nitrogen storage in vegetation was 16 Pg, which is of similar mag nitude to estimates found in other studies (e.g. 10, 11-14 and 12-15 Pg), w hile nitrogen storage in global soil was 280 Pg according to our model, whi ch also shows good agreement with previously reported values, which range f rom 70 to 820 Pg, with intermediate estimates of 170, 175, 300 and 760 Pg. Of the 280 Pg of nitrogen in soil, 25 Pg was in inorganic forms such as amm onium and nitrate, and 255 Pg was in organic forms such as detritus and hum us. Thus, more than 90% of the soil nitrogen was present in organic forms, a finding that agrees very well with other fields research. A sensitivity a nalysis on the uncertainties of the initial conditions of the model and the parameter values determined by model calibrations was also performed. Alth ough additional work on model validation is still necessary, this model's a bility to simulate the nitrogen cycle in the natural ecosystem and to quant itatively estimate potential nitrogen storage in global vegetation and soil has been documented. We therefore can conclude at this stage that the basi c framework of a global biogeochemical nitrogen cycle, which can be used as a tool for quantitative evaluation of anthropogenic disturbances, has been developed. (C) 2000 Elsevier Science B.V. All rights reserved.