Modelling the effect of soil moisture and organic matter degradation on biogenic NO emissions from soils in Sahel rangeland (Mali)

[摘要] This work is an attempt to provide seasonal variation of biogenic NO emissionfluxes in a Sahelian rangeland in Mali (Agoufou,15.34° N, 1.48° W) for years 2004, 2005,2006, 2007 and 2008. Indeed, NOis one of the most important precursors for tropospheric ozone, and previous studies have shown that arid areaspotentially display significant NO emissions (due to both biotic and abiotic processes). Previous campaignsin the Sahel suggest that the contribution of this region in emitting NO is no longer considered as negligible.However, very few data are available in this region, therefore this study focuses on model development.The link between NO production in the soil and NO release to the atmosphereis investigated in this modelling study, by taking into account vegetationlitter production and degradation, microbial processes in the soil, emissionfluxes, and environmental variables influencing these processes, using acoupled vegetation–litter decomposition–emission model. This model includesthe Sahelian Transpiration Evaporation and Productivity (STEP) model for thesimulation of herbaceous, tree leaf and faecal masses, the GENDEC model (GENeral DEComposition) for the simulation of the buried litter decomposition and microbial dynamics, and the NO emission model (NOFlux) for the simulation of the NO release to the atmosphere.Physical parameters (soil moisture and temperature, wind speed, sandpercentage) which affect substrate diffusion and oxygen supply in the soiland influence the microbial activity, and biogeochemical parameters (pH andfertilization rate related to N content) are necessary to simulate the NOflux. The reliability of the simulated parameters is checked, in order toassess the robustness of the simulated NO flux. Simulated yearly average ofNO flux ranges from 2.09 to 3.04 ng(N) m⁻² s⁻¹ (0.66 to0.96 kg(N) ha⁻¹ yr⁻¹), and wet season average ranges from 3.36 to 5.48 ng(N) m⁻² s⁻¹ (1.06 to 1.73 kg(N) ha⁻¹ yr⁻¹). These results are of thesame order as previous measurements made in several sites where the vegetation and the soil are comparable to the onesin Agoufou. This coupled vegetation–litter decomposition–emission model could be generalized at the scale of the Sahelregion, and provide information where few data are available.

[学科分类] 地球化学与岩石