Surface atmosphere exchange of NO and CO2 in a grazed semi-arid ecosystem: comparison of measurements and model predictions

Claire Delon1*, Corinne Galy-Lacaux1, Dominique Serça1, Ndiobo Camara2, Eric Gardrat1, Idrissa Saneh3, Rasmus Fensholt4, Torbern Tagesson4, Valérie Le Dantec5, Bienvenu Sambou2, Cheikh Diop2, Manuela Grippa6, Eric Mougin6.

1 Laboratoire d’Aerologie, Université de Toulouse, CNRS, UPS, France, *

2 Institut des Sciences de l’Environnement, Université Cheick Anta Diop, Dakar, Sénégal

3 Centre de Recherche Zootechnique, Dahra, Sénégal

4 Institute of Geography, University of Copenhagen, Copenhagen, Danemark

5 Centre d’Etudes Spatiales de le BIOsphère, Université de Toulouse, CNES, CNRS, IRD, UPS, France

6 Geosciences Environnement Toulouse, Université de Toulouse, CNES, CNRS, IRD, UPS, France


This paper presents a comparison between measurements and model predictions of biogenic nitric oxide emissions and respiration (CO2 emissions) from soils in a Sahelian grazed ecosystem in Senegal (Dahra site, 15.2°N, 15.2°W). Nitric oxide (NO) and CO2 emissions are large at the beginning of the wet season when the first rains fall on dry soils (pulse emissions), due to microbial and biological processes reactivated in the soil when moisture conditions are favourable. The model shows a correct representation of pulses of NO and CO2, but underestimates fluxes in the drier periods between rain events and after the wet season. We hypothesize that in the drier periods the model over-predicts the death rate of microbes, involving a lag between mineral N content availability and N emissions. Spatial heterogeneity of soil and vegetation characteristics and presence of livestock also involve differences between modelled and measured fluxes.