Modelling land–atmosphere daily exchanges of NO, NH3, and CO2 in a semi-arid grazed ecosystem in Senegal

• Three different models (STEP–GENDEC–NOflux, Zhang2010, and Surfatm) are used to simulate NO, CO2, and NH3 fluxes at the daily scale for 2 years (2012–2013) in a semi-arid grazed ecosystem at Dahra (15∘24′10′′ N, 15∘25′56′′ W, Senegal, Sahel). Model results are evaluated against experimental results acquired during three field campaigns. At the end of the dry season, when the first rains re-wet the dry soils, the model STEP–GENDEC–NOflux simulates the sudden mineralization of buried litter, leading to pulses in soil respiration and NO fluxes. The contribution of wet season fluxes of NO and CO2 to the annual mean is respectively 51 % and 57 %. NH3 fluxes are simulated by two models: Surfatm and Zhang2010. During the wet season, air humidity and soil moisture increase, leading to a transition between low soil NH3 emissions (which dominate during the dry months) and large NH3 deposition on vegetation during wet months. Results show a great impact of the soil emission potential, a difference in the deposition processes on the soil and the vegetation between the two models with however a close agreement of the total fluxes. The order of magnitude of NO, NH3, and CO2 fluxes is correctly represented by the models, as well as the sharp transitions between seasons, specific to the Sahel region. The role of soil moisture in flux magnitude is highlighted, whereas the role of soil temperature is less obvious. The simultaneous increase in NO and CO2 emissions and NH3 deposition at the beginning of the wet season is attributed to the availability of mineral nitrogen in the soil and also to microbial processes, which distribute the roles between respiration (CO2 emissions), nitrification (NO emissions), volatilization, and deposition (NH3 emission/deposition). The objectives of this study are to understand the origin of carbon and nitrogen compounds exchanges between the soil and the atmosphere and to quantify these exchanges on a longer timescale when only a few measurements have been performed.

• Three different models (STEP–GENDEC–NOflux, Zhang2010, and Surfatm) are used to simulateNO, CO2, and NH3 fluxes at the daily scale for 2 years(2012–2013) in a semi-arid grazed ecosystem at Dahra(152401000 N, 152505600W, Senegal, Sahel). Model resultsare evaluated against experimental results acquired duringthree field campaigns. At the end of the dry season, when thefirst rains re-wet the dry soils, the model STEP–GENDEC–NOflux simulates the sudden mineralization of buried litter,leading to pulses in soil respiration and NO fluxes. Thecontribution of wet season fluxes of NO and CO2 to theannual mean is respectively 51% and 57 %. NH3 fluxes aresimulated by two models: Surfatm and Zhang2010. Duringthe wet season, air humidity and soil moisture increase,leading to a transition between low soil NH3 emissions(which dominate during the dry months) and large NH3deposition on vegetation during wet months. Results show agreat impact of the soil emission potential, a difference in thedeposition processes on the soil and the vegetation betweenthe two models with however a close agreement of the totalfluxes. The order of magnitude of NO, NH3, and CO2 fluxesis correctly represented by the models, as well as the sharptransitions between seasons, specific to the Sahel region.The role of soil moisture in flux magnitude is highlighted,whereas the role of soil temperature is less obvious. Thesimultaneous increase in NO and CO2 emissions and NH3deposition at the beginning of the wet season is attributedto the availability of mineral nitrogen in the soil and alsoto microbial processes, which distribute the roles betweenrespiration (CO2 emissions), nitrification (NO emissions),volatilization, and deposition (NH3 emission/deposition).The objectives of this study are to understand the origin ofcarbon and nitrogen compounds exchanges between the soiland the atmosphere and to quantify these exchanges on alonger timescale when only a few measurements have beenperformed.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Naturgeografi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Physical Geography (hsv//eng)

Publikations- och innehållstyp

art (ämneskategori)

ref (ämneskategori)