TY - JOUR

T1 - Very high CO2 exchange fluxes at the peak of the rainy season in a West African grazed semi-arid savanna ecosystem

AU - Tagesson, Håkan Torbern

AU - Ardoe, Jonas

AU - Guiro, Idrissa

AU - Cropley, Ford

AU - Mbow, Cheikh

AU - Horion, Stéphanie Marie Anne F

AU - Ehammer, Andrea

AU - Mougin, Eric

AU - Delon, Claire

AU - Galy-Lacaux, Corinne

AU - Fensholt, Rasmus

PY - 2016

Y1 - 2016

N2 - Africa is a sink of carbon, but there are large gaps in our knowledge regarding the CO2 exchangefluxes for many African ecosystems. Here, we analyse multi-annual eddy covariance data of CO2exchange fluxes for a grazed Sahelian semi-arid savanna ecosystem in Senegal, West Africa. The aimof the study is to investigate the high CO2 exchange fluxes measured at the peak of the rainy seasonat the Dahra field site: gross primary productivity and ecosystem respiration peaked at values upto −48 μmol CO2 m−2 s−1 and 20 μmol CO2 m−2 s−1, respectively. Possible explanations for such highfluxes include a combination of moderately dense herbaceous C4 ground vegetation, high soilnutrient availability and a grazing pressure increasing the fluxes. Even though the peak net CO2uptake was high, the annual budget of −229 ± 7 ± 49 g C m−2 y−1 (±random errors ± systematicerrors) is comparable to that of other semi-arid savanna sites due the short length of the rainyseason. An inter-comparison between the open-path and a closed-path infrared sensor indicated nosystematic errors related to the instrumentation. An uncertainty analysis of long-term NEE budgetsindicated that corrections for air density fluctuations were the largest error source (11.3% out of24.3% uncertainty). Soil organic carbon data indicated a substantial increase in the soil organiccarbon pool for the uppermost .20 m. These findings have large implications for the perception ofthe carbon sink/source of Sahelian ecosystems and its response to climate change.

AB - Africa is a sink of carbon, but there are large gaps in our knowledge regarding the CO2 exchangefluxes for many African ecosystems. Here, we analyse multi-annual eddy covariance data of CO2exchange fluxes for a grazed Sahelian semi-arid savanna ecosystem in Senegal, West Africa. The aimof the study is to investigate the high CO2 exchange fluxes measured at the peak of the rainy seasonat the Dahra field site: gross primary productivity and ecosystem respiration peaked at values upto −48 μmol CO2 m−2 s−1 and 20 μmol CO2 m−2 s−1, respectively. Possible explanations for such highfluxes include a combination of moderately dense herbaceous C4 ground vegetation, high soilnutrient availability and a grazing pressure increasing the fluxes. Even though the peak net CO2uptake was high, the annual budget of −229 ± 7 ± 49 g C m−2 y−1 (±random errors ± systematicerrors) is comparable to that of other semi-arid savanna sites due the short length of the rainyseason. An inter-comparison between the open-path and a closed-path infrared sensor indicated nosystematic errors related to the instrumentation. An uncertainty analysis of long-term NEE budgetsindicated that corrections for air density fluctuations were the largest error source (11.3% out of24.3% uncertainty). Soil organic carbon data indicated a substantial increase in the soil organiccarbon pool for the uppermost .20 m. These findings have large implications for the perception ofthe carbon sink/source of Sahelian ecosystems and its response to climate change.

KW - Net ecosystem exchange

KW - Sahel

KW - gross primary productivity

KW - dryland

KW - savanna

KW - ecosystem respiration

U2 - 10.1080/00167223.2016.1178072

DO - 10.1080/00167223.2016.1178072

M3 - Journal article

VL - 116

SP - 93

EP - 109

JO - Geografisk Tidsskrift

JF - Geografisk Tidsskrift

SN - 0016-7223

IS - 2

ER -