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

Tagesson, Torbern LU ; Ardö, Jonas LU ; Guiro, Idrissa; Cropley, Ford LU ; Mbow, Cheikh; Horion, Stephanie; Ehammer, Andrea; Mougin, Eric; Delon, Claire and Galy-Lacaux, Corinne, et al. (2016) In Geografisk Tidsskrift 116(2). p.93-109
Abstract

Africa is a sink of carbon, but there are large gaps in our knowledge regarding the CO2 exchange fluxes for many African ecosystems. Here, we analyse multi-annual eddy covariance data of CO2 exchange fluxes for a grazed Sahelian semi-arid savanna ecosystem in Senegal, West Africa. The aim of the study is to investigate the high CO2 exchange fluxes measured at the peak of the rainy season at the Dahra field site: gross primary productivity and ecosystem respiration peaked at values up to −48 μmol CO2 m−2 s−1 and 20 μmol CO2 m−2 s−1, respectively. Possible explanations for such high fluxes include a combination of moderately dense herbaceous... (More)

Africa is a sink of carbon, but there are large gaps in our knowledge regarding the CO2 exchange fluxes for many African ecosystems. Here, we analyse multi-annual eddy covariance data of CO2 exchange fluxes for a grazed Sahelian semi-arid savanna ecosystem in Senegal, West Africa. The aim of the study is to investigate the high CO2 exchange fluxes measured at the peak of the rainy season at the Dahra field site: gross primary productivity and ecosystem respiration peaked at values up to −48 μmol CO2 m−2 s−1 and 20 μmol CO2 m−2 s−1, respectively. Possible explanations for such high fluxes include a combination of moderately dense herbaceous C4 ground vegetation, high soil nutrient availability and a grazing pressure increasing the fluxes. Even though the peak net CO2 uptake was high, the annual budget of −229 ± 7 ± 49 g C m−2 y−1 (±random errors ± systematic errors) is comparable to that of other semi-arid savanna sites due the short length of the rainy season. An inter-comparison between the open-path and a closed-path infrared sensor indicated no systematic errors related to the instrumentation. An uncertainty analysis of long-term NEE budgets indicated that corrections for air density fluctuations were the largest error source (11.3% out of 24.3% uncertainty). Soil organic carbon data indicated a substantial increase in the soil organic carbon pool for the uppermost.20 m. These findings have large implications for the perception of the carbon sink/source of Sahelian ecosystems and its response to climate change.

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publication status
published
subject
keywords
dryland, ecosystem respiration, gross primary productivity, Net ecosystem exchange, Sahel, savanna
in
Geografisk Tidsskrift
volume
116
issue
2
pages
17 pages
publisher
Taylor & Francis
external identifiers
  • scopus:84979010311
  • wos:000382974900001
ISSN
0016-7223
DOI
10.1080/00167223.2016.1178072
language
English
LU publication?
yes
id
0380e5c5-45fb-4924-8b7e-b51fc3e5e5ab
date added to LUP
2017-01-16 14:30:36
date last changed
2017-09-18 11:31:57
@article{0380e5c5-45fb-4924-8b7e-b51fc3e5e5ab,
  abstract     = {<p>Africa is a sink of carbon, but there are large gaps in our knowledge regarding the CO<sub>2</sub> exchange fluxes for many African ecosystems. Here, we analyse multi-annual eddy covariance data of CO<sub>2</sub> exchange fluxes for a grazed Sahelian semi-arid savanna ecosystem in Senegal, West Africa. The aim of the study is to investigate the high CO<sub>2</sub> exchange fluxes measured at the peak of the rainy season at the Dahra field site: gross primary productivity and ecosystem respiration peaked at values up to −48 μmol CO<sub>2</sub> m<sup>−2</sup> s<sup>−1</sup> and 20 μmol CO<sub>2</sub> m<sup>−2</sup> s<sup>−1</sup>, respectively. Possible explanations for such high fluxes include a combination of moderately dense herbaceous C4 ground vegetation, high soil nutrient availability and a grazing pressure increasing the fluxes. Even though the peak net CO<sub>2</sub> uptake was high, the annual budget of −229 ± 7 ± 49 g C m<sup>−2</sup> y<sup>−1</sup> (±random errors ± systematic errors) is comparable to that of other semi-arid savanna sites due the short length of the rainy season. An inter-comparison between the open-path and a closed-path infrared sensor indicated no systematic errors related to the instrumentation. An uncertainty analysis of long-term NEE budgets indicated that corrections for air density fluctuations were the largest error source (11.3% out of 24.3% uncertainty). Soil organic carbon data indicated a substantial increase in the soil organic carbon pool for the uppermost.20 m. These findings have large implications for the perception of the carbon sink/source of Sahelian ecosystems and its response to climate change.</p>},
  author       = {Tagesson, Torbern and Ardö, Jonas and Guiro, Idrissa and Cropley, Ford and Mbow, Cheikh and Horion, Stephanie and Ehammer, Andrea and Mougin, Eric and Delon, Claire and Galy-Lacaux, Corinne and Fensholt, Rasmus},
  issn         = {0016-7223},
  keyword      = {dryland,ecosystem respiration,gross primary productivity,Net ecosystem exchange,Sahel,savanna},
  language     = {eng},
  month        = {07},
  number       = {2},
  pages        = {93--109},
  publisher    = {Taylor & Francis},
  series       = {Geografisk Tidsskrift},
  title        = {Very high CO<sub>2</sub> exchange fluxes at the peak of the rainy season in a West African grazed semi-arid savanna ecosystem},
  url          = {http://dx.doi.org/10.1080/00167223.2016.1178072},
  volume       = {116},
  year         = {2016},
}