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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-407
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-407
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 23 Oct 2019

Submitted as: research article | 23 Oct 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Soil Greenhouse Gas Emissions under Different Land-Use Types in Savanna Ecosystems of Kenya

Sheila Wachiye1,2,5, Lutz Merbold3, Timo Vesala2, Janne Rinne4, Matti Räsänen2, Sonja Leitner3, and Petri Pellikka1,2 Sheila Wachiye et al.
  • 1Earth Change Observation Laboratory, Department of Geosciences and Geography, University of Helsinki, Finland
  • 2Institute for Atmosphere and Earth System Research, University of Helsinki, Finland
  • 3Mazingira Centre, International Livestock Research Institute (ILRI), Nairobi, Kenya
  • 4Department of Physical Geography and Ecosystem Science, Lund University, Sweden
  • 5School of Natural Resources and Environmental Management, University of Kabianga, Kenya

Abstract. For effective climate change mitigation strategies, adequate data on greenhouse gas (GHG) emissions from a wide range of land-use and land cover types area prerequisite. However, GHG field measurement data are still scarce for many land-use types in Africa, causing a high uncertainty in GHG budgets. To address this knowledge gap, we present in situ measurements of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) emissions in the lowland part of southern Kenya. We conducted chamber measurements on gas exchange from four dominant land-use types (LUTs) and included (1) cropland, (2) grazed savanna, (3) bushland, and (4) conservation land. Between 29 November 2017 to 3 November 2018, eight measurement campaigns were conducted accounting for regional seasonality (including wet and dry seasons and transitions periods) in each LUT. Mean CO2 emissions for the whole observation period were significantly higher (p-value < 0.05) in the conservation land (75 ± 6 mg CO2-C m−2 h−1) compared to the three other sites, which ranged from 45 ± 4 mg CO2-C m−2 h−1 (bushland) to 50 ± 5 mg CO2-C m−2 h−1 (grazing land). Furthermore, CO2 emissions varied between seasons, with significantly higher emissions during the wet season than the dry season. In contrast, mean N2O emissions were not different between the four sites, ranging from 1.2 ± 0.4 μg N2O-N m−2 h−1 (in bushland) to 2.7 ± 0.6 μg N2O-N m−2 h−1 (in cropland). However, N2O emissions were slightly elevated during the early days of the wet season. CH4 emissions did not show any significant differences between LUTs and seasons, and most values were below the limit of detection (LOD, 0.03 mg CH4-C m−2 h−1). We attributed the difference in soil CO2 emissions between the four sites to soil C content, which differed between the sites and was highest in the conservation land. CO2 and N2O emissions positively correlated to soil moisture, thus an increase in soil moisture led to an increase in emissions. Soil temperature did not show a clear correlation with either, most likely due to the low annual variation in soil temperature. We found a strong positive correlation between soil CO2 and the normalized difference vegetation index (NDVI), but we observed no correlation with soil N2O emissions. We conclude that soil moisture is a key factor in soil GHG emissions in these tropical savanna LUTs. In addition, including vegetation indices in the model greatly improved the results, thus showing the importance of vegetation cover in predicting soil emissions. Our results are within the range of previous GHG flux measurements from soils from various land-use types in other parts of Kenya and contribute to more accurate baseline GHG emission estimates from Africa, which are key for informing policymakers when discussing low-emission development strategies.

Sheila Wachiye et al.
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Sheila Wachiye et al.
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Short summary
Limited data on emissions in Africa transcend to uncertainty during GHG budgeting. We studied annual CO2, N2O, and CH4 emissions in four land-use types in Kenyan savanna using static chambers and gas chromatography. CO2 emissions varied between seasons and land-use types. Soil moisture and vegetation explained the seasonal variation while soil temperature was insignificant. N2O and CH4 emissions did not vary at all sites. Our results are useful in climate change mitigation interventions.
Limited data on emissions in Africa transcend to uncertainty during GHG budgeting. We studied...
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