Greenhouse Gas Emissions as Impacted by Topography and Vegetation Cover in Wooded Grasslands of Laikipia County, Kenya

Authors

• Janeth Chepkemoi * ¹
• Richard Ndemo Onwonga ¹
• Richard Nyankanga ²
• Angela Nduta Gitau ¹

1. Department of Land Resource Management and Agricultural Technology, University of Nairobi, Kagemi, Nairobi
2. Department of Plant Science and Crop Protection, Faculty of Agriculture, University of Nairobi, Kagemi, Nairobi

Abstract

Global climate change has been linked to the increase in greenhouse gas (GHG) emissions. Wooded grasslands refer to an understudied landscape contributing an unknown quantity of GHGs to global climate change. The objective of this study was to determine the effects of topography and vegetation cover on carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes. The study was carried out in Ilmotiok community ranch, Laikipia County. An in situ experiment was done during the January, February, March and April of 2017. Randomized complete block design (RCBD) with split plot arrangement was used main plots topographical zones (TZ) (mid-slope (MS), foot slope (FS), and toe slope (TS)) and subplots vegetation cover (VC) (tree (T), grass (G) and bare (B)). Static chamber frames were installed for the three VC (T, G and B) in three TZ (MS, FS, and TS). GHGs were measured every 7-10 days from January, February, March and April between 8 and 12 hr local time. Sampling was done after fitting the lid at time zero (T0), 10 minutes (T1), 20 minutes (T2) and 30 minutes (T3). During the rainy season, CH₄N₂O and CO₂ fluxes were significantly higher than the dry season. Methane fluxes ranged from -0.32 to 0.24 mg.m^-2.h^-1 with the lowest (-0.32 mg.m^-2.h^-1) recorded under TS*T whereas CO₂ was highest under TS*G (47 mg.m^-2.h^-1) as compared to MS*G (19 mg.m^-2.h^-1). TZ*VC significantly influence N₂O with MS*B recording the lowest (0.008) as compared to TS*B (2.228 mg.m^-2.h^-1). CO₂, N₂O and CH₄ emissions were low in January and February and it increased in March and April in all the TZ*VC. From the study results, soil greenhouse gas emissions were significantly increased by topography and vegetation cover. Topography and vegetation cover primarily control the patterns of soil N₂O, CO₂ and CH₄ fluxes, therefore, topography and vegetation features must be explicitly included in the predictions of the responses of soil GHGs emissions.

Keywords

• Climate Change
• Greenhouse gas fluxes
• Methane
• Nitrous oxide
• Topography
• Vegetation cover

Main Subjects

• Carbon Capture and Storage