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Methane sources and sinks in a periodically flooded South African savanna
Author(s) -
Otter Luanne B.,
Scholes Mary C.
Publication year - 2000
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/1999gb900068
Subject(s) - environmental science , floodplain , dry season , hydrology (agriculture) , nutrient , subtropics , wet season , methane , flux (metallurgy) , soil water , flood myth , atmospheric sciences , water content , soil science , ecology , chemistry , geology , geography , geotechnical engineering , organic chemistry , biology , archaeology
Methane (CH 4 ) fluxes were measured over a 2‐year period at subtropical savanna and floodplain sites located in South Africa. No significant differences were detected in fluxes from the nutrient‐rich and nutrient‐poor savannas. Savannas were not always sinks and showed some CH 4 emissions during the wet, summer season with fluxes in the range of −1.6 to 1.68 mg m −2 d −1 . Soil temperature did not have a significant effect on the flux, while CH 4 consumption decreased and emissions increased with an increase in soil moisture between 5% and 50% water‐filled‐pore‐space (WFPS). Understanding the factors which control the production and emission of CH 4 in aerobic environments is extremely important for predicting net emissions from a region. Dry floodplain soil fluxes were near zero and did not differ significantly from savanna fluxes. During a flood, saturated sites emitted CH 4 at an average rate of 69.4 mg m −2 d −1 . Flooded areas with a water depth of 0.3 ‐ 0.4 m emitted CH 4 from the water surface at rates between 0.48 and 466.3 mg m −2 d −1 with the highest emission occurring during summer. Emission rates were exponentially related to sediment temperature, which had a greater influence on the emission rate than the flood regime. The length of the dry period preceding the flood and the extent of a flood did not have a significant effect on CH 4 fluxes from saturated and flooded sites. Emission rates were highest when the water level was between 0.1 m below the soil surface and 0.4 m above the soil surface, with emission rates declining to near zero as the water became deeper than 0.4 m. Savannas were estimated to consume an average of 0.04 g CH 4 m −2 d −1 , with southern African savannas consuming 0.23 Tg CH 4 yr −1 . Saturated and flooded sites were estimated to produce 25.3 and 57.2 g CH 4 m −2 d −1 , respectively. Southern African floodplains are estimated to produce between 0.2 and 10 Tg CH 4 yr −1 (excluding the effects of vegetation‐mediated emissions) and therefore produce more CH 4 than the savannas consume.