Growing season methane budget of an Inner Mongolian steppe

We present a methane (CH4) budget for the area of the Baiyinxile Livestock Farm, which comprises approximately 1/3 of the Xilin river catchment in central Inner Mongolia, P.R. China. The budget calculations comprise the contributions of natural sources and sinks as well as sources related to the main land-use in this region (non-nomadic pastoralism) during the growing season (May–September). We identified as important CH4 sources floodplains (mean 1.55 ± 0.97 mg CH4–C m−2 h−1) and domestic ruminants, which are mainly sheep in this area. Within the floodplain significant differences between investigated positions were detected, whereby only positions close-by the river or bayous emitted large amounts of CH4 (mean up to 6.21 ± 1.83 mg CH4–C m−2 h−1). Further CH4 sources were sheepfolds (0.08–0.91 mg CH4–C m−2 h−1) and pasture faeces (1.34 ± 0.22 mg CH4–C g−1 faeces dry weight), but they did not play a significant role for the CH4 budget. In contrast, dung heaps were not a net source of CH4 (0.0 ± 0.2 for an old and 0.0 ± 0.3 μg CH4–C kg−1 h−1 for a new dung heap). Trace gas measurements along two landscape transects (volcano, hill slope) revealed expectedly a mean CH4 uptake (volcano: 76.5 ± 4.3; hill: 28.3 ± 5.3 μg CH4–C m−2 h−1), which is typical for the aerobic soils in this and other steppe ecosystems. The observed fluxes were rarely influenced by topography. 4 emissions from the floodplain and the sheep were not compensated by the CH4 oxidation of aerobic steppe soils and thus, this managed semi-arid grassland did not serve as a terrestrial sink, but as a source for this globally important greenhouse gas. The source strength amounted to 1.5–3.6 kg CH4–C ha−1 during the growing season, corresponding to 3.5–8.7 kg C ha−1 yr−1.