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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 mu g 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 mu g 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.

The CH4 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). (C) 2009 Elsevier Ltd. All rights reserved.