Land use change converts temperate dryland landscape into a net methane source

Drylands cover approximately 40% of the global land surface and are
thought to contribute significantly to the soil methane sink. However,
large-scale methane budgets have not fully considered the influence of
agricultural land use change in drylands, which often includes irrigation
to create land cover types that support hay or grains for livestock
production. These land cover types may represent a small proportion of the
landscape but could disproportionately contribute to greenhouse gas
exchange and are currently omitted in estimates of dryland methane fluxes.
We measured greenhouse gas fluxes among big sagebrush, introduced
wetlands, and hay meadows in a semi-arid temperate dryland in Wyoming, USA
to investigate how these small-scale irrigated land cover types
contributed to landscape-scale methane dynamics. Big sagebrush ecosystems
dominated the landscape while the introduced wetlands and hay meadows
represented 1% and 12%, respectively. Methane uptake was consistent in the
big sagebrush ecosystems, emissions and uptake were variable in the hay
meadows, and emissions were consistent in the introduced wetlands. Despite
making up 1% of the total land area, methane production in the introduced
wetlands overwhelmed consumption occurring throughout the rest of the
landscape, making this region a net methane source. Our work suggests that
introduced wetlands and other irrigated land cover types created for
livestock production may represent a significant, previously overlooked
source of anthropogenic methane in this region and perhaps in drylands
globally.