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.

Raw flux data for methane, carbon dioxide, and other species were measured using a paired Picarro-Licor trace gas analyzer from June – August 2021 (flux data is in ghg_raw.csv, data for statistical analysis in ghg_stats.csv). Net nitrogen mineralization data was collected through ion exchange resins (data is in n_raw.csv). Bulk density, soil texture, pH, and soil carbon and nitrogen were completed on soil samples analyzed at Yale University (data is in soilcn.csv). Carbon and nitrogen were measured on an elemental analyzer. Soil texture was estimated using particle size analysis. pH was measured using a bench top pH meter. Land cover classification was done using the NatureServe database for Sublette County, WY (data is in landcover.xlsx). In 'included' tab on landcover.xlsx, there are two sections of data on the left and right, not one rectangular table of data.

Funding provided by: Yale UniversityCrossref Funder Registry ID: https://ror.org/03v76x132Award Number: