Low methane emissions from nutrient-rich former river channels in a hydrologically managed dryland delta

Abstract

Anthropogenic stresses in dryland regions can alter hydrology, salinization, and biogeochemical processes. How these pressures influence methane (CH₄) cycling and emissions from aquatic ecosystems remains poorly understood. Over the course of 1 year, we measured diffusive and ebullitive CH₄ emissions from resacas—shallow, hydrologically managed distributary channels prevalent throughout the Lower Rio Grande Valley along the US–Mexico border. Despite warm, nutrient-rich waters, CH₄ emissions from resacas were low, and more comparable to rates observed in estuarine systems. CH₄ fluxes were positively related to temperature but negatively related to salinity and rainfall. Elevated salinity, driven by evaporation and source water from the salinized Rio Grande, may suppress methanogenesis. These findings highlight the complex interplay of salinity, hydrology, and management in shaping aquatic CH₄ emissions from dryland regions. As dryland water bodies face growing salinization and warming temperatures, resacas offer valuable insight into CH₄ dynamics in increasingly altered freshwater ecosystems.