Methane dynamics in the subsaline ponds of the Chihuahuan Desert: A first assessment.

The Cuatro Cienegas Basin (CCB) in the Chihuahuan desert is characterized by the presence of over 500 ponds located in an endorheic basin. These ponds are subsaline ecosystems characterized by a low productivity and a particularly high sulfate concentration, comparable to marine environments. This study focused on assessing the main physicochemical parameters in these ponds along with the characterization of the CH dynamics through the determination of fluxes, dissolved CH concentrations, and net methanotrophic and methanogenic activity. Despite a sulfate concentration ranging from 1.06 to 4.73 g L, the studied ponds showed moderate but clear CH production and emission, which suggests that methanogenesis is not completely outcompeted by sulfate reduction. CH fluxes ranged from 0.12 to 0.98 mg m d, which falls within the higher range of marine emissions and within the lower range reported for coastal saline lagoons and saline ponds. During summer, significant CH production in the oxic water column was observed. In addition to CH, CO fluxes were determined at levels from 0.2 to 53 g m d, which is within the range recorded for saline lakes in other parts of the world. Our results provide additional evidence that subsaline/saline aquatic ecosystems play an important role in the emission of greenhouse gases to the atmosphere.