Underground Sources of the Western Coastal Zone of the Hypersalted Lake Baskunchak: Hydrochemical Features and Greenhouse Gas Emissions

In the western coastal zone of Lake Baskunchak, about 300 dispersed groundwater outlets have been identified, unloading in the form of low-flow jets and seeps in shallow bowl-shaped holes or gullies. Gas bubbles are observed in many operating sources. The waters of the studied underground sources are characterized by a low flow rate (0.32-50 l/h), high mineralization (16.6-284.4 g/l), low concentrations of dissolved oxygen (0.144-1.75 mg/l), high concentrations of methane (14.9-74.8 µl/l), dissolved forms of iron (41.1-55.4 mg/l) and manganese (2.35-2.90 mg/l), slightly acidic - neutral pH (5.89-7.07). Specific fluxes of methane and carbon dioxide into the atmosphere from the surface of the water sources vary between 0,13-2,31 mg CH4/(m2∙h) and 72.4-1683.6 mg CO2/(m2∙h). At the same time, the flow of carbon dioxide into the atmosphere from the sediment surface at some distance from the unloading sources was an order of magnitude lower (16.3-23.7 mg CO2/(m2∙h)). Despite the higher specific fluxes from the surface of the water of underground sources, the total emission of carbon dioxide as a result of unloading of all underground sources is 30 times less than its total emission from the coastal dry basin, within which these underground sources are discharged.