Подземные источники балки Пещерная озера Баскунчак: гидрохимические особенности и эмиссия парниковых газов

Abstract

For the first time, full-scale measurements of methane and carbon dioxide emissions by the chamber method were carried out in summer for groundwater sources discharged in the valley of the Peshernaya Gulch creek, located in the north-west of Lake Baskunchak. pH values, concentrations of CH4, basic ions, gross Fe and Mn were determined in the water of the sources; concentrations of CH4, H2S, organic matter, Eh and pH values, density and humidity were determined in various layers of bottom sediments (up to 27 cm). A detailed description of the identified groundwater sources was carried out, their primary morphometric and morphological characteristics were measured, as well as the flow rate. It was found that more than 10 ascending karst sources of groundwater are discharged in the Peshchernaya beam, 5 of which were active during the research period and mainly confined to the left screw of the beam. The active sources of the left screw of the beam are characterized by a small flow rate and are sodium chloride brines with a mineralization of 93.9–107.1 g/l. The bottom sediments accumulating in the sinkholes of underground sources are characterized by a neutral acid-base environment and restorative conditions. The concentrations of CH4 and ∑H2S in the sediments of the sources varied, respectively, in the range of 0.08–0.77 µg/g vl.o. and 0.023–2.63 mg/g vl.o. with minimal values for both gases in the lower less reduced layer with a low content of Sorg. The concentration of methane in the water of active sources varied from 26.3 up to 38.4 µl/l and was on average 2 times higher than in the waters of a stream fed by them and an inactive source. The specific methane flux from the water surface of active sources varied in the range of 0.6–1.5 mg/(m2∙h), which is 2 orders of magnitude lower than the specific CO2 flux of 46.4–106.1 mg/(m2∙h). The isotopic composition of carbon (δ13C) CH4 and CO2 measured in gas bubbles rising from the bottom of one of the ascending sources indicates the modern biochemical genesis of these greenhouse gases.