Dissolved organic carbon, CO2, and CH4 concentrations and their stable isotope ratios in thermokarst lakes on the Qinghai-Tibetan Plateau

Abstract

<p>Thermokarst lakes are widely distributed on the Qinghai-Tibetan Plateau (QTP), which accounts for 8% of the global permafrost area. These lakes probably promote organic matter biodegradation and thus accelerate the emission of carbon-based greenhouse gases. However, little is known about greenhouse gas concentrations and their stable isotopes characteristics of these lakes. In this study, we measured the concentrations of dissolved organic carbon (DOC), dissolved CO<sub>2</sub> and CH<sub>4</sub>, as well as the distribution of δ<sup>13</sup>C<sub>C</sub><sub>O2</sub>, δ<sup>13</sup>C<sub>C</sub><sub>H4</sub>, and δ<sup>13</sup>C<sub>OM</sub> (organic matter) of lake sediments in thermokarst lakes on the QTP. Results showed that the OM of the lake sediments was highly decomposed. The concentrations of DOC, CO<sub>2</sub> and CH<sub>4</sub> in the lake water on the QTP were 1.2–49.6 mg L<sup>–1</sup>, 3.6–45.0 μmol L<sup>–1</sup> and 0.28–3.0 μmol L<sup>–1</sup>, respectively. The highest CO<sub>2</sub> and CH<sub>4</sub> concentrations were recorded in July while the lowest values in September, which suggested that temperature had an effect on greenhouse gas production, although this pattern may also relate to thermal stratification of the water column. The results implied that thermokast lakes should be paid more attention to regarding carbon cycle and greenhouse gas emissions on the QTP.</p>