Effect of Salinity in Alpine Lakes on the Southern Tibetan Plateau on Greenhouse Gas Diffusive Fluxes

Abstract

AbstractInland waters play an important role in the global carbon cycle and are potential hotspots of greenhouse gas (GHG) production and emission. However, considerable uncertainty exists in GHG estimations from lakes on the Tibetan Plateau due, in part, to the lack of direct in situ observations and key predictor analyses. Considering that salinity is an important factor regulating lake GHGs, diffusive methane flux (FCH4) and carbon dioxide flux (FCO2) and concentrations of dissolved CH4 (dCH4) and CO2 (dCO2) were measured in 16 freshwater and brackish Tibetan lakes in Shigatse. The results demonstrated that FCH4 at the water–air interface in freshwater lakes (45.14 ± 58.86 μmol·m−2·s−1) was 15 times higher than that in brackish lakes (2.92 ± 3.85 μmol·m−2·s−1). There was a significant decrease in FCH4 from the littoral zone to the pelagic area in these lakes. The FCO2 in freshwater lakes (−0.18 ± 0.39 μmol·m−2·s−1) was significantly lower than that in brackish lakes (0.38 ± 0.22 μmol·m−2·s−1). Therefore, freshwater lakes were regarded as CO2 sinks, while brackish lakes were regarded as CO2 sources. According to the comprehensive CO2 equivalent diffusive fluxes (FCO2eq, 0.66 ± 0.97 μmol·m−2·s−1), the 16 lakes were a carbon source to the atmosphere during the sampling period. FCO2 enhancement could be compensated by the decrease in FCH4 at the water–air interface as a result of salinity gradients across lakes. Under the scenarios of climate warming and drying in southern Tibet from 2020 to 2035, lake FCO2eq tended to decrease in this area.