Quantifying the CO₂ sink intensity of large and small saline lakes on the Tibetan Plateau

This study quantitatively evaluates the carbon dioxide (CO₂) sink intensity of a large saline lake (area > 2000 km²) and a small saline lake (area 1.4 km²) on the Tibetan Plateau (TP), alongside an alpine meadow, by analysing their net ecosystem exchange (NEE) figures obtained by eddy covariance (EC) measurements. Specifically, the "large lake" exhibits an NEE value of -122.51 g C m^-2 yr^-1, whereas the small lake has an NEE value of -47.17 g C m^-2 yr^-1. The alpine meadow, in contrast, demonstrates an NEE value of -128.18 g C m^-2 yr^-1. Through standardization of the eddy flux data processing and accounting for site-specific conditions with a wind direction filter and footprint analysis, the study provides robust estimates of CO₂ sink intensity. The "large lake" was found to absorb CO₂ primarily during non-icing cold periods with minimal exchange occurring during ice-covered season, whereas the "small lake" showed no significant CO₂ exchange throughout the year. On the other hand, alpine meadows engaged in CO₂ uptake during the vegetative growth season but showed weak CO₂ release in winter. CO₂ uptake in lakes is mainly controlled by ice barrier and chemical processes, while biological processes dominate the alpine meadow. The carbon sink intensity of the TP's saline lakes is estimated to be 1.87-3.01 Tg C yr^-1, smaller than the previous reported estimations. By evaluating the CO₂ sink intensity of different lakes, the study highlights the importance of saline lakes in regional carbon balance assessments. It specifically points out the differential roles lakes of various sizes play in the carbon cycle, thereby enriching our understanding of carbon dynamics in high-altitude lacustrine ecosystems.