Analysis of the diurnal and seasonal variations of NEE exchange over a large lake, a small lake and meadow surface of Lake Nam Co basin, Tibetan Plateau

Abstract

Saline lakes play an important role in the global carbon cycle by burying carbon in sediments and emitting CO2 to the atmosphere. A series of recent studies have found that Saline lakes of the Tibetan Plateau (TP) have a strong carbon sink function, which exhibits very different characteristics from lakes in other regions of the world.A period of five-year data recorded by the eddy covariance (EC) systems built at Lake Nam-Co (“large lake”, area: more than 2000 km2), Lake small Nam-Co (“small lake”, area: 1.4 km2) and Nam-Co land site (“land station”, plateau meadow) have been used to study on net ecosystem exchange (NEE) characteristics over the different underlying surfaces at Lake Nam-Co Basin. The results revealed that significant differences exist in their carbon exchange processes at diurnal and seasonal variations. (1) CO2  uptake in “large lake” occurs mainly during the freeze period, and the NEE uptake at the “land station” appears mainly in spring and summer, while “small lake” has no significant CO2 uptake during the winter ice covered season。(2) “Large lake” has significant intra-day variation during the ice-forming season; the “land station” has close to zero values in winter but shows significant intra-day variation in spring and summer for the NEE exchange, while the “small lake” shows significant differences for wind direction from the water and from the surrounding land. Under global climate change, the lakes over the TP have expanded a large proportion right now and will continue to enlarge in the future. Our study revealed that there are significant differences in the functions of CO2 source/sink between lakes and land, and even in different sizes of lakes on the TP. This will provide an important reference for the prediction and estimation of the carbon function changes of lakes on the TP.