Water and carbon dioxide fluxes over a "floating blanket" wetland in southwest of China with eddy covariance method

Large uncertainties exist in carbon sequestration and water exchange process in wetland ecosystems under climate change. Beihai wetland is a very rare special type of alpine marsh with plants floating on the water surface located in the southeast margin area of the Tibetan Plateau. Based on the eddy covariance measurements from July 2015 to December 2016 over Baihai wetland, we have investigated the patterns of energy and carbon dioxide fluxes between the air and the alpine marsh and their main drivers. The latent heat flux (LE) was the main consumer of available radiation which accounted for 63% of net radiation (R-n) in 2016. R-n was the main factor determining H at both wet and dry season. Air temperature (T-a) and vapor pressure deficit (VPD)were most influenced with half-hourly LE during both wet and dry season, and VPD showed a larger influence on NEE in dry season than that in wet season. The total evapotranspiration (ET) in wet season occupied 60% of annual ET with an amount of 762.3 mm yr(-1) in 2016, which was much lower than the annual total precipitation (1780.2 mm yr(-1)). Photosynthetic active radiation (PAR) was the main controller in the half-hourly net ecosystem exchange (NEE), while T-a mainly controlled the seasonal variations in NEE. The annual total NEE, gross primary production (GPP) and ecosystem respiration (RE) were -233.8, 796.6 and 562.8 g C m(-2) yr(-1) in 2016. The fraction of vegetation to water surface changed from 66% to 74% in the study period. A positive linearly relationship was both found between the fraction of vegetation to water surface and CO2 uptake and evapotrans-piration. The fraction of vegetation to water surface could explain 40% variation of ET and 62% variation of NEE, respectively.