THE TAIHU EDDY FLUX NETWORK An Observational Program on Energy, Water, and Greenhouse Gas Fluxes of a Large Freshwater Lake

MOTIVATION AND SCIENCE QUESTIONS. Lakes are an important component of the climate system. Even though lakes and reservoirs occupy only about 4% of the global terrestrial surface (Downing et al. 2006), their societal importance is disproportionately large because many large municipalities are located near lake shorelines. The large thermal contrast between a lake and its surrounding land often triggers thermal circulations, having significant impact on air pollution dispersion and transport in the lake catchment. Being important sources of atmospheric moisture, large lakes can enhance storm formation in the downwind area (Samuelsson et al. 2010; Zhao et al. 2012). Except at times of high algal activities (Hari et al. 2008; Balmer and Downing 2011), lake water is usually supersaturated in CO2 with respect to the atmosphere and acts as a source of atmospheric carbon (Cole et al. 1994). Lakes are also sources of atmospheric CH4 (Bastviken et al. 2011) and N2O (Huttunen et al. 2003). Eddy covariance (EC) is an in situ technique for measuring momentum, heat, water, and greenhouse gas fluxes. It determines the flux continuously and nonintrusively from simultaneous measurements, in the atmospheric surface layer, of turbulent fluctuations in the air velocity and the scalar quantity of interest. The method is a key measurement tool deployed by several large observational networks,