Seasonal contribution and interannual variation of evapotranspiration over a reed marsh (Phragmites australis) in Northeast China from 3-year eddy covariance data

At present, one of unresolved critical issues relating to climate change is whether evapotranspiration (ET) is increasing or decreasing with global warming. There has been great interest, therefore, in studying ET in a variety of ecosystems to better understand the nature of the controlling interactions and the links between ET and other ecosystem processes. Especially, relatively few studies on ET have been conducted in wetland environments. In this paper, we present the results from 3 years (2005-2007) of direct ET measurements, using eddy covariance method, over a reed (Phragmites australis) marsh in Liaohe Delta, Northeast China. The seasonal and interannual variation of daily ET and its main controls were analysed. Annual ET for the reed marsh was 432, 480, and 445 mm in 2005, 2006 and 2007, respectively. The contribution of ET during non-growing season was not negligible; it ranged from 13% to 16% of the annual ET for the investigated years. On annual course, ET increased associating with increasing temperature and reed plant growth in late-April and early-May, and peaked in the rapid growing season with weekly mean rates of 3D7 mm day(-1) (2005), 3D7 mm day(-1) (2006), and 3D4 mm day(-1) (2007). Decoupling factor (Omega) also varied seasonally, with its minimum values occurred in the non-growing season and the maximum values in the rapid growing season, especially in July. During the rapid growing season, the values of decoupling factor (Omega) were generally between 0.5 and 0.8, indicating that solar radiation was main factor affecting ET other than vapour pressure deficit (VPD). Moreover, biological factor and canopy conduction also controlled the interannual ET variation in the reed marsh. The results would be helpful to better understand ET for this particular reed marsh. Copyright (C) 2009 John Wiley & Sons, Ltd.