Abstract
Wetland and maize farmland are main ecosystems in Northeast China, which play important roles in water, heat and energy exchanges between land and atmosphere. In this study, we used the eddy covariance system to examine the characteristics of water, heat and energy exchanges over a rainβfed maize agricultural ecosystem and a reed wetland ecosystem. The results showed that water and heat exchanges had significant differences between the two ecosystems, which were attributed to obvious distinction in their surface properties. Heat exchange (H) was stronger over reed wetland, while water vapour exchange (LE) was greater over maize farmland. Wetland has great thermal capacity that tends to slow down the energy exchange; therefore, halfβhour peak values of LE and H over the wetland delayed for half an hour compared to the maize farmland. The ratio of evapotranspiration (ET) to potential evapotranspiration (ET~p~) indicated that ET over the reed wetland was most of the time close to ET~p~ in the nonβgrowing season, while ET over the maize farmland was closer to ET~p~ in the growing season. A weak linear relationship was found between ET and leaf area index (LAI) over the reed wetland in the growing season, indicating that the transpiration from canopy provided few contributions to ET. In addition, uncertain water resources brought external energy into reed wetland, resulting in poor energy closure, which provided some uncertainty to the partition of available energy. Copyright Β© 2009 John Wiley & Sons, Ltd.