A simple method for estimating water loss by transpiration in wetlands

Estimates of transpiration are often needed for hydrological management in wetlands. A new and simple method, using a portable steady-state porometer, is presented for estimating transpiration in three aquatic emergent macrophytes (reed, cut-sedge, and cattail). The method was established on the basis of the relationships between transpiration, solar radiation, relative humidity and air temperature. By assessing relationships between all variables in piecewise linear regressions with breakpoint, water loss by transpiration can be estimated. The regression equations are calculated from direct observations including daily averages of climatic variables. Other data used in the model are area-defined leaf density of macrophytes and yearly macrophyte cover. The results of this method in comparison with literature transpiration data confirm the importance of transpiration in the water balance in aquatic ecosystems. The advantage of this method relies on the possibility to determine the physiological variability of transpiration in relation to climatic variables determined in situ. This permits a closer approximation of processes taking place in nature. Given that the required information is easily obtainable and that good estimates of transpiration in emergent macrophytes are provided, the method serves as a valuable tool for wetland hydrology management.