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 macrop hytes (reed, cut-sedge, and cattail). The method was established on the bas is of the relationships between transpiration, solar radiation, relative hu midity and air temperature. By assessing relationships between all variable s in piecewise linear regressions with breakpoint, water loss by transpirat ion can be estimated. The regression equations are calculated from direct o bservations including daily averages of climatic variables. Other data used in the model are area-defined leaf density of macrophytes and yearly macro phyte cover. The results of this method in comparison with literature trans piration data confirm the importance of transpiration in the water balance in aquatic ecosystems. The advantage of this method relies on the possibili ty to determine the physiological variability of transpiration in relation to climatic variables determined in situ. This permits a closer approximati on 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.