Evapotranspiration in semi-arid wetlands: relationships between inundation and the macrophyte-cover:open-water ratio

Open water evaporation and macrophyte transpiration rates were analyzed in a semi-arid, freshwater wetland in Central Spain over two meteorological periods between 1993 and 1998. The aim was identifying the importance of these variables in the dynamics of evapotranspiration in different water level scenarios. Throughout the vegetation growth period, transpiration versus evaporation ratios were about 2 for cut-sedge, 1 for reed and 0.5 for cattail, but these values declined significantly when calculated on a yearly basis. Open water area to macrophyte cover ratios showed significant dependence on inundation. Increased vegetation cover did not result in a statistically significant reduction of evapotranspiration, but it did increase the transpiration to evaporation ratio. Increased open water area resulted in increased wetland evapotranspiration. The results indicate that Linacre's theory needs to be modified to take into account emergent macrophyte strategies to flood tolerance and plant physiological traits. The authors provide a conceptual model to explain wetland evapotranspiration dynamics in relation to vegetation cover, physiological strategies and inundation.