Evapotranspiration of small-scale constructed wetlands planted with ligneous species

Evapotranspiration from small constructed wetlands continuously supplied by wastewater was estimated directly during four periods each two weeks long. Constructed wetland of the Station Experimentale in Viville consists of 10 tanks with surface area of about 1 m(2), the tanks are planted with various wetland woody species. The Station is situated in drained agriculture fields near city of Arlon and the evapotranspiration was measured in summer months (June, July) in order to evaluate effect of heat advection from drained surroundings on real evapotranspiration. Therefore, the potential evapotranspiration calculated from global radiation and temperature was compared with real evapotranspiration measured as water budget (load/discharge) in individual small constructed wetlands. The potential evapotranspiration ranged between 1.8 and 3.9 L m(-2) whereas real evapotranspiration from constructed wetlands planted by Salix cinerea ranged from 16.4 to 27.4 L m(-2), by Alnus glutinosa and Alnus cordata from 4.3 to 21.5 L m(-2), by Populus tremula from 8.8 to 16.0 L m(-2), by Prunus padus from 5.8 to 9.0 L m(-2) and by Fraxinus excelsior from 5.8 to 8.4 L m(-2). High evapotranspiration of Salix cinerea is explained both by high biomass, high leaf area index and the best physiological adaptation to waterlogging, and consequently anoxia. The daily courses of water saturation deficit, transpiration, and leaf conductivity measured on individual leaves and daily courses of PhAR (photosynthetically active radiation), air humidity and temperatures show fast increase of transpiration early morning and relatively low leaf conductivity and low water saturation deficit during the day. It is concluded that evapotranspiration in wetlands supplied well with water and isolated in drained landscape can be several times higher than it would correspond to the potential evapotranspiration.