QUANTIFICATION OF CONSTRUCTED WETLAND EVAPOTRANSPIRATION USING LYSIMETERS

摘要

The role and importance of evapotranspiration (ET) on constructed wetland (CW) operation is examined through controlled experiments. For this, ten pilot-scale, cylindrical, thermally insulated metal tanks, of diameter 1.5 m and height 1.0 m, operated as lysimeters to evaluate CW ET. Four different substrate materials were used, i.e., river sand, medium gravel, cobbles and clay soil, with a total thickness of 0.5 m. The plant types used were Phragmites australis (reeds) in two CW units, Arundo Donax (giant reeds) in two units and Typha latifolia (cattails) in four units, while two units were unplanted. Six units simulated horizontal subsurface flow (HSF) CWs and four units free water surface (FWS) systems. Under this configuration, interesting conclusions were drawn about the effect of substrate material, plant and CW type on ET rates. All units operated for nine months (April to December 2009), during which daily measurements of ET were made based on the water budget method. Results show a seasonal variation of ET values (higher values in summer, lower in winter) for all planted units, while the unplanted units had signifi cantly lower variations. Overall, higher ET values were observed for the units planted with reeds, while cattails were more active during the summer months. Pearson correlation coefficients were computed to identify mete orological and other parameters affecting CW ET. The measured data were also used to produce simple empirical relations to predict daily ET rates based on meteorological and other parameters.