EVAPOTRANSPIRATION, CROP COEFFICIENTS AND WATER USE EFFICIENCY OF CYPERUS ALTERNIFOLIUS L. AND TYPHA LATIFOLIA L. IN A PILOT-SCALE HORIZONTAL SUBSURFACE FLOW CONSTRUCTED WETLAND IN THE WEST OF SICILY (ITALY) UNDER MEDITERRANEAN CONDITIONS

In constructed wetland systems (CWs) for wastewater treatment, the efficiency of the system is highly affected by the system’s water balance. This study shows the results of a series of water balance measurements obtained in 2013 from a pilot horizontal-subsurface flow (HSSF) system in the West of Sicily (Italy). The system included three separate units, one planted with Cyperus alternifolius L., one planted with Typha latifolia L. and an unplanted unit. The system was fed with urban wastewater from an activated-sludge wastewater treatment plant. The aim of the study was to compare evapotranspiration rates (ET), crop coefficients (Kc) and water use efficiency (WUE) of two root emergent macrophytes in typically Mediterranean climate conditions in order to estimate water loss for each of the two planted units. ET values were calculated by determining three components of a simplified water balance model without taking subsurface and surface water into consideration. Kc values were estimated using the FAO 56 method used for herbaceous crops in open-field cultivation. The reedmace-unit was found to have higher cumulative evapotranspiration (3579 mm) than the umbrella sedge-unit (3142 mm). For both macrophytes, ET values were constantly found to be higher during the spring-summer season when the plants reached maximum vegetative growth. Crop coefficients were found to be higher than those of traditional crops grown in the Mediterranean area for all growth stages. WUE for umbrella sedge (0.66 g/L) and reedmace (0.75 g/L) was rather low on average compared to traditional open-field crops. Results highlight the need to use knowledge on the evapotranspiration processes of the species being used in the CWs. Further knowledge on water losses could provide useful information when designing CWs. The incidence of water loss from ET is highly important for arid areas, especially where the water at the outflow of the CW is needed for reuse.