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Evaluation of Phragmites australis (Cav.) Trin. evapotranspiration in Northern and Southern Italy

Borin, Maurizio, Milani, Mirco, Salvato, Michela, Toscano, Attilio
Ecological engineering 2011 v.37 no.5 pp. 721-728
Phragmites australis, constructed wetlands, crop coefficient, developmental stages, environmental factors, evapotranspiration, models, plant age, pollutants, subsurface flow, tanks, vegetation, wastewater treatment, Italy, Sicily
The design, operation, pollutant removal as well as hydraulic modeling of wetland systems for wastewater treatment can be improved by better understanding and simulating the evapotranspiration process. To this purpose, two experiments were carried out in Northern (Veneto region) and Southern (Sicily region) Italy to measure evapotranspiration (ET) and determine the crop coefficient of Phragmites australis (Cav.) Trin. using the FAO 56 approach. The experimental set-up consisted of a combination of vegetated and unvegetated plastic tanks (Veneto) or pilot sub-surface flow beds (Sicily). The ET values were obtained by measuring the amount of water needed to restore the initial volume in the tanks and in the beds after a certain period. All the needed climatic variables were measured and taken into account in the ET measurements. In the two experimental sites cumulative reference evapotranspiration (ET₀) was similar to the cumulative ET measured in the control tanks and beds (without vegetation, ETcₒₙ), while ET measured for P. australis (ETₚₕᵣ) was significantly higher, underlining the strong effect of vegetation. From June 2009 to September 2009 the cumulative ET₀, ETcₒₙ and ETₚₕᵣ in Veneto were 455, 424 and 3048mm, in Sicily 653, 556 and 3899mm, respectively. The plant coefficient trend of P. australis (Kₚ) estimated in Veneto was similar to that in Sicily, suggesting that the role of the plant in dispersing water is similar under different environmental conditions. Additional measurements made in the Veneto plant showed that Kₚ assumes different patterns and values in relation to plant age and growth stage. These results highlight the importance of the plants in regulating water losses from a wetland system, above all from small-scale constructed wetlands where the effect of the advection in ET rates is evident.