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In this study, the effect of reed vegetation on evapotranspiration (ET) and treatment performance was estimated, and a commonly used meteorological estimate of potential evapotranspiration (PET) was compared with ET with vertical subsurface flow constructed wetlands (VSSFs) in the treatment of the high salinity of landfill leachates. The experimental approaches consisted of three runs: Run A was a poor reed vegetation bed, Run B was a dense reed vegetation bed, and Run C was a bed without reeds. The results of this study are as follows: The salinities of the leachate inflow in Run A and Run B were 15.8 ± 1.9g Cl-/L and 15.5 ± 2.8g Cl-/L, respectively. The average ETs of Run A, Run B and Run C were 4.2mm/d, 7.4mm/d and 3mm/d, respectively. The annual ET rates of Run A, Run B and Run C were 1535mm, 2702mm and 1101mm, respectively. On the other hand, those of PET estimated on the basis of the Hamon equation of 2017and 2018 were 741mm and 791mm, respectively. The PET rate was much less compared to the ET rate in the dense vegetation bed. It was necessary to consider site-specific factors such as growth of plants in the evaluation of the water budget. The water loss by evapotranspiration in Run B was much more than those in Run A and Run C. Although the removal rates calculated from the concentration between inflow and outflow did not differ between the dense vegetation bed and the poor vegetation bed, the load reduction rates calculated from the water budget differed between dense vegetation and poor vegetation.

In this study, the influence of growth of reeds on evapotranspiration (ET) was estimated, and a commonly used meteorological estimate of potential evapotranspiration (PET) was compared with direct measurements of ET. The salinity of the inside of HSF of the raw leachate inflow was 15.0±3.4g Cl-/L and that of the double diluted inflow was 9.3±1.9g Cl-/L. Although the growth of reeds in the raw leachate inflow was impeded remarkably compared to that of the double diluted leachate inflow, the reeds in the double diluted inflow bed showed healthy growth. The difference in the salinity gave rise to large differences in the growth of the reed. The annual ET rates in the poor vegetation bed, the dense vegetation bed and the unplanted bed were 656.5mm, 2,334.3mm and 22.2mm, respectively. The difference of the growth of the reed provided a large difference in the ET rate. The annual PET estimated on the basis of the Hamon equation was 751.6mm. The PET rate was much lower compared to the ET rate in the dense vegetation bed. It was necessary to consider site-specific factors such as the growth of plants in the evaluation of the water budget in the HSFs.