Evapotranspiration from pilot-scale vertical flow subsurface constructed wetlands in arid area

Abstract

This paper aims to conduct a comparative evaluation of evapotranspiration (ET) rates in two experimental pilot-scales vertical flow subsurface constructed wetlands carried out in south east of Algeria (Touggourt), planted separately with P. australis (Ph) and T. latifolia (Ty) in two different substrate types with constant hydraulic loading rate under arid climatic conditions. An estimate of crop coefficient (Kc) for the two macrophytes based on climate conditions and the plant growth was also provided. Two kinds of vertical flow subsurface systems has been tested in the hottest period of the year 2018 over five months (April-August): first with fine gravel (G) (experiment 1), and second with sand (S) (experiment 2). During this period, the cumulative ETTy-G, ETPh-G and ETNp-G in the 1st experiment were 206, 276 and 125 mm, whereas in the 2nd experiment; the cumulative ETTy-S, ETPh-S and ETNp-S were 833, 968 and 635 mm, respectively. Comparing these results with cumulative reference evapotranspiration (ET0), ET0 value (426 mm) was higher than ET in the 1st experiment, and lower than in the 2nd experiment. Cumulative ET values in planted lysimeters were found to be different and higher than unplanted ones. Moreover, the highest accumulated ET value was obtained with P. australis bed which was found to have higher accumulated ET values than T. latifolia bed. Regarding the crop coefficient (Kc), the average seasonal value of Kc in the 1st experiment was relatively smaller than 2nd experiment. The Kc Ph-S value was almost three times the Kc Ph-G, and Kc Ty-S values were also almost four times the Kc Ty-G.In general, this study demonstrated that ET and Kc are dependent on climate conditions, the macrophytes growth as well as on the type of substrate in which the macrophytes are planted.