Evaluation of the evapotranspiration rate of lacustrine wetland macrophytes in Lake Tana, Ethiopia

Abstract

This study quantified the total evapotranspiration (ET) flux of three major types of macrophytes that cover lacustrine fringe wetlands in Lake Tana, Ethiopia during the dry season, April and May, 2022. This study was conducted to understand lacustrine wetland macrophytes' ET rates and provide an important guideline for designing their conservation and restoration plans. To assess ET rates during the peak dry season, three macrophytes of lacustrine wetlands in Lake Tana were chosen: Eichhornia crassipes (water hyacinth), Cyperus papyrus, and Echinochloa stagnina. Three replicate lysimeters for each of the three treatment types (macrophytes) and one control type (open water) were applied to measure ET. To calculate reference evapotranspiration (ET_o), FAO's ET_o Calculator Version 3.2 was applied. All statistical analyses were carried out using R software. The results of ET rates from wetland macrophytes (9.05mm/day) were considered to be significantly higher than open water evaporation (5.90mm/day). There was a significant difference in mean ET among the macrophytes [F (3, 488) = 194.6, p < 2e-16 ***]. In this study, crop coefficient (K_c1) (1.99 ± 0.65) referenced to FAO Penman–Monteith ET_o is greater than K_c2 (1.58 ± 0.59) referenced to open water evaporation (E_ow). In terms of wetland macrophyte type, E. crassipes had the maximum mean Kc values (K_c1 = 2.51±0.70 and K_c2 = 2.02±0.67). E. stagnina had the minimum mean Kc values (K_c1 = 1.52±0.32 and K_c2 = 1.19±0.24). Except for open water which strongly correlated with sunshine hours (r = 0.61) and solar radiation (r = 0.60), the correlation among daily ET values and meteorological variables was found to be weak. The result of our research indicated that the presence of floating macrophytes of E. crassipes will increase the ET flux during the dry season more than emergent macrophytes and open water surfaces. Our findings could provide an important guideline for designing conservation and restoration plans for C. papyrus and E. stagnina to reverse the spread of E. crassipes and maintaining lacustrine fringe wetlands for fish breeding ground and sediment control.