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Effect of submerged, freshwater aquatic macrophytes and littoral sediments on pan evaporation in the Lake Balaton region, Hungary

Anda, A., Simon, B., Soos, G., Teixeira da Silva, J.A., Kucserka, T.
Journal of hydrology 2016 v.542 pp. 615-626
Myriophyllum spicatum, Najas marina, Potamogeton perfoliatus, air, evaporation, evapotranspiration, freshwater, growing season, lakes, littoral zone, macrophytes, sediments, solar radiation, water temperature, Hungary, United States
The evaporation (Ep) of a US Class A pan (C) with submerged, freshwater aquatic macrophytes (Potamogeton perfoliatus, Myriophyllum spicatum and Najas marina), hereafter macrophytes (Ps) and a sediment-covered bottom (S) was measured in Hungary during 2014–2015 using reference E of Shuttleworth (Eo) and Penman-Monteith crop reference evapotranspiration (crop ETo). There were two main climatic controls affecting variation in E: direct (air and water temperature) and indirect (wind-mediated change affecting the penetration of sunlight; precipitation inflow, impacting plant emergence). Lower seasonal mean Ep rates of 2.75±0.89, 2.83±0.91and3.06±1.14mmday−1 were observed in C, S and Ps, respectively, during the wet 2014. In the 2015 season, higher overall daily mean Ep rates for C, S and Ps were 3.76±1.3, 4.19±1.34and4.65±1.52mmday−1, respectively. A comparison of US Class A pan Ep containing macrophytes/sediments with that of a standard US Class A pan showed that pan coefficients (Kap and Kas) might allow for more accurate on-site lake E estimates. In 2014, seasonal mean Kas and Kap were 1.04±0.14and1.09±0.18, respectively. Slightly higher Ka values were observed during the warm and dry 2015 (Kas: 1.15±0.22; Kap: 1.26±0.23). A Ka value greater than 1 indicates that the Ep of a US Class A pan containing macrophytes and sediment is always higher than that of C. The calculated Eo overestimated measured Ep of Ps during the course of this study. During the warm-dry growing season, crop ETo was closest to Ep of Ps. Empirical coefficients can be useful for estimating E of lakes with submerged macrophytes more precisely. The accuracy of the estimate of Keszthely Bay’s E improved by 9.85% when Ka was determined on site.