The Impact of Helophyte Transpiration on Vertical Water Exchange in Water Bodies

The article presents the results of experimental research on evapotranspiration and transpiration of a common reed bed. The study was conducted in 2014–2015 on Lake Raduńskie Górne (Kashubian Lakeland) in the summer half-year from 1 May to 31 October. In the experiment two sets of standard evaporimeters GGI-3000 were used. One of the evaporimeters was filled with water, while the second additionally contained common reed. During the experiment medium reed bed density was 240 shoots per square metre. The results of the study showed that during the research period the average daily common reed transpiration was 3.9 mm, and the daily maxima reached 12.1–12.5 mm. Average monthly transpiration totals ranged from 42.8 (October) to 208.5 mm (August). During the growing season, the loss of water to transpiration reached 872–971 mm. The average transpiration rate, determined in the conditions of already well developed reed bed (June-September), was 1.83 dm³ m⁻² d⁻¹. The values of the ratios T_h/E_O and ET_h/E_O, determined during the experiment, were within the ranges reported in most previous research. The average ratio T_h/E_O was 1.6, and the ratio ET_h/E_O was 2.0. These values indicate that during the vegetation period common reed transpiration is higher by 60% from open water evaporation, and the total water losses from the common reed bed to evapotranspiration are twice as high as water loss in open water evaporation.