Quantifying actual evapotranspiration in fen ecosystems: Implications of management and vegetation structure

Alkaline fens are ecosystems with extraordinarily high biodiversity. However, they belong to the most threatened ecosystems in Europe due to drainage, land use intensification and cessation of traditional management. In such systems, evapotranspiration (ET) is an important hydrological process as it is the principal way of water loss. However, there is a knowledge gap concerning the effect of vegetation structure and management on this process. Thus, we quantify actual ET rate based on diurnal groundwater fluctuation in different vegetation and management types (forested, only-mowed, mowed/cleared) as well as analyze the differences in vegetation composition. We utilize medium-term, high frequency hydrological data from an alkaline fen in northern Germany as well as data on floral species composition and light availability. Our results show that ET rates are similar in the mowed fen with tree clearance (cleared/mowed fen) and in the only-mowed fen. The only-mowed fen has significantly higher ET rates compared to the alder carr and one part of the willow forest. Similarly the cleared/mowed fen also had significantly higher ET rates than those in the alder carr. Although the results are not entirely consistent with those of other authors, few studies support our findings. We conclude that the difference we observe may be caused by differences in microclimate such as lower temperature and wind speed and higher humidity in the forest, compared to the open fens. Species composition was significantly different between the forested fen and the cleared fen. (C) 2020 European Regional Centre for Ecohydrology of the Polish Academy of Sciences. Published by Elsevier B.V. All rights reserved.