Evapotranspiration rates of willow and reed in a riverine fen –

Autor: Frahm, Enrico
Mitarbeiter: Konrad Miegel; Thomas Salzmann
In:

Evapotranspiration rates of willow and reed in a riverine fen
estimated using Penman-Monteith and diurnal groundwater fluctuations
Autor: Frahm, Enrico
Mitarbeiter: Miegel, Konrad; Salzmann, Thomas
Ort: 5th European Conference on ecological restoration, Greifswald
Jahr: 2006

Einordung:
Institut: Professur Hydrologie und Angewandte Meteorologie

Abstract:
The aim of this study is to estimate the evapotranspiration rate of two vegetation sites - willow (Salix spp.) and reed (Phragmites australis) - in a riverine fen by two different methods. The common Penman-Monteith equation will be compared with the use of diurnal groundwater fluctuations to calculate evapotranspiration.
For a successful wetland restoration a detailed knowledge of the hydraulic cycle and its compartments is fundamental. One important part of the hydraulic cycle in wetlands is the evapotranspiration. The causes of this are the subject of current investigations by the University of Rostock. These investigations are focused on the water regime of the riverine fen, which is related to the river Warnow and its discharge regime. A strong relationship between discharge behaviour of the river and fen evapotranspiration is assumed. The study site itself is located in a typical riverine fen area of the German northeast lowlands along the river Warnow.
The first method used - the meteorological Penman-Monteith equation after ALLEN 1994 - calculates grass-reference evapotranspiration (ET0) and, on the basis of estimated resistance parameters, the actual evapotranspiration (ETa). In using the Penman-Monteith equation it will be necessary to determine characteristic surface resistance (rs) and aerodynamic resistance (ra). The second method is a hydrological approach - the “Draw Down Recharge” method HAYS, 2003 - which uses diurnal groundwater level fluctuation measurements.
All required meteorological input parameters for the use of Penman-Monteith equation are measured in the field with a time slice of 15 minutes, additionally rainfall, wind speed and wind. For the hydrological method, measurements required include the recording of diurnal fluctuations of groundwater level, soil moisture and soil moisture tension with the same short time interval. It is also necessary to measure the leaf area index and – in order to characterise the interception storage - the throughfall within the willow.
The results confirm the utility of applying the “Draw Down Recharge” method to estimate evapotranspiration in the researched wetland. There are significant differences between the evapotranspiration rates of reed and willow, depending on climatic conditions and vegetation season. The maximum ETa/ET0 ratio estimated by “Draw Down Recharge” method and grass-reference evapotranspiration in September 2003 was 1.49 for willow and 0.97 for reed.

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