Tuesday, 11 July 2006

Comparison of Gravitation Lysimeter and Passive-Wick Fluxmeter on Two Sites in Germany.

Wolfgang Berger1, Ralph Meissner2, Holger Rupp2, Juliane Seeger2, and Ina Scheuering1. (1) Bavarian Agency for Environment, Demollstraße 31, Wielenbach, D-82407, Germany, (2) UFZ Centre for Environmental Research Leipzig-Halle, Department of Soil Science, Lysimeter Station, Dorfstrasse 55, Falkenberg, 39615, Germany

Different set-ups of lysimeters are used for detailed water and solute flux investigations during the last 45 years. Our investigation program focussed on the comparison of a high sophisticated and expensive gravitation lysimeter constructed according to Meissner et al. (2000) with a low cost passive-wick fluxmeter designed by Gee et al. (2002). The weighable gravitation lysimeter enables us to measure the soil water balance of soil monoliths (with a surface area of 1.0 m² and a depth of 2.0 m) with high precision. It is possible to ascertain experimentally beside precipitation and seepage water, the mass input of dew and to calculate the actual evapotranspiration. The passive-wick fluxmeter is a deep drainage fluxmeter installed below the root zone. The fluxmeter has a surface area of 0.03 m² and a monolith funnel with a depth of 0.6 m. The lower end of the funnel contains fibreglass wicks which extends to a depth of 0.7 m. The primary goal of our study was to compare the two different lysimeter systems regarding the amount of seepage water measuring. Both constructions are tested on two different German landscapes: A) an agricultural used grassland in the lowland area (Elbe river catchment) of northern Germany with an average annual precipitation of 560 mm, soil type: sand and B) an agricultural used grassland in the floodplain of the Ammer river at the foothills of the Alps mountain in southern Germany with an average annual precipitation of 1100 mm, soil type: loamy sand. At each site the results from 1 gravitation lysimeter have been compared with 2 fluxmeters. At site A we measured during a 496 days period, between 04/01/2004 until 08/10/2005. During this period the total amount of precipitation was 788.2 mm (with minimal intensity of 0 mm d-1 and a maximum intensity of 27.7 mm d-1). We counted a seepage amount of 113.3 mm by the gravitation lysimeter (GL 1). The seepage of the two sites equipped with passive-wick fluxmeters ranged between 104.0 mm (DDM 1) and 109.1 mm (DDM 2). At site B we made the comparison for a period of 393 days, between 07/26/04 until 08/22/05. During this time a precipitation amount of 869.8 mm was registered. The daily precipitation amplitude ranged between 0 mm d-1 up to 61.2 mm d-1. The amount of seepage water measured with the gravitation lysimeter was 276.5 mm (GL 2). Between the tested fluxmeters the amount of seepage water reached from 207.7 mm (DDM 3)to 700.4 mm (DDM 4). The results show that there is a reasonable correspondence regarding the amount of seepage water between the tested lysimeter types at both landscapes. Further research is necessary to compare the different lysimeter types in detail (it means response to different precipitation events and soil types) and to explain the enormous differences between the tested fluxmeters. References: Gee, G.W.; Ward, A.L.; Caldwell, T.G.; Ritter, J.C. (2002): A vadose zone water fluxmeter with divergence control. In: Water Resources Research, Vol. 38, No. 8. Meissner, R., Rupp, H., Schubert, M (2000): Novel lysimeter techniques - a basis for the improved investigation of water, gas, and solute transport in soils. In: J. Plant Nutr. Soil Sci., 163 No. 6, 603-608.

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