A contribution to water flow characterization in the unsaturated zone of vegetated lysimeters using numerical and analytical modeling approaches

Anne Imig1, Fatemeh Shajari1, Arno Rein1, Einsiedl Florian1
1 Lehrstuhl Hydrogeologie, TU München

11.5 in Isotopenmethoden zur Analyse von Stoffumsatz und Fließprozessen

28.03.2020, 10:30-10:45, Weißer Saal

To satisfy the food demand of our growing world population, agricultural activities accompanied by an increase in the use of fertilizers and pesticides are documented. Even though regulations on chemical management are passed, for many agricultural areas, a decrease in groundwater quality is observed. The impact of chemicals on water quality and related risks cannot be identified without the understanding of water flow processes in the saturated and unsaturated zone.

In this work, two lysimeters with maize cultivation installed at a test field south of Munich, Germany, were investigated. Lysimeter soil cores are characterized by sandy gravels (Lysimeter 1) and sandy-clayey silt (Lysimeter 2). For three years, lysimeter outflow seepage water was sampled in 1-2 week intervals. The characterization of the water flow in the unsaturated zone of the two lysimeters was done with different methods. First an analytical lumped-parameter model approach (LPM) was chosen for interpreting the measurements. Mean transit time of water, dispersion parameters and the contribution of preferential flow paths were estimated. As a second method, unsaturated flow was simulated numerically using Hydrus 1D in order to investigate water flow dynamics. Goals were to improve process understanding and to validate the findings from LPM application.

The findings from LPM application could generally be confirmed by numerical modeling. Due to the consideration of steady-state flow for LPM modeling, deviations between measured and modeled values were obvious at some periods. An attempt was made to improve the modeled data fit from the LPM by subdividing the whole observation period into seasonal/vegetative periods with quasi steady-state flow. By that, variable flow conditions could be mimicked more adequately with the LPM approach. Investigations are currently continued for improving the consideration of preferential flow paths.

Both modeling methods revealed to be a strong tool for the characterization of unsaturated water flow, in order to support decision making e.g. for sustainable agricultural practices that minimize chemical impacts to soil and groundwater quality.

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