Abstract
Abstract. Water collection from undisturbed unsaturated soils to estimate in situ water and solute fluxes in the field is a challenge, in particular if soils are heterogeneous. Large sampling devices are required if preferential flow paths are present. We present a modular plate system that allows installation of large zero-tension lysimeter plates under undisturbed soils in the field. To investigate the influence of the lysimeter on the water flow field in the soil, a numerical 2-D simulation study was conducted for homogeneous soils with uni- and bimodal pore-size distributions and stochastic Miller-Miller heterogeneity. The collection efficiency was found to be highly dependent on the hydraulic functions, infiltration rate, and lysimeter size, and was furthermore affected by the degree of heterogeneity. In homogeneous soils with high saturated conductivities the devices perform poorly and even large lysimeters (width 250 cm) can be bypassed by the soil water. Heterogeneities of soil hydraulic properties result into a network of flow channels that enhance the sampling efficiency of the lysimeter plates. Solute breakthrough into zero-tension lysimeter occurs slightly retarded as compared to the free soil, but concentrations in the collected water are similar to the mean flux concentration in the undisturbed soil. To validate the results from the numerical study, a dual tracer study with seven lysimeters of 1.25×1.25 m area was conducted in the field. Three lysimeters were installed underneath a 1.2 m filling of contaminated silty sand, the others deeper in the undisturbed soil. The lysimeters directly underneath the filled soil material collected water with a collection efficiency of 45%. The deeper lysimeters did not collect any water. The arrival of the tracers showed that almost all collected water came from preferential flow paths.
Highlights
Pollutant movement toward the groundwater has become a severe problem in the last decades
In homogeneous soils, even very large lysimeters can be largely bypassed by the soil water
This study shows that the collection efficiency single realizations gave remarkably different results, so that repetitions are necessary
Summary
Pollutant movement toward the groundwater has become a severe problem in the last decades. Since every invasive soil water sampling system has an impact on the system behavior, it is still an unsolved problem to get representative measurements of pollutant fluxes through a certain horizontal area. This is even more problematic in heterogeneous soils with preferential flow paths, that are rather common on the field scale (Flury et al, 1994). An inexpensive strategy to determine the chemical composition of the soil solution is soil coring It does not allow flux estimation nor repeated sampling at the same site. This is done either actively by porous devices such as suction cups (Hagedorn et al, 1999) or suction plates (Kosugi and Katsuyama, 2004), Published by Copernicus Publications on behalf of the European Geosciences Union
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
