Rend. Online Soc. Geol. It., Vol. XX (201X), pp. XX-XX, 1 fig., x pl., x tab. (doi: 10.3301/Rol.2012.xx) © Società Geologica Italiana, Roma 2012 (Stile: intestazione prima pagina) Influenza di lisimetri a suzione sul flusso insaturo in un suolo argilloso organico Lo studio è volto a determinare l’influenza dei lisimetri a suzione sulla percolazione dell’acqua in un suolo argilloso e ricco di materia organica. L’esperimento di laboratorio è avvenuto in un modello tridimensionale di dimensioni 50 x 50 x 20 cm. Il modello è stato duplicato e riempito con suolo organico. Ogni modello è stato equipaggiato con sonde TDR per la misura del contenuto volumetrico d’acqua e sonde per la misura della pressione matriciale. Per valutare l’influenza dei lisimetri a suzione sui risultati ottenuti, due lisimetri sono stati inseriti alla stessa altezza dei sensori. I risultati mostrano che, in questo tipo di suoli caratterizzati da elevate capacità di ritenzione idrica, la propagazione del fronte umido viene influenzata dalla presenza dei lisimetri ed è quindi necessario piazzare i dispositivi per il campionamento delle acque a distanze maggiori di 25 cm dai sensori per la misurazione del contenuto d’acqua. KEY WORDS: water percolation, soil parameters, suction cups. INTRODUCTION The flow and contaminant transport through the unsaturated zone are driven by the soil water content and the unsaturated hydraulic conductivity. The quantification of such variables, both in laboratory or in field conditions is inherently difficult and time consuming (ROWELL 1994). Standard methods to define these soil hydraulic functions in the laboratory and in the field have been widely reviewed in the literature (DANE & TOPP 2002; JABRO 1992). To collect consistent data sets of water-related parameters, like matric pressure head (MPH), volumetric water content (VWC) and soil solutions, there is the need to minimize the horizontal sampling distance to avoid as much as possible local heterogeneities that could influence the vertical flow line. In theory all the acquisition probes should be placed along a vertical axis, but this could potentially disturb the vertical water flow, especially if suction cups are employed to sample the soil water in unsaturated conditions. This effect should be more relevant in soil with an elevated retention capacity, like the clay soils. The aim of this study is to evaluate the influence of the suction cups on the determination of both MPH and VWC in marsh soils with elevated organic matter content. MATERIALS AND METHODS The soil analyzed in this experiment was taken from an agricultural field situated near Codigoro town; the area is located in the eastern part of the Province of Ferrara (Italy). This area is part of the Po delta lowland and is a reclaimed zone consisting of marsh soils. From the grain size analysis, the soil is composed on average by 8% of sand, 49% of silt, 42% of clay and 8% of organic matter. It is therefore a silty clay soil with high organic content following the WRB classification (WORLD REFERENCE BASE FOR SOIL RESOURCES 1998). To carry out this experiment, a tridimensional model with size of 100 x 50 (divided in two section of 50 x 50 cm each) was constructed in laboratory. The tank was then filled with soil until 20 cm of height (Fig. 1). The filling method was to manually compact successive layers of about 2 cm each. During the filling procedure, sensor probes were inserted at -4 cm and -16 cm below ground level (b.g.l.) in both plots and they were connected to two data logger (Fig. 1). Two different kind of sensor probes were employed, cylindrical soil moisture sensor measuring the MPH with a range of 0-250 centibars and TDR sensor probes all connected to data loggers recording data every 15 minutes (NOBORIO 2001). In plot B two ceramic suction cups were also installed at -4 cm and -16 cm b.g.l., exerting a matric pressure of about 80-90 centibars. The tridimensional model initially filled with air dry soil, was then gradually wet with water until its almost complete saturation from day 1 to day 10 from the beginning of the experiment. Successively, from day 27 to day 43, a drying step was carried out installing two lamps of 60 watts each, to provide a constant evaporation surface. Suction cups influence on the unsaturated water flow in a marsh soil HILARIA GUERZONI (*), NICOLÓ COLOMBANI (**), DARIO DI GIUSEPPE (*), BARBARA FACCINI (*), MICÓL MASTROCICCO (*) & MASSIMO COLTORTI (*) Fig. 1 – Schematic representation of the box model and position of the monitoring devices _________________________ (*) Dipartimento di Fisica e Scienze della Terra, Università di Ferrara (**) Dipartimento di Fisica e Scienze della Terra, Università di Ferrara e Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Università “Alma Mater” di Bologna; clo@unife.it