Vincenzo Comegna

Effectiveness of equilibrium and physical non-equilibrium approaches for interpreting solute transport through undisturbed soil columns

This study observes the dispersion process of chloride through three undisturbed soil columns (sabA, sabB and arg) of different texture under both saturated and unsaturated conditions. Overall, 17 leaching experiments were conducted by means of an equipment designed and built in Portici together with the DITEC of the University of Basilicata. During the experiments, both symmetric and positive asymmetric breakthrough curves of the chloride anion were measured. As expected, manifest asymmetry was obtained especially for soil columns labeled as sabA and arg. In such columns, it was also noted that the degree of asymmetry increased as the flow density increased at the sample surface. The experiments conducted on soil column labeled as sabB resulted in more symmetric BTCs. The experimental data were firstly analysed using the classical two-parameter CD model. The variation of the dispersion coefficient, D, with pore water velocity, upsilon 0, and porous medium characteristics was explored in detail. The application to all experimental data of the four-parameter MIM model, which compartmentalises the pore water in the mobile-stagnant domains provided an insignificant different description of BTCs, even of the asymmetric ones. Furthermore, it resulted in ill-defined parameters, especially those related to the partitioning in the mobile-immobile phases. However, for all the three soils examined the two parameter CD model proved to be very powerful even in interpreting asymmetric BTCs. In any case, it should be emphasised that the agreement of outflow experimental data with a mechanistic model does not unequivocally identify the mechanism of solute transport in the soil. In fact, when we applied the CLT model, which is based on a stochastic approach, the BTCs were comparably well predicted.

Darcian preferential water flow and solute transport through bimodal porous systems: Experiments and modelling

Soils often exhibit a variety of small-scale heterogeneities such as inter-aggregate pores and voids which partition flow into separate regions. In this paper a methodological approach is discussed for characterizing the hydrological behaviour of a heterogeneous clayey-sandy soil in the presence of structural inter-aggregate pores. For the clay soil examined, it was demonstrated that, coupling the transfer function approach for analyzing BTCs and water retention data obtained with different methods from laboratory studies captures the bimodal geometry of the porous system along with the related existence of fast and slow flow paths. To be effectively and reliably applied this approach requires that the predominant effects of the soil hydrological behaviour near saturation be supported by accurate experimental data of both breakthrough curves (BTCs) and hydraulic functions for high water content values. This would allow the separation of flow phases and hence accurate identification of the processes and related parameters.

Nonreactive solute transport in variously structured soil materials as determined by laboratory-based time domain reflectometry (TDR)

Abstract The possibility of using the time domain reflectometry technique (TDR) is tested for estimating transport parameters of an inert solute (KCl) in the soil. Undisturbed soil samples underwent steady flow processes in the laboratory in near-saturation conditions. Space/time distributions of the chloride ion concentration were analysed with the two-parameter convection–dispersion model (CD). Conventional nonlinear optimisation algorithm was used for the derivation of the parameter values. Applied to soil samples of different textures and structures, the method supplied satisfactory results, which indicates that the straightforward use of TDR may permit the method to be more widely applied, both in the laboratory and in the field. Research is currently going on to study the spatial variability of characteristic parameters of solute transport.

A Review of Approaches for Measuring Soil Hydraulic Properties and Assessing the Impacts of Spatial Dependence on the Results

The movement of water in the soil and associated solute transport perform a role of primary importance in many applications in the field of hydrology and agriculture. In the sound management of irrigation water, in relation to specific environmental conditions and cropping systems, knowledge of local water flow conditions in zones affected by the root systems is indispensable. Once the irrigation method has been established, only knowledge of the laws governing water flow allows the necessary irrigation frequencies and rates to be established to optimise the distribution of soil moisture, reducing within established limits the effects of water stress and containing water wastage.