Evaluating the Role of Soil Variability on Potential Groundwater Pollution and Recharge in a Mediterranean Agricultural Watershed

Abstract

Regional-scale studies on groundwater vulnerability assessment of non-point source agrochemical contamination suffer either from no evaluation of uncertainty in data output, in that of qualitative modelling, or from prohibitively costly computational efforts, in that of deterministic modelling. By contrast, a methodology is presented here which integrates a solute transport model based on transfer function (TF) and a geographic information system (GIS). The methodology (1) is capable of solute concentration estimation at a depth of interest within a known error confidence class, (2) uses available soil survey and climatic and irrigation information and requires minimal computational cost for application and (3) can dynamically support decision-making through thematic mapping. Raw data (coming from different sources) include: i) water table depth, ii) soil texture properties, iii) land use, and iv) climatic information with reference to a study area located in southern Italy. Such information has been then manipulated in order to generate data required for the subsequent hydrological modelling. Simulated breakthrough curves were generated for each soil textural class. They are texture-based travel time probability density functions (TFtb), describing the leaching behaviour of soil profiles with similar soil hydrological properties. The latter, in turn, were estimated by indirect estimation techniques such as pedotransfer functions (PTFs) to overcome the trouble of intensive in situ and/or laboratory determinations of soil hydraulic and hydrodispersive properties, which are generally lacking for regional-scale studies. Results showed large differences in the magnitude of the different travel times and related uncertainties among different profiles. The lower or higher vulnerability was found to be mainly related to the average silt content of the soil profiles.