TIME-DEPENDENT METHODS TO EVALUATE THE EFFECTS OF URBAN SPRAWL ON GROUNDWATER QUALITY

Abstract

As groundwater resources are becoming more vulnerable due to the increasing number of contamination sources in developed and developing countries (such as urbanization and agricultural activities), practical actions, strategies and solutions to protect the resource are widely required. The most efficient tool, which helps supporting land use development, while protecting groundwater from contamination, is represented by groundwater vulnerability assessment. European Directives require member states, for the protection of groundwater quality, to assess the current groundwater quality status, detect changes or trends in groundwater quality, assess the threat of deterioration and predict future changes in groundwater quality. In order to cope with the EU requirements, this study focuses on the development of a time-dependent approach, which could take into account both the current groundwater quality status and its changes, assessing groundwater vulnerability to nitrate contamination in the Po Plain area of Lombardy Region, through a Bayesian spatial statistical method (Weights of Evidence). In addition, an innovative dataset to delineate urban areas with satellite scatterometer data (QuikSCAT-DSM) is explored. To evaluate its reliability in groundwater vulnerability assessments, QuikSCAT-DSM dataset is compared with population density and land use derived from aerial images. Results showed that: a) urbanization prevails on agricultural activities in causing the degradation of groundwater quality; b) QuikSCAT-DSM data is a reliable variable to represent urban nitrate sources, with the advantages of a worldwide coverage, a continuous data collection and an adequate resolution; c) the time-dependent approach allows to identify areas both affected by nitrate contamination and characterized by an upward concentration trend of contamination; d) the time-dependent approach allows to determine what could happen to groundwater resources if land use policies are maintained or new ones will be proposed and/or if natural factors are changing under climatic or anthropogenic stresses.