Groundwater nitrate risk assessment using intrinsic vulnerability methods: A comparative study of environmental impact by intensive farming in the Mediterranean region of Sicily, Italy

Abstract

Groundwater contamination by nitrate and other nutrients is a major problem throughout the world, often occurring as the result of anthropogenic activities, lack of management, and over-exploitation of groundwater resources. In the last fewdecades in the majority of the Italian regions, the nitrate concentrations in groundwater have dramatically increased, mainly as a consequence of the large-scale agricultural application of manure and fertilizers. This excessive use of chemicals and fertilizers increases the risk of surface and groundwater pollution fromdiffuse sources, which have an important impact on human health and the environment. Sicily is located in the central Mediterranean, the total area of the island is 25,711 km2, with more than 5 million inhabitants. The terrain of inland Sicily is mostly hilly and intensively cultivated wherever it was possible, nitrate vulnerable zone about 40% of flat areas and 5.37% of total. The test site is located in Canicattì (central Sicily); the current land use (grape, olive and almond cultivation) constitutes the main source of groundwater pollution. In order to investigate the effect of over-farming on groundwater quality and to indentify an appropriate methodology for pollution risk management, we have carried out a comparative study on the potential risk of contamination from nitrate of agricultural origin, according to the conventional parametrical methods used in Europe; the IPNOA parametric model (agricultural nitrates hazard index) method combined with the SINTACS and DRASTIC intrinsic aquifer vulnerabilitymethods. All parameters used in this risk assessment were prepared, classified, weighed, and integrated in a GIS environment. For calibrating the models and optimizing and/or weighing the examined factors, the modeling results were validated by comparing them with groundwater quality data, in particular nitrate content, and with census data fromthe potential pollution sources. The criterion for checking this method was the correlation coefficient of each model with the nitrate concentration in the groundwater. A relative coincidence of a high nitrate concentration and risk mapping was observed, but this correlation was only significant using the SINTACS method. In fact, the final risk maps show significant differences in risk quality assessment; the DRASTIC model values show an over-evaluation of the real contest. In conclusion, the SINTACS parametric method appears to be the most suitable for constructing a relevant risk map of the contamination of these aquifers, which are considered to be typical of the Mediterranean region for their hydrogeological and hydrochemical features