Risk of groundwater contamination from nitrates in the Po basin (Italy)

Abstract

In 1991, the EU promulgated the Nitrates Directive 91/676/EEC, with which it obliged member states to set up monitoring systems, to designate areas vulnerable to nitrate pollution, especially that of agricultural origin, and to activate protection plans, setting the initial target as 1993. After a long delay, Italy assimilated the directive in 1999 with the D.Lgs. 152/99 (legislative decree), which basically transferred responsibility for identifying vulnerable zones to the Regional Authorities. The Po river basin was, and still is, particularly problematical, with its surface aquifers containing generally high levels of NO3− particularly in the lower Piedmontese plain, in the Alessandria area, in the upper Milan valley and in the Emilia-Romagna plain. Taking these pollution levels into consideration, along with continual eutrophication of the Adriatic Sea, the EU enjoined Italy to define the entire Po valley as vulnerable, to avoid being penalised. Such a restrictive designation would, however, have had a highly negative effect on agriculture and to avoid this, the Regions of the Po basin, after long delays, set in motion a series of scientific studies in order to be able to limit the areas defined as vulnerable. This paper, in line with Regional policies, proposes a method that can be applied on a regional scale for identifying areas vulnerable to nitrate pollution. It uses a parametric indicator of Pollution Risk, which is the product of the sintacs r5 and the ipnoa indicators: since the former indicator assesses the vulnerability of an aquifer, that is its susceptibility to absorption and spread of fluid or water-borne pollutant over time, while the latter studies the risk of pollution by nitrates of agricultural origin (that is, the amount of nitrates persisting in the territory), it is clear to us that the product of the two indicates the nitrate that may actually be present in the aquifer waters. The easy availability of input parameters for the model, the reliability of the output data, as compared with the results of monitoring various test sites in the Po valley, and the production of thematic maps, using GIS software, make the method a valid tool for the Regions when identifying zones vulnerable to nitrate pollution. The method is presented here with application to a test site of about 250 km2, situated in the lower Alessandria plain (Eastern Piedmont, Italy).