Application of Indicator kriging to Evaluate the Probability of Exceeding Nitrate Contamination Thresholds

Abstract

Nitrate contamination is one of the main risks for groundwater in agricultural areas. The<br />evaluation of the effect of agricultural practices on groundwater nitrate concentration, especially in highly<br />sensitive areas, is crucial for a correct land planning, and a good agronomic intervention scheduling. Aim of this paper is to map the probability to exceed nitrate regulatory threshold applying a non-parametric geostatistical approach, the Indicator Kriging (IK). A study in the Fucino Plain (Abruzzo, Central Italy), characterized by highly profitable intensive agriculture with mainly irrigated horticultural and short rotation crops, was carried out. The Plain has a shallow and controlled groundwater table, and channels draining the surplus water during winter. Water samples were collected monthly from piezometers and analysed for nitrate. IK provided a model of spatial uncertainty, representing the probability that the threshold of 50 mg/L fixed by the European Nitrate Directive is exceeded, and results were transferred into a GIS. Maps obtained for each month showed how the probability to exceed the threshold changes during an average year. The methodology can provide an effective operative tool to support decision-makers for the identification and the designation of nitrate vulnerable zones.