Assessment of the Spatial Uncertainty of Nitrates in the Aquifers of the Campania Plain (Italy)

Nazzareno Diodato, Libera Esposito, Gianni Bellocchi, Luisa Vernacchia, Francesco Fiorillo, Francesco Maria Guadagno

Environmental Geology Department, University of Sannio, Benevento, Italy.
Met European Research Observatory, HyMex-GEWEX Experiment, World Climate Research Programme, Benevento, Italy.
Met European Research Observatory, HyMex-GEWEX Experiment, World Climate Research Programme, Benevento, Italy;Grassland Ecosystem Research Unit, French National Institute of Agricultural Research, Clermont-Ferrand, France.

DOI: 10.4236/ajcc.2013.22013                

Abstract

We present a non-parametric hydro-geostatistical approach for mapping design nitrate hazard in groundwater. The approach is robust towards the uncertainty of the parametric models used to map groundwater pollution. In particular, probability kriging (PK) estimates the probability that the true value of a pollutant exceeds a set of threshold values using a binary response variable (probability indicator). Such soft description of the pollutant can mitigate the uncertainty in pollutant concentration mapping. PK was used for assessing nitrate migration hazard across the Campania Plain groundwater (Southern Italy) as exceeding typical critical values set to 25 and 50 mg^.L^-1. Cross-validation indicated that the PK is more suitable than ordinary kriging (OK), which yields large uncertainty in absolute values prediction of nitrate concentration. This means that spatial variability is critical for contaminant transport because critical contaminants concentration could be exceeded due to preferential flows allowing the pollutant to migrate rapidly through the caveats aquifer. Accordingly with PK application, about 250 km² (40% of the total600 km² of the Campania Plain) were classified as very sensitive areas (western zone) to maximum permissible concentration of nitrates (>50 mg^.L^-1). When the probability to exceed 25 mg^.L^-1 was considered, the contaminated surface increased to 70% of the total area.

Keywords

Campania Plain (Italy); Nitrate; Probability Kriging

Conflicts of Interest

The authors declare no conflicts of interest.

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