The Use of the Weights-of-Evidence Modeling Technique to Estimate the Vulnerability of Groundwater to Nitrate Contamination |
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Authors: | M Masetti S Poli S Sterlacchini |
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Institution: | (1) Department of Earth Sciences, University of Milan, Via Mangiagalli 34, 20133 Milan, Italy;(2) Department of Environmental Science (DISAT), University of Milan-Bicocca, Piazza della Scienza 1, 20126 Milan, Italy;(3) Institute for the Dynamic of Environmental Processes, National Research Council (CNR-IDPA), Piazza della Scienza 1, 20126 Milan, Italy |
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Abstract: | The occurrence of elevated nitrate (NO3−) concentration in the aquifer of the Province of Milan (northern Italy) is related to both natural and anthropogenic variables.
Using the weights-of-evidence modeling technique a specific vulnerability assessment has been performed. This study presents
an evolution of previous applications of the proposed methodology as a consequence of an updating of the available database,
in terms of data type, quality, and accuracy, and of a more specific and enhanced statistical controls onto the final results.
A comparison between the spatial distribution of vulnerability classes and the frequency of occurrences of nitrate in wells
shows a high degree of correlation, both for low and high nitrate concentration. Similar results may be evidenced considering
the correlation between posterior probability classes and mean nitrate concentrations in wells located in each of these classes:
a high R
2 value (0.99) and the agreement with the threshold concentration value used to define prior probability testifies a general
good quality of results. Groundwater-specific vulnerability has been classified in terms of vulnerability classes and, according
to the outcomes of the model, the density of population can be considered the most impacting source of nitrate. Mean annual
irrigation and groundwater depth can be identified as influencing factors in the distribution of nitrate, while agricultural
practice appears a negligible factor. |
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Keywords: | Aquifer vulnerability nitrate weights-of-evidence |
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