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Nitrate occurrence in ground water hosted in hard rock aquifers; estimating background values at a regional scale

Riccardo Biddau, Rosa Cidu, Giorgio Ghiglieri, Stefania Da Pelo, Alberto Carletti and Daniele Pittalis
Nitrate occurrence in ground water hosted in hard rock aquifers; estimating background values at a regional scale
Italian Journal of Geosciences (February 2017) 136 (1): 113-124

Abstract

This study was aimed at assessing the occurrence of nitrate in poorly anthropized areas at a regional scale, as an attempt to estimate the nitrate background in areas far from intense agriculture, farming, industrial activities and urban areas. Nitrate concentrations, together with physical-chemical parameters and major anions and cations, were determined in 49 spring waters flowing out of granitic and metamorphic rocks in Sardinia (Italy). Nitrate in the spring waters was in the range of <0.1 mg/L to 47 mg/L, a range similar to that observed in 404 rain samples collected in Sardinia, with highest values mostly occurring in spring waters located downstream villages.The median nitrate might be considered an estimate of background values in the study area. The median nitrate in waters from metamorphic aquifers was 1.9 mg/L, close to the 1.3 mg/L median value observed in the Sardinian rain. The median values of nitrate in waters from granitic aquifers was higher, i.e. 7.0 mg/L. These results were compared with an historical dataset consisting of 183 spring water samples collected between 2000 and 2012 in the same area. Again, nitrate in spring waters from granitic rocks was higher (maximum value 80 mg/L, median: 7.6 mg/L) than nitrate in spring waters from metamorphic rocks (maximum value 48 mg/L, median 1.5 mg/L). Geogenic factors may affect nitrate occurrence in groundwater and might explain the higher median values observed in springs flowing out of granitic rocks. In the study area, the soils developed on granitic rocks had higher permeability and lower cation exchange capacity, as compared to soils developed on metamorphic rocks. Such characteristics may favor a rapid leaching of nitrate to groundwater. Moreover, the redox potentials in granitic springs higher than those in metamorphic springs might have favored the persistence of nitrate in granitic environments. Overall results of this study showed that the granitic aquifers were more susceptible to nitrate contamination as compared to the metamorphic aquifers.


ISSN: 2038-1719
EISSN: 2038-1727
Coden: BOGIAT
Serial Title: Italian Journal of Geosciences
Serial Volume: 136
Serial Issue: 1
Title: Nitrate occurrence in ground water hosted in hard rock aquifers; estimating background values at a regional scale
Affiliation: Universita di Cagliari, Dipartimento di Scienze Chimiche e Geologiche, Cagliari, Italy
Pages: 113-124
Published: 201702
Text Language: English
Publisher: Societa Geologica Italiana, Rome, Italy
References: 91
Accession Number: 2017-055749
Categories: HydrochemistryEnvironmental geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch map
N38°49'60" - N41°30'00", E08°15'00" - E09°45'00"
Secondary Affiliation: Universita di Sassari, ITA, ItalyUniversita di Parma, ITA, Italy
Country of Publication: Italy
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Societa Geologica Italiana. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201730

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