Abstract
Nitrate is one of the most common groundwater contaminants in rural areas. In this work, the presence of high levels of nitrate in groundwater of the aquifers of the west part of Hoya de Huesca County (NE Spain) has been studied by coupling hydrogeological information with water sampling techniques through a wide areal sampling of 90 surface water and groundwater points belonging to several aquifers. The results showed a general hydrochemistry of calcium carbonate to calcium sulfate waters. Unlike other case studies in Mediterranean areas, in which nitrate pollution was associated with irrigated crops, the highest concentrations in the present study were found in dry farming areas in which winter cereal is grown. A monthly nitrate level monitoring, conducted in 21 selected points between 2016 and 2017, showed that the nitrate evolution pattern followed the N fertilizer application schedules in the sampling points in which the highest concentrations were recorded, whereas an annual regularity could be observed in the sampling points with low nitrate levels. The compilation of data for 16 selected points since 1990 shows that the problem is persistent and points to the need of implementing new aquifer pollution control measures, since the ones currently in force have not been successful.
Highlights
Artificial nitrogen fertilization is one of the pillars of modern agriculture
The non-natural presence of high levels of N species in groundwater (GW) is a matter of concern in many irrigated and non-irrigated agricultural regions of the world [7,8,9,10], including Europe [11,12,13]. This issue is considered a serious threat to GW quality [14] and has resulted in the promulgation of two European Union directives to address the problem: Council Directive 91/676/EEC [15], which establishes that both surface freshwater and groundwater can be considered affected by nitrate pollution when they contain, or could potentially contain, more than 50 mg·L−1 of nitrate; and Directive 2000/60/electrical conductivity (EC) [16], which establishes a recommended limit for nitrate in drinking water and for the eutrophication of freshwaters of 25 mg·L−1
The results presented in this study differ from those reported for neighboring areas with Mediterranean crops, in which nitrate pollution is associated with irrigated crops, as fertilization is coupled with water application to obtain high agronomical and economical profits [13,17,18,39,40]
Summary
Artificial nitrogen fertilization is one of the pillars of modern agriculture. it is widely recognized that its uptake by the roots of the crops features a medium-low efficiency, in spite of valuable research efforts aimed at improving the efficiency of the agricultural management of N fertilizers, manure, and crop residues [1,2,3,4,5,6]. The non-natural presence of high levels of N species in groundwater (GW) is a matter of concern in many irrigated and non-irrigated agricultural regions of the world [7,8,9,10], including Europe [11,12,13] This issue is considered a serious threat to GW quality [14] and has resulted in the promulgation of two European Union directives to address the problem: Council Directive 91/676/EEC [15], which establishes that both surface freshwater and groundwater can be considered affected by nitrate pollution when they contain, or could potentially contain, more than 50 mg·L−1 of nitrate; and Directive 2000/60/EC [16], which establishes a recommended limit for nitrate in drinking water and for the eutrophication of freshwaters of 25 mg·L−1.
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