Abstract
Defining natural background levels (NBL) of geochemical parameters in groundwater is a key element for establishing threshold values and assessing the environmental state of groundwater bodies (GWBs). In the Apulia region (Italy), carbonate sequences and clastic sediments host the 29 regional GWBs. In this study, we applied the Italian guidelines for the assessment of the NBLs, implementing the EU Water Framework Directive, in a south-European region characterized by the typical Mediterranean climatic and hydrologic features. Inorganic compounds were analyzed at GWB scale using groundwater quality data measured half-yearly from 1995 to 2018 in the regional groundwater monitoring network (341 wells and 20 springs). Nitrates, chloride, sulfate, boron, iron, manganese and sporadically fluorides, boron, selenium, arsenic, exceed the national standards, likely due to salt contamination along the coast, agricultural practices or natural reasons. Monitoring sites impacted by evident anthropic activities were excluded from the dataset prior to NBL calculation using a web-based software tool implemented to automate the procedure. The NBLs resulted larger than the law limits for iron, manganese, chlorides, and sulfates. This methodology is suitable to be applied in Mediterranean coastal areas with high anthropic impact and overexploitation of groundwater for agricultural needs. The NBL definition can be considered one of the pillars for sustainable and long-term groundwater management by tracing a clear boundary between natural and anthropic impacts.
Highlights
The EU Water Directives [1,2,3], implemented in Italy by Acts [4,5,6], require Member States that good status of groundwater bodies (GWBs) is achieved or maintained to protect all dependent ecosystems
Chemical status is determined based on quality standards set in Europe for nitrates and pesticides, and threshold values (TVs) that have to be set by Member States for all contaminants or groups of contaminants characterizing the GWBs as being at risk of failing the environmental objectives
The EU Directives do not provide any methodology for the TVs and natural background levels (NBL) establishment in the groundwater and the Member States are left free to apply their own approach considering the conceptual models of the groundwater bodies
Summary
The EU Water Directives [1,2,3], implemented in Italy by Acts [4,5,6], require Member States that good status of groundwater bodies (GWBs) is achieved or maintained to protect all dependent ecosystems. The NBL can be defined as the concentration of a substance, or the value of an indicator, in a given GWB or group of GWBs, with no or extremely limited anthropogenic modifications. In this perspective, the TV of a considered natural substance may be redefined by the local authorities based on the NBL. Chemical composition of groundwater depends on a wide range of natural factors such as water-rock interaction, residence time, rainfall input, chemical and biological processes that occur in the unsaturated and saturated zone, interactions with other water bodies [7]
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