Natural background levels and threshold values of chemical species in three large-scale groundwater bodies in Northern Italy

We analyze natural background levels (NBLs) and threshold values (TVs) of spatially distributed chemical species (NH4, B and As) which may be a potential pressure and concern in three large scale alluvial and fluvio-deltaic aquifers at different depths of the Apennines and Po river plains in Emilia–...

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Bibliographic Details
Published in:The Science of the total environment 2012-05, Vol.425, p.9-19
Main Authors: Molinari, Antonio, Guadagnini, Laura, Marcaccio, Marco, Guadagnini, Alberto
Format: Article
Language:English
Subjects:
Ammonia - analysis
Animal, plant and microbial ecology
Anthropogenic impact
Applied ecology
Aquifers
Arsenic - analysis
Biological and medical sciences
Boron - analysis
Chemical status
Component separation
Dynamic tests
Dynamics
Ecotoxicology, biological effects of pollution
Environmental Monitoring
Fundamental and applied biological sciences. Psychology
General aspects
Geochemistry
Groundwater
Groundwater - analysis
Groundwater - chemistry
Groundwater quality
Italy
Monitoring
Natural background level
Temporal logic
Threshold values
Thresholds
Water Pollutants, Chemical - analysis
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Summary:We analyze natural background levels (NBLs) and threshold values (TVs) of spatially distributed chemical species (NH4, B and As) which may be a potential pressure and concern in three large scale alluvial and fluvio-deltaic aquifers at different depths of the Apennines and Po river plains in Emilia–Romagna, Northern Italy. Our results are based on statistical methodologies designed to separate the natural and anthropogenic contributions in monitored concentrations by modeling the empirical distribution of the detected concentration with a mixture of probability density functions. Available chemical observations are taken over a 20years period and are associated with different depths and cover planar investigation scales of the order of hundreds of kilometers. High concentration values detected for NH4 and B appear to be related to high natural background levels. Due to interaction with the host rock in different geochemical environments we observed that concentration vary in time and space (including in depth) consistently with the hydrogeochemical features and the occurrence of natural attenuation mechanisms in the analyzed reservoirs. Conversely, estimated As NBLs are not consistent with the conceptual model of the hydrogeochemical behavior of the systems analyzed and experimental evidences of As content in aquifer cores. This is due to the inability of these techniques to incorporate the complex dynamics of the processes associated with the specific hydrogeochemical setting. Statistical analyses performed upon aggregating the concentration data according to different time observation windows allow identifying temporal dynamics of NBLs and TVs of target compounds within the observation time frame. Our results highlight the benefit of a dynamic monitoring process and analysis of well demarcated groundwater bodies to update the associated NBLs as a function of the temporal dependence of natural processes occurring in the subsurface. Monitoring protocols could also include the detailed evaluation of the geochemistry (redox) of the aquifers. [Display omitted] ► NBLs of boron, ammonium and arsenic in three groundwater bodies are analyzed. ► Global statistical tools are employed to separate anthropogenic/natural components. ► Time evolution of anthropogenic/natural pressures on the chemical status is assessed. ► Relative strength of anthropogenic/natural components changes among the aquifers. ► Estimated NBLs of As are not consistent with As content in aquifer
ISSN:0048-9697
1879-1026
DOI:10.1016/j.scitotenv.2012.03.015