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The vulnerability to salinization is a major issue for coastal aquifers. The resulting rapid modifications of hydro-geochemical characteristics, driven by the different origin of water inputs, can modify the properties of the resident biological communities. The study of structural and functional properties of groundwater microbial community, posed at the base of the heterotrophic food web, assumes an increasing importance to describe the effect of water quality on C-cycling and the resilience of groundwater systems to changes.Within the framework of the VIOLA project, this study was entailed to explore the groundwater quality and the functional responses of the microbial community across the gradient of salinity in a coastal karst aquifer located in Apulia Region (Southern Italy). The investigated area (1227 km2) is located in a semi-arid climate region with predominantly agricultural vocation. In this area, an excess of withdrawals for irrigation and other uses, often results in a significant decline of the water table, facilitating saline intrusion.The main physical-chemical parameters of 47 groundwater sampling sites (T, pH, oxidation-reduction potential, electrical conductivity, major anions/cations, trace elements, dissolved oxygen, ammonia, nitrites, cyanides and dissolved organic carbon) were measured, along with microbial community analyses including the total cell abundance, the High Nucleic Acid and Low Nucleic Acid content cell ratio (Flow Cytometry), the total coliform and Escherichia Coli contamination (Colilert-18 assay), the microbial metabolic potential (Biolog EcoPlates), and the microbial respiration (Biolog MT2 MicroPlates). The preliminary results allowed identifying two major groups of waters with different salinity levels and concentrations of Cl, Na, Mg and SO4. Prokaryotic cell abundance (mean 3.5 x 104 ± 4.6 x 104 cells/ml) showed higher values in saline waters, so as HNA cell percentages and total coliforms. Saline waters were also characterised by relatively higher metabolic potential and respiration values. In conclusion, the observed groundwater quality changes induced the stimulation of the functional microbial properties and the functional diversity. These changes in the metabolic potential of the resident communities could alter the ability to exploit the available resources and modify the related groundwater biogeochemical cycling.

Inorganic potentially toxic elements in groundwater may derive from both natural processes and anthropogenic activities. Natural background levels (NBL) are often assessed to distinguish the anthropic impact and assess the environmental status of groundwater bodies, as requested by the Water Framework Directive. The geochemical approach for the NBL assessment requires the identification of groundwater with no or negligible human impact, using markers such as nitrates/ammonia in oxidising/reducing environments, organic compounds, isotopes, etc. The statistical approach involves the separation of uninfluenced and influenced populations by means of statistical procedures. Recently, a national guideline for the NBL assessment was published in Italy. The procedure is based on the preselection method and the percentile calculation; it takes into account the groundwater body conceptual model and different assessment paths are proposed according to the sample size both in the spatial and time dimensions. In this study, we apply the national procedure to a study case in the volcanic province of Latium (central Italy). Redox facies were separated using DO (>/< 3 mg/L). The "influenced" samples were discarded using NO3 > 37.5 mg/L to obtain the "pre-selected dataset". Then, the natural background levels of As, F, Mn, Ni, Fe and SO4 were estimated as follows. When one or more outliers exist, we assume they represent different populations and processes. Regardless their anthropic or natural origin, the outliers usually represent localised phenomena, which differentiate from the background, and should be treated as such. When data approximate one normal population, we assume that they all refer to the background population and the maximum concentration value is proposed as NBL. When the normality test fails, the 95th percentile is selected as NBL. In the oxidizing facies, the NBL obtained for As and F are always above the EU Drinking Water standards, while Mn, Fe, Ni and SO4 show rather different NBLs, largely below the limits of the Italian legislation for the groundwater body chemical status definition. As for the reducing facies, the number of samples does not allow for a sound NBL definition.

Maximum contaminant levels in groundwater are set in Italy by national acts as threshold values (TV), the exceedance of which in a landfill facility obliges to perform a risk analysis, unless it is proved that the observed levels are of natural origin. At an urban landfill facility located in central Italy, arsenic, iron and manganese concentrations were reported largely above their national TVs. The landfill lies above a Pleistocene thick lacustrine sequence with clay, silt and sandy levels rich in peats and organic matter, with a local groundwater circulation N to S. Reducing conditions enhance the mobilisation of these compounds from the hosting rocks. Our research entailed to address fundamental research questions that remained largely unexplored: is this a natural process or partly enhanced by the landfill activity? To which extent do the redox conditions and geochemistry influence the characteristics of the autochthonous microbial community in groundwater? Can the microbial community properties tell us something on the ongoing processes? How can a multidisciplinary approach allow for a deeper understanding of the active processes? Four groundwater monitoring campaigns were conducted in 2016-2017 at the site. Field parameters (T, EC, pH, DO, ORP) were measured with probes in a flow through cell, ammonia was measured in the field (UV-VIS). Due to strongly anoxic conditions, groundwater sampling was performed with an in-line device in order to minimize sample disturbance. Lab analysis were performed for major and trace elements, environmental isotopes (d18O, d2H, Tritium, d13C), DOC, IPA, PCB, VOC. Microbial cell counting (flow cytometry), microbial functional diversity (BIOLOG EcoPlates(TM)) and total coliforms/E.coli were assessed. Groundwater mostly has an anoxic facies and reducing conditions, less pronounced in the NW side. As, Fe and Mn largely exceed the TVs, broadly following the Eh-DO patterns. IPA were below the detection limits in all monitoring wells while traces of VOCs were found in all the points, with a small exceedance for benzene at one downstream well. Cell abundance ranges between 8E+04 and 2E+07 cells/ml, with the lowest values in the northern wells and the highest one in one well where rain water was supposed to infiltrate during storms. High EC and SO4 also characterize this well. Microbial functional properties follow a spatial distribution, implying a diverse structure of the communities inhabiting different parts of this area. The presence of total coliforms in most of the sites let infer a communication of the aquifer with the surface environment. Moreover, E.coli detection in three of the wells suggested a preferential pathway for contaminants. Environmental isotopes suggest that groundwater is fed by rainfall infiltration processes with long residence time (for the low 3H values), except for the well with benzene above the national bound, where d13C has a less negative value (indicating a different carbon source) and tritium has a slightly higher value (indicating younger waters). As a general remark, the integration of geochemical methods and biomonitoring resulted in a greater depth of interpretation of the data, and seems a very promising tool for the detection of human impacts on groundwater.

Light Non-Aqueous Phase Liquid, Pancake Model, Vertical Equilibrium Model, Flowpath 2017, National meeting on hydrogeology 2017