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.

The disposal of municipal solid wastes in landfills represents a major threat for aquifer environments at the global scale. The aim of this study was to explore how groundwater geochemical characteristics can influence the microbial community functioning and the potential degradation patterns of selected organic substrates in response to different levels of landfill-induced alterations. Groundwaters collected from a landfill area were monitored by assessing major physical-chemical parameters and the microbiological contamination levels (total coliforms and fecal indicators—Colilert-18). The aquatic microbial community was further characterized by flow cytometry and Biolog EcoPlates^TM assay. Three groundwater conditions (i.e., pristine, mixed, and altered) were identified according to their distinct geochemical profiles. The altered groundwaters showed relatively higher values of organic matter concentration and total cell counts, along with the presence of fecal indicator bacteria, in comparison to samples from pristine and mixed conditions. The kinetic profiles of the Biolog substrate degradation showed that the microbial community thriving in altered conditions was relatively more efficient in metabolizing a larger number of organic substrates, including those with complex molecular structures. We concluded that the assessment of physiological profiling and functional diversity at the microbial community level could represent a supportive tool to understand the potential consequences of the organic contamination of impacted aquifers, thus complementing the current strategies for groundwater management.

Aquaculture practices generate nutrient-rich effluents with associated microbiological hazards, such as pathogens and antimicrobial resistance genes (ARGs). Despite their growing popularity as nature-based solutions, little is known about how constructed wetlands (CWs) affect the dynamics of microbial communities at the field scale. By combining flow cytometry, 16S rRNA gene sequencing, shotgun metagenomics, and metabolic potential assays, we investigated the structural and functional responses of the aquatic microbial community following the recurrent exposure to CW-treated effluents from an intensive marine fish farm (Orbetello lagoon, Italy). While the CW promoted abundant, metabolically active, and functionally redundant microbial communities, the phylogenetic composition diverged primarily between water and sediments. Microbial profiles in CW outlet waters converged towards those of the lagoon baselines, suggesting gradual ecological recovery. The CW attenuated the occurrence of potential pathogens, such as members of the genera Francisella and Campylobacter, and acted as a buffer system in ARG dissemination, with sediments serving as reservoirs of microbial and genetic signatures. Functional profiles, dominated by chemoheterotrophy, denitrification, and sulfur respiration, remained stable across environments, reflecting microbial resilience. Our results highlight CWs as effective, field-proven solutions to mitigate aquaculture wastewater impacts while preserving core ecosystem services.

Aquaculture practices generate nutrient-rich effluents with associated microbiological hazards, such as pathogens and antimicrobial resistance genes (ARGs). Despite their growing popularity as nature-based solutions, little is known about how constructed wetlands (CWs) affect the dynamics of microbial communities at the field scale. By combining flow cytometry, 16S rRNA gene sequencing, shotgun metagenomics, and metabolic potential assays, we investigated the structural and functional responses of the aquatic microbial community following the recurrent exposure to CW-treated effluents from an intensive marine fish farm (Orbetello lagoon, Italy). While the CW promoted abundant, metabolically active, and functionally redundant microbial communities, the phylogenetic composition diverged primarily between water and sediments. Microbial profiles in CW outlet waters converged towards those of the lagoon baselines, suggesting gradual ecological recovery. The CW attenuated the occurrence of potential pathogens (e.g., Francisella spp., Campylobacter spp.) and limited ARG dissemination, though sediments remained reservoirs of microbial and genetic signatures. Functional profiles, dominated by chemoheterotrophy, denitrification, and sulfur respiration, remained stable across environments, reflecting microbial resilience. Our results highlight CWs as effective, field-proven solutions to mitigate aquaculture wastewater impacts while preserving core ecosystem services.

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.

Coastal areas worldwide are often highly impacted due to the concurrence of aquifer exploitation for irrigation, human consumption exacerbated during touristic seasons and industrial activities. In order to meet the objectives of the GWD, European groundwater bodies’ status (chemical and quantitative) is evaluated every 6 years. Criteria for good status include chemicals exceeding standards and threshold values, saline intrusion and others. Apulian region features a very high ratio coastline/area (44 m/km2, for Italy is 25 m/km2) thus seawater intrusion is a very common phenomenon, due to both natural and anthropogenic drivers.In this contribution, the first results of the VIOLA project (Natural Background Values for the Apulian groundwater bodies) are presented, supplying a preliminary geochemical characterization of the coastal Murgia groundwater body. This is part of a fractured and karstified calcareous-dolomitic aquifer with groundwater naturally flowing to the Adriatic sea. Exceedances were reported for nitrates, as well as for EC, Cl, SO4, Fe, Mn. The main objective for this groundwater body is to assess the natural background levels for the aforementioned parameters, and discriminate between the natural and anthropogenic origin of saline intrusion. Four sampling campaigns have been planned, and we present here the result of the first two sampling rounds carried out in spring and fall 2019.Groundwater sampling was performed at 47 wells with submergible pumps or with a water depth sampler. Field parameters (T, EC, pH, DO, ORP) were measured with a multiparametric probe in a flow through cell. Ammonia, cyanides and nitrites were measured in the field (UV-VIS). Laboratory analysis were performed for major anions, major cations, minor and trace elements, environmental isotopes, DOC and microbial parameters.Natural background values (NBLs) for the critical parameters have been provisionally assessed using the preselection method. Sampled waters show neutral/weakly alkaline and mostly oxidizing conditions, with conductivity values between about 700 and 20.000 µS/cm. The high salinity detected in some water points (chlorides up to 10 g/L, sulphates up to 1 g/L) is clearly linked to mixing with seawater. On a Piper diagram, the samples show a clear transition from earth alkaline-bicarbonate water towards mean seawater composition. A clear trend from coastline to inland can be recognized, with the most extended contamination in the northern and southern sectors. Trace elements (B, Sr, Ba), show a similar pattern. From spring (beginning of the irrigation season) to fall (end of the irrigation season) only a slight increase in salinity/chloride concentration can be observed. Nitrates are widespread in the study area, as well as the agricultural pressures, with values even higher than 100 mg/L without a specific spatial pattern.As for the NBLs derivation, classic indicators of anthropogenic contamination (e.g. nitrates, ammonia, NaCl) for the pre-selection of uninfluenced samples failed, due to the extensive distribution of saline groundwaters in the study area. Thus, new solutions, including environmental isotope analysis, for discriminating the anthropogenic and natural origin of the salinity are under evaluation.