Groundwater is becoming an increasingly strategic resource in drought-prone Mediterranean regions, yet recharge pathways and contaminant transfer processes in urban aquifers remain poorly constrained due to the coexistence of multiple natural and anthropogenic sources. Here, we applied an enhanced open-source mixing model (SOUPY) integrating hydrochemical and isotopic tracers to quantify recharge-source contributions and associated contaminant transport in a Mediterranean urban aquifer under drought and post-drought conditions. River-derived recharge was identified as the dominant control on groundwater composition, accounting for ~58% of total recharge, with a marked partitioning between dry-season and wet-season river contributions linked to hydroclimatic conditions. Natural recharge represented the second largest contribution (~28%), whereas sewage seepage, water-supply leakage, and direct urban runoff contributed comparatively minor fractions. Following drought recovery, recharge dynamics shifted toward increasing wet-season river influence and decreasing dry-season river contributions. Despite limited direct infiltration, temporal increases in Zn and Cu during wetter periods indicate that runoff-derived contaminants are efficiently transferred to groundwater indirectly via river–aquifer interaction. Ecotoxicological assessment based on passive samplers and Biotic Ligand Model calculations identified recurrent exceedances of ecological risk thresholds in both groundwater and river water, with Zn emerging as the primary risk driver. Overall, the results demonstrate that river–aquifer interactions exert a primary control on contaminant transport and groundwater quality in highly urbanized aquifers under hydroclimatic stress. The proposed framework provides a transferable approach for disentangling recharge dynamics and identifying dominant contamination pathways in urban groundwater systems increasingly exposed to drought and hydrological extremes.

Sustainable water management in porphyry copper tailings storage facilities (TSFs) is essential for environmental protection and regulatory compliance, particularly in Chile, which ranks third globally in TSF numbers. This study applies a multi-isotope framework (delta H-2-H2O, delta O-18-H2O, delta S-34-SO42- and delta O-18-SO42-) to trace the fate of tailings seepage towards groundwater and to evaluate hydraulic barriers effectiveness in porphyry Cu TSFs, demonstrating its applicability to systems characterized by complex mixing of multiple water sources with contrasting recharge conditions. Unlike previous studies where water sources shared similar recharge altitudes, this work addresses an "altitude-offset" scenario in which tailings water originates from high-altitude recharge zones while downstream aquifers are located at much lower elevations, creating additional isotopic end-members. To illustrate the usefulness of this approach, the Car & eacute;n TSF (Chile) serves as case study. Isotopic data indicate that tailings waters are strongly evaporated, enriched in elevated SO42- concentrations on the order of thousands of mg L-1 (approximate to 2,000 mg L-1), mainly derived from sulfide ore oxidation (60-80 %), and recharged at high altitude (similar to 2,000 masl). In contrast, surrounding freshwater is recharged at lower altitude (similar to 220 masl) and shows significantly lower SO42- concentrations on the order of tens of mg L-1 (approximate to 20 mg L-1). Groundwater downstream of the TSF reflects variable mixing between these sources. Using Cl-/SO42-, delta H-2-H2O/delta O-18-H2O, delta S-34-SO42-/delta O-18-SO42- and delta S-34-SO42-/ln(SO42-) mixing models, the contribution of mine tailing water was quantified to be generally lower than 20 % but reaching 30-40 % in some groundwater samples located close to the TSF. In addition, delta S-34-SO42- and delta O-18-SO42- results suggest that bacterial sulfate reduction may occur in deeper zones of the TSF, promoting natural attenuation of dissolved metals. These findings highlight the usefulness of stable isotopes for tracing water sources, assessing hydraulic barrier efficiency, and estimating the proportion of pumped water exempt from water rights in TSFs.

Denitrification is the main natural process to attenuate nitrate contamination in groundwater. In this work the attenuation of nitrate by denitrification has been studied in groundwater used for different purposes in urbanizations with a high index of social vulnerability located in the middle basin of the Matanza-Riachuelo River, Buenos Aires, Argentina. The denitrification process and its extent have been characterized using the isotopic composition of nitrogen and oxygen of dissolved nitrate (δ15N-NO3- y δ18O-NO3-). In addition, stable nitrate isotopes have been used to identify the source of nitrate contamination in groundwater. The dissolved nitrate in the studied groundwater varied between 45 and 128 mg/L. The isotopic composition of δ15NNO3 varied between +7.4 ‰ and +18.4 ‰ and δ18ONO3 varied between +3.6 ‰ and +9.3 ‰. Most water samples taken from private supply wells show isotopic values ​​similar to those of the nitrate source from leakage from septic system. The estimated percentage of denitrification varied between 5% and 31%, suggesting that natural nitrate attenuation is low. Hence, only a low proportion of nitrate is removed by natural denitrification in the groundwater analyzed.

Several groundwater quality investigations have been conducted in coastal regions that are commonly exposed to multiple anthropogenic stressors. Nonetheless, such studies remain challenging because they require focused-diagnostic approaches for a comprehensive understanding of groundwater contamination. Therefore, this study integrates a multi-tracer approach to acquire comprehensive information allowing for an improved understanding of the origins of groundwater contamination, the relative contribution of contaminants, and their biogeochemical cycling within a coastal groundwater system. This multi-tracer approach, focusing on nitrate (NO3) and sulfate (SO4) groundwater contamination, is applied to a Mediterranean coastal aquifer underlying an important economically strategic agricultural area. Dissolved NO3 in groundwater has concentrations up to 89 mg/L, whereas SO4 concentrations in groundwater are up to 458 mg/L. By integrating isotope tracers (i.e., δ15NNO3, δ18ONO3, δ11B, δ34SSO4, and δ18OSO4), NO3 and SO4 in the groundwater are found to have originated from multiple anthropogenic and natural sources including synthetic fertilizers, manure, sewage, atmospheric deposition, and marine evaporites. Chemical and isotopic data are coupled to identify the dominant hydro(geo)logic processes and the major subsurface biogeochemical reactions that govern the NO3 and SO4 occurrences. Nitrate and SO4 concentrations are identified to be respectively controlled by nitrification/denitrification and by bacterial dissimilatory SO4 reduction. Identifying these subsurface biogeochemical processes constrained the Bayesian isotope MixSIAR model, that is used for apportioning the relative contributions of the identified groundwater contamination sources, by informed site-specific isotopic fractionation effects. Results from MixSIAR indicate that manure is distinguished as the predominant source for NO3 (61 %), whereas SO4 in groundwater is mostly supplied from two sources (i.e., synthetic fertilizers and soil-derived sulfate) identified with similar contributions (30 %). This study particularly demonstrates the utility of initially describing the subsurface processes, not only to predict the fate of NO3 and SO4 concentrations within the groundwater system, but also to constrain the MixSIAR model with justified site-specific isotopic fractionation effects for subsurface transformation processes affecting NO3 and SO4.

Nitrous oxide (N2O) is a potent greenhouse gas and a significant contributor to global warming and ozone layer depletion. It is primarily emitted from soils through microbial processes such as nitrification and denitrification and shows spatial and temporal variations driven by environmental factors such as the availability of nitrogen (e.g., in the form of fertilizers), organic carbon, soil moisture, temperature and oxygen levels. However, estimates on the relative contribution of different N2O producing pathways are frequently uncertain and knowledge on how environmental factors influence N2O emissions dynamics is still limited. Therefore, closing these knowledge gaps is crucial for improving mitigation strategies.This study aims to analyze the patterns of N₂O emissions across diverse forest and agricultural soils, taking geographic variations into account, and to determine the relative contributions of the primary N2O producing and consuming pathways specific to each soil type.Batch experiments were conducted using four agricultural soils and four forest soils from sites of the ICOS (https://www.icos-cp.eu) and FLUXNET (https://fluxnet.org/about/) networks. Agricultural soils were obtained in France, Belgium, Italy and Switzerland, while forest soils were obtained in Finland, Sweden, Belgium and Italy. These soils exhibited a range of intrinsic characteristics, such as texture, organic matter content and type, and nitrogen sources. The incubations took place in complete darkness at a constant temperature of 22 ºC for approximately 30 hours after rewetting dry soil. Each soil type was tested with five replicates across five time points (i.e., 25 reactors for soil type). For each reactor we measured the production of N2O and its isotopic composition including the δ15N-N2Obulk, δ18O-N2Obulk, and site preference δ15N-N2OSP (i.e., the intramolecular distribution of N isotopes, since the N2O molecule has an asymmetric linear structure [N-N-O]). Additionally, the isotopic compositions of nitrate and ammonium from soil KCl extracts are being analyzed (δ15N-NO3-, δ18O-NO3-, δ15N-NH4+) and microbiological characterization is also being performed.Preliminary results revealed significantly higher N2O production in agricultural soils compared to forest soils during the 30-hour incubation period, with rates reaching up to 130 μg N-N2O/kg/h in agricultural soils and only 0.3 μg N-N2O/kg/h in forest soils. Notable differences were also observed among the four tested soils within each category (agricultural or forest). These differences might be mainly attributed to differences in the nitrogen and organic carbon content as well as the texture. The isotopic analysis of N2O suggests that denitrification is the primary process driving N₂O emissions in the studied soils, with nitrification also contributing to varying extents depending on the soil type.Ongoing isotopic analyses of nitrate and ammonium in soil KCl extracts alongside microbial characterization, will provide deeper insights into the dominant processes driving N2O emissions in each soil type and the key environmental factors influencing them.

The combined use of isomeric fraction (IF) and multi-element compound-specific isotope analysis (ME-CSIA) was evaluated for the first time to assess the fate and degradation of methoxychlor in the environment. The concentration and carbon and chlorine isotope composition of methoxychlor and its transformation products were monitored in water and solid phases of a fractured aquifer. The results from the interception trenches water samples demonstrated that induced alkaline conditions promoted alkaline hydrolysis. Natural attenuation of methoxychlor isomers was evidenced by carbon and chlorine isotopic fractionation. The field C-Cl isotope slope (ΛC/Cl = 0.42 ± 0.06; R² = 0.98) was statistically indistinguishable (p > 0.05) from that obtained in a previous experiment (0.44 ± 0.14), confirming the occurrence of reductive dechlorination of methoxychlor isomers. P,p'-methoxychlor δ13C values in groundwater samples revealed variations linked to rainfall patterns. The extent of p,p'-methoxychlor biodegradation was calculated to be greater than 89 % across the monitoring period. The combined use of CSIA and IF evidenced that alkaline hydrolysis and reductive dechlorination did not exhibit isomeric selectivity. Differences in IF values between slurry and water samples, as well as between upstream and downstream wells, suggested variations in the environmental behaviour of the p,p' and o,p'-isomers, likely due to differing water solubilities. Overall, ME-CSIA proved to be a valuable tool for identifying, quantifying, and tracing methoxychlor degradation in this aquifer. Additionally, IF provided insights into the distinct environmental behaviour of the p,p'- and o,p'-isomers. These tools offer crucial information, valuable for decision-makers in developing remediation strategies for methoxychlor-contaminated sites.

Multi-element compound-specific stable isotope analysis (ME-CSIA) allows monitoring the environmental behavior and transformation of most common and persistent contaminants. Recent advancements in analytical techniques have extended the applicability of ME-CSIA to organic micropollutants, including pesticides. Nevertheless, the application of this methodology remains unexplored concerning harmful insecticides such as methoxychlor, a polar organochlorine pesticide usually detected in soil and groundwater. This study introduces methods for dual carbon and chlorine compound-specific stable isotope analysis (δ13C-CSIA and δ37Cl-CSIA) of both methoxychlor and its metabolite, methoxychlor olefin, with a sensitivity down to 10 and 100 mg/L, and a precision lower than 0.3 and 0.5 ‰ for carbon and chlorine CSIA, respectively. Additionally, three extraction and preconcentration techniques suitable for ME-CSIA of the target pesticides at environmentally relevant concentrations were also developed. Solid-phase extraction (SPE) and liquid-solid extraction (LSE) effectively extracted methoxychlor (107 ± 27 % and 87 ± 13 %, respectively) and its metabolite (91 ± 27 % and 106 ± 14 %, respectively) from water and aquifer slurry samples, respectively, with high accuracy (Δδ13C and Δδ37Cl ≤ ± 1 ‰). Combining CSIA with polar organic chemical integrative samplers (POCISs) for the extraction of methoxychlor and methoxychlor olefin from water samples resulted in insignificant fractionation for POCIS-CSIA (Δδ13C ≤ ± 1 ‰). A relevant sorption of methoxychlor was detected within the polyethersulfones membranes of the POCISs resulting in temporary carbon isotope fractionation depending on the sorbed mass fraction during the first deployment days. This highlights the critical role of the interactions of polar analytes with POCIS sorbents and membranes in the performance of this method. Altogether, this study proposes a proof of concept for ME-CSIA of methoxychlor and its metabolites, opening the door for future investigations of their sources and transformation processes in contaminated sites.

Agricultural run-off exposes recipient water bodies to nitrate (NO3-) pollution. Biological denitrification is a suitable method for removing NO3- in water resources that can be induced by the use of industrial organic liquid waste as an electron donor source. In light of this, batch and column laboratory experiments were performed to assess the potential of two industrial wine residues (l & iacute;as and v & iacute;nico) to induce biological denitrification of NO3- contaminated water from a constructed wetland and to evaluate the efficiency of these treatments using chemical and isotopic tools. In batch experiments (performed at a C/N ratio of 1.25), v & iacute;nico was not efficient enough in removing N species, attenuating only 35% NO3- and was not used in column experiments. In similar experimental conditions, l & iacute;as completely removed N species from water in both batch and column experiments. The calculated isotope fractionation (epsilon 15NNO3 and epsilon 18ONO3) was the same in both batch and column experiments biostimulated with l & iacute;as and differed from those for v & iacute;nico. The isotopic data confirmed that denitrification was the principal NO3- attenuation pathway in all the experiments. The isotopic fractionation can be later applied to field studies to quantify the efficiency of biologically enhanced denitrification. A numerical geochemical model that accounts for the changes in nitrate, nitrite concentration and isotopic composition due to the degradation of l & iacute;as and v & iacute;nico, including transport in the case of the column experiment, was performed to simulate the experimental results and can be up-scaled in field treatments. Groundwater nitrate pollution is a significant global concern resulting from excessive fertilizer use in agriculture. This pollution poses health risks to humans and ecosystems by contaminating drinking water supplies and aquatic ecosystems. Sustainable remediation of nitrate is necessary to safeguard human health and the environment. Successful field-scale remediation requires laboratory feasibility studies to find the appropriate compounds to reduce nitrate (electron donors) and the best application measures to remove nitrate at a minimum cost. In our research, laboratory experiments were carried out using two industrial wine wastes as electron donors to evaluate their potential to remove nitrate from nitrate-polluted water. Chemical, isotopic, and numerical modeling tools have been used to quantify the amount of nitrate removed. The results indicate that one product successfully removed nitrate and can be implemented in the field as a mitigation strategy, while the other was ineffective and cannot be used. The isotopic fractionation from the laboratory experiments and the numerical model would be subsequently applied in the field to quantify the efficiency of nitrate removal. Wine industry residues induced nitrate attenuation in laboratory batch and column experiments Denitrification efficiency varied with the wine residue type, showing epsilon 15N between -16.5--32.0 parts per thousand and epsilon 18O between -12.1--27.6 parts per thousand A geochemical model describing the trends of the experimental results has been developed and can be used for field applications

Nitrite reduction has often been treated as a biotic process in water treatment systems, but it also occurs abiotically, and it is difficult to distinguish both reactions as they can co-occur at field-scale. The potential reduction of NO2- was tested in 3 anaerobic experimental scenarios using a NO2- bearing solution amended with: i) siderite (FeCO3) (Sid experiment); ii) Fe(II) solution from FeCl2.4H2O(s) (DFe experiment); and iii) siderite mixed with Fe(II) solution (Sid+DFe experiment). Non-sterilized batch experiments were carried out in anaerobic conditions with an initial ratio of nitrogen to dissolved iron of 5 in DFe and Sid+DFe (Sid had no initially dissolved Fe(II)) and 1000 mg L-1 of siderite in Sid and Sid+DFe experiments. At the end of the experiments, the NO2- removed was 3% for Sid, 54% for DFe and 84% for Sid+DFe. The NO2- concentration decrease over time was characterized by an enrichment in the delta 15NNO2 of the unreacted NO2-, increasing from -26.9 %o to -26.4 %o (Sid), -18.0 %o (DFe) and -15.9 %o (Sid+DFe). The calculated epsilon 15NNO2 for Sid was -11.8 %o, whereas for DFe was -12.0 %o and Sid+DFe was -13.0 %o, suggesting a common NO2- degradation mechanism in all experiments. The Rayleigh distillation equation showed that the generated N2O was the final product of the abiotic nitrite reduction reaction, and the calculated N2O site preference (SP) was 22.5 +/- 0.7 %o for DFe and 23.5 +/- 0.5 %o for Sid+DFe. The continuous N2O measurement showed that only 25.3 +/- 5.1% in DFe and 31.0 +/- 6.3% in Sid+DFe of the generated N2O in water was recovered in the headspace vials, suggesting that a large portion of the produced N2O(aq) in solution did not diffuse from water. The coupled NO2- reduction and Fe(II) oxidation followed a second-order kinetic reaction with a rate equal to (9.39 +/- 0.36)& sdot;10-4 & sdot;[NO2-]& sdot;[Fe(II)] (mol L-1 s- 1) in all experiments. The experimental conditions supported by the Rayleigh distillation equation using the experimentally calculated epsilon 15N values, coupled with NO2- isotopic data and N2O SP values, showed that biological denitrification had a negligible influence on nitrite reduction and that chemodenitrification was the main NO2- attenuation pathway. A geochemical model coupling the kinetic chemodenitrification, isotope fractionation, aqueous speciation in equilibrium and precipitation and dissolution of calcite has been implemented and reproduced the experimental results. The geochemical model developed in our study can be applied to similar experimental studies and to field-scale studies to predict the efficiency of abiotic nitrite reduction treatments using Fe(II).

This study investigates the use of multi-element compound-specific isotope analysis (ME-CSIA) to monitor degradation processes of methoxychlor, a persistent organochlorine insecticide. Laboratory experiments examined the kinetics, release of transformation products, and carbon and chlorine isotope effects during methoxychlor degradation through alkaline hydrolysis, oxidation with alkaline-activated persulfate, and biotic reductive dechlorination. Results showed that hydrolysis and oxidation did not cause significant carbon and chlorine isotope fractionation, indicating that C-H rather than C-Cl bond cleavage was the rate-determining step. Conversely, biotic reductive dechlorination by a field-derived microcosm under strictly anoxic conditions displayed significant carbon (epsilon C C =-0.9 f 0.3 %o ) and chlorine (epsilon Cl Cl =-1.9 f 1.0 %o ) isotope fractionation. Its corresponding calculated dual isotope slope ( Lambda C/Cl = 0.4 f 0.1) and apparent kinetic isotope effects (AKIEC C = 1.014 f 0.005 and AKIECl Cl = 1.006 f 0.003) indicate a C-Cl bond cleavage as the rate-determining step, highlighting the difference with respect to the other studied degradation mechanisms. Changes in the microbial community diversity revealed that families such as Dojkabacteria, Anaerolineaceae, , Dysgonomonadaceae, , Bacteroidetes vadinHA17, , Pseudomonadaceae, , and Spirochaetaceae, , may be potential agents of methoxychlor reductive dechlorination under anoxic conditions. This study advances the understanding of degradation mechanisms of methoxychlor and improves the ability to track its transformation in contaminated environments, including for the first time an isotopic perspective.

Porphyry-style copper deposits are characterized by low Cu grades and high tonnages, resulting in large mine tailing volumes disposed in impoundments. Due to the mining tailing sizes, waterproofing techniques cannot be applied along the dam base. Therefore, to minimize seepage towards the aquifers, pumping wells are usually installed as hydraulic barriers. Currently, there is a controversy over whether or not the water extracted from hydraulic barriers should be counted as the use of new water rights. Consequently, a growing interest to develop tools to trace and quantify the tailing impacts in groundwater and to determine the water pumped amount subjected to water rights exist. In the present study, isotope data (delta H-2-H2O, delta O-18-H2O, delta(34S)-SO42- and delta O-18-SO42-) are proposed as a tool to quantify tailings seepage towards groundwater and to assess hydraulic barriers effectiveness. To illustrate this approach usefulness, the Quillayes porphyry Cu tailing impoundment (Chile) case study is presented. The multi-isotopic approach revealed that tailing waters are highly evaporated showing high SO42- content (similar to 1900 mg L-1) derived from primary sulfate ore dissolution, whereas freshwaters, derived from recharge water, have low SO42- contents (10-400 mg L-1) resulting from the interaction with geogenic sulfides from barren host rock.The delta H-2 and delta O-18 values of groundwater samples collected downstream from the impoundment suggest a mixing at different proportions of highly evaporated water from the mine tailing waters and non-evaporated regional fresh groundwater. Cl-/SO42-, delta S-34-SO42-/delta O-18-SO42-, delta S-34-SO42-/ln(SO42-) and delta H-2-H2O/delta O-18-H2O mixing models allowed to determine that groundwater located closer to the impoundment had a mine tailing water contribution from 45 to 90 %, whereas those located farther away had lower contribution (5-25 %). Results confirmed the stable isotope usefulness to determine the water origin and to calculate the hydraulic barrier efficiencies and the pumped water proportions unrelated to the mining tailing subject to the water rights.

Soil Aquifer Treatment (SAT) is used to increase groundwater resources and enhance the water quality of wastewater treatment plant (WWTP) effluents. The resulting water quality needs to be assessed. In this study, we investigate attenuation pathways of nitrogen (N) compounds (predominantly NH4+) from a secondary treatment effluent in pilot SAT systems: both a conventional one (SAT-Control system) and one operating with a permeable reactive barrier (PRB) to provide extra dissolved organic carbon to the recharged water. The goal is to evaluate the effectiveness of the two systems regarding N compounds by means of chemical and isotopic tools. Water chemistry (NO3-, NH4+, Non-Purgeable Dissolved Organic Carbon (NPDOC), and O2) and isotopic composition of NO3- (ẟ15N-NO3- and ẟ18O-NO3-) and NH4+ (ẟ15N-NH4+) were monitored in the inflow and at three different sections and depths along the aquifer flow path. Chemical and isotopic results suggest that coupled nitrification-denitrification were the principal mechanisms responsible for the migration and distribution of inorganic N in the systems and that nitrification rate decreased with depth. At the end of the study period, 66% of the total N in the solution was removed in the SAT-PRB system and 69% in the SAT-Control system, measured at the outlet of the systems. The residual N in solution in the SAT-PRB system had an approximately equal proportion of N-NH4+ and N-NO3- while in the SAT-Control system, the residual N in solution was primarily N-NO3-. Isotopic data also confirmed complete NO3- degradation in the systems from July to September with the possibility of mixing newly generated NO3- with the residual NO3- in the substrate pool.

Stable isotope fingerprinting is widely applied to plant-soil-groundwater systems in an aim to identify and even quantify the sources of nitrates found in groundwater. Frequently, in such studies, the δ15N and δ18O values of nitrogen sources, such as inorganic fertilizers and manure, are directly compared to the isotope signatures of nitrate encountered in groundwater bodies below agricultural watersheds. We submit that the underlying assumptions (conservative behavior of isotope composition, rapid transfer from surface to groundwater) may only be realistic under very specific conditions whereas, in most cases, significant isotope effects exerted by the soil-microbial-plant system on the δ15N and δ18O values of nitrate need to be taken into account when attempting a quantitative apportionment of sources of groundwater nitrate. We hypothesise that the isotopic signature of nitrate exported from below the root zone and migrating towards the groundwater will reflect the nitrogen isotope composition of the soil organic N pool, rather than the isotope composition of source fertilizer or organic amendments, due to processes that reset source isotope compositions within soil N pools. We test this hypothesis using empirical observations from a diversity of settings, in France, Spain and Canada with a relatively constant historic anthropogenic N source or a simple and well constrained landuse history. Furthermore, through the use of a process-based model (SIMSONIC, Billy et al., 2010) we estimate to what extent the isotopic composition of the predominant N input to the soil-microbial-plant system and the soil N pool has been modified in an attempt to consider these changes in source apportionment studies elucidating the sources of groundwater nitrate. This research was supported through the Consortium award MUTUAL, by the LE STUDIUM® Loire Valley Institute for Advanced Studies via its SMART LOIRE VALLEY (SLV) fellowship programme, co-funded by the H2020 Marie Sklodowska-Curie programme, Contract No. 665790. Billy C., Billen G., Sebilo M., Birgand F., Tournebize J. (2010) Nitrogen isotopic composition of leached nitrate and soil organic matter as an indicator of denitrification in a sloping drained agricultural plot and adjacent uncultivated riparian buffer strips. Soil Biology and Biochemistry, 42, 108-117.

Nitrogen losses from intensive agricultural production may end up as high nitrate (NO3-) concentrations in groundwater, with a long-term impact on groundwater quality. The main objective of this study was to evaluate the impact of fertilization practices used for grape cultivation on groundwater quality of Tidone Valley, northwest of Italy, following an integrated socio-hydrogeological approach that consists on (i) the involvement of 175 farmers in the description of agricultural and fertilization practices, using a survey of ad hoc questionnaires, (ii) the evaluation of NO3- occurrence in groundwater and ( iii) the identification of NO3- sources through isotopic and hydrochemical analysis. In this area, as for certain particular Apennines shallow aquifers, groundwater is of reduced interest due to its limited storage capacity and there arc insufficient wells currently monitored by the local Environmental Agency (ARPAE) to evaluate the impact of agricultural fertilization on existing local aquifers. Farmers questionnaires results highlighted an extensive use of inorganic nitrogen fertilization and a tendency of farmers to follow their own experience for fertilization. Chemical analyses revealed high variability of major and trace elements concentrations isotope data. NO3- concentrations were significantly higher in deeper wells with respects to shallow wells. Isotopic results indicated that groundwater NO3- origin is inorganic, in agreement with the land use and the declared viticultural practices. Comparing groundwater NO3- occurrence from the studied area with values of entire Emilia-Romagna Region, only 7.7% of groundwater samples showed values above the EQS. (50 mg NO3- IL) between Nov 2017 and Sept 2018, while in the entire region 11.5% of groundwater samples showed values above the EQS in the same period. Considering that the vineyards surface in the studied area represents almost 75% of the entire regional vineyard surface, the obtained results suggest a low to moderate impact of viticulture on NO3- concentration of regional groundwater. (C) 2020 Elsevier B.V. All rights reserved.

Estuarine sediments are often characterized by abundant iron oxides, organic matter, and anthropogenic nitrogen compounds (e.g., nitrate and nitrite). Anoxic dissimilatory iron reducing bacteria (e.g., Shewanella loihica) are ubiquitous in these environments where they can catalyze the reduction of Fe(III) (oxyhydr)oxides, thereby releasing aqueous Fe(II). The biologically produced Fe(II) can later reduce nitrite to form nitrous oxide. The effect on nitrite reduction by both biologically produced and artificially amended Fe(II) was examined experimentally. Ferrihydrite was reduced by Shewanella loihica in a batch reaction with an anoxic synthetic sea water medium. Some of the Fe(II) released by S. loihica adsorbed onto ferrihydrite, which was involved in the transformation of ferrihydrite to magnetite. In a second set of experiments with identical medium, no microorganism was present, instead, Fe(II) was amended. The amount of solid-bound Fe(II) in the experiments with bioproduced Fe(II) increased the rate of abiotic NO2- reduction with respect to that with synthetic Fe(II), yielding half-lives of 0.07 and 0.47 d, respectively. The delta O-18 and delta N-15 of NO2- was measured through time for both the abiotic and innoculated experiments. The ratio of epsilon O-18/epsilon N-15 was 0.6 for the abiotic experiments and 3.1 when NO2- was reduced by S. loihica, thus indicating two different mechanisms for the NO2- reduction. Notably, there is a wide range of the epsilon O-18/epsilon N-15 values in the literature for abiotic and biotic NO2- reduction, as such, the use of this ratio to distinguish between reduction mechanisms in natural systems should be taken with caution. Therefore, we suggest an additional constraint to identify the mechanisms (i.e. abiotic/biotic) controlling NO2- reduction in natural settings through the correlation of delta N-15-NO2- and the aqueous Fe(II) concentration. (C) 2020 Elsevier Ltd. All rights reserved.