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Increasing energy consumption and food production worldwide results in anthropogenic emissions of reactive nitrogen into the atmosphere. To date, however, little information is available on tropical urban environments where inorganic nitrogen is vastly transported and deposited through precipitation on terrestrial and aquatic ecosystems. To fill this gap, we present compositions of water stable isotopes in precipitation and atmospheric nitrate (δ18O-H2O, δ2H-H2O, δ15N-NO3-, and δ18O-NO3-) collected daily between August 2018 and November 2019 in a tropical urban atmosphere of central Costa Rica. Rainfall generation processes (convective and stratiform rainfall fractions) were identified using stable isotopes in precipitation coupled with air mass back trajectory analysis. A Bayesian isotope mixing model using δ15N-NO3- compositions and corrected for potential 15N fractionation effects revealed the contribution of lightning (25.9 ± 7.1%), biomass burning (21.8 ± 6.6%), gasoline (19.1 ± 6.4%), diesel (18.4 ± 6.0%), and soil biogenic emissions (15.0 ± 2.6%) to nitrate wet deposition. δ18O-NO3- values reflect the oxidation of NOx sources via the ·OH + RO2 pathways. These findings provide necessary baseline information about the combination of water and nitrogen stable isotopes with atmospheric chemistry and hydrometeorological techniques to better understand wet deposition processes and to characterize the origin and magnitude of inorganic nitrogen loadings in tropical regions. El aumento del consumo de energía y la producción de alimentos en todo el mundo da como resultado emisiones antropogénicas de nitrógeno reactivo a la atmósfera. Sin embargo, hasta la fecha, se dispone de poca información sobre los entornos urbanos tropicales donde el nitrógeno inorgánico se transporta y se deposita en gran medida a través de la precipitación en los ecosistemas terrestres y acuáticos. Para llenar este vacío, presentamos composiciones de isótopos estables en agua en precipitación y nitrato atmosférico (δ18O-H2O, δ2H-H2O, δ15N-NO3- y δ18O-NO3-) recolectados diariamente entre agosto de 2018 y noviembre de 2019 en una atmósfera urbana tropical. del centro de Costa Rica. Los procesos de generación de lluvia (fracciones de lluvia convectiva y estratiforme) se identificaron utilizando isótopos estables en la precipitación junto con el análisis de la trayectoria inversa de la masa de aire. Un modelo de mezcla de isótopos bayesianos utilizando composiciones de δ15N-NO3- y corregido por los posibles efectos de fraccionamiento de 15N reveló la contribución de los rayos (25,9 ± 7,1%), la quema de biomasa (21,8 ± 6,6%), la gasolina (19,1 ± 6,4%), el diésel (18,4%). ± 6,0%) y emisiones biogénicas del suelo (15,0 ± 2,6%) a la deposición húmeda de nitrato. Los valores de δ18O-NO3- reflejan la oxidación de las fuentes de NOx a través de las vías · OH + RO2. Estos hallazgos proporcionan la información de referencia necesaria sobre la combinación de isótopos estables de nitrógeno y agua con la química atmosférica y las técnicas hidrometeorológicas para comprender mejor los procesos de deposición húmeda y caracterizar el origen y la magnitud de las cargas de nitrógeno inorgánico en las regiones tropicales. Universidad Nacional, Costa Rica Escuela de Química

We present the application of dual stable isotope analyses of NO3 (δ15N-NO3 and δ18O-NO3) to provide a comprehensive assessment of the provenance, partitioning, and conversion of nitrate across the Day River Basin (DRB), Vietnam, which is heavily impacted by agriculture and urbanization. Stable isotope compositions of river water δ18O-H2O, in addition to their δ15N-NO3 and δ18O-NO3 signatures, were sampled at 12 locations in the DRB. Sample collection was conducted during three different periods to capture changes in regional weather and agricultural fertilization regimes; April (the dry season and key fertilization period), July (the rainy season and another key fertilization period) and October (the rainy season with no regional fertilization). Ranges of NO3 stable isotopes are − 7.1 to + 9.2‰ and − 3.9 to + 13.2‰ for δ18O and δ15N, respectively. Interpretation of the stable isotope data characterizes 4 main sources of NO3 in the DRB; (1) nitrified urea fertilizer derived from an intensive agricultural irrigation network, (2) soil and groundwater leaching from within the basin (3) manure and sewage inputs (which is more prevalent in downstream river sections) and (4) upstream inflow from the Red River which discharges into the Day River through the Dao River. We applied a mixing model for the DRB consisting of 4 variables, representing these 4 different sources. The partition calculation shows that during the fertilization and rainy period of July, more than 45% of river NO3 is derived from nitrified urea sources. During the other sampling periods (April and October), manure and sewage contribute more than 50% of river NO3 and are derived from the middle portion of the DRB, where the Day River receives domestic wastewater from the Vietnamese capital, Hanoi. Stable isotope data of O and N reveal that nitrification processes are more prevalent in the rainy season than in dry season and that this predominantly takes place in paddy field agricultural zones. In general, data demonstrate that nitrate loss in the DRB is due to denitrification which takes place in polluted stretches of the river and dominates in the dry season. This study highlights that (i) domestic waste should be treated prior to its discharge into the Day River and (ii) the need for better catchment agricultural fertilization practices as large portions of fertilizer currently discharge into the river, which greatly impacts regional water quality.

Earth’s climate history is traced through the long-term covariance between the isotopic (δ18O) composition of archived meteoric waters (groundwater, ice cores) with air temperature (T) and amount of precipitation (P). To assess recent multi-decadal climatic changes, we analysed δ18O, T and P, and the relationships between these parameters at 20 stations having 60 years of continuous monthly isotopic records. Using nonparametric regressions and time series modelling we found significant linear and non-linear relationships for δ18O with T and P and showed that the δ18O dependency on these two parameters varied over decadal scales, thereby revealing complex relationships related to recycled moisture, large-scale convective processes and atmospheric-oceanic oscillations. Due to multiple factors controlling the δ18O composition of precipitation including P and T effects, we found that time-varying relationships between δ18O in precipitation P and T were better explained using the non-linear regressions. Our results affirmed that δ18O distributions in global precipitation are integrative indicators of climate dynamics whose patterns can be applied to better understand region-specific climatic changes in the present, past, and future.

The stable isotopic composition of water (δ18O, δ2H) is used to trace different components of the hydrological cycle, particularly interactions between precipitation, surface, and ground water. In Greece, insufficient spatial coverage for isotopes in precipitation hinders investigations of relationship between ground water and precipitation, information that is required to help quantify aquifer replenishment rates. We used precipitation, geospatial, ground water isotope data and General Linear Models (GLM) to predict the spatial distribution of isotopes in phreatic ground water in Greece. Prediction covariates of elevation, latitude, distance to nearest coastline, drainage basin (western vs. eastern Greece), and amount of precipitation predicted 62% of the isotopic variance in ground water. The GLM model yielded predictions of the isotopic composition of shallow aquifers, which allowed us to construct maps for use in hydrological and other forensic applications in Greece. A comparison of the stable isotope values predicted by our GLM to those of existing precipitation models revealed that phreatic aquifers in Greece are mainly recharged during the annual wet period, between November and March, as documented by the high overlap coefficients of 0.77 and 0.82, respectively. Rainy-period-biased aquifer recharge has implications for water quality and management issues, for example, nitrate pollution may be enhanced in the non-growing rainy period when crop uptake is the lowest, or for water resource management if climatic changes alter these temporal rainfall patterns.

Remediation of nitrate pollution of Earth’s rivers and aquifers is hampered by cumulative biogeochemical processes and nitrogen sources. Isotopes (δ15N, δ18O) help unravel spatiotemporal nitrogen(N)-cycling of aquatic nitrate (NO3−). We synthesized nitrate isotope data (n = ~5200) for global rivers and shallow aquifers for common patterns and processes. Rivers had lower median NO3− (0.3 ± 0.2 mg L−1, n = 2902) compared to aquifers (5.5 ± 5.1 mg L−1, n = 2291) and slightly lower δ15N values (+7.1 ± 3.8‰, n = 2902 vs +7.7 ± 4.5‰, n = 2291), but were indistinguishable in δ18O (+2.3 ± 6.2‰, n = 2790 vs +2.3 ± 5.4‰, n = 2235). The isotope composition of NO3− was correlated with water temperature revealing enhanced N-cascading in warmer climates. Seasonal analyses revealed higher δ15N and δ18O values in wintertime, suggesting waste-related N-source signals are better preserved in the cold seasons. Isotopic assays of nitrate biogeochemical transformations are key to understanding nitrate pollution and to inform beneficial agricultural and land management strategies.

The objective of this work is to enhance the conceptual hydrogeological model in the Río Cuarto River basin by using isotope and hydrochemical techniques. The precipitation pattern, as reflected in the average values of

Nitrate (NO3−) is one of the most widespread contaminants in groundwater primarily due to agricultural activities utilizing N-containing fertilizers and the presence of animal wastes. Hydrochemical and nitrate isotope data (δ15N-NO3− and δ18O-NO3−) from the unconfined aquifer in the urban area of Del Campillo city and its surrounding rural area with different land-use types, i.e. individual sanitation systems, agricultural areas and livestock breeding facilities, were generated to investigate the impact of nitrogen pollution sources and to assess N-biogeochemical processes. The Principal Component Analysis of hydrochemical and isotopic data were used to compare the factors that control the groundwater quality and particularly the nitrate concentrations in the urban and the rural area. The results showed that nitrate pollution in the urban area of Del Campillo city originated mainly from the on-site sanitation systems and/or animal domestic wastes, whereas in the rural area nitrate pollution was mostly attributed to a combination of urea-based fertilizers and manure from livestock breeding activities. The aquifer is under oxic to suboxic conditions in the rural area and becomes suboxic in the urban area where the higher supply of organic matter consumes oxygen. As a result, denitrification was more significant in the urban area compared to the rural area, as evidenced by the higher N and O isotope enrichment factor (e). This work will be used to benchmark the current nitrate contamination status in the region and evaluate effective planning of environmental measures and remediation strategies.

Severe droughts during the dry season and floodings during the rainy season are among the major problems encountered in the valleys along the Ping River in Thailand. Improving our understanding of the groundwater resources in this agricultural area is an important issue for the sustainable development of the region. Hence, in order to gain understanding on the groundwater flow dynamics in the unconsolidated shallow aquifers along the Ping River, stable (13C, 18O, 2H, noble gases) and radioactive (3H, 14C) isotope techniques were combined with hydrogeochemical tools. The comprehensive interpretation of the chemical and isotope data consistently showed different origins for groundwater in the northern and southern areas of the investigated aquifers. Groundwaters in the northern part have younger 3H/3He ages, are less mineralized, and have suffered a stronger evaporation than groundwaters in the southern part of the aquifer. Overall, our results are consistent with the hydrogeological situation of the investigated area, namely shallow groundwaters and a spatially extended recharge. 3H/3He apparent ages indicated that young groundwater (

The assessment of nitrate pollution origin using stable isotope techniques is a fundamental prerequisite for the application of sustainable groundwater management plans. Although nitrate pollution is a worldwide groundwater quality problem, existing knowledge on the origin of nitrate pollution in arid and semi-arid regions is still scarce. Using the example of the Grombalia aquifer (NE Tunisia), this work summarizes the main strengths and constraints of multi-isotope techniques targeting at nitrate source identification and apportionment The results highlighted that, even in the case of well-established methodologies, like those of isotope hydrogeochemistry (δ15NNO3, δ 18ONO3 and δ 11B) and mixing modelling for source apportionment, it is fundamental to take into account regional and local end-members to avoid biased data interpretation and to fully exploit the potential of such accurate tools.

Eutrophication is a globally significant challenge facing aquatic ecosystems, mostly associated with human induced enrichment of these ecosystems with nitrogen and phosphorus. Given the complexity of assigning eutrophication issues to local primary N sources in field-based studies, this paper proposes a multi-stable isotope and biological framework to track nitrogen biogeochemical transformations, inputs and fate of nitrate in groundwater-dependent shallow lakes. Three representative freshwater ecosystems from the Pampa Plain (Argentina), with different land uses and topographic features were selected. Groundwater (N = 24), lake (N = 29) and stream (N = 20) samples were collected for isotope (δ15N-NO3− and δ18O-NO3−, δ18O-H2O) and hydrogeochemical (major ions and nutrients) determinations, and in the case of surface water, also for biological determinations (chlorophyll-a, fecal coliforms and nitrifying bacteria abundance). Both chemical and isotopic characteristics clearly indicated that denitrification was limited in lakes and streams, while evidence of assimilation in shallow lakes was confirmed. The results suggested that groundwater denitrification plays a role in the nitrate concentration pattern observed in the Pampeano Aquifer. The proportional contribution of nitrate sources to the inflow streams for all years were estimated by using Bayesian isotope mixing models, being ammonium nitrified in the system from soil and fertilizers ~50 - 75 %, sewage/manure ~20 - 40 % and atmospheric deposition ~5 - 15 %. In this sense, agricultural practices seem to have a relevant role in the eutrophication and water quality deterioration for these watersheds. However, limnological, bacterial and algal variables, assessed simultaneously with isotopic tracers, indicated spatio-temporal differences within and between these aquatic ecosystems. In the case of Nahuel Rucá Lake, animal manure was a significant source of nitrogen pollution, in contrast to La Brava Lake. In Los Padres Lake, agricultural practices were considered the main sources of nitrate input to the ecosystem. Fil: Romanelli, Asunción. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Geología de Costas y del Cuaternario. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto de Geología de Costas y del Cuaternario; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Soto, David X.. Katholieke Universiteit Leuven ; Bélgica Fil: Matiatos, Ioannis. International Atomic Energy Agency; Austria Fil: Martinez, Daniel Emilio. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Geología de Costas y del Cuaternario. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto de Geología de Costas y del Cuaternario; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Esquius, Karina Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina

Contamination of groundwater resources from nitrates is a worldwide problem, and Jordan is not an exception. Source identification of contamination is a prerequisite for the protection of water resources and human health. Moreover, investigating the controlling processes of groundwater quality is essential for groundwater sustainability, especially in water-poor countries like Jordan. Environmental isotopes of nitrate (15N and 18O of NO3-) have been applied for the first time in Jordan to assess the origin and cycling of nitrogen pollution in two phreatic aquifer systems: Shallala aquifer (B5/B4) and Amman/Wadi Sir aquifer (B2/A7), hosted in multiple land use area in northern Jordan. The nitrate concentration exceeded the natural background (5–10 mg/L) in all samples, ranging from 14 to 251 mg/l as NO3- in both groundwater systems. About 46% of the samples showed NO3- concentration exceeding the WHO threshold of 50 mg/l in drinking water. Isotope values of nitrate (15N and 18O of NO3-) indicated that manure, urban wastewaters, and nitrified synthetic fertilizers were the main sources of nitrate in the groundwater resources in the study area. SIAR (Stable Isotope Analysis in R) model showed that synthetic fertilizers contributed least to nitrate in groundwater in the study area (average = 3.3%). Nitrified synthetic fertilizers contribution was higher in the B2/A7 aquifer (61%) than in B5/B4 aquifer (49%), whereas anthropogenic organic matter contribution in the B5/B4 (46%) is higher than in the B2/A7 aquifer (36%). Anthropogenic organic matter contribution in the B5/B4 aquifer varied from 20% in the west to 85% in east. Nitrified synthetic fertilizers contribution varied from 10% in the east to 74% in the west. Sustainable management of groundwater resources in the study area necessitates application of best management practices and proper land use planning.

Sixty years of monthly data series of δ18O in precipitation revealed distinctive decadal long-term patterns and break points for the isotope composition of global precipitation. Our results showed that at the multi-decadal scale, δ18O in precipitation displayed changes due to large-scale hydroclimate processes, and particularly, from atmospheric oscillations. Break point and segmented regression trend analyses for δ18O and air temperature revealed influences of the North Atlantic Oscillation (NAO) on the long-term isotope variability for most continental stations in Northern Hemisphere. Long-term trends of δ18O and precipitation amount for Southern Hemisphere stations were mostly indicative of changes in regional hydroclimate processes driven by the larger scale Atlantic and Pacific atmospheric oscillations. For oceanic island stations, the δ18O variations could be described by sinusoidal trends with a ~ 20–40 years-time cycle and δ18O amplitude of ~1–2‰, suggesting these stations have a higher sensitivity to multi-decadal atmospheric circulation. Our findings reveal that coordinated long-term monitoring of stable isotopes in precipitation, coupled with basic meteorological parameters such as air temperature and precipitation amount, are essential to better understand the impact of larger scale hydroclimate variation on regional and local climate variability, and to help interpret long-term hydroclimatic changes of the past, present and future.

Nitrate pollution of surface and groundwater resources is a major worldwide environmental problem. In this study nitrogen isotopes of water, soil, fertilizer and manure were analyzed to determine the pollution sources of nitrate in the groundwater and surface waters of Anthemountas basin. The SIAR model and multivariate statistical analysis were used to determine and quantify the contribution of different NO3 sources in groundwater and surface water. Additionally, a detailed literature overview was carried out to identify the origin of nitrate pollution in surface and ground waters based on ΝΟ3− isotopes. The Piper diagram identified the dominant water types as Mg-Ca-HCO3 and Ca-Mg-HCO3. Nitrate concentrations reached 162.0 mg/L in groundwater and 39.0 mg/L in surface waters. The main source of nitrate in groundwater was mainly nitrified ammonium-based synthetic urea and less nitrate-based synthetic fertilizers. The correlation of SIAR results with other trace elements revealed a negative correlation between hexavalent chromium and a) nitrate-based synthetic fertilizers, and b) nitrification of urea synthetic fertilizers. However, a positive correlation was observed between hexavalent chromium and anthropogenic organic matter. The literature overview provided the basis to design a novel management protocol for nitrate pollution that includes three steps: a) fundamental research, b) management tools, c) monitoring and preservation actions. However, an integrated management protocol for nitrate pollution requires a deeper understanding of the hydro-system and the full participation of local farmers and stakeholders.

Understanding water flow paths and chemical inputs from the catchment to downstream water bodies is essential for determining sensitivity and response of water resources to climatic, land use and environmental changes. Multivariate analysis of hydrochemical data and estimation of water balance using chloride as a chemical tracer, and oxygen and hydrogen stable isotopes in water as physical tracers were applied to explore surface and subsurface hydrological pathways of water, organic and inorganic solutes in the unmanaged mountain catchment of Plesne Lake (Czech Republic). Nitrate 18O and 15N data were used to support hydrochemical data and hydrological pathways identification. Our results showed that even small variations of water transit time had an important influence on chemical composition in surface and subsurface flows. Water flowing through the subsurface weathered granite had mean transit time of about 11 months and a higher content of geogenic ions due to longer contact with bedrock materials. In contrast, surface flows with a transit time of about 5 months had higher concentrations of dissolved organic carbon, total phosphorus and organic nitrogen due to a higher proportion of water originating from the upper, organic-rich soil horizon. Stratification of oxygen isotopes in the water column of the lake were related to subsurface inlets into the lake. Our results were used to describe the transformation of chemical and isotopic signals by surface and subsurface hydrological pathways in the sensitive headwater catchment.

The present study involves an integration of the hydrogeological, hydrochemical and isotopic (both stable and radiogenic) data of the groundwater samples taken from aquifers occurring in the region of northeastern Peloponnesus. Special emphasis has been given to health-related ions and isotopes in relation to the WHO and USEPA guidelines, to highlight the concentrations of compounds (e.g., As and Ba) exceeding the drinking water thresholds. Multivariate statistical analyses, i.e. two principal component analyses (PCA) and one discriminant analysis (DA), combined with conventional hydrochemical methodologies, were applied, with the aim to interpret the spatial variations in the groundwater quality and to identify the main hydrogeochemical factors and human activities responsible for the high ion concentrations and isotopic content in the groundwater analysed. The first PCA resulted in a three component model, which explained approximately 82% of the total variance of the data sets and enabled the identification of the hydrogeological processes responsible for the isotopic content i.e., δ(18)Ο, tritium and (222)Rn. The second PCA, involving the trace element presence in the water samples, revealed a four component model, which explained approximately 89% of the total variance of the data sets, giving more insight into the geochemical and anthropogenic controls on the groundwater composition (e.g., water-rock interaction, hydrothermal activity and agricultural activities). Using discriminant analysis, a four parameter (δ(18)O, (Ca+Mg)/(HCO3+SO4), EC and Cl) discriminant function concerning the (222)Rn content was derived, which favoured a classification of the samples according to the concentration of (222)Rn as (222)Rn-safe (11 Bq·L(-1)) and (222)Rn-contaminated (11 Bq·L(-1)). The selection of radon builds on the fact that this radiogenic isotope has been generally related to increased health risk when consumed.

Nitrate (NO3) is one of the most common contaminants in aquatic environments and groundwater. Nitrate concentrations and environmental isotope data (d15N-NO3 and d18O-NO3) from groundwater of Asopos basin, which has different land-use types, i.e., a large number of industries (e.g., textile, metal processing, food, fertilizers, paint), urban and agricultural areas and livestock breeding facilities, were analyzed to identify the nitrate sources of water contamination and N-biogeochemical transformations. A Bayesian isotope mixing model (SIAR) and multivariate statistical analysis of hydrochemical data were used to estimate the proportional contribution of different NO3 sources and to identify the dominant factors controlling the nitrate content of the groundwater in the region. The comparison of SIAR and Principal Component Analysis showed that wastes originating from urban and industrial zones of the basin are mainly responsible for nitrate contamination of groundwater in these areas. Agricultural fertilizers and manure likely contribute to groundwater contamination away from urban fabric and industrial land-use areas. Soil contribution to nitrate contamination due to organic matter is higher in the south-western part of the area far from the industries and the urban settlements. The present study aims to highlight the use of environmental isotopes combined with multivariate statistical analysis in locating sources of nitrate contamination in groundwater leading to a more effective planning of environmental measures and remediation strategies in river basins and water bodies as defined by the European Water Frame Directive (Directive 2000/60/EC). © 2015 Elsevier B.V.

Summarization: Benchmarking of different numerical models simulating groundwater flow and contaminant mass transport is the aim of the present study, in order to determine criteria for the selection of numerical model(s) that could be better tailored to the needs of a specific region. This analysis aims at evaluating the performance of a finite difference-based numerical model (MODFLOW-ΜΤ3DMS), a finite element-based numerical model (FEFLOW), and a hybrid finite element-finite difference coupling numerical model (Princeton Transport Code-PTC), all developed to simulate groundwater flow and nitrate mass transport in an alluvial aquifer. The evaluation of the models’ performance is assessed based on statistical measures and graphical performance analysis of the model point predictions to the observed values. The outcome of the analysis showed that among the three groundwater simulation models, FEFLOW algorithm exhibited the best performance in simulating both groundwater level and nitrate mass distribution. All simulation algorithms were found to offer different advantages, so in principle the selection of the appropriate model(s) should be done in accordance with the problem’s characteristics and/ or in a complementary way in order to achieve accurate representation of the aquifer system and thus optimal groundwater resources management. Even though the selection of the most suitable groundwater simulation algorithm is case-oriented, however, fractional gross error (FGE) was proven to be a reliable indicator that could be used by modelers to select the most suitable groundwater algorithm based on the available groundwater data. Παρουσιάστηκε στο: Environmental Modeling and Assessment