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The main scope of the study is to evaluate the prognostic accuracy of a one-dimensional convolutional neural network model (1D-CNN), in flood susceptibility assessment, in a selected test site on the island of Euboea, Greece. Logistic regression (LR), Naïve Bayes (NB), gradient boosting (GB), and a deep learning neural network (DLNN) model are the benchmark models used to compare their performance with that of a 1D-CNN model. Remote sensing (RS) techniques are used to collect the necessary flood related data, whereas thirteen flash-flood-related variables were used as predictive variables, such as elevation, slope, plan curvature, profile curvature, topographic wetness index, lithology, silt content, sand content, clay content, distance to faults, and distance to river network. The Weight of Evidence method was applied to calculate the correlation among the flood-related variables and to assign a weight value to each variable class. Regression analysis and multi-collinearity analysis were used to assess collinearity among the flood-related variables, whereas the Shapley Additive explanations method was used to rank the features by importance. The evaluation process involved estimating the predictive ability of all models via classification accuracy, sensitivity, specificity, and area under the success and predictive rate curves (AUC). The outcomes of the analysis confirmed that the 1D-CNN provided a higher accuracy (0.924), followed by LR (0.904) and DLNN (0.899). Overall, 1D-CNNs can be useful tools for analyzing flood susceptibility using remote sensing data, with high accuracy predictions.

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

The Atalanti basin is an intensively cultivated area in central Greece, facing groundwater quality deterioration threats due to natural and anthropogenic-related contamination sources. A combination of statistical and hydrogeochemical techniques, and stable isotope compositions (δ

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.

Nitrate stable isotopes provide information about nitrate contamination and cycling by microbial processes. The Fischa-Dagnitz (Austria) spring and river system in the agricultural catchment of the Vienna basin shows minor annual variance in nitrate concentrations. We measured nitrate isotopes (δ15N, δ18O) in the source spring and river up to the confluence with the Danube River (2019–2020) with chemical and water isotopes to assess mixing and nitrate transformation processes. The Fischa-Dagnitz spring showed almost stable nitrate concentration (3.3 ± 1.0 mg/l as NO3–-N) year-round but surprisingly variable δ15N, δ18O-NO3– values ranging from +5.5 to +11.1‰ and from +0.5 to +8.1‰, respectively. The higher nitrate isotope values in summer were attributed to release of older denitrified water from the spring whose isotope signal was dampened downstream by mixing. A mixing model suggested denitrified groundwater contributed > 50 % of spring discharge at baseflow conditions. The isotopic composition of NO3– in the gaining streams was partly controlled by nitrification during autumn and winter months and assimilation during the growing season resulting in low and high δ15N-NO3– values, respectively. NO3– isotope variation helped disentangle denitrified groundwater inputs and biochemical cycling processes despite minor variation of NO3– concentration.

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.

Exponential human population growth and the rapid co-development of agricultural and industrial sectors have caused a sharp increase of nitrogen loading to rivers and groundwaters worldwide since the 1950s. Reactive nitrogen species (e.g., nitrate, ammonium) are widely distributed compounds in rivers and groundwaters primarily as a result of diverse agricultural activities utilizing N-containing fertilizers and anthropogenic non-point sources, such as the disposal of sewage by centralized and individual systems, animal feeding operations, and elevated atmospheric N deposition. Systematic efforts to identify global patterns in nitrogen loss processes using nitrogen isotopes have mostly targeted soil and plant systems but remain rather limited for surface and/or groundwater systems. Here, synthesized published (4,492) and new data (425) for nitrogen and oxygen isotopes of nitrate in rivers and groundwater generated under an IAEA Coordinated Research Project, which aimed to utilize the application of nitrogen isotope techniques to assess nitrogen pollution in rivers and groundwaters, are presented. Among the two water types, we found that groundwater had higher average nitrate concentrations (~5.0 mg L-1 NO3-N) versus rivers (~2.0 mg L-1 NO3-N), slightly higher δ15N and much higher δ18O (+7.6 ‰ and +4.3 ‰, respectively) compared to rivers (+7.0 ‰ and +1.8 ‰, respectively). Seasonal variations in the concentrations and the isotopic compositions of N-species were found to be temperature related, given that biological activity increases with water temperature. Across a range of Köppen climate types, we found the δ15N and δ18O of NO3 in rivers systematically increased when moving from temperate to tropical climates, following the increase of the average air temperature.

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 (

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 NO

River deltas sustain important ecosystems with rich biodiversity and large biomass, as well as human populations via the availability of water and food sources. Anthropogenic activities, such as urbanization, tourism and agriculture, may pose threats to river deltas. The knowledge of the factors controlling the regional water quality regime in these areas is important for planning sustainable use and management of the water resources. Here, hydrochemical methods and multivariate statistical techniques were combined to investigate the shallow aquifer of the Pinios River (Thessaly) deltaic plain with respect to water quality, hydrogeochemical evolution and interactions between groundwater and surface water bodies. Water quality assessment indicated that most of the river and groundwater samples fully comply with the criteria set by the Drinking Water Directive (98/83/EC). The river is recharged mainly from springs of the Tempi valley and the shallow aquifer, and to a lesser degree from precipitation, throughout the year. The hydrogeochemical characteristics indicated a cation (Ca, Mg, and Na) bicarbonate water type, which evolves to calcium-chloride, sodium-bicarbonate and sodium-chloride water type, in the northern part of the delta. Calcite and dolomite dissolution determined the major ion chemistry, but other processes, such as silicate weathering and cation exchange reactions, also contributed. In the northern part of the plain, the interaction with the deeper aquifer enriched the shallow aquifer with Na and Cl ions. Principal Component Analysis showed that five components (PCs) explain 77% of the total variance of water quality parameters; these are: (1) salinity; (2) water-silicate rocks interaction; (3) hardness due to calcite dissolution, and cation exchange processes; (4) nitrogen pollution; and (5) non-N-related artificial fertilizers. This study demonstrated that the variation of water hydrochemistry in the deltaic plain could be attributed to natural and anthropogenic processes. The interpretation of the PCA results dictated the parameters used for the development of a modified Water Quality Index (WQI), to provide a more comprehensive spatial representation of the water quality of the river delta.

In the urban area of Rio Cuarto groundwater is used for domestic supply. The objective of the current research was to investigate the water dynamics and nitrate contamination in an unconfined aquifer system of Rio Cuarto River basin. Stable isotopes of water (δ18O and δ2H) and nitrate (δ15N–NO3 and δ18O–NO3) were used and combined with conventional chemical techniques and mixing modelling approaches to determine the recharge areas and identify the main origin of nitrate pollution. More enriched water isotope values were recorded in Rio Cuarto city than in the piedmont and mountains indicating local recharge for well batteries 2 and 3. The well battery 1 and the infiltration gallery showed more negative isotopic values, demonstrating a strong influence by the recharge from the piedmont sector (impoverished groundwater). The δ15N–NO3 values and the Bayesian modeling showed that the dominant nitrate contamination source in the urban area is the on-site sanitation systems whereas in the peri-urban area nitrate contamination originates mostly from animal wastes. Both sources supply the aquifer with anthropogenic organic matter (>50%). The highest δ15N–NO3 values were correlated with low dissolved oxygen values, indicating the occurrence of denitrification processes in some places. High NO3 ions in the rural sector were attributed to the application of fertilizers and consequent nitrification processes. The samples from Rio Cuarto river located upstream of the Rio Cuarto City and close to the infiltration gallery showed the highest input from fertilizers (~40%), due to surrounding agricultural fields. The municipal well batteries showed good water quality (freshwater of low to extremely low nitrate concentration) which is linked to the high hydraulic conductivity of the aquifer that increases its capacity to dilute the contaminants. These results will be useful for local water administrators to improve water management.

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

The main objective of this study was to provide a methodological approach in order to identify the spatial patterns of extreme rainfall values for events with return periods of 5 years and to construct a continuous surface that represented the spatial distribution by utilizing support vector machines (SVMs). A genetic algorithm (GA) was implemented to optimize the parameters cost, epsilon, and gamma used in SVM. Several R packages, namely, “e1071,” “GA,” and “raster,” were implemented in R in order to use SVM and GA, whereas a geographic information system was utilized to process spatial data and create the continuous surface. In order to evaluate the developed methodology, the Alfeios water basin, Peloponnesus, Greece, was selected as an appropriate test site. Based on the available intensity–duration–frequency curves concerning 38 meteorological stations located within the research area, the daily extreme rainfall value for a 5-year return period was estimated, which served as the depended variable. The model had as independent variables, the longitude, latitude, elevation, slope angle, and slope aspect of the meteorological stations, the minimum, mean and maximum elevation, the mean slope angle, and the mean slope aspect within a radius of 5 km around the stations, the distance of each station from the coastline. The results of a basic statistical analysis revealed that the elevation variables were highly correlated, with values between 0.83 and 0.93. The results of a basic statistical analysis revealed that the elevation variables were highly correlated, with values between 0.82 and 0.93. Also, the analysis revealed that the most important variables among the 1 variables were longitude, distance from the coastline, mean slope aspect, within a 5-km radius and elevation. The performance of the methodology was evaluated using three standard statistical evaluation criteria, the root mean squared error (RMSE), the r square (r2) and the mean squared error (MSE), applied to the study area, and showed good performance. The outcomes of the SVM-GA model were compared with the results of a multilinear regression analysis. The optimized SVM-GA model achieved higher predictive accuracy, with RMSE, r2, and MSE values of 6.35, 0.63, and 40.31, respectively. The developed SVM-GA model proved to be an excellent alternative spatial interpolation tool, producing highly accurate results, whereas the information and knowledge gained could improve the accuracy of analysis concerning hydrology and hydrogeological models, ground water studies, flood-related applications, and climate analysis studies.

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.

Tacit knowledge in environmental health (EH) responds to the strong need to relate environmental conditions with health effects and implement the ideas produced in the educational framework. Training programs on EH have to educate professionals in dealing with problems where environmental degradation threatens health and to answer the currently increasing volume of question society asks on these issues. Therefore, an EH professional should not only be equipped with theoretical knowledge but also with the “know-how” knowledge (or tacit knowledge) that enables in-depth understanding of the mechanisms that links environment with health and facilitates the prevention of incidents and chronic exposure to pollutants. This was the main driver behind the establishment of the Master’s Degree Program “Environment and Health: Capacity building for decision making” at the Medical School of the National and Kapodistrian University of Athens—Greece (UoA). The program builds on the expertise of academic partners on EH issues. The experience of non-academic professionals is an important part of the program, which is aimed at developing innovative methods of knowledge alliance management, introducing the “tacit knowledge” approach, contributing to understanding and managing health-related environmental problems. In order to evaluate the accomplishment of the program’s objectives, a questionnaire was completed by current MSc holders. The program impact regarding its tacit knowledge content was highly regarded (>80.0 %) by the alumni. This adds to the evidence-based strength of tacit knowledge, which is increasingly profiled as a mandatory element of EH academic programs. A SWOT analysis discussion puts the assessment of tacit knowledge in a wider context.

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.

Η παρούσα διδακτορική διατριβή είχε ως βασικό στόχο τη σύζευξη των αποτελεσμάτων της ισοτοπικής σύστασης των υδάτων της χερσονήσου της Αργολίδας με τις υδρογεωλογικές συνθήκες που διαμορφώνονται στην περιοχή αυτή και αντιστρόφως. Συγκεκριμένα, εξετάστηκε το τμήμα που εκτείνεται νότια της νοητής γραμμής Νέα Επίδαυρος – Τολό το οποίο χαρακτηρίζεται από πολύπλοκη γεωλογική δομή, από αλματώδη τουριστική – παραθεριστική ανάπτυξη, από έλλειψη υδατικών πόρων και από το ότι οι παράκτιοι υδροφορείς (Ίρια, Τολό, Κρανίδι, Ερμιόνη, Γαλατάς κ.α.) έχουν υποστεί έντονη υφαλμύρινση. Η έκταση της ερευνηθείσας περιοχής ξεπερνάει τα 1300Km2 και οι σημαντικότεροι ορεινοί όγκοι τους οποίους φιλοξενεί και στους οποίους αναπτύσσεται υδροφορία είναι το όρος «Αραχναίο» (1200m), η οροσειρά των «Αδερών» (726m) και το όρος «Δίδυμα» (1110m). Η μελέτη των υδρογεωλογικών συνθηκών αρχικά περιελάμβανε τον εντοπισμό και την απογραφή των θέσεων εκφόρτισης του υπόγειου νερού στη χερσόνησο με στόχο την εξέταση του μηχανισμού λειτουργίας αυτών. Αξίζει να σημειωθεί ότι οι περισσότερες από τις θέσεις πηγαίων εκφορτίσεων δεν είχαν απογραφεί επίσημα και ως εκ τούτου τα διαθέσιμα υδρογεωλογικά δεδομένα από προηγούμενους μελετητές ήταν ελάχιστα έως ανύπαρκτα. Η προσέγγιση που έγινε αφορούσε στη γεωλογική χαρτογράφηση των περιοχών σε κλίμακα 1/5000 με τη βοήθεια της οποίας δόθηκαν απαντήσεις σχετικά με την παρουσία και τον τρόπο λειτουργίας των πηγαίων εκφορτίσεων. Στη συνέχεια, εξεταστήκαν επισταμένως τα υδροχημικά χαρακτηριστικά του υπόγειου νερού στις θέσεις ενδιαφέροντος τα οποία έδωσαν τη δυνατότητα εξαγωγής συμπερασμάτων που συνδέονται με την κίνηση του υπόγειου νερού και τις αντιδράσεις που λαμβάνουν χώρα από την επαφή του υπόγειου νερού με τα πετρώματα μέχρι τη θέση της πηγαίας εκδήλωσής του. Το δεύτερο μέρος της ερευνητικής δραστηριότητας εστιάστηκε στην εφαρμογή των ισοτοπικών μεθόδων στην επίλυση επιμέρους υδρογεωλογικών ζητημάτων στα οποία δύσκολα δίνεται απάντηση μέσα από τις κλασσικές μεθόδους έρευνας. Έτσι, η συμβολή της παρούσας εργασίας έγκειται στην εμβάθυνση σε θέματα Ισοτοπικής Υδρολογίας σταθερών και ραδιενεργών ισοτόπων και στην προσπάθεια εφαρμογής των μεθόδων αυτών σε μια περιοχή του ελληνικού χώρου, όπως είναι η χερσόνησος της Αργολίδας. Αν και το επιστημονικό πεδίο της Ισοτοπικής Υδρολογίας είναι γνωστό σε παγκόσμια κλίμακα από τις τα τέλη της δεκαετίας του 1950, στην Ελλάδα δεν βρήκε την ανταπόκριση που του αναλογεί. Η συγκεκριμένη διδακτορική διατριβή προσπαθεί να προσεγγίσει με συστηματικό τρόπο και όχι επιδερμικά τα ισοτοπικά χαρακτηριστικά της περιοχής μελέτης δίνοντας έτσι την ευκαιρία ανάδειξης των δυνατοτήτων αλλά και της προοπτικής που μπορούν να έχουν οι εν λόγω μέθοδοι και στον ελληνικό χώρο. Η σημασία της εφαρμογής των σταθερών και ραδιενεργών ισοτόπων στην υδρογεωλογία εκφράστηκε από πρωτοπόρους ερευνητές όπως οι: H. Craig, A.O. Nier, W. Dansgaard, S. Epstein, E. Eriksson, I. Friedman, W.F. Libby, K.O. Munnich, E. Tongiorgi και J.C. Vogel, ενώ ο Διεθνής Οργανισμός Ατομικής Ενέργειας συνέβαλλε προς την κατεύθυνση αυτή με τη δημιουργία ενός ανεξάρτητου τομέα Ισοτοπικής Υδρολογίας στη Βιέννη το 1958. .....................................

Η χρονική μεταβολή των υδροχημικών παραμέτρων των υπόγειων νερών αποτελεί ένα χρήσιμο εργαλείο για την ερμηνεία της κυκλοφορίας του νερού μέσα σε λιθολογικά διαφορετικούς γεωλογικούς σχηματισμούς στην ανατολική Πελοπόννησο. Στην παρούσα μελέτη, εξετάστηκαν οι χρονικές διακυμάνσεις διαφόρων φυσικών- χημικών παραμέτρων του υπόγειου νερού, όπως η ηλεκτρική αγωγιμότητα, η μερική πίεση του CO2, ο δείκτης κορεσμού σε ασβεστίτη προκειμένου να δώσουν πληροφορίες σχετικά με τη φύση του γεωλογικού σχηματισμού, το χρόνο παραμονής των υπογείων υδάτων, καθώς και το είδος της κυκλοφορίας του νερού μέσα στα διάφορα υδρογεωλογικά συστήματα. Ταυτόχρονα, προσδιορίστηκαν οι χρονικές μεταβολές των σταθερών ισοτόπων (δ18Ο) με στόχο την περαιτέρω υποστήριξη των κατά τη διάρκεια τριών ετών προσδιορίστηκαν για ανεξάρτητες πηγές που εντοπίζονται στο γεωλογικό περιβάλλον της χερσονήσου της Αργολίδας, η οποία συνίσταται ως επί το πλείστον από ανθρακικούς (καρστικοποιημένους κατά θέσεις), οφιολιθικούς και φλυσχικούς σχηματισμούς. Για τη μελέτη της χρονικής διακύμανσης των παραμέτρων προσδιορίστηκε επίσης ο συντελεστής μεταβλητότητας ο οποίος χρησιμοποιείται για να διαπιστωθεί αν η ροή του υπόγειου νερού είναι διάχυτης μορφής ή/και λαμβάνει χώρα μέσα σε αγωγούς. Τιμές του συντελεστή μεταβλητότητας μικρότερες από 5% θεωρούνται ενδεικτικές της ροής διάχυτης μορφής και, συνεπώς, ενός μεγαλύτερου χρόνου παραμονής του νερού στο υπέδαφος, ενώ οι υψηλότερες τιμές του συντελεστή μεταβλητότητας συνδέονται με υψηλότερης ταχύτητας ροή. Ωστόσο, η ανάλυση των ισοτοπικών και όλων των υδροχημικών παραμέτρων σε συνδυασμό με επιτόπου παρατηρήσεις έδειξε ότι μια πηγή μπορεί να τροφοδοτείται από ένα σύστημα ροής διάχυτης μορφής, ακόμα και αν εμφανίζει έναν υψηλό συντελεστή μεταβλητότητας., The temporal variation of groundwater hydrochemistry has been used to support observations on the nature of groundwater circulation inside geological terrains of various lithological formations in Eastern Peloponnesus. In the present study, variations in groundwater physical-chemical properties such as electric conductivity, CO2 partial pressure, and calcite saturation index were used to give indications with regard to the nature of the geological formation, the groundwater residence time, and the mode of water circulation inside the hydrogeological systems. Additional isotopic values (δ18Ο) were defined in order to support the aforementioned objectives. The seasonal variations of these properties during three years of monitoring were determined for individual springs appearing in the geological setting of Argolis peninsula, which is mostly composed of carbonate (karstificated in places), ophiolitic and flysch formations. The variation of the parameters was also approached by calculating the coefficient of variation used to detect whether the groundwater flow is of diffuse or/and conduit type. Coefficient of variation values of less than 5% were considered as indicative of the diffuse flow type and therefore a long contact residence time, while higher values were associated with fast-flowing water. However, the isotopic measurements and the overall hydrochemical analysis combined with in situ observations, related to the flow characteristics of the springs, revealed that a spring can be fed by a common diffuse type system although it shows a rather high coefficient of variation.

The present study examines the isotopic and hydrochemical composition of 18 inland spring waters and 3 coastal karstic spring waters, covering the period between October 2005 and March 2008. The stable isotopes ((18)O, (2)H) processing has revealed the absence of significant evaporation phenomena and that the origin of fresh water samples is meteoric. Using (18)O values in rainfall waters, an average line of isotopic depletion with altitude has been constructed, extracting a rate of-0.45‰/100 m as typical for the study area. Furthermore, the mean altitude of recharge of the springs has been estimated by plotting the groundwater sampling points on a δ(18)O versus altitude diagram. Hydrochemistry results have shown that the dissolution of carbonate, flysch and ophiolitic formations defines the hydrochemical characteristics of groundwater. Moreover, seawater intrusion in the coastal area is significantly high, causing the water in the three karstic springs to be brackish.

In the present study, the isotopic composition (δ18Ο) of several spring waters in Argolis peninsula is examined. The use of the specific isotope aimed at the determination of the altitude of recharge areas, while the credibility of the extracted results was verified by in situ geological observations. The applied methodology included the construction of a linear diagram which correlates the stable isotopic values (δ18Ο) in meteoric waters and the altitude. Isotopic data, concerning meteoric waters, came from: a) rain gauge stations of GNIP network (IAEA/WMO), b) rain tanks and selected wells located in Mt. Arachnaio, c) improvised rain collectors which were put in several sites in the peninsula. A decrease of 0.45‰ δ18Ο per 100m altitude was determined. The average isotopic composition of the examined springs, as far as δ18Ο is concerned, resulted from 14 sampling periods between October 2005 and March 2008. This 18O-content of spring waters was used to derive the recharge area and consequently to evaluate the mechanism of water renewal.

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