Knowledge of the hydraulic and geological properties of karst systems is particularly valuable to hydrogeologists because these systems represent an important source of potable water in many countries. However, the high heterogeneity that characterizes karst systems complicates the definition of karst hydrogeological properties, and their estimation involves complex and expensive techniques. In this study, a workflow for karst spring characterization was used to analyze two springs, Nanto spring and Mossano spring, located in the Berici Mountains (NE Italy). Based on the data derived from 4 years of continuous hourly monitoring of discharge, water temperature and specific electrical conductivity, a hydrogeological conceptual model for the monitored springs was proposed. Flow rate measurements, which combined recession curve, flow duration curve and autocorrelation function techniques, were used to evaluate the spring discharge variability. Changes in spring discharge can be related both to the degree of karstification/permeability and to the size of the karst aquifer. Moreover, combining monitored parameters and rainfall—analyzed by the cross-correlation function and VESPA (Vulnerability Estimator for Spring Protection Areas) index approach—permitted assessment of the spring response to recharge and the behavior of the drainage system. Although the responses to the recharge events were quite similar, the two springs showed some differences in terms of the degree of karstification. In fact, Mossano spring showed a more developed karst system than Nanto spring. Three systems (two karsts and one matrix/fractured) are outlined for Mossano spring, while two systems (one karst and one matrix/fractured) are outlined for Nanto spring. La connaissance des propriétés hydrauliques et géologiques des systèmes karstiques est. particulièrement utile pour les hydrogéologues, car ces systèmes constituent des ressources en eau importantes dans de nombreux pays. Cependant, la grande hétérogénéité qui caractérise les systèmes karstiques rend difficile la définition des propriétés hydrogéologiques, et leur estimation implique la mise en œuvre de techniques complexes et onéreuses. Dans cette étude, une méthode de travail pour la caractérisation des sources karstiques a été utilisée pour l’analyse de deux sources (sources Nanto et Mossano), localisées dans les Monts Berici (Nord-Est de l’Italie). Sur la base des données issues de quatre ans de suivi horaire des débits, de la température et de la conductivité électrique de l’eau, un modèle hydrogéologique conceptuel des sources suivies a été proposé. Les mesures de débits, qui combinent les courbes de récession, les courbes de durée d’écoulement et les techniques de fonction d’autocorrélation, ont été utilisées pour évaluer la variabilité du débit des sources. Les changements du débit des sources peuvent être corrélés à la fois au degré de karstification/perméabilité et à la taille du système karstique. De plus, la combinaison des paramètres de suivi avec les données de pluie (analysée avec la fonction de corrélation croisée et l’approche indicielle VESPA - Estimateur de Vulnérabilité pour les Aires de Protection des Sources) a permis d’évaluer la réponse des sources à la recharge et le comportement du système de drainage. Bien que les réponses aux événements de recharge soient quasi similaires, les deux sources présentent certaines différences en termes de degré de karstification. En fait, la source Mossano montre un système karstique plus développé que la source Nanto. Trois systèmes (deux karstiques et un matriciel/fracturé) sont mis en évidence pour la source Mossano, alors que deux systèmes (un karstique et un matriciel/fracturé) caractérisent la source Nanto. El conocimiento de las propiedades hidráulicas y geológicas de los sistemas kársticos es especialmente valioso para los hidrogeólogos, ya que estos sistemas representan una importante fuente de agua potable en muchos países. Sin embargo, la gran heterogeneidad que caracteriza a los sistemas kársticos complica la definición de sus propiedades hidrogeológicas, y su estimación implica técnicas complejas y costosas. En este estudio, se utilizó un flujo de trabajo para la caracterización de manantiales kársticos para analizar dos de ellos, el manantial de Nanto y el manantial de Mossano, situados en las montañas Berici (NE de Italia). Basado en los datos derivados de cuatro años de monitoreo horario continuo de la descarga, temperatura del agua y conductividad eléctrica específica, se propuso un modelo conceptual hidrogeológico para los manantiales monitoreados. Se utilizaron medidas de caudal, que combinaron la curva de recesión, la curva de duración del caudal y técnicas de función de autocorrelación, para evaluar la variabilidad de la descarga de los manantiales. Los cambios en la descarga de los manantiales pueden estar relacionados tanto con el grado de karstificación/permeabilidad como con el tamaño del acuífero kárstico. Además, la combinación de los parámetros monitoreados y la lluvia—analizados por la función de autocorrelación y el enfoque del índice VESPA (Vulnerability Estimator for Spring Protection Areas)—permitió la evaluación de la respuesta del manantial en la recarga y del comportamiento del sistema de drenaje. Aunque las respuestas a los eventos de recarga fueron bastante similares, los dos manantiales mostraron algunas diferencias en términos del grado de karstificación. De hecho, el manantial de Mossano mostró un sistema kárstico más desarrollado que el de Nanto. Tres sistemas (dos kársticos y uno de matriz/fracturado) se perfilan para el manantial Mossano, mientras que dos sistemas (uno kárstico y otro de matriz/fracturado) son descriptos para el manantial Nanto....

This work proposed a novel method to elucidate the controls of As mobility in complex aquifers based on an unsupervised machine learning algorithm, Self‐Organizing Map (SOM) and process‐based geochemical modeling. The approach is tested in the shallow aquifers of the Venetian Alluvial Plain (VAP) near Venice, Italy, where As concentrations seasonally and locally exceed recommended drinking water limits. SOM was fed using information from two geochemical surveys on eight VAP boreholes, and continuous reading of hourly groundwater head levels and weekly geochemical analyses from three VAP boreholes between mid‐October 2017 and end of January 2018. The SOM analysis is consistent with redox‐controlled dissolution‐precipitation hydrous ferric oxides (HFOs) as a key control of As mobility in the aquifer. Dissolved As is positively correlated to Fe and NH₄⁺ and negatively to the oxidizing‐reducing potential (ORP). Negative correlation between As and groundwater head levels suggests a redox control by rainfall‐driven recharge, which adds oxidants to the aquifer while progressively attenuating As. This mechanism is tested using process‐based geochemical modeling, which simulates different transport modalities of oxidants entering the aquifer. Starting from reducing aquifer conditions, the model reproduces correctly the observed ORP and the trends in As and Fe, when the function describing the occurrence of oxidizing events scales according to the temporal occurrence of rainfall events. Heterogeneity can strongly control the local‐scale effectiveness of recharge as a natural As attenuating factor, requiring a different model analysis to be properly assessed to be developed in a follow‐up study.

Stochastic multicomponent reactive transport modeling is a powerful approach to quantify the probability of non-exceedance (PNE) of arsenic (As) critical concentration thresholds in groundwater. The approach is applied to a well-characterized shallow alluvial aquifer near Venice, Italy. Here, As mobility depends primarily on rainfall-controlled redox-dependent precipitation-dissolution of iron hydroxides. A Monte-Carlo analysis based on a calibrated three-dimensional flow and transport model targeted the geochemical initial conditions as the main source of uncertainty of As concentrations in the studied aquifer. It was found that, during 115 simulated days, the fraction of the entire aquifer volume with As > 10 μgL⁻¹ decreased on average from ~43% to ~39% and the average As concentration from ~32 μgL⁻¹ to ~27 μgL⁻¹. Meanwhile, PNE increased from 55% to 60% when 10 μgL⁻¹ was set as target threshold, and from 71% to 78% for 50 μgL⁻¹. The time dependence of As attenuation can be ascribed to the increase of oxidizing conditions during rainfall-dependent aquifer recharge, which causes As sorption on precipitating iron hydroxides. When computing the same statistics for the shallowest 6 m, As attenuation was even more evident. The volume fraction of aquifer with As > 10μgL⁻¹ dropped from 40% to 28% and the average As concentration from 31 μgL⁻¹ to 20 μgL⁻¹, whereas PNE increased from 58% to 70% for As < 10 μgL⁻¹ and from 71% to 86% for As < 50 μgL⁻¹. Thus, the wells screen depth in the aquifer can be a critical aspect when estimating As risk, owing to the depth-dependent relative change in redox conditions during rainfall events.