1,720,986 research outputs found
Mediterranean catchments post-fire hydrogeological behavior and water quality: insights from the Pisano Mount area (Tuscany, Italy)
Full text linkWildfires are recognized as one of the most affecting ecological agents, altering geomorphological processes, hydrologic cycles, and water quality. On average from 50,000 to 65,000 fires occur in Europe every year, burning approximately 500,000 ha of forested areas. Between September 2018 and February 2019 two large wildfires burnt nearly 1,400 ha of forests and farmlands in the Pisano Mount area (northwestern Tuscany). The mountainous morphology of the area linked to the proximity to the sea causes high precipitation variability and intensity. This, joined with low permeability bedrock (mainly quartzites, schists, and phyllites) and with the extensive vegetation coverage, make the study site a hot spot for surface waters analysis. Moreover, burnt catchments are of primary importance in the recharge processes of the groundwater resources of the costal plain, which are exploited by a large number of inhabitants and agricultural facility. Consequently, the present study is aimed at understanding and quantifying the wildfire impacts on the hydrogeological dynamics and water quality in the studied catchments. Such impacts are being evaluated by comparing burnt and unburnt catchments, which were selected to be as similar as possible from geological, morphological, and vegetational perspectives. The multi-parameter selection method involved Principal Component Analysis and Distance analysis on many potentially feasible catchments. A network of automatic monitoring instruments was deployed on site. Five hydraulic sections of the main streams draining the area were monitored for hydraulic level and physico-chemical parameters. Hydrographs analysis was performed to infer differences in hydrogeological dynamics between burnt and unburnt basins. Monthly samples were collected for stream water and groundwater chemical analysis. In addition, four plate lysimeters were installed to sample soil water for its chemical characterization. The chemical analysis involved major anions and cations, trace elements, water isotopes, and organic compounds, to search for chemical perturbation potentially arising from the wildfire. The investigation highlighted various differences between the burnt and unburnt basin, mainly for the surface waters. The streams draining the burnt areas present different hydraulic behaviour and changes in physiochemical parameters in response to rainfall events. Moreover, the yearly variation of physiochemical parameters and chemical characteristics present an higher variance for those streams draining wildfire affected catchments
Soils hydraulic conductivity tests in slopes affected by fire: an example on Pisani Mountains (Tuscany, Italy)
No full textForest fires are responsible for altering the hydrological dynamics and hydraulic properties of soils, including hydraulic conductivity. This affects several processes, including surface runoff, infiltration into the unsaturated zone, leaching and transport of soil chemical components into groundwater. In August 2021 a forest fire burnt 25 hectares of pine tree forest and olive groves in the southern part of the Pisani Mountains (Tuscany, Italy). The objective of the work is to provide a characterization of in-situ hydraulic conductivity values of the soils of a small catchment intersecting the burnt area. To perform rapid in-situ repeatable soil measurements, four replicas of the Di Prima (2015) automatic single ring infiltrometer were built. These infiltrometers are capable of performing autonomous infiltration test thanks to the automated data acquisition system and their water supply system, reducing disturbances of the tested material. The infiltrometric survey allowed for identification of statistically significant differences in soil hydraulic conductivity between vegetational types, and between burnt and unburnt areas. The soil hydraulic conductivity results lower in the burnt pine tree forest compared with the olive groves. The automatic infiltrometers proved to be a repeatable and rapid soil hydraulic properties survey devices also in a rough mountainous environment
Misure di permeabilità dei suoli in un bacino montano interessato da incendio: un esempio sui Monti Pisani (Toscana, Italia).
No full textGli incendi boschivi costituiscono un agente di forte alterazione delle aree montane e sono responsabili di alterazione delle dinamiche idrologiche e delle proprietà idrauliche dei suoli. La permeabilità rappresenta una proprietà di primaria importanza dei suoli, la quale influenza differenti processi, tra cui il deflusso superficiale, l’infiltrazione nella zona insatura e la lisciviazione ed il trasporto dei componenti chimici del suolo verso le acque di falda.
Come noto, la determinazione in situ del coefficiente di permeabilità permette di minimizzare il disturbo del suolo stesso, rispetto a procedure di laboratorio che prevedono il prelievo di campioni. Al fine di ottenere una sufficiente rappresentatività e distribuzione spaziale del coefficiente di permeabilità si rendono necessarie metodologie di misura rapide e il più possibile ripetibili, che possano coprire l’elevata variabilità spaziale delle proprietà dei suoli.
Nell’agosto 2021, un incendio boschivo ha interessato un’area di circa 25 ettari nei Monti Pisani, vicino al paese di Vicopisano (Toscana, Italia), principalmente caratterizzata da bosco di Pinus Pinaster ed olivete terrazzate. Il presente studio si pone come obiettivo una caratterizzazione preliminare dei valori di permeabilità dei suoli delle aree incendiate. Al fine di eseguire prove ripetibili e con alta densità spaziale è stato deciso di usare una tipologia d’infiltrometro e di applicare la metodologia di misura descritte in Di Prima, (2015) . Tale infiltrometro, dotato di sistema automatizzato di acquisizione dei dati, ha permesso di ottenere in tempi rapidi un dataset di misure con elevata copertura spaziale.
Nel presente studio verranno esposti i dati ottenuti ed alcune interpolazioni spaziali degli stessi. I primi risultati hanno evidenziato sia l’alta variabilità spaziale del coefficiente di permeabilità che la maggior capacità di infiltrazione delle aree terrazzate, rispetto alle aree boschive. Inoltre, saranno presentate possibilità di sviluppo miglioramento sia della metodologia che degli strumenti applicati
Moisture sources and climatic effects controlling precipitation stable isotope composition in a western Mediterranean island (Pianosa, Italy)
Full text linkThe Mediterranean basin is indicated as a hot spot of climate change, which is an area whose climate is especially responsive to variations. The insular environment is one of the most threatened by the current climate change, especially in terms of drought events, with serious consequences for water scarcity and water stress. This issue is even enhanced in small islands, whose ecosystems are among more sensitive to climatic changes and water availability. The stable isotope composition of hydrogen (delta 2H) and oxygen (delta 18O) in precipitation is globally recognized as a powerful natural tracer in the water cycle and represents the starting point to investigate hydrological processes. The understanding of the prevailing factors that drive the isotopic variability of precipitation in the Mediterranean is therefore essential to unravel the hydrological processes and to ensure proper and sustainable management of potentially vulnerable resources to climate change. Here, we discuss the results of multi-year isotopic monitoring in the period 2014-2021 of monthly precipitation collected on Pianosa Island (Italy), a small island located in the northern Tyrrhenian (western Mediterranean). The lower slope and intercept of the Local Meteoric Water Line of the island compared to the Global Meteoric Water Line indicated warmer and drier climatic conditions, suggesting the existence of sub-cloud evaporation processes of raindrops during precipitation, especially in summer. The mean delta 18O of precipitation was lower with respect to other sites placed at higher elevation in this Mediterranean region, due to the lack of summer precipitation which were generally enriched in heavy isotopes. Temperature and amount effects may explain part of the delta 18O variability observed at the monthly and seasonal scale. An HYSPLIT-based moisture uptake analysis indicated the area between the western Mediterranean basin, Italy, and the Adriatic Sea as the region that supplied most of the humidity associated with monthly precipitation samples on Pianosa Island. Less moisture was picked from the northwestern areas of Europe, the North Atlantic Ocean, the proximal Atlantic Ocean, the Iberian Peninsula and North Africa. Consistently with the rainout effect, the higher the moisture fraction picked from the more proximal regions, the more positive the delta 18O of precipitation occurring on Pianosa Island; conversely, the higher the percentage of moisture sourced from more distal regions, the more negative the delta 18O. A multiple linear model was proposed to predict the delta 18O of monthly precipitation from temperature, precipitation amount and moisture origin data, which explained 45% of the delta 18O variability. The deuterium excess variability on the island was partly controlled by the local climatic variables, whose effect potentially modifies the original d-excess signature imprinted at the moisture source. No relationship was found between the precipitation deuterium excess and moisture sources, suggesting that more attention should be paid when using the deuterium excess as a tracer of moisture origin, especially in the Mediterranean
MODELLISTICA CONCETTUALE E NUMERICA PER UNA GESTIONE SOSTENIBILE DELL'ACQUIFERO DELL'ALTA-MEDIA PIANURA VENETA
No full textL’obiettivo principale di questa Tesi è stato quello di realizzare un modello matematico di flusso del sistema acquifero dell’Alta-Media Pianura Veneta in stato stazionario, basato su un modello idrogeologico concettuale elaborato mediante un approccio integrato multidisciplinare. La realizzazione del modello concettuale è stata definita, infatti, attraverso un approccio multidisciplinare che ha coinvolto la raccolta e l’elaborazione di dati geologici, idrogeologici, meteo-climatici, nonché di dati geochimici e isotopici. I dati utilizzati derivano da varie reti di monitoraggio, tra cui la rete ETRA S.P.A. (Energia Territorio Risorse Ambientali), la società Sinergeo S.R.L., e la rete ARPAV (Agenzia Regionale per la Protezione Ambientale del Veneto), oltre ai dati raccolti nell’ambito del progetto HydroBrenta. Questo studio ha portato alla definizione dell’assetto idro-strutturale dell’area di studio attraverso la realizzazione di sezioni idrogeologiche e un modello solido 3D utilizzando il software di Modellazione delle Acque Sotterranee (GMS). Sono stati, successivamente, elaborati e analizzati i dati idro-meteoclimatici relativi al periodo di studio, che va dal 2010 al 2022. Questi dati hanno riguardato la temperatura, le precipitazioni mensili e annuali, nonché l’evapotraspirazione reale e potenziale, stimate mediante il metodo empirico di Turc e Thornthwaite. Queste informazioni sono state fondamentali per il calcolo del bilancio idrologico, il quale ha incluso la stima della precipitazione e infiltrazione efficace, oltre al deflusso idrico superficiale nell’area di interesse. Inoltre, sono state analizzate le mappe piezometriche elaborate nel progetto HydroBrenta e sono state individuate le principali componenti di alimentazione mediante l’elaborazione dei dati geochimici e isotopici. È stato infine stimato un bilancio di massa andando a quantificare i valori di portata in ingresso e in uscita della falda idrica sotterranea, quest’ultima calcolata in funzione dei valori di trasmissività medi e del carico idraulico nell’area di interesse, includendo le portate del fiume Brenta e l’utilizzo della risorsa idrica nell’area per scopi idropotabili, agricoli e industriali. Basandosi, sul modello idrogeologico concettuale, è stato sviluppato un modello numerico di flusso in stato stazionario utilizzando il codice di calcolo MODFLOW, il quale ha previsto una serie di operazioni svolte tramite l’interfaccia grafica Groundwater Vistas, versione 8. La fase di implementazione del modello ha riguardato la discretizzazione spaziale del dominio, l’attribuzione delle proprietà idrauliche del sistema acquifero e la definizione delle condizioni iniziali e al contorno. Il modello è stato poi calibrato utilizzando il metodo manuale, noto come “trial and error adjustment”, al fine di migliorare la rappresentatività del modello. Nonostante alcune limitazioni e approssimazioni, soprattutto legate agli emungimenti agricoli e industriali dei pozzi nell’area di studio, per i quali non sono noti i quantitativi emunti, il modello si è dimostrato adeguatamente rappresentativo del sistema acquifero oggetto di studio, fornendo una base solida per futuri studi e gestione delle risorse idriche. Infine, sono state fatte delle simulazioni previsionali per valutare la risposta del sistema acquifero a possibili varianti legati ai cambiamenti globali, come l’aumento dei consumi idrici nell’area di studio. Queste simulazioni hanno consentito di comprendere meglio come il sistema acquifero reagirebbe a tali scenari ipotetici, offrendo una prospettiva importante per la gestione sostenibile delle risorse idriche
Contributo allo sviluppo di un modello numerico di flusso del sistema acquifero dell'Isola di Pianosa (Arcipelago Toscano)
No full textL’obbiettivo principale di questo lavoro di Tesi di Laurea è la creazione di un modello numerico di flusso del sistema acquifero dell’Isola di Pianosa, basato su un solido modello idrogeologico concettuale, definito utilizzando un approccio multidisciplinare che ha preso in considerazione aspetti geologico-stratigrafici, idrogeologici, geofisici, geochimici e meteoclimatici. Nello specifico, particolare importanza è stata rivolta alla costruzione del modello geologico 3D del sistema acquifero stesso.
Per lo sviluppo del modello concettuale sono stati utilizzati i dati provenienti da studi e campagne pregresse, oltre a quelli derivanti da una ulteriore campagna idrogeologica-geochimica effettuata in ottobre 2022 nell’ambito di questo lavoro di tesi. Per la determinazione dell’assetto idrostrutturale e la creazione del modello geologico solido 3D sono stati utilizzati ed elaborati i dati provenienti dalle stratigrafie pregresse disponibili e di un carotaggio continuo recentemente realizzato, le misure di strato ricavate dalla carta geologica CARG, la colonna stratigrafica relativa alla Formazione del Golfo della Botte ricostruita dagli affioramenti lungo la costa occidentale dell’isola e i dati di una campagna geofisica pregressa. Sono stati inoltre elaborati i dati relativi alle misure dei livelli piezometrici, dei parametri fisico-chimici e dati geochimici sia pregressi che recenti, con la creazione di carte piezometriche, diagrammi di classificazione e diagrammi di correlazione. In particolare, a partire da queste elaborazioni, sembrerebbe che la ricarica dell’acquifero superficiale avvenga principalmente per infiltrazione delle acque meteoriche locali, mentre la ricarica degli acquiferi profondi risulterebbe in gran parte legata alla connessione idraulica che esiste tra le calcareniti ospitanti la falda freatica e i conglomerati ospitanti gli acquiferi confinati. I dati geochimici non escludono inoltre un’alimentazione di quest’ultimi da parte di una circolazione profonda a carattere regionale. È stato, quindi, calcolato il bilancio idrico in cui sono state stimate le principali voci in entrata e in uscita dal sistema acquifero (per il periodo 2015-2022). Per la stima delle precipitazioni efficaci sono stati utilizzati i dati di temperatura e precipitazioni misurati direttamente sull’isola, utilizzando il metodo di Thornthwaite per il calcolo dell’evapotraspirazione reale e potenziale. L’infiltrazione efficace è stata stimata considerando il deflusso superficiale nullo. Ulteriore voce in uscita è il volume di acqua emunto dal pozzo PN3, unico pozzo attivo sull’isola, stimata sulla base dei periodi di accensione del pozzo stesso.
Sulla base del modello concettuale elaborato è stato costruito un modello numerico di flusso in stato stazionario del sistema acquifero, utilizzando il codice di calcolo MODFLOW e l’interfaccia grafica Groundwater Vista. La discretizzazione spaziale del dominio e l’assegnazione delle zone di conducibilità idraulica sono stati creati sulla base del modello solido 3D costruito durante la definizione del modello concettuale. Successivamente sono state implementate le condizioni iniziali e le condizioni al contorno. La calibrazione del modello è stata effettuata utilizzando il metodo manuale “trial and error adjustment”, cercando di minimizzare il più possibile il valore dei residui (differenza fra il valore misurato e quello calcolato dal modello). La fase di calibrazione, unitamente all’analisi di sensitività, hanno permesso anche di definire i parametri del modello più “sensibili”, ovvero quei parametri che influenzano maggiormente i risultati del modello. Questi sono risultati le geometrie e la conducibilità idraulica dei livelli acquiferi (calcareniti e conglomerati) e le zone di fratturazione/faglia. Il modello numerico realizzato ha confermato, nel complesso, il modello concettuale elaborato precedentemente mettendo anch’ esso in risalto, all’interno del bilancio idrico restituito dal modello, il processo dell’ingressione marina. Sono state però evidenziate anche quali sono le lacune da dover colmare per poter comprendere maggiormente nel dettaglio il sistema acquifero. Nello specifico è stato visto come la complicata geometria del sistema acquifero (es. le zone a maggior fratturazione) giochino un ruolo fondamentale nell’idrodinamica del sistema stesso e che una maggiore conoscenza di questi aspetti dovrebbe essere necessaria per avere un modello numerico maggiormente rappresentativo. A tal proposito sarebbero necessarie ulteriori indagini di sottosuolo, perforazioni di ulteriori sondaggi o metodi indiretti, per una migliore ricostruzione delle idrostrutture e delle zone di fratturazione, spostandosi anche verso mare per meglio comprendere anche i rapporti acqua dolce/acqua di mare.
The main objective of this thesis work is the creation of a numerical flow model of the Pianosa Island aquifer system, based on a solid conceptual hydrogeological model, defined using a multidisciplinary approach that took into consideration geological-stratigraphic, hydrogeological, geophysical, geochemical and meteoclimatic aspects. Specifically, particular importance was given to the construction of the 3D geological model of the aquifer system itself.
For the development of the conceptual model data were used from previous studies and campaigns and from the hydrogeological-geochemical campaign in which I participated in October 2022. For the determination of the hydro-structural structure and the creation of the 3D solid geological model were used and processed data from the stratigraphies of the deep wells and a piezometer, layer measurements taken from the geological map, the stratigraphic column related to the Gulf of Botte Formation emerging along the west coast of the island and the data of the geophysical campaign carried out by the INGV of Rome in October 2015. Data on measurements of piezometric levels, physico-chemical parameters and previous geochemical data (period 2015-2022) were also processed, with the creation of piezometric charts, classification diagrams and correlation diagrams. In particular, from these elaborations, it would seem that the recharge of the surface aquifer occurs mainly by infiltration of local rainwater, while the recharge of deep aquifers would be largely linked to the hydraulic connection that exists between the calcarenites hosting the groundwater and the conglomerates hosting the confined aquifers. Moreover, geochemical data do not exclude a feeding of the latter by a deep regional circulation. The water balance was then calculated, in which the main entries in and out of the aquifer system were estimated (period 2015-2022). For the estimation of effective precipitation, temperature and precipitation data measured directly on the island were used, using the Thornthwaite method for the calculation of real and potential evapotranspiration. The effective infiltration was estimated considering zero the surface outflow. Further output is the volume of water taken out from the PN3 well, the only active well on the island, estimated on the basis of the periods of ignition of the well itself.
On the basis of the conceptual model developed, a numerical model in steady state flow of the aquifer system was built, using the MODFLOW calculation code and the Groundwater Vista graphical interface. Spatial domain discretization and conductivity zone assignment were created on the basis of the solid 3D model built during the conceptual model definition. After the initial conditions and boundary conditions were implemented. The calibration of the model was carried out using the manual method "trial and error adjustment" trying to minimize as much as possible the value of the residues (difference between the measured value and that calculated by the model). The calibration and sensitivity analysis also allowed to define the most "sensitive" model parameters, those parameters had the most influence on the model’s results. These were the geometries and hydraulic conductivity of aquifer levels (calcarenites and conglomerates) and fracture/fault zones. The numerical model produced has confirmed, on the whole, the conceptual model elaborated previously putting also it in prominence, inside of the returned water balance from the model, the process of the marine ingression. However, the gaps to be filled in order to better understand the aquifer system have also been highlighted. Specifically, it has been seen as the complicated geometry of the aquifer system, such as the fracture zones identified, play a fundamental role in the hydrodynamics of the system itself and that a greater knowledge of these aspects should be necessary to have a more representative numerical model. In this regard, further underground investigations, drilling of further surveys or indirect methods would be necessary for a better reconstruction of hydrostructures and fracture zones, also moving towards the sea to better understand the freshwater/ sea water ratios
Modélisation numérique de la variation saisonnière de la qualité des eaux souterraines de l'aquifère de Magra, Italie
Full text linkL'aquifère de la rivière Magra est la principale source de l'eau potable, de l'industrie et de l'agriculture dans la zone de La Spezia (NW de l'Italie). Toutefois, la nappe souffre d'une forte vulnérabilité aux problèmes de la surexploitation et de la pollution. A cet effet, après l'établissement du modèle conceptuel du système et la définition des conditions aux limites en utilisant, nous avons réalisé une modélisation hydrodynamique et de transport de solutés par le biais du code MODFLOW/GMS7.1. Le modèle est calé en régime permanent puis en transitoire sur la période 2004-2011. Le calage du modèle a montré l'importance des apports de la rivière de Magra dans le bilan de la nappe. Ces apports participent avec 66 % des entrées vers la nappe. En plus, le calage en régime transitoire montre une variation saisonnière de la piézométrie, la différence d'amplitude peut atteindre 2 m dans les zones de captage. Cette variation a été observée également lors de l'analyse de certains éléments chimiques des eaux de la nappe de Magra tels que Cl, SO4 ainsi que pour le total des solides dissous (TDS). Afin de contrôler ce phénomène, nous avons élaboré un modèle de transport par le code MT3DMS/GMS après avoir défini les paramètres et les conditions aux limites relatives au modèle de transport. La dispersivité et la porosité effective ont étés calées et sont respectivement de l'ordre de 4 m et 11-29 %. Les simulations ont montré que le transport dans l'aquifère de Magra est conditionné plutôt par l'advection que par la diffusion-dispersion
A multidisciplinary approach to define the hydrogeological model of aquifer systems in the "Fiume Versilia" catchment and the adjacent coastal plain (Northwest Tuscany, Italy)
No full textThis PhD-research regards a hydrogeological study carried out on important aquifer systems located in the Versilia area, in which high water demand is present and consequently a detailed knowledge of the same systems is necessary to optimize the groundwater resources management. In this scenario a multidisciplinary approach, geological, hydrogeological and hydro-chemical-isotopic has allowed to achieve significant results as regards the fractured/karst aquifer systems in the "Fiume Versilia" catchment and the aquifer systems of the adjacent coastal plain.
Fractured/karst aquifer of the mountain area.
The two main aims of the research regarding these aquifers were: i) to describe and to model the water-rock interaction processes to define a geochemical conceptual model; ii) to individuate the feeding areas of the most important springs by means of the analyses of the main geological structures and hydrogeological/geochemical-isotopic considerations.
The geochemical conceptual model allowed to draw the following considerations:
- The air particulate matter collected reflects the outcropping lithologies in different parts of the study area, but there seems to be no obvious phenomena of interaction between the particles and rainwater, whose chemical composition derives mainly from sea spray;
- Stable water isotopes confirm that groundwaters have a meteoric origin and that the wide range of values found depends essentially on the different average altitude of feeding zone;
- Based on the major dissolved elements of the sampled springs, 3 main chemical facies were identified: Ca-HCO3, Ca-SO4 and Na-Cl. The first two highlight the interaction of water with limestone and carbonate-evaporite rocks, respectively, for a time sufficient to acquire these chemical compositions and to achieve saturation/supersaturation in calcite and dolomite. The Na-Cl groundwaters show a composition not very different from that of rainwater indicating a circulation in rocks containing minerals not very reactive and/or short interaction time with carbonate rocks. These two main types of water-rock interaction are confirmed by the isotopic ratio 13C/12C. In fact, for the first two types (Ca-HCO3 and Ca-SO4 water), 13C values require a significant contribution of carbon derived from dissolution of calcite, while for Na-Cl water, 13C/12C values are consistent with the addition of biogenic CO2 in rainwater;
- As regards the reaction path modeling, the two theoretical trends, which describe the dissolution of a local average rock into a local average rainwater, can explain the chemical characteristics of most springs. Finally, with respect to trace metals the theoretical approaches do not show substantial changes from the initial concentrations in the aqueous solution, suggesting that there is a low input of these chemical components in the aqueous phase during the progressive dissolution of carbonate rock.
In conclusion, comparing the geological and hydrogeological features with the results of the geochemical processing, it is reasonable to assume that: i) the Na-Cl springs are representative of the shallow circuits, with small feeding zones and very low residence times in the aquifer; ii) the Ca-HCO3 and Ca-SO4 springs are representative of relatively deep circuits developed in extensive aquifers with high permeability, like Marmi, dolomitic marbles and Grezzoni. The firsts type of springs were used to obtain the relationship between the 18O/16O ratio and the altitude of rainwater infiltration. In fact taking into account that they drain a small basin and considering the regulator effect of the aquifers, the isotopic compositions of these springs are very similar to the annual average isotopic values of the local meteoric waters. This relationship was than used to evaluate the average altitude of the feeding area of the second type of springs.
Feeding areas were individuated through a multidisciplinary approach using geological, hydrogeological and geochemical-isotopic tools. In particular 17 hydrogeological sections were elaborated in order to define the geometry of the main hydrostructures and to individuate possible groundwater divides. Moreover, in the hydrogeological domain under examination were considered: the injection and recovering points of the tracer tests performed before this research; the zone included between the altitude + 50 m and – 50 m with respect to the average infiltration altitude evaluated by means of isotopic ratios; the possible groundwater divides individuated by means of hydrostructural considerations. All these elements, together with the indications obtained from geochemical processing on the types of rocks mainly involved in water-rock interaction, allowed us to delimit the hydrogeological basins probably drained by the most important springs under study. In addition for each hydrogeological system, a simplified water balance using meteorological data and the effective infiltration coefficients reported in the literature was performed, verifying that the delimited feeding areas are entirely consistent with the flow rate data of the springs.
Aquifer system of the coastal plain
As regards the coastal plain aquifer system, the main object of the study was to define a reliable conceptual model based on a multidisciplinary approach that highlight the main feeding components and the main processes occurring in the system, based on geological, hydrogeological, and geochemical considerations. A secondary purpose was the implementation of a hydrogeological numerical model and a preliminary calibration under steady-state condition.
The first step was the realization of 9 hydrostratigraphic sections to delineate the geometry and thickness of the various hydrogeological complexes constituting the aquifer system. Once delineated the hydrostructural model, all stratigraphic information was re-processed with the “Groundwater Modeling Software” for 3D reconstruction and calculation of the volume and grainsize for each horizon. The hydrostratigraphic elaboration highlights the multilayer type of the aquifer system due to the alternation of sandy and gravelly permeable layers with low and very-low permeability layers consisting of silty and clayey deposits. However the limited thickness and the lack of continuity of the impervious layers allows locally a direct connection between different permeable horizons giving to the system a monolayer character. As evidenced by both water level data and hydrogeochemical data processing, the hydraulic connection between the aquifer horizons is likely present throughout aquifer system, also probably due to the presence of many multiscreening wells.
Taking into account the literature data and the results of pumping test performed during this study, the hydraulic conductivity of the permeable horizons is variable from 10-3 m/s to 10-4 m/s.
Water level contours, elaborated both in wet and dry season, highlight that an important feeding component toward the coastal plain is the groundwater flow from the upper zone of the Versilia River fan. On the base of the piezometric surface morphology and the transmissivity value of 1,4 E-02 m2/sec, deriving from a pumping test performed on May 2010, the flow rate of this component was evaluated to be closed to 0,38 m3/s and 0,18 m3/s, for high level and low level conditions respectively.
Analysing groundwater flow paths, minor inputs toward the coastal plain are individuated on the fans of the secondary rivers and where the limestone complexes of the mountain zone are directly in contact with the permeable horizons of the coastal plain aquifer system.
Two principal piezometric minima, with hydraulic head below sea level, are located in the middle part of the plain and near the shoreline, respectively. The first one is caused by drinking water well pumping, whereas the second one is linkable to artificial drainage of the humid area located in the south-western part of the study zone.
Geochemical data confirm that Ca-HCO3 waters have meteoric origin and shallow circulation. It is likely that their chemical composition is the result of dissolution of calcite, in a limited or relatively limited time, due to the high kinetic of dissolution of this carbonate mineral. The recharge from the mountain provided by low salinity Ca-HCO3 waters is particularly evident from the foothills to the central strip. Samples collected in the coastal strip have Ca-HCO3 composition only at shallow depths (maximum 10 m). Among Ca-HCO3 waters some samples have a high sulphate content due to partial interaction with carbonate-evaporite rocks and/or other reasons. The Na-Cl-HCO3, mix-Cl-HCO3, mix-HCO3 and Na-HCO3 water are located in the coastal strip and especially near of Forte dei Marmi. It should be emphasized that the presence of these waters must be understood as a positive signal, that is an improvement of water quality previously deteriorated by sea water intrusion. Finally, Na-Cl waters (usually found in relatively deep wells, >30m) are located near the coastline and are likely related to sea water intrusion. The wells that have these characteristics are generally 30m deep or more.
The 18O/16O isotopic ratio allowed to identify the different components involved in the aquifer system of the coastal plain. In particular:
i) A component characterized by the low isotopic ratios is recognizable starting from the upper part of the Versilia River fan up to the middle strip of the coastal plain. The relatively large extension of territory in which this component found highlights the importance of this input, in agreement with the indication deriving from piezometric surfaces. The low isotopic ratio is not compatible with a local origin of water but requires an input from the mountain area. Considering the hydrostructural features, a groundwater flow from rock reliefs to the porous aquifer of the plain is unlikely in this zone; consequently the input of water from the mountains is through the Versilia River, as confirmed by water levels;
ii) a further component, even if less important than the last one, is represented by contributions from permeable carbonate rocks, where these are close to the coastal plane, and from other minor alluvial fans, as T.Baccatoio in the southern part and T.Montignoso in the northern part;
iii) a further and significant component is the local rainwater characterized by a specific isotopic ratio. This input is well recognizable in the part of the plain close to the coastline, although its influence on the other input is evident also in the inner part.
Finally, the study of isotopes has contributed to investigate in more detail the sea water intrusion phenomenon occurring both directly and through inflow along stream courses, as well as the relationship between groundwaters and main rivers. Direct marine ingression is evident in wells with depths higher than 25-30 m and located in a strip of about 1 km from the coastal line. The ingression inside the water courses, instead, is particularly evident in the Versilia river where the sea water reaches the intermediate strip (travelling for more than 2 km along the course of the river, with about 15% of mixing). The ingression inside the water course occurs also in the T.Baccatoio/F.Motrone with a maximum distance of about 1 km from the coastline. Finally, for the Fiumetto ditch the ingression is stopped by the Vinciane Port at 500 m from the coastline.
In agreement with stream water level/groundwater head level relationship, geochemical and isotopic features of water show that rivers/streams/ditches are in hydraulic connection with the aquifer almost throughout the coastal plain. Since the Versilia River has an important role in aquifer feeding, a detailed geochemical survey was carried out to better investigate the stream water-groundwater relationship. Obtained results indicate that the river feeds the aquifer from the upper part of the plain up to the middle one (ex-Lago di Porta zone) and in the final stretch of the river course. In the ex-Lago di Porta zone the river is likely not connected with the aquifer.
In conclusion, based on hydrostructural, hydrogeological, and geochemical-isotopic considerations the main input to the aquifer system are:
- an important component from the Versilia River alluvial fan, which is essentially recharged by the river itself;
- a component, less important than the previous one, developed in minor alluvial fans and some carbonate rocks in the foothill strip;
- an important local rainwater infiltration;
- stream water infiltration;
- a sea water component, even if of minor importance, developed both directly from the shoreline to the aquifer and indirectly through of the stream courses.
Based on the above described hydrogeological conceptual model, a numerical flow model was implemented and calibrated under steady state condition. The results of the calibration generally confirm the conceptual model, although in some zones differences between observed and model values are significant and suggest that model refinement is necessary. This is essentially due to the insufficient and not homogeneous distribution of some type of data, as hydraulic parameters and stratigraphic information. Following these possible improvements, a transient flow model and transport model could be implemented also thanks to the amount and quality of data produced during this research.
Lastly, the results of this PhD-research not only are scientifically interesting but can also have practical implications for the protection and the correct management of the groundwater resource. For example, the multidisciplinary approach used for delimiting the hydrogeological basin of some important springs in the mountain area responds to the need to define the protection zones of water resources, as recommended by the European Community normative and the national normative. On the other hand, the conceptual/numerical model obtained for the coastal plain aquifer system represents an important tool for a correct planning and regulation of groundwater exploitation, to preclude a qualitative and quantitative deterioration of this indispensable resource
DEGASSAMENTO DIFFUSO IN ITALIA: contributo alla valutazione del rischio gas nell’area geotermica di Larderello
No full textNell’ambito del progetto V5 (INGV-DPC), denominato “Diffuse Degassing in Italy”, l’Unità di Ricerca del IGG-CNR di Pisa ha il compito di valutare il flusso globale di CO2 emesso in atmosfera dal settore sud-occidentale della Toscana ed in particolare dal campo geotermico di Larderello.
Gli obiettivi principali del progetto sopra citato sono quelli di individuare e mappare le zone caratterizzate da flussi anomali di CO2 dal suolo per creare un archivio di schede in formato elettronico disponibili in rete delle principali manifestazioni gassose presenti nel territorio italiano. La presente tesi di laurea si inserisce nel quadro di queste attività sia per ciò che riguarda l’individuazione di tutte le zone termicamente anomale sia per ciò che concerne lo studio della composizione chimica ed isotopica dei gas emessi dalle principali manifestazioni termali e l’acquisizione di tutte le informazioni che sono necessarie per scopi di protezione civile-gas hazard (ad esempio le relazioni esistenti fra emissione gassosa ed assetto strutturale ed idrogeologico, ecc).
Le attività hanno inizialmente previsto la raccolta di dati di letteratura disponibili sulle manifestazioni note da tempo (ubicazione, composizione chimica e isotopica ecc.). Successivamente la ricerca è stata volta all’individuazione di nuove aree sede di emissione anomala di gas (sia emissioni diffuse che puntuali). Date le peculiari caratteristiche della zona in oggetto (tutto il settore sud-occidentale della Toscana è caratterizzata da un flusso anomalo di calore) è stato deciso di utilizzare inizialmente alcune immagini satellitari per individuare le aree termicamente anomale sulle quali concentrare l’attenzione e approfondire lo studio. Per teli aree sono state utilizzate alcune foto aeree per individuare le relazioni esistenti con la morfologia e per meglio delimitare le aree prive di vegetazione.
Dopo questa fase preliminare sono stati effettuati numerosi e accurati rilievi di terreno per accertarsi dell’effettiva presenza di tali manifestazioni e per quantificare la loro estensione areale. Nell’intera area sono state individuate numerose tipologie di manifestazioni termali: zone di emissione diffusa, fumarole, pozze gorgoglianti e sorgenti calde.
Le informazioni derivanti dall’osservazione delle immagini da satellite e/o aeree, unite a quelle derivanti dai rilievi di terreno, sono state utilizzate per selezionare alcuni siti particolarmente sensibili al rilascio di gas in atmosfera e caratterizzati da una morfologia che può favorire il ristagno al suolo dei gas emessi.
Sulle aree ad emissione diffusa selezionate sono state realizzate direttamente in campagna alcune riprese effettuate con un radiometro IR per meglio delimitare eventuali anomalie termiche locali, alle quali in genere sono associati elevati flussi di vapore e gas.
Successivamente sono state effettuate due campagne di esplorazione geochimica (Novembre 2005 e Luglio 2006) durante le quali sono stati prelevati 26 campioni di acque e 15 campioni di gas. Il doppio campionamento ha lo scopo di individuare eventuali variazioni stagionali delle sorgenti termali mettendo in evidenza dei circuiti idrici a ricarica rapida.
Le analisi chimiche ed isotopiche delle acque e dei gas campionati sono state effettuate presso i laboratori dell’IGG del CNR di Pisa. Per le acque sono stati determinati i contenuti dei costituenti principali (Na, K, Ca, Mg, Alcalinità, SO4, Cl, NO3), alcuni minori (B, Li, SiO2, NH4, F,Al) e i metalli in tracce (Fe, Mg, Zn, Cu, Cr, Cd, Pb, As, Sr, Ni).Per i gas sono stati analizzati i contenuti di CO2, H2S, H2, CH4, CO, N2, Ar, He e O2.
Le acque sono state classificate tramite i classici diagrammi di Langelier-Ludwig e relative sezioni al fine di identificare i tipi chimici principali e l’eventuale esistenza di fenomeni di mescolamento tra le acque stesse; inoltre è stata effettuata l’analisi delle componenti principali e della regressione lineare multipla per l’individuazione delle anomalie di fuga (T, PCO2, B e NH4); sono state applicate delle tecniche geotermometriche sui soluti; ed infine è stato utilizzato un software di calcolo (EQ3/6) per lo studio della speciazione chimica e per la verifica dell’esistenza delle condizioni di equilibrio tra le acque campionate e le principali fasi mineralogiche delle rocce presenti.
Lo studio sui gas ha previsto l’applicazione delle principali tecniche geotermometriche.
Tutte le informazioni raccolte durante le campagne di rilevamento e le successive analisi di laboratorio sono state inserite nelle schede in formato elettronico che sono già disponibili in rete per tutte le unità di ricerca del progetto in esame
Contamination Assessment and Temporal Evolution of Nitrates in the Shallow Aquifer of the Metauro River Plain (Adriatic Sea, Italy) after Remediation Actions
Full text linkOver the last decades, groundwater resources at global level have suffered a significant deterioration due to nitrate pollution, mainly related to the input of agricultural fertilizers, manure, sewage, and untreated urban and industrial effluents. The most impacted waters are those forming surface and shallow reservoirs, which usually play a key role in supplying waters to civil, agricultural, and industrial activities. The terminal portion of the Metauro River plain, located in central Italy along the Adriatic Sea coastline, hosts a strategic phreatic aquifer that, along with the surface water of the Metauro River, supplies water to the local population (i.e., about 60,000 people). This shallow coastal aquifer experiences a long-lasting story of nitrate contamination since the 1970s when the increase in the use of agricultural fertilizers contributed to very high levels of pollution (NO3− > 100 mg/L). This fact prompted the local authorities to carry out remediation actions that involve a pumping system to inject the NO3−-poor waters from the Metauro River course directly into the shallow aquifer. The present work was aimed at defining the contamination of nitrates in this important water resource. The main geochemical characteristics and the temporal evolution of NO3− concentrations (between 2009 and 2020), in the shallow coastal aquifer of the Metauro River plain, were analyzed by means of classical geochemical analyses and multivariate methods accounting for the compositional nature of the data, to assess the efficiency of the in-situ remediation over time
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