1,720,962 research outputs found
Interazione tra acquifero superficiale e profondo nella Piana di Tivoli (Roma): Approccio multi-isotopico e modello numerico geochimico
No full textInteraction between shallow and deep groundwater flow systems has been investigated in the Tivoli Plain aquifer system (Rome, Central Italy). During the last decade an intense activity in the travertine quarries in the Acque Albule Basin has caused a significant drop in the water table of the shallow travertine aquifer. As a consequence, subsidence and high instability risk are affecting buildings in this area constructed on top of Holocene sediments composed of mainly silty clay with high level of organic content, which are underlying by travertine deposits. A multi-isotope approach was used to have a better understanding of interactions between shallow and deep aquifers and to improve the knowledge of the hydrogeological conceptual model, which has implication for groundwater management in the Tivoli plain.
Environmental isotopes are largely used for investigation of water origin, residence time and flowpaths (Kendall et al., 1998; Coplen et al., 1999). They are also useful for a better understanding of chemical reactions during water-rock interaction.
A combined hydrogeologic and isotopic investigation using chemical and isotopic tracers such as SO4/Cl, δ18O, δ 2H, 87Sr/86Sr, δ34S, and δ13C was carried out in order to determine the sources of water recharge to the aquifer, the origin of solutes, and the mixing processes, in the Tivoli Plain, a Quaternary basin filled by travertines (Faccenna et al., 2008). The study area is located 30 km East of Rome.
The recharge areas for the shallow groundwater in the travertine aquifer are supposed to be the carbonate ridges of Lucretili and Tiburtini mountains (Capelli et al., 2005: Petitta et al., 2010). The travertine aquifer also receives a contribution of mineralized fluids from a deep aquifer contained in the buried meso-cenozoic carbonates, which are separated from the shallow aquifer by low-permeability volcanic and clayed deposits. Representative samples of the water cycle in Tivoli Plain, which included springs, lakes, deep groundwater and water from the quarries were sampled for chemical and isotope analysis. Base-flow springs are generally saturated or oversaturated with respect to calcite, which explains the travertine formation (Minissale et al., 2002).
A large number of samples including groundwater and surface water were collected in the Acque Albule Basin, while other samples come from the recharge area (S4, S5, S6, P6) (Fig. 3.2). S2 is a spring located out of the Basin, which is directly fed by a deep contribution from buried carbonate bedrock.
Major ion chemistry data showed a groundwater stratification in the travertine aquifer, associated with mixing of the shallow groundwater with discharge mineralized fluids from the deep aquifer, partially enhanced by increasing pumping in the quarries. Results indicate that the hydrochemistry of groundwater in Tivoli Plain and adjacent recharge areas is characterized by a mixing among three end-members:
A. groundwater of recharge area,
B. groundwater of the shallow travertine aquifer (Acque Albule Basin),
C. groundwater of deep carbonate aquifer.
The end-members are represented by three different geochemical facies:
Facies A: Ca – HCO3 type groundwater: TDS (0-0,8 g L-1); SO4 (0-250 mg L-1); DIC (0-7 mmol kg-1); EC (0-2 mS cm-1).
Facies B: Ca – HCO3–SO4 type groundwater: TDS (0,8-2,4 g L-1); SO4 (250-800 mg L-1); DIC (7-16 mmol kg-1); EC (2-3,5 mS cm-1).
Facies C: Ca-Mg – HCO3-SO4 type groundwater: TDS (2,4-3,6 g L-1); SO4 (800-1200 mg L-1); DIC (16-18 mmol kg-1); EC (3,5-4,5 mS cm-1).
A multi-isotope approach (18O, 2H in water, 34S and 18O in sulphate, 13C in DIC and 87Sr/86Sr ratios) has been adopted in the study to obtain a better understanding of interactions between shallow and deep groundwater. The stable isotope data, collected in rain stations at different altitude and in groundwater, suggest the existence of different flowpaths and mixing of shallow groundwater associated with recharge in the Tivoli Plain. Based on seasonal changes in 18O and 2H, the recharge contribution coming from the carbonate ridges to deep groundwater has also been documented.
The 13C data in DIC show a wide range in 13C values that varies between -12.3‰ and +8.6‰. The more depleted 13C values are considered representatives of the recharge area, where a input of soil CO2 occurs during rainfall infiltration mixing with DIC from dissolution of carbonates. Samples from Acque Albule Basin show values between +0.4‰ and +8.6‰, where an input of 13C enriched CO2 is associated with a deep contribution of hydrothermal fluids from the buried carbonate aquifer. The correlations in chapter 4 show two separated sources for DIC in the water samples, with some samples (P5, S6, C4) placed in intermediate position, justified by the influence by mixing processes.
The 34S and 18O data in sulphate also highlight the existence of two different sources for dissolved sulphates: the groundwater collected in Acque Albule Basin have sulphates which can be associated to the Triassic evaporites of the deep aquifer; otherwise, sulphates of secondary origin from the shallow aquifer characterize samples collected in the recharge area. The positive values of 34S (> 10‰) may exclude sulphate reduction as main process in sulphate contribution, especially because it could not explain the high sulphate concentration of the B-C facies. A possible relationship between dissolved sulphates and the occurrence of H2S uprising fluids in the shallow aquifer can be discarded.
Finally, the 87Sr/86Sr data with values ranging between 0,7076 and 0,7082 confirm that the contribution of dissolved solutes is associated with two sources: marine carbonates from the deep aquifer (groundwater influenced by deep flowpaths); continental and volcanic deposits in case of the shallow aquifer (groundwater having not interaction with deep flowpaths).
An Inverse Model carried out with Phreeqc 2.16 by Parkhurst & Appelo (1999) has developed a theoretical geochemical evolution with water-rock interaction processes. According to an inverse mixing model, it is possible to conclude that both dissolution/precipitation and ion exchange processes are the key of geochemical evolution along groundwater flowpath, confirmed also by the calculated mixing between deep and shallow aquifers.
The chemical and isotope tracers provided information for distinguishing different sources of dissolved salts and different groundwater circulation in the Tivoli Plain. The results of this study have improved the hydrogeological conceptual model, which can be summarized as follows:
• the Ca-HCO3 groundwater type represents a flow system fed directly by meteoric water in carbonate ridges of Lucretili and Tiburtini mountains, surrounding the Tivoli Plain. The flow system is subdivided in a shallower one, that fills directly the travertine aquifer of the Acque Albule Basin, and in a deeper one, circulating in the buried carbonate bedrock;
• the Ca-Mg–HCO3-SO4 groundwater type represents a deeper circulation having a contribution of high salinity fluids, uprising from the deep carbonate aquifer, probably related to the Colli Albani volcanic district.
Mixing processes, which characterize the travertine shallow aquifer have been recognized in several water samples, especially inside the quarries area. In this area the mixing between the two components is widely enhanced by the recent occurrence of intense pumping activity (Prestininzi, 2008). The chemistry of samples in this area corresponds to a Ca–HCO3–SO4 groundwater type.
Deep saline fluids rise and mix with recharge water in the shallow aquifer, evolving across dissolution/precipitation and ion exchange processes.
The 18O, 2H and 87Sr/86Sr isotope values confirmed the meteoric origin of the groundwater and the different flowpaths influencing the hydrochemistry composition of groundwater in Tivoli Plain.
The existence of two different sources of groundwater is supported by the results of 34S data in sulphates and 13C data in DIC. Both these two tracers support the existence of mixing in the shallow aquifer, showing intermediate values in the samples which are characterized by relative lower salinity
Interaction between shallow and deep aquifers in the Tivoli Plain (Central Italy) enhanced by groundwater extraction: A multi-isotope approach and geochemical modeling
No full textIn the Tivoli Plain (Rome, Central Italy) the interaction between shallow and deep groundwater flow systems enhanced by groundwater extraction has been investigated using isotopic and chemical tracers. A conceptual model of the groundwater flowpaths has been developed and verified by geochemical modeling. A combined hydrogeochemical and isotopic investigation using ion relationships such as DIC/Cl , Ca/(Ca + Mg)/SO4/(SO4 + HCO3), and environmental isotopes (delta O-18, delta H-2, Sr-87/Sr-86, delta S-34 and delta C-13) was carried out in order to determine the sources of recharge of the aquifer, the origin of solutes and the mixing processes in groundwater of Tivoli Plain. Multivariate statistical methods such as principal component analysis and Cluster analyses have confirmed the existence of different geochemical facies and the role of mixing in the chemical composition of the groundwater. Results indicate that the hydrochemistry of groundwater is characterized by mixing between end-members coming directly from carbonate recharge areas and to groundwater circulating in a deeply buried Meso-Cenozoic carbonate sequence. The travertine aquifer is fed by both flow systems, but a local contribution by direct input in the Plain has also been recognized. The stable isotope data (O-18, H-2, C-13 and S-34) supports the flow system conceptual model inferred from the geochemical data and represents key data to quantify the geochemical mixing in the different groundwaters of the Plain. The results of numerical modeling (PHREEQC) are consistent with the flowpaths derived from the hydrogeochemical conceptual model. The inverse models performed generated the main geochemical processes occurring in the groundwater flow system, which also included mixing. Geochemical and isotope modeling demonstrate an increasing influence of groundwater from the deeply buried aquifer in the travertine aquifer, enhanced by lowering of the travertine aquifer water table due to quarry pumping. (C) 2011 Elsevier Ltd. All rights reserved
Multi-chemical and isotope approach for studying shallow and deep groundwater interaction in an urban area: The case of Tivoli Plain (central Italy)
No full textInteraction between shallow and deep groundwater flow systems has been investigated by the means of chemical and isotopic tracers in the Tivoli Plain aquifer system (Rome, central Italy). During the last decade an intense activity in the travertine quarries in the Acque Albule basin has caused a significant drop in the water table of the shallow travertine aquifer. A multi-isotope approach was used to have a better understanding of interactions between shallow and deep aquifers, and to improve the knowledge of the conceptual hydrogeological model, which has implications for groundwater management in the Tivoli plain. The hydrochemistry of the travertine aquifer is characterized by a mixing between two end-members related, respectively, to groundwater coming directly from outcropping carbonate aquifers and to groundwater circulating in deep buried Meso-Cenozoic carbonate sequences. 18O and l3C isotope tracers are diagnostic for the geochemical mixing definition. Copyright © 2011 IAHS Press
PROSPEZIONI IDROGEOCHIMICHE NELLA PIANA DI TIVOLI: INTERAZIONI TRA ACQUIFERI E INFLUENZA ANTROPICA
No full textIl sito contaminato di interesse nazionale della Bassa Valle del Fiume Chienti (Italia): dal modello idrogeologico concettuale al modello numerico.
No full textIsotope hydrology and geochemical modeling: new insights into the recharge processes and water-rock interactions of a fissured carbonate aquifer (Gran Sasso, central Italy)
No full textThe goal of this paper was to characterize the recharge process and water-rock interactions in a regional homogeneous fractured carbonate aquifer in the Mediterranean environment (Gran Sasso, central Italy) through isotope data (δ2H, δ18O and δ13C-DIC) collected between 2006 and 2010. Samples were collected from the springs of the Gran Sasso aquifer and from the Underground Nuclear Physics Laboratories, located within the aquifer. Additionally, the hydrochemical data and the reference hydrogeological frameworks of previous studies have been used as a starting point for the geochemical modeling. The Gran Sasso aquifer, which is bounded by terrigenous and clastic units acting as aquitards, accommodates a uniquely broad regional groundwater, which feeds springs mainly at its border with high, steady discharge. In total, these springs discharge of more than 18 m3/s. At a local scale for the aquifer core and at a regional scale for the overall aquifer, δ 2H, δ18O and δ13C-DIC isotope data, the geochemical inverse modeling through PHREEQC and the δ13C-DIC fractionation modeling through NETPATH 2.0 show the following. (1) Clear processes of evaporation and related isotope enrichment may be ruled out. (2) Groundwater flow is active and extends to the overall aquifer without clear signs of layering and partitioning. (3) Groundwater flowpaths radiate from the core toward the periphery. (4) In L'Aquila Plain, Gran Sasso groundwater mixes with shallow Quaternary water at a ratio of one half. (5) The main geochemical processes are the dissolution of calcite and dolomite, and in some cases, ion exchange occurs (Mg2+ and SO4 2- release, Ca2+ adsorption). (6) In the less mineralized recharge groundwater, the δ13C-DIC value is influenced by the δ13C-DIC value of rainfall, while in more evolved groundwater, the final δ13C-DIC value is reached by fractionation during the flowpaths, indicating a lengthy interaction with limestone. © 2014 Springer-Verlag Berlin Heidelberg
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
