1,721,119 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Contrasting biogeochemical processes revealed by stable isotopes of H2O, N, C and S in shallow aquifers underlying agricultural lowlands
No full textLowland coastal areas as the Po Delta (Italy) are often intensively cultivated and affected by nitrogen imbalance due to fertilizers leaching to groundwater and export via run-off. To address this issue several agricultural best practices have been proposed, like limiting the amount of fertilizers and increasing soil organic matter content. In this study, groundwater samples were analysed for major ions and stable isotopes of H2O, C, N and S using multi-level sampler (MLS) from two contrasting depositional environments, one representative of alluvial plain (AP) and the other representative of a reclaimed coastal plain (RCP). In each site, controlled plots with different agriculture practice including fertilizers and tillage and compost amendment and no tillage were considered in the study. Tracer test results highlight that recharge water infiltrated at the start of the controlled study has not yet reached the saturated zone, thus current groundwater concentrations are representative of former agricultural practices. Stable isotopes show a clear distinction between different sources of nitrogen in both sites, from synthetic fertilizers to sedimentary nitrogen pool and atmospheric input. The main source of sulphate in groundwater is pyrite and fertilizers. Denitrification, sulphate reduction and methanogenesis were involved in the C, N and S cycle in the RCP site characterized by low hydraulic conductivity sediments and high SOM. These processes were not relevant in the AP site characterized by oxic condition and low SOM, but some evidence of denitrification was found in one of the AP sites. High resolution monitoring was a key tool to identify the different redox zones responsible for N, C and S cycling in these aquifers. This study shows that a clear understanding of transit times in the vadose zone is a key prerequisite to evaluate the effect of controlled agriculture practice on the quality of shallow groundwater.Lowland coastal areas as the Po Delta (Italy) are often intensively cultivated and affected by nitrogen imbalance due to fertilizers leaching to groundwater and export via run-off. To address this issue several agricultural best practices have been proposed, like limiting the amount of fertilizers and increasing soil organic matter content. In this study, groundwater samples were analysed for major ions and stable isotopes of H2O, C, N and S using multi-level sampler (MLS) from two contrasting depositional environments, one representative of alluvial plain (AP) and the other representative of a reclaimed coastal plain (RCP). In each site, controlled plots with different agriculture practice including fertilizers and tillage and compost amendment and no tillage were considered in the study. Tracer test results highlight that recharge water infiltrated at the start of the controlled study has not yet reached the saturated zone, thus current groundwater concentrations are representative of former agricultural practices. Stable isotopes show a clear distinction between different sources of nitrogen in both sites, from synthetic fertilizers to sedimentary nitrogen pool and atmospheric input. The main source of sulphate in groundwater is pyrite and fertilizers. Denitrification, sulphate reduction and methanogenesis were involved in the C, N and S cycle in the RCP site characterized by low hydraulic conductivity sediments and high SOM. These processes were not relevant in the AP site characterized by oxic condition and low SOM, but some evidence of denitrification was found in one of the AP sites. High resolution monitoring was a key tool to identify the different redox zones responsible for N, C and S cycling in these aquifers. This study shows that a clear understanding of transit times in the vadose zone is a key prerequisite to evaluate the effect of controlled agriculture practice on the quality of shallow groundwater. (c) 2019 Elsevier B.V. All rights reserved
Interaction between deep and shallow groundwater systems in areas affected by Quaternary tectonics (Central Italy): A geochemical and isotope approach
No full textHydro- and isotope geochemistry are used to
refine groundwater conceptual models in two areas of
central Italy (Acque Albule Basin and Velino River Valley)
affected by extensional Quaternary tectonics, where deep
and shallow groundwater flow systems are interacting. The
role of geology, of recent deposits filling the plains and of
main tectonic features controlling groundwater flowpaths
and deep-seated fluids emergences are investigated and
discussed. Environmental isotopes (2H and 18O) confirm
recharge in the surrounding carbonate aquifers, and meteoric
origin of both shallow and deep groundwater. Major
ion chemistry indicates a mixing between shallow
Ca-HCO3 groundwater from carbonate aquifers and deep
Ca-HCO3-SO4 groundwater, characterised by higher salinity
and temperature and high concentration in sulphates. Isotopic
composition of dissolved sulphates (d34S and d18O)
and dissolved inorganic carbon (d13C), henceforth indicated
as DIC, are used to verify the presence of different
sources of groundwater, and to validate the mixing model
suggested by the major ion analyses. Sulphate isotope
composition suggests a marine origin for the groundwater
characterised by elevated sulphate concentration, whose
source is present in the deep buried sequences. Carbon
isotope composition confirms the role of a DIC source
associated to CO2 degassing of a deep reservoir. Groundwater
conceptual models are improved underlining the
importance of Plio-Pleistocene sequences filling the tectonic
depression. In the Acque Albule area, the travertine
plateau represents a mixing stratified aquifer, where deep
groundwater contribution is spread into the shallow aquifer.
The alluvial–clastic–lacustrine leaky aquifer of Velino
Valley enables a complete mixing of shallow and deep
groundwater allowing spot-located discharge of deep
groundwater along tectonic patterns and facilitating sulphate
reduction in the lacustrine sediments, explaining
locally the presence of H2S
Dual-flow in karst aquifers toward a steady discharge spring (Presciano, Central Italy): influences on a subsurface groundwater dependent ecosystem and on changes related to post-earthquake hydrodynamics
No full textUse of an integrated methodological approach to assess contaminant fate and transport in a coastal aquifer
No full textField demonstration for the solvent-based sampling method to perform compound-specific isotope analysis on gas-phase VOC
No full textThe solvent-based sampling method for collecting gas-phase volatile organic compounds (VOCs) and conducting compound-specific isotope analysis (CSIA) was deployed during a controlled field study. The solvent-based method used methanol as a sink to accumulate petroleum hydrocarbons during the sampling of soil air and effluent gas. For each gaseous sample collected, carbon isotope analysis (δ13C) was conducted for a selection of five VOCs (benzene, toluene, o-xylene, cyclopentane and octane) emitted by a synthetic hydrocarbon source emplaced in the subsurface. The δ13C values obtained for gaseous VOCs (collected from soil gas and effluent gas) were compared to measurements obtained for the same VOCs present in the source material (none aqueous phase liquid - NAPL) and dissolved in groundwater to evaluate the reliability of the solvent-based sampling method in providing accurate isotope measurements. Since the NAPL source was composed of only 12 VOCs, potential bias related to the analytical procedure (such as co-elution) were avoided, hence emphasizing on field-related bias. This field evaluation demonstrated the capacity of the solvent-based method to produce precise and accurate δ13C measurements. The isotopic discrepancies between the gaseous and the NAPL values were < 1 ‰ for 39 out of the 41 comparison points, thus deemed not statistically different based on a common isotopic uncertainty error of ±0.5 ‰. Moreover, the current field study is the first field study to report δ13C measurements for up to five gas-phase VOCs obtained from the same sample, which appears to be of interest for VOC fate or forensic studies. The possibility to use several VOC isotopic measurements enabled by the sampling method would contribute to strengthen the connection assessment between gaseous VOCs and the suspected emitting source. Accordingly, the field results presented herein support the application of this sampling methodology to conduct CSIA assessment in the frame of VOC vapor studies
Un singolare plume di cloruro di vinile in acquifero confinato: campionamento a basso flusso in sondaggi direct-push e fingerprinting isotopico preliminare.
No full textThe paper deals with an alluvial sandy confined aquifer contaminated by vynil chloride and located in the eastern sector of the Padana plain immediately to the south of the Po river and about 3 km to the north of the city of Ferrara (Northern Italy). Plume investigation followed three steps in temporal succession and with a progressive downscaling: 1) a regional hydrogeological characterization of the aquifer watershed, intended as the whole of the recharge and transmission area of the groundwater reservoir; 2) a hydrochemical survey of existing long-filtered boreholes (wells, piezometers) with a gross definition of the plume; 3) a direct-push drillings based horizontal and vertical characterization of the plume conducted according a dynamic investigation work-plan. The investigated land size has been, respectively, 35, 20 and 6 km2; the plume resulted with a length of 3 km and a maximum width of about 0.5 km. The first step of the investigation, based on the interpretation of collected stratigraphic logs, two piezometric surveys in opposite hydrological conditions and one 3 days pumping test, put in evidence lateral recharge of Po river and the leaky character of the aquifer; the second step, based on 37 boreholes sampling, identified, inside a fully urbanized area, 10 boreholes with VC concentration higher than MAC (3 with values higher than 1000 ppb and one higher than 8000 ppb); the third step, with a total of 15 direct-push drillings down to a maximum of 30 m depth with 3 GW samples for each, put in evidence also the vertical occurrence of the contamination. It has been verified also the effectiveness of GW sampling by a combined use of a inertial pump for collecting the sample preceded by a short term low flow purging by peristaltic pump. The implications for the source definition and plume remediation are also discussed
Use of hydrogeological and geochemical methods to investigate the origin and fate of vinyl chloride in groundwater in an urban environment, Ferrara, Italy.
No full textVinyl chloride (VC) groundwater contamination around the city of Ferrara, Italy, is rather widespread and has created a serious environmental problem in this highly urbanized region. The paper discusses recent data derived from a geochemical and isotopic fingerprinting study carried out at the Pandora site, which is characterized by the existence of a long VC plume, and at the Caretti site where high concentrations of chlorinated compounds, including VC, occur. Data was also collected at an unconfined aquifer under¬neath a major petrochemical plant. The isotopes data show that the unusual negative δ13C values observed in the VC at both sites (Pandora –43 and
–65‰; Caretti: –62 and –72‰) could not be attributed to reductive dechlorination of manufactured primary PCE or TCE. Unusual negative δ13C values for PCE and TCE also characterise the impacted aquifer beneath the petrochemical plant and the Caretti site. Based on the industrial history of the region, which includes production of PVC and chloromethanes (ClM), it is postulated that contamination in the Ferrara region is linked to wastes originating from the production of chloromethanes. The primary organic compound used in ClM production is methane, which is strongly depleted in 13C similar to the values observed in VC, PCE and TCE at the investigated sites. It is also postulated that the contamination is linked to dumping of industrial waste in the abandoned lagoons used by the sugar industry and in clay pits associated with the clay industry
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