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Valenti Rodellas - One of the best experts on this subject based on the ideXlab platform.
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Temporal variations in Porewater fluxes to a coastal lagoon driven by wind waves and changes in lagoon water depths
Journal of Hydrology, 2020Co-Authors: Valenti Rodellas, Aladin Andrisoa, Samuel Meulé, Peter Cook, James Mccallum, Thomas StieglitzAbstract:Porewater fluxes, including fresh groundwater discharge and circulation of surface waters through sediments, are increasingly documented to play an important role in hydrological and biogeochemical cycles of coastal water bodies. In most studies, the magnitude of Porewater fluxes is inferred from geochemical tracers, but a detailed understanding of the underlying physical forces driving these fluxes remains limited. In this study, we evaluate the mechanisms driving Porewater fluxes in the shallow coastal La Palme lagoon (France). We combined measurements of variations of salinity and temperature in the subsurface with 1-dimensional fluid, salt and heat transport models to evaluate the dynamics of Porewater fluxes across the sediment-water interface in response to temporally variable forcings. Two main processes were identified as major drivers of Porewater fluxes: i) temporal variations of lagoon water depths (forcing Porewater fluxes up to 25 cm d−1) and ii) locally-generated wind waves (Porewater fluxes of ~50 cm d−1). These processes operate over different spatial and temporal scales; Wind-driven waves force the shallow circulation of surface lagoon waters through sediments (mostly < 0.2 m), but are restricted to strong wind events (typically lasting for 1–3 days). In contrast, Porewater fluxes driven by variations of lagoon water depths flush a much greater depth of sediment (>1 m). The spatial and temporal scales of driving forces will largely determine the significance of Porewater fluxes, as well as their chemical composition. Thus, an appropriate evaluation of the magnitude of Porewater-driven solute fluxes and their consequences for coastal ecosystems requires a solid and site-specific understanding of the underlying physical forces.
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Temporal variations in Porewater fluxes to a coastal lagoon driven by wind waves and changes in lagoon water depths
Journal of Hydrology, 2020Co-Authors: Valenti Rodellas, Peter G. Cook, James L. Mccallum, Aladin Andrisoa, Samuel Meulé, Thomas StieglitzAbstract:Porewater fluxes, including fresh groundwater discharge and circulation of surface waters through sediments, are increasingly documented to play an important role in hydrological and biogeochemical cycles of coastal water bodies. In most studies, the magnitude of Porewater fluxes is inferred from geochemical tracers, but a detailed understanding of the underlying physical forces driving these fluxes remains limited. In this study, we evaluate the mechanisms driving Porewater fluxes in the shallow coastal La Palme lagoon (France). We combined measurements of variations of salinity and temperature in the subsurface with 1-dimensional fluid, salt and heat transport models to evaluate the dynamics of Porewater fluxes across the sediment-water interface in response to temporally variable forcings. Two main processes were identified as major drivers of Porewater fluxes: i) temporal variations of lagoon water depths (forcing Porewater fluxes up to 25 cm d−1) and ii) locally-generated wind waves (Porewater fluxes of ~50 cm d−1). These processes operate over different spatial and temporal scales; Wind-driven waves force the shallow circulation of surface lagoon waters through sediments (mostly 1 m). The spatial and temporal scales of driving forces will largely determine the significance of Porewater fluxes, as well as their chemical composition. Thus, an appropriate evaluation of the magnitude of Porewater-driven solute fluxes and their consequences for coastal ecosystems requires a solid and site-specific understanding of the underlying physical forces.
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using the radium quartet to quantify submarine groundwater discharge and Porewater exchange
Geochimica et Cosmochimica Acta, 2017Co-Authors: Valenti Rodellas, Jordi Garciaorellana, Giada Trezzi, Pere Masque, Thomas Stieglitz, Henry Bokuniewicz, Kirk J Cochran, Elisa BerdaletAbstract:Abstract The specific ingrowth rates of different radium isotopes make them valuable tracers to distinguish processes occurring at different temporal scales. Here we demonstrate the use of the radium quartet (223Ra, 224Ra, 226Ra and 228Ra) to differentiate flows of submarine groundwater discharge and Porewater exchange to a coastal embayment (Alfacs Bay, NW Mediterranean Sea), based on the assumption that these processes occur on different time scales. In order to evaluate the seasonal dynamics of groundwater and Porewater inputs to the bay, we conducted three seasonal samplings at Alfacs Bay, during which samples for Ra isotopes were collected from bay waters, groundwater springs, Porewaters and irrigation channels. Activities of short-lived Ra isotopes in the bay showed a strong seasonality, (e.g. average 224Ra activities in summer (∼32 dpm 100 L−1) up to 4 times higher than in winter (∼8 dpm 100 L−1)). In contrast, the activities of the long-lived Ra isotopes were fairly constant throughout the year (e.g. activities of 226Ra were ∼16 and ∼14 dpm 100 L−1 in summer and winter, respectively). The relatively short exposure to sediments of recirculation fluxes resulted in Porewaters significantly enriched in short-lived Ra isotopes relative to the long-lived ones (e.g. 224Ra = 1100–1300 dpm 100 L−1; 226Ra = 17–99 dpm 100 L−1), whereas coastal groundwaters were enriched in all the Ra isotopes (e.g. 224Ra = 120–150 dpm 100 L−1; 226Ra = 200–400 dpm 100 L−1). The distinct signatures of different sources allowed us to construct seasonal Ra mass balances to estimate both groundwater discharge, which ranges from (40 ± 60)·103 m3·d−1 in summer to (310 ± 200)·103 m3·d−1 in winter, and Porewater exchange fluxes, ranging from (1200 ± 120)·103 m3·d−1 in summer to (270 ± 40)·103 m3·d−1 in winter. Whereas the seasonal variability of groundwater inputs is likely governed by the terrestrial hydraulic gradient, a qualitative evaluation of the drivers of Porewater exchange suggested that the strong seasonality of the seawater recirculation inputs is likely mediated by seasonal cycles on the activity of benthic infauna. Ra isotopes are thus valuable tracers to differentiate fluxes of both submarine groundwater discharge and Porewater exchange, allowing a more accurate evaluation of the fluxes of freshwater and solutes to coastal ecosystems, as well as their implications for coastal biogeochemical cycles.
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Using the radium quartet to quantify submarine groundwater discharge and Porewater exchange
Geochimica et Cosmochimica Acta, 2017Co-Authors: Valenti Rodellas, Giada Trezzi, Pere Masque, Thomas Stieglitz, Henry Bokuniewicz, Jordi Garcia-orellana, J. Kirk Cochran, Elisa BerdaletAbstract:The specific ingrowth rates of different radium isotopes make them valuable tracers to distinguish processes occurring at different temporal scales. Here we demonstrate the use of the radium quartet (Ra-223, Ra-224, Ra-226 and Ra-228) to differentiate flows of submarine groundwater discharge and Porewater exchange to a coastal embayment (Alfacs Bay, NW Mediterranean Sea), based on the assumption that these processes occur on different time scales. In order to evaluate the seasonal dynamics of groundwater and Porewater inputs to the bay, we conducted three seasonal samplings at Alfacs Bay, during which samples for Ra isotopes were collected from bay waters, groundwater springs, Porewaters and irrigation channels. Activities of short-lived Ra isotopes in the bay showed a strong seasonality, (e.g. average Ra-224 activities in summer (similar to 32 dpm 100 L-1) up to 4 times higher than in winter (similar to 8 dpm 100 L-1)). In contrast, the activities of the long-lived Ra isotopes were fairly constant throughout the year (e.g. activities of Ra-226 were similar to 16 and similar to 14 dpm 100 L-1 in summer and winter, respectively). The relatively short exposure to sediments of recirculation fluxes resulted in Porewaters significantly enriched in short-lived Ra isotopes relative to the long-lived ones (e.g. Ra-224 = 1100-1300 dpm 100 L-1; Ra-226 = 17-99 dpm 100 L-1), whereas coastal groundwaters were enriched in all the Ra isotopes (e.g. 224 Ra = 120-150 dpm 100 L-1; Ra-226 = 200-400 dpm 100 L-1). The distinct signatures of different sources allowed us to construct seasonal Ra mass balances to estimate both groundwater discharge, which ranges from (40 +/- 60).10(3) m(3). d(-1) in summer to (310 +/- 200).10(3) m(3).d(-1) in winter, and Porewater exchange fluxes, ranging from (1200 +/- 120).10(3) m(3).d(-1) in summer to (270 +/- 40).10(3) m(3) .d(-1) in winter. Whereas the seasonal variability of groundwater inputs is likely governed by the terrestrial hydraulic gradient, a qualitative evaluation of the drivers of Porewater exchange suggested that the strong seasonality of the seawater recirculation inputs is likely mediated by seasonal cycles on the activity of benthic infauna. Ra isotopes are thus valuable tracers to differentiate fluxes of both submarine groundwater discharge and Porewater exchange, allowing a more accurate evaluation of the fluxes of freshwater and solutes to coastal ecosystems, as well as their implications for coastal biogeochemical cycles. (C) 2016 Elsevier Ltd. All rights reserved.
Thomas Stieglitz - One of the best experts on this subject based on the ideXlab platform.
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Temporal variations in Porewater fluxes to a coastal lagoon driven by wind waves and changes in lagoon water depths
Journal of Hydrology, 2020Co-Authors: Valenti Rodellas, Aladin Andrisoa, Samuel Meulé, Peter Cook, James Mccallum, Thomas StieglitzAbstract:Porewater fluxes, including fresh groundwater discharge and circulation of surface waters through sediments, are increasingly documented to play an important role in hydrological and biogeochemical cycles of coastal water bodies. In most studies, the magnitude of Porewater fluxes is inferred from geochemical tracers, but a detailed understanding of the underlying physical forces driving these fluxes remains limited. In this study, we evaluate the mechanisms driving Porewater fluxes in the shallow coastal La Palme lagoon (France). We combined measurements of variations of salinity and temperature in the subsurface with 1-dimensional fluid, salt and heat transport models to evaluate the dynamics of Porewater fluxes across the sediment-water interface in response to temporally variable forcings. Two main processes were identified as major drivers of Porewater fluxes: i) temporal variations of lagoon water depths (forcing Porewater fluxes up to 25 cm d−1) and ii) locally-generated wind waves (Porewater fluxes of ~50 cm d−1). These processes operate over different spatial and temporal scales; Wind-driven waves force the shallow circulation of surface lagoon waters through sediments (mostly < 0.2 m), but are restricted to strong wind events (typically lasting for 1–3 days). In contrast, Porewater fluxes driven by variations of lagoon water depths flush a much greater depth of sediment (>1 m). The spatial and temporal scales of driving forces will largely determine the significance of Porewater fluxes, as well as their chemical composition. Thus, an appropriate evaluation of the magnitude of Porewater-driven solute fluxes and their consequences for coastal ecosystems requires a solid and site-specific understanding of the underlying physical forces.
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Temporal variations in Porewater fluxes to a coastal lagoon driven by wind waves and changes in lagoon water depths
Journal of Hydrology, 2020Co-Authors: Valenti Rodellas, Peter G. Cook, James L. Mccallum, Aladin Andrisoa, Samuel Meulé, Thomas StieglitzAbstract:Porewater fluxes, including fresh groundwater discharge and circulation of surface waters through sediments, are increasingly documented to play an important role in hydrological and biogeochemical cycles of coastal water bodies. In most studies, the magnitude of Porewater fluxes is inferred from geochemical tracers, but a detailed understanding of the underlying physical forces driving these fluxes remains limited. In this study, we evaluate the mechanisms driving Porewater fluxes in the shallow coastal La Palme lagoon (France). We combined measurements of variations of salinity and temperature in the subsurface with 1-dimensional fluid, salt and heat transport models to evaluate the dynamics of Porewater fluxes across the sediment-water interface in response to temporally variable forcings. Two main processes were identified as major drivers of Porewater fluxes: i) temporal variations of lagoon water depths (forcing Porewater fluxes up to 25 cm d−1) and ii) locally-generated wind waves (Porewater fluxes of ~50 cm d−1). These processes operate over different spatial and temporal scales; Wind-driven waves force the shallow circulation of surface lagoon waters through sediments (mostly 1 m). The spatial and temporal scales of driving forces will largely determine the significance of Porewater fluxes, as well as their chemical composition. Thus, an appropriate evaluation of the magnitude of Porewater-driven solute fluxes and their consequences for coastal ecosystems requires a solid and site-specific understanding of the underlying physical forces.
Bart Baeyens - One of the best experts on this subject based on the ideXlab platform.
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Porewater chemistry in compacted re saturated mx 80 bentonite
Journal of Contaminant Hydrology, 2003Co-Authors: Michael H Bradbury, Bart BaeyensAbstract:Abstract Bentonites of various types are being investigated in many countries as backfill materials in high-level radioactive waste disposal concepts. Being able to understand the chemistry of the Porewater in compacted bentonite is very important since it is critical to predicting radionuclide solubilities and to the synthesis of sorption data bases, and hence to repository safety studies. In this paper, Porewater compositions in compacted bentonites are calculated, taking into consideration such factors as montmorillonite swelling, semi-permeable membrane effects, very low “free water” volumes, and the highly effective buffering characteristics of the exchangeable cations and the amphoteric edge sites. The former buffer the cation concentrations and the latter fix the pH in the Porewater of a re-saturated bentonite. The above considerations are used in conjunction with previously measured physico-chemical characterisation data on MX-80 powder to calculate Porewater compositions in compacted bentonites. For the MX-80 material specified, the Porewaters calculated for initial dry densities between 1200 and 1600 kg m −3 had relatively high ionic strengths (I ∼0.3 M), similar cation concentrations and a pH equal to 8.0. The Porewaters changed from being Na 2 SO 4 -rich at 1200 kg m −3 to a NaCl/Na 2 SO 4 type water at 1600 kg m −3 .
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Porewater chemistry in compacted re-saturated MX-80 bentonite.
Journal of contaminant hydrology, 2003Co-Authors: Michael H Bradbury, Bart BaeyensAbstract:Bentonites of various types are being investigated in many countries as backfill materials in high-level radioactive waste disposal concepts. Being able to understand the chemistry of the Porewater in compacted bentonite is very important since it is critical to predicting radionuclide solubilities and to the synthesis of sorption data bases, and hence to repository safety studies. In this paper, Porewater compositions in compacted bentonites are calculated, taking into consideration such factors as montmorillonite swelling, semi-permeable membrane effects, very low "free water" volumes, and the highly effective buffering characteristics of the exchangeable cations and the amphoteric edge sites. The former buffer the cation concentrations and the latter fix the pH in the Porewater of a re-saturated bentonite. The above considerations are used in conjunction with previously measured physico-chemical characterisation data on MX-80 powder to calculate Porewater compositions in compacted bentonites. For the MX-80 material specified, the Porewaters calculated for initial dry densities between 1200 and 1600 kg m(-3) had relatively high ionic strengths (I approximately 0.3 M), similar cation concentrations and a pH equal to 8.0. The Porewaters changed from being Na(2)SO(4)-rich at 1200 kg m(-3) to a NaCl/Na(2)SO(4) type water at 1600 kg m(-3).
Yan Liu - One of the best experts on this subject based on the ideXlab platform.
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Salinization of Porewater in a multiple aquitard-aquifer system in Jiangsu coastal plain, China
Hydrogeology Journal, 2017Co-Authors: Xing Liang, Yanian Zhang, Yan Liu, Chen Naijia, Alhassan Abubakari, Menggui JinAbstract:Chemical and isotopic compositions were analyzed in Porewater squeezed from a clayey aquitard in Jiangsu coastal plain, eastern China, to interpret the salinity origin, chemical evolution and water-mass mixing process. A strong geochemical fingerprint was obtained with an aligned Cl/Br ratio of 154 in the salinized aquitard Porewater over a wide Cl− concentration range (396–9,720 mg/L), indicating that Porewater salinity is likely derived from a mixing with old brine with a proportion of less than 20%. Very small contributions of brine exerted limited effects on water stable isotopes. The relationships between Porewater δ18O and δD indicate that shallow and intermediate Porewaters could be original seawater and were subsequently diluted with modern meteoric water, whereas deep Porewaters with depleted stable isotopic values were probably recharged during a cooler period and modified by evaporation and seawater infiltration. The cation–Cl relationship and mineralogy of associated strata indicate that Porewater has been chemically modified by silicate weathering and ion-exchange reactions. 87Sr/86Sr ratios of 0.7094–0.7112 further confirm the input source of silicate minerals. Numerical simulations were used to evaluate the long-term salinity evolution of the deep Porewater. The alternations of boundary conditions (i.e., the third aquifer mixed with brine at approximately 70 ka BP, followed by recharge of glacial meltwater at 20–25 ka BP, and then mixing with Holocene seawater at 7–10 ka BP) are responsible for the shift in Porewater salinity. These timeframes correspond with the results of previous studies on ancient marine transgression-regression in Jiangsu coastal plain.
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Origin and Geochemical Processes of Porewater in Clay-Rich Deposits in the North Jiangsu Coastal Plain, China
Geofluids, 2017Co-Authors: Xing Liang, Menggui Jin, Yan LiuAbstract:The hydrogeochemical and stable isotope compositions of aquitard Porewater samples from three boreholes were investigated to determine the origin, salinization, and hydrochemical evolution of water in the North Jiangsu coastal plain, China. Three Porewater groups were identified based on the water-bearing subsystems. The total dissolved solids (TDS) of Porewater samples highly varied from 0.03 to 26.1 g/L. Molar Cl/Br ratios and δ18O and δ2H data indicate that the source of Group 1 salinized Porewater was the Holocene seawater, whereas Group 3 salinized samples were probably related to the remnant palaeoseawater of the Late Pleistocene. Group 2 samples had low salinity (TDS < 1 g/L) and undetectable Br− concentrations, which were probably recharged during a colder period and without evidence of seawater involvement. The salinized Porewater was likely diluted by freshwater, as evidenced by its depleted isotopes and low salinity relative to standard seawater. The ionic ratios and ionic deltas indicate that considerable water-rock interactions (e.g., cation exchange and mineral weathering) also accounted for the hydrochemical constituents of Porewaters, and cation exchange seems to be more noticeable at low salinity.
Menggui Jin - One of the best experts on this subject based on the ideXlab platform.
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Origin and Evolution of Aquitard Porewater in the Western Coastal Plain of Bohai Bay, China.
Ground water, 2017Co-Authors: Xing Liang, Menggui Jin, Jilong YangAbstract:High-salinity paleowater from low-permeability aquitards in coastal areas can be a major threat to groundwater resources; however, such water has rarely been studied. The chemical and isotopic compositions of Porewater extracted from a 200-m-thick Quaternary sedimentary sequence in the western coastal plain of Bohai Bay, China, were analyzed to investigate the salinity origin and chemical evolution of Porewater in aquitards. Porewater samples derived at depths shallower than 32 m are characterized by Cl-Na type saline water (total dissolved solids [TDS], 10.9-84.3 g/L), whereas those at depths greater than 32 m comprise Cl·SO4 -Na type brackish water (TDS, 2.2-6.3 g/L). Saline Porewater is interpreted as evaporated seawater prior to halite saturation, as evidenced by Cl-Br relationships. Although substantial dilution of saline Porewater with meteoric water is supported by a wider Cl- range and δ2 H-δ18 O covariance, the original marine waters were not completely flushed out. The deeper brackish Porewater is determined to be a mixture of fresher Porewater and brine groundwater and had a component of old brine of less than 10%, as indicated by a mixing model defined using δ2 H and Cl- tracers. Porewater δ2 H-δ18 O relationships and negative deuterium excess ranging from -25.9‰ to -2.9‰ indicate the existence of an arid climate since Late Pleistocene in Tianjin Plain. The aquitard Porewaters were chemically modified through water-rock interactions due to the long residence time.
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Salinization of Porewater in a multiple aquitard-aquifer system in Jiangsu coastal plain, China
Hydrogeology Journal, 2017Co-Authors: Xing Liang, Yanian Zhang, Yan Liu, Chen Naijia, Alhassan Abubakari, Menggui JinAbstract:Chemical and isotopic compositions were analyzed in Porewater squeezed from a clayey aquitard in Jiangsu coastal plain, eastern China, to interpret the salinity origin, chemical evolution and water-mass mixing process. A strong geochemical fingerprint was obtained with an aligned Cl/Br ratio of 154 in the salinized aquitard Porewater over a wide Cl− concentration range (396–9,720 mg/L), indicating that Porewater salinity is likely derived from a mixing with old brine with a proportion of less than 20%. Very small contributions of brine exerted limited effects on water stable isotopes. The relationships between Porewater δ18O and δD indicate that shallow and intermediate Porewaters could be original seawater and were subsequently diluted with modern meteoric water, whereas deep Porewaters with depleted stable isotopic values were probably recharged during a cooler period and modified by evaporation and seawater infiltration. The cation–Cl relationship and mineralogy of associated strata indicate that Porewater has been chemically modified by silicate weathering and ion-exchange reactions. 87Sr/86Sr ratios of 0.7094–0.7112 further confirm the input source of silicate minerals. Numerical simulations were used to evaluate the long-term salinity evolution of the deep Porewater. The alternations of boundary conditions (i.e., the third aquifer mixed with brine at approximately 70 ka BP, followed by recharge of glacial meltwater at 20–25 ka BP, and then mixing with Holocene seawater at 7–10 ka BP) are responsible for the shift in Porewater salinity. These timeframes correspond with the results of previous studies on ancient marine transgression-regression in Jiangsu coastal plain.
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Origin and Geochemical Processes of Porewater in Clay-Rich Deposits in the North Jiangsu Coastal Plain, China
Geofluids, 2017Co-Authors: Xing Liang, Menggui Jin, Yan LiuAbstract:The hydrogeochemical and stable isotope compositions of aquitard Porewater samples from three boreholes were investigated to determine the origin, salinization, and hydrochemical evolution of water in the North Jiangsu coastal plain, China. Three Porewater groups were identified based on the water-bearing subsystems. The total dissolved solids (TDS) of Porewater samples highly varied from 0.03 to 26.1 g/L. Molar Cl/Br ratios and δ18O and δ2H data indicate that the source of Group 1 salinized Porewater was the Holocene seawater, whereas Group 3 salinized samples were probably related to the remnant palaeoseawater of the Late Pleistocene. Group 2 samples had low salinity (TDS < 1 g/L) and undetectable Br− concentrations, which were probably recharged during a colder period and without evidence of seawater involvement. The salinized Porewater was likely diluted by freshwater, as evidenced by its depleted isotopes and low salinity relative to standard seawater. The ionic ratios and ionic deltas indicate that considerable water-rock interactions (e.g., cation exchange and mineral weathering) also accounted for the hydrochemical constituents of Porewaters, and cation exchange seems to be more noticeable at low salinity.
