In Situ Measurements of Pore Water Diffusion Coefficients Using Tritiated Water

1980 ◽  
Vol 37 (3) ◽  
pp. 545-551 ◽  
Author(s):  
R. H. Hesslein
Keyword(s):  
Pore Water ◽  
Diffusion Coefficients ◽  
Molecular Diffusion ◽  
Solid Phase ◽  
Tritiated Water ◽  
Water Diffusion ◽  
Pore Waters ◽  
Sediment Depth ◽  
Constant Diffusivity

In situ diffusion coefficients in the pore waters of Lake 227 were measured by monitoring the movement of tritiated water into the pore waters. The diffusion coefficients were determined by analytical and numerical modeling of the tritium profiles. During the summer, tritiated water diffuses into the sediment by molecular diffusion and this process is well approximated by a constant diffusivity model. The summer coefficients for diffusion were 1–2 × 10−5 cm2∙s−1 at a water depth of 1.5 m (20 °C) and 0.3–0.8 × 10−6 cm2∙s−1 at 8.75 m (4 °C). During fall overturn, clear evidence was found for enhanced mixing of pore waters to a sediment depth of 10 cm at water depths of 0.75 and 3.85 m. This enhanced mixing was not accompanied by mixing of the solid phase of the sediments.Key words: sediments, pore water, diffusion coefficients, tritium, lake sediments

Early diagenetic processes in Labrador Sea sediments: uranium-isotope geochemistry

1994 ◽  
Vol 31 (1) ◽  
pp. 28-37 ◽  
Author(s):  
C. Gariépy ◽  
B. Ghaleb ◽  
C. Hillaire-Marcel ◽  
A. Mucci ◽  
S. Vallières
Keyword(s):  
Isotopic Composition ◽  
Pore Water ◽  
Iron Reduction ◽  
Molecular Diffusion ◽  
Solid Phase ◽  
Redox Conditions ◽  
Labrador Sea ◽  
Benthic Boundary Layer ◽  
Ionization Mass ◽  
Pore Waters

The concentration and isotopic composition of U dissolved in pore waters from hemipelagic sediments of the Labrador Sea were determined by thermal ionization mass spectrometry in two 30 cm long box cores. The present fluxes of seawater U that diffuses across the sediment–seawater interface are on the order of 2–4 μg/(cm2∙ka). This diffusion imposes decreasing gradients of dissolved U downwards, but the U concentration in pore waters immediately below the surface is much lower than that of open-ocean seawater. This is a primary feature that cannot be explained by carbonate precipitation due to decompression during core retrieval. More likely, it reflects the presence of a stagnant benthic boundary layer above the sediment–water interface, in which molecular diffusion of U is slower than in the overlying turbulently mixed seawater, and (or) of microzones near the interface where U is bioaccumulated. Uranium is adsorbed at depths onto the solid phase in response to changes in the redox conditions within the sediments. In the Labrador Sea, this occurs at the onset of iron reduction and corresponds to a colour transition from brown to grey. Adsorption of U is sufficiently large to alter the initial content and the isotopic composition of U in the detrital component. Accumulation of authigenic U on the solid phase does not proceed at a steady state. This is due to the uneven burial rates of organic matter, which is essential to the establishment of redox conditions appropriate for U reduction, and concomitant stepwise displacement of the redox fronts. This indicates that discrete periods of enhanced primary productivity recurred over the last millenium in the Labrador Sea, inducing U fluxes to the sediments greater than they are now. Measured pore-water U concentrations are greater than the overlying seawater at depth in the cores, despite the fact that none of the conditions necessary to release U under reducing conditions are present in the sediments. More likely, U-bearing particles < 0.45 μm were transferred with the solution phase through the filtering device, artificially increasing the pore-water U content.

Dissolution and recrystallization in modern shelf carbonates: evidence from pore water and solid phase chemistry

1993 ◽  
Vol 344 (1670) ◽  
pp. 27-36 ◽  
Keyword(s):  
Organic Matter ◽  
Pore Water ◽  
Solid Phase ◽  
Chemical Exchange ◽  
Isotope Composition ◽  
Geochemical Data ◽  
Carbonate Sediments ◽  
Pore Waters ◽  
Carbonate Minerals ◽  
Carbonate Production

We present an overview of geochemical data from pore waters and solid phases that clarify earliest diagenetic processes affecting modern, shallow marine carbonate sediments. Acids produced by organic matter decomposition react rapidly with metastable carbonate minerals in pore waters to produce extensive syndepositional dissolution and recrystallization. Stoichiometric relations among pore water solutes suggest that dissolution is related to oxidation of H 2 S which can accumulate in these low-Fe sediments. Sulphide oxidation likely occurs by enhanced diffusion of O 2 mediated by sulphide-oxidizing bacteria which colonize oxic/anoxic interfaces invaginating these intensely bioturbated sediments. Buffering of pore water stable isotopic compositions towards values of bulk sediment and rapid 45 Ca exchange rates during sediment incubations demonstrate that carbonate recrystallization is a significant process. Comparison of average biogenic carbonate production rates with estimated rates of dissolution and recrystallization suggests that over half the gross production is dissolved and/or recrystallized. Thus isotopic and elemental composition of carbonate minerals can experience significant alteration during earliest burial driven by chemical exchange among carbonate minerals and decomposing organic matter. Temporal shifts in palaeo-ocean carbon isotope composition inferred from bulk-rocks may be seriously compromised by facies-dependent differences in dissolution and recrystallization rates.

scholarly journals Diagenetic Processes in Aquaculture Ponds Showing Metal Accumulation on Shrimp Gills

2021 ◽  
Vol 8 ◽  
Author(s):  
Hugues Lemonnier ◽  
Florence Royer ◽  
Florian Caradec ◽  
Etienne Lopez ◽  
Clarisse Hubert ◽  
...  
Keyword(s):  
Pore Water ◽  
Solid Phase ◽  
Acid Volatile Sulfide ◽  
Pore Waters ◽  
Dissolved Metals ◽  
Ecological Processes ◽  
Physico Chemical ◽  
Aquaculture Ponds ◽  
Tropical Aquaculture ◽  
Carbon Acid

The gill is the organ by which many toxic metals are taken up by crustaceans. Iron is known to precipitate at its surface, a phenomenon recently observed in some tropical aquaculture ponds. The present study uses a field approach to understand better the environmental conditions and ecological processes involved in this deposit. Because shrimp are exposed to reduced products originating from organic waste accumulated in the sediment, spatial variation in pH, redox potential and concentrations of dissolved metals in pore water were investigated in these ponds. Total organic carbon, acid volatile sulfide and pyrite were also analyzed in the solid phase. Fe2+ in pore waters showed high spatial variability between ponds and within the same pond with concentrations up to 1,193 μmol l–1. Behaviors of Fe2+, Mn2+ and Co2+ in pore water were similar. Four geochemical environments were identified, based on their physico-chemical characteristics. Highest concentrations for Fe2+, Mn2+ and Co2+ in sediment pore water occurred in slightly acidic and suboxic conditions. When the sediment became anoxic, the H2S produced reacted with Fe2+ and/or Co2+ to form acid volatile sulfide and pyrite. When pH increased, the concentration of free H2S rose up to 736 μmol l–1. With neutral and suboxic conditions, dissolved metal concentrations could be controlled by their precipitation as oxides and hydroxides. The production of pyrite suggested the existence of a possible process of sediment acidification between two crop periods through the production of sulfuric acid. This acidification could increase with pond age and be the cause of the accumulation of reduced metal after 30 years of aquaculture activity.

scholarly journals COMPARISON OF TWO SAMPLING METHODS (CORER AND IN SITU SEDIMENT SIPPER METHODS) FOR THE PORE WATER OF SEDIMENT

2018 ◽  
Vol 29 ◽  
pp. 1-11
Author(s):  
Muswerry Muchtar
Keyword(s):  
Pore Water ◽  
Sampling Methods ◽  
Sampling Techniques ◽  
Sediment Depth ◽  
Sediment Pore Water ◽  
Advantages And Disadvantages ◽  
Phosphate Nitrate ◽  
Vertical Variations

Effect of two sampling techniques (i.e. corer and sipper samplers) of sediment pore water on measured concentrations of phosphate, nitrate and ammonia was examined. The concentrations of nitrate and ammonia in relation to sediment depth (vertical variations) collected by corer and sipper sampler do not show significant differences, while for phosphate concentrations significant differences occurred. The advantages   and disadvantages of both techniques are discussed.

scholarly journals Halogens in pore water of peat bogs – the role of peat decomposition and dissolved organic matter

2006 ◽  
Vol 3 (1) ◽  
pp. 53-64 ◽  
Author(s):  
H. Biester ◽  
D. Selimović ◽  
S. Hemmerich ◽  
M. Petri
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Pore Water ◽  
Peat Bogs ◽  
Pore Waters ◽  
Peat Pore Water ◽  
Icp Ms ◽  
Halogen Species

Abstract. Halogens are strongly enriched in peat and peatlands and such they are one of their largest active terrestrial reservoir. The enrichment of halogens in peat is mainly attributed to the formation of organohalogens and climatically controlled humification processes. However, little is known about release of halogens from the peat substrate and the distribution of halogens in the peat pore water. In this study we have investigated the distribution of chlorine, bromine and iodine in pore water of three pristine peat bogs located in the Magellanic Moorlands, southern Chile. Peat pore waters were collected using a sipping technique, which allows in situ sampling down to a depth greater than 6m. Halogens and halogen species in pore water were determined by ion-chromatography (IC) (chlorine) and IC-ICP-MS (bromine and iodine). Results show that halogen concentrations in pore water are 15–30 times higher than in rainwater. Mean concentrations of chlorine, bromine and iodine in pore water were 7–15 mg l−1, 56–123 μg l−1, and 10–20 μg l−1, which correspond to mean proportions of 10–15%, 1–2.3% and 0.5–2.2% of total concentrations in peat, respectively. Organobromine and organoiodine were the predominant species in pore waters, whereas chlorine in pore water was mostly chloride. Advection and diffusion of halogens were found to be generally low and halogen concentrations appear to reflect release from the peat substrate. Release of bromine and iodine from peat depend on the degree of peat degradation, whereas this relationship is weak for chlorine. Relatively higher release of bromine and iodine was observed in less degraded peat sections, where the release of dissolved organic carbon (DOC) was also the most intensive. It has been concluded that the release of halogenated dissolved organic matter (DOM) is the predominant mechanism of iodine and bromine release from peat.

In situ Raman measurement of HS− and H2S in sediment pore waters and use of the HS−:H2S ratio as an indicator of pore water pH

2016 ◽  
Vol 184 ◽  
pp. 32-42 ◽  
Author(s):  
Edward T. Peltzer ◽  
Xin Zhang ◽  
Peter M. Walz ◽  
Melissa Luna ◽  
Peter G. Brewer
Keyword(s):  
Pore Water ◽  
Pore Waters ◽  
In Situ Raman ◽  
Water Ph ◽  
Raman Measurement

scholarly journals First assessment of the pore water composition of Rupel Clay in the Netherlands and the characterisation of its reactive solids

2016 ◽  
Vol 95 (3) ◽  
pp. 315-335 ◽  
Author(s):  
Thilo Behrends ◽  
Iris van der Veen ◽  
Alwina Hoving ◽  
Jasper Griffioen
Keyword(s):  
The Netherlands ◽  
Pore Water ◽  
Solid Phase ◽  
Clay Material ◽  
Pore Waters ◽  
Calcium Carbonates ◽  
Boom Clay ◽  
Water Composition ◽  
Dilution Experiments ◽  
Chloride Concentrations

AbstractThe Rupel Clay member in the Netherlands largely corresponds to the Boom Formation in Belgium, and this marine, clay-rich deposit is a potential candidate to host radioactive waste disposal facilities. Prediction of the speciation of radionuclides in Rupel Clay pore water and their retardation by interactions with Rupel Clay components requires knowledge about the composition of Rupel Clay pore water, the inventory of reactive solids and understanding of interactions between Rupel Clay and pore water. Here, we studied Rupel Clay material which was obtained from cores collected in the province of Zeeland, the Netherlands, and from drilling cuttings retrieved from a drilling in the province of Limburg, the Netherlands. Pore water was obtained by mechanical squeezing of Rupel Clay material from Zeeland. Additionally, anaerobic dilution experiments were performed in which the clay material was suspended with demineralised water or a 0.1M NaHCO3solution. Solid-phase characterisation included determination of carbon, nitrogen and sulphur contents, measurement of cation exchange capacity (CEC) and sequential extraction of iron phases.In contrast to the pore water in Belgian Boom Clay, pore water collected from the location in Zeeland has a higher salinity, with chloride concentrations corresponding to 70–96% of those in seawater. The high chloride concentrations most likely result from the intrusion of ions from saline waters above the Rupel Clay in Zeeland. Cation exchange during salinisation might account for the observed deficit of marine cations (Na, K, Mg) and excess of Ca concentrations, in comparison with seawater. The measured CEC values at both locations in the Netherlands vary between 7 and 35 meq(100g)−1and are, for most samples, in the range reported for Boom Clay in Belgium (7–30meq(100g)−1).Pore water and solid-phase composition indicate that Rupel Clay from Zeeland has been affected by oxidation of pyrite or other Fe(II)-containing solids. When coupled to the dissolution of calcium carbonates, oxidation of pyrite can account for the elevated sulphate and calcium concentrations measured in some of the pore waters. The relatively low concentrations of pyrite, organic carbon and calcite in the Rupel Clay in Zeeland, in comparison to Limburg, might be an indicator for an oxidation event. Higher contents of dithionite-extractable Fe in Rupel Clay in Zeeland (0.7–2.6mg Fe / g clay) than in Limburg (0.4–0.5mg Fe / g clay) might also be a consequence of the oxidation of Fe(II) minerals. Oxidation in the past could have accompanied partial erosion of Rupel Clay in Zeeland before deposition of the Breda Formation. However, indications are given that oxidation occurred in some of the pore waters after sampling and that partial oxidation of the cores during storage cannot be excluded. Results from dilution experiments substantiate the influence of equilibration with calcium carbonates on pore water composition. Furthermore, removal of dissolved sulphate upon interaction with Rupel Clay has been observed in some dilution experiments, possibly involving microbial sulphate reduction.

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