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 Benthic fluxes of dissolved organic nitrogen in the Lower St. Lawrence Estuary and implications for selective organic matter degradation

2013 ◽  
Vol 10 (5) ◽  
pp. 7917-7952
Author(s):  
M. Alkhatib ◽  
P. A. del Giorgio ◽  
Y. Gelinas ◽  
M. F. Lehmann
Keyword(s):  
Organic Matter ◽  
Pore Water ◽  
Dissolved Organic Nitrogen ◽  
Organic Nitrogen ◽  
Bottom Water ◽  
Estuarine Sediments ◽  
Pore Waters ◽  
Lower Estuary ◽  
Lawrence Estuary ◽  
St Lawrence Estuary

Abstract. The distribution of dissolved organic nitrogen (DON) and carbon (DOC) in sediment pore waters was determined at nine locations along the St. Lawrence Estuary and in the Gulf of St. Lawrence. The study area is characterized by gradients in the sedimentary particulate organic matter (POM) reactivity, bottom water oxygen concentrations, as well as benthic respiration rates. Based on pore water profiles we estimated the benthic diffusive fluxes of DON and DOC. Our results show that DON fluxed out of the sediments at significant rates (110 to 430 μmol m−2 d−1). DON fluxes were positively correlated with sedimentary POM reactivity and sediment oxygen exposure time (OET), suggesting direct links between POM quality, aerobic remineralization and the release of DON to the water column. DON fluxes were on the order of 30% to 64% of the total benthic inorganic fixed N loss due to denitrification, and often exceeded the diffusive nitrate fluxes into the sediments. Hence they represented a large fraction of the total benthic N exchange. This result is particularly important in light of the fact that DON fluxes are usually not accounted for in estuarine and coastal zone nutrient budgets. The ratio of the DON to nitrate flux increased from 0.6 in the Lower Estuary to 1.5 in the Gulf. In contrast to DON, DOC fluxes did not show any significant spatial variation along the Laurentian Channel (LC) between the Estuary and the Gulf (2100 ± 100μmol m−2 d−1), suggesting that production and consumption of labile DOC components proceed at similar rates, irrespective of the overall benthic characteristics and the reactivity of POM. As a consequence, the molar C/N ratio of dissolved organic matter (DOM) in pore water and the overlying bottom water varied significantly along the transect, with lowest C/N in the Lower Estuary (5–6) and highest C/N (> 10) in the Gulf. We observed large differences between the C/N of pore water DOM with respect to POM, and the degree of the C– versus –N element partitioning seems to be linked to POM reactivity and/or redox conditions in the sediment pore waters. Our results thus highlight the variable effects selective OM degradation and preservation can have on bulk sedimentary C/N ratios, decoupling the primary source C/N signatures from those in sedimentary archives. Our study further underscores that the role of estuarine sediments as efficient sinks of bioavailable nitrogen is strongly influenced by the release of DON during early diagenetic reactions, and that DON fluxes from continental margin sediments represent an important internal source of N to the ocean.

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.

Biogeochemical carbon transformations in a drained coastal peatland of the southern Baltic Sea: An isotope and trace element perspective

2021 ◽  
Author(s):  
Anna-Kathrina Jenner ◽  
Iris Schmiedinger ◽  
Jens Kallmeyer ◽  
Cordula Gutekunst ◽  
Gerald Jurasinski ◽  
...  
Keyword(s):  
Organic Matter ◽  
Trace Metals ◽  
Baltic Sea ◽  
Pore Water ◽  
Research Training ◽  
Isotope Composition ◽  
Carbon Mineralization ◽  
Training Group ◽  
Iron Cycling ◽  
Coast Line

<p>Peatlands serve as important ecosystems since they store a substantial fraction of global soil carbon. Through draining the internal biogeochemical processes may be changed impacting the transformation of stored carbon and plant material. Pristine peatlands are primarily associated with methanogenic and iron-cycling conditions, however, minor sulfur cycling may contribute to carbon mineralization in these ecosystems depending on the amount of atmospheric sulfur deposition and accumulation. In near coastal peatlands the element budget may be altered through natural or artificial flooding by brackish/marine waters. When introducing sulfate-bearing solutions, the concentrations of electron acceptors for anaerobic mineralization or organic matter increase when compared to fresh water conditions. The investigated area is planned to be flooded by Baltic Sea coastal waters in the near future.</p><p>Here we present results from a study from a drained peatland located in the southern part of the Baltic Sea. In the past the area was agriculturally used as grassland. Soil cores were retrieved along a transect perpendicular to the coast line for (isotope) biogeochemical analyses of pore water and solid phases. Analyses included the CNS composition of soils, and dissolved major elements, nutrients, sulphide, trace metals and stable isotopes of water, DIC, and sulfate (H, O, C, S). Furthermore, acid-extractions of metals were carried out to identify zones of dissolution and formation of authigenic phases. For quantification of microbial sulphate reduction rates (SRR) additional cores were retrieved and SRR were measured in whole-core incubations.<span> </span></p><p>The pore water isotopic composition is close to the local meteoric water line at the German Baltic Seas coast line. Concentration and stable isotope composition of DIC indicate mineralization of C3 type organic matter. Pore water trace metals content indicates the importance of anaerobic mineralization for release of metals into the pore and surface waters.</p><p> </p><p>Acknowledgement: This study is supported by the DFG research training group BALTIC TRANSCOAST and Leibniz IOW.</p>

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.

scholarly journals Small-Scale Geochemical Heterogeneities and Seasonal Variation of Iron and Sulfide in Salt Marshes Revealed by Two-Dimensional Sensors

2021 ◽  
Vol 9 ◽  
Author(s):  
Qingzhi Zhu ◽  
J. Kirk Cochran ◽  
Christina Heilbrun ◽  
Hang Yin ◽  
Huan Feng ◽  
...  
Keyword(s):  
Organic Matter ◽  
Hydrogen Sulfide ◽  
Seasonal Variation ◽  
Pore Water ◽  
Salt Marshes ◽  
Solid Phase ◽  
Distribution Patterns ◽  
Reactive Iron ◽  
Different Seasons ◽  
Dimensional Distribution

Loss of tidal wetlands is a world-wide phenomenon. Many factors may contribute to such loss, but among them are geochemical stressors such as exposure of the marsh plants to elevated levels on hydrogen sulfide in the pore water of the marsh peat. Here we report the results of a study of the geochemistry of iron and sulfide at different seasons in unrestored (JoCo) and partially restored (Big Egg) salt marshes in Jamaica Bay, a highly urbanized estuary in New York City where the loss of salt marsh area has accelerated in recent years. The spatial and temporal 2-dimensional distribution patterns of dissolved Fe2+ and H2S in salt marshes were in situ mapped with high resolution planar sensors for the first time. The vertical profiles of Fe2+ and hydrogen sulfide, as well as related solutes and redox potentials in marsh were also evaluated by sampling the pore water at discrete depths. Sediment cores were collected at various seasons and the solid phase Fe, S, N, C, and chromium reducible sulfide in marsh peat at discrete depths were further investigated in order to study Fe and S cycles, and their relationship to the organic matter cycling at different seasons. Our results revealed that the redox sensitive elements Fe2+ and S2– showed significantly heterogeneous and complex three dimensional distribution patterns in salt marsh, over mm to cm scales, directly associated with the plant roots due to the oxygen leakage from roots and redox diagenetic reactions. We hypothesize that the oxic layers with low/undetected H2S and Fe2+ formed around roots help marsh plants to survive in the high levels of H2S by reducing sulfide absorption. The overall concentrations of Fe2+ and H2S and distribution patterns also seasonally varied with temperature change. H2S level in JoCo sampling site could change from <0.02 mM in spring to >5 mM in fall season, reflecting significantly seasonal variation in the rates of bacterial oxidation of organic matter at this marsh site. Solid phase Fe and S showed that very high fractions of the diagenetically reactive iron at JoCo and Big Egg were associated with pyrite that can persist for long periods in anoxic sediments. This implies that there is insufficient diagenetically reactive iron to buffer the pore water hydrogen sulfide through formation of iron sulfides at JoCo and Big Egg.

Dissolved organic matter in pore water of carbonate sediments from Bermuda

1979 ◽  
Vol 43 (3) ◽  
pp. 433-437 ◽  
Author(s):  
Wm.Berry Lyons ◽  
Henri E. Gaudette ◽  
Alan D. Hewitt
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Pore Water ◽  
Carbonate Sediments

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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