Biogeochemical cycling of nutrients and trace metals in anoxic freshwater sediments of the Neckar River, Germany

1995 ◽  
Vol 46 (1) ◽  
pp. 237 ◽  
Author(s):  
Y Song ◽  
G Muller
Keyword(s):  
Organic Matter ◽  
Trace Metals ◽  
Pore Water ◽  
Sediment Cores ◽  
Sharp Decrease ◽  
Metal Sulfides ◽  
Pore Waters ◽  
Overlying Water ◽  
Mineralization Of Organic Matter ◽  
Cycling Of Nutrients

Pore-water components (SO42-, Fe2+, Mn2+), including nutrients (NH4+:, NO3-, PO43-), alkalinity and pH were determined at three sites in the Neckar River. Sequential extraction procedures and trace metals in both pore waters and sediments are reported in order to evaluate the mobility of trace metals in contaminated sediments. The results show that the mineralization of organic matter plays an important role in the cycling of nutrients and trace metals. Pore-water profiles (Zn, Cu, Pb, Cd) suggest that the element maximums at the sediment-water interface are caused by the decomposition of biomass. Low concentrations of dissolved Zn, Cu, Pb and Cd in the anoxic sediments can be explained by a sharp decrease of SO42- in pore water concomitant with HS- production. This leads to the formation of highly insoluble metal sulfides. Solubility calculations show that the sediments act as a sink for trace metals with respect to trace metal sulfides. The organic/sulfidic-bound fraction accounts for 64-81% of Cd in the sediment cores, 36-67% of Pb and 51-69% of Cu. In contrast, Cr in pore water increases with depth because of its release from Fe/Mn oxides. NH4+ and PO43- are also released into the pore water owing to the mineralization of organic matter. No significant fluxes of NH4+ and PO43- into overlying water were found because of the existence of an oxic surface layer.

scholarly journals Hydrochemistry of sediment pore water in the Bratsk reservoir (Baikal region, Russia)

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
V. I. Poletaeva ◽  
E. N. Tirskikh ◽  
M. V. Pastukhov
Keyword(s):  
Pore Water ◽  
Ionic Composition ◽  
Water System ◽  
Water Reservoir ◽  
Environmental Parameters ◽  
Water Area ◽  
Pore Waters ◽  
Overlying Water ◽  
Major Ion ◽  
Bratsk Reservoir

AbstractThis study aimed to identify the factors responsible for the major ion composition of pore water from the bottom sediments of the Bratsk water reservoir, which is part of the largest freshwater Baikal-Angara water system. In the Bratsk reservoir, the overlying water was characterized as HCO3–Ca–Mg type with the mineralization ranging between 101.2 and 127.7 mg L−1 and pore water was characterized as HCO3–SO4–Ca, SO4–Cl–Ca–Mg and mixed water types, which had mineralization varying from 165.9 to 4608.1 mg L−1. The ionic composition of pore waters varied both along the sediment depth profile and across the water area. In pore water, the difference between the highest and lowest values was remarkably large: 5.1 times for K+, 13 times for Mg2+, 16 times for HCO3−, 20 times for Ca2+, 23 times for Na+, 80 times for SO42−, 105 times for Cl−. Such variability at different sites of the reservoir was due to the interrelation between major ion concentrations in the pore water and environmental parameters. The major factor responsible for pore water chemistry was the dissolution of sediment-forming material coming from various geochemical provinces. In the south part of the reservoir, Cl−, Na+ and SO42− concentrations may significantly increase in pore water due to the effect of subaqueous flow of highly mineralized groundwater.

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 Sediment-water column fluxes of carbon, oxygen and nutrients in Bedford Basin, Nova Scotia, inferred from <sup>224</sup>Ra measurements

2013 ◽  
Vol 10 (1) ◽  
pp. 53-66 ◽  
Author(s):  
W. J. Burt ◽  
H. Thomas ◽  
K. Fennel ◽  
E. Horne
Keyword(s):  
Organic Matter ◽  
Nova Scotia ◽  
Water Column ◽  
Explicit Knowledge ◽  
Dissolved Inorganic Carbon ◽  
Chemical Constituents ◽  
Water Interface ◽  
Benthic Fluxes ◽  
Pore Waters ◽  
Overlying Water

Abstract. Exchanges between sediment pore waters and the overlying water column play a significant role in the chemical budgets of many important chemical constituents. Direct quantification of such benthic fluxes requires explicit knowledge of the sediment properties and biogeochemistry. Alternatively, changes in water-column properties near the sediment-water interface can be exploited to gain insight into the sediment biogeochemistry and benthic fluxes. Here, we apply a 1-D diffusive mixing model to near-bottom water-column profiles of 224Ra activity in order to yield vertical eddy diffusivities (KZ), based upon which we assess the diffusive exchange of dissolved inorganic carbon (DIC), nutrients and oxygen (O2), across the sediment-water interface in a coastal inlet, Bedford Basin, Nova Scotia, Canada. Numerical model results are consistent with the assumptions regarding a constant, single benthic source of 224Ra, the lack of mixing by advective processes, and a predominantly benthic source and sink of DIC and O2, respectively, with minimal water-column respiration in the deep waters of Bedford Basin. Near-bottom observations of DIC, O2 and nutrients provide flux ratios similar to Redfield values, suggesting that benthic respiration of primarily marine organic matter is the dominant driver. Furthermore, a relative deficit of nitrate in the observed flux ratios indicates that denitrification also plays a role in the oxidation of organic matter, although its occurrence was not strong enough to allow us to detect the corresponding AT fluxes out of the sediment. Finally, comparison with other carbon sources reveal the observed benthic DIC release as a significant contributor to the Bedford Basin carbon system.

Microbial mineralization of organic matter: mechanisms of self-organization and inferred rates of precipitation of diagenetic minerals

1993 ◽  
Vol 344 (1670) ◽  
pp. 69-87 ◽  
Keyword(s):  
Organic Matter ◽  
Pore Water ◽  
Microbial Reduction ◽  
Chemical Compositions ◽  
Outward Diffusion ◽  
Self Organized ◽  
Geological Processes ◽  
Carbonate Concretions ◽  
Inorganic Species ◽  
Mineralization Of Organic Matter

Carbonate concretions attract study because, unlike intergranular cements, they form conspicuous spheroidal or laterally extensive bodies. However, they pose a fundamental challenge to uniformitarianism because no concretions identical to geologically preserved ones are forming today. Nevertheless, understanding their origin can be accomplished by simulation of geological processes, using present-day processes and pore-water compositions. The successive reactions (mainly microbial) degrading organic-matter during sediment burial produce inorganic species which may form carbonate and sulphide minerals and can be characterized by stable isotope and chemical compositions. Pyrite-rimmed, spheroidal carbonate carbonate concretions (Jurassic) resulted from outward diffusion of microbially produced sulphide which reacted with inwardly diffusing iron. Extensive, bedded siderite concretions (Coal Measures) were formed by microbial reduction of Fe(III) which could only proceed because the reaction was buffered by precipitation of carbonate produced by methanogens degrading more deeply buried organic matter. Byproducts of the reactions may either inhibit or promote initiation of similar precipitation reactions locally. The former case leads to situations where initial random localization of reaction sites causes self-organized reaction within the sediment (applicable to the Jurassic example). Simulations of the Jurassic concretions’ growth process, using present day pore-water solute concentrations of calcium, sulphide and iron, give results which correspond with the spatial distribution of mineral precipitates observed in geological samples. Calculated rates of mineral precipitation give minimum durations 7400 to 52000 years, much shorter than previous estimates. These results suggest that low rates of microbial sulphate reduction, relative to present day measured values, were needed and accord with the inferred depth of formation and pore-water sulphate concentrations.

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 &amp;pm; 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.

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

&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;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.&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;&lt;p&gt;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.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Acknowledgement: This study is supported by the DFG research training group BALTIC TRANSCOAST and Leibniz IOW.&lt;/p&gt;

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.

Spatial distribution of labile and total forms of copper and zinc in sediments from the Port of Gdansk

2007 ◽  
Vol 36 (4) ◽  
Author(s):  
Barbara Radke ◽  
Grażyna Dembska ◽  
Barbara Aftanas ◽  
Aneta Kowalczyk ◽  
Jerzy Bolałek
Keyword(s):  
Grain Size ◽  
Organic Matter ◽  
Spatial Distribution ◽  
Trace Metals ◽  
Sediment Cores ◽  
Size Fraction ◽  
Copper And Zinc ◽  
The Mean ◽  
Mean Concentration ◽  
Grain Size Fractions

Spatial distribution of labile and total forms of copper and zinc in sediments from the Port of GdanskSediment cores were collected from a number of sites in the Port of Gdansk in 1997 and 1998. The samples were segregated by depth then dried, homogenised and sieved into four grain size fractions (>2.00 mm, 2.00 - 0.063 mm, 0.063 - 0.032 mm, and 0.032 mm) Small-grained sand with a low admixture of silt predominated in all samples, whilst the amount of organic matter and water varied between samples. The 2.00 - 0.063 mm size fraction was the most abundant; and also showed the highest accumulation of trace metals. In the >2.00 mm size fraction the mean concentration of labile forms of copper was 9.06 mg kg

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