scholarly journals DOC-dynamics in a small headwater catchment as driven by redox fluctuations and hydrological flow paths – are DOC exports mediated by iron reduction/oxidation cycles?

2013 ◽  
Vol 10 (2) ◽  
pp. 891-904 ◽  
Author(s):  
K.-H. Knorr
Keyword(s):  
Ionic Strength ◽  
Pore Water ◽  
Surface Waters ◽  
Iron Reduction ◽  
Stream Water ◽  
Riparian Wetlands ◽  
Pore Waters ◽  
Flow Paths ◽  
Discharge Patterns ◽  
Iron Concentrations

Abstract. Dissolved organic carbon (DOC) exports from many catchments in Europe and North-America are steadily increasing. Several studies have sought to explain this observation. As possible causes, a decrease in acid rain or sulfate deposition, concomitant reductions in ionic strength and increasing temperatures were identified. DOC often originates from riparian wetlands; but here, despite higher DOC concentrations, ionic strength in pore waters usually exceeds that in surface waters. In the catchment under study, DOC concentrations were synchronous with dissolved iron concentrations in pore and stream water. This study aims at testing the hypothesis that DOC exports are mediated by iron reduction/oxidation cycles. Following the observed hydrographs, δ18O of water and DOC fluorescence, the wetlands were identified as the main source of DOC. Antecedent biogeochemical conditions, i.e., water table levels in the wetlands, influenced the discharge patterns of nitrate, iron and DOC during an event. The correlation of DOC with pH was positive in pore waters, but negative in surface waters; it was negative for DOC with sulfate in pore waters, but only weak in surface waters. Though, the positive correlation of DOC with iron was universal for pore and surface water. The decline of DOC and iron concentrations in transition from anoxic wetland pore water to oxic stream water suggests a flocculation of DOC with oxidising iron, leading to a drop in pH in the stream during high DOC fluxes. The pore water did not per se differ in pH. There is, thus, a need to consider processes more thoroughly of DOC mobilisation in wetlands when interpreting DOC exports from catchments. The coupling of DOC with iron fluxes suggested that increased DOC exports could at least, in part, be caused by increasing activities in iron reduction, possibly due to increases in temperature, increasing wetness of riparian wetlands, or by a shift from sulfate dominated to iron reduction dominated biogeochemical regimes.

scholarly journals DOC-dynamics in a small headwater catchment as driven by redox fluctuations and hydrological flow paths – are DOC exports mediated by iron reduction/oxidation cycles?

2012 ◽  
Vol 9 (9) ◽  
pp. 12951-12984 ◽  
Author(s):  
K.-H. Knorr
Keyword(s):  
Ionic Strength ◽  
Pore Water ◽  
Surface Waters ◽  
Iron Reduction ◽  
Stream Water ◽  
Riparian Wetlands ◽  
Pore Waters ◽  
Flow Paths ◽  
Discharge Patterns ◽  
Iron Concentrations

Abstract. Dissolved organic carbon (DOC) exports from many catchments in Europe and North-America are steadily increasing. Several studies have sought to explain this observation. As possible causes, a decrease in acid rain or sulfate deposition, concomitant reductions in ionic strength and increasing temperatures were identified. DOC often originates from riparian wetlands; but here, despite higher DOC concentrations, ionic strength in pore waters usually exceeds that in surface waters. In the catchment under study, DOC concentrations were synchronous with dissolved iron concentrations in pore and stream water. This study aims at testing the hypothesis that DOC exports are mediated by iron reduction/oxidation cycles. Following the observed hydrographs, δ18O of water, and DOC fluorescence, the wetlands were identified as main source of DOC. Antecedent biogeochemical conditions, i.e. water table levels in the wetlands, influenced the discharge patterns of nitrate, iron, and DOC during an event. The correlation of DOC with pH was positive in pore waters but negative in surface waters; it was negative for DOC with sulfate in pore waters but only weak in surface waters. The positive correlation of DOC with iron was universal for pore and surface water, though. The decline of DOC and iron concentrations in transition from anoxic wetland pore water to oxic stream water suggests a flocculation of DOC with oxidizing iron, leading to a drop in pH in the stream during high DOC fluxes. The pore water did not per se differ in pH. There is thus a need to more thoroughly consider processes of DOC mobilization in wetlands when interpreting DOC exports from catchments. The coupling of DOC with iron fluxes suggested that increased DOC exports could at least in part be caused by increasing activities in iron reduction, possibly due to increases in temperature or wetness of riparian wetlands.

scholarly journals Geochemistry of intertidal sediment pore waters from the industrialized Santos-Cubatão Estuarine System, SE Brazil

2012 ◽  
Vol 84 (2) ◽  
pp. 427-442 ◽  
Author(s):  
Winston F.O. Gonçalves ◽  
Wanilson Luiz-Silva ◽  
Wilson Machado ◽  
Erico C. Nizoli ◽  
Ricardo E. Santelli
Keyword(s):  
Surface Water ◽  
Pore Water ◽  
Surface Waters ◽  
Water Concentration ◽  
Point Sources ◽  
Intertidal Sediment ◽  
Estuarine System ◽  
Pore Waters ◽  
Geochemical Composition ◽  
Se Brazil

The geochemical composition of sediment pore water was investigated in comparison with the composition of sediment particles and surface water in an estuary within one of the most industrialized areas in Latin America (Santos-Cubatão estuarine system, SE Brazil). Pore and surface waters presented anomalously high levels of F-, NH4+, Fe, Mn and P due to two industrial point sources. In the summer, when SO4(2-)/Cl- ratios suggested an enhanced sulfate reduction, the higher dissolved levels observed in pore waters for some metals (e.g., Cu and Ni) were attributed to reductive dissolution of oxidized phases. Results evidenced that the risks of surface water concentration increase due to diffusion or advection from pore water are probably dependent on coupled influences of tidal pumping and groundwater inputs.

scholarly journals Benthic alkalinity and DIC fluxes in the Rhône River prodelta generated by decoupled aerobic and anaerobic processes

2019 ◽  
Author(s):  
Jens Rassmann ◽  
Eryn M. Eitel ◽  
Cécile Cathalot ◽  
Christophe Brandily ◽  
Bruno Lansard ◽  
...  
Keyword(s):  
Pore Water ◽  
Iron Reduction ◽  
Iron Sulfide ◽  
Dissolved Inorganic Carbon ◽  
River Mouth ◽  
Total Alkalinity ◽  
Pore Waters ◽  
Rhône River ◽  
Net Production ◽  
Rhone River

Abstract. Estuarine regions are generally considered a net source of atmospheric CO2 as a result of the high organic carbon (OC) mineralization rates in the water column and their sediments. Yet, the intensity of anaerobic respiration processes in the sediments tempered by the reoxidation of reduced metabolites controls the net production of alkalinity from sediments that may partially buffer the metabolic CO2 generated by OC respiration. In this study, a benthic chamber was deployed in the Rhône River prodelta and the adjacent continental shelf (Gulf of Lions, NW Mediterranean) to assess the fluxes of total alkalinity (TA) and dissolved inorganic carbon (DIC) from the sediment. Concurrently, in situ O2 and pH microprofiles, electrochemical profiles, pore water and solid composition were measured in surface sediments to identify the main biogeochemical processes controlling the net production of alkalinity in these sediments. The benthic fluxes of TA and DIC, ranging between 14 and 74 mmol m−2 d−1 and 18 and 78 mmol m−2 d−1, respectively, were up to 8 times higher than the DOU fluxes (10.4 ± 0.9 mmol m−2 d−1) close to the river mouth, but their intensity decreased offshore, as a result of the decline in OC inputs. Low nitrate concentrations and strong pore water sulfate gradients indicated that the majority of the TA and DIC was produced by sulfate and iron reduction. Despite the complete removal of sulfate from the pore waters, dissolved sulfide concentrations were low due to the precipitation and burial of iron sulfide minerals (12.5 mmol m−2 d−1 near the river mouth), while soluble organic-Fe(III) complexes were concurrently found throughout the sediment column. The presence of organic-Fe(III) complexes together with low sulfide concentrations and high sulfate consumption suggests a dynamic system driven by the variability of the organic and inorganic particulate input originating from the river. By preventing reduced substances from being reoxidized, the precipitation and burial of iron sulfide decouples the iron and sulfur cycles from oxygen, therefore allowing a flux of alkalinity out of the sediments. In these conditions, the sediment provides a source of alkalinity to the bottom waters which mitigates the effect of the benthic DIC flux on the carbonate chemistry of coastal waters.

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.

A multi-tracer study of submarine groundwater discharge into Wismar Bay, southern Baltic Sea

2020 ◽  
Author(s):  
Catia Milene Ehlert von Ahn ◽  
Jan Scholten ◽  
Iris Schmiedinger ◽  
Bo Liu ◽  
Michael Böttcher
Keyword(s):  
Baltic Sea ◽  
Pore Water ◽  
Surface Waters ◽  
Submarine Groundwater Discharge ◽  
Isotope Composition ◽  
Groundwater Discharge ◽  
Pore Waters ◽  
Southern Baltic Sea ◽  
Submarine Groundwater ◽  
Southern Baltic

&lt;p&gt;Submarine groundwater discharge (SGD) is considered as an important route for water and dissolved material exchange between land and coastal seas. Both freshwater and (recirculated) seawater are referred to as SGD and may impact the composition and biogeochemical processes in coastal waters. The present study focuses on the identification and the spatial variability of SGD into the Wismar Bay, in the southern Baltic Sea. On across-shore transects covering Wismar Bay waters were sampled for analysis of Radium (Ra) isotopes, stable isotopes (H, O, C, S), dissolved inorganic carbon (DIC), nutrients and major cations. In addition, sediment cores were retrieved from several stations. The detection of short-living radium isotopes (&lt;sup&gt;223&lt;/sup&gt;Ra and&lt;sup&gt;224&lt;/sup&gt;Ra) in surface waters of the bay indicate benthic-pelagic coupling via pore water exchange with the water column that may be an indication for SGD. Moreover, enhanced concentration of dissolved manganese and barium, resulted from anoxic pore waters, were found in areas with higher Ra activity. Pore water profiles of salinity and major ions highlight the presence of freshwater about 50 cmbsf in sediments in the central part of the bay, probably related to the presence of a coastal aquifer. In contrast, other sediments demonstrate relatively constant pore water salinity distribution with increasing depth. Slight salinity maxima in almost all core at around 6 to 12 cmbsf seems to be relict from changing bottom water salinity in the past. The water isotope composition (&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O, &amp;#948;&lt;sup&gt;2&lt;/sup&gt;H) of the low saline pore water is plot close to the local meteoric water line established for Warnem&amp;#252;nde. Saline pore waters, in contrast, have water isotope composition aligned with southern Baltic Sea surface waters. The DIC concentrations increased with depths suggesting the mineralization of organic matter within the 50 cm sediments depth at all sides. Moreover, the values of DIC even exceeding the concentration found on the percolating fresh ground water. Thus, the overall contribution of elements to the coastal ecosystem is a function of the transport processes regulating element flux across the sediment-water interface.&lt;/p&gt;&lt;p&gt;The investigation is supported by the DFG research training school Baltic TRANSCOAST, DAAD, and Leibniz IOW.&lt;/p&gt;

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 Particulate organic carbon (POC) in relation to other pore water carbon fractions in drained and rewetted fens in Southern Germany

2008 ◽  
Vol 5 (6) ◽  
pp. 1615-1623 ◽  
Author(s):  
S. Fiedler ◽  
B. S. Höll ◽  
A. Freibauer ◽  
K. Stahr ◽  
M. Drösler ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
Pore Water ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Relative Importance ◽  
Pore Waters ◽  
Calcareous Fens ◽  
Essential Components ◽  
The Individual

Abstract. Numerous studies have dealt with carbon (C) contents in Histosols, but there are no studies quantifying the relative importance of the individual C components in pore waters. For this study, measurements were taken of all the carbon components (particulate organic carbon, POC; dissolved organic carbon, DOC; dissolved inorganic carbon, DIC; dissolved methane, CH4) in the soil pore water of calcareous fens under three different water management regimes (re-wetted, deeply and moderately drained). Pore water was collected weekly or biweekly (April 2004 to April 2006) at depths between 10 and 150 cm. The main results obtained were: (1) DIC (94–280 mg C l−1) was the main C-component. (2) POC and DOC concentrations in the pore water (14–125 mg C l−1 vs. 41–95 mg C l−1) were pari passu. (3) Dissolved CH4 was the smallest C component (0.005–0.9 mg C l−1). Interestingly, about 30% of the POM particles were colonized by microbes indicating that they are active in the internal C turnover. Certainly, both POC and DOC fractions are essential components of the C budget of peatlands. Furthermore, dissolved CO2 in all forms of DIC appears to be an important part of peatland C-balance.

scholarly journals Stream plant chemistry as indicator of acid sulphate soils in Sweden

2008 ◽  
Vol 14 (1) ◽  
pp. 83 ◽  
Author(s):  
K. LAX
Keyword(s):  
Surface Waters ◽  
Stream Water ◽  
Low Ph ◽  
Fontinalis Antipyretica ◽  
Acid Sulphate ◽  
Fine Grained ◽  
Acid Sulphate Soils ◽  
Trace Element Chemistry ◽  
Study Results ◽  
The Impact

Results from the biogeochemical mapping (roots of aquatic plants and Fontinalis antipyretica) conducted by the Geological Survey of Sweden (SGU) reflects the metal load of surface waters draining acid sulphate (AS) soils in Sweden. In this study, results from the biogeochemical, soil geochemical and Quaternary mapping programmes at SGU were used to investigate the impact of fine-grained deposits hosting AS soils on stream water trace element chemistry in two separate areas. In the area around Lake Mälaren, postglacial sediments contain the highest levels of most trace elements studied. Owing to the low pH of AS soils and subsequent leaching, levels of nickel (Ni), cobalt (Co), copper (Cu), sulphur (S), yttrium (Y), uranium (U), tungsten (W), and molybdenum (Mo) were significantly elevated in aquatic roots. Levels were lower in the Skellefteå area, which may be explained by lower concentrations in source deposits. Concentrations of arsenic (As) and lead (Pb) were normal or impoverished in biogeochemical samples from postglacial, finegrained sediment areas. Maps based on ratios (Ni:Pb or Y:Pb) in biogeochemical samples can, together with results from Quaternary mapping, be used to predict areas with AS soils in Sweden.;

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