Anoxic Sediment Samples Research Articles

Preservation of Dinoflagellate Cysts in Different Oxygen Regimes: Differences in Cyst Survival between Oxic and Anoxic Natural Environments

This quantitative dinoflagellate cyst study reveals an enormous difference in survival rates in oxygenated versus anoxic sediments. Replicate samples of concentrated natural dinoflagellate cysts with the same initial species composition (1.4 × 104 resting cysts·cm−3 sediment, 61% filled with live-appearing contents) were placed in bags of 20 µm plankton screen. Replicate bags containing 10.0 cm−3 concentrated cyst samples were placed on the seafloor in different environments in Long Island Sound, USA (anoxic and oxygenated), as well as refrigerated in test tubes in the laboratory. Three sets of 15 bags were placed in each environment. Once every year for four consecutive years, three bags were recovered from each set, and the contents were analyzed by cyst counting and germination experiments. An enormous difference in preservation potential between samples in oxygenated versus anoxic environments was revealed. The number of dinoflagellate cysts decreased abruptly within the first year in the oxygen-rich environment; living cysts became very rare (only 5% remained) and also empty walls of cysts disappeared (20% of total cysts remained). In anoxic sediment samples, living cysts also decreased significantly with time, but less quickly. After 1 year, 35% of the living cysts in the anoxic environment and 70% of the living cysts refrigerated in test tubes remained intact. After 4 years, 21% of the cysts with contents in the anoxic environment remained, and 31% in test tubes. The empty cyst walls remained intact for a longer time under anoxic conditions, especially of species known to fossilize well. Germination experiments showed that cysts with live-appearing contents were likely alive, because species with identifiable live-appearing cysts were also identified as vegetative cells in corresponding slurry cultures. The cyst assemblage was dominated by Protoperidinaceae, Dipolopsalidaceae, and Gonyaulacaceae. Of special interest is the ichthyotoxic Margalefodinium polykrikoides, the bloom-forming Peridinium quinquecorne, which has an undescribed resting cyst, and a previously undescribed Krypoperidinium species. The results show greater preservation of dinoflagellate cysts in “dead-zone sea bottoms” and may also provide an answer to the question of the absence of cyst beds in an area despite observed sedimentation of dense blooms.

A modern framework for the interpretation of 238U/235U in studies of ancient ocean redox

The abundance and isotope composition of redox sensitive elements in ancient sediments are increasingly used to understand the past ocean's geochemical state and the oxygenation history of the Earth. The redox transition of uranium (U) from soluble U+6 to relatively insoluble U+4 and its subsequent incorporation into reduced sediments has been used to deduce the redox state of the oceans in the past. Furthermore, recent analytical improvements have revealed significant 238U/235U fractionation during this redox transition, offering the potential for U isotopes to act as a redox proxy. However, the development of U isotopes as a geochemical tracer requires that U isotope systematics associated with redox changes, are well-characterized.This study focuses on U isotopes in recent sediments from the two largest modern anoxic ocean basins, the Black Sea and the Cariaco Basin, with the aim of advancing our understanding of the U isotope systematics in reducing marine environments. These anoxic sediments have high U accumulation rates and high 238U/235U ratios relative to seawater, in general agreement with a process that accumulates reduced U with a heavy isotopic composition. Using Al and Ca concentrations to correct for detrital and biogenic carbonate-bound U, we estimate the reduced authigenic U accumulated in the sediments and its 238U/235U.These results highlight the importance of isotopic mass balance constraints during diffusive transport and reaction of U from seawater and through pore-water, affecting the observed 238U/235U in sediments. Using these constraints, the average percentages of U depletion from top to bottom of the water column can be estimated, assuming batch-removal of U into anoxic sediments in a restricted basin. Using this framework, 238U/235U in modern anoxic sediments from the Black Sea imply U depletions in the water column of ∼30%, which is close to the observed ∼40% U depletion in the modern Black Sea water column at these depths. Similar U depletion in the water column is estimated from anoxic sediment samples of the Cariaco Basin. These recent anoxic sediments provide a basis for interpreting authigenic 238U/235U in ancient sediments. In particular, such analyses may offer insights, based on mass balance relationships, into whether particular ancient sediments were deposited in an open ocean or restricted basin. As such, this approach may provide key insight into the controls on local versus ocean-scale redox and, in that light, constraints the capacity of other proxies to capture global signals for anoxia/euxinia.

Pollution and potential mobility of Cd, Ni and Pb in the sediments of a wastewater-receiving river in Hanoi, Vietnam

Large quantities of untreated industrial and domestic wastewater are discharged from the city of Hanoi into urban rivers. Sediment samples from three sites in the To Lich River in Hanoi were assessed with respect to the concentrations and potential mobility of cadmium (Cd), nickel (Ni) and lead (Pb). Due to very high Cd concentrations up to 700 mg kg(-1) at one site, the sediment was considered highly unsuitable for any types of land use if dredged and disposed of on land. Chemical sequential extractions of wet and anoxic sediment samples showed that Cd and Pb were largely associated with the redox-sensitive fractions and could thus be mobilised following measures such as resuspension or dredging. To assess the potential mobilisation of heavy metals from the anoxic sediment due to oxidation, the samples were exposed to different oxidants (i.e. atmospheric air and hydrogen peroxide) and afterwards submitted to a leaching test. These experiments showed that although oxidation may increase the equilibrium pore water concentrations of heavy metals in the sediments, other sediment mineral fractions seem to effectively immobilise heavy metals potentially released from the oxidisable fraction.

On metal diagenesis in contaminated sediments of the Deûle river (northern France)

The objective of the present work was to assess depth-related variations in the (bio)geochemical processes involved in anoxic sediments from the Deûle river, and to examine particularly their impacts on the distribution of anthropogenically sourced metals. Anoxic sediment samples were sliced and analyzed to determine total concentrations vs. depth of elements and corresponding pore waters were analyzed to determine concentration profiles with depth of pH, Eh, alkalinity, O2, dissolved organic carbon (DOC), and main inorganic anions and cations present in the medium. It was shown that rapid depletions of O2, NO3- and SO42-, accompanied with HCO3- generation and a sharp decrease in the redox potential occurred within the first centimeters of the surface sediment as a consequence of early diagenesis. Bacterial reductive dissolution of Mn(III and IV) and Fe(III) oxides/hydroxides to Mn(II) and Fe(II) accompanied by microbial degradation of organic matter took place as well, and resulted in trace metal increases in the pore water at levels that raised the possibility of mineral generation. Thermodynamic calculations predicted removal of metals from interstitial waters through combinations with carbonates and/or sulfides. These took place either by direct precipitation to form pure crystals, or by coprecipitation/sorption with/into calcite and with pyritic compounds. Chemical sequential extraction data were useful in this work to support, at least partially, some thermodynamic predictions concerning the existence of interactions between trace metals and carbonate and sulfide ions to generate (co)precipitates. Electron paramagnetic resonance (EPR) studies on Deûle sediments revealed the presence of Mn(II) adsorbed onto sedimentary calcite surfaces. X-ray diffractograms of heavy minerals from Deûle sediments extracted with CHBr3 by density separation exhibited peaks ascribed to galena, sphalerite and pyrite. In addition to these compounds, using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS), micro-analyses of sedimentary heavy minerals confirmed successfully the existence of other thermodynamically predicted associations: covellite; chalcopyrite, greenockite and/or amorphous CdS.

Investigation of Hopanoid Biomarkers in Lake Sediments by GC‐MS and RP‐HPLC‐APCI‐MS

Hopanoids are mainly derived from bacteriohopanpolyols that occur especially in bacteria, show the importance of bacterial lipid contributions in geological materials. In this work, GC‐MS and RP‐HPLC‐APCI‐MS analyses of hopanoid biomarkers in oxic and anoxic sediment samples from Lake Cadagno (Swiss Alps) and Lake Voua de la Motte (Haute Savoie, France) are presented and discussed. Samples were ultrasonically extracted, fractionated by flush chromatography on silica gel and derivatised before the analyses. Periodic acid/ sodium borohydride cleavage was used to identify highly functionalised hopanoids

Halogenated organic contaminants in sediments of the Havel and Spree rivers (Germany). Part 5 of organic compounds as contaminants of the Elbe river and its tributaries.

To give a detailed and comprehensive view on the state of pollution of the Havel and Spree rivers nontarget screening as well as quantitative (target) analyses were applied to anoxic sedimentsamples. Based on nontarget GC/MS analysis a significant contribution to the anthropogenic contamination could be attributed to halogenated compounds. Three groups of contaminants corresponding either to diffuse or local contamination could be distinguished. Several commonly observable compounds including pentachloroanisol, polychlorinated biphenyles, 2,4-dichlorobenzoic acid, and chlorinated benzenes were detected with a distribution reflecting the contribution of nonpoint source emissions. A second group of chlorinated as well as brominated compounds was attributed to a strong point source emission at the Teltow Canal. At the sampling locations influenced by this point source the amount of mono- and dibrominated naphthalenes, chlorinated naphthalenes, and hexachlorocyclohexanes as well as DDT- and methoxychlor-related compounds increased significantly as compared to the background concentrations. A third group of halogen compounds emitted at this site consisted of the pesticides bromopropylate, methoxychlor, and chlorfensone as well as specific brominated aromatics including 2,4,6-tribromoaniline, 4,4'-dibromobenzophenone, and brominated benzenes. In addition, tetrabromochlorotoluenes, tribromodichlorotoluenes, dibromotrichlorotoluenes, and 2,2-bis(4-bromophenyl)acetic acid isopropyl ester were identified and are reported for the first time as environmental contaminants. The amounts of brominated compounds detected in Teltow Canal sediments occurred at a similar concentration level as their chlorinated analogues. Therefore, investigations on the occurrence of such a broad spectrum of brominated compounds as established in this work are presumably required more frequently to assess the environmental impact of this type of emissions.

Speciation patterns of heavy metals in tropical estuarine anoxic and oxidized sediments by different sequential extraction schemes

The speciation patterns of Cu, Cd, Zn, Pb, Fe and Mn in sediment samples under anoxic and oxidized conditions were investigated using three-stage, four-stage and five-stage sequential extraction schemes. All the extraction schemes identify the non-residual metal among three basic operationally-defined host fractions, namely, exchangeable, reducible and organic/sulfide bound. The anoxic sediment samples were found to have been oxidized during the extraction stage for the reducible fraction under the three-stage and four-stage schemes and the moderately reducible fraction under the five-stage scheme despite the maintenance of an oxygen-free environment. This artifact has resulted in an over-representation of the reducible fraction and an under-representation of the organic/sulfide fraction in the heavy metal speciation patterns of anoxic sediment samples. For Cd, Zn and Pb which had >70% associated with the acid volatile sulfide in the organic/sulfide fraction, this artifact has resulted in the observation of a decrease in the reducible fraction and, in some cases, an increase in the organic/sulfide fraction upon oxidation of the anoxic sediment samples.

Identification of novel bacterial lineages as active members of microbial populations in a freshwater sediment using a rapid RNA extraction procedure and RT-PCR.

A rapid method for the extraction of RNA from the indigenous bacterial communities in environmental samples was developed. The method was tested using anoxic sediment samples from a productive freshwater lake (Priest Pot, Cumbria, UK). The simple protocol yielded rRNA and mRNA of a purity suitable for amplification by reverse transcriptase PCR (RT-PCR). The integrity of the RT-PCR was demonstrated by amplifying 16S rRNA and mRNA for the mercury resistance regulatory gene merR. The diversity of 16S rRNA sequences recovered from RNA and DNA extracted from anoxic Priest Pot sediments was analysed. The 5' end of extracted 16S rRNA was amplified by RT-PCR and the 16S rRNA PCR products were cloned and sequenced to identify active constituents of the sediment bacterial community. Corresponding analyses were performed upon DNA templates from the same sediment samples. Partial 16S rRNA sequences were obtained from a total of 147 clones (71 rRNA-derived and 76 rDNA-derived). The clone libraries included sequences related to Pirellula staleyi, an aerobic planktonic member of the Planctomycetales, and the recently described candidate bacterial division OP5. Sequences from these groups were recovered in libraries generated from a DNA template but were also present in RNA-derived libraries. Previous studies of anoxic environments have identified sequences most closely related to Pirellula spp. This study, which utilized RT-PCR of 16S rRNA, has provided the first evidence that Pirellula-like bacteria are active in situ in an anoxic environment. Furthermore, members of the recently described candidate division, OP5, were also identified as active constituents of the bacterial community of anoxic Priest Pot sediments. This not only supports the widespread occurrence of OP5 members in diverse environments but suggests that they are active under anoxic conditions.

Psalteriomonas lanterna gen. nov., sp. nov., a free-living amoeboflagellate isolated from freshwater anaerobic sediments

A novel amoeboflagellate, isolated from anoxic sediment samples, is described and named Psalteriomonas lanterna gen. nov., sp. nov. The cells of the flagellate stage show a fourfold rotational symmetry with four nuclei, four ventral grooves and four mastigont systems. Each mastigont has four flagella of equal length. Microtubular roots, striated roots or rhizoplasts and electron-dense structures are associated with their basal bodies. A Golgi apparatus is absent. Organelles surrounded by rough endoplasmic reticulum (RER) are presumably modified mitochondria. Methanogenic endosymbiotic bacteria are closely associated with microbodies and form a central body. Nuclear division shows the characteristics of a closed mitosis. Cells of the amoeboid stage are mononucleated and lack the methanogenic endosymbionts. Reproduction occurs in both stages of the life cycle.

Fermentative degradation of putrescine by new strictly anaerobic bacteria

Three strains of new strictly anaerobic, Grampositive, non-sporeforming bacteria were isolated from various anoxic sediment samples with putrescine as sole carbon and energy source. Optimal growth in carbonate-buffered defined medium occurred at 37°C at pH 7.2–7.6. The DNA base ratio of strain NorPut1 was 29.6±1 mol% guanine plus cytosine. In addition to a surface layer and the peptidoglycan layer, the cell wall contained a second innermost layer with a periodic arrangement of subunits. All strains fermented putrescine to acetate, butyrate, and molecular hydrogen; the latter originated from both oxidative putrescine deamination and 4-aminobutyraldehyde oxidation. In defined mixed cultures with methanogens or homoacetogenic bacteria, methane or additional acetate were formed due to interspecies hydrogen transfer. Also 4-aminobutyrate and 4-hydroxybutyrate were fermented to acetate and butyrate, but no hydrogen was released from these substrates. No sugars, organic acids, other primary amines or amino acids were used as substrates. Neither sulfate, thiosulfate, sulfur, nitrate nor fumarate was reduced. Most of the enzymes involved in putrescine degradation could be demonstrated in cell-free extracts. A pathway of putrescine fermentation via 4-aminobutyrate and crotonyl-CoA with subsequent dismutation to acetate and butyrate is suggested.

Effect of sample pretreatment on the reliability of solid speciation data of heavy metals — implications sesfor the study of early diagenetic processes

Experimental data on anoxic freshwater sediments from the Hamburg harbor indicate that commonly performed storage and pretreatment methods including aeration by drying strongly change the original associations of heavy metals with different sediment components. Oven-drying as well as freeze-drying under ‘vacuum’ affects metals originally bound to carbonate (Fe, Mn) and to the sulfidic/organic fraction (Zn, Cd, Cu, Pb), as indicated by sequential chemical extractions. While the easily oxidizable Cu and Pb portions are transferred mainly into the moderately reducible fraction, those of Zn and especially Cd are found in easily reducible and labile exchangeable fractions upon aeration of the sediment. Metals from only the latter fractions are potentially mobilizable via pore-water fluxes. Useful information on solid speciation influencing the mobility of contaminants in biogeochemically reactive sediments by the chemical leaching approach requires, therefore, proper and careful handling of the anoxic sediment samples.

Anaerobic degradation of nonionic and anionic surfactants in enrichment cultures and fixed-bed reactors

Anaerobic biodegradation and inhibitory effects of nonionic and anionic surfactants on methanogenic fermentation were tested in incubation experiments with anoxic sediment samples and sewage sludge. Alkylsulfonates and alkylbenzenesulfonates were not degraded but inhibited methanogenesis from sludge constituents at concentrations ≥10 mgl −1. Sodium dodecylsulfate was at least partly degraded after adaptation at concentrations ⩽100 mgl −1 and the sulfate group was reduced to sulfide. The polyethyleneglycol moiety of alkylphenolethoxylates was fermented to methane at concentrations ⩽500 mgl −1 whereas the alkylphenol residue probably remained unchanged. Alkylethoxylates were completely degraded to methane and CO 2 at concentrations up to 1.0 gl −1. Complete anaerobic degradation of this surfactant type to methane, CO 2, and traces of acetate and propionate was demonstrated in a lab scale anaerobic fixed-bed reactor, either with prereduced mineral salts medium or with air-saturated artificial wastewater. This process lends itself as a suited, inexpensive means for treatment of wastewaters containing enhanced loads of nonionic surfactants, e.g. from the surfactant manufacturing or processing industry.

Simple Assay for Accurate Determination of [ 35 S]sulfate Reduction Activity

A method is described for the assay of [S]sulfate reduction in which filter paper wicks are used to trap [S]sulfide. The simplicity of the technique enables large numbers of samples to be conveniently processed. Enhanced sensitivity is achieved since all acid-volatile [S]sulfides produced during the incubation period are counted. Recovery of radioactivity from added Na(2)S is excellent (mean, 100.1%; standard deviation, 1.81; n = 9) and is unaffected by sulfide concentrations of up to 400 mug per sample. Field trial results with anoxic sediment samples are presented.