Behaviour of toluene, benzene and naphthalene under anaerobic conditions in sediment columns

The biotransformation of toluene, benzene and naphthalene was examined in anaerobic sediment columns. Five columns filled with a mixture of sediments were operated in the presence of bicarbonate, sulfate, iron, manganese, or nitrate as electron acceptor. The columns were continuously percolated with a mixture of the three organic compounds (individual concentrations 25–200 μM) at 20°C. Toluene was transformed readily (within 1 to 2 months) under all redox conditions tested. Benzene was recalcitrant over the test period of 375–525 days in all five columns. Naphthalene was partly transformed in the column with nitrate or manganese as electron acceptor present; the addition of benzoate had a positive effect in the column with nitrate. In the column with sulfate, the majority of the added naphthalene disappeared. No effect was observed after adding and omitting an easier degradable substrate. [¹⁴C]naphthalene was used to confirm this disappearance to be the result of degradation; two third of the naphthalene was converted to CO₂.     

Behaviour of toluene, benzene and naphthalene under anaerobic conditions in sediment columns

The biotransformation of toluene, benzene and naphthalene was examined in anaerobic sediment columns. Five columns filled with a mixture of sediments were operated in the presence of bicarbonate, sulfate, iron, manganese, or nitrate as electron acceptor. The columns were continuously percolated with a mixture of the three organic compounds (individual concentrations 25–200 M) at 20°C.Toluene was transformed readily (within 1 to 2 months) under all redox conditions tested. Benzene was recalcitrant over the test period of 375–525 days in all five columns. Naphthalene was partly transformed in the column with nitrate or manganese as electron acceptor present; the addition of benzoate had a positive effect in the column with nitrate. In the column with sulfate, the majority of the added naphthalene disappeared. No effect was observed after adding and omitting an easier degradable substrate. [¹⁴C]naphthalene was used to confirm this disappearance to be the result of degradation; two third of the naphthalene was converted to CO₂.     

Advective Mixing of Pore Waters and Ecology of Sandy Sediments of the Ocean Shelf

Sand sediments are widely distributed in the shelf zone of the World Ocean. The main physical and ecological peculiarity of marine sands is the mobility of pore waters and their mixing with the near-bottom waters of the sea. The mixing is closely related to turbulent processes in the water column; the most important of these processes is wave mixing. This causes filtration of seawater through the sand, ensuring therefore, perhaps, the most large-scale filtration process on the Earth. Advective mixing redistributes dissolved oxygen and nutrients between the pore waters of the sand and the bulk of the seawater column and determines redox conditions in the sediment column, which usually are either oxidative or suboxic; the metals with variable valence, mostly iron, serve as a redox buffer. The regeneration of nutrients and nitrification of ammonia also take place in the sand column. The instability of advective mixing is considered as the major difficulty for qualitative assessment of energetic metabolism and regeneration of nutrients in sands as well as for revealing the ecological role of marine sands in coastal ecosystems.     

Detection of Horizontal Gene Transfer by Natural Transformation in Native and Introduced Species of Bacteria in Marine and Synthetic Sediments

Both naturally occurring marine sediments and artificial sediments were used as supports for natural transformation of marine bacteria. While transformation of Pseudomonas stutzeri ZoBell suspended in artificial seawater was not detected when recipient cells and rifampin resistance DNA were loaded onto sterile sediment columns, transformation could be detected at frequencies 4 to 20 times that of spontaneous resistance when recipient cells and rifampin resistance DNA were loaded onto sterile sediment columns. Treatment of these columns with DNase I reduced transformation frequencies to levels comparable to those of spontaneous-resistance frequencies. Sediments with higher organic contents supported higher frequencies of transformation than did those with lower amounts of organic matter. Transformation was also detected when recipient cells and DNA were loaded on columns prepared from nonsterile sediments, although the frequencies of transformation were lower than when sterile sediments were used. Finally, nonsterilized sediments that were not supplemented with laboratory strains did not support detectable levels of transformation in sediment columns, but when these same sediments were transferred to filters and placed on complex media, transformation was detected at a frequency three times that for spontaneous resistance. This transformation frequency was partially reduced to levels near that for spontaneous resistance by the addition of DNase I to sediment filters. These results indicate that marine sediments facilitate the uptake and expression of exogenous DNA by transformable marine bacteria and that sediments are a more likely niche for natural transformation than the water column in the marine environment.     

A method for cultivation of microorganisms oxidizing iron and manganese in bottom sediments of Lake Baikal

Methods for cultivation of microorganisms oxidizing iron and manganese in bottom sediments of Lake Baikal were tested. Bacteria were grown on selective media with a characteristic accumulation of metal oxides. The morphology and developmental patterns of the isolated microbial group were studied. The studied sediment core was used to isolate 42 strains of bacteria oxidizing iron and manganese. The cultivated bacteria were confined to the upper sediment layers (down to 11 cm) and their abundance depended on sediment type and redox conditions.     

Biogeochemistry of manganese- and iron-rich sediments in Toolik Lake,Alaska

The sediments within Toolik Lake in arctic Alaska are characterized by extremely low rates of organic matter sedimentation and unusually high concentrations of iron and manganese. Pore water and solid phase measurements of iron, manganese, trace metals, carbon, nitrogen, phosphorus, and sulfur are consistent with the hypothesis that the reduction of organic matter by iron and manganese is the most important biogeochemical reaction within the sediment. Very low rates of dissolved oxygen consumption by the sediments result in an oxidizing environment at the sediment-water interface. This results in high retention of upwardly-diffusing iron and manganese and the formation of metal-enriched sediment. Phosphate in sediment pore waters is strongly adsorbed by the metal-enriched phases. Consequently, fluxes of phosphorus from the sediments to overlying waters are very small and contribute to the oligotrophic nature of the Toolik Lake aquatic system. Toolik Lake contains an unusual type of lacustrine sediment, and in many ways the sediments are similar to those found in oligotrophic oceanic environments.     

The influence of water quality and sediment geochemistry on the horizontal and vertical distribution of phosphorus and nitrogen in sediments of a large,shallow lake

Distinct horizontal water column concentration gradients of nutrients and chlorophyll a (Chl a) occur within large, shallow, eutrophic Lake Taihu, China. Concentrations are high in the north, where some of the major polluted tributaries enter the lake, and relatively low in the south, where macrophytes generally are abundant. It is not clear, however, whether these water column concentration gradients are similarly reflected in spatial heterogeneity of nutrient concentrations within the bottom sediments. The main objective of this study was therefore to test if horizontal and vertical variations in the phosphorus and nitrogen content in bottom sediments of Lake Taihu are significantly related to (1) horizontal variations in overlying water column nutrient concentrations and (2) other sediment geochemical constituents. We measured the concentration of total phosphorus (TP) and total nitrogen (TN) in surficial sediments (0–2 cm) and TP, TN and Chl a concentrations in water column samples, collected from 32 sites in 2005. In 2006 sediment, TP, TN, carbon, iron and manganese concentrations were measured vertically at 2 cm intervals, extending to a depth of approximately 20 cm, at an additional eight sites. Linear correlation analysis revealed that surficial sediment TP concentrations across the 32 stations were related significantly, though weakly, to annual mean water column concentrations of TP, TN as well as Chl a. Correlations of surficial sediment TN with water column variables were, however, not significant (P > 0.05). Amongst the geochemical variables tested, the vertical variability of sediment TP concentrations was most strongly related to sediment manganese and carbon concentrations. A multiple stepwise linear regression revealed that the combination of sediment manganese and carbon concentrations explained 91% of the horizontal variability in sediment TP concentrations and 65% of the vertical variability. Handling editor: Luigi Naselli-Flores     

Microbial diversity and stratification of South Pacific abyssal marine sediments

Abyssal marine sediments cover a large proportion of the ocean floor, but linkages between their microbial community structure and redox stratification have remained poorly constrained. This study compares the downcore gradients in microbial community composition to porewater oxygen and nitrate concentration profiles in an abyssal marine sediment column in the South Pacific Ocean. Archaeal 16S rRNA clone libraries showed a stratified archaeal community that changed from Marine Group I Archaea in the aerobic and nitrate-reducing upper sediment column towards deeply branching, uncultured crenarchaeotal and euryarchaeotal lineages in nitrate-depleted, anaerobic sediment horizons. Bacterial 16S rRNA clone libraries revealed a similar shift on the phylum and subphylum level within the bacteria, from a complex community of Alpha-, Gamma- and Deltaproteobacteria, Actinobacteria and Gemmatimonadetes in oxic surface sediments towards uncultured Chloroflexi and Planctomycetes in the anaerobic sediment column. The distinct stratification of largely uncultured bacterial and archaeal groups within the oxic and nitrate-reducing marine sediment column provides initial constraints for their microbial habitat preferences.     

Geochemical processes of iron and manganese in a seasonally stratified lake affected by coal-mining drainage in China

Lake water, pore water, and sediments were sampled in a seasonally stratified lake affected by coal-mining drainage. Contrasting geochemical processes of iron and manganese in summer were investigated by studying the seasonal distributions of iron and manganese species in the water column, pore water, and sediments. The results show that iron buildup in the water during summer was mainly from the gradual dissolution of particulate matter due to the pH decrease, whereas manganese oxide reduction and manganese-bound carbonate dissolution near the sediment–water interface were mainly responsible for manganese accumulation in the stratified hypolimnion. The geochemical processes of iron and manganese in the sediments during early diagenesis were also discussed in terms of the possible influence on the overlying water. Received: November 29, 1999 / Accepted: June 30, 2000     

Microbial community diversity associated with carbon and nitrogen cycling in permeable shelf sediments

Though a large fraction of primary production and organic matter cycling in the oceans occurs on continental shelves dominated by sandy deposits, the microbial communities associated with permeable shelf sediments remain poorly characterized. Therefore, in this study, we provide the first detailed characterization of microbial diversity in marine sands of the South Atlantic Bight through parallel analyses of small-subunit (SSU) rRNA gene (Bacteria), nosZ (denitrifying bacteria), and amoA (ammonia-oxidizing bacteria) sequences. Communities were analyzed by parallel DNA extractions and clone library construction from both sediment core material and manipulated sediment within column experiments designed for geochemical rate determinations. Rapid organic-matter degradation and coupled nitrification-denitrification were observed in column experiments at flow rates resembling in situ conditions over a range of oxygen concentrations. Numerous SSU rRNA phylotypes were affiliated with the phyla Proteobacteria (classes Alpha-, Delta-, and Gammaproteobacteria), Planctomycetes, Cyanobacteria, Chloroflexi, and Bacteroidetes. Detectable sequence diversity of nosZ and SSU rRNA genes increased in stratified redox-stabilized columns compared to in situ sediments, with the Alphaproteobacteria comprising the most frequently detected group. Alternatively, nitrifier communities showed a relatively low and stable diversity that did not covary with the other gene targets. Our results elucidate predominant phylotypes that are likely to catalyze carbon and nitrogen cycling in marine sands. Although overall diversity increased in response to redox stabilization and stratification in column experiments, the major phylotypes remained the same in all of our libraries, indicating that the columns sufficiently mimic in situ conditions.     

Sediment resuspension effects on alkaline phosphatase activity

Sediment cores, including the associated lake water, were collected from a shallow hypereutrophic lake located in central Florida. Alkaline phosphatase activity (APA) was measured as an indicator of potential organic P mineralization. In both the sediment and water columns, APA was mainly associated with particulate matter; < 10% of APA was within the soluble phase. This suggests that for enzymatic hydrolysis to occur the hydrolyzable organic compounds must be in close proximity to the particle-bound enzyme complex. Both total P (TP) and APA decreased with depth in the sediment, whereas soluble reactive P increased in the 20–40 cm fraction. Resuspension of surficial sediments resulted in an immediate increase in APA, total suspended solids, TP, total Kjeldahl N, and total organic C within the overlying water column. However, these concentrations decreased rapidly following cessation of turbulence and settling of the sediments, emphasizing the close association of these parameters with the sediment.     

Observations on the diagenetic behavior of arsenic in a deep coastal sediment

Vertical profiles of total dissolved arsenic, manganese and iron, pH, Eh and rates of sulfate reduction were determined in a freshly-collected box core from a 335m depth station in the Laurentian Trough. The relationships observed between the profiles were further examined in the laboratory by measuring these same parameters with time in surficial sediment slurries as the Eh decreased in response to biological activity or chemical alteration.Both field and laboratory observations have shown that arsenic is released predominantly as As(III) into reducing sediment porewaters. This occurs after the dissolution of manganese oxides and at the same time as the dissolution of iron oxyhydroxides and the onset of sulfate reduction. Laboratory experiments indicated that sulfate reduction and the production of sulfide ions are not solely responsible for the release of arsenic to the porewaters, although this process is necessary to create and maintain a highly reducing environment conducive to rapid iron dissolution.The diagenesis of arsenic in Laurentain Trough sediments involves the simultaneous release of arsenic and iron at a subsurface depth, followed by its removal from porewaters by precipitation and adsorption reactions after migration by diffusion along concentration gradients. A qualitative model is presented to describe the behavior of arsenic in coastal marine sediments.Present address: Department of Geological Sciences, McGill University, 3450 UniversityStreet, Montreal, Quebec H3A 2A7, Canada     

Sediment geochemistry of phosphorus at two intertidal sites on the Great Ouse estuary,S.E. England

The Great Ouse estuary in southern England is a macrotidal estuary with rather coarse sediment. Two intertidal sites were sampled five times over the year at low tide. The sediments are suboxic, organic poor (approximately 1.5% organic carbon). They are composed mainly of detrital quartz and feldspar with some calcite. At both sites the total phosphorus in the sediments ranges from 0.03 – 0.12% dry weight and total iron from 0.42–1.22% dry weight. Of the total phosphorus 20% is organic and 80% is inorganic of which 10% is water extractable. Total iron and phosphorus correlate well and the ratio of iron:phosphorus is 8.4 which is similar to that found when phosphorus is adsorbed by iron oxyhydroxides, suggesting that iron oxyhydroxides are an important substrate for phosphorus sorption in these sediments. Fluxes of phosphorus from the sediment to the overlying water, measured in cores incubated in the laboratory, are low and show no seasonality. The sodium concentration in the porewaters at both sites is variable suggesting that there is movement of water through the sediment to depths of at least 20 cm. This is borne out by variable phosphorus, iron and phosphorus concentrations in the porewaters and ill defined redox zones in the sediments.     

Lake Biwa and the ocean: geochemical similarity and difference

The average composition of water, bottom sediments, manganese (Mn) crusts, and Mn concretions from Lake Biwa (the largest freshwater lake in Japan) are re-examined, in conjunction with those of seawater, oceanic pelagic clay, and deep-sea Mn nodules. The purpose is to gain additional insights into the geochemical behaviors of elements in Lake Biwa and the ocean, which are quite different in ionic strength (or salinity), pH, water residence times, sediment accumulation rates, carbon fluxes to sediments, and the redox potential in sediments. Excluding a few millimeters of oxic surface sediment, there is no appreciable accumulation of Mn in the Lake Biwa bottom sediments due to reducing condition there. Consequently, other B-type cations [such as iron (Fe), gallium (Ga), copper (Cu), lead (Pb), cobalt (Co), tin (Sn), and bismuth (Bi), with subshell valence electron configuration of d ¹⁻¹⁰] are also less concentrated in the lake sediments than in the oceanic pelagic clay. In turn, B-type cations have much higher dissolved concentrations in the lake water than in the ocean. The rare earth elements (REE) mainly form organic complexes in the lake water and carbonate complexes in the ocean. REE are mostly associated with detritus aluminosilicate phases in Lake Biwa sediments but with phosphate phases in deep-sea sediments. Fe and Mn oxide phases are clearly separated in marine Mn nodules and crusts but not in Mn crusts and concretions from Lake Biwa. Useful parameters such as the enrichment factor (E _Al) and logarithms of the distribution coefficient (log K _d) of elements between solid and liquid phases were estimated in both systems for further discussions.     

Bioturbation in a declining oxygen environment, in situ observations from Wormcam

Bioturbation, the displacement and mixing of sediment particles by fauna or flora, facilitates life supporting processes by increasing the quality of marine sediments. In the marine environment bioturbation is primarily mediated by infaunal organisms, which are susceptible to perturbations in their surrounding environment due to their sedentary life history traits. Of particular concern is hypoxia, dissolved oxygen (DO) concentrations ≤2.8 mg l(-1), a prevalent and persistent problem that affects both pelagic and benthic fauna. A benthic observing system (Wormcam) consisting of a buoy, telemetering electronics, sediment profile camera, and water quality datasonde was developed and deployed in the Rappahannock River, VA, USA, in an area known to experience seasonal hypoxia from early spring to late fall. Wormcam transmitted a time series of in situ images and water quality data, to a website via wireless internet modem, for 5 months spanning normoxic and hypoxic periods. Hypoxia was found to significantly reduce bioturbation through reductions in burrow lengths, burrow production, and burrowing depth. Although infaunal activity was greatly reduced during hypoxic and near anoxic conditions, some individuals remained active. Low concentrations of DO in the water column limited bioturbation by infaunal burrowers and likely reduced redox cycling between aerobic and anaerobic states. This study emphasizes the importance of in situ observations for understanding how components of an ecosystem respond to hypoxia.     

Factors influencing the extent and development of the oxic zone in sediments

Dissolved oxygen concentrations in river-sediment porewaters are reported and modelled using a zero-order reaction rate and the Monod equation. After mixing the sediments and allowing settling, the dissolved oxygen profile in the bed-sediment was expected to reach a steady-state rapidly (< 1 h). However changes in the vertical profile of oxygen over a period of 38 days revealed that the penetration of oxygen increased and the dissolved oxygen flux at the interface decreased with time, probably as the oxidation kinetics of organic matter and redox reactions in the sediment changed. Experiments with three contrasting silt and sand dominated sediments (organic matter content between 0.9 and 18%) at two water velocities (ca 10 and 20 cm s^–1) showed that the dissolved oxygen profiles were independent of velocity for each of the sediments. The most important controls on the reaction rate were the organic matter content and specific surface area of the sediment. A viscous diffuse-boundary-layer above the sediment was only detected in the experiments with the silt sediment where the sediment oxygen demand was relatively high. In the coarser sediments, the absence of a diffuse layer indicated that slow oxidation processes in the sediment controlled the dissolved oxygen flux at the interface. The problem of determining a surface reference in coarse sediment is highlighted. The results are discussed with reference to other studies including those concerned with estuarine and marine sediments.     

Effects of added organic matter on iron and manganese redox systems in sediment

Addition of five types of organic matter to Lake Washington sediments resulted in release of high concentrations of iron, organic carbon, and manganese into the interstitial water, and caused an increase in observed sediment oxygen consumption rates. The depressed electrode potentials (E_h < —150 mV) that should accompany such reduction processes did not occur, indicating that E_h was being poised by redox systems present in the sediment. Iron redox systems [Fe(OH)₃‐Fe²⁺, Fe₃(OH)₈‐Fe²⁺, and Fe(OH)₃‐Fe₃(OH)₈] were shown to be poising the E_h of control sediments throughout 13 weeks of incubation and dominating the potential of several of the organically amended sediments following the first three weeks of incubation. Depression of calculated iron system E_o values relative to that of the control sediment early in the incubation appeared to be due to the decreased pH and non‐equilibrium conditions in the organic matter‐amended sediment during the first weeks of incubation. Manganese redox systems exerted no discernable impact on the E_h of the sediment.     

Determination of Manganese Stability in a Constructed Wetland Sediment Using Redox Gel Probes

Redox gel probes containing immobilized particulate manganese compounds (MnO 2 , MnCO 3 , and MnS) were placed on a surveyed grid in the sediment of a wetland receiving coal mine drainage in western Pennsylvania (USA). The stability of these compounds in the wetland was shown to be highly variable both temporally and spatially, indicating that apparent manganese removal based on water quality data did not result in long-term manganese retention in sediments. Contour maps of the gel probe data revealed the importance of local environmental conditions, such as surface water velocity, on geochemical conditions influencing manganese compound stability in sediments, as well as seasonal changes in the ability of the wetland to retain MnO 2 in sediments. Estimates of in situ MnO 2 reduction rates using gel probe data agree with earlier published estimates based on laboratory studies. Although the factors influencing particulate metal stability in sediments are extremely complex and difficult to study, the redox gel probe method is demonstrated to be a cost-effective means of obtaining an areal and depth-related picture of that stability during a particular period of time.     

In situ study of short-term variations of redox species chemistry in intertidal permeable sediments of the Arcachon lagoon

We investigated the composition of porewaters in intertidal sediments in response to the diurnal rise and fall of tides. For this reason, we deployed an in situ voltammetric system to measure vertical distribution and time-series at defined depths of O₂, Mn(II), Fe(II), and S(?II) in the porewater of permeable sediments from a protected beach in the Arcachon Bay. We also report microprofiles of O₂ and pH together with sediment properties (organic carbon, particulate reactive manganese and iron, porosity and permeability). Results shows that the oxygen dynamics in the upper sediment at low tide appeared to be mainly controlled by microphytobenthos activity, which may migrate downward just before immersion. The tidal forcing seemed to influence the oxygen dynamic in a minor way through flushing of the uppermost sediment porewater layer at the beginning and end of immersion. Vertical profiles and time-series measurements showed that the distributions of reduced species varied with tides. Although this work reveals that the upper sediment layer was subject to redox changes, the response of vertical distributions of redox species to tidal and night?Cday cycles did not have a cyclic pattern.     

Invertebrate bioturbation can reduce the clogging of sediment: an experimental study using infiltration sediment columns

1. Invertebrate bioturbation can strongly affect water‐sediment exchanges in aquatic ecosystems. The objective of this study was to quantify the influence of invertebrates on the physical characteristics of an infiltration system clogged with fine sediment. 2. Two taxa (chironomids and tubificids) with different bioturbation activities were studied in experimental slow infiltration columns filled with sand and gravel and clogged with a 2 cm layer of fine sediment at the surface. We measured the effects of each taxon separately and combined on hydraulic head, water mobility and sediment reworking. 3. The results showed that invertebrates could reduce sediment clogging and this effect was linked to the functional mode of bioturbation of each group. Tubificid worms dug networks of galleries in the fine sediment, creating pathways for water flow, which reduced the clogging of sediment. In contrast, the U‐shaped tubes of chironomids were restricted to the superficial layer of fine sediments and did not modify the hydraulic conductivity of experimental columns. The combination of invertebrates did not show any interactive effects between tubificids and chironomids. The occurrence of 80 tubificids in the combination was enough to maintain the same hydraulic conductivity that 160 worms did in monospecific treatment. 4. The invertebrates like tubificid worms can have a great benefit on functioning of clogged interfaces by maintaining high hydraulic conductivity, which contributes to increased water‐sediment exchanges and stimulates biogeochemical and microbial processes occurring in river sediments.