Sediment Solid Phase Research Articles

Multi-disciplinary investigation of fluid seepage on an unstable margin: The case of the Central Nile deep sea fan

We report on a multidisciplinary study of cold seeps explored in the Central Nile deep-sea fan of the Egyptian margin. Our approach combines in situ seafloor observation, geophysics, sedimentological data, measurement of bottom-water methane anomalies, pore-water and sediment geochemistry, and 230Th/U dating of authigenic carbonates. Two areas were investigated, which correspond to different sedimentary provinces. The lower slope, at ∼ 2100 m water depth, indicates deformation of sediments by gravitational processes, exhibiting slope-parallel elongated ridges and seafloor depressions. In contrast, the middle slope, at ∼ 1650 m water depth, exhibits a series of debris-flow deposits not remobilized by post-depositional gravity processes. Significant differences exist between fluid-escape structures from the two studied areas. At the lower slope, methane anomalies were detected in bottom-waters above the depressions, whereas the adjacent ridges show a frequent coverage of fractured carbonate pavements associated with chemosynthetic vent communities. Carbonate U/Th age dates (∼ 8 kyr BP), pore-water sulphate and solid phase sediment data suggest that seepage activity at those carbonate ridges has decreased over the recent past. In contrast, large (∼ 1 km 2) carbonate-paved areas were discovered in the middle slope, with U/Th isotope evidence for ongoing carbonate precipitation during the Late Holocene (since ∼ 5 kyr BP at least). Our results suggest that fluid venting is closely related to sediment deformation in the Central Nile margin. It is proposed that slope instability leads to focused fluid flow in the lower slope and exposure of ‘fossil’ carbonate ridges, whereas pervasive diffuse flow prevails at the unfailed middle slope.

Distribution, partitioning and sources of polycyclic aromatic hydrocarbons in Daliao River water system in dry season, China

Eighteen polycyclic aromatic hydrocarbons (PAHs) were analyzed in 29 surface water, 29 suspended particulate matter (SPM), 28 sediment, and 10 pore water samples from Daliao River water system in dry season. The total PAH concentration ranged from 570.2 to 2318.6 ng L −1 in surface water, from 151.0 to 28483.8 ng L −1 in SPM, from 102.9 to 3419.2 ng g −1 in sediment and from 6.3 to 46.4 μg l −1 in pore water. The concentration of dissolved PAHs was higher than that of particulate PAHs at many sites, but the opposite results were generally observed at the sites of wastewater discharge. The soluble level of PAHs was much higher in the pore water than in the water column. Generally, the water column of the polluted branch streams contained higher content of PAHs than their mainstream. The environmental behaviors and fates of PAHs were examined according to some physicochemical parameters such as pH, organic carbon, SPM content, water content and grain size in sediments. Results showed that organic carbon was the primary factor controlling the distribution of the PAHs in the Daliao River water system. Partitioning of PAHs between sediment solid phase and pore water phase was studied, and the relationship between log K oc and log K ow of PAHs on some sediments and the predicted values was compared. PAHs other than naphthalene and acenaphthylene would be accumulated largely in the sediment of the Dalaio River water system. The sources of PAHs were evaluated employing ratios of specific PAHs compounds and different wastewater discharge sources, indicating that combustion was the main source of PAHs input.

Application of a new sediment contact test with Myriophyllum aquaticum and of the aquatic Lemna test to assess the sediment quality of Lake Skadar

Situated in the transboundary belt between Montenegro and Albania, Lake Skadar is the largest freshwater reservoir in Southeastern Europe. Because of the wide range of endemic, rare or endangered plant and animal species it supports, Lake Skadar and its extensive adjacent wetlands are internationally recognised as a site of significance and importance (Ramsar site). Within the last 10 to 20 years, Lake Skadar was exposed to intensive pollution. For the assessment of the ecotoxic load of the sediments sampled in Lake Skadar, a triad approach was recently applied. Overall, a complex spectrum of ecotoxic loads was elucidated. The aim of the present study was to use plant-based bioassays for assessing the sediment quality of Lake Skadar in order to facilitate and complement the triad test battery. The newly developed sediment contact test with Myriophyllum aquaticum and the aquatic growth inhibition test with Lemna minor were applied to native sediments and pore water, respectively, allowing the investigation of different toxicity-effects caused by particle-bound pollutants as well as pollutants in the interstitial water. This investigation is the first application of the novel sediment contact test with Myriophyllum aquaticum to lake sediments. Sediment samples were taken from nine selected sites at Lake Skadar and investigated by the sediment contact assay with Myriophyllum aquaticum. The pore water was extracted from these sediment samples to be analysed in the aquatic growth inhibition test with Lemna minor. The results of the sediment contact tests were compared with each other and with those of the aquatic growth inhibition test. Both applied macrophyte biotests revealed distinct changes in the growth behaviour of the two macrophytes subsequent to the exposure to the investigated natural sediments of Lake Skadar. The Myriophyllum sediment contact test revealed significant toxicity in the sediment samples from Radus and Kamenik, whereas the aquatic Lemna test showed inhibition effects for the samples from Sterbeq, Plavnica and Kamice. Data obtained with the newly developed Danio rerio contact test and the Arthrobacter globiformis contact test confirmed the Myriophyllum results. Analyses of the heavy metal content in the sediments revealed low or moderate contamination levels. Correlation analyses between the content of heavy metals in the sediments and growth inhibition of Myriophyllum aquaticum showed a significant correlation between Cr concentrations and growth inhibition. Comparable findings are available for a German river system. In contrast, no significant correlation between inhibition rates and concentration of metals could be observed with Lemna minor. It was shown that the newly developed sediment contact test with Myriophyllum aquaticum is applicable to lake sediments. In both the sediment contact test with Myriophyllum aquaticum on whole sediments and the aquatic growth inhibition test with Lemna minor on pore water, plant growth was influenced by the natural sediments and its components. Therefore, both test systems were found to be suitable for the detection of phytotoxic effects upon exposure to sediments. Myriophyllum aquaticum as test organism of the contact test grows directly in the sediment without an additional water-layer. Thus, it is able to detect toxicity caused by particle-bound phytotoxic substances as well as pore water-related contamination, while the floating Lemna minor can only detect effects emanating from pore water. Significant differences of the results were observed between these two test systems and, accordingly, the two different exposure scenarios. Hence, none of the tests can replace the other one and, as a consequence, both should be included into a test battery for the assessment of sediment toxicity. Both plant assays were shown to be reliable tools for the evaluation of the eco-toxicological risk potentials of pore water and solid-phase sediment. They should become a complement to the standardised test battery generally used for comprehensive hazard assessment.

Sr/Ca and Mg/Ca ratios in Niger Delta sediments: Implications for authigenic carbonate genesis in cold seep environments

We report on a reconnaissance analysis of the geochemical composition of authigenic carbonates and sediment samples collected from various seepage sites on the Niger deep-sea fan. Our aim has been to investigate whether evidence for the presence of authigenic carbonates and gas hydrates within sediments is discernible from solid-phase sediment geochemistry. We show that sedimentary Sr/Ca and Mg/Ca ratios can be used to infer the presence of authigenic aragonite (Sr-rich) and Mg-rich carbonate phases (high-Mg calcite, dolomite) in cold seep settings. Using Sr/Ca and Mg/Ca ratios, the proportion (wt.%) of authigenic carbonates in Niger Fan sediments can be calculated from a mixing model between sediment fractions of terrigenous material, biogenic calcite, aragonite and high-Mg calcite. This approach was applied to high-resolution geochemical profiles along sediment cores recovered from various cold seep settings (mud volcano, diapirs, pockmarks, gas-hydrate bearing sediments). Our data reveal that authigenic carbonates occur as discrete phases in sediments from gas-hydrate-bearing areas, suggesting that such carbonate-rich sediment layers may represent paleo-indicators for ancient methane seepage in marine sediments, possibly associated to gas-hydrate reservoirs.

A combination of magnetic permeability detection with nanometer-scaled superparamagnetic tracer and its application for one-step detection of human urinary albumin in undiluted urine

A rapid (6.5 min) and simple one-step magnetic immunoassay (MIA) has been developed for analysis of human urinary albumin in near patient settings. Polyclonal rabbit anti-human albumin was used as a capture antibody and monoclonal mouse anti-human albumin as a detection antibody in a two-site immunometric assay requiring no additional washing procedures. The polyclonal anti-human albumin was conjugated to silica microparticles (solid phase) and the monoclonal antibody to dextran-coated nanoscaled superparamagnetic particles (tracer). Quantification of human albumin in undiluted urine was performed by adding 2 microL urine to a measuring vial containing solid-phase, superparamagnetic tracer and reaction buffer and then inverting the vial by hand for 20 s. The measuring vial was allowed to stand for 6 min prior to detection, in order for the solid-phase sediment to form at the bottom of the vial. Lastly, the measuring vial was placed into a magnetic permeability detector, which measured the enrichment of superparamagnetic tracer in the sediment due to complex formation with human albumin. Total analysis time was 6.5 min. A linear response was obtained for 0-400 mg/L albumin with a detection limit of 5 mg/L. The total coefficient of variation (CV) was 11% calculated from four consecutive runs on a urine sample containing 11.1 mg/L human albumin during 3 consecutive days. Human urinary albumin analysis was performed on 149 patient samples using the MIA technique and the obtained results showed good correlation with the hospital immunoturbidimetric reference method (y = 1.004x + 4.01, R2 = 0.978, N = 149) and a commercially available point of care albumin analysis provided by HemoCue Inc. (y = 0.98x + 5.8, R2 = 0.833, N = 90).

Detection of C-Reactive Protein Utilizing Magnetic Permeability Detection Based Immunoassays

A new sensing technology platform integrating magnetic permeability detection and a two-site heterogeneous immunoassay in a one-step analysis is described. As a platform model, measurements of C-reactive protein (CRP), a cardiac and inflammation marker, were performed in a rapid (11.5 min) high-sensitivity (hs) procedure with a low detection limit (0.2 mg/L) and accuracy (CV = 11%). The two-site heterogeneous immunoassay was performed in 1.2-mL disposable reagents vials containing solid phase (polyclonal anti-CRP conjugated silica microparticles), labeling agent (monoclonal anti-CRP conjugated superparamagnetic nanoparticles), and reaction buffer. Whole blood (20 muL) was assayed by introducing the sample into a reagent vial using a glass capillary and mixing its contents by hand for 30 s. After a 11-min sedimentation step, the vial was placed into the coil of the magnetic permeability detector, which measured the enrichment of superparamagnetic nanoparticles in the solid-phase sediment. Magnetic permeability detection and quantification is based on the principle that when paramagnetic materials are placed inside a coil, the inductance of the coil is influenced. Screening of CRP on whole blood patient samples showed good correlation with central hospital measurements for hsCRP (y = 1.018x - 0.021, R(2) = 0.980, n = 103) and normal range CRP (y = 1.02x + 2.53, R(2)= 0.991, n = 33) analyses. The mean differences of the two methods according to the Bland and Altman plots were -0.03 +/- 1.12 mg/L for hsCRP analysis and -3.4 +/- 8.64 mg/L for normal range CRP analysis.

Potential impact of dare county landfills on Alligator River National Wildlife Refuge

Runoff of leachate from East Lake and Dare County Construction and Demolition Debris landfills has the potential to impact wildlife resources at Alligator River National Wildlife Refuge, Dare and Hyde Counties, North Carolina. Sediment quality of samples collected in August 2000 at 14 locations down-gradient from the landfills was assessed by measuring metal and organic contaminants in the sediments, chronic toxicity of solid-phase sediment (28-d static-renewal exposures; survival and growth as test endpoints) and acute toxicity of sediment porewater (96-h static exposures) to Hyalella azteca (Crustacea: Amphipoda). In addition, contaminant bioaccumulation from 4 sediments was determined using 28-d exposures of Lumbriculus variegatus (freshwater oligochaete). Although survival was not impaired, length of H. azteca was significantly reduced in sediments from 5 locations. Pore water from 4 locations was acutely toxic to H. azteca. Metals and a few polycyclic aromatic hydrocarbons (PAHs) were bioaccumulated by L. variegatus from the sediments. Several metals and PAHs exceeded sediment quality guidelines, and metals in porewater from several sites exceeded water quality criteria for the protection of aquatic wildlife. Runoff of leachate from the landfills has reduced sediment quality and has the potential to adversely affect wildlife resources at Alligator River National Wildlife Refuge.

In-situ partitioning of butyltin compounds in estuarine sediments

The in-situ solid/pore-water partitioning of tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT) was determined for an estuarine sediment profile collected from a commercial marina. Total butyltin levels exceeded sediment quality guideline values, and were 220–8750 μg/kg for TBT, 150–5450 μg/kg for DBT and 130–4250 μg/kg for MBT. Pore-water butyltin concentrations ranged from 0.05 to 2.35 μg/l for TBT, 0.07–3.25 μg/l for DBT, and 0.05–0.53 μg/l for MBT. The partitioning of butyltin compounds between the sediment solid-phase and pore-water was described by an organic carbon normalised distribution ratio ( D OC). The observed D OC values were similar for TBT, DBT and MBT, and were 10 5–10 6 l/kg. Values for the Butyltin Degradation Index (BDI) were larger than 1 at depths greater than 10 cm below the sediment/water-column interface. This indicates that substantial TBT degradation has occurred in the sediments, and suggests that natural attenuation may be a viable sediment remediation strategy.

Sediment quality in freshwater impoundments at Savannah National Wildlife Refuge.

Freshwater impoundments at Savannah National Wildlife Refuge (NWR), South Carolina, provide an important habitat for wildlife species, but degraded sediment quality in the Savannah River downstream of the discharge from two impoundments have caused concern about potential contaminant problems within the impoundments. The quality of sediments from five impoundments (impoundments no. 1, 2, 6, 7, and 17) on the NWR was evaluated using physical and chemical characterization, contaminant concentrations (metals, organochlorine pesticides, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons), and toxicity testing. Survival of Hyalella azteca (freshwater amphipod) exposed for 28 days to solid-phase sediments was not significantly different from controls, but growth was significantly decreased at several sites. Survival in 96-hour exposures to sediment pore water was significantly decreased at most sites. Factors contributing to the toxic responses were low pH (3.7 to 4.1), ammonia (20 mg/L), and increased concentrations of cations in the pore water. The excess of simultaneously extracted metals over the acid volatile sulfides in the sediments was also typical of sites displaying decreased sediment quality. Elemental concentrations in pore water were negatively correlated with pH, and the highest concentrations were observed in impoundment no. 7. The acidic nature of the sediment in this impoundment was exacerbated by recent draining, burning, and disking, which allowed oxidation of the previously anoxic wetland sediment. Sediment disturbance and mixing of vegetation into the sediments by disking may also have contributed to the formation of ammonia caused by microbial decomposition of the fragmented organic matter. Contaminants were not detected in sediments from the impoundments, but releases of acidic water with increased levels of sediment cations from the impoundments may have contributed to the degraded sediment conditions previously observed in the river. The practice of dewatering sediments for vegetation control may exacerbate the acidification of vulnerable sediments within impoundments of this NWR.

Evaluating toxicity of Asana XL ® (esfenvalerate) amendments in agricultural ditch mesocosms

Agricultural ditches primarily serve to remove and store excess water associated with irrigation and storm events. The ability of these ecosystems to mitigate potential contaminants is not well understood. Five sites along a 650-m agricultural ditch located in the Mississippi Delta Management Systems Evaluation Area (MDMSEA) were used to measure fate and effects of an esfenvalerate (insecticide) exposure. Following a 0.64-cm simulated storm event, samples were collected from water and sediments and analyzed spatially from five sites and temporally from 0.5 h to 56 d. Results of aqueous toxicity bioassays indicated that lethality progressed downstream throughout all sampling intervals, while sediment toxicity bioassays only elicited biological responses at the point of pesticide application to the ditch (0 m). Significant reductions in survival of Ceriodaphnia dubia and Pimephales promelas in water were measured at the 0-, 20-, and 80-m sites following application. Ten-day solid phase sediment testing of Chironomus tentans indicated persistent toxicity only at the point of application (0 m) and throughout 56 d (mean=14.4% survival). No lethality or significant reduction in midge growth was measured for remaining downstream sites. These measurements were used to evaluate the potential of agricultural ditches to reduce potential deleterious effects of contaminants in agricultural drainage systems that precede receiving streams.

Carbon and Nutrient Cycling at the Sediment-water Boundary in Western Lake Superior

Organic carbon and nutrient settling rates, benthic recycling rates, and material burial rates were measured in the western arm of Lake Superior. Organic carbon settling rates, measured using particle-intercepting sediment traps, averaged 2.3 mmol m −2 day −1 over the course of the experiment. Measured particle settling fluxes exhibit a minimum during winter and a maximum during spring. Sediment oxygen uptake rates measured throughout the basin average 2.2 ± 0.8 mmol m −2 day −1 (n = 16) and nitrate, soluble reactive phosphorus, and silicic acid efflux rates average 0.15 ± 0.07 (n = 25), 0.005 ± 0.006 (n = 23), and 1.34 ± 0.4 mmol m −2 day −1 (n = 26), respectively. Sediment solid-phase, particle settling rate, and benthic efflux data demonstrate that organic carbon, nitrogen, and biogenic silica are recycled at the sediment- water interface with an efficiency of ∼60% or greater in western Lake Superior. In contrast to these constituents, phosphorus recycling efficiency is lowest at sites close to the two major river inputs of (∼10%) and highest at our deepest site (∼40%). Despite these low recycling efficiencies for phosphorus, the benthic flux of phosphorous is an essential and dominant component to the lake's annual internal budget contributing ∼50% of the total annual phosphorus inputs to the water column.

A new sediment contact assay to assess particle-bound pollutants using zebrafish (danio rerio) embryos

Goal, Scope and Background. Based on a bioassay battery covering only primary producers and consumers as well as degraders, the potential ecological hazard of sediments to vertebrates cannot be estimated comprehensively. Therefore, there is an urgent need to develop and standardize integrated vertebrate-based test systems for sediment investigation strategies. Whereas vertebratebased in vitro systems have frequently been used for the investigation of aqueous samples, there is a significant lack of whole sediment assays. Thus, the purpose of the present study was: (1) to develop a rapid and reliable, but comprehensive method to investigate native sediments and particulate matters without preceding extraction procedures; (2) to compare the hazard potential of solid phase sediments to the effects of corresponding pore waters and organic extracts in order to characterize the bioavailability of the particle-bound pollutants; and (3) to relatively evaluate the embryotoxic effects of sediments from the catchment areas of the rivers Rhine, Neckar and Danube.Methods (or Main Features).To investigate the toxicity of sediment samples on vertebrates, the standard embryo toxicity test with the zebrafish (Danio rerio; Hamilton-Buchanan 1922) according to DIN 38415-6 was modified with respect to exposure scheme and toxicological endpoints. Sediments from the catchment area of the Neckar River were assessed using pore waters, acetonic extracts and native sediments in order to get inside into the potential bioavailability of particle-bound pollutants. A comprehensive test protocol for the investigation of native sediments in the embryo toxicity test with the zebrafish is presented.Results and Discussion.The fish embryo assay with Danio rerio can be carried out with both aqueous and organic sediment extracts as well as native (whole, solid phase) sediment samples. Elongation of exposure time from 48 to up to 196 h significantly increased the mortality. Using the fish egg assay with native sediments, a broad range of embryotoxic effects could be elucidated, including clear-cut dose-response curves for the embryotoxic effects of contaminated sediments; in contrast, absence of embryotoxic effects could be demonstrated even for the highest test concentrations of unpolluted sediments. With native sediments, embryotoxicity was clearly higher than with corresponding pore waters, thus corroborating the view that — at least for fish eggs — the bioavailability of particle-bound lipophilic substances in native sediments is higher than generally assumed. The relative ranking of sediment toxicity was identical using both native sediments and sediment extracts, EC20 values of the latter, however, being eight time lower higher than with the native sediments. A comparison of the embryo toxic effects of samples from the Neckar area with locations along the Rhine and Danube rivers elucidated a broad range of results, thus indicating different levels of contamination.Conclusions.A modified protocol of the zebrafish embryo test allows the assessment of sediment toxicity in both aqueous extracts and native sediments. The isolated investigation of pore waters may result in a clear-cut underestimation of the bioavailability of lipophilic particle-bound substances (as determined by native sediments).Recommendations and Perspectives.The zebrafish embryo test with native (whole, solid phase) sediments appears very promising for the evaluation of the bioavailable fraction of lipophilic particle-bound substances and can therefore be recommended for the evaluation of vertebrate toxicity in tiered sediment test strategies and dredging directives such as the HABAB-WSV. Whereas acetone extracts may be tested as a rough estimation of embryotoxicity, native sediment samples will provide a more comprehensive and realistic insight into the bioavailable hazard potential

Early diagenesis and isotopic composition of lead in Lake Laisan, northern Sweden

Water column (dissolved/suspended phase, sediment traps) and sediment data (pore-water, solid-phase sediment) were combined with stable Pb and 210Pb isotope data to trace the early diagenetic behaviour and geochemical cycling of Pb in Lake Laisan, a lake which has received large quantities of anthropogenic Pb since the early 1940s. Early diagenetic remobilisation of Pb is indicated by a subsurface pore-water Pb maximum (120 μg l −1) in the oxic surface layer of the sediment, where the solid-phase Pb concentration is 3400–4600 μg g −1. The remobilisation of Pb appears to be caused by a pH-controlled desorption of Pb from solid-phase sediment, which is consistent with a model describing surface complexation of Pb(II) on hydrous goethite surfaces. The diffusive Pb flux from the subsurface pore-water maximum towards the sediment surface (36 μg cm −2 year −1) exceeds the depositional Pb flux (8.6 μg cm −2 year −1) by approximately a factor of four, indicating that Pb is highly mobile in the sediment. Stable Pb isotope data and a mass balance calculation suggest that Pb diffusing upwards is, to a large extent, trapped in the surface sediment. Lead that may diffuse into the slightly alkaline lake water appears to be efficiently sorbed to suspended particulate matter, resulting in low dissolved Pb concentrations in the water column (0.040–0.046 μg l −1). Sorption of Pb to suspended particulate matter is consistent with the elevated suspended particulate Pb concentrations in the hypolimnion (3800–4000 μg g −1), and the fact that the stable Pb isotopic compositions of suspended matter and pore-water are similar.

Seasonal Dynamics of the Sulphate Reduction Rate on the North-western Black Sea Shelf

The microbial sulphate reduction rate (SRR) in the surface layer (0–30 cm) of shallow water sediments of the north-western Black Sea shelf has been measured using the 35S radioisotopic technique. It was shown that SRR is accompanied by changes of salt composition of porewaters and isotopic (δ 34S) composition of sulphate. The hydrogen sulphide-derived minerals are formed in the solid phase of sediments. An expected exponential dependence of the isotopic composition of reduced sulphur compounds on the SRR was observed. In near-shore sediments, terrestrial organic carbon (δ 13C≈−26‰) as well as marine phytoplankton organic carbon (δ 13C≈−22‰) are associated with the SR processes. In August 1995 and May 1997–1998, anoxic conditions in near-bottom waters of coastal areas were not detected. The average value of H 2S production in nearshore sediments varied from 3·62 mmol S m −2 day −1 in spring to 8·89 mmol S m −2 day −1 in summer 1995; these fluxes were twice as high as those measured in spring 1997 and 1998.

Germanium-68 as a tracer for silicon fluxes in freshwater sediment

The sorption of Si may decisively influence the P dynamics in surface sediment through competitive ligand exchange mechanisms. Many aspects of the process, such as the impact of Si dissolving from diatoms, are both insufficiently known and difficult to monitor by quantitative analyses due to the ubiquitousness of Si in sediment. Since the radioactive isotopes of Si have impractical half-times, the applicability of 68Ge as a tracer for Si additions in both inorganic and biogenic form to freshwater sediment (Lake Vesijärvi, Southern Finland) was studied in a 24-h laboratory experiment. The 68Ge-label was added to the sediment with either inorganic Si (940 mg l −1) or diatoms (3.2×10 6 cells l −1), and the distributions of the 68Ge-label and the different forms of added Si between the interstitial water and sequentially extracted, solid-phase sediment pools were critically examined. The inorganic Si addition significantly increased the amount of Si in the interstitial water and in the reversibly bound fraction, while the diatom addition had no discernible effects. The relative distribution of Si and 68Ge between the various sediment pools indicated that the first sorption phase of the added inorganic Si was similar to that reported for P. The high concentration of diatom-derived 68Ge-labelled Si in the interstitial water and in the easily soluble, reversibly bound pool indicated rapid dissolution of the added diatoms. The comparable distributions of the diatom-derived and inorganic Si-derived 68Ge-label within the studied pools indicated that the sorption of Si dissolving from diatoms in surface sediment closely resembles that of an inorganic addition of Si. Caution about the chemical speciation of the 68Ge-label is, however, advisable in sediment environments. Fractionation procedures designed for e.g. P may also be of limited use when applied to a different element, such as Si.

Toxicity assessment of sediments from the Grand Calumet River and Indiana Harbor Canal in Northwestern Indiana, USA.

The objective of this study was to evaluate the toxicity of sediments from the Grand Calumet River and Indiana Harbor Canal located in northwestern Indiana, USA. Toxicity tests used in this assessment included 10-day sediment exposures with the amphipod Hyalella azteca, 31-day sediment exposures with the oligochaete Lumbriculus variegatus, and the Microtox Solid-Phase Sediment Toxicity Test. A total of 30 sampling stations were selected in locations that had limited historic matching toxicity and chemistry data. Toxic effects on amphipod survival were observed in 60% of the samples from the assessment area. Results of a toxicity test with oligochaetes indicated that sediments from the assessment area were too toxic to be used in proposed bioaccumulation testing. Measurement of amphipod length after the 10-day exposures did not provide useful information beyond that provided by the survival endpoint. Seven of the 15 samples that were identified as toxic in the amphipod tests were not identified as toxic in the Microtox test, indicating that the 10-day H. azteca test was more sensitive than the Microtox test. Samples that were toxic tended to have the highest concentrations of metals, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs). The toxic samples often had an excess of simultaneously extracted metals (SEM) relative to acid volatile sulfide (AVS) and had multiple exceedances of probable effect concentrations (PECs). Metals may have contributed to the toxicity of samples that had both an excess molar concentration of SEM relative to AVS and elevated concentrations of metals in pore water. However, of the samples that had an excess of SEM relative to AVS, only 38% of these samples had elevated concentration of metals in pore water. The lack of correspondence between SEM-AVS and pore water metals indicates that there are variables in addition to AVS controlling the concentrations of metals in pore water. A mean PEC quotient of 3.4 (based on concentrations of metals, PAHs, and PCBs) was exceeded in 33% of the sediment samples and a mean quotient of 0.63 was exceeded in 70% of the thirty sediment samples from the assessment area. A 50% incidence of toxicity has been previously reported in a database for sediment tests with H. azteca at a mean quotient of 3.4 in 10-day exposures and at a mean quotient of 0.63 in 28-day exposures. Among the Indiana Harbor samples, most of the samples with a mean PEC quotient above 0.63 ( i.e., 15 of 21; 71%) and above 3.4 ( i.e., 10 of 10; 100%) were toxic to amphipods. Results of this study and previous studies demonstrate that sediments from this assessment area are among the most contaminated and toxic that have ever been reported.

Evaluation and use of sediment toxicity reference sites for statistical comparisons in regional assessments

Sediment reference sites were used to establish toxicity standards against which to compare results from sites investigated in San Francisco Bay (California, USA) monitoring programs. The reference sites were selected on the basis of low concentrations of anthropogenic chemicals, distance from active contaminant sources, location in representative hydrographic areas of the Bay, and physical features characteristic of depositional areas (e.g., fine grain size and medium total organic carbon [TOC]). Five field-replicated sites in San Francisco Bay were evaluated over three seasons. Samples from each site were tested with nine toxicity test protocols and were analyzed for sediment grain size and concentrations of trace metals, trace organics, ammonia, hydrogen sulfide, and TOC. The candidate sites were found to have relatively low concentrations of measured chemicals and generally exhibited low toxicity. Toxicity data from the reference sites were then used to calculate numerical tolerance limits to be used as threshold values to determine which test sites had significantly higher toxicity than reference sites. Tolerance limits are presented for four standard test protocols, including solid-phase sediment tests with the amphipods Ampelisca abdita and Eohaustorius estuarius and sea urchin Strongylocentrotus purpuratus embryo/larval development tests in pore water and at the sediment-water interface (SWI). Tolerance limits delineating the lowest 10th percentile (0.10 quantile) of the reference site data distribution were 71% of the control response for Ampelisca, 70% for Eohaustorius, 94% for sea urchin embryos in pore water, and 87% for sea urchins embryos exposed at the SWI. The tolerance limits are discussed in terms of the critical values governing their calculation and the management implications arising from their use in determining elevated toxicity relative to reference conditions.

Interactions between metal oxides and species of nitrogen and iodine in bioturbated marine sediments

By using a gold amalgam (Au/Hg) voltammetric microelectrode, we have measured simultaneously and with millimeter resolution the distributions of O 2, Mn(II), Fe(II), I(−I), and HS(−I) in bioturbated sediment cores from the Laurentian Trough. We also measured nitrate and ammonia in the pore water, total I and ascorbate- and HCl-extractable Fe and Mn in the solid-phase sediment, and fluxes of O 2, NO 3 −, and NH 4 + across the sediment–water interface. The concentrations of O 2 and Mn(II) were below their respective detection limits of 3 and 5 μM between 4 and 12 mm depth, but a sharp iodide maximum occurred at the depth where upward diffusing Mn(II) was being removed. We propose that the iodide peak is maintained through the reduction of IO 3 − by Mn(II), reoxidation of I(−I) to IO 3 − in the oxic zone above the peak and oxidation to I 2 below where it is ultimately trapped by reaction with organic matter. The iodide production rate is sufficient to account for the oxidation of all of the upward diffusing Mn(II) by IO 3 −. Nitrate plus nitrite (ΣNO 3) decreased to a minimum within 10 mm of the sediment–water interface, in agreement with flux measurements which showed ΣNO 3 uptake by the sediment. Below the minimum, ΣNO 3 rebounded, and reached a maximum at 40- to 50-mm depth. This rebound is attributed to the anaerobic oxidation of ammonia by manganese oxides. Fe(II) was always first detected below the anoxic ΣNO 3 maximum, and was accompanied by colloidal or complexed Fe(III). A sharp upward-directed ammonia gradient was recorded near the sediment–water interface, but no ammonia was released during the first 48 h of the incubations. If the ammonia removal were due to coupled bacterial nitrification–denitrification, more than one half of the total measured oxygen uptake (6.7 to 7.3 mmol/m 2/d) would be required, and more organic carbon would be oxidized by nitrate than by oxygen. This scenario is not supported by nitrate flux calculations. Alternatively, the oxidation of ammonia to N 2 by manganese oxides is a potential removal mechanism. It would require one quarter of the total oxygen flux. The high-resolution profiles of redox species support the conceptualization of bioturbated sediments as a spatially and temporally changing mosaic of redox reactions. They show evidence for a multitude of reactions whose relative importance will vary over time, and for reaction pathways complementing those usually considered in diagenetic studies.

Effects of contaminants in dredge material from the lower Savannah River.

Contaminants entering aquatic systems from agricultural, industrial, and municipal activities are generally sequestered in bottom sediments. The environmental significance of contaminants associated with sediments dredged from Savannah Harbor, Georgia, USA, are unknown. To evaluate potential effects of contaminants in river sediments and sediments dredged and stored in upland disposal areas on fish and wildlife species, solid-phase sediment and sediment pore water from Front River, Back River, an unnamed Tidal Creek on Back River, and Middle River of the distributary system of the lower Savannah River were tested for toxicity using the freshwater amphipod Hyalella azteca. In addition, bioaccumulation of metals from sediments collected from two dredge-disposal areas was determined using the freshwater oligochaete Lumbriculus variegatus. Livers from green-winged teals (Anas crecca) and lesser yellowlegs (Tringa flavipes) foraging in the dredge-spoil areas and raccoons (Procyon lotor) from the dredge-disposal/river area and an upland site were collected for metal analyses. Survival of H. azteca was not reduced in solid-phase sediment exposures, but was reduced in pore water from several locations receiving drainage from dredge-disposal areas. Basic water chemistry (ammonia, alkalinity, salinity) was responsible for the reduced survival at several sites, but PAHs, metals, and other unidentified factors were responsible at other sites. Metal residues in sediments from the Tidal Creek and Middle River reflected drainage or seepage from adjacent dredge-disposal areas, which could potentially reduce habitat quality in these areas. Trace metals increased in L. variegatus exposed in the laboratory to dredge-disposal sediments; As, Cu, Hg, Se, and Zn bioaccumulated to concentrations higher than those in the sediments. Certain metals (Cd, Hg, Mo, Se) were higher in livers of birds and raccoons than those in dredge-spoil sediments suggesting bioavailability. Cadmium, Cr, Hg, Pb, and Se in livers from raccoons collected near the river and dredge-disposal areas were significantly higher than those of raccoons from the upland control site. Evidence of bioaccumulation from laboratory and field evaluations and concentrations in sediments from dredge-disposal areas and river channels demonstrated that some metals in the dredge-disposal areas are mobile and biologically available. Drainage from dredge-disposal areas may be impacting habitat quality in the river, and fish and wildlife that feed and nest in the disposal areas on the lower Savannah River may be at risk from metal contamination.

Geochemistry of barium in marine sediments: implications for its use as a paleoproxy

Variations in the accumulation rate of barium in marine sediments are thought to be indicative of variations in marine biological productivity through time. However, the use of Ba as a proxy for paleoproductivity is partly dependent upon its being preserved in the sediment record in a predictable or consistent fashion. Arguments in favor of high Ba preservation are partly based on the assumption that sediment porewaters are generally at saturation with respect to pure barite. The idea is that because nondetrital sedimentary Ba predominantly exists as barite, porewater saturation would promote burial. We present sediment porewater, sediment solid phase, and benthic incubation chamber data suggesting that solid-phase Ba preservation may be compromised in some geochemical settings. We propose that under suboxic diagenetic conditions, characterized by low bottom water oxygen and high organic carbon respiration rates, Ba preservation may be reduced. Independent of the mechanism, if this assertion is true, then it becomes important to know when the Ba record is unreliable. We present evidence demonstrating that the sedimentary accumulation of authigenic U may serve as a proxy for when the Ba record is unreliable. We then provide an example from the Southern Ocean during the last glacial period where high authigenic U concentrations coincide with high Pa:Th ratios and high accumulation rates of biogenic opal, but we find low accumulation rates of sedimentary Ba. Thus, for the study sites presented here during the last glacial, we conclude that Ba is an unreliable productivity proxy.