Estuarine Surface Sediments Research Articles

Widespread release of old carbon across the Siberian Arctic echoed by its large rivers

Abstract. Over decadal-centennial timescales, only a few mechanisms in the carbon-climate system could cause a massive net redistribution of carbon from land and ocean systems to the atmosphere in response to climate warming. The largest such climate-vulnerable carbon pool is the old organic carbon (OC) stored in Arctic permafrost (perennially frozen) soils. Climate warming, both predicted and now observed to be the strongest globally in the Eurasian Arctic and Alaska, causes thaw-release of old permafrost carbon from local tundra sites. However, a central challenge for the assessment of the general vulnerability of this old OC pool is to deduce any signal integrating its release over larger scales. Here we examine radiocarbon measurements of molecular soil markers exported by the five Great Russian-Arctic Rivers (Ob, Yenisey, Lena, Indigirka and Kolyma), employed as natural integrators of carbon release processes in their watersheds. The signals held in estuarine surface sediments revealed that average radiocarbon ages of n-alkanes increased east-to-west from 6400 yr BP in Kolyma to 11 400 yr BP in Ob. This is consistent with westwards trends of both warmer climate and more degraded organic matter as indicated by the ratio of high molecular weight (HMW) n-alkanoic acids to HMW n-alkanes. The dynamics of Siberian permafrost can thus be probed via the molecular-radiocarbon signal as carried by Arctic rivers. Old permafrost carbon is at present vulnerable to mobilization over continental scales. Climate-induced changes in the radiocarbon fingerprint of released permafrost carbon will likely depend on changes in both permafrost coverage and Arctic soil hydraulics.

Influence of Microbially Reducible Fe(III) on the Bacterial Community Structure of Estuarine Surface Sediments

We analyzed PCR-amplified 16S rRNA genes from native and Fe(III)-enriched surface sediments of a major tidal channel in the Tijuana River Estuary, California, USA. Clones from native sediments were most closely affiliated with photosynthetic taxa (Cyanobacteria, Chloroflexi, and Halochromatium) and microorganisms known to reduce (Desulfatibacillus, Desulfobacterium, and Desulfuromusa) or oxidize (Microcoleus, Phormidium, and Halochromatium) various sulfur species, reflective of the fluctuating redox conditions in the tidal zone. Fe(III) was rapidly reduced in anaerobic microcosms amended with 2-line ferrihydrite, with or without the sulfate reduction inhibitor sodium molybdate. The addition of ferrihydrite without molybdate caused a major shift in community structure to a dominance of the Fe(III)-reducing genus Shewanella, while at the same time the sulfate-reducing and sulfide-oxidizing populations were replaced by taxa known to cycle elemental sulfur. Sediments amended with both ferrihydrite and molybdate were again populated by Shewanella clones, but also numerically important were clones most similar to Marinobacterium, Pseudomonas, and Bacillus, suggesting a role for these taxa in Fe(III) reduction in marine habitats.

Bulk organic δ 13C and C/N as indicators for sediment sources in the Pearl River delta and estuary, southern China

Preservation of organic matter in estuarine and coastal areas is an important process in the global carbon cycle. This paper presents bulk δ 13C and C/N of organic matter from source to sink in the Pearl River catchment, delta and estuary, and discusses the applicability of δ 13C and C/N as indicators for sources of organic matter in deltaic and estuarine sediments. In addition to the 91 surface sediment samples, other materials collected in this study cover the main sources of organic material to estuarine sediment. These are: terrestrial organic matter (TOM), including plants and soil samples from the catchment; estuarine and marine suspended particulate organic carbon (POC) from both summer and winter. Results show that the average δ 13C of estuarine surface sediment increases from −25.0 ± 1.3‰ in the freshwater environment to −21.0 ± 0.2‰ in the marine environment, with C/N decreasing from 15.2 ± 3.3 to 6.8 ± 0.2. In the source areas, C 3 plants have lower δ 13C than C 4 plants (−29.0 ± 1.8‰ and −13.1 ± 0.5‰ respectively). δ 13C increases from −28.3 ± 0.8‰ in the forest soil to around −24.1‰ in both riverbank soil and mangrove soil due to increasing proportion of C 4 grasses. The δ 13C POC increases from −27.6 ± 0.8‰ in the freshwater areas to −22.4 ± 0.5‰ in the marine-brackish-water areas in winter, and ranges between −24.0‰ in freshwater areas and −25.4‰ in brackish-water areas in summer. Comparison of the δ 13C and C/N between the sources and sink indicates a weakening TOM and freshwater POC input in the surface sedimentary organic matter seawards, and a strengthening contribution from the marine organic matter. Thus we suggest that bulk organic δ 13C and C/N analysis can be used to indicate sources of sedimentary organic matter in estuarine environments. Organic carbon in surface sediments derived from anthropogenic sources such as human waste and organic pollutants from industrial and agricultural activities accounts for less than 10% of the total organic carbon (TOC). Although results also indicate elevated δ 13C of sedimentary organic matter due to some agricultural products such as sugarcane, C 3 plants are still the dominant vegetation type in this area, and the bulk organic δ 13C and C/N is still an effective indicator for sources of organic matter in estuarine sediments.

Assessment of heavy metal pollution in estuarine surface sediments of Tangxi River in Chaohu Lake Basin

A total of 30 surface sediments samples from the estuary wetland of the Tangxi River, Chaohu Lake Basin were obtained and tested. Enrichment factor (EF) and geoaccumulation index (Igeo) as well as multivariate statistical analysis methods including Factor Analysis (FA) and Hierarchical Cluster Analysis (HCA) were applied for the assessment of heavy metal pollution in surface sediments. The results of EF values show that the pollution of copper (Cu) and cadmium (Cd) occurs in the estuarine sediments, and that zinc (Zn), lead (Pb) and chrome (Cr) may originate from crustal materials or natural weathering process. The mean EF values of the five heavy metals are in the decreasing order: Cu>Cd>Zn>Pb>Cr. Based on the Igeo of target heavy metals, the surface sediments collected from the study area can be approximately categorized as unpolluted with Zn, Pb and Cr, and moderately polluted with Cu and Cd. The degree of heavy metal pollution decreases in the order of Cu>Cd>Zn>Pb>Cr. Three groups of pollution factors are presented from FA: Zn-TOC, Cu-Cd and Cr-Pb, which respectively accounte for 27.22%, 25.20% and 21.05% of variance. By means of HCA, a total number of seven groups are distinguished from 30 sampling sites. Results indicate that Cu and Cd are the prior controlled pollutants in the estuarine sediments of the Tangxi River.

Identification of active methylotrophic bacteria inhabiting surface sediment of a marine estuary

Methylotrophs play an essential role in the global carbon cycle due to their participation in methane oxidation and C1 metabolism. Despite this important biogeochemical role, marine and estuarine microorganisms that consume C1 compounds are poorly characterized. In this study, we investigated the diversity of active methylotrophs and methanotrophs in sediment from the Colne Estuary (Brightlingsea, UK). Aerobic surface sediment samples were examined for the presence of C1 -utilizing communities using DNA stable-isotope probing (DNA-SIP) with (13) C-labelled methane, methanol and monomethylamine. Active methylotrophic bacteria were confirmed after DNA-SIP and denaturing gradient gel electrophoresis analyses. Clone libraries of 16S rRNA gene amplicons revealed the presence of methylotrophic bacteria affiliated with Methylophaga spp. in methanol and monomethylamine incubations. The addition of marine ammonium mineral salts medium to the microcosms increased the rate of substrate metabolism in DNA-SIP incubations, although nutrient addition did not affect the active populations contributing (13) C-labelled DNA. The (13) CH4 SIP incubations indicated the predominant activity of type I methanotrophs and microarray hybridization of amplified particulate methane monooxygenase (pmoA) genes confirmed the role of type Ia methanotrophs in SIP incubations. Type II methanotrophs (i.e. Methylocystis and Methylosinus) were only detected in the original sediment and in the unlabelled DNA fractions, which indicated that type II methanotrophs were not actively involved in C1 compound assimilation in DNA-SIP incubations with estuarine surface sediment samples.

Pan‐Arctic patterns in black carbon sources and fluvial discharges deduced from radiocarbon and PAH source apportionment markers in estuarine surface sediments

A pan‐arctic geospatial picture of black carbon (BC) characteristics was obtained from the seven largest arctic rivers by combining with molecular combustion markers (polycyclic aromatic hydrocarbons) and radiocarbon (14C) analysis. The results suggested that the contribution from modern biomass burning to BC ranged from low in the Yukon (8%) and Lena (5%) Rivers to high in the Yenisey River (88%). The Mackenzie River contributed almost half of the total arctic fluvial BC export of 202 kton a−1 (kton = 109 g), with the five Russian‐Arctic rivers contributing 10–36 kton a−1 each. The 14C‐based source estimate of fluvially exported BC to the Arctic Ocean, weighted by the riverine BC fluxes, amount to about 20% from vegetation/biofuel burning and 80% from 14C‐extinct sources such as fossil fuel combustion and relict BC in uplifted source rocks. Combining these pan‐arctic data with available estimates of BC export from other rivers gave a revised estimate of global riverine BC export flux of 26 × 103 kton a−1. This is twice higher than a single previous estimate and confirms that river export of BC is a more important pathway of BC to the oceans than direct atmospheric deposition.

Contrasting chemical and isotopic compositions of organic matter in Changjiang (Yangtze River) estuarine and East China Sea shelf sediments

To examine the source and preservation of organic matter in the shelf sediments of the East China Sea (ECS), we measured bulk C/N and isotopes, organic biomarkers (n-alkanes and fatty acids) and compound-specific (fatty acids) stable carbon isotope ratios in three sediment cores collected from two sites near the Changjiang Estuary and one in the ECS shelf. Contrasting chemical and isotopic compositions of organic matter were observed between the estuarine and shelf sediments. The concentrations of total n-alkanes and fatty acids in the shelf surface sediments (0–2 cm) were 5–10 times higher than those in estuarine surface sediments but they all decreased rapidly to comparable levels below the surface layer. The compositions of n-alkanes in the estuarine sediments were dominated by C26-C33 long-chain n-alkanes with a strong odd-to-even carbon number predominance. In contrast, the composition of n-alkanes in the shelf sediment was dominated by nC15 to nC22 compounds. Long-chain (>C20) fatty acids (terrestrial biomarkers) accounted for a significantly higher fraction in the estuarine sediments compared to that in the shelf sediment, while short-chain (<C20) saturated and unsaturated fatty acids were more abundant in the shelf surface sediments than in the estuarine sediments. Stable carbon isotopic ratios of individual fatty acids showed a general positive shift from estuarine to shelf sediments, consistent with the variations in bulk δ 13CTOCTOC. These contrasts between the estuarine and shelf sediments indicate that terrestrial organic matter was mainly deposited within the Changjiang Estuary and inner shelf of ECS. Post-depositional diagenetic processes in the surface sediments rapidly altered the chemical compositions and control the preservation of organic matter in the region.

Concentration and fate of persistent organochlorine pesticides in estuarine sediments using headspace solid-phase microextraction

The concentration and fate of persistent organochlorine pesticides (OCPs) in estuarine surface sediments in Erh-jen and Lan-yang rivers, Taiwan were investigated using headspace solid-phase microextraction (HSSPME) method to evaluate the possible pollution potential and guideline for OCP concentrations in Taiwan. The HSSPME method exhibits a good analytical performance with low detection limits for OCP determination in sediment. In addition, results obtained using the developed HSSPME method were in good agreement with those obtained using Soxhlet extraction in a certified sample. The developed analytical method was further applied to the determination of concentrations of OCP residues in surface sediments from the estuaries of the selected rivers in Taiwan. A total of 20 surface sediments from each river was collected from 10 sampling stations. The total OCP concentrations in sediments from Erh-jen River ranged from 0.17 to 5.04 ng/g-dw with the mean values of 0.25–1.24 ng/g-dw for HCHs, 0.10–0.89 ng/g-dw for cyclodienes and 0.16–0.64 ng/g-dw for DDTs. The concentrations of OCPs in sediments from Lan-yang River were in the range 0.37–0.9 ng/g-dw with an average of lower than 0.5 ng/g-dw. HCHs and DDTs were abundant in the estuarine sediments from the selected rivers. Results obtained in this study show that the origin of OCPs in the surface sediments from Erh-jen River is a combination of erosion of the weathered soils and long-range atmospheric transport, while the OCP concentrations found in Lan-yang River could be regarded as the background levels of OCPs in Taiwan.

Litter dynamics and particulate organic matter outwelling from a subtropical mangrove in Okinawa Island, South Japan

Litter dynamics and outwelling of particulate organic matter (POM) was investigated in a subtropical mangrove (Okinawa Island, South Japan) in order to quantify the impact of mangrove POM on adjacent intertidal sediments. A distinct seasonal pattern was found with maximum litter fall during the autumn season, and minimum during winter. Total litter production between sites did not differ significantly. Tall mangroves (average 7 m) did not show any higher contribution to the litter production than short mangroves (average 4 m). The mean annual litter production was 12.95 ± 2.95 t ha −1 (dry weight) with leaf fall contributing more than 70% of the total litter production. Analysis of fatty acids (FAs) in the surface sediments of an adjacent mud flat and sand flat during the winter, spring and autumn seasons indicated that outwelling of POM from the mangrove ecosystem occurs. However, it is spatially restricted to within 300 m from the mangrove forest. The magnitude of the outwelling increased during spring and autumn consistent with the increase in the total litter production. Despite the presence of mangrove-derived organic matter in the estuarine surface sediments, autochthonous sources of organic matter, green macroalgae ( Ulva pertusa and Enteromorpha intestinalis), diatoms and bacteria are the main contributors of sedimentary organic matter and ω3 and ω6 PUFAs than mangrove-derived (POM) during winter and spring. While the contribution of mangrove-derived POM to sedimentary organic matter is limited to the autumn season.

Interaction between shallow groundwater, saline surface water and contaminant discharge at a seasonally and tidally forced estuarine boundary

This paper presents findings from a 2-year field investigation of a dissolved hydrocarbon groundwater plume flowing towards a tidally and seasonally forced estuarine river system in Perth, Western Australia. Samples collected from transects of multiport wells along the riverbank and into the river, enabled mapping of the fine scale (0.5 m) vertical definition of the hydrocarbon plume and its longitudinal extent. Spear probing beneath the river sediments and water table, and transient monitoring of multiport wells (electrical conductivity) was also carried out to define the zone of mixing between river water and groundwater (the hyporheic zone) and its variability. The results showed that groundwater seepage into the estuarine surface sediments occurred in a zone less than 10 m from the high tide mark, and that this distance and the hyporheic transition zone were influenced by tidal fluctuations and infiltration of river water into the sediments. The dissolved BTEXN (benzene, toluene, ethylbenzene, the xylene isomers and naphthalene) distributions indicated the behaviour of the hydrocarbon plume at the groundwater/surface water transition zone to be strongly influenced by edge-focussed discharge. Monitoring programs and risk assessment studies at similar contaminated sites should therefore focus efforts within the intertidal zone where contaminants are likely to impact the surface water and shallow sediment environments.

Metal equilibration in laboratory-contaminated (spiked) sediments used for the development of whole-sediment toxicity tests

The equilibration and bioavailability of metals in laboratory-contaminated sediments have been investigated in order to provide better guidance on acceptable procedures for spiking sediments with metals for use in the development of whole-sediment toxicity tests. The equilibration rates of Cd, Cu, Ni and Zn spiked into three estuarine surface sediments with varying properties were investigated. Changes to sediment pH, redox potential, porewater and acid-soluble metals, acid-volatile sulfide and bacterial activity during equilibration, effects of temperature and disturbances following equilibration are reported. The addition of metals to sediments caused major decreases in pH and increases in redox potential as metals displaced iron(II) into the porewaters and added metals and iron (following oxidation) were hydrolyzed. The rates of equilibration of metals in porewaters varied considerably and were dependent on sediment and metal properties. For the oxic/sub-oxic sediments studied, metal-spikes of Cd, Cu, Ni and Zn appeared near equilibrium after 25–45, 10–15, 30–70 and 20–40 days, respectively. Acid-soluble metal concentrations decreased during the equilibration period indicating that the metals become more strongly associated with the sediments with time (less bioavailable). Bacterial activity was greatest in the sediment equilibrated at pH 7 and decreased following the addition of metals. During the equilibration period, bacterial activity increased in sediments equilibrated at pH 6, remained low in sediments at pH 8 and varied erratically in sediments at pH 7. Spiked sediments were shown to equilibrate more slowly at lower temperatures resulting in high porewater metal concentrations. Disturbances to equilibrated sediments because of sample manipulation caused significant iron(II) oxidation and losses of metals from porewaters. The importance of documenting spiking and equilibration procedures and carefully measuring and reporting sediment parameters is highlighted so that contaminant bioavailability and exposure pathways can be interpreted and organism sensitivity accurately determined. Recommendations are given for the preparation of metal-spiked sediments for toxicity testing purposes.

In situ, High-Resolution Measurement of Dissolved Sulfide Using Diffusive Gradients in Thin Films with Computer-Imaging Densitometry

The technique of diffusive gradients in thin films (DGT) has been developed for the measurement of dissolved sulfide. Sulfide species from the sampled waters diffuse through a polyacrylamide hydrogel and then react with pale yellow AgI((s)), incorporated at the surface of a second gel, to form black Ag(2)S((s)). The accumulated sulfide can be measured with a conventional purge-and-trap method followed by colorimetry (methylene blue). This enables the dissolved-sulfide concentration to be calculated under suitable conditions. Alternatively, the color change in the accumulating gel can be used to measure sulfide. A conventional flat-bed scanner, allied to imaging software, provided a densitometric measurement that was quantitatively related to the amount of sulfide accumulated. DGT measurements on synthetic solutions accurately determined the sulfide concentration (95% recovery), thereby confirming the unobstructed diffusion of HS(-) through the gel. The accumulated mass was inversely proportional to the diffusion-layer thickness as theoretically predicted. With the selected geometry, the limit of detection of the densitometric procedure for a 24-h deployment was 0.13 μmol L(-)(1), and the maximum concentration measurable was 60 μmol L(-)(1). When used in anoxic lacustrine waters, DGT provided sensible concentrations. It was also used to measure depth profiles at submillimeter resolution in estuarine surface sediments.

Evidence for Intracellular and Extracellular Dimethylsulfoniopropionate (DMSP) Lyases and DMSP Uptake Sites in Two Species of Marine Bacteria

The kinetics of dimethylsulfoniopropionate (DMSP) uptake and dimethylsulfide (DMS) production from DMSP in two bacterial species, Alcaligenes sp. strain M3A, an isolate from estuarine surface sediments, and Pseudomonas doudoroffii, from seawater, were investigated. In Alcaligenes cells induced for DMSP lyase (DL) activity, DMS production occurred without DMSP uptake. In DL-induced suspensions of P. doudoroffii, uptake of DMSP preceded the production of DMS, indicating an intracellular location of DL; intracellular DMSP levels reached ca. 7 mM. DMSP uptake rates in noninduced cells showed saturation at three concentrations (K(inft) [transport] values, 3.4, 127, and 500 (mu)M). In DL-induced cells of P. doudoroffii, DMSP uptake rates increased ca. threefold (V(infmax), 0.022 versus 0.065 (mu)mol of DMSP taken up min(sup-1) mg of cell protein(sup-1)), suggesting that the uptake binding proteins were inducible. DMSP uptake and DL activity in P. doudoroffii were both inhibited by CN(sup-), 2,4-dinitrophenol, and membrane-impermeable thiol-binding reagents, further indicating active uptake of DMSP by cell surface components. The respiratory inhibitors had limited or no effect on DL activity by the Alcaligenes sp. Of the structural analogs of DMSP tested for their effect on DMSP metabolism, glycine betaine (GBT), but not methyl-3-mercaptopropionic acid (MMPA), inhibited DMSP uptake by P. doudoroffii, suggesting that GBT shares a binding protein with DMSP and that MMPA is taken up at a separate site. Two models of DMSP uptake, induction, and DL location found in marine bacteria are presented.

Diffusivity in surficial sediments and benthic mats determined by use of a combined N 2O-O 2 microsensor

Diffusional characteristics of two biologically active surface sediments were determined by use of a combined N 2O-O 2 microsensor. By analyzing changes in the N2O-gradients in these sediments, it was possible to determine the product ( φD s ) for this species with submillimetre depth resolution, where φ is the porosity and D s the substrate diffusion coefficient. The ( φD s )-value for O 2 could be calculated then from ( φD s )-value for N 2O, because the diffusivity of the two molecules were modified in the same way within the sediment. Both sediments exhibited fine-scale horizontal and vertical variability in diffusion characteristics, and this must be accounted for when analyzing microprofile data. The average ( φD s )-value for N 2O at 20°C for an estuarine surface sediment was 0.93 × 10 −5 cm2 s −1 (at 0–4 mm depth), while the value for the upper 2 mm of a stream sediment covered by a microbial mat was 1.42 × 10 −5 cm 2 s −1. Biological inactivation and oxidation by exposure to an O 2 atmosphere had no effect on the measured ( φD s ) for the estuarine sediment; however, the value for the sediment covered by a microbial mat, with dense populations of meiofauna, decreased by 20%. The method presented is ideal for measurements of diffusivity at a high spatial resolution in surficial sediments and densely packed microbial communities.

Sewage influence in a macrotidal estuary: Fatty acid and sterol distributions

Estuarine surface sediment and suspended matter from the Morlaix River estuary were analysed for fatty acids and sterols by HPLC and GC. This estuary represents a typical example of a coastal river estuary subjected to strong tides and receiving domestic wastes in its upper reaches. Wastewater fatty acid and sterol distribution patterns have been used to estimate the anthropogenic matter influx and its behaviour as an estuarine organic matter component. The 5 β -stanols, specific to fecal material and relatively persistent in the environment, provide a spatial view of sewage dispersion in estuarine waters and sediments and are used to calculate the relative importance of anthropogenic inputs in the degradable organic matter. Their distribution at high and low water indicates that anthropogenic particles are distributed throughout the estuary and may reach the coastal areas. However, owing to the dilution and the sedimentation processes, the anthropogenic matter contribution to the total organic matter is low in the outer estuary. By contrast, sediments from the upper estuary are strongly influenced by fresh anthropogenic inputs which may be detected by fatty acid fingerprint. The 18:1( n − 7)/18:1( n − 9) ratio which indicates the ability of the sediment to degrade the anthropogenic fresh material demonstrates a perturbation all along the narrow upper estuary.

Natural variations in 15N content of riverine and estuarine sediments

A study of the natural variations of 15N in the sediments of the river Tamar estuary and its catchment, south-west England, is described. The mean δ 15N for freshwater sediments was +2·3‰ (SD ± 0·9) and distinct from the majority of estuarine sediments. Three catchment areas that together comprise the riverine system could be distinguished by a combination of the δ 15N of the sediments and the riverine NO 3 − concentrations. Estuarine surface sediments fell into three groups: upper-estuary (mean δ 15N = 5·6‰); mid-estuary (mean δ 15N = 2·7‰) and lower-estuary (mean δ 15N = 5·3‰). These distributions confirm earlier, non-isotopic, observations of the complex patterns of transportation of surface sediments in this estuary.

The carbohydrates in relation to mineralogic and granulometric composition of surface sediments in the karst estuary (River Krka estuary, Yugoslavia)

The investigation of mineral, granulometric and chemical composition of sediments of the River Krka estuary (Yugoslavia) were performed in order to elucidate the origin of the sediments and the pattern of sedimentation. Estuarine surface sediments were found to be fine-grained with a bimodal distribution. Environmental conditions in estuarine sediments favour conservation of the organic matter (anoxic conditions). The carbohydrates in the sediments were investigated to determine whether they are of terrigenous or authigenous origin. Glucose, galactose, mannose, xylose, rhamnose, glucosamine and glucuronic acid were detected in the sediments. Their mutual relationship indicates a preferentially terrigenous source of sedimented organic material in estuarine sediments.

The behaviour of iodine and bromine in estuarine surface sediments

The distribution of iodine and bromine was examined in sediments which receive inputs of marine and terrigenous organic matter. The I and Br concentrations are directly related to the content of ‘marine’ organic matter defined using carbon/nitrogen ratios. In the Etive sediments both Br and I may be used as an indicator of ‘marine’ organic matter; Br is of general application as the Br C mar ratio (180 × 10 −4) is similar to ratios in other sedimentary environments but the use of I is restricted as the I C mar ratio is unlike those in other sediments. Experimental study of iodine sorption clearly shows the importance of decaying marine organic matter and oxygenated conditions in the incorporation of iodine by sediments. This suggests that the mechanism of incorporation of iodine by seston previously proposed is probably an important pathway to sediments. The similarity of Br association with marine organic matter suggests that Br sorption as opposed to residual enrichment may be important for sediment Br accumulation.

In-vivo estimates for the uptake of caesium-137 by cattle grazing contaminated pasture around the Esk and Irt estuaries, Cumbria, U.K.

Sea water contaminated with diluted radioactive effluent from the Windscale nuclear complex in Cumbria periodically floods low-lying grazing pasture around the estuaries of the rivers Esk, Irt and Mite near Ravenglass. During 1979, an experiment was carried out to measure the transfer of caesium-137 from grass to muscle in cows grazing these pastures. Grass samples were taken and in vivo external gamma-ray measurements were made on cattle. A very low transfer coefficient was found, less than 9 × 10 −4 days kg −1 with a best estimate of 4 × 10 −4 days kg −1, compared with a more usual value of around 3 × 10 −2 days kg −1. The low transfer seems to occur because the bulk of the caesium-137 on the grass is bound to resuspended estuarine surface sediment deposited during flooding. In this form, the caesium-137 is only poorly absorbed across the gut of the grazing cattle.

Provenance and Diagenesis of Clay Minerals in Sediments from Anclote River and Anchorage, West-Central Florida: ABSTRACT

Surface and subsurface sediments from a small river basin and lagoon (the Anclote River system in west-central Florida) were examined by X-ray diffraction methods to reveal the factors controlling clay minerals distribution in paludal (swamp), fluviatile, estuarine, and nearshore marine environments. In the swamp environment, smectite is the predominant clay mineral in surface sediments. Relative concentration and crystallinity of smectite increase with a corresponding decrease in kaolin minerals (including kaolinite, halloysite, and kaolinite-montmorillonite mixed-layer) from the surface down the cores indicating kaolinization is prevalent in the upper swampy sediments. In the fluviatile environment, clay minerals in surface sediments are transported from upper stream swamps and mixed with the residual clays of the bed rock. Subsurface clay minerals in the Tampa Limestone are mainly illite with minor amounts of smectite. In downstream estuarine surface sediments, smectite decreases while chlorite, chlorite-vermiculite mixed layer, and illite increase. This change results from the combined effects of tidal inflow and transport by the river as indicated by the study of suspended sediments in this area. The relatively high concentration of smectite in the subsurface sediments of the lower Anclote River, an estuarine environment, suggests that the distribution pattern of clay minerals in this area may have been affected by the lower stand of sea level during the last glacial period. Clay mineral assemblages in the Anclote Anchorage are a combination of residual sedimentary clays mixed with river-borne and marine clays. The uniformly distributed clays indicated a mixed and reworked environment (by current and wave) rather than one formed by a uniform, single source. End_of_Article - Last_Page 1683------------