Differential presence of anthropogenic compounds dissolved in the marine waters of Puget Sound, WA and Barkley Sound, BC

Organic compounds were evaluated in March 2010 at 22 stations in Barkley Sound, Vancouver Island Canada and at 66 locations in Puget Sound. Of 37 compounds, 15 were xenobiotics, 8 were determined to have an anthropogenic imprint over natural sources, and 13 were presumed to be of natural or mixed origin. The three most frequently detected compounds were salicyclic acid, vanillin and thymol. The three most abundant compounds were diethylhexyl phthalate (DEHP), ethyl vanillin and benzaldehyde (∼600 ng L⁻¹ on average). Concentrations of xenobiotics were 10-100 times higher in Puget Sound relative to Barkley Sound. Three compound couplets are used to illustrate the influence of human activity on marine waters; vanillin and ethyl vanillin, salicylic acid and acetylsalicylic acid, and cinnamaldehyde and cinnamic acid. Ratios indicate that anthropogenic activities are the predominant source of these chemicals in Puget Sound.     

Compression behaviour of minerogenic low energy intertidal sediments

Existing geotechnical approaches that describe volumetric changes in intertidal sediments in response to applied vertical effective stresses are limited by a lack of empirical research into their one-dimensional compression behaviour. In this paper we address this deficiency by presenting the results of an investigation into the compression behaviour of minerogenic low marsh and tidal flat sediments. We have tested samples of these sediment types obtained from Greatham Creek (Cowpen Marsh, Tees Estuary, UK). Analysis of physical properties and oedometer compression tests demonstrates that, contrary to the implicit assumptions of existing models, the surface sediments studied are overconsolidated. Structural variability between samples arises due to sedimentological factors, notably variations in organic content. We attribute overconsolidation to tidal exposure and falls in groundwater level that permit desiccation and cause capillary suction stresses. Greater rates of compression with respect to effective stress occur in sediments with higher initial voids ratios and more open, unstable initial structures. Variability in structure decreases with application of higher effective stresses due to the destructuration of the sediments, which also creates increased homogeneity of compression behaviour under higher effective stresses. We subsequently develop a new conceptual framework to describe compression behaviour in minerogenic intertidal sediments that incorporates overconsolidation. We advocate a statistical approach that accounts for structural variability and variations in compression behaviour at effective stresses less than and greater than the yield stress. We argue that our conceptual framework is broadly applicable to minerogenic intertidal sediments at different locations and burial depths within Holocene stratigraphic sequences providing site-specific compression data are collected. Inter-site transfer and application of measured material properties should not be undertaken due to local variations in compression behaviour resulting from varying ecological, sedimentological, geochemical, climatic, geomorphic and hydrographic conditions. The individual characteristics of different field locations should be carefully considered before the suggested framework is routinely applied.     

Identification and composition of secondary meniscus calcite in fossil coral and the effect on predicted sea surface temperature

This study uses electron backscatter diffraction (EBSD) and atomic force microscopy (AFM) to identify secondary calcite in coral skeletons. Secondary calcite appears to have nucleated on the original aragonite dissepiments, producing horizontal structures that mimic the morphology of the original coral aragonite, forming dissepiment-like meniscus structures. The Sr/Ca and δ¹⁸O of the pristine aragonite and secondary calcite were analysed by secondary ion mass spectrometry (SIMS). The effect of calcite inclusion on the mean geochemistry of the coral carbonate and subsequent sea surface temperature (SST) calculations were determined for both Sr/Ca and δ¹⁸O. Inclusion of as little as 1% secondary calcite within the primary coral aragonite elevates the Sr/Ca-derived SST by 1.2 °C and could markedly offset estimates of past tropical climate. Conversely, inclusion of 10% secondary calcite has little effect on the SST estimated from δ¹⁸O (+ 0.6 °C) indicating that this proxy is relatively robust to even large amounts of calcite. The different extents to which the two proxies would be influenced by inadvertent inclusion of such meniscus calcite demonstrate the importance of a multi-proxy approach.     

Evidence for multiple modes of uranium immobilization by an anaerobic bacterium

Microbial reduction of hexavalent uranium has been studied widely for its potential role in bioremediation and immobilization of soluble U(VI) in contaminated groundwater. More recently, some microorganisms have been examined for their role in immobilization of U(VI) via precipitation of uranyl phosphate minerals mediated by microbial phosphate release, alleviating the requirement for long-term redox control. Here, we investigated the mechanism of U(VI) removal mediated by an environmental isolate, strain UFO1, that is indigenous to the Field Research Center (FRC) in Oak Ridge, TN and has been detected in U(VI)-contaminated sediments. Changes in U(VI) speciation were examined in the presence and absence of the electron-shuttling moiety, anthraquinone-2,6-disulfonate (AQDS). Cell suspensions were capable of nearly complete removal of 100 μM U(VI) from solution within 48 h; U(VI) removal was not dependent on the presence of an exogenous electron donor or AQDS, although AQDS increased the rate of U(VI) removal. X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopic measurements indicated that U(IV) was the predominant oxidation state of uranium in cell suspensions in both the absence and presence of 100 μM AQDS. Interestingly, 17% of the cell-associated precipitates in a U(VI)-treated suspension that lacked AQDS had spectral characteristics consistent with a uranyl phosphate solid phase. The potential involvement of phosphate was consistent with observed increases in soluble phosphate concentrations over time in UFO1 cell suspensions, which suggested phosphate liberation from the cells. TEM-EDS confirmed the presence of uranyl phosphate with a U:P ratio consistent with autunite (1:1). EXAFS analyses further suggested that U(IV) was bound to low-Z neighbors such as C or P, inferred to be present as functional groups on biomass. These results suggest that strain UFO1 has the ability to facilitate U(VI) removal from solution via reductive and phosphate precipitation mechanisms. Both mechanisms offer potential for the remediation of U-contaminated sediments at the FRC or elsewhere.     

Large-Scale Differences in Community Structure and Ecosystem Services of Eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis>) Beds Across Three Regions in Eastern Canada

Eelgrass (Zostera marina) forms extensive beds in temperate coastal and estuarine environments worldwide and provides important ecosystem services, including habitat for a wide range of species as well as nutrient cycling and carbon storage. However, little is known about how eelgrass ecosystem structure and services differ naturally among regions. Using large-scale field surveys, we examined differences in eelgrass bed structure, carbon and nitrogen storage, community composition, and habitat services across three distinct regions in Eastern Canada. We focused on eelgrass beds with low anthropogenic impacts to compare natural differences. In addition, we analyzed the relationships of eelgrass bed structure with environmental conditions, and species composition with bed structure and environmental conditions, to elucidate potential drivers of observed differences. Our results indicate that regional differences in eelgrass bed structure were weakly correlated with water column properties, whereas differences in carbon and nitrogen storage were mainly driven by differences in eelgrass biomass. There were distinct regional differences in species composition and diversity, which were particularly linked to temperature, as well as eelgrass bed structure indicating differences in habitat provision. Our results highlight natural regional differences in ecosystem structure and services which could inform spatial management and conservation strategies for eelgrass beds.