SW England Research Articles

Nitrogen isotope record of a perturbed paleoecosystem in the aftermath of the end‐Triassic crisis, Doniford section, SW England

The Triassic‐Jurassic transition (TJ) is characterized by successive perturbations of the carbon cycle during a time of biotic disruption as recorded by the carbon isotopic composition of organic matter (δ13Corg). The nitrogen isotopic composition of sedimentary organic matter (δ15Norg) constitutes a key parameter to explore the functioning of the ecosystem during carbon cycle perturbations and biological crises, because it provide information on seawater redox conditions and/or nutrient cycling. Here we report the first continuous δ15Norg record across the TJ transition at the Doniford Bay section (Bristol Channel Basin, UK), combined with δ13Corg, kerogen typology and carbon (δ13Cmin) and oxygen (δ18Omin) isotopic composition of bulk carbonates. The end Triassic is characterized by a major negative excursion both in δ13Corg and δ13Cmin, very low TOC (Total Organic Carbon, wt%) and high δ15Norg values, associated with a sea level lowstand. A second δ13Corg negative excursion occurs during the lower Hettangian. This interval is characterized by phases of carbonate production increase alternated with phases of exceptional accumulations of type I organic matter (up to 12%) associated with lower δ15Norg and δ13Corg. This alternation likely reflects a succession of nutrient input increase to the basin leading to enhanced productivity and eutrophication, which promoted a primary production driven by organic‐walled prokaryotic organisms. The following OM export increase generates anaerobic conditions within the basin. These events occur between periods of relatively good seawater column ventilation and nutrient recycling boosting the carbonate producer recovery. Ecosystems remain perturbed in the Bristol Channel Basin during the aftermath of the end‐Triassic crisis.

The use of ground‐penetrating radar to extend the results of archaeological excavation

ABSTRACTThis paper describes the use of ground‐penetrating radar (GPR) to extrapolate from data generated by a long‐term training excavation in Gloucestershire, SW England for which geophysical survey techniques including GPR had been used. Due to external circumstances beyond the control of the archaeological team, the ownership of the site changed hands and all excavation and associated investigation had to cease. However, an adjacent landowner granted permission for a GPR survey across his land. These latest GPR survey results have been used to supplement the excavation results, significantly extending the information available to the archaeological team. The data demonstrate the accuracy with which GPR data can be matched to excavation data and the improvement in target definition possible with reduction of transect spacing. The impact of some of this information is still being evaluated.

Early Hettangian benthic–planktonic coupling at Doniford (SW England): Palaeoenvironmental implications for the aftermath of the end-Triassic crisis

This paper presents a high-resolution micropalaeontological study, integrated with geochemical and sedimentological analyses of the Triassic–Jurassic (Tr–J) transition at the Doniford section (SW England). Our analyses indicate the renewal of surface carbonate production in the Blue Lias Formation (early Hettangian) after the end-Triassic mass extinction. Based on the high abundance of surface carbonate producers (schizosphaerellids), which occurred in phase with development at sea-floor of calcareous hyaline benthic foraminifers, we deduce that a benthic–pelagic coupling resulted in both the initial restoration of the biological carbonate pump, and also a more efficient export production. The presence of monospecific phytoplankton assemblages and benthic foraminiferal assemblages typical of poorly oxygenated environments suggest that the environmental stress continued after the end-Triassic maximal perturbation. Complete environmental recovery was prevented by a succession of alternating dysaerobic and anoxic phases that favoured the deposition of black-shale sediments. The hypothesis of a methane-release mechanism as a trigger for the global carbon cycle perturbation and greenhouse conditions during the early Jurassic is discounted, based on evidence from the decoupled carbon isotope records of carbonate and organic matter. Apart from local control of a high amplitude sea-level change across the Tr–J boundary, the succession and nature of events at Doniford are consistent with a scenario of global environmental and biotic changes triggered by the physical and chemical effects of the Central Atlantic Magmatic Province (CAMP) volcanism. A super greenhouse climate in the aftermath of the end-Triassic mass extinction appears to be the results of the combination of the long-term CO 2 accumulation in the atmosphere system due to the CAMP volcanic activity, as well as the inefficiency of the biological pump due to reduced export production.

Symptom recognition and help seeking for depression in young adults: a vignette study

Many young people with psychological problems do not seek help. Recognition of problems and knowledge of appropriate sources of help may increase the likelihood of help seeking. This study aimed to explore whether young adults recognised depressive symptoms in a vignette, and how they thought a young person might respond to these symptoms. A postal survey was sent to 3,004 young people aged 16-24 in SW England. The survey included a two-part vignette; the first part depicted mild depressive symptoms, and the second part depicted severe depressive symptoms. Open-ended questions exploring symptom recognition and illness behaviour were answered by 1,125 respondents. Severe depressive symptoms were recognised by 61.4% of respondents. Young men, particularly those from deprived backgrounds were less likely than women to recognise a mental health problem. Men were also less likely to suggest seeing a doctor than women. 64.7% of the respondents who recognised a mental health problem suggested seeing a doctor, however, only 16.4% thought a severely depressed person actually would see a doctor. Whilst the majority of young people recognised symptoms of severe depression, the gap between perceived options for help and proposed help seeking behaviour is clinically relevant. The sociodemographic groups at greatest risk of suicide are the least likely to recognise depression, highlighting a need to develop interventions targeting men, particularly those from deprived backgrounds.

Nitrogen uptake in organically managed spring sown lupins and residual effects on leaching and yield of a following winter cereal

Three unfertilized spring sown species of lupins (Lupinus angustifolius and peas Pisum sativa) were compared in terms of N fixation and subsequent leaching under a following winter barley crop in an organically managed rotation. Fallow plots were included to assess the potential weed burden and the ability of the sown crops to compete with weeds when no herbicides were applied. Although peas out-yielded lupins (5.4 t compared with 3.5 t grain respectively), the yellow lupin (Wodjil) fixed more N than peas (180 compared with 120 kg N/ha) and all three lupins had higher protein contents ( > 30%) than peas (22%). Winter leaching amounted to > 50 kg nitrate-N/ha from winter barley, regardless of whether it followed treatments which were previously fallow or cropped with legumes. There were no significant differences in leaching between the lupin species. Leachate in the first 350 mm of drainage under winter barley, following the different legume species, exceeded the European Union limit for nitrate in drinking water in all treatments. Yields of winter barley, grown without fertilizers or herbicides following legumes, were not significantly different (mean 4 t/ha), but there were higher levels of P and K in the grain compared with the amounts made available from the previously fallow soil. At this site in SW England, the crops grew well and our results suggest that lupins could provide a useful break crop in an organic arable cropping rotation and an alternative source of home-grown, high protein feed.

Detecting changes in seasonal precipitation extremes using regional climate model projections: Implications for managing fluvial flood risk

There is growing evidence of coherent, global patterns of change in annual precipitation and runoff with high latitudes experiencing increases consistent with climate model projections. This paper describes a methodology for estimating detection times for changes in seasonal precipitation extremes. The approach is illustrated using changes in UK precipitation projected by the European Union PRUDENCE climate model ensemble. We show that because of high variability from year to year and confounding factors, detection of anthropogenic climate change at regional scales is not generally expected for decades to come. Overall, the earliest detection times were found for 10 day winter precipitation totals with 10 year return period in SW England. In this case, formal detection could be possible within a decade from now if the climate model projections are realized. The outlook for changes in summer flash flood risk is highly uncertain. Our analysis further demonstrates that existing precautionary allowances for climate change used for flood management may not be sufficiently robust in NE England and east Scotland. These findings imply that for certain types of flood mechanism, adaptation decisions might have to be taken in advance of formally detected changes in flood risk. This reinforces the case for long‐term environmental monitoring and reporting of climate change indices at “sentinel” locations.

A PORTABLE FLOW INJECTION ANALYZER FOR THE IN SITU DETERMINATION OF FILTERABLE REACTIVE PHOSPHORUS (FRP) IN FRESHWATER

The development and deployment of a portable flow injection analyzer for continuous, real-time monitoring of filterable reactive phosphorus (FRP) in the Tamar catchment is described. The optimized method can be used for the determination of FRP in freshwater systems (4–150 μg L−1 P) and is capable of sampling with high temporal resolution (up to 15 samples h−1). The analyzer, fitted with a pre-filter and an in-line membrane filter (0.45 μm, cellulose acetate), was used in situ (bank-side and shipboard deployment) to provide real-time FRP data and in the laboratory to determine FRP in freshwater samples. The portable FRP analyzer was reproducible (RSD < 5%; n = 3) over the range 4–150 μg L−1 P and accurate, achieving good agreement with a laboratory based air-segmented continuous flow analyzer reference method for a range of freshwater samples from the Tamar catchment in SW England.

Sedimentary pools of phosphorus in the eutrophic Tamar estuary (SW England)

The speciation of phosphorus in Tamar estuary sediment has been determined at eight stations from Gunnislake (riverine end-member) to Torpoint (marine end-member) using the SEDEX (sedimentary extraction) sequential extraction scheme. The seasonal variability of total phosphorus and each of the five fractions is discussed. Total phosphorus, in the range 26-51 micromol g(-1), was stored in the relatively labile fractions, particularly in the iron oxide fraction. The well oxygenated waters of the macrotidal Tamar estuary ensure that the surface sediment layer remains oxic, providing an effective barrier that retains dissolved reactive phosphorus (DRP) within the sedimentary iron oxide fraction and prevents phosphorus migration from the sediment to the water column. The exchangeable and organic phosphorus sedimentary pools, although small, are therefore the main potential sources of phosphorus release to the water column. In particular, this study shows that exchangeable phosphorus and dissolved organic phosphorus (DOP) in the pore water are intimately linked. Finally, the distribution of phosphorus in the estuary is strongly influenced by particle morphology, with most of the sedimentary phosphorus forms exhibiting significant positive correlations with the percent of each grain size.

Biodynamic modelling and the prediction of Ag, Cd and Zn accumulation from solution and sediment by the polychaete Nereis diversicolor

Biodynamic modelling has been used to predict bioaccumulated concentrations of Ag, Cd and Zn in the deposit-feeding polychaete Nereis diversicolor from 5 metal-contaminated estuar- ies in SW England and a relatively non-contaminated estuary in SE England. The modelling employed previously measured physiological parameters of bioaccumulation — uptake rate constant, assimilation efficiency (AE) and efflux rate constants after uptake from water and sediment inges- tion — and measured sediment metal concentrations specific for each population. AEs were consid- ered to relate to metals in the organic component of the ingested sediment and ingestion rates were therefore expressed in these terms, with the further assumption that the total sediment metal concen- tration is a proxy for the metal concentration in the sediment organic component. A range of growth rate constants was extracted from the literature, as were concentration ranges of dissolved Ag, Cd and Zn in contaminated coastal waters. The model showed that >99% Cd and >98% Zn accumulated by N. diversicolor is derived from sediment ingestion; more bioaccumulated Ag is derived from solu- tion, the percentage contribution of the dissolved source increasing from 46 to 80% with an increase in Ag dissolved concentration from low to high values for coastal waters. Bioaccumulated metal con- centrations predicted from the model generally showed excellent agreement with independently measured concentrations in field-collected worms, supporting the assumptions made in the model.

Microbial water pollution: A screening tool for initial catchment-scale assessment and source apportionment

The European Union Water Framework Directive requires that Management Plans are developed for individual River Basin Districts. From the point of view of faecal indicator organisms (FIOs), there is a critical need for screening tools that can provide a rapid assessment of the likely FIO concentrations and fluxes within catchments under base- and high-flow conditions, and of the balance (‘source apportionment’) between agriculture- and sewage-derived sources. Accordingly, the present paper reports on: (1) the development of preliminary generic models, using water quality and land cover data from previous UK catchment studies for assessing FIO concentrations, fluxes and source apportionment within catchments during the summer bathing season; (2) the calibration of national land use data, against data previously used in the models; and (3) provisional FIO concentration and source-apportionment assessments for England and Wales. The models clearly highlighted the crucial importance of high-flow conditions for the flux of FIOs within catchments. At high flow, improved grassland (and associated livestock) was the key FIO source; FIO loadings derived from catchments with high proportions of improved grassland were shown to be as high as from urbanised catchments; and in many rural catchments, especially in NW and SW England and Wales, which are important areas of lowland livestock (especially dairy) farming, ≥ 40% of FIOs was assessed to be derived from agricultural sources. In contrast, under base-flow conditions, when there was little or no runoff from agricultural land, urban (i.e. sewerage-related) sources were assessed to dominate, and even in rural areas the majority of FIOs were attributed to urban sources. The results of the study demonstrate the potential of this type of approach, particularly in light of climate change and the likelihood of more high-flow events, in underpinning informed policy development and prioritisation of investment.

Temporal variability of colloidal material in agricultural storm runoff from managed grassland using flow field-flow fractionation

This paper reports the use of flow field-flow fractionation (FlFFF) to determine the temporal variability of colloidal (<1 μm) particle size distributions in agricultural runoff waters in a small managed catchment in SW England during storm events. Three storm events of varying intensity were captured and the colloidal material in the runoff analysed by FlFFF. The technique had sufficient sensitivity to determine directly the changing colloidal profile over the 0.08–1.0 μm size range in the runoff waters during these storm events. Rainfall, total phosphorus and suspended solids in the bulk runoff samples were also determined throughout one storm and showed significant correlation ( P < 0.01) with the amount of colloidal material. Whilst there are some uncertainties in the resolution and absolute calibration of the FlFFF profiles, the technique has considerable potential for the quantification of colloidal material in storm runoff waters.

Palaeoenvironmental significance of carbon- and oxygen-isotope stratigraphy of marine Triassic–Jurassic boundary sections in SW Britain

Abstract: Carbon-isotope stratigraphy is a useful tool for stratigraphic correlation, especially for strata deposited during major perturbations of the carbon cycle that affected the marine, terrestrial and atmospheric reservoirs. For the Triassic–Jurassic boundary, effectively defined by a first-order mass extinction, major fluctuations in carbon-isotope values have been well documented, but these datasets have generally been derived from bulk-rock samples. Hence, the extent to which features of the isotopic curve reflect diagenetic alteration or changing proportions of constituent materials is unconstrained. Here, carbon- and oxygen-isotope data are presented from well-preserved oyster shells ( Liostrea ) comprising low-magnesium calcite, a mineral species relatively resistant to diagenetic alteration. Samples were obtained from Lavernock Point, Glamorgan, Wales, a coastal section close to a candidate stratotype for the base of the Jurassic at St Audrie's Bay, Somerset, England. The carbon-isotope signature from St Audrie's Bay, previously defined on the basis of analysis of bulk organic matter, is confirmed by our new data. Major features are (1) the upper part of an ’initial' negative isotope excursion in the lowest part of the section, followed by (2) a pronounced positive excursion, and (3) an extended ’main' negative isotope excursion in the highest part of the section. The data confirm that the carbon-isotope stratigraphy previously documented from bulk organic matter in SW England records the chemical composition of the contemporaneous seawater. Bulk carbonates sampled over the same interval near Lyme Regis, England, show similar trends to those from oyster calcite in the lower part of the study section, but there are more 13 C-depleted values up-section. These lower values probably result from an admixture of primary and diagenetic carbonate. Palaeotemperatures calculated from oxygen-isotope values from Lavernock Point oyster shells are relatively cool at the beginning of the positive carbon-isotope excursion, and increased by up to 10 °C during the main negative carbon-isotope excursion. The new results are compatible with the view that positive carbon-isotope excursions correspond to times of low atmospheric carbon dioxide content, whereas negative carbon-isotope excursions correspond to times of high atmospheric carbon dioxide content, as is also found to be the case during the Early Jurassic (Toarcian) Oceanic Anoxic Event. The Mg/Ca and Sr/Ca ratios and δ 18 O of investigated Liostrea hisingeri show no correlation, supporting data from modern bivalves that indicate that incorporation of Mg and Sr is controlled mainly by factors other than temperature.

Comparing quality of estuarine and nearshore intertidal habitats for Carcinus maenas

Estuarine and nearshore marine areas are vital habitats for several fish and benthic invertebrates. The shore crab Carcinus maenas (Crustacea: Brachyura: Portunidae) inhabits a variety of coastal, estuarine and lagoon habitats. At low tide, habitat structural complexity may be most important for crabs in the intertidal, providing refuge from predation and desiccation. The quality of different vegetated and nonvegetated estuarine and rocky shore habitats in SW Portugal and SW England was evaluated for intertidal C. maenas populations. We estimated population density, size–structure, and potential growth (RNA/DNA ratios) to investigate habitat quality. Vegetated estuarine habitats supported higher crab densities, than nonvegetated estuarine and rocky shore habitats. Investigation of population size–structure revealed that all habitats seem important recruitment and nursery areas although estuarine habitats in SW Portugal appeared to support higher densities of new recruits than equivalent habitats in SW England. Significant variation was found in RNA/DNA ratios among habitats. Ratios were highest in the rocky shore suggesting a high quality habitat where growth potential is high. We speculate that competition from other top-predators ( Pachygrapsus spp.) rather than low habitat quality may limit the occurrence of C. maenas in intertidal rocky shore habitats in SW Portugal. In estuarine environments RNA/DNA ratios were significantly higher in the vegetated than in the nonvegetated estuarine habitats in SW Portugal but not in SW England, suggesting geographic differences in the extent to which highly structure habitats represent high quality. Our results challenge the current paradigm that structured habitats are necessarily those of higher quality for C. maenas.

Influence of genotype and geography on shell shape and morphometric trait variation among North Atlantic blue mussel (Mytilus spp.) populations

The influence of geography and genotype on shell shape (outline) and trait (morphometric) variation among North Atlantic blue mussels and their hybrids has been examined. Shape differences among reference taxa (Mytilus trossulus, Mytilus edulis and Mytilus galloprovincialis) were consistent with an association between taxon-specific genes and shape genes. Newfoundland M. edulis × M. trossulus populations and northern Quebec M. trossulus populations exhibited an uncoupling of taxon-specific genes from shape genes, whereas Nova Scotia M. trossulus populations and SW England M. edulis × M. galloprovincialis populations exhibited an association between taxon-specific genes and shape genes. We found no evidence of a geographic effect (NE versus NW Atlantic) for shape variation, indicating that the genotype effect is stronger than any geographic effect at macrogeographic scales. Pronounced differences were observed in trait variability consistent with an association between taxon-specific genes and trait genes in European populations, and trait divergence of New York M. edulis from all European mussels. Trait variability in mussels from Newfoundland, Nova Scotia and northern Quebec indicated an uncoupling of taxon genes from trait genes, whereas trait variability in SW England M. edulis × M. galloprovincialis populations was consistent with background genotype, indicating a strong association between taxon genes and trait genes. A pronounced macrogeographic split (NE versus NW Atlantic) regardless of taxonomy was observed, indicating that geography exerts a greater influence than genotype on trait variation at the macrogeographic scale. This is consistent with pronounced within-taxon genetic divergence, indicative of different selection regimes or more likely of different evolutionary histories of mussels on either side of the North Atlantic. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 875–897.

The use of monitoring data for identifying factors influencing phytoplankton bloom dynamics in the eutrophic Taw Estuary, SW England

Using the Taw Estuary as an example, data routinely collected by the Environment Agency for England and Wales over the period 1990–2004 were interrogated to identify the drivers of excessive algal growth. The estuary was highly productive with chlorophyll concentrations regularly exceeding 100 μg L −1, mostly during periods of low freshwater input from the River Taw when estuarine water residence times were longest. However, algal growth in mid estuary was often inhibited by ammonia inputs from the adjacent sewage treatment works. The reported approach demonstrates the value of applying conventional statistical analyses in a structured way to existing monitoring data and is recommended as a useful tool for the rapid assessment of eutrophication. However, future estuarine monitoring should include the collection of dissolved organic nutrient data and targeted high temporal resolution data because the drivers of eutrophication are complex and often very specific to a particular estuary.

Dynamic cycles, ice streams and their impact on the extent, chronology and deglaciation of the British–Irish ice sheet

We present results from a suite of forward transient numerical modelling experiments of the British and Irish Ice Sheet (BIIS), consisting of Scottish, Welsh and Irish accumulation centres, spanning the last Glacial period from 38 to 10 ka BP. The 3D thermomechanical model employed uses higher-order physics to solve longitudinal (membrane) stresses and to reproduce grounding-line dynamics. Surface mass balance is derived using a distributed degree-day calculation based on a reference climatology from mean (1961–1990) precipitation and temperature patterns. The model is perturbed from this reference state by a scaled NGRIP oxygen isotope curve and the SPECMAP sea-level reconstruction. Isostatic response to ice loading is computed using an elastic lithosphere/relaxed asthenosphere scheme. A suite of 350 simulations were designed to explore the parameter space of model uncertainties and sensitivities, to yield a subset of experiments that showed close correspondence to offshore and onshore ice-directional indicators, broad BIIS chronology, and the relative sea-level record. Three of these simulations are described in further detail and indicate that the separate ice centres of the modelled BIIS complex are dynamically interdependent during the build up to maximum conditions, but remain largely independent throughout much of the simulation. The modelled BIIS is extremely dynamic, drained mainly by a number of transient but recurrent ice streams which dynamically switch and fluctuate in extent and intensity on a centennial time-scale. A series of binge/purge, advance/retreat, cycles are identified which correspond to alternating periods of relatively cold-based ice, (associated with a high aspect ratio and net growth), and wet-based ice with a lower aspect ratio, characterised by streaming. The timing and dynamics of these events are determined through a combination of basal thermomechanical switching spatially propagated and amplified through longitudinal coupling, but are modulated and phase-lagged to the oscillations within the NGRIP record of climate forcing. Phases of predominant streaming activity coincide with periods of maximum ice extent and are triggered by abrupt transitions from a cold to relatively warm climate, resulting in major iceberg/melt discharge events into the North Sea and Atlantic Ocean. The broad chronology of the modelled BIIS indicates a maximum extent at ∼20 ka, with fast-flowing ice across its western and northern sectors that extended to the continental shelf edge. Fast-flowing streams also dominate the Irish Sea and North Sea Basin sectors and impinge onto SW England and East Anglia. From ∼19 ka BP deglaciation is achieved in less than 2000 years, discharging the freshwater equivalent of ∼2 m global sea-level rise. A much reduced ice sheet centred on Scotland undergoes subsequent retrenchment and a series of advance/retreat cycles into the North Sea Basin from 17 ka onwards, culminating in a sustained Younger Dryas event from 13 to 11.5 ka BP. Modelled ice cover is persistent across the Western and Central Highlands until the last remnant glaciers disappear around 10.5 ka BP.

Differences in trace metal bioaccumulation kinetics among populations of the polychaete Nereis diversicolor from metal-contaminated estuaries

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 376:173-184 (2009) - DOI: https://doi.org/10.3354/meps07821 Differences in trace metal bioaccumulation kinetics among populations of the polychaete Nereis diversicolor from metal-contaminated estuaries P. S. Rainbow1,*, B. D. Smith1, S. N. Luoma1,2 1Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK 2John Muir Institute of the Environment, University of California at Davis, Davis, California 95616, USA *Email: p.rainbow@nhm.ac.uk ABSTRACT: Aquatic organisms exposed to atypically high local bioavailabilities of a toxic metal may come under selection for changes in one or more physiological processes, including the rate of metal uptake from an available source of the metal, the rate of efflux and the rate of detoxification of accumulated metal into a relatively metabolically inert form. We investigated parameters of the bioaccumulation kinetics of the toxic metals Ag, Cd and Zn in populations of the estuarine polychaete worm Nereis diversicolor from differentially metal-contaminated sediments of 5 metal-rich estuaries in SW England and a relatively non-contaminated control estuary in SE England. One population (from Restronguet Creek, Cornwall) is known to be tolerant to raised availabilities of Zn and Cu. We compared uptake rate constants from solution (Ku) and assimilation efficiencies (AE) from sediment, and subsequent efflux rate constants (Ke) after uptake (from either water or ingested sediment) for each of the 3 metals among all populations. There was some limited interpopulation variation in the biodynamic parameters controlling bioaccumulation (and potential ecotoxicity) of trace metals between populations. There did not, however, appear to be consistent patterns to such variation. The basis of Zn tolerance in the Restronguet Creek population is not due to a reduction of Zn uptake from either solution or ingested sediment, or increased efflux of Zn accumulated after uptake from either route. The most likely mechanism is, therefore, an increased capacity for storage detoxification of Zn accumulated after regulation of Zn body concentration has broken down. KEY WORDS: Trace metals · Bioaccumulation · Biodynamics · Tolerance · Uptake assimilation · Efflux Full text in pdf format PreviousNextCite this article as: Rainbow PS, Smith BD, Luoma SN (2009) Differences in trace metal bioaccumulation kinetics among populations of the polychaete Nereis diversicolor from metal-contaminated estuaries. Mar Ecol Prog Ser 376:173-184. https://doi.org/10.3354/meps07821 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 376. Online publication date: February 11, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

The mineralogy of efflorescence on As calciner buildings in SW England

Arsenic is a very common by-product of the processing of Cu, Au and polymetallic ores worldwide, where the ore is roasted (calcined) to remove volatile elements. In southwest England, a diverse range of As-mineral species occur as efflorescent secondary mineral growths on historic calciner buildings. Gypsum occurs as abundant dendritic growths comprising either interlocking blades or tabular crystals. Ca-arsenate minerals are locally very abundant as white colloform masses. Positively identified Ca arsenates include pharmacolite, weilite and haidingerite. Other secondary minerals include arsenolite, scorodite, bukovskyite and an As-bearing potassium alum, together with a wide variety of unidentified minerals, including an Al-As-S phase and As-rich F-bearing phases. Gypsum contains As concentrations up to ~7 wt.%. Efflorescent growth at sites exposed to the prevailing weather systems is less abundant than at sheltered sites. This is interpreted as being due to ‘pressure washing’ of exposed sites by driving rain. Successive concentric growths of gypsum and Ca arsenate on masonry are interpreted as being the result of seasonal crystallization.Understanding both current and historicalmining and mineralprocessing methods is criticalin the evaluation of the potential impact on the modern environment. In particular, due to the abundance of As-bearing minerals in a wide range of ore types, many buildings worldwide are potentially significantly contaminated with As even though few are directly related to As production or handling. Characterizing the secondary As mineralspecies present at mine and mineralprocessing sites is critical in understanding the potentialheal th risk these sites might pose.

The Rhenohercynian passive margin of SW England: Development, inversion and extensional reactivation

The SW England Rhenohercynian passive margin initiated with rift-related non-marine sedimentation and bimodal magmatism (Late Lockhovian). Continued lithospheric extension resulted in the exhumation of mantle peridotites and limited seafloor spreading (Emsian-Eifelian). Variscan convergence commenced during the Late Eifelian and was coeval with rifting further north. Collision was marked by the Early Carboniferous emergence of deep marine sedimentary/volcanic rocks from the distal continental margin, oceanic lithosphere, pre-rift basement and upper plate gneisses (correlated with the Mid-German Crystalline High of the Saxothuringian Zone). Progressive inversion of the passive margin was strongly influenced by rift basin geometry. Convergence ceased in the Late Carboniferous and was replaced by an extensional regime that reactivated basin controlling/thrust faults and reorientated earlier fabrics (Start-Perranporth Zone). The resultant exhumation of the lower plate was accompanied by emplacement of the Early Permian SW England granites and was contemporaneous with upper plate sedimentary basin formation above the reactivated Rhenohercynian suture. The Rhenohercynian passive margin probably developed in a marginal basin north of the Rheic Ocean or, possibly, a successor basin following its closure. The Lizard ophiolite is unlikely to represent Rheic Ocean floor or associated forearc (SSZ) crust. The Rheic and Rhenohercynian sutures may be coincident or the Rheic suture may be located further south in the Léon Domain.

Towards a budget approach to Pleistocene terraces: preliminary studies using the River Exe in South West England, UK

This paper presents a first approach to using a sediment budget methodology for paired terrace staircase sediments in SW England. Although a budget approach has become firmly established in Holocene fluvial studies, it has not been used in Pleistocene sequences due to the problems of temporal resolution, catchment changes and downstream loss from the system. However, this paper uses a budget approach in a paired non-glaciated basin, primarily as a method of interrogating the terrace record concerning the degree of reworking and new sediment input required to produce the reconstructed terrace sequences. In order to apply a budget approach a number of assumptions have to be made and these are justified in the paper. The results suggest that the Exe system can most parsimoniously be explained principally by the reworking of a Middle Pleistocene floodplain system with relatively little input of new resistant clasts required and a cascade-type model in geomorphological terms. Whilst this maybe partially a result of the specific geology of the catchment, it is likely to be representative of many Pleistocene terrace systems in NW Europe due to their litho-tectonic similarities. This cascade-type model of terrace formation has archaeological implications and sets the context for the Palaeolithic terrace record in the UK. Future work will involve the testing of this and similar budget models using a combination of landscape modelling and chronometric dating.