SW England Research Articles

Impacts of boat paint chips on the distribution and availability of copper in an English ria

Discarded paint chips collected from a leisure boat maintenance facility on the Kingsbridge estuary, SW England, have been fractionated to <63 μm and chemically characterised. At about 16% by weight, Cu was the most abundant metallic component, reflecting its biocidal application in antifouling paint. Bioavailability of Cu in the chips, determined by protein digestion, was about 4%, and sea water leachability was about 8%. Copper concentrations in fractionated intertidal sediment from the estuary were highly variable (<10–460 μg g −1). Specifically, greatest concentrations and greatest variability among replicates were found in samples collected near boat maintenance facilities. Bioavailability of Cu in sediment averaged 7% but was also variable. We attribute Cu “hot spots” to heterogeneous contamination of local sediment by small quantities of paint chips. Contamination may arise directly, from relatively inert particulates, or indirectly, via release of Cu from chips to interstitial waters and its subsequent adsorption to local sediment.

Recovery of meiofauna communities following mudflat disturbance by trampling associated with crab-tiling

The provision of artificial shelters for the collection of crabs, known as crab-tiling, and the subsequent harvesting of the soft "peeler" crabs for angling bait, are associated with trampling disturbance of intertidal mudflats in the United Kingdom. Recovery of meiofauna communities following crab-tiling activity was investigated on an intertidal mudflat in SW England. Harvesting of experimental plots was reproduced six times over a 2-week period. Meiofauna was collected at low tides 12h, 36 h and 144 h after treatment. Meiofaunal and nematode abundance, and nematode species number, was significantly greater in controls compared to crab-tile stations at 12h. At 36 h and 144 h there were no significant differences between treatments, indicating recovery had occurred in 12-36 h. Multivariate analysis showed nematode assemblage composition from control plots to be significantly different from crab-tile plots at 12h. No significant differences were observed between sediment physical parameters with treatment. Results suggest that the predominant effect of disturbance may be vibration-induced burial, which causes nematodes to bury deeper into the sediment, beyond the depth sampled, and explains the rapid recovery.

GEOLOGICAL MODEL EVALUATION THROUGH WELL TEST SIMULATION: A CASE STUDY FROM THE WYTCH FARM OILFIELD, SOUTHERN ENGLAND

This paper presents an approach to the evaluation of reservoir models using transient pressure data. Braided fluvial sandstones exposed in cliffs in SW England were studied as the surface equivalent of the Triassic Sherwood Sandstone, a reservoir unit at the nearby Wytch Farm oilfield. Three reservoir models were built; each used a different modelling approach ranging in complexity from stochastic pixel‐based modelling using commercially available software, to a spreadsheet random number generator. In order to test these models, numerical well test simulations were conducted using sector models extracted from the geological models constructed. The simulation results were then evaluated against the actual well test data in order to find the model which best represented the field geology.Two wells at Wytch Farm field were studied. The results suggested that for one of the sampled wells, the model built using the spreadsheet random number generator gave the best match to the well test data. In the well, the permeability from the test interpretation matched the geometric average permeability. This average is the “correct” upscaled permeability for a random system, and this was consistent with the random nature of the geological model. For the second well investigated, a more complex “channel object” model appeared to fit the dynamic data better.All the models were built with stationary properties. However, the well test data suggested that some parts of the field have different statistical properties and hence show non‐stationarity. These differences would have to be built into the model representing the local geology.This study presents a workflow that is not yet considered standard in the oil industry, and the use of dynamic data to evaluate geological models requires further development. The study highlights the fact that the comparison or matching of results from reservoir models and well‐test analyses is not always straightforward in that different models may match different wells. The study emphasises the need for integrated analyses of geological and engineering data. The methods and procedures presented are intended to form a feedback loop which can be used to evaluate the representivity of a geological model.

Influence of cockle Cerastoderma edule bioturbation and tidal-current cycles on resuspension of sediment and polycyclic aromatic hydrocarbons

Experiments were performed to investigate the impact of cockle population density Cerastoderma edule on the resuspension of naturally contaminated sediments collected from the Tamar estuary (SW England). Annular flumes generated tidal-current cycles for 7 to 9 d. The sus- pended sediment concentration (SSC) at peak flow increased 5-fold with increasing cockle popu- lation density, although the 2 highest densities yielded similar resuspension. Polycyclic aromatic hydrocarbons (PAHs) in the sediment were analysed by gas chromatography/mass spectrometry (GC/MS) at the beginning of the experiment, and in the water column of each flume after 2 and 6 d at both the maximum and minimum current speeds. At the end of each experiment sediment erod- ability was measured as a function of a stepwise increase in current speed. Sediment erosion increased up to 10-fold with increasing cockle population density. However, at the highest density the SSC was lower than that observed for the medium density, probably due to binding resulting from higher mucus secretion and pseudofaeces production. Current-induced resuspension of conta- minated sediment was dependent on the density of the cockles. The correlation between the suspended sediment concentrations and the concentrations of PAH was weak for low molecular weight PAHs (phenanthrene and anthracene) due to their higher water solubility. In contrast, higher molecular weight PAHs (fluoranthene, pyrene, benz(a)anthracene and chrysene) showed a strong correlation with suspended particulates as a result of their higher hydrophobicity.

Identifying and understanding factors influencing the uptake of new technologies on dairy farms in SW England using the theory of reasoned action

Whilst much is known of new technology adopters, little research has addressed the role of their attitudes in adoption decisions; particularly, for technologies with evident economic potential that have not been taken up by farmers. This paper presents recent research that has used a new approach which examines the role that adopters’ attitudes play in identifying the drivers of and barriers to adoption. The study was concerned with technologies for livestock farming systems in SW England, specifically oestrus detection, nitrogen supply management, and, inclusion of white clover. The adoption behaviour is analysed using the social–psychology theory of reasoned action to identify factors that affect the adoption of technologies, which are confirmed using principal components analysis. The results presented here relate to the specific adoption behaviour regarding the Milk Development Council’s recommended observation times for heat detection. The factors that affect the adoption of this technology are: cost effectiveness, improved detection and conception rates as the main drivers, whilst the threat to demean the personal knowledge and skills of a farmer in ‘knowing’ their cows is a barrier. This research shows clearly that promotion of a technology and transfer of knowledge for a farming system need to take account of the beliefs and attitudes of potential adopters.

Lough Neagh: the site of a Cenozoic pull-apart basin

Synopsis The Lough Neagh Basin in Northern Ireland is the site of a Cenozoic depocentre defined by gravity measurements and a thick succession of Paleocene basaltic lavas and Upper Oligocene clays. Much of the Cenozoic outcrop is concealed by Lough Neagh, but the rhombic outline of the lough provides some indication of the underlying structural control of the depocentre. Several authors have inferred that a Cenozoic pull-apart basin lies within the Lough Neagh area and suggest it is one of a number of transtensional basins, including the Bovey and Petrockstow basins in SW England, associated with NW to NNW-trending strike-slip fault zones. Solid geology maps and gravity data show that the structure of the Lough Neagh Basin is dominated by a segmented, orthogonal pattern of offset NNW and NE-trending faults. It is proposed that pull-apart basin formation took place in the Mid-Paleocene by dextral movement on these offset faults. The potential link between strike-slip tectonics and Cenozoic volcanism in the north of Ireland is briefly considered.

Seasonal variations in mussel, Mytilus edulis L. shell thickness and strength and their ecological implications

The shell thickness and strength of the mussel, Mytilus edulis L. were investigated across the season on the Exe estuary, SW England. Collection and measurements of mussels across the season showed that the average ventral thickness of their shells increased from end of September to mid-November and stayed constant till early December, and then significantly decreased and reached a minimum during mid-December. The initial increase is thought to be due to the selective predation of thin-shelled mussels by oystercatchers Haematopus ostralegus L., but there is no evidence of any processes selectively removing the thick-shelled mussels. The subsequent decrease in average thickness must therefore be due to individual mussels becoming thinner. Furthermore, when mussels were smashed using an artificial oystercatcher bill, results indicated that even with the effect of ventral thickness taken into account, the strength was approximately constant until mid-January then increased and became strongest during mid-March. We suggest that the shell thinning and changes is due to reduced estuarine salinity and temperature, which the increases in thickness at the beginning of winter and in strength at the end of winter are due to selective predation by oystercatchers.

Water content of granitic melts from Cornwall and Erzgebirge: A Raman spectroscopy study of melt inclusions

Melt inclusions (MIs) occurring in quartz of late-Variscan Sn-specialized granites from the Land's End pluton in SW England and from the eastern Erzgebirge volcano-plutonic complex in Germany were analyzed by Raman spectroscopy, secondary ion mass spectrometry and electron microprobe. Crystallized MIs were homogenized using cold-sealed autoclaves operating at 850°C and 2 kbar for 24 hours. The H2O concentration of homogenized MIs from the Land's End granites determined by confocal Ramanspectroscopyrangebetween1.5and5.4wt.%.SeveralMIsfromtheLand'sEndgranitescontainahypersalinefluidwith18.2 to38.6wt.%H2O.Such mixedfluidandsilicate-MIsare typical for magmasthat were oversaturatedinvolatiles. The ratioofsilicate glass/saline phase decreases with increasing degree of differentiation of the granite host. The H2O content of MIs from the Niederbobritzsch granite, Schonfeld rhyodacite, Teplice rhyolite, Altenberg-Frauenstein microgranite and Schellerhau granite inthe eastern Erzgebirge varies between 0.7 and 11.9 wt.%. The MIs from the volcanic rocks have more variable concentrations than the MIs from the granites. The high chemical discrepancies between MIs and whole rock suggest that the quartz phenocrysts in the Schonfeld rhyodacite were injected into a stratified magma chamber during the course of multiple recharge events at the chamber's base. MIs from granites from the eastern Erzgebirge do not contain hypersaline fluids, however they have F concentrations of up to 11.2 wt.%. The Li, Be and B contents of representative homogenized MIs were determined by SIMS. The light lithophile element ratios of MIs are constant for eachmagmatic province despite different fractionation degrees of the host rocks. MIs from rocks of the eastern Erzgebirge volcano-plutonic complexare relatively enriched in Li and Be, whereas MIs in granites of the Land's End pluton have higher B contents. The distinctive ratio of light lithophile elements of the silicate melt is also reflected in the light lithophile element ratio of the magmatic host quartz.

Glacial modification of granite tors in the Cairngorms, Scotland

AbstractA range of evidence indicates that many granite tors in the Cairngorms have been modified by the flow of glacier ice during the Pleistocene. Comparisons with SW England and the use of a space–time transformation across 38 tor groups in the Cairngorms allow a model to be developed for progressive glacial modification. Tors with deeply etched surfaces and no, or limited, block removal imply an absence of significant glacial modification. The removal of superstructure and blocks, locally forming boulder trains, and the progressive reduction of tors to stumps and basal slabs represent the more advanced stages of modification. Recognition of some slabs as tor stumps from which glacial erosion has removed all superstructure allows the original distribution of tors to be reconstructed for large areas of the Cairngorms. Unmodified tors require covers of non‐erosive, cold‐based ice during all of the cold stages of the Middle and Late Pleistocene. Deformation beneath cold‐based glacier ice is capable of the removal of blocks but advanced glacial modification requires former wet‐based glacier ice. The depth of glacial erosion at former tor sites remains limited largely to the partial or total elimination of the upstanding tor form. Cosmogenic nuclide exposure ages (Phillips et al., 2006) together with data from weathering pit depths (Hall and Phillips, 2006), from the surfaces of tors and large erratic blocks require that the glacial entrainment of blocks from tors occurred in Marine Isotope Stages (MIS) 4–2, 6 and, probably, at least one earlier phase. The occurrence of glacially modified tors on or close to, the main summits of the Cairngorms requires full ice cover over the mountains during these Stages. Evidence from the Cairngorms indicates that tor morphology can be regarded as an important indicator of former ice cover in many formerly glaciated areas, particularly where other evidence of ice cover is sparse. Recognition of the glacial modification of tors is important for debates about the former existence of nunataks and refugia. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Linking current environments and processes to fungal spore assemblages: Surface NPM data from woodland environments

While the basic premise of palaeoecological research is that the past and present can be linked, qualitatively or quantitatively, this has not been the case with much of the work in fungal spores and other non-pollen palynomorphs (NPPs). This relates partly to the shortage of ecological data, especially in terms of microfungi on plants or in soils. To address this problem, modern samples have been analysed from moss and from subsurface soil from Quercus woodland in SW England. This paper reports modern fungal and pollen assemblage data from grazed and ungrazed sites in order to test the use of fungal NPMs as indicators of grazing in prehistory. Preliminary conclusions, based here on a small number of samples, suggest that spores of coprophilous fungi are, as expected, more prevalent in soil samples from grazed woodland, but that a zero count does not mean absence of animals. Other fungal types also respond to grazing through indirect mechanisms, probably due to changes in the abundance of host plants and ground conditions.

Mid-Holocene environmental change at Black Ridge Brook, Dartmoor, SW England: A new appraisal based on fungal spore analysis

Black Ridge Brook is an upland peat site in a high rainfall area of SW England. Pollen evidence has shown that it was once wooded, with Betula and Corylus dominant, before periods of change to more open ground and the spread of mire vegetation. Previous palaeoecological work at the site inferred a history of burning based on microscopic charcoal levels, with the burning periods reducing Betula cover. These changes occurred between 9000 and 6300 BP (radiocarbon years) during the Mesolithic archaeological period, and have been linked to the impacts of hunter–gatherers using fire, as suggested elsewhere in upland Britain. In this paper, hypotheses of deliberate burning, grazing and the reasons for using fire are tested using non-pollen palynomorphs in addition to the microcharcoal and pollen data. While indicators of dung are present, the frequencies are low, and not always in the levels expected on the basis of vegetation change, although some correlation of disturbance indicators is seen in the earlier Holocene before woodland cover reached a maximum. There is evidence for increased and sustained growth of Corylus following increases in inferred fire frequency. Statistical analysis of the combined data set shows the association of some non-pollen types with specific stages in the development, and then recession, of woodland. Other types show the presence of on-site burning or host plants, and help distinguish between local and regional vegetation changes. The nature of the depositional environment is both shown by, but also affects, the non-pollen microfossil record.

Measurements of the critical erosion threshold of surface sediments along the Tamar Estuary using a mini-annular flume

Critical erosion thresholds of intertidal sediments have been measured throughout the Tamar Estuary, SW England, between March 2004 and August 2005. Erosion measurements were made with a miniature, portable annular flume, which could be deployed in situ or on large cores transferred to a research vessel or to the laboratory. Parallel measurements were made of sediment bulk properties (silt content, water content, wet bulk density, chlorophyll and carbohydrate). The data set included sediments with bulk densities ranging from 1555 kg m −3 in the lower, marine estuary where silt and water contents were low (45% and 43%, respectively) to 1138 kg m −3 in the upper estuary, at the upper limit of the estuarine turbidity maximum, where silt and water contents were higher (75% and 84%, respectively). For this data set, spanning the region from almost fully marine to the summer, low river flow, limit of the turbidity maximum, critical erosion thresholds ranged from 0.245 to 0.025 Pa and were highly correlated with sediment wet bulk density. There were no significant correlations with chlorophyll or carbohydrate. This is interpreted, at the whole-estuary scale, as reflecting an underlying physical control of sediment properties. The control is exerted through the combined influence of tidal pumping of fine material up-estuary to form the turbidity maximum, resulting in a reduction in sand content with distance up-estuary, and the generation of increasingly wet, low-density sediments in the upper estuary through repeated tidal mobilisation and deposition. It is speculated that adverse environmental conditions of low and fluctuating salinity, combined with regular tidal sediment disturbance in the upper estuary, prevent the benthic stabilisers (mainly algae) from colonising the sediment to the same extent as they do in the lower, marine estuary. The implication is that the distribution of benthic species in macro-tidal estuaries is determined by a combination of physical influences that (a) control the nature of the sediment along the estuary and, (b) result in a hostile, fluctuating salinity in the low-salinity region associated with variable river flows. Conversely, because of the less variable conditions in the marine end of the estuary, elements of the biota are able to colonise the mud flats where they can modify sediment properties. In these physically dominated, macro-tidal estuaries, seasonal (biological) effects on sediment stability contribute to the variability of the erosion–bulk density relationship.

Four closely related but forgotten species of Rhipidocotyle Diesing, 1858 (Digenea: Bucephalidae) in fishes from European seas

The following species of Rhipidocotyle are described: R. minima (Wagener, 1852) from Chelidonichthys gurnardus, C. lastoviza and Aspitrigla cuculus at various localities off the British Isles; R. nicolli n. sp. from A. cuculus off Plymouth, SW England; R. triglae (van Beneden, 1870) from C. lucernus in the Gulf of Marseilles, western Mediterranean; and R. viperae (van Beneden, 1870) from Echiichthys vipera at various localities off the British Isles. The distinguishing features of the species are discussed in detail. A list of the bucephalid species reported from the Mediterranean Sea is appended.

Post-depositional 137Cs Mobility in the Sediments of Three Shallow Coastal Lagoons, SW England

We present 137Cs profiles for three low lying coastal lagoons in Southwest England that show a decline in activity with sediment depth. 137Cs inventories are lower than expected by comparison with local reference inventories despite the fact that sampling was undertaken in the deep-water zone of each lake where sediment and 137Cs focusing would be expected. At all three locations, lake sediment 7Be and unsupported 210Pb (210Pbun) inventories are not significantly lower than the local reference inventory. 137Cs inventories in the study cores range from 38 to 95% of local reference inventories. The standing water level and mud: water interface at two sites are below maximum tide level and, at all three sites, salinity increases significantly in the water columns between low and high tide and in the pore waters of the underlying sediments. We suggest that the difference in hydrostatic pressure between sea level and standing water levels in the lagoons forces salt water up through the sediment column and that monovalent cations (especially Na+ and K+) replace 137Cs on exchange sites leading to the upward migration and loss of 137Cs. Rising sea levels may therefore contribute to remobilisation and release of 137Cs to the aquatic environment from the sediments of coastal lagoons.

New Dental School in SW England: A Step in the Right Direction

New Dental School in SW England: A Step in the Right Direction

Clay mineralogy of the Permo-Triassic strata of the British Isles: onshore and offshore

AbstractThe regional distribution, mineralogy, petrology and chemistry of the detrital and authigenic clay minerals associated with the Permo-Triassic strata (excluding the Rotliegend: see Ziegler, 2006; this volume), of the onshore and offshore regions of the British Isles are reviewed within their stratigraphical framework. The origin of these clay minerals is discussed in relation to current hypotheses on the developments of the Mg-rich clay mineral assemblages associated with the evaporitic red-bed Germanic facies of Europe and North Africa.Composite clay mineral successions are described for seven regions of the British Isles — the Western Approaches Trough; SW England; South Midlands; Central Midlands; the Cheshire Basin; NE Yorkshire; and the Central North Sea. The detrital clay mineral assemblages of the Early Permian strata are variable, consisting of mica, smectite, smectite-mica, kaolin and chlorite, whereas those of the Late Permian and the Trias are dominated by mica, usually in association with minor Fe-rich chlorite. The detrital mica consists of a mixture of penecontemporaneous ferric mica, probably of pedogenic origin, and recycled Pre-Permian mica. In the youngest Triassic strata (Rhaetian), the detrital clay assemblages may contain appreciable amounts of poorly defined collapsible minerals (irregular mixed-layer smectite-mica-vermiculite) and kaolin, giving them a Jurassic aspect. There are two types of authigenic clay mineral assemblages. Kaolin may occur as a late-stage diagenetic mineral where the original Permo-Triassic porewaters of the sediment have been replaced by meteoritic waters. A suite of early-stage diagenetic clay minerals, many of them Mg-rich, are linked to the evaporitic red-bed facies — these include sepiolite, palygorskite, smectite, irregular mixed- layer smectite-mica and smectite-chlorite, corrensite, chlorite and glauconite (sensu lato). The sandstones and mudstones of the onshore regions of the British Isles display little or no difference in their detrital and authigenic clay mineral assemblages. In contrast, the sandstones of the offshore regions (North Sea) show major differences with the presence of extensive chloritic cements containing Mg-rich and Al-rich chlorite, irregular mixed-layer serpentine-chlorite, and mica.

Calcrete as a source of heterogeneity in Triassic fluvial sandstone aquifers (Otter Sandstone Formation, SW England)

Abstract Carbonate is not generally considered as a potential source of large-scale heterogeneity in Permo-Triassic sandstone aquifers. This study shows that carbonate, in the form of early diagenetic calcrete, forms an abundant component of the Triassic Otter Sandstone Formation in south Devon. Three types of calcrete are described from the outcrop of this fluvial sandstone dominated aquifer: rhizocretions; calcrete sheets; and calcrete conglomerates. Data obtained from core plugs show that calcrete reduces sandstone permeability to less than 10 −15 m 2 and porosity to less than 12%. Calcrete can be sufficiently abundant to produce a significant (up to 30%) reduction in the total effective porosity of the aquifer. Moreover, calcrete conglomerates can form laterally extensive (up to 1 km) low-permeability sheets that will represent major baffles to vertical flow.

Trophic transfer of trace metals from the polychaete worm Nereis diversicolor to the polychaete N. virens and the decapod crustacean Palaemonetes varians

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 321:167-181 (2006) - doi:10.3354/meps321167 Trophic transfer of trace metals from the polychaete worm Nereis diversicolor to the polychaete N. virens and the decapod crustacean Palaemonetes varians P. S. Rainbow1,*, L. Poirier2, B. D. Smith1, K. V. Brix3,4, S. N. Luoma1, 5 1Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK 2Groupe SMAB, UPRES EA 2160, Laboratoire d’Ecotoxicologie, Université de Nantes, Pôle Mer et Littoral - BP 92208, 44322 Nantes Cedex 3, France 3EcoTox, 8963 Hampton Landing Drive E, Jacksonville, Florida 32256, USA 4Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, Florida 33149, USA 5United States Geological Survey, 345 Middlefield Road, Mail Stop 465, Menlo Park, California 94025, USA *Email: p.rainbow@nhm.ac.uk ABSTRACT: Diet is an important exposure route for the uptake of trace metals by aquatic invertebrates, with trace metal trophic transfer depending on 2 stages — assimilation and subsequent accumulation by the predator. This study investigated the trophic transfer of trace metals from the sediment-dwelling polychaete worm Nereis diversicolor from metal-rich estuarine sediments in southwestern UK to 2 predators — another polychaete N. virens (Cu, Zn, Pb, Cd, Fe) and the decapod crustacean Palaemonetes varians (Cu, Zn, Pb, Cd, Fe, Ag, As, Mn). N. virens showed net accumulation of Cu, Zn, Pb and Cd from the prey; accumulation increased with increasing prey concentration, but a coefficient of trophic transfer decreased with increasing prey concentration, probably because a higher proportion of accumulated metal in the prey is bound in less trophically available (insoluble) detoxified forms. The trace metal accumulation patterns of P. varians apparently restricted significant net accumulation of metals from the diet of N. diversicolor to just Cd. There was significant mortality of the decapods fed on the diets of metal-rich worms. Metal-rich invertebrates that have accumulated metals from the rich historical store in the sediments of particular SW England estuaries can potentially pass these metals along food chains, with accumulation and total food chain transfer depending on the metal assimilation efficiencies and accumulation patterns of the animal at each trophic level. This trophic transfer may be significant enough to have ecotoxicological effects. KEY WORDS: Trace metals · Trophic availability · Assimilation efficiency · Accumulation pattern · Nereis · Palaemonetes Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 321. Online publication date: September 08, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Modelling of dripwater hydrology and hydrogeochemistry in a weakly karstified aquifer (Bath, UK): Implications for climate change studies

A better knowledge of dripwater hydrology in karst systems is needed to understand the palaeoclimate implications of temporal variations in Mg/Ca and Sr/Ca of calcareous cave deposits. Quantitative modelling of drip hydrology and hydrochemistry was undertaken at a disused limestone mine (Brown's Folly Mine) in SW England overlain by 15 m of poorly karstified Jurassic limestones, with sub-vertical fracturing enhanced by proximity to an escarpment. Discharge was monitored at 15 sites intermittently from the beginning of 1996, and every 10–20 days from later 1996 to early 1998. Samples for hydrochemical parameters (pH, alkalinity, cations, anions, fluorescence) were taken corresponding to a sub-set of these data and supplemented by bedrock and soil sampling, limited continuously logged discharge, and soil water observations. Three sites, covering the range of discharge (approximately 1 μL s −1 to 1 ml s -1 maximum discharge) and hydrochemical behaviours, were studied in more detail. A quantitative flow model was constructed, based on two parallel unit hydrographs: responsive and relatively unresponsive to discharge events, respectively. The linear response and conservative mixing assumptions of the model were tested with hydrogeochemical data. Dripwaters at many of sites are characterized by evidence of prior calcite precipitation in the flowpath above the mine, which in the higher discharging sites diminishes at high flow. Also at low flow rates, dripwaters may access seepage reservoirs enriched in Mg and/or Sr, dependent on the site. The discharge at all three sites can be approximated by the flow model, but in each case, hydrochemical data show violations of the model assumptions. All sites show evidence of non-conservative mixing, and there are temporal discontinuities in behaviour, which may be stimulated by airlocks generated at low flow. Enhanced Mg/Ca and Sr/Ca often do relate to low-flow conditions, but the relationships between climate and hydrogeochemical response are non-linear.

Origin of quartz cores in tourmaline from Roche Rock, SW England

AbstractThe nature and mode of origin of quartz-cored tourmalines (QCT) are studied from hydrothermal quartz veins within massive quartz-tourmaline (MQT) rocks at Roche, SW England. The QCT are annular, have blue maximum absorption colour and occur together with tourmalines with brown cores rimmed by blue tourmaline. Where the quartz core is not continuous throughout the length of the QCT crystals, the tourmaline core has brown maximum absorption colour, similar to tourmalines without quartz cores. Both the blue and brown tourmalines are schorl, but are compositionally distinct showing different Fe/(Mg + Ti) ratios and Ca concentrations. Fluid inclusion data indicate quartz precipitation from a moderate salinity (∼20–25 wt.% NaCl eq.) brine which periodically boiled following pressure drops within the vein system. The QCT show rheomorphic and lobate textures on their inner margins indicating selective dissolution of their brown, relative Mg-, Ti- and Ca-rich tourmaline cores and replacement with quartz. This presents a problem in terms of the nature of the fluid responsible for such selective dissolution because tourmaline is generally highly resistant under the normal range of hydrothermal fluid conditions. It is proposed that the relatively high concentrations of Ti, Mg and Ca in the brown tourmaline caused significant lattice strain, which together with an increase in pH, and probably Al, in the boiling hydrothermal fluid caused the brown cores to become unstable compared with the Fe-rich blue tourmaline rims.