Sediment geochemistry of streams draining abandoned lead / zinc mines in central Wales: the Afon Twymyn

Purpose Despite the decline of metal mining in the UK during the early 20th century, a substantial legacy of heavy metal contamination persists in river channel and floodplain sediments. Poor sediment quality is likely to impede the achievement of ’good’ chemical and ecological status for surface waters under the European Union Water Framework Directive. This paper examines the environmental legacy of the Dylife lead/zinc mine in the central Wales mining district. Leachable heavy metal concentrations in the bed sediments of the Afon Twymyn are established and the geochemical partitioning, potential mobility and bioavailability of sediment-associated heavy metals are established. Materials and methods Sediment samples were collected from the river bed and dry-sieved into two size fractions (<63 μm and 64–2,000 μm). The fractionated samples were then subjected to a sequential extraction procedure to isolate heavy metals (Pb, Zn, Cu, Cd, Fe, Mn) in three different geochemical phases. Sediment samples were then analysed for heavy metals using ICP-AES. Results and discussion The bed sediment of the Afon Twymyn is grossly polluted with heavy metals. Within the vicinity of the former mine, Pb concentrations are up to 100 times greater than levels reported to have deleterious impacts on aquatic ecology. Most heavy metals exist in the most mobile easily exchangeable and carbonate-bound geochemical phases, potentially posing serious threats to ecological integrity and constituting a significant, secondary, diffuse source of pollution. Metal concentrations decrease sharply downstream of the former mine, although there is a gradual increase in the proportion of readily extractable Zn and Cd. Conclusions Implementation of sediment quality guidelines is important in order to achieve the aims of the Water Framework Directive. Assessments of sediment quality should include measurements of background metal concentrations, river water physico-chemistry and, most importantly, metal mobility and potential bioavailability. Uniformity of sediment guidelines throughout Europe and flexibility of targets with regard to the most heavily contaminated mine sites are recommended

Large-scale climatic phenomena drive fluctuations in macroinvertebrate assemblages in lowland tropical streams, Costa Rica: The importance of ENSO events in determining long-term (15y) patterns

Understanding how environmental variables influence the distribution and density of organisms over relatively long temporal scales is a central question in ecology given increased climatic variability (e.g., precipitation, ENSO events). The primary goal of our study was to evaluate long-term (15y time span) patterns of climate, as well as environmental parameters in two Neotropical streams in lowland Costa Rica, to assess potential effects on aquatic macroinvertebrates. We also examined the relative effects of an 8y whole-stream P-enrichment experiment on macroinvertebrate assemblages against the backdrop of this long-term study. Climate, environmental variables and macroinvertebrate samples were measured monthly for 7y and then quarterly for an additional 8y in each stream. Temporal patterns in climatic and environmental variables showed high variability over time, without clear inter-annual or intra-annual patterns. Macroinvertebrate richness and abundance decreased with increasing discharge and was positively related to the number of days since the last high discharge event. Findings show that fluctuations in stream physicochemistry and macroinvertebrate assemblage structure are ultimately the result of large-scale climatic phenomena, such as ENSO events, while the 8y P-enrichment did not appear to affect macroinvertebrates. Our study demonstrates that Neotropical lowland streams are highly dynamic and not as stable as is commonly presumed, with high intra- and inter-annual variability in environmental parameters that change the structure and composition of freshwater macroinvertebrate assemblages.This study was financed by National Science Foundation (DEB 1122389) to Catherine M. Pringle. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR

Melt Inclusions in Primitive Olivine Phenocrysts: the Role of Localized Reaction Processes in the Origin of Anomalous Compositions

Melt inclusions are small portions of liquid trapped by growing crystals during magma evolution. Recent studies of melt inclusions have revealed a large range of unusual major and trace element compositions in phenocrysts from primitive mantle-derived magmatic rocks [e.g. in high-Fo olivine (Fo > 85 mol %), spinel, high-An plagioclase]. Inclusions in phenocrysts crystallized from more evolved magmas (e.g. olivine Fo < 85 mol %), are usually compositionally similar to the host lavas. This paper reviews the chemistry of melt inclusions in high-Fo olivine phenocrysts focusing on those with anomalous major and trace element contents from mid-ocean ridge and subduction-related basalts.We suggest that a significant portion of the anomalous inclusion compositions reflects localized, grainscale dissolution-reaction-mixing (DRM) processes within the magmatic plumbing system. The DRM processes occur at the margins of primitive magma bodies, where magma is in contact with cooler wall rocks and/or pre-existing semi-solidified crystal mush zones (depending on the specific environment). Injection of hotter, more primitive magma causes partial dissolution (incongruent melting) of the mush-zone phases, which are not in equilibrium with the primitive melt, and mixing of the reaction products with the primitive magma. Localized rapid crystallization of high-Fo olivines from the primitive magma may lead to entrapment of numerous large melt inclusions, which record the DRM processes in progress. In some magmatic suites melt inclusions in primitive phenocrysts may be naturally biased towards the anomalous compositions. The occurrence of melt inclusions with unusual compositions does not necessarily imply the existence of new geologically significant magma types and/or melt-generation processes, and caution should be exercised in their interpretation

Narrative foresight in technical organizations: epistemological and methodological contributions from a practice of scenario method in Argentina

Abstract The following paper explores the experience of narrative Foresight applied to the use of the scenario method in Argentina in the light of the contributions of critical Future Studies concerning the narrative dimension in the last years. This research is specifically focused on analyzing applications of the scenario method in an institute of technology development in Argentina (“Instituto Nacional de Tecnología Agropecuaria”) using the causal layered analysis as a method of examination and adopting the narrative Foresight approach. We analyze how the narrative approach permeates the scenario method in the process of development, thus increasing the potential usefulness and impact of the method. Moreover, we also reflect on the utility of this approach in order to increase the strategic vision of complex organizations which are shaped, to a great extent, by linear schemes of thought where the empiric dimension of reality operates with a value of truth