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The use of stable Pb isotope analyses in conjunction with recent ( 210 Pb and anthropogenic radionuclide) chronologies has become a well-established method for evaluating historical trends in depositional fluxes and sources of atmospherically deposited Pb using archival records in lake sediment or peat cores. Such studies rely upon (i) simple radioactive disequilibrium between unsupported 210 Pb and longer-lived members of the 238 U decay series and (ii) well-defined values for the isotopic composition of contaminant Pb and indigenous Pb in the study area. However, areas of high natural radioactivity can present challenging environments for such studies, with potential complications arising from more complex disequilibria in the 238 U decay series and the occurrence, at local or regional level, of anomalous, ill-defined stable isotope ratios due to the presence of elevated levels of radiogenic Pb. Results are presented here for a study of a sediment core from a freshwater lake, Loch Einich, in the high natural radioactivity area of the Cairngorm Mountains of Scotland. 238 U decay series disequilibria revealed recent diagenetic re-deposition of both U and 226 Ra, the latter resulting in a requirement to use a modified calculation to derive a 210 Pb chronology for the core. Confidence in the chronology was provided by good agreement with the independent 241 Am chronology, but the 137 Cs distribution was affected by significant post-depositional mobility in the organic-rich sediment. The systematics of variations in 230 Th, 232 Th and stable Pb isotope ratio distributions were used to establish the indigenous Pb characteristics of the sediment. The relatively high radiogenic content of the indigenous Pb resulted in complications in source apportionment, in particular during the 20th century, with multiple natural and anthropogenic sources precluding the use of a simple binary mixing model. Consequently, 206 Pb/ 207 Pb ratios in Scottish moss samples from an archive collection were used to provide the input term for atmospheric deposition in order to establish historical trends in indigenous and anthropogenic Pb fluxes. A test of the accuracy of the derived Pb fluxes was provided by analysis of a core from a nearby blanket peat deposit, Great Moss. Independent atmospheric and basal inputs gave a complex distribution of 210 Pb in the peat, but this did not affect calculation of a 210 Pb chronology. Once again, the 210 Pb chronology was supported by the 241 Am distribution. Temporal trends in anthropogenic Pb deposition derived for the Loch Einich sediment core were in generally good agreement with those for the Great Moss peat core, other peat cores and some other lake sediment cores from northern Scotland, providing confidence in the use of the archive moss data to characterise atmospheric deposition. However, sustained input of Pb to Loch Einich sediment at relatively high levels in the late 20th century, after the regional decline in atmospheric Pb deposition, suggested that catchment-derived Pb is now a significant component of the depositional flux for Loch Einich. [ABSTRACT FROM AUTHOR]

Abstract: The rise of organised illegal fishing and trade in abalone from the late 1990s destabilised South Africa’s historically stable, quota-managed fishery, culminating in its closure in 2008. The development of the fishery is described in a historical context, including the evolution of South Africa’s science-based abalone fishery management system. The diverse suite of responses deployed to combat illegal fishing and the black market trade in abalone are reviewed, including;- fishery reform to expand rights to a greater number of previously disadvantaged fishers, a territorial user rights fishery (TURF) system, special compliance operations and courts, the CITES listing of abalone, and the serial reduction in the TAC, culminating in the controversial and legally contested closure of the fishery. The main causes of the rise of the illegal fishery are diagnosed as 1) the massive increase in the abalone price that occurred in the 1990s triggering an abalone fishing “gold-rush” and 2) the failure of the post-Apartheid fishery reform process to accommodate many traditional fishers in a legal fishing rights framework resulting in them operating outside the formal fishery management system. By contextualising the abalone fishery as a complex system, embedded in South Africa’s socio-political setting, we show how the resource focussed fishery management system did not have the capacity to incorporate the powerful social, political and economic drivers determining fisher behaviour. We conclude with the need to revisit South Africa’s abalone fishery management paradigm, and argue that a more integrated governance approach is required that takes into account the biological, socio-political and economic factors determining the fishery activities. [Copyright &y& Elsevier]

River sediment at a disused lead–zinc mine was analysed to provide an understanding of the chemical nature of the source term for contaminated sediment exported from the site. Changes in concentration and geochemical associations of Pb and Zn were measured using aqua regia digestion and the BCR sequential extraction procedure. Sediment in the immediate vicinity of the mine was highly contaminated with Pb (max. c. 11,000mg kg−1) and Zn (max. c. 30,000mg kg−1), but these values declined rapidly within 1km of the mine due to dilution and hydraulic sorting. Lead fractionation changed from being predominantly in the reducible fraction to being in the acetic acid-extractable fraction, whereas Zn was predominantly in the residual fraction. This material is transported as fine sediment in the river system. [Copyright &y& Elsevier]

Abstract: Oxidizing conditions normally prevail in surface waters and near-surface groundwaters, but there is usually a change to reducing conditions in groundwater at greater depth. Dissolved O2 originally present is consumed through biogenic and inorganic reactions along the flow paths. Fracture minerals participate in these reactions and the fracture mineralogy and geochemistry can be used to trace the redox front. An important task in the safety assessment of a potential repository for the disposal of nuclear waste in crystalline bedrock, at an approximate depth of 500m in Sweden, is to demonstrate that reducing conditions can be maintained for a long period of time. Oxygen may damage the Cu canisters that host nuclear waste; additionally, in the event of a canister failure, oxidizing conditions may increase the mobility of some radionuclides. The present study of the near-surface redox front is based on mineralogical (redox-sensitive minerals), geochemical (redox-sensitive elements) and U-series disequilibrium investigations of mineral coatings along open fractures. The fractures have been sampled along drill cores from closely spaced, 100m deep boreholes, which were drilled during the site investigation work in the Laxemar area, south-eastern Sweden, carried out by the Swedish Nuclear Fuel and Waste Management Co. (SKB). The distribution of the redox-sensitive minerals pyrite and goethite in open fractures shows that the redox front (switch from mainly goethite to mainly pyrite in the fractures) generally occurs at about 15–20m depth. Calcite leaching by recharging water is indicated in the upper 20–30m and positive Ce-anomalies suggest oxidation of Ce down to 20m depth. The U-series radionuclides show disequilibrium in most of the samples, indicating mobility of U during the last 1Ma. In the upper 20m, U is mainly removed (due to oxidation) or has experienced complex removal and/or deposition. At depths of 35–55m, both deposition and removal of U are indicated. Below 55m, recent deposition of U is generally indicated which suggests removal of U near surface (oxidation) and deposition of U below the redox front. Scattered goethite occurrences below the general redox front (down to ca 80m) and signs of U removal at 35–55m mostly correlate with sections of high transmissivity (and/or high fracture frequencies). This shows that highly transmissive fractures are generally required to allow oxygenated groundwaters at depth greater than ca 30m. Removal of U (oxidation) below 55m within the last 300ka is not observed. Although penetration of glacial waters to great depths has been confirmed in the study area, their potential O2 load seems to have been reduced near the surface. [Copyright &y& Elsevier]

Depleted uranium (DU) has become a soil contaminant of considerable concern in many combat zones and weapons-testing sites around the world, including locations in Europe, the Middle East and the USA, arising from its dispersion via the application of DU-bearing munitions. Once DU is released into the environment its mobility and bioavailability will, like that of other contaminants, largely depend on the type of associations it forms in soil and on the nature of the soil components to which it binds. In this study we used the BCR sequential extraction scheme to determine the partitioning of DU amongst soil fractions of texturally varying soils from locations affected by weapons-testing activities. Isotopic analyses (MC-ICP-MS and alpha-spectrometry) were performed to verify the presence of DU in whole soils and soil fractions and to determine any preferential partitioning of the contaminant. Results identified soil organic matter as being consistently the most important component in terms of DU retention, accounting for 30–100% of DU observed in the soils examined. However, at greater distances from known contamination points, DU was also found to be largely associated with the exchangeable fraction, suggesting that DU can be mobilised and transported by surface and near-surface water and does remain in an exchangeable (and thus potentially bioavailable) form in soils. [Copyright &y& Elsevier]