Application of environmental groundwater tracers at the Sulphur Bank Mercury Mine, California, USA

Boron, chloride, sulfate, δD, δ¹⁸O, and ³H concentrations in surface water and groundwater samples from the Sulphur Bank Mercury Mine (SBMM), California, USA were used to examine geochemical processes and provide constraints on evaporation and groundwater flow. SBMM is an abandoned sulfur and mercury mine with an underlying hydrothermal system, adjacent to Clear Lake, California. Results for non-³H tracers (i.e., boron, chloride, sulfate, δD, and δ¹⁸O) identify contributions from six water types at SBMM. Processes including evaporation, mixing, hydrothermal water input and possible isotopic exchange with hydrothermal gases are also discerned. Tritium data indicate that hydrothermal waters and other deep groundwaters are likely pre-bomb (before ~1952) in age while most other waters were recharged after ~1990. A boron-based steady-state reservoir model of the Herman Impoundment pit lake indicates that 71–79% of its input is from meteoric water with the remainder from hydrothermal contributions. Results for groundwater samples from six shallow wells over a 6–month period for δD and δ¹⁸O suggests that water from Herman Impoundment is diluted another 3% to more than 40% by infiltrating meteoric water, as it leaves the site. Results for this investigation show that environmental tracers are an effective tool to understand the SBMM hydrogeologic regime.

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Résumé Les concentrations en bore, chlorure, sulfate, δD, δ¹⁸O, et ³H d’échantillons d’eaux de surface et souterraine prélevés dans le banc de soufre de la mine de mercure (SBMM en anglais) en Californie, USA, ont été utilisées pour étudier les processus géochimiques et pour fournir des contraintes à l’évaporation et à l’écoulement des eaux souterraines. La SBMM est une mine de soufre et de mercure abandonnée, adjacente au lac Clear en Californie et sous laquelle se trouve un système hydrothermal.Les résultats des traceurs autres que le tritium (bore, chlorure, sulfate, δD, et δ¹⁸O) ont permis d’identifier des contributions de six types d’eaux à SBMM. Des processus tels que l’évaporation, le mélange, l’entrée d’eau hydrothermale et de possibles échanges isotopiques avec des gaz hydrothermaux ont également été identifiés. Les données de tritium montrent que les eaux hydrothermales et d’autres eaux profondes sont probablement d’age antérieure à la bombe (avant ~1952), alors que la plupart des autres eaux sont issues de la recharge après ~1990. Un modèle de réservoir représentant le lac situé dans la partie Herman Impoundment de l’ancienne mine, en régime permanent et basé sur le bore, montre que 71–79% de l’eau provient des précipitations, le reste provenant de contributions hydrothermales. Les résultats de δD et δ¹⁸O pour des échantillons d’eau souterraine de six puits peu profonds sur une période de 6 mois suggèrent que l’eau de Hermann Impoundment est encore diluée entre 3% jusqu’à plus de 40% lorsqu’elle quitte le site du fait de l’infiltration d’eau météorique. Les résultats de cette étude montrent que les traceurs environnementaux constituent un outil efficace pour comprendre le régime hydrogéologique de la SBMM.

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Resumen Se han utilizado datos de concentraciones de boro, cloruros, sulfatos, δD, δ¹⁸O, y ³H en muestras de aguas superficiales y subterráneas procedentes de la Mina de Mercurio Sulphur Bank (SBMM), California, USA, para estudiar los procesos geoquímicos y caracterizar la evaporación y el flujo del agua subterránea. SBMM es una mina abandonada de azufre y mercurio con un sistema hidrotermal subyacente, cercano al Lago Clear, California.Los resultados de los trazadores que no son ³H (por ejemplo, boro, cloruros, sulfatos δD, y δ¹⁸O) identifican las contribuciones de seis tipos de agua en la SBMM. Se han identificado diversos procesos, como evaporación, mezcla, entrada de agua hidrotermal y la posibilidad de intercambios isotópicos con gases hidrotermales. Los datos de tritio indican que las aguas hidrotermales y otras aguas subterráneas profundas son probablemente pre-bombas (previas a ~1952) en edad mientras que la mayoría de las otras aguas se han recargado después de ~1990. Un modelo estacionario basado en el boro de la fosa del lago Herman Impoundment indica que el 71–79% de su entrada procede de agua meteórica con restos de contribución hidrotermal. Los resultados para las muestras de aguas subterráneas procedentes de seis pozos superficiales en un periodo de 6 meses para δD y δ¹⁸O sugieren que el agua procedente de Herman Impoundment se diluye en otro 3% hasta más del 40% debido a la infiltración de agua meteórica., que sale del sitio. Los resultados de esta investigación muestran que los trazadores ambientales son una herramienta efectiva para entender el régimen hidrogeológico de la SBMM.

     

Distribution of asbestos in the bedrock of the northern New Jersey area

Asbestos has been identified at fifty-five locations in the bedrock of the northern New Jersey area. Most occurrences are confined to (1) The Precambrian rocks of the New Jersey Highlands, particularly the marbles; (2) the Paleozoic serpentinites of Staten Island, New York, and Hoboken, New Jersey; and (3) the Mesozoic basaltic rocks of the Newark Basin. Chrysotile and tremolite asbestos are present in local concentrations in the marbles. In the most extensive exposure of the marble, the Franklin band, traces of tremolite-actinolite asbestos are commonly present. Crocidolite asbestos occurs in localized areas associated with fracture systems in Precambrian pegmatites and associated rocks. The Paleozoic serpentinites contain chrysotile asbestos as a major component in deformed zones. Megascopic chrysotile and anthophyllite asbestos veins occur locally in the serpentinites. Actinolite asbestos occurs in the Mesozoic basaltic rocks of the Newark Basin. Potential environmental problems associated with asbestosbearing bedrock include production and use of rock products containing asbestos, introduction of asbestos into environments surrounding excavations, and asbestos contamination of soils and water supplies.     

Relative effects of physical and biological processes on nutrient and phytoplankton dynamics in a shallow estuary after a storm event

The effects of advection, dispersion, and biological processes on nitrogen and phytoplankton dynamics after a storm event in December 2002 are investigated in an estuary located on the northern New South Wales coast, Australia. Salinity observations for 16 d after the storm are used to estimate hydrodynamic transports for a one-dimensional box model. A biological model with nitrogen limited phytoplankton growth, mussel grazing, and a phytoplankton mortality term is forced by the calculated transports. The model captured important aspects of the temporal and spatial dynamics of the bloom. A quantitative analysis of hydrodynamic and biological processes shows that increased phytoplankton biomass due to elevated nitrogen loads after the storm was not primarily regulated by advection or dispersion in spite of an increase in river flow from <1 to 928×10³ m³ d⁻¹. Of the dissolved nitrogen that entered the surface layer of the estuary in the 16 d following the storm event, the model estimated that 28% was lost through exchange with the ocean or bottom layers, while 15% was removed by the grazing of just one mussel species,Xenostrobus securis, on phytoplankton, and 50% was lost through other biological phytoplankton loss processes.X. securis grazing remained an important loss process even when the estimated biological parameters in the model were varied by factors of ± 2. The intertidal mangrove pneumatophore habitat ofX. securis allows filtering of the upper water column from the lateral boundaries when the water column is vertically stratified, exerting top-down control on phytoplankton biomass.     

The creative reconstruction of the Internet: Google and the privatization of cyberspace and DigiPlace

The Internet has often been portrayed as the ultimate leveler of information where existing hierarchies of power and privilege are undermined by meritocracy. Some websites and functions are, however, more equal than others. In particular, search engines such as Google have been a key means to construct meaning out of disorder. This ordering (or enclosing of the Internet commons), however, comes at a cost as a location within the top 10 Google search results, marks the boundary (albeit a fluid one) between the core and the periphery of the Internet. The recent incorporation of spatial elements into the Google indexing raises fresh and geographically relevant concerns. This article focuses on the construction, access and use of Google derived rankings to deploy geo-referenced information in the physical environment and the way this melding of code and place affects how people interact with place. Using the theoretical concept of DigiPlace this article analyzes how Google Maps and Google Earth are structured and shape what appears (and what does not) in cyberspace and DigiPlace. Of particular concern are the implications of a private corporation controlling this new space.     

Late Holocene environmental conditions in Coronation Gulf,southwestern Canadian Arctic Archipelago: evidence from dinoflagellate cysts,other non‐pollen palynomorphs,and pollen

Boxcore 99LSSL‐001 (68.095° N, 114.186° W; 211 m water depth) from Coronation Gulf represents the first decadal‐scale marine palynology and late Holocene sediment record for the southwestern part of the Northwest Passage. The record was studied for organic‐walled microfossils (dinoflagellate cysts, non‐pollen palynomorphs), pollen, terrestrial spores, and sediment characteristics. ²¹⁰Pb, ¹³⁷Cs, and three accelerator mass spectrometry ¹⁴C dates constrain the chronology. Three prominent palaeoenvironmental zones were identified. During the interval AD 1470–1680 (Zone I), the climate was warmer and wetter than at present, and environmental conditions were more favourable to biological activity and northward boreal forest migration, with reduced sea‐ice and a longer open‐water (growing) season. The interval AD 1680–1940 (Zone II) records sea‐ice increase, and generally cool, polar conditions during the Little Ice Age. During AD 1940–2000 (Zone III), organic microfossils indicate an extended open‐water season and decreased sea‐ice, with suggested amelioration surpassing that of Zone I. Although more marine studies are needed to place this record into an appropriate context, the succession from ameliorated (Zone I) to cooler, sea‐ice influenced conditions (Zone II) and finally to 20th‐century warming (Zone III) corresponds well with several terrestrial climatic records from the neighbouring mainland and Victoria Island, and with lower‐resolution marine records to the west. Copyright © 2011 John Wiley & Sons, Ltd.     

The Geysers - Cobb Mountain Magma System, California (Part 1): U-Pb zircon ages of volcanic rocks, conditions of zircon crystallization and magma residence times

Combined U-Pb zircon and ⁴⁰Ar/³⁹Ar sanidine data from volcanic rocks within or adjacent to the Geysers geothermal reservoir constrain the timing of episodic eruption events and the pre-eruptive magma history. Zircon U-Pb concordia intercept model ages (corrected for initial ²³⁰Th disequilibrium) decrease as predicted from stratigraphic and regional geological relationships (1σ analytical error): 2.47 ± 0.04 Ma (rhyolite of Pine Mountain), 1.38 ± 0.01 Ma (rhyolite of Alder Creek), 1.33 ± 0.04 Ma (rhyodacite of Cobb Mountain), 1.27 ± 0.03 Ma (dacite of Cobb Valley), and 0.94 ± 0.01 Ma (dacite of Tyler Valley). A significant (∼0.2-0.3 Ma) difference between these ages and sanidine ⁴⁰Ar/³⁹Ar ages measured for the same samples demonstrates that zircon crystallized well before eruption. Zircons U-Pb ages from the underlying main-phase Geysers Plutonic Complex (GPC) are indistinguishable from those of the Cobb Mountain volcanics. While this is in line with compositional evidence that the GPC fed the Cobb Mountain eruptions, the volcanic units conspicuously lack older (∼1.8 Ma) zircons from the shallowest part of the GPC. Discontinuous zircon age populations and compositional relationships in the volcanic and plutonic samples are incompatible with zircon residing in a single long-lived upper crustal magma chamber. Instead we favor a model in which zircons were recycled by remelting of just-solidified rocks during episodic injection of more mafic magmas. This is consistent with thermochronologic evidence that the GPC cooled below 350° C at the time the Cobb Mountain volcanics were erupted.     

Sediment transport,biotic modifications and selection of grain size in a surface deposit-feeder

Deposit-feeders often select for particles on the basis of grain size. The available pool of particles at the sediment surface may be modified both by deposit-feeder activity and by sediment transport, but the effects of these alterations on deposit-feeder diet composition have received little attention. In laboratory experiments the spionid polychaeteParaprionospio pinnata altered the grain-size composition in its foraging area, and these alterations were reflected in grain-size changes in the diet. After simulated transport of fine-grain sediments,P. pinnata diets also changed in grain-size composition. Field data were collected from 9 m depth in the lower Chesapeake Bay. A video camera, deployed near the bottom, identified times of sediment transport over a 6-h Period;P. pinnata were collected concurrently for gut analysis. Consistent with predictions from the laboratory experiments,P. pinnata ingested primarily small-grain sizes. During periods of no sediment transport this feeding pattern reduced the relative availability of small particles; larger sediments were incorporated into the diet. Sediment transport may resupply the foraging area with fine-grain particles which are then incorporated into the diet. On these small spatial and time scales, deposit-feeder activity may affect the availability of food resources.     

Stochastic groundwater modeling of a sedimentary aquifer: evaluation of the impacts of abstraction scenarios under conditions of reduced recharge

A transient finite difference groundwater flow model has been calibrated for the Nasia sub-catchment of the White Volta Basin. This model has been validated through a stochastic parameter randomization process and used to evaluate the impacts of groundwater abstraction scenarios on resource sustainability in the basin. A total of 1500 equally likely model realizations of the same terrain based on 1500 equally likely combinations of the data of the key aquifer input parameters were calibrated and used for the scenario analysis. This was done to evaluate model non-uniqueness arising from uncertainties in the key aquifer parameters especially hydraulic conductivity and recharge by comparing the realizations and statistically determining the degree to which they differ from each other. Parameter standard deviations, computed from the calibrated data of the key parameters of hydraulic conductivity and recharge, were used as a yardstick for evaluating model non-uniqueness. All model realizations suggest horizontal hydraulic conductivity estimates in the range of 0.03–78.4 m/day, although over 70 % of the area has values in the range of 0.03–14 m/day. Low standard deviations of the horizontal hydraulic conductivity estimates from the 1500 solutions suggest that this range adequately reflects the properties of the material in the terrain. Lateral groundwater inflows and outflows appear to constitute significant components of the groundwater budgets in the terrain, although estimated direct vertical recharge from precipitation amounts to about 7 % of annual precipitation. High potential for groundwater development has been suggested in the simulations, corroborating earlier estimates of groundwater recharge. Simulation of groundwater abstraction scenarios suggests that the domain can sustain abstraction rates of up to 200 % of the current estimated abstraction rates of 12,960 m³/day under the current recharge rates. Decreasing groundwater recharge by 10 % over a 20-year period will not significantly alter the results of this abstraction scenario. However, increasing abstraction rates by 300 % over the period with decreasing recharge by 10 % will lead to drastic drawdowns in the hydraulic head over the entire terrain by up to 6 m and could cause reversals of flow in most parts of the terrain.     

Understanding geomorphic responses to environmental change: a 19 000‐year case study from semi‐arid central Texas,USA

Understanding the impact of past climatic changes on landscape stability is crucial in order to predict and mitigate the effects of future changes. However, in arid and semi‐arid environments, reconstructions are often hampered by a poor understanding of the relationship between sediment deposition and climate. We present here data from central Texas, a region that is sensitive to environmental change but has received relatively little attention. The study integrates a chronology of 29 optically stimulated luminescence (OSL) ages from six sedimentary sites in a range of depositional contexts with a 19 000 a climate record derived from pollen extracted from the adjacent Boriack Bog. By comparing the two records, we aimed to assess the relationship between climate change and geomorphic activity. Data show that extensive aeolian and colluvial deposition occurred during the mid to late Holocene, with sedimentation generally increasing during more arid phases. However, a number of depositional events on slopes were associated with moister episodes, and sediment was also deposited in a summit setting immediately after phases of increased precipitation. Linkages between climate change and geomorphic response were therefore complex, being controlled by both sediment supply and transport energy. The climatic fluctuations identified in the Boriack Bog record highlight the sensitivity of central Texas to environmental change, while disparities in conditions recorded between it and other palaeoenvironmental sites in the southern USA emphasise the need for further work in order to enhance understanding of landscape sedimentary response to climate. Copyright © 2010 John Wiley & Sons, Ltd.