The occurrence and geochemistry of arsenic in groundwaters of the Newark basin of Pennsylvania

Elevated As concentrations in groundwater in the eastern United States have been recognized predominantly in the accretionary geologic terranes of northern New England. A retrospective examination of more than 18,000 existing groundwater samples from the Pennsylvania Department of Environmental Protection (PA DEP) Drinking Water and Sampling Information System database indicates that elevated groundwater As concentrations occur throughout the northern half of the Piedmont Province of Pennsylvania. Chemical analyses of 53 samples collected in 2005 from drinking water wells in this area all had detectable As, and 23% of these samples contained elevated (>133 nmol/L or >10 μg/L) concentrations of As. Elevated concentrations of As in the groundwater samples were most common in the Mesozoic sedimentary strata composed of sandstone and red mudstone with interbedded gray shale, and gray to black siltstone and shale. Arsenic was typically not elevated in groundwater of diabase intrusions of the Newark Basin or in crystalline and calcareous aquifers to the north of the Newark Basin. Geochemical parameters such as pH and oxidation–reduction potential can indicate mobility mechanisms of As in some regions. In this area, measured groundwater conditions were predominantly oxidizing (Eh > +50 mV), and more than 85% of samples contained arsenate as the dominant As species. Variations in pH were strongly correlated to the As concentration, with highest As concentrations observed at pH values greater than 6.4. The original source of As is most likely the black and gray shales that contain some arsenian pyrite with groundwater concentrations likely to be controlled by adsorption/desorption reactions with Fe oxides in the red mudstone aquifer materials.     

Analysis of Re, Au, Pd, Pt and Rh in NIST Glass Certified Reference Materials and Natural Basalt Glasses by Laser Ablation ICP-MS

A new technique for the in situ analysis of Re, Au, Pd, Pt and Rh in natural basalt glass by laser ablation (LA)-ICP-MS is described. The method involves external calibration against NIST SRM 612/613 or 614/615 glass certified reference materials, internal standardisation using Ca, and ablation with a 200 μm wide beam spot and a pulsed laser repetition rate of 50 Hz. Under these conditions, sensitivities for Re, Au, Pd, Pt and Rh analyte ions are ˜ 5000 to 100,000 cps/μg g^-1. This is sufficient to make measurements precise to ˜ 10% at the 2-10 μg g^-1 level, which is well within the range of concentrations expected in many basalts. For LA-ICP-MS calibration and a demonstration of the accuracy of the technique, concentrations of Re, Au, Pd, Pt and Rh in the NIST SRM 610/611 (˜ 1 to 50 μg g^-1), 612/613 (˜ 1 to 7 μg g^-1), 614/615 (˜ 0.2 to 2 μg g^-1) and 616/617 (˜ 0.004 to 2 μg g^-1) glasses were determined by solution-nebulisation (SN)-ICP-MS. Using the 612/613 or 614/615 glasses as calibration standards, LA-ICP-MS measurements of these elements in the other NIST glasses fell within ˜ 15% of those determined by SN-ICP-MS. Replicate LA-ICP-MS analyses of the 612/613 and 614/615 glasses indicate that, apart from certain anomalous domains, the glasses are homogeneous for Re, Au, Pd, Pt and Rh to better than 3.5%. Two LA-ICP-MS analyses of natural, island-arc basalt glasses exhibit large fractionations of Re, Au and Pd relative to Pt and Rh, compared to the relative abundances in the primitive mantle.     

Evidence for centennial-scale Lateglacial and early Holocene climatic complexity from Quoyloo Meadow,Orkney, Scotland

The influence of the North Atlantic on the margins of Europe means the region is particularly sensitive to changes in the ocean–atmospheric system. During the Last Glacial–Interglacial Transition (16–8 cal ka bp ) this system was repeatedly disrupted, leading to a series of abrupt and short-lived shifts in climate. Despite much research, the number and magnitude of these ‘centennial-scale’ events is not well understood. To address this, we expand upon investigations at Quoyloo Meadow, Orkney, Scotland, one of the best chronologically constrained palaeoclimate records in northern Britain. By coupling stable isotope and chironomid fossil analyses with existing data, this study identifies multiple phases of centennial-scale disturbance at: c. 14.0, 11.1, 10.8, 10.5, 10.45 and 10.3 cal ka bp , with the events at 14.0 and 10.3 exhibiting a particularly pronounced cold-climate signature. During the Holocene, the strongest response to climate forcing was at c. 10.3–10.0 cal ka bp , expressed as a two-stage drop in mean July temperatures, a shift in pollen spectra indicative of ‘less-stable’ climatic regimes, and a depletion in δ¹⁸O values. We interpret this as the first reliably dated incidence of the ‘10.3-ka event’ in the British Isles and consider the wider impact of this climatic reversal in other Holocene records.     

The distribution of meteoric <Superscript>36</Superscript>Cl/Cl in the United States: a comparison of models

The natural distribution of ³⁶Cl/Cl in groundwater across the continental United States has recently been reported by Davis et al. (2003). In this paper, the large-scale processes and atmospheric sources of ³⁶Cl and chloride responsible for controlling the observed ³⁶Cl/Cl distribution are discussed.The dominant process that affects ³⁶Cl/Cl in meteoric groundwater at the continental scale is the fallout of stable chloride from the atmosphere, which is mainly derived from oceanic sources. Atmospheric circulation transports marine chloride to the continental interior, where distance from the coast, topography, and wind patterns define the chloride distribution. The only major deviation from this pattern is observed in northern Utah and southern Idaho where it is inferred that a continental source of chloride exists in the Bonneville Salt Flats, Utah.In contrast to previous studies, the atmospheric flux of ³⁶Cl to the land surface was found to be approximately constant over the United States, without a strong correlation between local ³⁶Cl fallout and annual precipitation. However, the correlation between these variables was significantly improved (R ²=0.15 to R ²=0.55) when data from the southeastern USA, which presumably have lower than average atmospheric ³⁶Cl concentrations, were excluded. The total mean flux of ³⁶Cl over the continental United States and total global mean flux of ³⁶Cl are calculated to be 30.5±7.0 and 19.6±4.5 atoms m^–2 s^–1, respectively.The ³⁶Cl/Cl distribution calculated by Bentley et al. (1986) underestimates the magnitude and variability observed for the measured ³⁶Cl/Cl distribution across the continental United States. The model proposed by Hainsworth (1994) provides the best overall fit to the observed ³⁶Cl/Cl distribution in this study. A process-oriented model by Phillips (2000) generally overestimates ³⁶Cl/Cl in most parts of the country and has several significant local departures from the empirical data.

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Resumen Davis et al. (2003) han informado de la distribución natural de la proporción ³⁶Cl/Cl en las aguas subterráneas de la parte continental de los Estados Unidos de América [EUA]. En este artículo, se discute cuáles son los procesos a gran escala y las fuentes atmosféricas del ³⁶Cl y del cloruro que dan lugar a la distribución observada de ³⁶Cl/Cl.El proceso dominante que afecta a la relación ³⁶Cl/Cl en las aguas subterráneas de origen meteórico a escala continental es el aporte de cloruro estable desde la atmósfera, que procede principalmente de los océanos. La circulación atmosférica transporta el cloruro marino hacia el interior, donde la distancia a la costa, topografía y corrientes del viento definen la distribución del cloruro. La única desviación principal de este esquema tiene lugar al norte de Utah y en el sur de Idaho, donde se deduce que existe una fuente continental de cloruro en los Rellanos Salados de Bonneville (Salt Flats).En contraste con estudios previos (Knies et al. 1994; Phillips 2000), se ha descubierto que el flujo atmosférico de ³⁶Cl hacia la superficie terrestre es aproximadamente constante en todos los estados, sin deducirse una correlación fuerte entre el aporte de ³⁶Cl y la precipitación anual. Sin embargo, la correlación entre estas variables se ve mejorada de forma significativa, con coeficientes de regresión comprendidos entre 0,15 y 0,55, cuando se excluyen los datos recogidos en el sudeste de los EUA, que tienen concentraciones de ³⁶Cl atmosférico presuntamente inferiores a la media. El flujo medio total de ³⁶Cl calculado en la zona continental de los Estados Unidos vale 30,5±7,0 átomos por metro cuadrado y segundo, mientras que el flujo total global de ³⁶Cl es de 19,6±4,5 átomos por metro cuadrado y segundo.La distribución de ³⁶Cl/Cl calculada por Bentley et al. (1986) infravalora la magnitud y variabilidad observada en los valores medidos a lo largo de los Estados Unidos. El modelo propuesto por Hainsworth (1994) proporciona el mejor ajuste conjunto a la distribución observada de ³⁶Cl/Cl en este estudio. El modelo orientado a procesos de Phillips (2000) sobreestima por lo general la distribución de ³⁶Cl/Cl en la mayoría del país y difiere significativamente de algunos valores locales empíricos.

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Résumé La distribution naturelle du rapport ³⁶Cl/Cl dans les eaux souterraines des États-Unis a été récemment présentée par Davis et al. (2003). Dans ce travail, les processus à grande échelle et les sources atmosphériques de ³⁶Cl et de chlorure responsables du contrôle de la distribution observée du rapport ³⁶Cl/Cl sont discutés. Le processus dominant qui affecte le rapport ³⁶Cl/Cl dans les eaux souterraines dorigine météorique à léchelle continentale est lapport atmosphérique de chlorure stable, qui provient pour lessentiel de sources océaniques. La circulation atmosphérique transporte des chlorures marins vers lintérieur des continents, où la distribution de chlorure est définie par la distance à la côte, la topographie et les régimes des vents. La seule exception majeure à ce schéma est observée dans le nord de lUtah et le sud de lIdaho où lon suppose quil existe une source continentale de chlorure dans les bas-fonds salés de Bonneville. Au contraire de précédentes études (Knies et al. 1994; Phillips 2000), on trouve que le flux atmosphérique de ³⁶Cl vers le sol est approximativement constant sur lensemble des États-Unis, sans forte corrélation entre la retombée locale de ³⁶Cl et les précipitations annuelles. Cependant, la corrélation entre ces variables devient significative (R ²=0.15 à 0.55) lorsquon supprime les données du sud-est des États-Unis, dont on pense quelles présentent des concentrations en ³⁶Cl atmosphérique inférieures à la moyenne. Le flux total moyen de ³⁶Cl sur les États-Unis continentaux et le flux moyen global de ³⁶Cl sont respectivement évalués à 30.5 ± 7.0 et 19.6 ± 4.5 atomes.m^–2.s^–1. La distribution du rapport ³⁶Cl/Cl calculée par Bentley et al. (1986) sous-estime lordre de grandeur et la variabilité observés pour la distribution mesurée du rapport ³⁶Cl/Cl sur les États-Unis continentaux. Le modèle proposé par Hainsworth (1994) fournit le meilleur ajustement densemble à la distribution du rapport ³⁶Cl/Cl observée dans cette étude. Un modèle orienté vers les processus proposé par Phillips (2000) surestime dans lensemble le rapport ³⁶Cl/Cl dans la plupart des régions du pays et présente plusieurs désaccords locaux avec les données empiriques.

     

The geothermal potential of the basal clastics of Saskatchewan,Canada

The Winnipeg and Deadwood formations form deep clastic reservoirs in Saskatchewan, Canada, with temperatures exceeding 40 °C over most of southern Saskatchewan and reaching 100 °C in southwestern Saskatchewan. At these temperatures, the formations have geothermal potential for development of direct use and electricity generation systems. Numerous disposal wells operating at rates of 30 L/s or more are currently installed in these formations, suggesting that electricity could be generated at rates exceeding 2 megawatts of electrical output (MW_e) from individual wells. These basal clastic units, thus, could provide significant energy supply over a broad region of Saskatchewan.     

The effects of pH, ionic strength, and iron-fulvic acid interactions on the kinetics of non-photochemical iron transformations. II. The kinetics of thermal reduction

A combination of flow-injection analysis and kinetic analysis was used to examine the speciation of iron(II) and iron(III) in fulvic acid solutions as a function of pH, ionic strength, and time. This methodology was used to follow a shift in iron speciation from faster to slower reacting species over a timescale of several days. This speciation data shows that both iron(II) and iron(III)-fulvic acid complexes are important iron species in humic-containing natural waters and that their amounts and their rates of transformation to colloidal iron are controlled primarily by the kinetics of thermal (dark) reduction and iron(II) oxidation. The kinetic analysis methodology also yielded the rate constants for the thermal reduction of iron by the fulvic acid. These rate constants decrease with increasing pH and are independent of ionic strength. While thermal reduction was found to be too slow to produce large amounts of steady state iron(II) at circumneutral pH, it does provide a mechanism for iron redox cycling in the absence of photochemical or biochemical processes.     

Nutrient enrichments and phytoplankton growth in the surface waters of the Louisiana Bight

Nitrate concentrations have increased twofold in the Mississippi River during the past three decades. The increased nitrogen loading to the Louisiana shelf has been postulated as a factor leading to eutrophication and the subsequent development of hypoxia west of the Mississippi River delta. While ratios of nitrogen:phosphorus and nitrogen:silica are relatively high in surface waters on the western Louisiana shelf, nitrogen has been posed as the ‘limiting’ nutrient in this region. Bioassays were performed with nutrient additions to surface waters collected from the Louisiana shelf to examine the potential for specific nutrient limitation. Experiments were conducted in March and September 1991, and May 1992. The growth responses of natural and cultured phytoplankton populations were determined by measuring the time course of in vivo and 3-(3,4 dichlorophenyl)-1, 1-dimethylurea (DCMU)-induced fluorescence, as well as initial and final chlorophylla concentrations. The results suggest that phosphate and silicate potentially limit phytoplankton growth during the winter-spring, particularly at low salinities. In late summer, in contrast, nitrogen limitation may be prominent at higher salinities.