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21.
Arsenic mobility in alteration products of sulfide-rich, arsenopyrite-bearing mine wastes, Snow Lake, Manitoba, Canada 总被引:2,自引:0,他引:2
Kristin A. Salzsauler Nikolay V. Sidenko Barbara L. Sherriff 《Applied Geochemistry》2005,20(12):2303-2314
The Arsenopyrite Residue Stockpile (ARS) in Snow Lake, Manitoba contains approximately 250,000 tons of cyanide treated, refractory arsenopyrite ore concentrate. The residue was deposited between 1950 and 1959 in an open waste rock impoundment, and remained exposed until 2000, when the pile was capped with layers of waste rock and clay. During the time when the ARS was exposed to the atmosphere, arsenopyrite, pyrrhotite, pyrite and chalcopyrite were oxidized producing scorodite, jarosite and two generations of amorphous Fe sulfo-arsenates (AISA). These secondary phases attenuated some of the As released to pore water during oxidation in the upper layers of the ARS. The imposition of the cap prevented further oxidation. The secondary As minerals are not stable in the reduced environment that currently dominates the pile. Therefore, As currently is being released into the groundwater. Water in an adjacent monitoring well has concentrations of >20 mg/L total As with relative predominance of As(III). 相似文献
22.
Obsidian is abundant in the Main Ethiopian Rift (MER). Petrological and geochemical features of obsidian from four volcanic centers in the MER, namely Birenti, Dofen, Fentale and Kone, are presented. Compositional and petrological variability is noted among the Dofen and Fentale obsidian, but not in those from Kone and Birenti where each have separate but uniform elemental composition. The Fentale and Kone obsidian were source materials for the artifacts of a number of Middle Stone Age and Later Stone Age/Neolithic sites in the region. We have yet to determine whether Dofen and Birenti were sources for archeological artifacts. The study also shows that volcanic episodes from a single center do not necessarily result in compositional variability. 相似文献
23.
Impacts of a large Sahelian city on groundwater hydrodynamics and quality: example of Niamey (Niger)
Aïssata B. Hassane Christian Leduc Guillaume Favreau Barbara A. Bekins Thomas Margueron 《Hydrogeology Journal》2016,24(2):407-423
The management of groundwater resources is very important in the semiarid Sahel region, which is experiencing rapid urban development. Impacts of urbanization on groundwater resources were investigated in the unconfined aquifer of the Continental Terminal beneath the city of Niamey, Niger, using water level and chemical data. Hydrodynamic and chemical changes are best described by a combination of factors including the historical development of the city, current land use, water-table depth and topography. Seasonal groundwater recharge occurs with high spatial variability, as indicated by water-level monitoring in all wells, but there was no interannual trend over the 5-year study period. Groundwater salinity shows high spatial variability and a minor rising trend. The highest salinity is in the old city centre, with Na–NO3 dominant, and it increases seasonally with recharge. Salinity is much lower and more variable in the suburbs (Ca–HCO3, Ca–NO3, and Na–NO3 dominant). Nitrate is the main ionic contaminant and is seasonally or permanently above the international guidelines for drinking water quality in 36 % of sampled wells, with a peak value of 112 mg L?1 NO3–N (8 meq L?1). Comparison of urban and rural sites indicates a long-term increase in groundwater recharge and nitrate enrichment in the urban area with serious implications for groundwater management in the region. 相似文献
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Barbara A. Muhling Carlos F. Gaitán Charles A. Stock Vincent S. Saba Desiree Tommasi Keith W. Dixon 《Estuaries and Coasts》2018,41(2):349-372
Estuaries are productive and ecologically important ecosystems, incorporating environmental drivers from watersheds, rivers, and the coastal ocean. Climate change has potential to modify the physical properties of estuaries, with impacts on resident organisms. However, projections from general circulation models (GCMs) are generally too coarse to resolve important estuarine processes. Here, we statistically downscaled near-surface air temperature and precipitation projections to the scale of the Chesapeake Bay watershed and estuary. These variables were linked to Susquehanna River streamflow using a water balance model and finally to spatially resolved Chesapeake Bay surface temperature and salinity using statistical model trees. The low computational cost of this approach allowed rapid assessment of projected changes from four GCMs spanning a range of potential futures under a high CO2 emission scenario, for four different downscaling methods. Choice of GCM contributed strongly to the spread in projections, but choice of downscaling method was also influential in the warmest models. Models projected a ~2–5.5 °C increase in surface water temperatures in the Chesapeake Bay by the end of the century. Projections of salinity were more uncertain and spatially complex. Models showing increases in winter-spring streamflow generated freshening in the Upper Bay and tributaries, while models with decreased streamflow produced salinity increases. Changes to the Chesapeake Bay environment have implications for fish and invertebrate habitats, as well as migration, spawning phenology, recruitment, and occurrence of pathogens. Our results underline a potentially expanded role of statistical downscaling to complement dynamical approaches in assessing climate change impacts in dynamically challenging estuaries. 相似文献
28.
Climatic Change - The severity and frequency of climate change hazards are increasing around the world. Because the impacts are most acutely felt in local communities, it is critical to improve... 相似文献
29.
An integrated mass balance and modelling approach for analysis of estuarine nutrient fluxes is demonstrated in the Swan River Estuary, a microtidal system with strong hydrological dependence on seasonal river inflows. Mass balance components included estimation of gauged and ungauged inputs to the estuary and losses to the ocean (outflow and tidal exchange). Modelling components included estimation of atmospheric (N fixation, denitrification) and sediment–water column nutrient exchanges. Gross and net denitrification derived using two independent methods were significantly correlated (r2 = 0.49, p < 0.01) with net rates averaging 40% of gross. Annual nitrogen (N) and phosphorus (P) loads from major tributaries were linearly correlated with annual freshwater discharge and were 3-fold higher in wet years than in dry years. Urban drains and groundwater contributed, on average, 26% of N inputs and 19% of P inputs, with higher relative contributions in years of low river discharge. Overall, ungauged inputs accounted for almost 35% of total nitrogen loads. For N, elevated loading in wet years was accompanied by large increases in outflow (7x) and tidal flushing (2x) losses and resulted in overall lower retention efficiency (31%) relative to dry years (70%). For P, tidal flushing losses were similar in wet and dry years, while outflow losses (4-fold higher) were comparable in magnitude to increases in loading. As a result, P retention within the estuary was not substantially affected by inter-annual variation in water and P loading (ca. 50% in all years). Sediment nutrient stores increased in most years (remineralisation efficiency ca. 50%), but sediment nutrient releases were significant and in some circumstances were a net source of nutrients to the water column. 相似文献
30.
Attila Petrik Lszl Fodor Lszl Bereczki Zsombor Klembala Rka Lukcs Viktria Baranyi Barbara Beke Szabolcs Harangi 《Basin Research》2019,31(2):380-404
The development of high‐resolution 3D seismic cubes has permitted recognition of variable subvolcanic features mostly located in passive continental margins. Our study area is situated in a different tectonic setting, in the extensional Pannonian Basin system (central Europe) where the lithospheric extension was associated with a wide variety of magmatic suites during the Miocene. Our primary objective is to map the buried magmatic bodies, to better understand the temporal and spatial variation in the style of magmatism and emplacement mechanism within the first order Mid‐Hungarian Fault Zone (MHFZ) along which the substantial Miocene displacement took place. The combination of seismic, borehole and log data interpretation enabled us to delineate various previously unknown subvolcanic‐volcanic features. In addition, a new approach of neural network analysis on log data was applied to detect and quantitatively characterise hydrothermal mounds that are hard to interpret solely from seismic data. The volcanic activity started in the Middle Miocene and induced the development of extrusive volcanic mounds south of the NE‐SW trending, continuous strike‐slip fault zone (Hajdú Fault Zone). In the earliest Late Miocene (11.6–9.78 Ma), the style of magmatic activity changed resulting in emplacement of intrusions and development of hydrothermal mounds. Sill emplacement occurred from south‐east to north‐west based on primary flow‐emplacement structures. The time of sill emplacement and the development of hydrothermal mounds can be bracketed by onlapped forced folds and mounds. This time coincided with the acceleration of sedimentation producing poorly consolidated, water‐saturated sediments preventing magma from flowing to the paleosurface. The change in extensional direction resulted in change in fault pattern, thus the formerly continuous basin‐bounding strike‐slip fault became segmented which could facilitate the magma flow toward the basin centre. 相似文献