The application of in situ permeable reactive (zero-valent iron) barrier technology for the remediation of chromate-contaminated groundwater: a field test

A small-scale field test was initiated in September 1994 to evaluate the in situ remediation of groundwater contaminated with chromate using a permeable reactive barrier composed of a mixture of zero-valent Fe, sand and aquifer sediment. The site used was an old chrome-plating facility located on a U.S. Coast Guard air base near Elizabeth City, North Carolina. Dissolved chromate concentrations were reduced to less than 0.01 mg/L via reduction from Cr(VI) to Cr(III) as a result of the corrosion of the Fe. As the Fe corrodes, pH increases, oxidation-reduction potential declines, dissolved oxygen is consumed, and Fe(II) is generated. Mineral phases formed as a result of the Fe corrosion include ferrous sulfides and various Fe oxides, hydroxides, and oxyhydroxides.     

Two-feldspar geothermometry,geobarometry in mesozonal granitic intrusions: Three examples from the Piedmont of Georgia

The equilibrium temperatures for coexisting plagioclase and potassium feldspar pairs have been calculated for various textural varieties of feldspar from 3 post-metamorphic granites from the Georgia Piedmont; the Danburg, Siloam, and Stone Mountain plutons. Assuming an intermediate structural state for the feldspars at time of equilibration, crystallization temperatures match those expected from experimental data for quartz monzonite magmas (650 to 780° C). The variations in solidus temperature, recorded in the feldspars, may be used to estimate relative differences in depth of intrusion. Sharp reversals in plagioclase compositional trends may be caused by isothermal decreases in confining pressure associated with upward migration through the crust. In fine grained and slowly cooled intrusions, albite tends to be lost from the alkali feldspar grains, and recrystallizes as separate unzoned grains of oligoclase, thus erasing the previous thermal history. Perthite exsolution and re-equilibration within the alkali feldspar grains appears to continue down to temperatures of 400° C or so, although the zoned plagioclase does not homogenize. The recrystallization associated with changes in structural state may facilitate exsolution within alkali feldspar grains.     

Variations of phytoplankton community structure related to water quality trends in a tropical karstic coastal zone

Phytoplankton community structure in coastal areas is a result of various environmental factors such as nutrients, light, grazing, temperature, and salinity. The Yucatan Peninsula is a karstic tropical region that is strongly influenced by submerged groundwater discharge (SGD) into the coastal zone. Phytoplankton community structure and its relationship with regional and local water quality variables were studied in four ports of the northwestern Yucatan Peninsula. Water quality was strongly related to SGD, and variations in phytoplankton community structure were related to local nutrient loading and hydrographic conditions, turbulence, and human impacts. Our study provides an ecological baseline for the Yucatan Peninsula and serves as a basis for establishing monitoring programs to predict changes at sites with high hydrological variation and in developing an early alert system for harmful toxic algal blooms.     

Structural control of low-sulfidation epithermal gold mineralization in the Rosario–Bunawan district, East Mindanao Ridge, Philippines

The Rosario–Bunawan district is situated about 200 km north of Davao City, the capital of the Mindanao Island, Southern Philippines. Gold is produced from the Co-O mine, containing about 2,034,000 t of ore at 10.9 g/t Au, and in numerous small-scale operations by local miners. Epithermal gold mineralization in the Rosario–Bunawan district and the Co-O mine is confined to narrow (0.2–4 m) low-sulfidation quartz–chalcedony–calcite veins in volcanic and volcaniclastic wall rocks. Three major vein orientations are distinguished: (1) the NNW–SSE-trending set with a sinistral strike-slip sense of deformation (Philippine Fault trend); (2) the ENE–WSW-trending dextral strike-slip set (Palawan trend) and associated veins in the Riedel geometry; and (3) the WNW–ESE-trending conjugate set (Co-O trend). Three structural stages are defined: (1) extensional shear or shear veins formed in the Co-O, the Philippine Fault, and Palawan trends during regional NW–SE compression and near vertical vein opening (D₁); (2) reactivation of veins in the Philippine Fault, veins associated with the Palawan, and, to a lesser extent, the Co-O trends during E–W compression and near horizontal N–S-oriented vein opening (D₂). New D₂ extensional shear or shear veins formed in the Philippine Fault, and structures associated with the Palawan and associated Riedel trends; (3) the D₃-stage block faulting subsequently displaced all of the auriferous veins. The auriferous Rosario–Bunawan district is situated between two splays of the Philippine Fault, which acted as a lateral ramp system during the oblique convergence of the Philippine Sea plate and the Eurasian plate. The oblique convergence resulted in a change from a compressional (D₁) to a transpressional (D₂) regime, which was a prerequisite for the two-stage vein opening and hydrothermal mineralization, leading to an economic gold enrichment. D₁ compressional tectonics may have caused an elevated geothermal gradient in shallow crustal levels, forming the heat source for the fluid plumbing system, which is at variance to typical epithermal deposits formed in extensional zones. D₂ thrusting of a limestone nappe together with syn-tectonic diorite intrusions may have further increased the geothermal gradient, maintaining the fluid plumbing system. The limestone nappe may, at the same time, have represented an aquitard forcing the hydrothermal fluids into the volcanic and volcaniclastic wall rocks, which is regarded as critical for the two-stage gold mineralization in the Rosario–Bunawan district.     

Ranching and the new global range: Amazônia in the 21st century

This paper seeks to understand how the Brazilian Amazon, which many thought unsuitable for agricultural development, has yielded to a dynamic cattle economy in only a few decades. It does so by embedding the Thunian model of location rents within the regime of capital accumulation that has driven the Brazilian economy since the mid-20th century. The paper addresses policies that have created location rents in Amazônia, the effect of these rents on land managers, and the spatial implications of their behavior on forests. Thus, the paper connects macro-processes and structures to agents on the ground, in providing a political ecological explanation relevant to land change science. The policy discussion focuses on reductions in transportation costs, improvements in animal health, and monetary and trade reforms. To illustrate the impact of policy, the paper presents data on the geography of Amazonian herd expansion, on the growth of Amazonian exports, and on the profitability of the region’s cattle economy. It follows the empirical presentation with more abstract consideration of the spatial relations between cattle ranching and soy farming, and implications for deforestation. The paper concludes on a speculative note by considering the likelihood of forest transition in the region, given the transformation of Amazônia into a global resource frontier.     

Infrared contamination in Galactic X-ray novae

The most widely used means of measuring the mass of black holes in Galactic binaries – specifically the X-ray novae – involves both radial velocity measurements of the secondary star, and photometric measurements of its ellipsoidal variability. The latter is important in constraining the inclination and mass ratio, and requires as direct a measure of the flux of the secondary as possible. Up to now, such measurements have been preferentially carried out in the near-infrared (NIR:  1–2.5 μm  ), where the flux from the cooler secondary is expected to dominate over that from the accretion disc. However, here we present evidence of a significant non-stellar contribution to the NIR flux in many of those quiescent X-ray novae that are thought to contain a black hole primary. We discuss origins of this excess and the effect of such contamination on Galactic black hole mass measurements.     

Using social media data to understand and assess disasters

This paper contributes to the understanding of disasters from the perspective of social media activities. We develop a measure based on Twitter activities that can be used to quantify the evolution of disasters and thus demonstrate temporal–spatial patterns of Twitter activities particularly near the coastline and in large urban areas during Hurricane Sandy. We also show a close relationship between hurricane damages and Twitter activities. Our findings suggest the potential of using social media activities for rapid damage assessment.     

Nutrient variability in the mixed layer of the subarctic Pacific Ocean, 1987–2010

Data collected primarily from commercial ships between 1987 and 2010 are used to provide details of seasonal, interannual and bidecadal variability in nutrient supply and removal in the surface ocean mixed layer across the subarctic Pacific. Linear trend analyses are used to look for impacts of climate change in oceanic domains (geographic regions) representing the entire subarctic ocean. Trends are mixed and weak (generally not significant) in both winter and summer despite evidence that the upper ocean is becoming more stratified. Overall, these data suggest little change in the winter resupply of the mixed layer with nutrients over the past 23 years. The few significant trends indicate a winter increase in nitrate (~0.16 μM year⁻¹) in the Bering Sea and in waters off the British Columbia coast, and a decline in summer phosphate (0.018 μM year⁻¹) in the Bering. An oscillation in Bering winter nutrient maxima matches the lunar nodal cycle (18.6 years) suggesting variability in tidal mixing intensity in the Aleutian Islands affects nutrient transport. Nitrate removal from the seasonal mixed layer varies between 6 μM along the subarctic–subtropical boundary and 18 μM off the north coast of Japan, with April to September new production rates in the subarctic Pacific being estimated at 2 and 6 moles C m⁻². Changes in nutrient removal in the Bering and western subarctic Pacific (WSP) suggest either the summer mixed layer is thinning with little change in new production or new production is increasing which would require an increase in iron transport to these high-nutrient low-chlorophyll (HNLC) waters. Si/N and N/P removal ratios of 2.1 and 19.7 are sufficient to push waters into Si then N limitation with sufficient iron supply. Because ~3 μM winter nitrate is transferred to reduced N pools in summer, new production calculated from seasonal nutrient drawdown should not be directly equated to export production.