Trace metals associated with deep-sea tailings placement at the Batu Hijau copper–gold mine,Sumbawa, Indonesia

The Batu Hijau copper–gold mine on the island of Sumbawa, Indonesia operates a deep-sea tailings placement (DSTP) facility to dispose of the tailings within the offshore Senunu Canyon. The concentrations of trace metals in tailings, waters, and sediments from locations in the vicinity of the DSTP were determined during surveys in 2004 and 2009. In coastal and deep seawater samples from Alas Strait and the South Coast of Sumbawa, the dissolved concentrations of Ag, As, Cd, Cr, Hg, Pb and Zn were in the sub μg/L range. Dissolved copper concentrations ranged from 0.05 to 0.65 μg/L for all depths at these sites. Dissolved copper concentrations were the highest in the bottom-water from within the tailings plume inside Senunu Canyon, with up to 6.5 μg Cu/L measured in close proximity to the tailings discharge. In general, the concentrations of dissolved and particulate metals were similar in 2004 and 2009.     

Natural and historical variability in fluvial processes,beaver activity,and climate in the Greater Yellowstone Ecosystem

Two centuries of human activities in the Greater Yellowstone Ecosystem (GYE) have strongly influenced beaver activity on small streams, raising questions about the suitability of the historical (Euro‐American) period for establishing stream reference conditions. We used beaver‐pond deposits as proxy records of beaver occupation to compare historical beaver activity to that throughout the Holocene. Forty‐nine carbon‐14 (¹⁴C) ages on beaver‐pond deposits from Grand Teton National Park indicate that beaver activity was episodic, where multi‐century periods lacking dated beaver‐pond deposits have similar timing to those previously documented in Yellowstone National Park. These gaps in the sequence of dated deposits coincide with episodes of severe, prolonged drought, e.g. within the Medieval Climatic Anomaly 1000–600 cal yr bp , when small streams likely became ephemeral. In contrast, many beaver‐pond deposits date to 500–100 cal yr bp , corresponding to the colder, effectively wetter Little Ice Age. Abundant historical beaver activity in the early 1900s is coincident with a climate cooler and wetter than present and more abundant willow and aspen, but also regulation of beaver trapping and the removal of wolves (the beaver's main predator), all favorable for expanded beaver populations. Reduced beaver populations after the 1920s, particularly in the northern Yellowstone winter range, are in part a response to elk overbrowsing of willow and aspen that later stemmed from wolf extirpation. Beaver populations on small streams were also impacted by low streamflows during severe droughts in the 1930s and late 1980s to present. Thus, both abundant beaver in the 1920s and reduced beaver activity at present reflect the combined influence of management practices and climate, and underscore the limitations of the early historical period for defining reference conditions. The Holocene record of beaver activity prior to Euro‐American activities provides a better indication of the natural range of variability in beaver‐influenced small stream systems of the GYE. Copyright © 2012 John Wiley & Sons, Ltd.     

Application of an Analytical Solution as a Screening Tool for Sea Water Intrusion

Sea water intrusion into aquifers is problematic in many coastal areas. The physics and chemistry of this issue are complex, and sea water intrusion remains challenging to quantify. Simple assessment tools like analytical models offer advantages of rapid application, but their applicability to field situations is unclear. This study examines the reliability of a popular sharp‐interface analytical approach for estimating the extent of sea water in a homogeneous coastal aquifer subjected to pumping and regional flow effects and under steady‐state conditions. The analytical model is tested against observations from Canada, the United States, and Australia to assess its utility as an initial approximation of sea water extent for the purposes of rapid groundwater management decision making. The occurrence of sea water intrusion resulting in increased salinity at pumping wells was correctly predicted in approximately 60% of cases. Application of a correction to account for dispersion did not markedly improve the results. Failure of the analytical model to provide correct predictions can be attributed to mismatches between its simplifying assumptions and more complex field settings. The best results occurred where the toe of the salt water wedge is expected to be the closest to the coast under predevelopment conditions. Predictions were the poorest for aquifers where the salt water wedge was expected to extend further inland under predevelopment conditions and was therefore more dispersive prior to pumping. Sharp‐interface solutions remain useful tools to screen for the vulnerability of coastal aquifers to sea water intrusion, although the significant sources of uncertainty identified in this study require careful consideration to avoid misinterpreting sharp‐interface results.     

Spatial and temporal variability of Atlantic salmon (Salmo salar L.) spawning activity in braided river channels: a preliminary assessment

The distribution of Atlantic salmon redds was recorded during two spawning seasons (2005 and 2006) along a 4?km braided reach of the river Feshie in the Cairngorm mountains, Scotland. Within this complex reach, four main channels types were differentiated on the basis of geographical water sources, channel morphology and hydrochemistry: (1) the main braided channels of the river Feshie; (2) groundwater channels fed by seepage at the edge of the floodplain; (3) hillslope tributary channels and (4) mixed channels downstream of confluences of two or more of types 1?C3. The 2005 season was characterised by high and variable flows. In total, 223 redds were observed which were mainly (64%) located in groundwater channels, with relatively few (9%) in the more extensive sections of main channel. The second year had much lower and more stable flows. Here, a total of 337 redds were observed. The largest number were again located in the groundwater channels (44%), though spawning was more evenly distributed in the other channel types, including the main river (19%). It is hypothesised that the apparently more suitable characteristics of groundwater-fed channels relate to a more stable, richer environment for embryo development and juvenile growth, whilst hydraulic conditions and sediment stability in the main channel may create more adverse conditions for successful recruitment.     

Screening for Heat Transport by Groundwater in Closed Geothermal Systems

Heat transfer due to groundwater flow can significantly affect closed geothermal systems. Here, a screening method is developed, based on Peclet numbers for these systems and Darcy's law. Conduction‐only conditions should not be expected where specific discharges exceed 10^?8 m/s. Constraints on hydraulic gradients allow for preliminary screening for advection based on rock or soil types. Identification of materials with very low hydraulic conductivity, such as shale and intact igneous and metamorphic rock, allow for analysis with considering conduction only. Variability in known hydraulic conductivity allows for the possibility of advection in most other rocks and soil types. Further screening relies on refinement of estimates of hydraulic gradients and hydraulic conductivity through site investigations and modeling until the presence or absence of conduction can be confirmed.     

Tributary confluences and discontinuities in channel form and sediment texture: Rio Chama,NM

Numerous morphological changes can occur where two channels of distinct sediment and flow regimes meet, including abrupt shifts in channel slope, cross‐sectional area, planform style, and bed sediment size along the receiving channel. Along the Rio Chama between El Vado and Abiquiu Dams, northern New Mexico, arroyo tributaries intermittently deliver sediment from erodible sandstone and shale canyon walls to the mainstem channel. Much of the tributary activity occurs in flash floods and debris flows during summer thunderstorms, which often load the channel with sand and deposit coarser material at the mainstem confluence. In contrast, mainstem channel flow is dominated by snowmelt runoff. To examine tributary controls, we systematically collected cross‐section elevation and bed sediment data upstream and downstream of 26 tributary confluences along a 17 km reach. Data from 203 cross‐sections were used to build a one‐dimensional hydraulic model for comparing estimated channel parameters at bankfull and low‐flow conditions at these sites As compared to intermediate reaches, confluences primarily impact gradient and bed sediment size, reducing both parameters upstream of confluences and increasing them downstream. Cross‐section area is also slightly elevated above tributary confluences and reduced below. Major shifts in slope and bed sediment size at confluences appear to drive variations in sediment entrainment and transport capacity and the relative storage of sand along the channel bed. The data were analyzed and compared to models of channel organization based on lateral inputs, such as the Network Variance Model and the Sediment Link Concept. At a larger scale, hillslope ? channel coupling increases in the downstream third of the study reach, where the canyon narrows, resulting in steeper slopes and more continuous coarse bed material along the mainstem, and thus, limiting the contrast with tributary confluences. However, channel form and sediment characteristics are highly variable along the study reach, reflecting variations in the size and volume of sediment inputs related to the surface geology in tributary watersheds, morphology of the Rio Chama at the junction (i.e. bends, confinement), and the relative magnitude and location of past depositional events. Copyright © 2014 John Wiley & Sons, Ltd.     

An AzTEC 1.1 mm survey of the GOODS-N field – II. Multiwavelength identifications and redshift distribution

We present results from a multiwavelength study of 29 sources (false detection probabilities <5 per cent) from a survey of the Great Observatories Origins Deep Survey-North (GOODS-N) field at 1.1 mm using the Astronomical Thermal Emission Camera (AzTEC). Comparing with existing 850 μm Submillimetre Common-User Bolometer Array (SCUBA) studies in the field, we examine differences in the source populations selected at the two wavelengths. The AzTEC observations uniformly cover the entire survey field to a 1σ depth of ∼1 mJy. Searching deep 1.4 GHz Very Large Array (VLA) and Spitzer 3–24 μm catalogues, we identify robust counterparts for 21 1.1 mm sources, and tentative associations for the remaining objects. The redshift distribution of AzTEC sources is inferred from available spectroscopic and photometric redshifts. We find a median redshift of   z = 2.7  , somewhat higher than   z = 2.0  for  850 μm  selected sources in the same field, and our lowest redshift identification lies at a spectroscopic redshift   z = 1.1460  . We measure the 850 μm to 1.1 mm colour of our sources and do not find evidence for '850 μm dropouts', which can be explained by the low signal-to-noise ratio of the observations. We also combine these observed colours with spectroscopic redshifts to derive the range of dust temperatures T , and dust emissivity indices β for the sample, concluding that existing estimates   T ∼ 30 K  and  β∼ 1.75  are consistent with these new data.     

Volatile organic compounds at a rural site in western Senegal

The objectives of this study were to identify species and levels of volatile organic compounds (VOCs), and determine their oxidation capacity in the rural atmosphere of western Senegal. A field study was conducted to obtain air samples during September 14 and September 15, 2006 for analyses of VOCs. Methanol, acetone, and acetaldehyde were the most abundant detected chemical species and their maximum mixing ratios reached 6 parts per billion on a volume basis (ppbv). Local emission sources such as firewood and charcoal burning strongly influenced VOC concentrations. The VOC concentrations exhibited little temporal variations due to the low reactivity with hydroxyl radicals, with reactivity values ranging from 0.001 to 2.6 s⁻¹. The conditions in this rural site were rather clean. Low ambient NO _x levels limited ozone production. Nitrogen oxide (NO _x ) levels reached values less than 2 ppbv and maximum VOC/NO _x ratios reached 60 ppbvC/ppbv, with an overall average of 2.4 ± 4.5 ppbvC/ppbv. This indicates that the rural western Senegal region is NO _x limited in terms of oxidant formation potential. Therefore, during the study period photochemical ozone production became limited due to low ambient NO _x levels. The estimated ozone formation reactivity for VOCs was low and ranged between −5.5 mol of ozone/mol of benzaldehyde to 0.6 mol/mol of anthropogenic dienes.     

A multi-data set comparison of the vertical structure of temperature variability and change over the Arctic during the past 100?years

We compare the daily, interannual, and decadal variability and trends in the thermal structure of the Arctic troposphere using eight observation-based, vertically resolved data sets, four of which have data prior to 1948. Comparisons on the daily scale between historical reanalysis data and historical upper-air observations were performed for Svalbard for the cold winters 1911/1912 and 1988/1989, the warm winters 1944/1945 and 2005/2006, and the International Geophysical Year 1957/1958. Excellent agreement is found at mid-tropospheric levels. Near the ground and at the tropopause level, however, systematic differences are identified. On the interannual time scale, the correlations between all data sets are high, but there are systematic biases in terms of absolute values as well as discrepancies in the magnitude of the variability. The causes of these differences are discussed. While none of the data sets individually may be suitable for trend analysis, consistent features can be identified from analyzing all data sets together. To illustrate this, we examine trends and 20-year averages for those regions and seasons that exhibit large sea-ice changes and have enough data for comparison. In the summertime Pacific Arctic and the autumn eastern Canadian Arctic, the lower tropospheric temperature anomalies for the recent two decades are higher than in any previous 20-year period. In contrast, mid-tropospheric temperatures of the European Arctic in the wintertime of the 1920s and 1930s may have reached values as high as those of the late 20th and early 21st centuries.     

Influence of carbon dioxide on coal permeability determined by pressure transient methods

The permeability of coal samples from Pittsburgh Seam was determined using carbon dioxide as the flowing fluid. The confining pressure was varied to cover a wide range of depths. The permeability was determined as a function of exposure time of carbon dioxide while the confining stress was kept constant. The porosities of the coal samples were found to be very low and most of the samples had porosities less than 1%. The permeability of these coal samples was very low—less than 1 μD. Since the objective of this study was to investigate the influence of CO₂ exposure on coal permeability, it was necessary to increase the initial permeability of the coal samples by introducing a fracture. A longitudinal fracture was induced mechanically, and CT scans were taken to ensure that the fracture was present throughout the sample and that the sample was not damaged otherwise during the process. In this study, the permeability of coal was determined by using pressure transient methods. Two types of pressure pulses were used: A-spike and Sine-6 pressure transients. It was first established that the permeability of fractured coal samples did not change with exposure time when an inert gas (Argon) was used as the fluid medium in the experiments. However, the permeability of coal samples decreased significantly when carbon dioxide was used as the fluid medium. This reduction can be attributed to the coal swelling phenomenon. The results show that the permeability reduction in fractured coal samples can be over 90% of the original value, and the exposure time for such reductions can range from 1.5 days up to a week, typically about 2 days under laboratory conditions. The permeability decreased significantly with the increase in confining pressure. The higher confining pressure appears to close internal fractures causing a reduction in permeability.