Diel behavior of stable isotopes of dissolved oxygen and dissolved inorganic carbon in rivers over a range of trophic conditions,and in a mesocosm experiment

Rates of diel (24-h) biogeochemical processes in rivers and their effect on daily changes in the concentration of metals and metalloids have been well documented in the literature over the last 20 years. Investigations into the effects of these processes on aquatic systems and the underlying mechanisms that control the processes can significantly improve our understanding of how natural aquatic environments function and will respond to changing environmental conditions and anthropogenic impacts. Daily changes in the rates of biogeochemical processes have, more recently, been shown to influence the stable isotope composition of dissolved oxygen and dissolved inorganic carbon in natural waters. Here we present a comprehensive picture of the persistence and reproducibility of diel cycles of the ¹⁸O composition of dissolved molecular oxygen (δ¹⁸O-DO) and the ¹³C composition of dissolved inorganic carbon (δ¹³C-DIC) across five Montana, USA rivers investigated over a 4-year period. A mesocosm experiment showed the same behavior in δ¹⁸O-DO and δ¹³C-DIC as seen in riverine settings across light and dark periods.A cross plot of δ¹⁸O-DO and δ¹³C-DIC from each stream exhibits a clockwise elliptical pattern which is attributed to the daily changes in the balance of metabolic rates as well as air–water gas exchange. The amplitude of the change in the isotope composition is shown to be directly related to the trophic state of the river and a relationship between net productivity and diel changes in δ¹⁸O-DO and δ¹³C-DIC is presented. This relationship between trophic status with δ¹⁸O-DO, δ¹³C-DIC and production emphasizes the significance of how rates of biogeochemical processes in natural systems can influence the daily changes in the composition of surface waters.     

The role of luminous substructure in the gravitational lens system MG 2016+112

MG 2016+112 is a quadruply imaged lens system with two complete images A and B and a pair of merging partial images in region C as seen in the radio. The merging images are found to violate the expected mirror symmetry. This indicates an astrometric anomaly which could only be of gravitational origin and could arise due to substructure in the environment or line of sight of the lens galaxy. We present new high-resolution multifrequency very long baseline interferometry (VLBI) observations at 1.7, 5 and 8.4 GHz. Three new components are detected in the new VLBI imaging of both the lensed images A and B. The expected opposite parity of the lensed images A and B was confirmed due to the detection of non-collinear components. Furthermore, the observed properties of the newly detected components are inconsistent with the predictions of previous mass models. We present new scenarios for the background quasar which are consistent with the new observations. We also investigate the role of the satellite galaxy situated at the same redshift as the main lensing galaxy. Our new mass models demonstrate quantitatively that the satellite galaxy is the primary cause of the astrometric anomaly found in region C. The detected satellite is consistent with the abundance of subhaloes expected in the halo from cold dark matter (CDM) simulations. However, the fraction of the total halo mass in the satellite as computed from lens modelling is found to be higher than that predicted by CDM simulations.     

High-redshift obscured quasars: radio emission at sub-kiloparsec scales

The radio properties of 11 obscured 'radio-intermediate' quasars at redshifts   z ≳ 2  have been investigated using the European Very-Long-Baseline-Interferometry Network (EVN) at 1.66 GHz. A sensitivity of  ∼25 μJy per 17 × 14 mas² beam  was achieved, and in seven out of 11 sources unresolved radio emission was securely detected. The detected radio emission of each source accounts for ∼30–100 per cent of the total source flux density. The physical extent of this emission is ≲150 pc, and the derived properties indicate that this emission originates from an active galactic nucleus (AGN). The missing flux density is difficult to account for by star formation alone, so radio components associated with jets of physical size ≳150 pc and ≲40 kpc are likely to be present in most of the sources. Amongst the observed sample steep, flat, gigahertz-peaked and compact-steep spectrum sources are all present. Hence, as well as extended and compact jets, examples of beamed jets are also inferred, suggesting that in these sources, the obscuration must be due to dust in the host galaxy, rather than the torus invoked by the unified schemes. Comparing the total to core (≲150 pc) radio luminosities of this sample with different types of AGN suggests that this sample of   z ≳ 2  radio-intermediate obscured quasars shows radio properties that are more similar to those of the high-radio-luminosity end of the low-redshift radio-quiet quasar population than those of Fanaroff–Riley type I (FR I) radio galaxies. This conclusion may reflect intrinsic differences, but could be strongly influenced by the increasing effect of inverse-Compton cooling of extended radio jets at high redshift.     

The multiwavelength study of two unique radio galaxies

We present the usage of multi-frequency and multi-band radio, VLA, observations as well as X-ray observations in order to study the environment around two powerful radio galaxies, namely Hercules A and 3C310. We study their environment both in pc- and kpc-scales. We have chosen these two radio galaxies as they present similar and unique characteristics, compared to the ones from our general knowledge about double radio galaxies associated with active galactic nuclei.     

The mid-IR radio correlation at high angular resolution: NGC253

We present high angular resolution (1.2), narrow band (/=0.1) images of the nucleus of NGC253 at three wavelengths in the mid-IR (8.5, 10.0, and 12.5 m). We find that most of the mid-IR flux in the nucleus of NGC253 derives from a very small region 120 pc in diameter. Within this small region there are three spatially and spectrally distinct IR components: two bright compact sources, and a surrounding envelope of low level, diffuse emission. The mid-IR and 6cm radio are loosely correlated in position but not in brightness. The implication is that the mid-IR - radio correlation may begin to break down on small spatial scales relevant to individual star forming regions and large individual sources. These variations in the mid-IR spectra and in the radio-IR correlation imply that the nuclear emission is excited by more than one mechanism and source type.     

Element concentrations and variations along a 120-km transect in southern Norway – Anthropogenic vs. geogenic vs. biogenic element sources and cycles

Rock samples and the C-, B- and O-horizons of soils developed on these rocks were collected in forested areas along a 120-km south–north transect in southern Norway, passing through the city of Oslo. Forty samples (1 site/3 km) were analysed for 37 chemical elements (Ag, Al, As, Au, B, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, K, La, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Sc, Se, Sr, Te, Th, Ti, Tl, U, V, W and Zn) following an aqua regia digestion; pH (water extract) and loss on ignition were also determined. The O-horizon soils were additionally analysed for Pt. Gold is the only element that shows a clear anthropogenic peak in the O-horizon soils collected from the city of Oslo. Silver, Au, Bi, Cd, Hg, Pb, S, Sb, Se and Sr all show a strong enrichment in the O-horizon when compared to the underlying C-horizon or the bedrock along the full length of the transect. Neither geology nor anthropogenic input of elements dominate the observed patterns. The most important factors for the observed element concentrations in the O-horizon are weathering, uptake (or rejection) of elements by plants and the kinetics of decay of the organic material in the O-horizon. Climate, especially temperature and precipitation, has an important influence on the formation and decay rates of the organic soil layer. Acid precipitation will delay the decomposition of the organic layer and lead to a natural enrichment of several metals in the O-horizon. Land use change, deforestation and liming can all increase the decay kinetics of organic matter and thus result in a release of the stored element pool.     

Quantitative measures of textural anisotropy resulting from magmatic compaction illustrated by a sample from the Palisades sill, New Jersey

Early in the crystallization of many tholeiitic basaltic magmas, plagioclase crystals cluster together into a 3-D cellular network, which forms a passive marker capable of recording the deformation that accompanies compaction of crystal mush. Although irregular in detail, the overall network is initially isotropic and only becomes anisotropic as a result of compaction. We have developed four independent methods to quantify the 3-D textural anisotropy of a basalt sample using at least three non-parallel thin sections. Three of the methods are based on the geometrical properties of digitized maps of the feldspar chain networks. One approach focuses on the angular variation of the mean intercept along parallel traverses through the network, another examines the orientation and size distribution of individual links, and the third considers the average shape of interstitial regions outlined by the plagioclase network. The fourth technique approximates the textural anisotropy by the variogram anisotropy of a scanned thin section image. We illustrate the methods using five oriented non-parallel thin sections from a sample of diabase 146 m above the base of the 300-m-thick Palisades sill of New Jersey. Compaction of crystal mush in this sill has previously been postulated on the basis of chemical evidence. The 3-D feldspar network anisotropy based on the first three approaches suggests nearly uniaxial compaction on the order of 8.6% in a direction within 3° of the intersection of the columnar joints at the sample site. A rigorous statistical test based on the statistics of elliptically contoured non-normal multivariate distributions documents that the link-vector distribution in vertical sections are statistically anisotropic at a 95% confidence level and that the overall compaction is 7.9±2.6%. The orientation and magnitude of the 3-D textural anisotropy determined by the image variogram of the non-opaque minerals is almost identical to the mean feldspar network anisotropy; 8.5% compaction in a direction 10° from the columnar joint intersections. The major silicate textural and feldspar network anisotropy axes both plunge almost directly down dip of the sill. On the other hand, the major axis of the variogram anisotropy of the opaque minerals is approximately parallel to the strike of the sill and to the major axis of the anisotropic magnetic susceptibility. The anisotropy of the silicate mineral fabric may reflect down-dip flow of a deformable melt-rich crystal mush, whereas the AMS and opaque textural anisotropy reflects the influence of gravitational stresses during the growth of magnetite in the final stages of melt crystallization. Evidently the Palisades sill was not originally horizontal but was intruded in an orientation close to its present attitude.     

Evaluation of the Johnson and Ettinger Model for Prediction of Indoor Air Quality

Screening level models are now commonly used to estimate vapor intrusion for subsurface volatile organic compounds (VOCs). Significant uncertainty is associated with processes and models and, to date, there has been only limited field-based evaluation of models for this pathway. To address these limitations, a comprehensive evaluation of the Johnson and Ettinger (J&E) model is provided through sensitivity analysis, comparisons of model-predicted to measured vapor intrusion for 11 petroleum hydrocarbon and chlorinated solvent sites, and review of radon and flux chamber studies. Significant intrusion was measured at five of 12 sites with measured vapor attenuation ratios (α_m's) (indoor air/source vapor) ranging from ∼1 × 10⁻⁶ to 1 × 10⁻⁴. Higher attenuation ratios were measured for studies using radon, inert tracers, and flux chambers; however, these ratios are conservative owing to boundary conditions and tracer properties that are different than those at most VOC-contaminated sites. Reasonable predictions were obtained using the J&E model with comparisons indicating that model-predicted vapor attenuation ratios (α_p's) were on the same order, or less than the α_m's. For several sites, the (m were approximately two orders of magnitude less than the a 's indicating that the J&E model is conservative in these cases. The model comparisons highlight the importance in using appropriate input parameters for the J&E model. The regulatory implications associated with use of the J&E model to derive screening criteria are also discussed.     

The relationship between oil droplet size and upper ocean turbulence

Oil spilled at sea often forms oil droplets in stormy conditions. This paper examines possible mechanisms which generate the oil droplets. When droplet Reynolds numbers are large, the dynamic pressure force of turbulent flows is the cause of droplet breakup. Using dimensional analysis, Hinze (1955, A.I.Ch.E. Journal 1, 289–295) obtained a formula for the maximum size of oil droplets that can survive the pressure force. When droplet Reynolds numbers are small, however, viscous shear associated with small turbulent eddies is the cause of breakup. For the shear mechanism, we obtain estimates of droplet size as a function of energy dissipation rate, the ratio of oil-to-water viscosity and the surface tension coefficient.

The two formulae are applied to oil spills in the ocean. At dissipation rates expected in breaking waves, the pressure force is the dominant breakup mechanism and can generate oil droplets with radii of hundreds of microns. However, when chemical dispersants are used to treat an oil slick and significantly reduce the oil-water interfacial tension, viscous shear is the dominant breakup mechanism and oil droplets with radii of tens of microns can be generated. Viscous shear is also the mechanism for disintegrating water-in-oil emulsions and the size of a typical emulsion blob is estimated to be tens of millimeters.     

High resolution images of Cygnus X-1

The classic black hole candidate Cygnus X-1 exhibits many similarities to Galactic jet sources (micro-quasars) in soft gamma and hard X-ray rays. This has fuelled suspicions that radio jets also may be present in Cygnus X-1. The lack of radio flaring in Cygnus X-1 has been associated with the presence of continuous jets rather than multiple plasmon ejection however no evidence for this has been observed with the VLA, or with MERLIN. Recent VLBA observations at 15 GHz have detected extended emission and further multi frequency observations are required to confirm the presence of jets on a milliarcsecond level.