Natural Attenuation of Perchlorate in Denitrified Groundwater     

William D. Robertson  James W. Roy  Susan J. Brown  Dale R. Van Stempvoort  Greg Bickerton 《Ground water》2014,52(1):63-70

Monitoring of a well‐defined septic system groundwater plume and groundwater discharging to two urban streams located in southern Ontario, Canada, provided evidence of natural attenuation of background low level (ng/L) perchlorate (ClO₄^?) under denitrifying conditions in the field. The septic system site at Long Point contains ClO₄^? from a mix of waste water, atmospheric deposition, and periodic use of fireworks, while the nitrate plume indicates active denitrification. Plume nitrate (NO₃^?‐N) concentrations of up to 103 mg/L declined with depth and downgradient of the tile bed due to denitrification and anammox activity, and the plume was almost completely denitrified beyond 35 m from the tile bed. The ClO₄^? natural attenuation occurs at the site only when NO₃^?‐N concentrations are <0.3 mg/L, after which ClO₄^? concentrations decline abruptly from 187 ± 202 to 11 ± 15 ng/L. A similar pattern between NO₃^?‐N and ClO₄^? was found in groundwater discharging to the two urban streams. These findings suggest that natural attenuation (i.e., biodegradation) of ClO₄^? may be commonplace in denitrified aquifers with appropriate electron donors present, and thus, should be considered as a remediation option for ClO₄^? contaminated groundwater.  相似文献   

Electron microbeam analysis of urban road-deposited sediment,Manchester, UK: Improved source discrimination and metal speciation assessment     

Kevin G. Taylor  Davina J. Robertson 《Applied Geochemistry》2009

Road-deposited sediment (RDS) is an accumulation of particulates upon street surfaces in urban centres. It is commonly highly contaminated and has major potential impacts upon surface water quality and human health, as well as becoming a waste material upon street sweeping. Although significant research has been undertaken upon the fine fraction within these systems, there is a lack of detailed, high-resolution grain-specific mineralogical and chemical data for the coarser fractions, which contain the bulk of the contamination by mass. The study reported here utilizes backscatter electron microscopic, electron microprobe and Raman spectroscopic analysis to provide novel data on RDS material from Manchester, UK, with significant implications for the improved understanding of source discrimination and contaminant metal speciation. The RDS samples studied are highly heterogeneous and the abundant nature of anthropogenic grains is particularly apparent. The RDS material has been found to be composed of a number of grain types: (i) silicate and alumino-silicate grains derived from a wide range of sources; (ii) iron oxide grains derived from the corrosion of galvanized steel; (iii) iron-rich glass grains derived as slag material from metal and waste processing activities and (iv) spherical Fe oxide and Fe-rich glass grains derived from high temperature combustion processes. Elemental metallic grains (Fe, Cu, Pb) are also present in minor amounts.  相似文献   

Developmental energetics of the southern pigfish (Teleostei: Congiopodidae)     

D. A. Robertson 《新西兰海洋与淡水研究杂志》2013,47(4):611-620

The embryonic wet weight, dry weight, yolk volume, energy content, and oxygen consumption of the southern pigfish Congiopodus leucopaecilus (Richardson, 1846) were followed from fertilisation to yolk sac absorption, at 11.5°c and salinity of 34.5%6. Measurements of yolk energy and catabolic energy changes did not show any evidence of an energy deficit before the onset of feeding capability.  相似文献   

Diplophos rebainsi Krefft & Parin, 1972, an addition to the mesopelagic fish fauna of New Zealand (note)     

D. A. Robertson 《新西兰海洋与淡水研究杂志》2013,47(3):411-415

Plankton samples taken in the south‐western Pacific Ocean and the Tasman Sea have provided, for the first time in these waters, a series of individuals of the gonostomatid Diplophos rebainsi. Observations are presented on some of the prejuvenile and adult features and on the seasonal distribution of prejuveniles off New Zealand.  相似文献   

Planktonic stages of Maurolicus muelleri (Teleostei Sternoptychidae) in New Zealand waters     

D. A. Robertson 《新西兰海洋与淡水研究杂志》2013,47(2):311-328

The seasonality and distribution, abundance, and hydrological affinities of the planktonic stages of the sternoptychid Maurolicus muelleri (Grnelin, 1788) are described for the New Zealand region. Spawning occurred from August to March, and the planktonic stages were widespread around New Zealand. Spawning probably takes place around midday at depths greater than 250 m. Eggs and larval stages were present over temperature ranges of 9.0–15.5°c and 13–22°c respectively.  相似文献   

The lithospheric transition between the Delamerian and Lachlan orogens in western Victoria: new insights from 3D magnetotelluric imaging     

K. E. Robertson  G. S. Heinson  D. H. Taylor  S. Thiel 《Australian Journal of Earth Sciences》2017,64(3):385-399

The magnetotelluric (MT) method was used to image the crust and upper mantle beneath the Delamerian and Lachlan orogens in western Victoria, Australia. During the Cambrian time period, this region changed from being the extended passive margin of Proterozoic Australia into an Andean-style convergent margin that progressively began to accrete younger oceanic terranes. Several broadband MT transects, which were collected in stages along coincident deep (full crust imaging) seismic reflection lines, have now been combined to create a continuous 500 km east–west transect over the Delamerian–Lachlan transition region in the Stawell Zone. We present the electrical resistivity structure of the lithosphere using both 3D and 2D inversion methods. Additionally, 1D inversions of long-period AusLAMP (Australian Lithospheric Architecture Magnetotelluric Project) MT data on a 55 km regionally spaced grid were used to provide starting constraints for the 3D inversion of the 2D profile. The Delamerian to Lachlan Orogen transition region coincides with the Mortlake Discontinuity, which marks an isotopic discontinuity in Cenozoic basalts, with higher strontium isotope enrichment ratios in the Lachlan Orogen relative to the Delamerian Orogen. Phase tensor ellipses of the MT data reveal a distinct change in electrical resistivity structure near the location of the Mortlake Discontinuity, and results of 3D and 2D inversions along the MT profile image a more conductive lower crust and upper mantle beneath the Lachlan Orogen than the Delamerian Orogen. Increased conductivity is commonly ascribed to mantle enrichment and thus supports the notion that the isotope enrichment of the Cenozoic basalts at least partially reflects an enriched mantle source rather than crustal contamination. Fault slivers of the lower crust from the more conductive Lachlan region expose Cambrian boninites and island arc andesites indicative of subduction, a process that can enrich the mantle isotopically, and also electrically, by introducing carbon (graphite) and water (hydrogen).  相似文献   

Subduction,ophiolite genesis and collision history of Tethys adjacent to the Eurasian continental margin: new evidence from the Eastern Pontides,Turkey     

Alastair Robertson  Osman Parlak  Timur Ustaömer  Kemal Taslı  Nurdan İnan  Paulian Dumitrica 《Geodinamica Acta》2013,26(3-4):230-293

This paper presents several types of new information including U–Pb radiometric dating of ophiolitic rocks and an intrusive granite, micropalaeontological dating of siliceous and calcareous sedimentary rocks, together with sedimentological, petrographic and structural data. The new information is synthesised with existing results from the study area and adjacent regions (Central Pontides and Lesser Caucasus) to produce a new tectonic model for the Mesozoic–Cenozoic tectonic development of this key Tethyan suture zone.

The Tethyan suture zone in NE Turkey (Ankara–Erzincan–Kars suture zone) exemplifies stages in the subduction, suturing and post-collisional deformation of a Mesozoic ocean basin that existed between the Eurasian (Pontide) and Gondwanan (Tauride) continents. Ophiolitic rocks, both as intact and as dismembered sequences, together with an intrusive granite (tonalite), formed during the Early Jurassic in a supra-subduction zone (SSZ) setting within the ?zmir–Ankara–Erzincan ocean. Basalts also occur as blocks and dismembered thrust sheets within Cretaceous accretionary melange. During the Early Jurassic, these basalts erupted in both a SSZ-type setting and in an intra-plate (seamount-type) setting. The volcanic-sedimentary melange accreted in an open-ocean setting in response to Cretaceous northward subduction beneath a backstop made up of Early Jurassic forearc ophiolitic crust. The Early Jurassic SSZ basalts in the melange were later detached from the overriding Early Jurassic ophiolitic crust.

Sedimentary melange (debris-flow deposits) locally includes ophiolitic extrusive rocks of boninitic composition that were metamorphosed under high-pressure low-temperature conditions. Slices of mainly Cretaceous clastic sedimentary rocks within the suture zone are interpreted as a deformed forearc basin that bordered the Eurasian active margin. The basin received a copious supply of sediments derived from Late Cretaceous arc volcanism together with input of ophiolitic detritus from accreted oceanic crust.

Accretionary melange was emplaced southwards onto the leading edge of the Tauride continent (Munzur Massif) during latest Cretaceous time. Accretionary melange was also emplaced northwards over the collapsed southern edge of the Eurasian continental margin (continental backstop) during the latest Cretaceous. Sedimentation persisted into the Early Eocene in more northerly areas of the Eurasian margin.

Collision of the Tauride and Eurasian continents took place progressively during latest Late Palaeocene–Early Eocene. The Jurassic SSZ ophiolites and the Cretaceous accretionary melange finally docked with the Eurasian margin. Coarse clastic sediments were shed from the uplifted Eurasian margin and infilled a narrow peripheral basin. Gravity flows accumulated in thrust-top piggyback basins above accretionary melange and dismembered ophiolites and also in a post-collisional peripheral basin above Eurasian crust. Thickening of the accretionary wedge triggered large-scale out-of-sequence thrusting and re-thrusting of continental margin and ophiolitic units. Collision culminated in detachment and northward thrusting on a regional scale.

Collisional deformation of the suture zone ended prior to the Mid-Eocene (~45?Ma) when the Eurasian margin was transgressed by non-marine and/or shallow-marine sediments. The foreland became volcanically active and subsided strongly during Mid-Eocene, possibly related to post-collisional slab rollback and/or delamination. The present structure and morphology of the suture zone was strongly influenced by several phases of mostly S-directed suture zone tightening (Late Eocene; pre-Pliocene), possible slab break-off and right-lateral strike-slip along the North Anatolian Transform Fault.

In the wider regional context, a double subduction zone model is preferred, in which northward subduction was active during the Jurassic and Cretaceous, both within the Tethyan ocean and bordering the Eurasian continental margin.  相似文献   

Cross-shelf transport into nearshore waters due to shoaling internal tides in San Pedro Bay, CA     

Marlene Noble  Burt Jones  Peter Hamilton  Jingping Xu  George Robertson  Leslie Rosenfeld  John Largier   《Continental Shelf Research》2009,29(15):1768-1785

In the summer of 2001, a coastal ocean measurement program in the southeastern portion of San Pedro Bay, CA, was designed and carried out. One aim of the program was to determine the strength and effectiveness of local cross-shelf transport processes. A particular objective was to assess the ability of semidiurnal internal tidal currents to move suspended material a net distance across the shelf. Hence, a dense array of moorings was deployed across the shelf to monitor the transport patterns associated with fluctuations in currents, temperature and salinity. An associated hydrographic program periodically monitored synoptic changes in the spatial patterns of temperature, salinity, nutrients and bacteria. This set of measurements show that a series of energetic internal tides can, but do not always, transport subthermocline water, dissolved and suspended material from the middle of the shelf into the surfzone. Effective cross-shelf transport occurs only when (1) internal tides at the shelf break are strong and (2) subtidal currents flow strongly downcoast. The subtidal downcoast flow causes isotherms to tilt upward toward the coast, which allows energetic, nonlinear internal tidal currents to carry subthermocline waters into the surfzone. During these events, which may last for several days, the transported water remains in the surfzone until the internal tidal current pulses and/or the downcoast subtidal currents disappear. This nonlinear internal tide cross-shelf transport process was capable of carrying water and the associated suspended or dissolved material from the mid-shelf into the surfzone, but there were no observation of transport from the shelf break into the surfzone. Dissolved nutrients and suspended particulates (such as phytoplankton) transported from the mid-shelf into the nearshore region by nonlinear internal tides may contribute to nearshore algal blooms, including harmful algal blooms that occur off local beaches.  相似文献   

Wavelength dependence of angular diameters of M giants: an observational perspective     

A. P. Jacob  T. R. Bedding  J. G. Robertson  M. Scholz 《Monthly notices of the Royal Astronomical Society》2000,312(4):733-746

We discuss the wavelength dependence of angular diameters of M giants from an observational perspective. Observers cannot directly measure an optical-depth radius for a star, despite this being a common theoretical definition. Instead, they can use an interferometer to measure the square of the fringe visibility. We present new plots of the wavelength-dependent centre-to-limb variation (CLV) of intensity of the stellar disc as well as visibility for Mira and non-Mira M giant models. We use the terms 'CLV spectra' and 'visibility spectra' for these plots. We discuss a model-predicted extreme limb-darkening effect (also called the narrow-bright-core effect) in very strong TiO bands which can lead to a misinterpretation of the size of a star in these bands. We find no evidence as yet that this effect occurs in real stars. Our CLV spectra can explain the similarity in visibilities of R Dor (M8IIIe) that have been observed recently, despite the use of two different passbands. We compare several observations with models, and find that the models generally underestimate the observed variation in visibility with wavelength. We present CLV and visibility spectra for a model that is applicable to the M supergiant α Ori.  相似文献   

Intra-annual variability of urban effects on streamflow     

Jeremy E. Diem  Luke A. Pangle  Richard A. Milligan  Ellis A. Adams 《水文研究》2021,35(9):e14371

While considerable research has established the impacts of urbanization on streamflow, there has been little emphasis on how intra-annual variations in streamflow can deepen the understanding of hydrological processes in urban watersheds. This study fills this critical research gap by examining, at the monthly scale, correlations between land-cover and streamflow, differences in streamflow metrics between urban and rural watersheds, and the potential for the inflow and infiltration (I&I) of extraneous water into sewers to reduce streamflow. We use data from 90 watersheds in the Atlanta, GA region over the 2013–2019 period to accomplish our objectives. Similar to other urban areas in temperate climates, Atlanta has a soil-water surplus in winter and a soil-water deficit in summer. Our results show urban watersheds have less streamflow seasonality than do rural watersheds. Compared to rural watersheds, urban watersheds have a much larger frequency of high-flow days during July–October. This is caused by increased impervious cover decreasing the importance of antecedent soil moisture in producing runoff. Urban watersheds have lower baseflows than rural watersheds during December–April but have baseflows equal to or larger than baseflows in rural watersheds during July–October. Intra-annual variations in effluent data from wastewater treatment plants provide evidence that I&I is a major cause of the relatively low baseflows during December–April. The relatively high baseflows in urban watersheds during July–October are likely caused by reduced evapotranspiration and the inflow of municipal water. The above seasonal aspects of urban effects on streamflow should be applicable to most urban watersheds with temperate climates.  相似文献