Microbial reduction of chromium from the hexavalent to divalent state     

Tyrone L. Daulton  Brenda J. Little  Douglas A. Blom 《Geochimica et cosmochimica acta》2007,71(3):556-565

We demonstrate that Shewanella oneidensis, a metal-reducing bacteria species with cytoplasmic-membrane-bound reductases and remarkably diverse respiratory capabilities, reduced Cr(VI) to Cr(II) in anaerobic cultures where chromate was the sole terminal electron acceptor. Individual cell microanalysis by transmission electron microscopy (TEM) using electron energy-loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS) demonstrates Cr(II) concentrated near the cytoplasmic membrane, suggesting the terminal reduction pathway is intracellularly localized. Further, estimated cellular Cr(II) concentrations are relatively high at upwards of 0.03-0.09 g Cr/g bacterium. Accumulation of Cr(II) is observed in S. oneidensis cells prior to the formation of submicron-sized precipitates of insoluble Cr(III) on their surfaces. Furthermore, under anaerobic conditions, Cr(III) precipitates that encrust cells are shown to contain Cr(II) that is likely bound in the net negatively charged extracellular biopolymers which can permeate the surfaces of the precipitates. In otherwise nearly identical incubations, Cr(III) precipitate formation was observed in cultures maintained anaerobic with bubbled nitrogen but not in three replicate cultures in an anaerobic chamber.  相似文献   

Tveitite,a new calcium yttrium fluoride     

Sveinung Bergstøl  Brenda B. Jensen  Henrich Neumann 《Lithos》1977,10(1):81-87

Tveitite is a new mineral with formula of the type $\text{Ca}{}_{\mathrm{1?x}}\text{(}\text{Y, RE}\text{)}{}_{\mathrm{x}}\text{F}{}_{\mathrm{2+x}}\text{where}\text{x}$ is approximately 0.3. It is found in a cleavelandite pegmatite at Høydalen in Tørdal, Telemark, S. Norway. The sub-cell is thought to be monoclinic, $\text{a}\text{′=3.924,}\text{b}\text{′=3.893,}\text{c}\text{′=5.525, ß=90°26′,}\text{Z}\text{=2}$. The structure is very similar to that of fluorite and can be described in terms of a pseudo-cubic cell $\text{[1}\text{1}\text{0]}{}_0\text{= 5.527, [110]}{}_0\text{= 5.527,}\text{c}\text{= 5.525, α = 90°18′, γ = 89°37′}$ which contains approximately 1[YCa₃F₉]. The mineral shows twinning in at lest three different directions giving a grating structure probably due to high-low inversion. DTA studies show an inversion point at about 670°C. Material heated above this temperature gives X-ray diffraction patterns corresponding to yttrofluorite (a₀ 5.528). The effect of trivalent ions on the stability of fluorite is discussed.  相似文献   

Glacier fluctuations in the southern Peruvian Andes during the late‐glacial period,constrained with cosmogenic 3He     

Gordon R.M. Bromley  Brenda L. Hall  Joerg M. Schaefer  Gisela Winckler  Claire E. Todd  Kurt M. Rademaker 《第四纪科学杂志》2011,26(1):37-43

The occurrence of pronounced climate reversals during the last glacial termination has long been recognised in palaeoclimate records from both hemispheres and from high to low latitudes. Accurate constraint of both the timing and magnitude of events, such as the Younger Dryas and Antarctic Cold Reversal, is vital in order to test different hypotheses for the causes and propagation of abrupt climate change. However, in contrast to higher‐latitude regions, well‐dated records from the Tropics are rare and the structure of late‐glacial tropical climate remains uncertain. As a step toward addressing this problem, we present an in situ cosmogenic ³He surface exposure chronology from Nevado Coropuna, southern Peru, documenting a significant fluctuation of the ice margin during the late‐glacial period. Ten tightly clustered ages from a pair of moraines located halfway between the modern glacier and the Last Glacial Maximum terminus range from 11.9 to 13.9 ka and give an arithmetic mean age of 12.8 ± 0.7 ka (1σ). These data constitute direct evidence for a readvance, or prolonged stillstand, of glaciers in the arid Andes of southwestern Peru. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Glacial Lake Victoria,a high‐level Antarctic Lake inferred from lacustrine deposits in Victoria Valley     

Brenda L. Hall  George H. Denton  Bret Overturf  Chris H. Hendy 《第四纪科学杂志》2002,17(7):697-706

We present evidence of a large lake (Glacial Lake Victoria) that existed in Victoria Valley in the dry valleys region of Antarctica between at least 20 000 and 8600 ¹⁴C yr BP. At its highstands, Glacial Lake Victoria covered 100 km² and was ca. 200 m deep. The chronology for lake‐level changes comes from 87 AMS radiocarbon dates of lacustrine algae preserved in deltas and glaciolacustrine deposits that extend up to 185 m above present‐day lakes on the valley floor. The existence of Glacial Lake Victoria, as well as other large lakes in the dry valleys, indicates a climate regime significantly different from that of today at the last glacial maximum and in the early Holocene. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Testing solar forcing of pervasive Holocene climate cycles     

Chris Turney  Mike Baillie  Steve Clemens  David Brown  Jonathan Palmer  Jonathan Pilcher  Paula Reimer  Hanns Hubert Leuschner 《第四纪科学杂志》2005,20(6):511-518

The temporal and spatial extent of Holocene climate change is an area of considerable uncertainty, with solar forcing recently proposed to be the origin of cycles identified in the North Atlantic region. To address these issues we have developed an annually resolved record of changes in Irish bog tree populations over the last 7468 years which, together with radiocarbon‐dated bog and lake‐edge populations, extend the dataset back to ～9000 yr ago. The Irish trees underpin the internationally accepted radiocarbon calibration curve, used to derive a proxy of solar activity, and allow us to test solar forcing of Holocene climate change. Tree populations and age structures provide unambiguous evidence of major shifts in Holocene surface moisture, with a dominant cyclicity of 800 yr, similar to marine cycles in the North Atlantic, indicating significant changes in the latitude and intensity of zonal atmospheric circulation across the region. The cycles, however, are not coherent with changes in solar activity (both being on the same absolute timescale), indicating that Holocene North Atlantic climate variability at the millennial and centennial scale is not driven by a linear response to changes in solar activity. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Well-being and environmental change in the arctic: a synthesis of selected research from Canada’s International Polar Year program     

Brenda Parlee  Chris Furgal 《Climatic change》2012,115(1):13-34

The social and cultural dimensions of arctic environmental change were explored through Canada??s International Polar Year (IPY) research program. Drawing on concepts of vulnerability, resilience and human security, we discuss preliminary results of 15 IPY research projects (of 52) which dealt with the effects and responses of northern communities to issues of ecological variability, natural resource development and climate change. This paper attempts to determine whether the preliminary results of these projects have contributed to the IPY program goal of building knowledge about well-being in the arctic. The projects were diverse in focus and approach but together offer a valuable pan-northern perspective on many themes including land and resource use, food security, poverty and best practices of northern engagement. Case study research using self-reported measures suggests individual views of their own well-being differ from regional and territorial standardized statistics on quality of life. A large body of work was developed around changes in land and resource use. A decline in land and resource use in some areas and consequent concerns for food security, are directly linked to the effects of climate change, particularly in coastal areas where melting sea ice, erratic weather events and changes in the stability of landscapes (e.g., erosion, slumping) are leading to increased risks for land users. Natural resource development, while creating some new economic opportunities, may be compounding rather than offsetting such stresses of environmental change for vulnerable populations. While the IPY program has contributed to our understanding of some aspects of well-being in the arctic, many other issues of social, economic, cultural and political significance, including those unrelated to environmental change, remain poorly understood.  相似文献   

Mapping mineralogy in evaporite basins through time using multispectral Landsat data: Examples from the Bonneville basin,Utah, USA     

Mark H. Radwin  Brenda B. Bowen 《地球表面变化过程与地形》2021,46(6):1160-1176

The Bonneville basin, located in north-western Utah, is a vast evaporite basin which is home to the world-renowned Bonneville Salt Flats international speedway and is a highly valued landscape undergoing rapid change and anthropogenic influence. Air quality, snowpack, the local hydrological system, and state tourism are all impacted by the nature of the surface sediments exposed in the Bonneville basin. Mapping the Bonneville basin over time with remote sensing methods provides insight into the dynamics and impacts of the changing surface landscape. Utilizing the Landsat-5 Thematic Mapper (TM) and Landsat-8 Operational Land Imager (OLI) sensors, a set of band math indices are empirically established to map the predominant halite, gypsum, and carbonates mineralogical zones of the Bonneville basin. Spectral comparisons of representative samples from the study area and image-derived spectra indicate the halite of the Bonneville basin is wet and that gypsum deposits are slightly mixed with halite. The established indices are assessed in four ways, all of which support the ability of the indices to accentuate the associated mineralogical endmembers. Two study areas within the Bonneville basin are investigated temporally from 1986, 1995, 2005, and 2016 and show changing patterns in mineral distribution that align with surface processes active through these timescales. These indices provide a resource for mapping mineralogy though time in evaporite basins globally with diverse applications for questions about land use and environmental change.  相似文献   

European Tree Rings and Climate in the 16th Century     

K.R. Briffa  P.D. Jones  R.B. Vogel  F.H. Schweingruber  M.G.L. Baillie  S.G. Shiyatov  E.A. Vaganov 《Climatic change》1999,43(1):151-168

We present a selective review of tree-ring variability and inferred climate changes in Europe during the 16th century. The dendroclimatological evidence is assessed within the context of the last 500 years and some interpretational problems are discussed. The tree-ring evidence is compared with various non-dendroclimatic evidence. The body of evidence shows that a large region of mid and northern Europe experienced a sharp cooling at around 1570/80 that, at least in the north, marked a shift towards a prolonged period of cool conditions. This region had its southern boundary in the Alps and there is little evidence for a major cooling in southern Europe.  相似文献   

Nitrate dynamics in a rural headwater catchment: measurements and modelling          下载免费PDF全文

Philip J. Smethurst  Kevin C. Petrone  Günter Langergraber  Craig C. Baillie  Dale Worledge  David Nash 《水文研究》2014,28(4):1820-1834

This study was designed to improve our understanding of, and mechanistically simulate, nitrate (NO₃) dynamics in a steep 9.8 ha rural headwater catchment, including its production in soil and delivery to a stream via surface and subsurface processes. A two‐dimensional modelling approach was evaluated for (1) integrating these processes at a hillslope scale annually and within storms, (2) estimating denitrification, and (3) running virtual experiments to generate insights and hypotheses about using trees in streamside management zones (SMZs) to mitigate NO₃ delivery to streams. Total flow was mathematically separated into quick‐ and slow‐flow components; the latter was routed through the HYDRUS software with a nitrogen module designed for constructed wetlands. Flow was monitored for two years. High surface‐soil NO₃ concentrations started to be delivered to the stream via preferential subsurface flow within two days of the storm commencing. Groundwater NO₃‐N concentrations decreased from 1.0 to less than 0.1 mg l^?1 from up‐slope to down‐slope water tables, respectively, which was attributed to denitrification. Measurements were consistent with the flushing of NO₃ mainly laterally from surface soil during and following each storm. The model accurately accounted for NO₃ turnover, leading to the hypotheses that denitrification was a minor flux (<3 kg N ha^?1) compared to uptake (98^?127 kg N ha^?1), and that SMZ trees would reduce denitrification if they lowered the water table. This research provides an example of the measurement and modelling of NO₃ dynamics at a small‐catchment scale with high spatial and temporal resolution. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Summer light‐trap catches of adult Trichoptera in hill‐country catchments of contrasting land use,Waikato, New Zealand     

Kevin J. Collier  Brian J. Smith  Brenda R. Baillie 《新西兰海洋与淡水研究杂志》2013,47(5):623-634

The distribution of adult Trichoptera in light traps was investigated alongside nine streams draining catchments under native forest, pine forest, or pasture near Hamilton, Waikato, New Zealand. The aim of the study was to determine the relationship between abundance, taxonomic richness, and community composition with respect to land use during summer, and to evaluate the use of adult Trichoptera compared with benthic invertebrates as potential bio‐indicators of the effectiveness of land‐management changes. Adult Trichoptera faunas alongside the native streams were dominated by Hydrobiosidae, Conoesucidae, and Helicopsychidae (each >10% of total Trichoptera numbers for at least two of the three sites), whereas Leptoceridae, Oeconescidae, and Hydrobiosidae were relatively abundant alongside at least two of the pine sites. Adult Trichoptera faunas at the pasture sites were strongly dominated by Hydroptilidae which made up 47–85% of numbers caught at all sites. The mean number of individuals and taxa caught in light traps increased from November to January and then declined in February for all land‐use types. Overall, total numbers and taxonomic richness of adult Trichoptera were significantly lower at the pine sites compared to the pasture or native sites. TWINSPAN classification of benthic invertebrates collected in November clearly differentiated sites based on land use for presence/absence and percentage abundance data. A similar pattern was evident for most sites when adult Trichoptera faunas were used for the four sampling dates combined, suggesting that light trapping has potential as a tool for bio‐monitoring.  相似文献