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781.
Quantification of Metals and Semimetals in Carbon‐Rich Rocks: A New Sequential Protocol Including Extraction from Humic Substances
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Renato Henrique‐Pinto Sarah‐Jane Barnes Dany Savard Sadia Mehdi 《Geostandards and Geoanalytical Research》2017,41(1):41-62
We have developed a new sequential extraction technique that does not require complex procedures and is efficient in determining metal and semimetal contents of carbon‐rich rocks. Six geological reference materials (SBC‐1, SCHS‐1, SCo‐1, SDO‐1, SGR‐1b and SLg‐1) and an in‐house black shale (SH‐1) were selected to test the method, which consists of four main digestion steps involving: (a) dilute HCl acid; (b) NaOH; (c) aqua regia; and (d) hydrofluoric acid. Compared with traditional aqua regia + hydrofluoric acid attack, this new protocol recovers more of the moderately volatile elements during early extraction of humic substances. In addition when compared with reference values, those for most elements are in agreement within uncertainty. Furthermore, this new protocol reveals important information on the partitioning of elements; for instance, steps one and two indicate which elements are associated with carbonates and organic phases from fulvic and humic acid extractions, whereas step three provides results for which elements are associated with sulfide minerals and step four indicates which elements remained in the silicate and oxide phases. 相似文献
782.
Stephanie?FludeEmail author Martin?R.?Lee Sarah?C.?Sherlock Simon?P.?Kelley 《Contributions to Mineralogy and Petrology》2012,163(6):983-994
Charge contrast imaging in the scanning electron microscope can provide new insights into the scale and composition of alkali
feldspar microtextures, and such information helps considerably with the interpretation of their geological histories and
results of argon isotope thermochronological analyses. The effectiveness of this technique has been illustrated using potassium-rich
alkali feldspars from the Dartmoor granite (UK). These feldspars contain strain-controlled lamellar crypto- and microperthites
that are cross-cut by strain-free deuteric microperthites. The constituent albite- and orthoclase-rich phases of both microperthite
generations can be readily distinguished by atomic number contrast imaging. The charge contrast results additionally show
that sub-micrometre-sized albite ‘platelets’ are commonplace between coarser exsolution lamellae and occur together to make
cryptoperthites. Furthermore, charge contrast imaging reveals that the orthoclase-rich feldspar is an intergrowth of two phases,
one that is featureless with uniform contrast and another that occurs as cross-cutting veins and grains with the {110} adularia
habit. Transmission electron microscopy shows that the featureless feldspar is tweed orthoclase, whereas the veins and euhedral
grains are composed of irregular microcline that has formed from orthoclase by ‘unzipping’ during deuteric or hydrothermal
alteration. The charge contrast imaging results are especially important in demonstrating that deuteric perthites are far
more abundant in alkali feldspars than would be concluded from investigations using conventional microscopy techniques. The
unexpected presence of such a high volume of replacement products has significant implications for understanding the origins
and geological histories of crustal rocks and the use of alkali feldspars in geo- and thermochronology. Whilst the precise
properties of feldspars that generate contrast remain unclear, the similarity between charge contrast images and corresponding
cathodoluminescence images of deuteric microperthites indicates that trace element chemistry and possibly also elastic strain
within the crystal play a major role. 相似文献
783.
Weston M. Eaton Francis R. Eanes Jessica D. Ulrich-Schad Morey Burnham Sarah P. Church J. Gordon Arbuckle 《社会与自然资源》2019,32(7):827-840
The sense of place (SOP) conceptual framework offers theoretical and empirical evidence that links peoples’ multifaceted connections to place(s) to their engagement in pro-environmental and conservation behaviors. The bulk of this research has focused on peoples’ connection to high-amenity places and landscapes. Recent research applies SOP in working landscapes—however, these studies encounter “troubles” that include measurement challenges and mixed results in predicting statistical relationships with conservation outcome variables. As authors of some of these studies, we propose three opportunities and corresponding survey items for developing meaningful SOP measures in future working landscapes research: (1) modify existing SOP dimensions and items to better capture the working landscape dynamics; (2) address how scale may affect behavior and SOP dimensions; and (3) incorporate a conservation ethic dimension into the SOP framework in working lands. 相似文献
784.
Nels R. Bjarke Ben Livneh Sarah C. Elmendorf Noah P. Molotch Eve-Lyn S. Hinckley Nancy C. Emery Pieter T. J. Johnson Jennifer F. Morse Katherine N. Suding 《水文研究》2021,35(9):e14320
The Niwot Ridge and Green Lakes Valley (NWT) long-term ecological research (LTER) site collects environmental observations spanning both alpine and subalpine regimes. The first observations began in 1952 and have since expanded to nearly 300 available datasets over an area of 99 km2 within the north-central Colorado Rocky Mountains that include hydrological (n = 101), biological (n = 79), biogeochemical (n = 62), and geographical (n = 56) observations. The NWT LTER database is well suited to support hydrologic investigations that require long-term and interdisciplinary data sets. Experimentation and data collection at the NWT LTER are designed to characterize ecological responses of high-mountain environments to changes in climate, nutrients, and water availability. In addition to the continuation of the many legacy NWT datasets, expansion of the breadth and utility of the NWT LTER database is driven by new initiatives including (a) a catchment-scale sensor network of soil moisture, temperature, humidity, and snow-depth observations to understand hydrologic connectivity and (b) snow-albedo alteration experiments using black sand to evaluate the effects of snow-disappearance on ecosystems. Together, these observational and experimental datasets provide a substantial foundation for hydrologic studies seeking to understand and predict changes to catchment and local-scale process interactions. 相似文献
785.
In arid and semi-arid regions, many rivers experience extremely low flow conditions during seasonal dry periods. During these times, effluent from wastewater treatment plants can make up the majority of flow in the river. However, water quality in urban systems can also be strongly influenced by the natural or human-influenced flow regime and discharge from other anthropogenic sources such as industrial operations and runoff from impervious surfaces. In this study, we aimed to determine whether water quality was controlled primarily by wastewater discharge in an effluent-dominated river. Between May 2016–May 2019, we systematically measured water temperature, pH, dissolved oxygen, biochemical oxygen demand, and the concentrations of nitrate-N, ammonia-N, and orthophosphate in the South Platte River in the Denver metropolitan area, Colorado, USA. We found that, despite being an effluent-dominated river, wastewater treatment plant discharge was not the principal factor controlling water quality in many of the sampled areas. Non-point source pollution from impervious surfaces, delivered to the river through storm drains and minor tributary streams, also contributed to the high nutrient conditions in several locations. We also noted a strong seasonality in water quality, with higher concentrations of nutrients and higher biochemical oxygen demand in the winter months when wastewater effluent can make up more than 90% of the flow in the river. Thus, the interaction of discharge location and reduced seasonal flow produced spatio-temporal hot spots of diminished water quality. More stringent enforcement of water quality regulations may improve water quality in this system. However, a large portion of the pollution seems to be from non-point sources, which are very difficult to control. 相似文献
786.
Jennifer J. Follstad Shah Ryan Bares Brenda B. Bowen Gabriel J. Bowen David R. Bowling David P. Eiriksson Benjamin Fasoli Richard P. Fiorella Anna Gannet Hallar Sarah J. Hinners John D. Horel Alexander A. Jacques Logan R. Jamison John C. Lin Daniel L. Mendoza Logan E. Mitchell Diane E. Pataki Sarah McKenzie Skiles Rose M. Smith Margaret A. Wolf Paul D. Brooks 《水文研究》2021,35(9):e14352
The 2085 km2 Jordan River Basin, and its seven sub-catchments draining the Central Wasatch Range immediately east of Salt Lake City, UT, are home to an array of hydrologic, atmospheric, climatic and chemical research infrastructure that collectively forms the Wasatch Environmental Observatory (WEO). WEO is geographically nested within a wildland to urban land-use gradient and built upon a strong foundation of over a century of discharge and climate records. A 2200 m gradient in elevation results in variable precipitation, temperature and vegetation patterns. Soil and subsurface structure reflect systematic variation in geology from granitic, intrusive to mixed sedimentary clastic across headwater catchments, all draining to the alluvial or colluvial sediments of the former Lake Bonneville. Winter snowfall and spring snowmelt control annual hydroclimate, rapid population growth dominates geographic change in lower elevations and urban gas and particle emissions contribute to episodes of severe air pollution in this closed-basin. Long-term hydroclimate observations across this diverse landscape provide the foundation for an expanding network of infrastructure in both montane and urban landscapes. Current infrastructure supports both basic and applied research in atmospheric chemistry, biogeochemistry, climate, ecology, hydrology, meteorology, resource management and urban redesign that is augmented through strong partnerships with cooperating agencies. These features allow WEO to serve as a unique natural laboratory for addressing research questions facing seasonally snow-covered, semi-arid regions in a rapidly changing world and an excellent facility for providing student education and research training. 相似文献
787.
April S. Dalton Minna Väliranta Peter J. Barnett Sarah A. Finkelstein 《Boreas: An International Journal of Quaternary Research》2017,46(3):388-401
We examine pollen, macrofossils and sedimentological proxies from the Ridge Site, an 18‐m sequence of glacial and non‐glacial sediments exposed along the bank of the Ridge River in the southern Hudson Bay Lowlands (HBL), Canada. As the HBL is located in the previously glaciated region of North America, palaeorecords from this region have important implications for understanding ice‐sheet palaeogeography and climate for the late Pleistocene. Two diamicton units were interpreted as subglacial till deposited by a glacier flowing toward the south‐southwest (lower diamicton) and west‐southwest (upper diamicton), respectively. Confined between these tills is a 6‐m non‐glacial unit, constrained to Marine Isotope Stage 3 (MIS 3; c. 57 000 to c. 29 000 a BP) by three radiocarbon dates. Quantitative analyses of the pollen record (dominated by Sphagnum, Cyperaceae, Pinus, Picea, Salix, Alnus and Betula) suggest that average summer temperature (June, July, August) was 14.6±1.51 °C, which is similar to that of the present day at the site. Total annual precipitation was 527±170 mm as compared to 705 mm present‐day. The macrofossil record confirmed the local presence of Betula, Salix and conifers. Our results, in combination with other records from the periphery of the Laurentide Ice Sheet, suggest that vast boreal forest‐type vegetation, along with a drier interstadial climate, existed in the region during MIS 3. We also compare pollen‐derived palaeoclimate reconstructions from the Ridge Site with reconstructions from a previously published site along the Nottaway River, HBL, which was dated to MIS 5a–d (c. 109 000 to c. 82 000 a BP). This comparison suggests that, with additional data, it may be possible to differentiate MIS 3 and MIS 5 deposits in the HBL on the basis of relative continentality, with MIS 3 characterized by lower total annual precipitation, and MIS 5 by values similar or greater than present‐day. 相似文献
788.
Spatial and temporal patterns of dissolved organic matter quantity and quality in the Mississippi River Basin, 1997–2013
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Sarah M. Stackpoole Edward G. Stets David W. Clow Douglas A. Burns George R. Aiken Brent T. Aulenbach Irena F. Creed Robert M. Hirsch Hjalmar Laudon Brian A. Pellerin Robert G. Striegl 《水文研究》2017,31(4):902-915
Recent studies have found insignificant or decreasing trends in time‐series dissolved organic carbon (DOC) datasets, questioning the assumption that long‐term DOC concentrations in surface waters are increasing in response to anthropogenic forcing, including climate change, land use, and atmospheric acid deposition. We used the weighted regressions on time, discharge, and season (WRTDS) model to estimate annual flow‐normalized concentrations and fluxes to determine if changes in DOC quantity and quality signal anthropogenic forcing at 10 locations in the Mississippi River Basin. Despite increases in agriculture and urban development throughout the basin, net increases in DOC concentration and flux were significant at only 3 of 10 sites from 1997 to 2013 and ranged between ?3.5% to +18% and ?0.1 to 19%, respectively. Positive shifts in DOC quality, characterized by increasing specific ultraviolet absorbance at 254 nm, ranged between +8% and +45%, but only occurred at one of the sites with significant DOC quantity increases. Basinwide reductions in atmospheric sulfate deposition did not result in large increases in DOC either, likely because of the high buffering capacity of the soil. Hydroclimatic factors including annual discharge, precipitation, and temperature did not significantly change during the 17‐year timespan of this study, which contrasts with results from previous studies showing significant increases in precipitation and discharge over a century time scale. Our study also contrasts with those from smaller catchments, which have shown stronger DOC responses to climate, land use, and acidic deposition. This temporal and spatial analysis indicated that there was a potential change in DOC sources in the Mississippi River Basin between 1997 and 2013. However, the overall magnitude of DOC trends was not large, and the pattern in quantity and quality increases for the 10 study sites was not consistent throughout the basin. 相似文献
789.
790.
Anne Sofie Sndergaard Nicolaj Krog Larsen Jesper Olsen Astrid Strunk Sarah Woodroffe 《第四纪科学杂志》2019,34(7):536-547
In this study, we present new information on the glacial history of the Greenland Ice Sheet (GrIS) and a local ice cap in Qaanaaq, northwest Greenland. We use geomorphological mapping, 10Be exposure dating of boulders, analysis of lake cores, and 14C dating of reworked marine molluscs and subfossil plants to constrain the glacial history. Our 14C ages of reworked marine molluscs reveal that the ice extent in the area was at or behind its present‐day position from 42.2 ± 0.4 to 30.6 ± 0.3k cal a BP after which the GrIS expanded to its maximum position during the Last Glacial Maximum. We find evidence of early ice retreat in the deep fjord (Inglefield Bredning) at 11.9 ± 0.6 ka whereas the Taserssuit Valley was deglaciated ~4 ka later at 7.8 ± 0.1k cal a BP. A proglacial lake record suggests that the local ice cap survived the Holocene Thermal Maximum but moss kill‐dates reveal that it was smaller than present for a period of time before 3.3 ± 0.1k until 0.9 ± 0.1k cal a BP, following which the ice in the area expanded towards its Little Ice Age extent. Copyright © 2019 John Wiley & Sons, Ltd. 相似文献