Quantifying the effect of humic matter on the emission of mercury from artificial soil surfaces     

Conrad Mauclair  Julie Layshock  Anthony Carpi 《Applied Geochemistry》2008

A set of surface samples was created using purified laboratory grade sand treated with 0.05 μg/g Hg as the HgCl₂ salt and various concentrations of purified humic and fulvic acids. Emissions of elemental Hg from these substrates to the atmosphere were inversely correlated with the organic content of the samples (99% confidence level). The greatest differences in Hg emissions were found between samples containing the lowest concentrations of humic matter (0% versus 0.01% humic, and 0.01% versus 0.1% humic), only small differences in Hg flux were found to exist for samples with higher concentrations of humic acid (1%, 5%, and 100%). This effect was independent of the type of humic substance used, with both humic and fulvic acids showing an inhibitory effect on surface Hg emissions.  相似文献   

Naming the land: San countermapping in Namibia’s West Caprivi     

Julie J. Taylor   《Geoforum》2008,39(5):1766-1775

Both ‘indigenous rights’ and environmental discourses brought a NGO-led natural resource mapping project to the West Caprivi Game Park in northern Namibia in the late 1990s. San countermapping elsewhere in southern Africa demonstrates how mapping has been used as a tool for ‘indigenous’ identity-building and asserting authority over land. At the same time, mapping and Geographic Information Systems (GIS) have increasingly been used by conservationists in Namibian Community Based Natural Resource Management (CBNRM), demonstrating the potential therein for state and NGO surveillance and intervention regarding both natural resources and their users in conservancies and national parks. Mapping in West Caprivi thus embodied a tension between ‘visibility’ and ‘legibility’. This paper explores how mapping activities reflected, and became part of, institutional and ethnic struggles over identity, authority and natural resources. It argues that members of a San group called Khwe used mapping to construct particular histories, promote a unified, exclusive ethnic identity, and bolster their authority in the area. This in turn presented particular challenges for NGO relationships with the state. The mapping project also showed that, in their bid to counteract their own exclusion, Khwe not only opened up the landscape to new forms of NGO and state legibility, but sought to exclude ethnic others. Like other CBNRM projects, mapping often served socio-political, rather than environmental, functions.  相似文献   

Tephrostratigraphy of the late glacial and Holocene sediments of Puyehue Lake (Southern Volcanic Zone, Chile, 40°S)     

Sébastien Bertrand  Julie Castiaux 《Quaternary Research》2008,70(3):343-357

We document the mineralogical and geochemical composition of tephra layers identified in the late Quaternary sediments of Puyehue Lake (Southern Volcanic Zone of the Andes, Chile, 40°S) to identify the source volcanoes and to present the first tephrostratigraphic model for the region. For the last millennium, we propose a multi-criteria correlation model based on five tephra layers identified at seven coring sites. The two upper tephras are thin fine-grained green layers composed of more than 80% rhyodacitic glass shards, and associated to the AD 1960 and AD 1921-22 eruptions of the Puyehue-Cordon de Caulle volcanic complex. The third tephra is a sandy layer dominated by orthopyroxene, and related to the AD 1907 eruption of Rininahue maar. An olivine-rich tephra was deposited at the end of the 16th century, and a tephra characterized by a two-pyroxene association marks the second half of the first millennium AD. In addition, we detail the tephra succession of an 11.22-m-long sediment core covering the last 18,000 yr. The results demonstrate that the central province of the Southern Volcanic Zone has been active throughout the last deglaciation and the Holocene, with no increase in volcanic activity during glacial unloading.  相似文献   

The Late Cretaceous igneous rocks of Romania (Apuseni Mountains and Banat): the possible role of amphibole versus plagioclase deep fractionation in two different crustal terranes     

Jacqueline Vander Auwera  Tudor Berza  Julie Gesels  Alain Dupont 《International Journal of Earth Sciences》2016,105(3):819-847

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A history of violence: magma incubation,timing and tephra distribution of the Los Chocoyos supereruption (Atitlán Caldera,Guatemala)     

Alejandro Cisneros de León  Julie C. Schindlbeck-Belo  Steffen Kutterolf  Martin Danišík  Axel K. Schmitt  Armin Freundt  Wendy Pérez  Janet C. Harvey  Kuo-Lung Wang  Hao-Yang Lee 《第四纪科学杂志》2021,36(2):169-179

The climactic Los Chocoyos (LCY) eruption from Atitlán caldera (Guatemala) is a key chronostratigraphic marker for the Quaternary period given the extensive distribution of its deposits that reached both the Pacific and Atlantic Oceans. Despite LCY tephra being an important marker horizon, a radioisotopic age for this eruption has remained elusive. Using zircon (U–Th)/He geochronology, we present the first radioisotopically determined eruption age for the LCY of 75 ± 2 ka. Additionally, the youngest zircon crystallization ²³⁸U–²³⁰Th rim ages in their respective samples constrain eruption age maxima for two other tephra units that erupted from Atitlán caldera, W-Fall (130 ⁺¹⁶/₋₁₄ ka) and I-Fall eruptions (56 ^+8.2/_−7.7 ka), which under- and overlie LCY tephra, respectively. Moreover, rim and interior zircon dating and glass chemistry suggest that before eruption silicic magma was stored for >80 kyr, with magma accumulation peaking within ca. 35 kyr before the LCY eruption during which the system may have developed into a vertically zoned magma chamber. Based on an updated distribution of LCY pyroclastic deposits, a new conservatively estimated volume of ~1220 ± 150 km³ is obtained (volcanic explosivity index VEI > 8), which confirms the LCY eruption as the first-ever recognized supereruption in Central America.  相似文献   

Geological mysteries of the Plain of Jars begin to unravel     

Jeremy Baldock  & Julie Van Den Bergh 《Geology Today》2009,25(4):145-150

The Plain of Jars in north-eastern Laos is home to over 2000 stone jars varying in size from 100 kg to over 30 tonnes. The jars were probably made between 1500 and 2500 years ago; however, who by is not known, as the indigenous people have only lived in the area for 1000 years. Local legend speaks of these jars being used to store Lao-Lao or rice whisky; research indicates that these jars were part of loca funerary rites. There are currently 60 known jar sites, where anywhere between one and 350 individual jars are recorded. The jars are constructed from a variety of lithologies although a few basic rules to selecting suitable rocks have been observed. This study outlines which rock types have been used and how the characteristics of the rock mass controlled the jar makers' selection.  相似文献   

Causes of systematic over‐ or underestimation of low streamflows by use of index‐streamgage approaches in the United States     

Ken Eng  Julie E. Kiang  Yin‐Yu Chen  Daren M. Carlisle  Gregory E. Granato 《水文研究》2011,25(14):2211-2220

Low‐flow characteristics can be estimated by multiple linear regressions or the index‐streamgage approach. The latter transfers streamflow information from a hydrologically similar, continuously gaged basin (‘index streamgage’) to one with a very limited streamflow record, but often results in biased estimates. The application of the index‐streamgage approach can be generalized into three steps: (1) selection of streamflow information of interest, (2) definition of hydrologic similarity and selection of index streamgage, and (3) application of an information‐transfer approach. Here, we explore the effects of (1) the range of streamflow values, (2) the areal density of streamgages, and (3) index‐streamgage selection criteria on the bias of three information‐transfer approaches on estimates of the 7‐day, 10‐year minimum streamflow (Q_{7, 10}). The three information‐transfer approaches considered are maintenance of variance extension, base‐flow correlation, and ratio of measured to concurrent gaged streamflow (Q‐ratio invariance). Our results for 1120 streamgages throughout the United States suggest that only a small portion of the total bias in estimated streamflow values is explained by the areal density of the streamgages and the hydrologic similarity between the two basins. However, restricting the range of streamflow values used in the index‐streamgage approach reduces the bias of estimated Q_{7, 10} values substantially. Importantly, estimated Q_{7, 10} values are heavily biased when the observed Q_{7, 10} values are near zero. Results of the analysis also showed that Q_{7, 10} estimates from two of the three index‐streamgage approaches have lower root‐mean‐square error values than estimates derived from multiple regressions for the large regions considered in this study. Published in 2011 by John Wiley & Sons, Ltd.  相似文献   

Evidence of multidecadal climate variability and the Atlantic Multidecadal Oscillation from a Gulf of Mexico sea-surface temperature-proxy record   总被引：1，自引：1，他引：0  

Richard Z. Poore  Kristine L. DeLong  Julie N. Richey  Terrence M. Quinn 《Geo-Marine Letters》2009,29(6):477-484

A comparison of a Mg/Ca-based sea-surface temperature (SST)-anomaly record from the northern Gulf of Mexico, a calculated index of variability in observed North Atlantic SST known as the Atlantic Multidecadal Oscillation (AMO), and a tree-ring reconstruction of the AMO contain similar patterns of variation over the last 110 years. Thus, the multidecadal variability observed in the instrumental record is present in the tree-ring and Mg/Ca proxy data. Frequency analysis of the Gulf of Mexico SST record and the tree-ring AMO reconstruction from 1550 to 1990 found similar multidecadal-scale periodicities (~30–60 years). This multidecadal periodicity is about half the observed (60–80 years) variability identified in the AMO for the 20th century. The historical records of hurricane landfalls reveal increased landfalls in the Gulf Coast region during time intervals when the AMO index is positive (warmer SST), and decreased landfalls when the AMO index is negative (cooler SST). Thus, we conclude that alternating intervals of high and low hurricane landfall occurrences may continue on multidecadal timescales along the northern Gulf Coast. However, given the short length of the instrumental record, the actual frequency and stability of the AMO are uncertain, and additional AMO proxy records are needed to establish the character of multidecadal-scale SST variability in the North Atlantic.  相似文献   

Observed and simulated water and energy budget components at SCAN sites in the lower Mississippi Basin     

Gabriëlle J. M. De Lannoy  Julie Ufford  Alok K. Sahoo  Paul Dirmeyer  Paul R. Houser 《水文研究》2011,25(4):634-649

Land surface models are typically constrained by one or a few observed variables, while assuming that the internal water and energy partitioning is sensitive to those observed variables and realistic enough to simulate unobserved variables. To verify these assumptions, in situ soil climate analysis network (SCAN) observations in the Lower Mississippi Basin (2002–2008) are analysed to quantify water and energy budget components and they are compared to Community Land Model (CLM3·5) simulations. The local soil texture is identified as a major indicator for water storage characteristics and the Normalized Difference Vegetation Index shows potential as a drought indicator in summer months. Both observations and simulations indicate a regime where, except in some summer months, evapotranspiration controls soil moisture. CLM simulations with different soil texture assignments show discharge sensitivity to soil moisture, but almost no impact on evapotranspiration and other energy balance components. The observed and simulated water budgets show a similar partitioning. However, the SCAN observed water balance does not close because of precipitation measurement errors, unobserved irrigation, lack of specific storage change measurements and errors in the computed actual evapotranspiration. The simulated heat flux partitioning differs from that ‘observed’, with a larger (resp. smaller) fraction of net radiation being used by latent (resp. sensible) heat flux, and unobserved freeze and thaw events. The comparison between observations and model simulations suggests that a consistent observation collection for multiple variables would be needed to constrain and improve the full set of land surface variable estimates. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Atmospheric control of the cooling rate of impact melts and cryolavas on Titan’s surface     

Ashley Gerard Davies  Christophe Sotin  Dennis L. Matson  Julie Castillo-Rogez  Torrence V. Johnson  Mathieu Choukroun  Kevin H. Baines 《Icarus》2010,208(2):887-895

As on Earth, Titan’s atmosphere plays a major role in the cooling of heated surfaces. We have assessed the mechanisms by which Titan’s atmosphere, dominantly N₂ at a surface pressure of 1.5 × 10⁵ Pa, cools a warm or heated surface. These heated areas can be caused by impacts generating melt sheets and (possibly) by endogenic processes emplacing cryolavas (a low-temperature liquid that freezes on the surface). We find that for a cooling cryolava flow, lava lake, or impact melt body, heat loss is mainly driven by atmospheric convection. Radiative heat loss, a dominant heat loss mechanism with terrestrial silicate lava flows, plays only a minor role on Titan. Long-term cooling and solidification are dependent on melt sheet or flow thickness, and also local climate, because persistent winds will speed cooling. Relatively rapid cooling caused by winds reduces the detectability of these thermal events by instruments measuring surface thermal emission. Because surface temperature drops by ≈50% within ≈1 day of emplacement, fresh flows or impact melt may be difficult to detect via thermal emission unless an active eruption is directly observed. Cooling of flow or impact melt surfaces are orders of magnitude faster on Titan than on airless moons (e.g., Enceladus or Europa).Although upper surfaces cool fast, the internal cooling and solidification process is relatively slow. Cryolava flow lengths are, therefore, more likely to be volume (effusion) limited, rather than cooling-limited. More detailed modeling awaits constraints on the thermophysical properties of the likely cryomagmas and surface materials.  相似文献