Sorption of uranium(VI) at the clay mineral–water interface     

Samer Bachmaf  Broder J. Merkel 《Environmental Earth Sciences》2011,63(5):925-934

Batch experiments were conducted to study the sorption of uranium on selected clay minerals (KGa-1b and KGa-2 reference kaolinite, SWy-2 and STx-1b reference montmorillonite, and IBECO natural bentonite) as a function of pH (4–9) and 0.001, 0.01, and 0.025 M NaCl in equilibrium with the CO₂ partial pressure of the atmosphere. Uranium concentrations were kept below 100 μg L⁻¹ to avoid precipitation of amorphous Uranium-hydroxides. Solely PTFE containers and materials were used, because experiments showed significant sorption at higher pH on glass ware. All batch experiments were performed over a period of 24 h, since kinetic experiments proved that the common 10 or 15 min are in many cases by far not sufficient to reach equilibrium. Kaolinite showed much greater uranium sorption than the other clay minerals due to the more aluminol sites available. Sorption on the poorly crystallized KGa-2 was higher than on the well-crystallized KGa-1b. Uranium sorption on STx-1b and IBECO exhibited parabolic behavior with a sorption maximum around pH 6.5. Sorption of uranium on montmorillonites showed a distinct dependency on sodium concentrations because of the effective competition between uranyl and sodium ions, whereas less significant differences in sorption were found for kaolinite. The presence of anatase as impurity in kaolinite enhanced the binding of uranyl-carbonate complexes with surface sites. The kinetic of uranium sorption behavior was primarily dependent on the clay minerals and pH. A multisite surface complexation model without assuming exchange is based on the binding of the most dominant uranium species to aluminol and silanol edge sites of montmorillonite, respectively to aluminol and titanol surface sites of kaolinite. For eight surface species, the log_k was determined from the experimental data using the parameter estimation code PEST together with PHREEQC.  相似文献   

Investigation of the potential surface–groundwater relationship using automated base-flow separation techniques and recession curve analysis in Al Zerba region of Aleppo,Syria     

Rudy K. Abo  Broder J. Merkel 《Arabian Journal of Geosciences》2015,8(12):10543-10563

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Architecture of the lower terraces and evolution of the Dordogne River at Bergerac (south‐west France) during the last glacial–interglacial cycle     

PASCAL BERTRAN  MARINE FROUIN  NORBERT MERCIER  FABIEN NAESSENS  FRÉDÉRIC PRODEO  ALAIN QUEFFELEC  COLETTE SIRIEIX  LUCA SITZIA 《第四纪科学杂志》2013,28(6):605-616

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Comparison of polar mesospheric cloud measurements from the Cloud Imaging and Particle Size experiment and the solar backscatter ultraviolet instrument in 2007     

Susanne Benze  Cora E. Randall  Matthew T. DeLand  Gary E. Thomas  David W. Rusch  Scott M. Bailey  James M. Russell  William McClintock  Aimee W. Merkel  Chris Jeppesen 《Journal of Atmospheric and Solar》2009,71(3-4):365-372

We compare measurements from the Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) experiment to the NOAA-17 solar backscatter ultraviolet (SBUV/2) instrument during the 2007 Northern Hemisphere polar mesospheric cloud (PMC) season. Daily average Rayleigh scattering albedos determined from identical footprints from the CIPS nadir camera and SBUV/2 agree to better than ～5% throughout the season. Average PMC brightness values derived from the two instruments agree to within ±10%. PMC occurrence frequencies are on average ～5% to nearly a factor of two higher in CIPS, depending on latitude. Agreement is best at high latitudes where clouds are brighter and more frequent. The comparisons indicate that AIM CIPS data are valid for scientific analyses. They also show that CIPS measurements can be linked to the long time series of SBUV/2 data to investigate long-term variability in PMCs.  相似文献   

QUARTZ WEATHERING IN FREEZE–THAW CYCLES: EXPERIMENT AND APPLICATION TO THE EL'GYGYTGYN CRATER LAKE RECORD FOR TRACING SIBERIAN PERMAFROST HISTORY     

GEORG SCHWAMBORN  LUTZ SCHIRRMEISTER  FRANZISKA FRÜTSCH  BERNHARD DIEKMANN 《Geografiska Annaler: Series A, Physical Geography》2012,94(4):481-499

The object of this study is to test the assumption that cryogenic weathering (here understood as in‐situ disintegration of rock under cold‐climate conditions including ice as a weathering agent) preferentially breaks up quartz grains. We apply the results of laboratory tests to a Quaternary sediment record. The combination of silt production, relative quartz enrichment in the silt fraction, and quartz grain micromorphology is traced in a multi‐100‐kyr lake sediment archive as indicator data for cryogenic weathering. Constant cryogenic weathering conditions are inferred for at least the last 220 000 years from a lake sediment core of El'gygytgyn Crater, northeast Russia. This is the longest continuous terrestrial archive currently known for the continental Arctic. Quartz enrichment in the fines evolves from seasonal freeze–thaw weathering as demonstrated in laboratory testing where over 100 freeze and thaw cycles crack quartz grains preferentially over feldspar. Microscopic grain features demonstrate that freeze–thaw cycling probably disrupts quartz grains along mineral impurities such as bubble trails, gas–liquid inclusions, or mineralogical sub‐grain boundaries. Single‐grain micromorphology (e.g. angular outlines, sharp edges, microcracks, brittle surfaces) illustrates how quartz becomes fragmented due to cryogenic cracking of the grains. The single‐grain features stemming from the weathering dynamics are preserved even after a grain is transported off site (i.e. in mobile slope material, in seasonal river run‐off, into a lake basin) and may serve as first‐order proxy data for permafrost conditions in Quaternary records.  相似文献   

Hydrochemical evolution and arsenic release in shallow aquifer in the Titas Upazila,Eastern Bangladesh     

Wael Kanoua  Broder Merkel 《Arabian Journal of Geosciences》2017,10(13):290

Groundwater arsenic (As) concentrations above 10 μg/L (World Health Organization; WHO standard) are frequently found in the Titas Upazila in Bangladesh. This paper evaluates the groundwater chemistry and the mechanisms of As release acting in an underground aquifer in the middle-northeast part of the Titas Upazila in Bangladesh. Previous measurements and analyses of 43 groundwater samples from the region of interest (ROI) are used. Investigation is based on major ions and important trace elements, including total As and Fe in groundwater samples from shallow (8–36 m below ground level: mbgl) and deep (85–295 mbgl) tube wells in the aforementioned ROI. Principal hydrochemical facies are Ca–HCO₃, with circumneutral pH. The different redox-sensitive constituents (e.g., As, Fe, Mn, NH₄, and SO₄) indicate overlapping redox zones, leading to differences regarding the redox equilibrium. Multivariate statistical analysis (factor analysis) was applied to reduce 20 chemical variables to four factors but still explain 81% of the total variance. The component loadings give hints as to the natural processes in the shallow aquifers, in which organic matter is a key reactant. The observed chemistry of As, Fe, and Mn can be explained by simultaneous equilibrium between Fe-oxide and SO₄ reduction and an equilibrium of rhodochrosite precipitation/dissolution. A correlation test indicates the likeliness of As release by the reductive dissolution of Fe-oxides driven by the degradation of sediments organic matter. Other mechanisms could play a role in As release, albeit to a lesser extent. Reactive transport modeling using PHREEQC reproduced the observed chemistry evolution using simultaneous equilibrium between Fe-oxide and SO₄ reduction and the equilibrium of rhodochrosite dissolution/precipitation alongside organic matter oxidation.  相似文献   

Implementing adaptation in developed countries: an analysis of progress and trends     

FRÉDÉRIC GAGNON-LEBRUN  SHARDUL AGRAWALA 《Climate Policy》2013,13(5):392-408

Little attention has been paid thus far to the experiences of developed countries in adapting to climate change. This article addresses this research gap by providing an assessment of broad trends in progress on planning and implementing adaptation in developed countries. Primary inputs are the National Communications (NCs) by these countries to the United Nations Framework Convention on Climate Change (UNFCCC), although the article also discusses illustrative examples of recent adaptation activities that have not been covered in the NCs. NCs reflect ‘whole government’ perspectives and follow a standardized reporting format, which facilitates cross-national comparisons. The analysis shows that impacts and adaptation receive limited attention within NCs. The discussion on impacts and adaptation has typically been dominated by climate scenarios and impacts analysis, while the discussion on adaptation is often limited to the identification of generic options. There are signs of recent progress, however, in the Third and especially the Fourth NCs, in which a growing number of developed countries report on establishing frameworks for adaptation and on efforts to implement adaptation measures that take future climate into account. Although an encouraging sign, it is still too early to assess the eventual impact of such measures.  相似文献   

Uranium in groundwater of the Al-Batin Alluvial Fan aquifer,south Iraq     

Majid Alkinani  Wael Kanoua  Broder Merkel 《Environmental Earth Sciences》2016,75(10):869

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Light-induced bird strikes on vessels in Southwest Greenland     

Merkel FR  Johansen KL 《Marine pollution bulletin》2011,62(11):2330-2336

Light-induced bird strikes are known to occur when vessels navigate during darkness in icy waters using powerful searchlight. In Southwest Greenland, which is important internationally for wintering seabirds, we collected reports of incidents of bird strikes over 2-3 winters (2006-2009) from navy vessels, cargo vessels and trawlers (total n = 19). Forty-one incidents were reported: mainly close to land (<4 km, 78%), but one as far offshore as 205 km. Up to 88 birds were reported killed in a single incident. All occurred between 5 p.m. and 6 a.m. and significantly more birds were involved when visibility was poor (snow) rather than moderate or good. Among five seabird species reported, the common eider (Somateria mollissima) accounted for 95% of the bird casualties. Based on spatial analyses of data on vessel traffic intensity and common eider density we are able to predict areas with high risk of bird strikes in Southwest Greenland.  相似文献   

Corrigendum to “Deformation of polycrystalline iron up to 30 GPa and 1000 K” [Phys. Earth Planet Inter. 145 (2004) 239–251]     

Sbastien Merkel  Hans-Rudolf Wenk  Philippe Gillet  Ho-kwang Mao  Russell J. Hemley 《Physics of the Earth and Planetary Interiors》2005,150(4):351-352

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