Chloride source delineation in an urban-agricultural watershed: Deicing agents versus agricultural contributions     

Andrew Oberhelman  Eric W. Peterson 《水文研究》2020,34(20):4017-4029

Analyses (n = 525) of chloride (Cl⁻), bromide (Br⁻), nitrate as nitrogen (NO₃-N), sodium (Na⁺), calcium (Ca²⁺) and potassium (K⁺) in stream water, tile-drain water and groundwater were conducted in an urban-agricultural watershed (10% urban/impervious, 87% agriculture) to explore potential differences in the signature of Cl⁻ originating from an urban source as compared with an agricultural source. Only during winter recharge events did measured Cl⁻ concentrations exceed the 230 mg/L chronic threshold. At base flow, nearly all surface water and tile water samples had Cl⁻ concentrations above the calculated background threshold of 18 mg/L. Mann–Whitney U tests revealed ratios of Cl⁻ to Br⁻ (p = .045), to NO₃-N (p < .0001), to Ca²⁺ (p < .0001), and to Na⁺ (p < .0001) to be significantly different between urban and agricultural waters. While Cl⁻ ratios indicate that road salt was the dominant source of Cl⁻ in the watershed, potassium chloride fertilizer contributed as an important secondary source. Deicing in watersheds where urban land use is minimal had a profound impact on Cl⁻ dynamics; however, agricultural practices contributed Cl⁻ year-round, elevating stream base flow Cl⁻ concentrations above the background level.  相似文献   

The capacity of European Higher Educational Institutions to address threats imposed by natural hazards     

Skevi Perdikou  Jiri Horak  Lena Halounová  Roshani Palliyaguru  Andrew Lees 《Natural Hazards》2016,81(3):1447-1466

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Late Pleistocene stratigraphy and sedimentary environments of the Severnaya Dvina‐Vychegda region in northwestern Russia     

Astrid Lyså  Eiliv Larsen  Jan‐Pieter Buylaert  Ola Fredin  Maria A. Jensen  Denis Kuznetsov  Andrew S. Murray  Dmitry A. Subetto  Aurelien van Welden 《Boreas: An International Journal of Quaternary Research》2014,43(4):759-779

The Late Pleistocene stratigraphy from the Severnaya Dvina‐Vychegda region of northwestern Russia is revised based on investigations of new localities, revisiting earlier localities, introduction of about 110 new OSL dates and burial depth corrections of earlier published OSL dates, in addition to six new radiocarbon dates. Most of the OSL samples studied here are from fluvial and subaquaeous sediments, which we found to be well bleached. Six chronostratigraphical units and their sedimentary environment are described, with the oldest unit consisting of pre‐Eemian glacial beds. For the first time, Early Weichselian sediments are documented from the region and a fluvial environment with some vegetation and permafrost conditions is suggested to have persisted from the end of the Eemian until at least about 92 ka ago. The period in which a Middle Weichselian White Sea Lake could have existed is constrained to 67?62 ka, but as the lake level never reached the thresholds of the drainage basin, the lake probably existed only for a short interval within this time‐span. Blocking and reversal of fluvial drainage started again around 21?20 ka ago when the Fennoscandian Ice Sheet advanced into the area, reaching its maximum 17?15 ka ago. At that time, an ice‐dammed lake reached its maximum water level, which was around 135 m above present sea level. Drainage of the lake started shortly after 15 ka ago, and the lake was emptied within 700 years. Severe periglacial conditions, with permafrost and aeolian activity, prevailed in the area until about 10.7 ka.  相似文献   

Clam community composition and prey shell size impacts moon snail (Gastropod: Naticidae) drilling frequencies in South Carolina,USA     

Dimitar B. Zlatev  Michael C. Lordon  Emma A. Schremp  Andrew C. Steffen  Allison E. Grecco  Jason S. Bystriansky  Jalene M. LaMontagne 《Marine Ecology》2019,40(3)

Moon snail predation on clams is a common model system of predator–prey interactions. In this system, the predator bores through the shell of its prey, leaving a distinct and identifiable hole. Some paleoecological and behavioral research on moon snails suggests a trend in predation preference directed toward clams with small shells. Rarely, however, have studies tested relative drilling frequencies across species and size ranges in natural assemblages of clam communities. We examined the clam community composition at two beaches in South Carolina, USA, and we then tested moon snail predator preferences for (a) clam prey species and (b) whether their selection is related to prey shell size. We collected a total of 1,879 clam shells, identified each shell to species and recorded their anteroposterior length. The species composition of clams differed significantly between the two beaches; Anadara ovalis was dominant at both sites, but three of ten total species were only collected at one beach. Folly Beach had nearly a 60% higher the overall drilling frequency (34.6%) versus Edisto Beach (21.8%), and this may be linked to the differences in clam community compositions at the sites. For A. ovalis and Mulinia lateralis, shells with larger lengths have lower probabilities of being bored by a moon snail. Anadara brasiliana, which generally is a thinner‐shelled clam species, had the highest total drilling frequency (77.2%), and Noetia ponderosa, a thicker‐shelled clam, had a considerably lower drilling frequency (12.0%). We conclude that both community level factors (species composition) and population characteristics (shell size distributions) may influence the local drilling frequency by moon snails.  相似文献   

Asymmetric intraseasonal events in the stochastic skeleton MJO model with seasonal cycle     

Sulian Thual  Andrew J. Majda  Samuel N. Stechmann 《Climate Dynamics》2015,45(3-4):603-618

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Uncertainty analysis of a model of wind-blown volcanic plumes     

Mark J. Woodhouse  Andrew J. Hogg  Jeremy C. Phillips  Jonathan C. Rougier 《Bulletin of Volcanology》2015,77(10):1-28

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The Life and Times of a Dissident Scientist     

Peter Andrew Sturrock 《Solar physics》2017,292(10):147

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The variability of ruthenium in chromite from chassignite and olivine‐phyric shergottite meteorites: New insights into the behavior of PGE and sulfur in Martian magmatic systems          下载免费PDF全文

Raphael J. Baumgartner  Marco L. Fiorentini  David Baratoux  Ludovic Ferrière  Marek Locmelis  Andrew Tomkins  Kerim A. Sener 《Meteoritics & planetary science》2017,52(2):333-350

The Martian meteorites comprise mantle‐derived mafic to ultramafic rocks that formed in shallow intrusions and/or lava flows. This study reports the first in situ platinum‐group element data on chromite and ulvöspinel from a series of dunitic chassignites and olivine‐phyric shergottites, determined using laser‐ablation ICP‐MS. As recent studies have shown that Ru has strongly contrasting affinities for coexisting sulfide and spinel phases, the precise in situ analysis of this element in spinel can provide important insights into the sulfide saturation history of Martian mantle‐derived melts. The new data reveal distinctive differences between the two meteorite groups. Chromite from the chassignites Northwest Africa 2737 (NWA 2737) and Chassigny contained detectable concentrations of Ru (up to ~160 ppb Ru) in solid solution, whereas chromite and ulvöspinel from the olivine‐phyric shergottites Yamato‐980459 (Y‐980459), Tissint, and Dhofar 019 displayed Ru concentrations consistently below detection limit (<42 ppb). The relatively elevated Ru signatures of chromite from the chassignites suggest a Ru‐rich (~1–4 ppb) parental melt for this meteorite group, which presumably did not experience segregation of immiscible sulfide liquids over the interval of mantle melting, melt ascent, and chromite crystallization. The relatively Ru‐depleted signature of chromite and ulvöspinel from the olivine‐phyric shergottites may be the consequence of relatively lower Ru contents (<1 ppb) in the parental melts, and/or the presence of sulfides during the crystallization of the spinel phases. The results of this study illustrate the significance of platinum‐group element in situ analysis on spinel phases to decipher the sulfide saturation history of magmatic systems.  相似文献   

Chemical and textural equilibration of garnet during amphibolite facies metamorphism: The influence of coupled dissolution–reprecipitation          下载免费PDF全文

Tim J Dempster  Julie La Piazza  Andrew G Taylor  Nicolas Beaudoin  Peter Chung 《Journal of Metamorphic Geology》2017,35(9):1111-1130

Metamorphic equilibration requires chemical communication between minerals and may be inhibited through sluggish volume diffusion and or slow rates of dissolution in a fluid phase. Relatively slow diffusion and the perceived robust nature of chemical growth zoning may preclude garnet porphyroblasts from readily participating in low‐temperature amphibolite facies metamorphic reactions. Garnet is widely assumed to be a reactant in staurolite‐isograd reactions, and the evidence for this has been assessed in the Late Proterozoic Dalradian pelitic schists of the Scottish Highlands. The 3D imaging of garnet porphyroblasts in staurolite‐bearing schists reveals a good crystal shape and little evidence of marginal dissolution; however, there is also lack of evidence for the involvement of either chlorite or chloritoid in the reaction. Staurolite forms directly adjacent to the garnet, and its nucleation is strongly associated with deformation of the muscovite‐rich fabrics around the porphyroblasts. “Cloudy” fluid inclusion‐rich garnet forms in both marginal and internal parts of the garnet porphyroblast and is linked both to the production of staurolite and to the introduction of abundant quartz inclusions within the garnet. Such cloudy garnet typically has a Mg‐rich, Mn‐poor composition and is interpreted to have formed during a coupled dissolution–reprecipitation process, triggered by a local influx of fluid. All garnet in the muscovite‐bearing schists present in this area is potentially reactive, irrespective of the garnet composition, but very few of the schists contain staurolite. The staurolite‐producing reaction appears to be substantially overstepped during the relatively high‐pressure Barrovian regional metamorphism reflecting the limited permeability of the schists in peak metamorphic conditions. Fluid influx and hence reaction progress appear to be strongly controlled by subtle differences in deformation history. The remaining garnet fails to achieve chemical equilibrium during the reaction creating distinctive patchy compositional zoning. Such zoning in metamorphic garnet created during coupled dissolution–reprecipitation reactions may be difficult to recognize in higher grade pelites due to subsequent diffusive re‐equilibration. Fundamental assumptions about metamorphic processes are questioned by the lack of chemical equilibrium during this reaction and the restricted permeability of the regional metamorphic pelitic schists. In addition, the partial loss of prograde chemical and textural information from the garnet porphyroblasts cautions against their routine use as a reliable monitor of metamorphic history. However, the partial re‐equilibration of the porphyroblasts during coupled dissolution–reprecipitation opens possibilities of mapping reaction progress in garnet as a means of assessing fluid access during peak metamorphic conditions.  相似文献   

Particle‐size evidence of barrier estuary regime as a new proxy for ENSO climate variability          下载免费PDF全文

David W. Clarke  John F. Boyle  Andrew J. Plater 《地球表面变化过程与地形》2017,42(10):1520-1534

We investigate a new proxy for ENSO climate variability based on particle‐size data from long‐term, coastal sediment records preserved in a barrier estuary setting. Corresponding ~4–8 year periodicities identified from Wavelet analysis of particle‐size data from Pescadero Marsh in Central Coast California and rainfall data from San Francisco reflect established ENSO periodicity, as further evidenced in the Multivariate ENSO Index (MEI), and thus confirms an important ENSO control on both precipitation and barrier regime variability. Despite the fact that barrier estuary mean particle size is influenced by coastal erosion, precipitation and streamflow, balanced against barrier morphology and volume, it is encouraging that considerable correspondence can also be observed in the time series of MEI, regional rainfall and site‐based mean particle size over the period 1871–2008. This correspondence is, however, weakened after c.1970 by temporal variation in sedimentation rate and event‐based deposition. These confounding effects are more likely when: (i) accommodation space may be a limiting factor; and (ii) particularly strong El Niños, e.g. 1982/1983 and 1997/1998, deposit discrete >cm‐thick units during winter storms. The efficacy of the sediment record of climate variability appears not to be compromised by location within the back‐barrier setting, but it is limited to those El Niños that lead to barrier breakdown. For wider application of this particle size index of ENSO variability, it is important to establish a well‐resolved chronology and to sample the record at the appropriate interval to characterize deposition at a sub‐annual scale. Further, the sample site must be selected to limit the influence of decreasing accommodation space through time (infilling) and event‐based deposition. It is concluded that particle‐size data from back‐barrier sediment records have proven potential for preserving evidence of sub‐decadal climate variability, allowing researchers to explore temporal and spatial patterns in phenomena such as ENSO. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献