Comment on “Elevated tungsten and cobalt in airborne particulates in Fallon,Nevada: Possible implications for the childhood leukemia cluster” by P.R. Sheppard,G. Ridenour,R.J. Speakman and M.L. Witten     

《Applied Geochemistry》2006,21(6):1083-1085

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Discriminating between pore‐filling load and bed‐structure load: a new porosity‐based method,exemplified for the river Rhine     

ROY M. FRINGS  MAARTEN G. KLEINHANS  STEFAN VOLLMER 《Sedimentology》2008,55(6):1571-1593

Sediments contained in the river bed do not necessarily contribute to morphological change. The finest part of the sediment mixture often fills the pores between the larger grains and can be removed without causing a drop in bed level. The discrimination between pore‐filling load and bed‐structure load, therefore, is of practical importance for morphological predictions. In this study, a new method is proposed to estimate the cut‐off grain size that forms the boundary between pore‐filling load and bed‐structure load. The method evaluates the pore structure of the river bed geometrically. Only detailed grain‐size distributions of the river bed are required as input to the method. A preliminary validation shows that the calculated porosity and cut‐off size values agree well with experimental data. Application of the new cut‐off size method to the river Rhine demonstrates that the estimated cut‐off size decreases in a downstream direction from about 2 to 0·05 mm, covariant with the downstream fining of bed sediments. Grain size fractions that are pore‐filling load in the upstream part of the river thus gradually become bed‐structure load in the downstream part. The estimated (mass) percentage of pore‐filling load in the river bed ranges from 0% in areas with a unimodal river bed, to about 22% in reaches with a bimodal sand‐gravel bed. The estimated bed porosity varies between 0·15 and 0·35, which is considerably less than the often‐used standard value of 0·40. The predicted cut‐off size between pore‐filling load and bed‐structure load (D_c,p) is fundamentally different from the cut‐off size between wash‐load and bed‐material load (D_c,w), irrespective of the method used to determine D_c,p or D_c,w. D_c,w values are in the order of 10^?1 mm and mainly dependent on the flow characteristics, whereas D_c,p values are generally much larger (about 10⁰ mm in gravel‐bed rivers) and dependent on the bed composition. Knowledge of D_c,w is important for the prediction of the total sediment transport in a river (including suspended fines that do not interact with the bed), whereas knowledge of D_c,p helps to improve morphological predictions, especially if spatial variations in D_c,p are taken into account. An alternative to using a spatially variable value of D_c,p in morphological models is to use a spatially variable bed porosity, which can also be predicted with the new method. In addition to the morphological benefits, the new method also has sedimentological applications. The possibility to determine quickly whether a sediment mixture is clast‐supported or matrix‐supported may help to better understand downstream fining trends, sediment entrainment thresholds and variations in hydraulic conductivity.  相似文献   

Pyrite formation driven by MSW landfill leachate in the Madrid Basin, Spain     

Ricardo Castelló  Clemente Recio  Pilar Morillas  Carmen Vizcayno 《Environmental Geology》2008,54(4):679-688

The role of municipal solid waste (MSW) landfill leachate on the genesis of minor amounts of pyrite associated with gypsum in an otherwise predominantly evaporitic sequence was studied in geological and geochemical terms. The potential association between landfill leachate and the conditions required for bacterial reduction of sulfate and fixation of H₂S as pyrite were examined. The lithological column was generally found to contain little or no Fe. The δ³⁴S values for sulfates were consistent with previously reported data; however, the measured δ¹⁸O values were slightly higher. Sulfides disseminated in the marl/lutite exhibited higher δ³⁴S values (≈−8‰) than gypsum-coating pyrite crystals (δ³⁴S < −30‰). Dissolution of gypsum to sulfate and the supply of metabolizable organic matter and Fe required for H₂S fixation as sulfides may have originated from landfill leachate. Intermittent availability of leachate, a result of the precipitation regime, can facilitate sulfur disproportionation and lead to fractionations as high as   相似文献   

Proterozoic (pre-Ediacaran) glaciation and the high obliquity,low-latitude ice,strong seasonality (HOLIST) hypothesis: Principles and tests     

《Earth》2008,88(3-4):61-93

Sedimentological observations and palaeomagnetic data for Cryogenian glacial deposits present the climatic paradox of grounded glaciers and in situ cold climate near sea-level, glaciomarine deposition, and accompanying large (up to 40 °C) seasonal changes of temperature, all in low to near-equatorial (< 10°) palaeolatitudes (equated with geographic latitudes). Neither the “snowball Earth” nor the “slushball Earth” hypothesis can account for such strong seasonality near the palaeoequator, which together with findings from sedimentology, chemostratigraphy, biogeochemistry, micropalaeontology, geochronology and climate modelling argue against those scenarios. An alternative explanation of glaciation and strong seasonality in low palaeolatitudes is offered by a high (> 54°) obliquity of the ecliptic, which would render the equator cooler than the poles, on average, and amplify global seasonality. A high obliquity per se would not have been a primary trigger for glaciation, but would have strongly influenced the latitudinal distribution of glaciers. The principle of low-latitude glaciation on a terrestrial planet with high obliquity is validated by theoretical studies and observations of Mars. A high obliquity for the early Earth is a likely outcome of a single giant impact at 4.5 Ga, the widely favoured mechanism for lunar origin. This implies that a high obliquity could have prevailed during most of the Precambrian, controlling the low palaeolatitude of glaciations in the early and late Palaeoproterozoic and Cryogenian. It is postulated that the obliquity changed to < 54° between the termination of the last Cryogenian low-palaeolatitude glaciation at ≤ 635 Ma and the initiation of Late Ordovician–Early Silurian circum-polar glaciation at 445 Ma.The High Obliquity, Low-latitude Ice, STrong seasonality (HOLIST) hypothesis for pre-Ediacaran glaciation emerges favourably from numerous glacial and non-glacial tests. The hypothesis is in accord with such established or implied features of Cryogenian glaciogenic successions as extensive and long-lived open seas, an active hydrological cycle, aridity and palaeowesterly (reversed zonal) winds in low palaeolatitudes, and the apparent diachronism or non-correlation of some low-palaeolatitude glaciations. A pre-Ediacaran high obliquity also offers a viable solution of the faint young Sun paradox of a warm Archaean Earth. Furthermore, reduction of obliquity during the Ediacaran–early Palaeozoic would have yielded a more habitable globe with much reduced seasonal stresses and may have been an important factor influencing the unique evolutionary events of the Ediacaran and Cambrian. The palaeolatitudinal distribution of evaporites cannot discriminate unambiguously between high- and low-obliquity states for the pre-Ediacaran Earth. Intervals of true polar wander such as postulated by others for the Ediacaran and Early Cambrian imply major mass-redistributions within the Earth at those times, which may provide a potential mechanism for reducing the obliquity during the Ediacaran–early Palaeozoic.  相似文献   

Sensitivity to stress of the estuarine bivalve Macoma balthica from areas between the Netherlands and its southern limits (Gironde)     

H. Hummel  C. Amiard-Triquet  G. Bachelet  M. Desprez  J. Marchand  B. Sylvand  J.C. Amiard  H. Rybarczyk  R.H. Bogaards  J. Sinke  Y. De Wit  L. De Wolf 《Journal of Sea Research》1996,35(4):315-321

Variation in the sensitivity to stress of Macoma balthica was measured in several French and Dutch estuaries. For adult and juvenile Macoma balthica exposed to copper under conditions of starvation, differences in mortality rate, condition, glycogen, burrowing rate and copper content were assessed. No significant differences were observed between adults and juveniles; the influence of treatment and origin was always evident. Animals from the most southern estuaries, Loire and Gironde, near to the species's southern limit of distribution, showed, in the field, the strongest deviations for the ecophysiological traits measured, and were in the experiments the most sensitive to stress.  相似文献   

Environmental overview of Eckernförde Bay,northern Germany     

T. H. Orsi  F. Werner  D. Milkert  A. L. Anderson  W. R. Bryant 《Geo-Marine Letters》1996,16(3):140-147

This environmental overview of Eckernförde Bay (northern Germany) summarizes the results of previous studies relevant to the Office of Naval Research's Coastal Benthic Boundary Layer (CBBL) Baltic field exercise conducted during 1993–1994. Significant environmental characteristics include the following: (1) surface sediment distribution is related to water depth, dictated primarily by hydrodynamic reworking of older glacial deposits; (2) the origin and characteristics of small-scale sedimentary structures depend on storm-generated waves and currents; (3) the proximity of the sea surface and sediment —water interface results in a pelagic—benthic coupling that drives biogeochemical processes and produces organicrich, acoustically turbid sediments; and (4) the bay floor is complicated topographically by pockmarks and manmade sedimentary structures.  相似文献   

Site fidelity and dispersal patterns of domestic triploid steelhead trout (Oncorhynchus Mykiss Walbaum) released to the wild     

Bridger  C. J.; Booth  R. K.; McKinley  R. S.; Scruton  D. A. 《ICES Journal of Marine Science》2001,58(2):510-516

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The dynamics of wave induced ship motions in shallow water     

I.A. Svendsen  P.A. Madsen 《Ocean Engineering》1981,8(5):443-479

The analytical method developed by Svendsen (1968) for a forced heave motion is extended to the general problem of wave induced heave, roll and sway motions of a long ship at a depth of water which is only slightly larger than the draught of the ship. This corresponds, for example, to the situation of a fully loaded ship in a harbour area.After linearization of the problem, the water motion is considered for each of the three individual motions and for the wave reflection-transmission problem for a fixed ship. The ensuing results for the forces on the ship are then synthesized to form the equations of motion, which are presented with all coefficients given, including mooring forces.Analytical and numerical results are given for the three components of motion, for the associated resonance frequencies, and for the hydrodynamic masses and moments of inertia. Finally, the assumptions used are analyzed and evaluated by comparison with measurements and with other results for a special case.  相似文献   

Rare species, habitat diversity and functional redundancy in marine benthos   总被引：1，自引：0，他引：1  

Kari E. Ellingsen  Judi E. Hewitt  Simon F. Thrush 《Journal of Sea Research》2007,58(4):291-301

Macro-ecological theories relating species richness, abundance, range size, biological traits and environmental tolerance have rarely been tested in marine soft-sediments, despite the spatial extent of these habitats and the inherent richness of resident communities. This study examines the contribution of rare species to marine soft-sediment communities from New Zealand, focussing on the relationships of range size with abundance, environment, habitat diversity and life history traits. 54% of the 351 species sampled exhibited restricted ranges (found at ≤ 2 sites). In contrast to many terrestrial systems, we observed only a weak positive relationship between abundance and frequency of occurrence. Restricted-range species were not randomly distributed, with their distribution related to habitat characteristics, suggesting an important link between habitat diversity and rarity. They exhibited a similar range of traits to the total observed species pool, suggesting that they are not only important to biodiversity but could play a role in stability. Restricted range species were generally not small and this, together with the number of different biological traits represented, suggests that rare species are important to the functioning of marine systems. Thus, our results highlight the importance of considering rare species in habitat-based approaches to conservation.  相似文献   

内蒙古兴安盟杜尔基岩体特征研究          下载免费PDF全文

丛利民  李国志 《甘肃地质》2008,(3):74-79

内蒙古兴安盟杜尔基岩体位于大兴安岭中南段,岩性主要为中—细粒二长花岗（斑）岩、中—粗粒二长花岗岩、细粒二长花岗岩。岩石化学分析结果属于碱性岩系列,具有高硅、高钾、富碱、过铝、贫铁、镁、钙特征。稀土元素总量平均值为112．43μg／g,球粒陨石标准化曲线整体平缓右倾,具有Eu负异常;微量元素蛛网图解表现为“W”型形态．具有明显的Sr、Ba、Ti负异常,反映了强烈的分离结晶作用存在。4个样品K-Ar全岩法测年结果为100．15-120．29Ma,说明岩体形成于早白垩世。反映杜尔基地区在早自垩世可能处于相对稳定的拉张环境。  相似文献