Dissolved organic matter tracers reveal contrasting characteristics across high arsenic aquifers in Cambodia:A fluorescence spectroscopy study     

Laura A.Richards  Dan J.Lapworth  Daniel Magnone  Daren C.Gooddy  Lee Chambers  Peter J.Williams  Bart E.van Dongen  David A.Polya 《地学前缘(英文版)》2019,10(5):1653-1667

Organic matter in the environment is involved in many biogeochemical processes,including the mobilization of geogenic trace elements,such as arsenic,into groundwater.In this paper we present the use of fluorescence spectroscopy to characterize the dissolved organic matter(DOM)pool in heavily arsenicaffected groundwaters in Kandal Province,Cambodia.The fluorescence DOM(fDOM)characteristics between contrasting field areas of differing dominant lithologies were compared and linked to other hydrogeochemical parameters,including arsenic and dissolved methane as well as selected sedimentary characteristics.Absorbance-corrected fluorescence indices were used to characterize depth profiles and compare field areas.Groundwater fDOM was generally dominated by terrestrial humic and fulvic-like components,with relatively small contributions from microbially-derived,tryptophan-like components.Groundwater fDOM from sand-dominated sequences typically contained lower tryptophan-like,lower fulvic-like and lower humic-like components,was less bioavailable,and had higher humification index than clay-dominated sequences.Methane concentrations were strongly correlated with fDOM bioavailability as well as with tryptophan-like components,suggesting that groundwater methane in these arsenic-prone aquifers is likely of biogenic origin.A comparison of fDOM tracers with sedimentary OM tracers is consistent with the hypothesis that external,surface-derived contributions to the aqueous DOM pool are an important control on groundwater hydrogeochemistry.  相似文献   

Late Quaternary stratigraphic signature, offshore from the Dutch barrier shoreline     

Elisabeth C. Kosters  Bart E. J. M. VanMierlo  Nico H. Verbeek  Bart J. Posthumus  Thomas M. McGee  Jan Brouwer 《Sedimentary Geology》1992,80(3-4):199-212

More than 400 km of high-resolution, partially digitally acquired seismic data were collected in a 30 × 60 km area offshore from the Dutch mesotidal barrier island shoreline, in order to analyze the Holocene transgressive sequence.

The investigated area was subaerially exposed during the most recent (Weichselian) Pleistocene lowstand and glaciated during the previous (Saale/Illinoian) glacial period. Sea level was probably at a level comparable to that of the present during the intervening Eem/Sangamonian highstand.

The area's seismic signature is characterized by several levels of channelization, separated by major, area-wide high-amplitude reflectors. The lowermost aerial reflector represents the Saale boulder clay. The largest channel system, which cuts this reflector, was incised during the Older Dryas cooling event and filled during the Allerød warming period. It was subsequently re-incised during the Younger Dryas and refilled during the early Holocene. The most pronounced and extensive reflector represents the base of the Holocene, and almost everywhere equals the planed-off top of the Eem highstand section. This reflector is overlain by aggradational facies, separated by one level of channelization and one planed-off (ravinement?) surface. The most prominent type of seismic facies above the lowermost level of channelization is a set of progradational clinoforms, which is interpreted as a preserved ebb-tidal delta system. This system is associated with the first Holocene shoreline of ca. 7500 yrs BP.

The eastern part of the study area contains sand ridges with a complex pattern of internal cross-stratification. Ridge-crest sediments are very well-sorted with a mean grain size of 2.8-2.6 φ (ca. 0.15 mm), whereas sediments in the troughs are well-sorted with a mean grain size of 1.8-0.8 φ (0.25–0.5 mm). Origin of these ridges is tentatively thought to be related to reworking since 5000 yrs BP, when the dynamic regime was more or less similar to that of the present and sediment supply had decreased substantially.  相似文献   

On volatile element trends in gas-rich meteorites     

Gerhard Bart  Michael E. Lipschutz 《Geochimica et cosmochimica acta》1979,43(9):1499-1504

Study of 10 volatile elements (and non-volatile Co) in co-existing light and dark portions of 5 gas-rich chondrites indicates patterns of distinct but non-uniform enrichment of volatile elements. Only Cs is enriched in all samples; Hi and Tl enrichments covary. The observed enrichments are inconsistent with prior suggestions of admixture of C1 or C2 chondritic matter, whether pristine or partly devolatilized, but suggest that both light and dark portions of each chondrite represents a compositionally more extended sampling of parental nebular material than hitherto known.  相似文献   

Erratum to Michael H. Bradbury and Bart Baeyens (2005) “Experimental measurements and modeling of sorption competition on montmorillonite”, Geochimica et Cosmochimica Acta 69, 4187-4197     

Michael H. Bradbury  Bart Baeyens 《Geochimica et cosmochimica acta》2005,69(24):5863-5864

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Soil and stream sediment geochemical dispersion over the Bell Springs deposit, Hog Ranch Mine, Washoe County, Nevada     

Steven D. Bussey  Paul M. Taufen  Bart J. Suchomel  Malcolm Ward 《Journal of Geochemical Exploration》1993,47(1-3)

The Bell Springs deposit is a bulk-tonnage, low-grade gold deposit, formed in a hot-spring environment, that is hosted by middle Miocene weakly peralkaline, high-silica rhyolite ash flows and rheomorphic tuffs. Ore grade mineralization over about 460 × 460 m was controlled by northeast- and northwest-trending structures. Sixty-nine soil samples collected along a traverse across the Bell Springs deposit, screened into six mesh size fractions, +10, −10+35, −35+80, −80+120, −120+200, and −200, were treated by low-detection-limit acid digestion/organic extraction procedures, and analyzed by ICP or graphite furnace techniques for Au, Ag, As, Bi, Cd, Cu, Ga, Hg, Mo, Pb, Sb, Se, Te, Tl, and Zn. Twenty-five stream-sediment samples were collected from a drainage crossing mineralization and from a nearby tributary. Sediment size fractions of −200 mesh and −10+200 mesh were analyzed by the same procedures used for soils. In addition, analyses of bulk leachable gold via cyanide leach method (BLEG) was done on bulk −10 mesh sediments.Anomalous Au, Ag, As, Sb, and Mo in all soil size fractions revealed the underlying ore. Areas with anomalous Sb and As were about three times larger than areas with anomalous Au and Ag. Analyses of fine-fractions of stream sediments provided the best-defined Au anomalies in drainages. A multi-element factor calculated by multiplying Au, As, Sb, and Mo reinforced anomalous Au in drainages and correlated well with Bell Springs mineralization.  相似文献   

Stabilizing greenhouse gas concentrations at low levels: an assessment of reduction strategies and costs   总被引：2，自引：8，他引：2  

Detlef P. van Vuuren  Michel G. J. den Elzen  Paul L. Lucas  Bas Eickhout  Bart J. Strengers  Bas van Ruijven  Steven Wonink  Roy van Houdt 《Climatic change》2007,81(2):119-159

On the basis of the IPCC B2, A1b and B1 baseline scenarios, mitigation scenarios were developed that stabilize greenhouse gas concentrations at 650, 550 and 450 and – subject to specific assumptions – 400 ppm CO₂-eq. The analysis takes into account a large number of reduction options, such as reductions of non-CO₂ gases, carbon plantations and measures in the energy system. The study shows stabilization as low as 450 ppm CO₂-eq. to be technically feasible, even given relatively high baseline scenarios. To achieve these lower concentration levels, global emissions need to peak within the first two decades. The net present value of abatement costs for the B2 baseline scenario (a medium scenario) increases from 0.2% of cumulative GDP to 1.1% as the shift is made from 650 to 450 ppm. On the other hand, the probability of meeting a two-degree target increases from 0%–10% to 20%–70%. The mitigation scenarios lead to lower emissions of regional air pollutants but also to increased land use. The uncertainty in the cost estimates is at least in the order of 50%, with the most important uncertainties including land-use emissions, the potential for bio-energy and the contribution of energy efficiency. Furthermore, creating the right socio-economic and political conditions for mitigation is more important than any of the technical constraints.  相似文献   

Poroelastic behaviour of saturated brittle rock with anisotropic damage     

M. Bart  J. F. Shao  D. Lydzba 《国际地质力学数值与分析法杂志》2000,24(15):1139-1154

A new anisotropic poroelastic damage model is proposed for saturated brittle porous materials. The model is formulated in the framework of the continuum damage mechanics. A second‐rank symmetric tensor is used to characterize material damage due to oriented microcracks. The classic Biot poroelastic theory is then extended to include poroelastic damage coupling. Both the deterioration of elastic properties and poroelastic coefficients is taken into account. A suitable procedure for determination of model parameters from standard laboratory tests is presented. The validity of the model is tested through comparison between numerical predictions and experimental data in various loading conditions. The overall performance of the model is evaluated. The choice of relevant effective stress for the microcrack propagation criterion in saturated cohesive geomaterials is discussed. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

One‐year monitoring of the Z24‐Bridge: environmental effects versus damage events     

Bart Peeters  Guido De Roeck 《地震工程与结构动力学》2001,30(2):149-171

When using the analysis of vibration measurements as a tool for health monitoring of bridges, the problem arises of separating abnormal changes from normal changes in the dynamic behaviour. Normal changes are caused by varying environmental conditions such as humidity, wind and most important, temperature. The temperature may have an impact on the boundary conditions and the material properties. Abnormal changes on the other hand are caused by a loss of stiffness somewhere along the bridge. It is clear that the normal changes should not raise an alarm in the monitoring system (i.e. a false positive), whereas the abnormal changes may be critical for the structure's safety. In the frame of the European SIMCES‐project, the Z24‐Bridge in Switzerland was monitored during almost one year before it was artificially damaged. Black‐box models are determined from the healthy‐bridge data. These models describe the variations of eigenfrequencies as a function of temperature. New data are compared with the models. If an eigenfrequency exceeds certain confidence intervals of the model, there is probably another cause than the temperature that drives the eigenfrequency variations, for instance damage. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Effect of channel deepening on tidal flow and sediment transport—part II: muddy channels     

Leo van Rijn  Bart Grasmeijer 《Ocean Dynamics》2018,68(11):1481-1501

Natural tidal channels often need deepening for navigation purposes (larger vessels). The depth increase may lead to tidal amplification, salt intrusion over longer distances, and increasing sand and mud import. Increasing fine sediment import, in turn, may start a process in which the sediment concentration progressively increases until the river becomes hyper-turbid, which may lead to increased dredging volumes and to decreased ecological values. These effects can be modeled and studied using detailed 3D models. Reliable simplified models for a first quick engineering evaluation are however lacking. In this paper, we apply both simplified and detailed 3D models to analyze the effects of channel deepening in prismatic and weakly converging tidal channels with saturated mud flow. The objective is to gain quantitative understanding of the effects of channel deepening on mud transport. We developed a simplified tidal mud model describing most relevant processes and effects in saturated mud flows with only minor horizontal transport gradients (quasi uniform conditions). The simplified model is not valid for non-saturated mud flow conditions. This model can either be used in standalone mode or in post-processing mode with computed near-bed velocities from a 3D hydrodynamic model as an input. The standalone model has been compared to various field data sets. Mud transport processes in the mouth region of muddy tidal channels can be realistically represented by the simplified model, if sufficient salinity and sediment data are available for calibration. The simulation of tidal mud transport and the behavior of an estuarine turbidity maximum (ETM) in saturated and non-saturated mud flow conditions cannot be represented by the simplified model and requires the application of a detailed 3D model.  相似文献   

Differential transport and degradation of bulk organic carbon and specific terrestrial biomarkers in the surface waters of a sub-arctic brackish bay mixing zone     

Bart E. van Dongen  Zdenek Zencak   rjan Gustafsson 《Marine Chemistry》2008,112(3-4):203-214

Detailed organic geochemical analyses were performed on surface water particulate samples of the lower Kalix River and northern Bothnian Bay collected during the spring flood of 2005. Both bulk geochemical and molecular biomarker analyses indicated a predominance of terrestrially-derived particulate organic matter (POM), both of higher plant and Sphagnum origin in the low salinity zone (LSZ) of the Kalix River estuary, with an increasing contribution of marine-derived POM in the offshore Bothnian Bay basin.Two-dimensional box modeling of the mixed surface layer in the LSZ indicated that 65% of the particulate organic carbon (POC) and between 73 and 93% of the terrestrial biomarker classes analyzed (high molecular weight n-alkanes, n-alkanoic acids and n-alkanols as well as sitosterol) were degraded in the course of their weeklong transit through the inner LSZ during the spring flood. This corresponds to field-based degradation rate constants for the biomarkers of 0.5 and 2.5 day^− 1, which are similar to results reported from mesocosm experiments for related compounds. The degradation rate constant for terrestrial POC of 0.38 day^− 1 was about 20 times larger than for DOC and suggests that POC mineralization stands for 44% of the total mineralization, which is much larger than previously considered.This sub-arctic river-export regime has a geochemistry resembling that of neighboring western Russian Arctic Rivers, suggesting that a large part of the OM coastally exported from northernmost Eurasian soils may be degraded within the vicinity of the river mouths and putatively be released as carbon dioxide. The 65% degradation of terrestrial POC in the coastal surface water of this sub-arctic recipient is substantially larger than a global-average of 35% used in recent budget estimates of the fate of terrestrially-exported POC on the pan-arctic shelves. Considering ongoing and predicted changes in the Arctic Region due to global warming a more efficient degradation of river-exported terrestrial POC may have far-reaching consequences for the large-scale biogeochemical cycling of carbon in the pan-arctic region and beyond.  相似文献