Groundwater Complexity in Urban Catchments: Shenzhen,Southern China     

Michele Lancia  Chunmiao Zheng  Xin He  David N. Lerner  Charles Andrews 《Ground water》2020,58(3):470-481

Groundwater interactions with surface water and sewers in an urban setting are complex, and classic hydrogeological approaches must be combined with anthropogenic elements to characterize them. The level of detail needed to understand these interactions is illustrated by the analysis of an urban subcatchment in the megacity of Shenzhen in southern China that has had a drastic urban expansion in the last 40 years. The study area is characterized by the Yanshanian granite that is widespread across southern-eastern China. The urban setting is studied using multitemporal analysis of satellite images, borehole investigations and field surveys. Given the local hydrostratigraphy, a conceptual model was developed to identify the physical and anthropogenic factors that regulate the urban groundwater system. Based on the conceptual model and the data collected from the field or compiled from the literature, the average annual effective recharge is estimated to be 290 mm/year, after the urbanization process. From rural to urban conditions, it is estimated that the effective recharge increased by 170% and sewers intercept at least 23% of the effective recharge. Groundwater captured by sewers reduces river flows and increases the required capacity and costs for waste water treatment plants.  相似文献   

Processes of alluvial fan sedimentation,basal rozel conglomerate formation,la têcte des hougues,Jersey, Channel Islands     

D. J. Went  M. J. Andrews  B. P. J. Williams 《Geological Journal》1988,23(1):75-84

The Rozel Conglomerate Formation, a coarse alluvial fan deposit, overlies the Bouley Rhyolite Formation beneath the headland called La Tete des Hougues, on the north coast of Jersey, Channel Islands. Here the rhyolites form an exhumed palaeotopography which in places is smoothly, but irregularly, eroded. Locally however, there is preservation of a deep Lower Palaeozoic weathering profile. Breccia is preserved spalled from these weathered profiles as a fossil scree deposit, which has subsequently been hydraulically reworked in a palaeotopographic low. Overlying the breccia is a prograding succession of alluvial fan sediments. A 4m thick, upwards-coarsening sequence of silty sandstones and fine pebble conglomerates is succeeded by the incision of a 3m deep channel. This is overlain by a 28m thick, upwards-fining sequence of coarse debris flow and streamflood conglomerates. The lower unit is interpreted as a prograding fan sector of reworked fan material, whilst the upper unit is thought to reflect the avulsive initiation and gradual abandonment of a fan lobe sourced from a northern hinterland.  相似文献   

Retreat of the Smith Sound Ice Stream in the Early Holocene     

Anne E. Jennings  John T. Andrews  Brett Oliver  Maureen Walczak  Alan Mix 《Boreas: An International Journal of Quaternary Research》2019,48(4):825-840

Nares Strait, a major connection between the Arctic Ocean and Baffin Bay, was blocked by coalescent Innuitian and Greenland ice sheets during the last glaciation. This paper focuses on the events and processes leading to the opening of the strait and the environmental response to establishment of the Arctic‐Atlantic throughflow. The study is based on sedimentological, mineralogical and foraminiferal analyses of radiocarbon‐dated cores 2001LSSL‐0014PC and TC from northern Baffin Bay. Radiocarbon dates on benthic foraminifera were calibrated with ΔR = 220±20 years. Basal compact pebbly mud is interpreted as a subglacial deposit formed by glacial overriding of unconsolidated marine sediments. It is overlain by ice‐proximal (red/grey laminated, ice‐proximal glaciomarine unit barren of foraminifera and containing >2 mm clasts interpreted as ice‐rafted debris) to ice‐distal (calcareous, grey pebbly mud with foraminifera indicative of a stratified water column with chilled Atlantic Water fauna and species associated with perennial and then seasonal sea ice cover) glacial marine sediment units. The age model indicates ice retreat into Smith Sound as early as c. 11.7 and as late as c. 11.2 cal. ka BP followed by progressively more distal glaciomarine conditions as the ice margin retreated toward the Kennedy Channel. We hypothesize that a distinct IRD layer deposited between 9.3 and 9 (9.4–8.9 1σ) cal. ka BP marks the break‐up of ice in Kennedy Channel resulting in the opening of Nares Strait as an Arctic‐Atlantic throughflow. Overlying foraminiferal assemblages indicate enhanced marine productivity consistent with entry of nutrient‐rich Arctic Surface Water. A pronounced rise in agglutinated foraminifers and sand‐sized diatoms, and loss of detrital calcite characterize the uppermost bioturbated mud, which was deposited after 4.8 (3.67–5.55 1σ) cal. ka BP. The timing of the transition is poorly resolved as it coincides with the slow sedimentation rates that ensued after the ice margins retreated onto land.  相似文献   

Varying sediment sources (Hudson Strait,Cumberland Sound,Baffin Bay) to the NW Labrador Sea slope between and during Heinrich events 0 to 4     

J. T. Andrews  D. C. Barber  A. E. Jennings  D. D. Eberl  B. Maclean  M. E. Kirby  J. S. Stoner 《第四纪科学杂志》2012,27(5):475-484

Core HU97048‐007PC was recovered from the continental Labrador Sea slope at a water depth of 945 m, 250 km seaward from the mouth of Cumberland Sound, and 400 km north of Hudson Strait. Cumberland Sound is a structural trough partly floored by Cretaceous mudstones and Paleozoic carbonates. The record extends from ～10 to 58 ka. On‐board logging revealed a complex series of lithofacies, including buff‐colored detrital carbonate‐rich sediments [Heinrich (H)‐events] frequently bracketed by black facies. We investigate the provenance of these facies using quantitative X‐ray diffraction on drill‐core samples from Paleozoic and Cretaceous bedrock from the SE Baffin Island Shelf, and on the < 2‐mm sediment fraction in a transect of five cores from Cumberland Sound to the NW Labrador Sea. A sediment unmixing program was used to discriminate between sediment sources, which included dolomite‐rich sediments from Baffin Bay, calcite‐rich sediments from Hudson Strait and discrete sources from Cumberland Sound. Results indicated that the bulk of the sediment was derived from Cumberland Sound, but Baffin Bay contributed to sediments coeval with H‐0 (Younger Dryas), whereas Hudson Strait was the source during H‐events 1–4. Contributions from the Cretaceous outcrops within Cumberland Sound bracket H‐events, thus both leading and lagging Hudson Strait‐sourced H‐events. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

A regional and global analysis of carbon dioxide physiological forcing and its impact on climate     

Timothy Andrews  Marie Doutriaux-Boucher  Olivier Boucher  Piers M. Forster 《Climate Dynamics》2011,36(3-4):783-792

An increase in atmospheric carbon dioxide concentration has both a radiative (greenhouse) effect and a physiological effect on climate. The physiological effect forces climate as plant stomata do not open as wide under enhanced CO₂ levels and this alters the surface energy balance by reducing the evapotranspiration flux to the atmosphere, a process referred to as ‘carbon dioxide physiological forcing’. Here the climate impact of the carbon dioxide physiological forcing is isolated using an ensemble of twelve 5-year experiments with the Met Office Hadley Centre HadCM3LC fully coupled atmosphere–ocean model where atmospheric carbon dioxide levels are instantaneously quadrupled and thereafter held constant. Fast responses (within a few months) to carbon dioxide physiological forcing are analyzed at a global and regional scale. Results show a strong influence of the physiological forcing on the land surface energy budget, hydrological cycle and near surface climate. For example, global precipitation rate reduces by ~3% with significant decreases over most land-regions, mainly from reductions to convective rainfall. This fast hydrological response is still evident after 5 years of model integration. Decreased evapotranspiration over land also leads to land surface warming and a drying of near surface air, both of which lead to significant reductions in near surface relative humidity (~6%) and cloud fraction (~3%). Patterns of fast responses consistently show that results are largest in the Amazon and central African forest, and to a lesser extent in the boreal and temperate forest. Carbon dioxide physiological forcing could be a source of uncertainty in many model predicted quantities, such as climate sensitivity, transient climate response and the hydrological sensitivity. These results highlight the importance of including biological components of the Earth system in climate change studies.  相似文献   

Unusual isotopic phenomena in Welsh quarry water and carbonate crusts     

Julian E. Andrews  Simon G. Gare  Paul F. Dennis 《地学学报》1997,9(2):67-70

Modern terrestrial speleothem-like calcareous deposits in streams draining a disused lime quarry on Black Mountain, South Wales have anomalously negative δ¹⁸O and δ¹³C compositions compared with other similar European deposits. Black Mountain water chemistry is unusual only in its locally very high pH (> 11.5) and carbonate ion concentrations. The high pH is caused by dissolution of lime spoil, resulting in high OH^– concentrations. This high alkalinity causes uptake of atmospheric CO₂ and strong fractionation of both carbon and oxygen stable isotopes, resulting in calcite precipitates with unusually negative isotopic compositions. Since shifts in δ¹⁸O of < 1° are highly significant for Holocene palaeoclimate reconstructions, depletions caused by hyperalkaline waters must be avoided. While extreme lime spoil contamination should be obvious, less heavily affected sites will record smaller fractionation effects and might escape detection. Even small depletions from low-level contamination will have large effects on palaeotemperatures based on carbonate crust δ¹⁸O values.  相似文献   

Exposure history of the St‐Robert (H5) fall     

I. Leya  R. Wieler  K. Aggrey  G. F. Herzog  C. Schnabel  K. Metzler  A. R. Hildebrand  M. Bouchard  A. J. T. Jull  H. R. Andrews  M‐S. Wang  T. E. Ferko  M. E. Lipschutz  J. F. Wacker  S. Neumann  R. Michel 《Meteoritics & planetary science》2001,36(11):1479-1494

Abstract— The compositionally typical H5 chondrite St‐Robert has an exposure age, 7.8 Ma, indistinguishable from that of the main cluster of H chondrites. Small values of the cosmogenic ²²Ne/²¹Ne ratio in interior samples imply a pre‐atmospheric radius on the order of 40 cm. Sample depths based on tracks and the production rates of Bhattacharya et al. (1973) range from 6 to ～40 cm and are generally larger than depths estimated from published ⁶⁰Co activities, perhaps because the track production rates adopted are too high. Depth profiles of the production rates of ¹⁴C, ³⁶Cl, ²⁶Al, ¹⁰Be, and ²¹Ne in stony material show increases with depth and reach levels 5% to 15% higher than expected from modeling calculations. The maximum concentrations in St‐Robert are, however, generally comparable to those measured for the L5 chondrite, Knyahinya, whose pre‐atmospheric radius of ～45 cm is thought to lead to the maximum possible production rates in chondrites. We infer that the pre‐atmospheric radius of St‐Robert was within 5 cm of the value that supports maximum production rates (i.e., 45 ± 5 cm). This radius corresponds to a pre‐atmospheric mass of (1.3 ± 0.4) × 10³ kg. The agreement of exposure ages for St‐Robert obtained in several different ways and the similarity of the depth profiles for ¹⁴C, ²⁶Al, ¹⁰Be, and ²¹Ne argue against a lengthy pre‐exposure of St‐Robert on the parent body and against a two‐stage exposure after launch from the parent body. Following Morbidelli and Gladman (1998), we suggest that St‐Robert was chipped from deep in its parent body, spent the next 7–8 Ma without undergoing a major collision, was nudged gradually into an orbital resonance with Jupiter, and then traveled quickly to Earth.  相似文献   

Vorticity in the magnetosphere     

F. B. Knox  M. K. Andrews 《Planetary and Space Science》1974,22(12):1703-1709

It is shown that Birkeland current and vorticity in the magnetosphere are intimately related, suggesting the importance of taking explicit account of vorticity, particularly velocity shear, when considering magnetospheric motions. An equation of motion for the magnetosphere coupled to the ionosphere is derived. It is suggested that experience with MHD fluids generally might fruitfully be brought to bear on certain problems in the magnetosphere to answer the question, not ‘why a sheet of Birkeland current,’ but rather ‘why a localised velocity shear.’  相似文献   

Assessment of buckling-restrained braced frame reliability using an experimental limit-state model and stochastic dynamic analysis     

Blake M.Andrews  Junho Song  Larry A.Fahnestock 《地震工程与工程振动(英文版)》2009,8(3):373-385

Buckling-restrained braces(BRBs)have recently become popular in the United States for use as primary members of seismic lateral-force-resisting systems.A BRB is a steel brace that does not buckle in compression but instead yields in both tension and compression.Although design guidelines for BRB applications have been developed,systematic procedures for assessing performance and quantifying reliability are still needed.This paper presents an analytical framework for assessing buckling-restrained braced f...  相似文献   

Galaxy clusters in the line of sight to background quasars – II. Environmental effects on the sizes of baryonic halo sizes     

Nelson Padilla  Ivan Lacerna  Sebastián Lopez  L. Felipe Barrientos  Paulina Lira  Heather Andrews  Nicolás Tejos 《Monthly notices of the Royal Astronomical Society》2009,395(2):1135-1145

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