Regional controls on geomorphology, hydrology, and ecosystem integrity in the Orinoco Delta, Venezuela     

Andrew G. Warne  Robert H. Meade  William A. White  Edgar H. Guevara  James Gibeaut  Rebecca C. Smyth  Andres Aslan  Thomas Tremblay 《Geomorphology》2002,44(3-4)

Interacting river discharge, tidal oscillation, and tropical rainfall across the 22,000 km² Orinoco delta plain support diverse fresh and brackish water ecosystems. To develop environmental baseline information for this largely unpopulated region, we evaluate major coastal plain, shallow marine, and river systems of northeastern South America, which serves to identify principal sources and controls of water and sediment flow into, through, and out of the Orinoco Delta.The regional analysis includes a summary of the geology, hydrodynamics, sediment dynamics, and geomorphic characteristics of the Orinoco drainage basin, river, and delta system. Because the Amazon River is a major source of sediment deposited along the Orinoco coast, we summarize Amazon water and sediment input to the northeastern South American littoral zone. We investigate sediment dynamics and geomorphology of the Guiana coast, where marine processes and Holocene history are similar to the Orinoco coast.Major factors controlling Orinoco Delta water and sediment dynamics include the pronounced annual flood discharge; the uneven distribution of water and sediment discharge across the delta plain; discharge of large volumes of water with low sediment concentrations through the Río Grande and Araguao distributaries; water and sediment dynamics associated with the Guayana littoral current along the northeastern South American coast; inflow of large volumes of Amazon sediment to the Orinoco coast; development of a fresh water plume seaward of Boca Grande; disruption of the Guayana Current by Trinidad, Boca de Serpientes, and Gulf of Paria; and the constriction at Boca de Serpientes.  相似文献   

Os isotope systematics in ocean island basalts   总被引：5，自引：0，他引：5  

Laurie Reisberg  Alan Zindler  Franco Marcantonio  William White  Derek Wyman  Barry Weaver 《Earth and Planetary Science Letters》1993,120(3-4):149-167

New ReOs isotopic results for Os-poor basalts from St. Helena, the Comores, Samoa, Pitcairn and Kerguelen dramatically expand the known range of initial ¹⁸⁶Os/¹⁸⁷Os ratios in OIBs to values as high as 1.7. In contrast to the Os isotopic uniformity of Os-rich basalts from the HIMU islands of Tubuai and Mangaia found by Hauri and Hart [1], our values for St. Helena span most of the known range of Os isotopic variability in oceanic basalts (initial ¹⁸⁷Os/¹⁸⁶Os ranges from 1.2 to 1.7). Generation of such radiogenic Os in the mantle requires melting of source materials that contain large proportions of recycled oceanic crust. The very low Os concentrations of most of the basalts analyzed here, however, leave them susceptible to modification via interaction with materials containing radiogenic Os in the near-surface environment. Thus the high ¹⁸⁶Os/¹⁸⁷Os ratios may result from assimilation of radiogenic Os-rich marine sediments, such as Mn oxides, within the volcanic piles traversed by these magmas en route to the surface. Furthermore, the Os isotopic signatures of Os-rich, olivine-laden OIBs may reflect the accumulation of lithospheric olivine, rather than simply their mantle source characteristics. The extent to which these processes alter the view of the mantle obtained via study of ReOs systematics in oceanic basalts is uncertain. These effects must be quantified before ReOs systematics in OIBs can be used with confidence to investigate the nature of mantle heterogeneity and its causes.  相似文献   

Negative inclination anomalies from the Medicine Lake Highland Lavas,Northern California     

Laurie Brown  Stanley A. Mertzman 《Earth and Planetary Science Letters》1979,42(1):121-126

Paleomagnetic directions have been determined for 21 flows of Quaternary age from the Medicine Lake Highlands in northern California. The mean direction for the area is I = 49.3° and D = 3.8° with an α₉₅ of 5.4°. The corresponding mean VGP is located at 78.0°N and 42.4°E, a point which is offset 12° to the far, right-handed side of the rotation axis from the sampling site. The results here indicate only order of magnitude agreement with proposed models for offset poles. Together with other data from western United States there is an indication that large-scale regional field variations produce the observed inclination anomalies.  相似文献   

Control of traffic-induced vibration in buildings using vehicle suspension systems     

M.O. Al-Hunaidi  J.H. Rainer  M. Tremblay 《Soil Dynamics and Earthquake Engineering》1996,15(4):245-254

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After the exodus: Exploring migrant attitudes to documentation,brokerage and employment following the 2014 mass withdrawal of Cambodian workers from Thailand          下载免费PDF全文

Sabina Lawreniuk  Laurie Parsons 《Singapore journal of tropical geography》2017,38(3):350-369

This paper uses the exodus of Cambodian migrant workers from Thailand in June 2014 as a focal point around which to explore Cambodian migrant attitudes towards the systems of documentation and brokerage that influence their movement. From the perspective of Cambodian returnees and their families, it builds on recent work exploring narratives of brokerage by demonstrating how documentation itself — and by extension the legality of migration — is viewed through a contextual lens. Specifically, it argues that documentation is not only viewed according to the formal regulatory framework governing migration between the two countries, but forms part of a more complex structure of influences in which norms of employment and brokerage are equally prominent. From this position, the paper suggests that migrants did not only respond directly to threats of a crackdown by authorities following the 2014 coup, but were additionally influenced by the actions of employers and brokers, whose guarantees of protection — or otherwise — were seen as vitally important in their migration decisions.  相似文献   

Carbon to nitrogen (C:N) stoichiometry of the spring–summer phytoplankton bloom in the North Water Polynya (NOW)     

Z.-P. Mei  L. Legendre  J.-. Tremblay  L.A. Miller  Y. Gratton  C. Lovejoy  P.L. Yager  M. Gosselin 《Deep Sea Research Part I: Oceanographic Research Papers》2005,52(12):2301-2314

The carbon to nitrogen (C:N) stoichiometry of phytoplankton production varied significantly during the spring–summer bloom in the North Water Polynya (NOW), from April through July 1998. The molar ratio of particulate organic carbon (POC) to nitrogen (PON) production by phytoplankton (ΔPOC:ΔPON) increased from 5.8 during April through early June to 8.9 in late June and July. The molar dissolved inorganic carbon (DIC) to nitrate+nitrite (NO₃) drawdown ratio (ΔDIC: ΔNO₃) increased from 6.7 in April and May, to 11.9 in June (no estimate for July because of ice melting). The discrepancy between ΔPOC:ΔPON and ΔDIC:ΔNO₃ was likely due to dissolved organic carbon (DOC) production. Increased ΔPOC:ΔPON of phytoplankton and surface water ΔDIC:ΔNO₃ throughout the phytoplankton blooms resulted from changes in physical properties of the upper water column, such as reduced thickness of the surface mixed layer that exposed phytoplankton to increased photosynthetically available radiation (PAR), accompanied by NO₃ depletion. This is expected to have significant effects on the cycling of carbon (C) and nitrogen (N) in pelagic ecosystems, as the increased C:N ratio of organic matter decreases its quality as substrate for grazers and microbial communities. Based on ΔPOC:ΔPON, the ratio of POC to chlorophyll a (Chl) production (ΔPOC:ΔChl) and the relationship between Chl yields and NO₃ depletion, we estimate that 71±17% and 46±20% of the depleted NO₃ went to PON production in the euphotic zone over the polynya from April to early June, and late June to July, respectively. The remaining NO₃ was likely channelled to dissolved organic nitrogen (DON) and heterotrophic bacteria, which were not returned to the dissolved inorganic nitrogen (DIN) pool through recycling during the course of the study. Hence, the autotrophic production of organic N and its recycling by the microbial food web were not coupled temporally.  相似文献   

Trophic structure and pathways of biogenic carbon flow in the eastern North Water Polynya   总被引：1，自引：0，他引：1  

Jean-ric Tremblay  Hiroshi Hattori  Christine Michel  Marc Ringuette  Zhi-Ping Mei  Connie Lovejoy  Louis Fortier  Keith A. Hobson  David Amiel  Kirk Cochran 《Progress in Oceanography》2006,71(2-4):402

In the eastern North Water, most of the estimated annual new and net production of carbon (C) occurred during the main diatom bloom in 1998. During the bloom, at least 30% of total and new phytoplankton production occurred as dissolved organic carbon (DOC) and was unavailable for short-term assimilation into the herbivorous food web or sinking export. Based on particle interceptor traps and ²³⁴Th deficits, 27% of the particulate primary production (PP) sank out of the upper 50 m, with only 7% and 1% of PP reaching the benthos at shallow (≈200 m) and deep (≈500 m) sites, respectively. Mass balance calculations and grazing estimates agree that ≈79% of PP was ingested by pelagic consumers between April and July. During this period, the vertical flux of biogenic silica (BioSi) at 50 m was equivalent to the total BioSi produced, indicating that all of the diatom production was removed from the euphotic zone as intact cells (direct sinking) or empty frustules (grazing or lysis). The estimated flux of empty frustules was consistent with rates of herbivory by the large, dominant copepods and appendicularians during incubations. Since the carbon demand of the dominant planktivorous bird, Alle alle, amounted to ≈2% of the biomass synthesized by its main prey, the large copepod Calanus hyperboreus, most of the secondary carbon production was available to pelagic carnivores. Stable isotopes indicated that the biomass of predatory amphipods, polar cod and marine mammals was derived from these herbivores, but corresponding carbon fluxes were not quantified. Our analysis shows that a large fraction of PP in the eastern North Water was ingested by consumers in the upper 50 m, leading to substantial carbon respiration and DOC accumulation in surface waters. An increasingly early and prolonged opening of the Artic Ocean is likely to promote the productivity of the herbivorous food web, but not the short-term efficiency of the particulate, biological CO₂ pump.  相似文献   

ArcGIS与SAS地统计分析方法应用于美国县区人口加权月温度估算的比较(英文)     

戚晓鹏  魏良  Laurie BARKER  Akaki LEKIACHVILI  张兴有 《资源与生态学报(英文版)》2012,3(3):220-229

气温变化对人群健康有重要的影响。通过对美国县区人口加权的月平均温度的准确估计可以用于气温与人群健康行为以及疾病的关联关系研究,如基于以县区为单位的抽样或者报告数据。针对气温的估计,多数学者都采用ArcGIS软件,很少使用SAS这一统计软件。本文比较了两种地统计模型的性能,并在同一个CITGO平台上采用ArcGIS9.3和SAS9.2工具软件估算全美48个州县区月平均温度。来自全美5435个气温监测站点2007年1-12月的平均温度和站点的海拔高度被用于估算县区人口中心点的温度,其中海拔数据是作为协变量。通过调整决定系数R2、均方误差、均方根误差和处理时间等指标来比较模型的效能。在ArcGIS中独立验证预测准确性在11个月中都达到90%以上,SAS中12个月均达到90%以上。与ArcGIS协同克里格相比,SAS协同克里格插值能获得更高的准确性和较低的偏差。两个软件包对于县区水平的气温估计值呈现正相关(调整R2在0.95-0.99之间);通过引入海拔高度作为协变量,使准确性和精确性都得以改善。两种方法对于美国县区层面的气温估计都是可靠的,但ArcGIS在空间数据前期处理和处理时间上的优势,尤其在涉及多年或者多个州的项目中是软件选择上的重要考虑。  相似文献   

Fluoride in Nebraska's Ground Water   总被引：1，自引：0，他引：1  

David C. Gosselin  Jacqueline Headrick  F. Edwin Harvey  Rod Tremblay  Kimberly McFarland 《Ground Water Monitoring & Remediation》1999,19(2):87-95

Fluoride concentrations in ground water are generally low but play an important role in dental health. This study evaluates the vertical and spatial distribution of fluoride in Nebraska's ground water and examines the geological and geochemical processes that control its concentration. Data from 1794 domestic wells sampled by the Nebraska Department of Health and Human Services. Regulation, and Licensure (NDOH) had a range of fluoride concentrations from <0.1 to 2.6 mg/L. and a median concentration of 0.3 mg/L. The median fluoride concentrations for Nebraska's 13 ground water regions varied from 0.2 to 0.7 mg/L. In each of these regions, individual wells may have either insufficient or overabundant F concentrations; we recommend that individual private water systems be tested for fluoride. Based on these data, system-specific recommendations can be made regarding the necessity for fluoridation.
Geochemical data indicated that the majority of fluoride occurs as F. Dissolution of F-bearing minerals controls fluoride occurrence. Apatite plus minor amounts of fluorite along with significant ground water residence times are the primary factors controlling F in the water from the Dakota Formation in Knox County, as well as in other parts of northeastern Nebraska. In western and southwestern Nebraska, dissolution of volcanic glass is the most probable source of F Long residence times plus fluorite also may contribute to the F concentrations in the Chadron Formation.  相似文献   

Australia and New Zealand: Economy, Society and Environment.: By Guy M. Robinson, Robert J. Loughran and Paul J. Tranter.     

Laurie J. Brown 《New Zealand geographer》2000,56(2):58-59

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