Wetlands and low-gradient topography are associated with longer hydrologic transit times in Precambrian Shield headwater catchments     

Daniel Lane  Colin P.R. McCarter  Murray Richardson  Chris McConnell  Tim Field  Huaxia Yao  George Arhonditsis  Carl P.J. Mitchell 《水文研究》2020,34(3):598-614

The estimation of hydrologic transit times in a catchment provides insights into the integrated effects of water storage, mixing dynamics, and runoff generation processes. There has been limited effort to estimate transit times in southern boreal Precambrian Shield landscapes, which are characteristically heterogeneous with surface cover including till, thin soils, bedrock outcrops, and depressional wetland features that play contrasting hydrologic roles. This study presents approximately 3.5 years of precipitation and streamflow water isotope data and estimates mean transit times (MTTs) and the young water fraction (p_y) across six small catchments in the Muskoka-Haliburton region of south-central Ontario. The main objectives were to define a typical range of MTTs for headwater catchments in this region and to identify landscape variables that best explain differences in MTTs/p_y using airborne light detection and ranging and digital terrain analysis. Of the transit time distributions, the two parallel linear reservoir and gamma distributions best describe the hydrology of these catchments, particularly because of their ability to capture more extreme changes related to events such as snowmelt. The estimated MTTs, regardless of the modelling approach or distribution used, are positively associated with the percent wetland area and negatively with mean slope in the catchments. In this landscape, low-gradient features such as wetlands increase catchment scale water storage when antecedent conditions are dryer and decrease transit times when there is a moisture surplus, which plausibly explains the increases in MTTs and mean annual runoff from catchments with significant coverage of these landscape features.  相似文献   

The radio nebula surrounding the Vela pulsar     

R. Dodson †  D. Lewis  D. McConnell  A. A. Deshpande 《Monthly notices of the Royal Astronomical Society》2003,343(1):116-124

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积雪变化导致格陵兰冰盖高度变化     

J.R.McConnell 《海洋地质前沿》2001,17(1)

地面冰盖对气候变化的反应可能会对未 来的海平面变化产生重大的影响.近年来格 陵兰南部的卫星调查显示,较大高度的冰盖 总体高度变化甚小,但空间变化很大.当然 仅仅依靠卫星数据难以测定是什么地球物理 过程引起了这种高度变化以及近年的变化速 率是否超过了正常变化速率.我们利用雪粒 密度增大的物理模型和根据高海拔12个冰 心再造的年雪堆积记录,获取了1978～1988 年格陵兰南部冰盖高度的变化. 地中海的干涸及其产生的后果 К.Н. Несис 很久以来就知道,地史最后阶段最具戏 剧性的事件之一就是大约在6Ma前的中新 世末期地中海的被隔离和完全干涸.据西西 里岛墨西拿城附近该时期著名的沉积剖面, 这个事件被称之为墨西拿盐量转变. 马建华摘译自 , 2000, Vol.406,No.24 周立君校  相似文献   

The solubility of [4H]Si defects in α-quartz and their role in the formation of molecular water and related weakening on heating     

J. D. C. McConnell  J. S. Lin  Volker Heine 《Physics and Chemistry of Minerals》1995,22(6):357-366

The nature of the solubility of water as [4H]_Si defects in quartz, and their role in providing a source of molecular water on heating, is investigated. Existing ab inito energy calculations on the incorporation of water in quartz are used to show that energetically 4H for Si substitution is likely to constitute the most prevalent mode of water uptake on the atomic scale in quartz under equilibrium conditions, and that the planar defects previously observed by a number of different authors by electron microscopy in wet quartz are likely to be planar rafts of aggregated [4H]_Si defects which are formed on supersaturation. These new conclusions call into question the previous identification of the planar defects as high pressure water clusters and require that their role in the production of molecular water in the context of recent theories of hydrolytic weakening be re-assessed. Accordingly the existing ab initio results have been used to establish the characteristics of the phase diagram for the system quartz-water in the temperature and pressure range of interest in hydrolytic weakening. Additional electron-optical experiments on wet quartz show that, on annealing at temperature in the electron microscope, similar planar defects develop in wet quartz by a diffusion process. In the context of existing theories of hydrolytic weakening it is now proposed that the conversion of [4H]_Si defects to molecular water, where this is dictated by the equilibrium phase diagram, leads to a relatively large increase in volume and to the appearance of the bubbles of free water and the nucleation of associated prismatic dislocation loops of Burgers vector b=1/3 a $\langle 11\bar 20\rangle $ as previously observed. Ultimately the development of these loops leads to dislocation-induced plasticity.  相似文献   

Analysis of COMPTEL gamma-ray burst locations and spectra     

R. M. Kippen  J. Ryan  A. Connors  M. McConnell  C. Winkler  L. O. Hanlon  V. Schönfelder  J. Greiner  M. Varendorff  W. Collmar  W. Hermsen  L. Kuiper 《Astrophysics and Space Science》1995,231(1-2):231-234

In its first three years of operation, the COMPTEL instrument on theCompton Gamma-Ray Observatory has measured the locations (mean accuracy 1°) and spectra (0.75-30 MeV) of 18 gamma-ray bursts and continues to observe new events at a rate of 1/month. With good angular resolution and sensitivity at MeV energies, the growing COMPTEL burst catalog is an important new piece of evidence in the on-going GRB mystery. The COMPTEL burst locations are consistent with an isotropic distribution of sources, yet the spatial coincidence of two of the bursts indicates the possibility of repetition. The COMPTEL burst spectra are in most cases consistent with a single power law model with spectral index in the range 2–3. However, two bursts show evidence of a spectral break in the MeV range. Measurement of rapid variability at MeV energies in the stronger bursts provides evidence that either the sources are nearby (within the Galaxy) or the gamma-ray emission is relativistically beamed. We present an overview of analysis results obtained from the COMPTEL burst catalog concentrating on the search for burst repetition and the implications of highly variable MeV emission.  相似文献   

Climate Suitability: For Stable Malaria Transmission in Zimbabwe Under Different Climate Change Scenarios   总被引：1，自引：0，他引：1  

Jessica Hartman  Kristie Ebi  K. John McConnell  Nathan Chan  John Weyant 《Global Change & Human Health》2002,3(1):42-54

As climate is one factor determining the potential range of malaria, climate change may work with or against efforts to bring malaria under control. We developed a model of future climate suitability for stable Plasmodium falciparum malaria transmission in Zimbabwe. Current climate suitability for stable malaria transmission is based on the MARA/ARMA model of climatic constraints on the survival and development of the Anopheles vector and the Plasmodium falciparum malaria parasite. We explored potential future geographic distributions of malaria using sixteen projections of climate in 2100. The results suggest that, assuming no future human-imposed constraints on malaria transmission, changes in temperature and precipitation could alter the geographic distribution of malaria in Zimbabwe, with previously unsuitable areas of dense human population becoming suitable for transmission. Among all scenarios, the highlands become more suitable for transmission, while the lowveld and areas currently limited by precipitation show varying degrees of change, depending on climate sensitivity and greenhouse gas emission stabilization scenarios, and depending on the general circulation model used. The methods employed can be used within or across other African countries. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Gold and associated trace elements in Newfoundland lake sediment: their application to gold exploration     

John McConnell  Peter Davenport 《Journal of Geochemical Exploration》1989,32(1-3)

Lake sediments were collected from four glaciated areas, three of which include significant Au mineralization. Neutron activation analyses for Au successfully delineate known mineralization and suggest areas for further follow-up. Gold is the only universal indicator although Sb gives a broader dispersion pattern at the Hope Brook deposit. Copper, Pb and Zn have above-background content down-ice from some mineralized zones. Gold values above 8.0 ppb in these study areas indicate the presence of Au mineralization. Gold analyses of site duplicates and analytical splits reproduce satisfactorily above 3.0 ppb.  相似文献   

The estuarine clamRangia cuneata as a biomonitor of dioxins and furans in the Neches River,Taylor Bayou,and Fence Lake,Texas     

Richard C. Harrel  Marc A. McConnell 《Estuaries and Coasts》1995,18(1):264-270

Polychlorinated dibenzo-para-dioxins (PCDDs) and dibenzofurans (PCDFs) were measured in the tissues of the estuarine clamRangia cuneata at four sites in the Neches River that had been subjected to paper mill effluent and at two remote sites. One of the river samplings was taken before dioxin control measures and another 2 yr after the control measures began. Measurable concentrations of PCDD/Fs were present at all sites, but higher concentrations were present at the Neches River sites. Whole tissue concentrations of 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) and all PCDD congeners for the two collections were not significantly different (p>0.05), but lipid-normalized concentrations for the two collections were significantly different (p<0.05). Highest concentrations of PCDDs at sites located 8 km and 16 km upriver from the paper mill effluent outfall indicated that the materials were transported upriver by saltwater intrusion and/or that nonpoint sources existed upriver. The presences of PCDD/Fs in clam tissues from the remote sites also indicated that other sources of these materials existed. Even under extreme physiological conditions (spent reproductive phase, low lipid contents, water temperature 10°C; ripe reproductive phase, high lipids, water temperature 32°C)Rangia cuneata was an effective biomonitor to determine the distribution of PCDD/Fs at specific sites. *** DIRECT SUPPORT *** A01BY069 00021  相似文献   

Spontaneous potential corrections for groundwater salinity calculations — Carter County,Oklahoma, U.S.A.     

Cary L McConnell 《Journal of Hydrology》1983,65(4):363-372

The spontaneous potential log was used to compute the thickness and distribution of groundwater with a total dissolved solids (TDS) of less than 1000 mg l^?1 for Carter County, Oklahoma. To compute accurate salinities from the spontaneous potential in high-resistivity zones, empirical correction factors had to be developed and applied. For the formations present equivalent water resistivity vs. water resistivity curves were developed from chemical analyses and digitized. Water resistivity vs. TDS curves were also developed and digitized. The existing empirical thin-bed corrections were curve-fit with equations and applied to each zone. Except in beds less than 3.65 m thick they had little effect.It was found that after applying the thin-bed corrections used by logging companies, the computed TDS was a function of resistivity of the mud filtrate at 24°C. An empirical relationship was developed between spontaneous potential and resistivity of the mud filtrate at 24°C, using well logs of beds with known water chemistry. This relationship was entered as a correction equation into a computer program developed by the author. The correction is necessary since the voltage drop in a freshwater formation is greater than predicted by earlier electric analog modeling, and the spontaneous potential is less than the static spontaneous potential. Testing of the correction factors shows that in a formation with TDS of ～750 mg l^?1 the average error decreases from ～37% to 10%.A data set of 704 well logs was built with data from each freshwater zone from the base of the regolith to a depth where the TDS was greater than 10,000 mg l^?1. The TDS was computed for each zone. Two maps were prepared from the results; an isopach of the formations with TDS of less than 1000 mg l^?1, and a depth to the base of the water with TDS of 1000 mg l^?1.  相似文献   

Global change and the intensification of agriculture in the tropics   总被引：3，自引：2，他引：3  

Eric Keys  William J. McConnell 《Global Environmental Change》2005,15(4):320-337

Bridging understanding of local environmental change with regional and global patterns of land-use and land-cover change (LUCC) remains a key goal and challenge for our understanding of global environmental change. This meta-analysis attempts to bridge local and regional scales of LUCC by demonstrating the ways in which previously published case studies can be compared and used for a broader regional synthesis in the tropics. In addition to providing results from a meta-analysis, this paper suggests ways to make future case studies more widely comparable.  相似文献