Tetravalent uranium in calcite   总被引：1，自引：0，他引：1  

NC Sturchio  MR Antonio  L Soderholm  SR Sutton  JC Brannon 《Science (New York, N.Y.)》1998,281(5379):971-973

X-ray absorption spectroscopy and x-ray fluorescence microprobe studies of 35-million-year-old calcite from a Mississippi Valley-type zinc ore deposit indicate substitution of tetravalent uranium for divalent calcium. Thus, tetravalent uranium has a stable location in calcite deposited under reducing conditions. This result validates uranium-series dating methods (including uranium/lead dating) for ancient calcite and shows that calcite provides a sink for uranium in deep groundwater aquifers and anoxic lacustrine and marine basins.  相似文献   

Causative factors influencing epizoochorous dispersal of weed seeds by sheep and associated carcass contamination in southern Australia     

Jane E. Kelly  Jane C. Quinn  Sharon G. Nielsen  Paul Weston  John C. Broster  Leslie A. Weston 《Weed Research》2020,60(3):221-231

Hordeum spp. (barley grass) and Bromus spp. (brome grass) are annual weed species that achieve long-distance seed dispersal via attachment to sheep, but also lead to sheep carcass damage due to the penetration of seeds into animal tissues. Range expansion of invasive weed populations predicted as a consequence of climate change may be associated with an increase in seed contamination incidence globally. An examination of Australian abattoir data (2006–2012), along with recent weed distribution patterns, indicates carcass contamination was associated with rainfall and abundance of key annual grass weeds, primarily Bromus spp. and Hordeum spp., although other factors may play a contributing role. Significant differences in seed contamination in slaughtered sheep were noted between states and regions, with widespread contamination occurring throughout all agro-ecological zones. Abattoir, sheep age and sex significantly influenced incidence, with contamination highest in adult males. Incidence increased with mean monthly rainfall, but declined with mean elevation, and significant interactions were noted between mean monthly temperature and state, and between mean elevation and year. Results show the need for vigilant recording of seed injuries in sheep to enhance weed surveillance efforts and effective integrated weed management of contributing annual grass weeds.  相似文献   

KNOWLEDGE MANAGEMENT FOR LAND DEGRADATION MONITORING AND ASSESSMENT: AN ANALYSIS OF CONTEMPORARY THINKING     

M. S. Reed  I. Fazey  L. C. Stringer  C. M. Raymond  M. Akhtar‐Schuster  G. Begni  H. Bigas  S. Brehm  J. Briggs  R. Bryce  S. Buckmaster  R. Chanda  J. Davies  E. Diez  W. Essahli  A. Evely  N. Geeson  I. Hartmann  J. Holden  K. Hubacek  A. A. R. Ioris  B. Kruger  P. Laureano  J. Phillipson  C. Prell  C. H. Quinn  A. D. Reeves  M. Seely  R. Thomas  M. J. van der Werff Ten Bosch  P. Vergunst  L. Wagner 《Land Degradation \u0026amp; Development》2013,24(4):307-322

It is increasingly recognised that land degradation monitoring and assessment can benefit from incorporating multiple sources of knowledge, using a variety of methods at different scales, including the perspectives of researchers, land managers and other stakeholders. However, the knowledge and methods required to achieve this are often dispersed across individuals and organisations at different levels and locations. Appropriate knowledge management mechanisms are therefore required to more efficiently harness these different sources of knowledge and facilitate their broader dissemination and application. This paper examines what knowledge is, how it is generated and explores how it may be stored, transferred and exchanged between knowledge producers and users before it is applied to monitor and assess land degradation at the local scale. It suggests that knowledge management can also benefit from the development of mechanisms that promote changes in understanding and efficient means of accessing and/or brokering knowledge. Broadly, these processes for knowledge management can (i) help identify and share good practices and build capacity for land degradation monitoring at different scales and in different contexts and (ii) create knowledge networks to share lessons learned and monitoring data among and between different stakeholders, scales and locations. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献