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821.
822.
Depositional and post-depositional controls on magnetic signals from saltmarshes on the north-west coast of Ireland 总被引:3,自引:0,他引:3
Magnetic measurements were carried out on samples from two saltmarshes deposited during the last century on the north-west coast of Ireland. Based on profiles from cliffed saltmarsh edge, mid-marsh and supratidal locations, the processes that affect the generation and persistence of magnetic properties in environments were investigated. This was done to help in understanding the geochemical processes affecting north-west Irish coast saltmarshes and to determine the frequency and provenance of sediment-laden flooding events; hence, disentangling the importance of clastic and organic contributions to saltmarsh growth. Magnetic properties indicate depositional and post-depositional effects varying on both temporal and spatial scales. The interpretations presented here suggest that both biogenic and diagenetic processes have a strong effect on the magnetic properties recorded: in the former case, the growth of magnetotactic bacteria is the main process; in the latter case, it is reductive diagenesis, associated with organic matter decomposition, that is important. The biogenic and diagenetic effects overprint and degrade the detrital magnetic signatures respectively. This suggests that magnetic measurements within the context of north-west Irish coast saltmarshes can provide limited information on clastic sediment input to these environments. Comparisons between sites on the north-west coast of Ireland show similar magnetic properties, despite differences in deposition rates, implying that significant post-depositional alteration of magnetic properties occurs within the first 20–40 years after deposition. Magnetic properties of north-west coast Irish saltmarshes are put into a regional context by comparison with magnetic profiles from similar sites. 相似文献
823.
国外可持续发展度量研究综述 总被引:12,自引:0,他引:12
虽然可持续发展80年代才明确提出,但从60年代开始的发展度量研究就为可持续发展度量研究提供了很好的基础。国外研制的可持续发展度量指标基本可分为四类:第一类是基于生态-环境观点的较微观层次的压力-状态-响应指标;第二类是以价值综合核算为前提的综合的可持续发展指数,如绿色GNP、国民财富指数等;第三类往往对资源、环境要素的价值核算持保留态度,避免作综合的价值核算,而是分别选取人口、资源、环境、经济、社会等多方面的指标进行系统分析,采用无量纲化和加权平均的方法求得衡量可持续发展水平的综合指数;第四类是从可持续性的反面着手,通过定义不可持续性来规定可持续性,建立不可持续性指标来度量可持续性。 相似文献
824.
825.
In plant ecology, site is a central concept. A site is the place where a plant species or plant community grows, and the
site provides the set of conditions in which it lives. Within an initially homogeneous parent material, gravity-driven groundwater
flow influences the site conditions through the spatial distribution of nutrients and other relevant chemical agents. Especially
upward seepage may produce and maintain site conditions that are essential for various relatively rare plant species and communities.
Increased attention to upward seepage among ecologists has resulted in cooperation with hydrologists and the emergence of
a discipline of its own – eco-hydrology – on the boundary of two scientific fields, linked by the site concept.
In the Netherlands, a simple classification of water types, based on the groundwater's subsurface history, was applied for
compiling a nationwide geographical database on ecologically relevant upward seepage. Correspondence analyses of this database
with data on plant-species occurrence demonstrate that in poor Pleistocene sandy soils upward seepage explains the occurrence
of some species and communities quite well, whereas in fluvial plains and polder areas with richer clay soils the influence
of seepage is blurred by the importance of soil characteristics. It is concluded, therefore, that plant species may be used
as seepage indicators in rapid assessments and surveys, but that constant awareness of the limitations is required.
Received, July 1998 · Revised, September 1998 · Accepted, October 1998 相似文献
826.
大西洋中部黄鳍金枪鱼(Thunnus albacares)的垂直分布与有关环境因子的关系 总被引:8,自引:0,他引:8
根据2001年6—10月在大西洋中部大洋性金枪鱼延绳钓作业中观测到的黄鳍金枪鱼的上钩钩号,应用悬链线钩深计算公式分别计算出各钩号的钩深;根据STD仪测得的温度、盐度的垂直分布以钩深为引数,查出该尾鱼捕获水深处的温、盐数据;根据黄鳍金枪鱼的取样数据,推算出各水层、各水温段、各盐度段的渔获率。渔获率最大的水层、水温段、盐度段为黄鳍金枪鱼的最适水层、水温段、盐度段;渔获率为前3位的水层、水温、盐度段为黄鳍金枪鱼活动较频繁的水层、水温段、盐度段。结果表明,在大西洋中部,黄鳍金枪鱼的最适水层为150.00—179.99m,最适水温段为13.00—13.99℃,最适盐度段为35.40—35.49;大西洋中部渔场黄鳍金枪鱼活动较频繁的水层为120.00—209.99m,水温段为12.00—14.99℃,盐度段为35.20—35.49。 相似文献
827.
828.
气候变化对环境与健康的影响日益受到关注。分析了气候变化对大气环境、水环境和土壤环境的胁迫效应,阐述了气候变化对生态系统和人体健康的影响,并概述了气候变化对不同介质环境以及对生态系统与人体健康影响研究的进展。这一工作可以为今后气象与环境领域开展进一步研究提供基本框架。 相似文献
829.
针对我国矿区煤矸石大量排放的现状,介绍了煤矸石的形成以及煤矸石大量堆放对环境所产生的危害和影响,并概述了煤矸石污染的防治措施及其综合利用途径。 相似文献
830.
The chemical degradation characteristics of reinforced concrete reefs, which had been fully immersed in Tongyeong waters of South Korea for 18–25 years, were studied. In order to investigate the marine environmental impact on the concrete reefs, environmental factors, for example pH, have been observed between 1997 and 2002. Then, four reinforced concrete reefs recovered from different sites in Tongyeong waters were nondestructively tested. Finally, those test results were analyzed to determine the chemical deterioration. Based on the test results, it is shown that the reinforced concrete reefs have sound chemical properties and their originally estimated service life is secure enough for a further service period in water depths of 28–32 m. A concrete cover depth of 40 mm is recommended for the design of reinforced concrete reefs to achieve safety in marine environments and special events occurring during installation and construction. 相似文献