Corrosion mechanisms relevant to high-level waste repositories

Corrosion is the destructive reaction of metals with their environment. The environment associated with a waste container is an extremely complex one, creating many possibilities for corrosion of the waste container. The different basic types of corrosion are governed by different equations and reactions. Schematic drawings and photographs illustrate the mechanisms of corrosion and factors which influence the forms of corrosion are outlined. There are techniques for testing the susceptibility to certain types of corrosion, and some standard test procedures have been developed. Predictive models have been proposed for crevice corrosion, stress corrosion cracking and scale formation. Existing models and extrapolations are all subject to limits on their applicability.     

Estimating ground motions using recorded accelerograms

A procedure for estimating ground motions using recorded accelerograms is described. The premise of the study is the assumption that future ground motions will be similar to those observed for similar site and tectonic situations in the past. Direct techniques for scaling existing accelerograms have been developed, based on relative estimates of local magnitude,M _L . Design events are described deterministically in terms of fault dimension, tectonic setting (stress drop), fault distance, and site conditions. A combination of empirical and theoretical arguments is used to develop relationships betweenM _L and other earthquake magnitude scales. In order to minimize scaling errors due to lack of understanding of the physics of strong ground motion, the procedure employs as few intermediate scaling laws as possible. The procedure conserves a meaningful measure of the uncertainty inherent when predicting ground motions from simple parameterizations of earthquake sources and site conditions.     

Relocating Policies for Sustainable Agriculture Under the Umbrella of Rural Development in Australia, USA and New Zealand

The concern of social scientists about the future of rural communities has filtered across to the policy arena at central government level. There analysis has been paralysed by lack of agreement about the issues. Many officials, especially those without social science training, do not understand concepts such as social sustainability, and few officials know how best to operationalise these concepts. A key step is the recognition of the need to consider people first in the development of policy, whether at the industry, community or household level, if the goal of sustainable agriculture is to be achieved.     

Spawning location and distribution of early life stages of alewife and blueback herring in a Virginia stream

During the 1992 spawning season of river herring, three sites in a tributary of the Rappahannock River, Virginia, were studied to characterize spawning and nursery habitats of alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) and to identify differences in habitat use along an upstream to downtream gradient. The sites were sampled (using drift and dip nets and a plankton sampler) and habitat variables were measured on a 5-d, four-time interval rotation: at the end of 5 d, each site had been sampled once at dawn, noon, dusk, and midnight. Considerable non-overlap in spawning seasonality was apparent between species. For both species, densities of river herring adults, eggs, and yolk-sac larvae were highest at the upstream site, indicating 1) that the upstream site is more important for spawning than downstream areas, and 2) these species do not use different spawning areas in this stream. Densities of post-yolk-sac larvae did not differ significantly among sites, indicating post-spawning dispersal to downstream areas. The upstream site was smaller in area, more acidic, had faster water flow, clearer water, more vegetation, and siltier substrate than the downstream sites. At times, pH levels in the upstream site were within the lethal range reported for blueback herring larvae. Possible reasons for selection of the upstream habitat include: 1) adults may migrate as far upstream as possible to avoid predation or potential competition with other species of fish for spawning habitat; or 2) adults may historically enjoy greater spawning success in the upstream habitat due to physicochemical features of this area. More study is needed to determine the reasons for river herring use of upstream habitats in Virginia streams.     

基于InVEST模型的1980–2100年长江中下游地区动植物生境质量时空变化研究

20世纪80年代以来,人类活动加速了长江流域的土地利用变化,这对当地动植物的生境质量造成了影响,在中国生态文明建设和长江经济带发展战略不断推进的大背景下,对长江中下游地区的生境质量变化开展长时间多时段的研究具有重要的现实意义。本研究以长江中下游地区7省的土地利用覆盖数据(1980–2018年)与未来土地利用模型模拟出未来四种情景(A1B,A2,B1,B2)下的土地利用覆盖数据(2050年,2100年)为基础,借助环境服务与权衡综合评估(In VEST)模型评估了长江中下游地区的生境质量时空变化。结果表明:(1)2000–2015年,研究区的坡度(R=0.502,P <0.01)和海拔(R=0.003,P <0.05)、人口密度(R=0.299,P <0.01)、NDVI(R=0.366,P <0.01)与生境质量显著相关;(2)从1980年到2018年,研究区总面积61.93%的土地生境质量下降,38.07%的土地生境质量上升;在A2情景(人口密度大,环境技术投入少,传统能源成本高)和B2情景(中等人口密度,中等绿色技术,区域政府间缺乏合作)下,研究区的生境质量将下降;(3)长江下游的生境质量恶化程度高于中游,研究区北部的生境质量恶化程度低于南部。整体上,积极的环境保护政策是有效的,但并未根本上遏制生境质量的整体退化趋势。区域发展应加大环境保护力度,控制人口增长,鼓励绿色技术创新,在处理生态问题时,要注重省际合作。本研究可为区域野生动植物保护规划和国际上的类似流域研究提供科学参考。     

Unprecedented last-glacial mass accumulation rates determined by luminescence dating of loess from western Nebraska

A high-resolution chronology for Peoria (last glacial period) Loess from three sites in Nebraska, midcontinental North America, is determined by applying optically stimulated luminescence (OSL) dating to 35–50 μm quartz. At Bignell Hill, Nebraska, an OSL age of 25,000 yr near the contact of Peoria Loess with the underlying Gilman Canyon Formation shows that dust accumulation occurred early during the last glacial maximum (LGM), whereas at Devil’s Den and Eustis, Nebraska, basal OSL ages are significantly younger (18,000 and 21,000 yr, respectively). At all three localities, dust accumulation ended at some time after 14,000 yr ago. Mass accumulation rates (MARs) for western Nebraska, calculated using the OSL ages, are extremely high from 18,000 to 14,000 yr—much higher than those calculated for any other pre-Holocene location worldwide. These unprecedented MARs coincide with the timing of a mismatch between paleoenvironmental evidence from central North America, and the paleoclimate simulations from atmospheric global circulation models (AGCMs). We infer that the high atmospheric dust loading implied by these MARs may have played an important role, through radiative forcing, in maintaining a colder-than-present climate over central North America for several thousand years after summer insolation exceeded present-day values.     

Experimental studies of predation on polychaetes associated with seagrass beds

Predation on benthic polychaetes associated with seagrass beds was examined in laboratory and field predator inclusion experiments with one fish and three invertebrate predators. Predation had differential effects on polychaete taxa which depended on their microhabitat utilization patterns. The magnitude of predation effects strongly depended on the predator species, with the shrimpPenaeus duorarum having the greatest impact and the pinfishLagodon rhomboides the least. Abundance of spionid polychaetes, which are located near the sediment-water interface, was reduced most often by predation. Nereid and capitellid polychaete abundances were reduced by some predators and not by others. The results emphasize the need for more detailed natural history information on polychaete species in order to improve the interpretation of results from predation experiments.