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41.
In this study, pulverized fuel ash (PFA) and ground granulated blast furnace slag (GGBS) were used to compensate for the loss of strength and durability of concrete containing recycled aggregate. As a result, 30% PFA and 65% GGBS concretes increased the compressive strength to the level of control specimens cast with natural granite gravel, but the tensile strength was still lowered at 28 days. Replacement with PFA and GGBS was effective in raising the resistance to chloride ion penetrability into the concrete body, measured by a rapid chloride ion penetration test based on ASTM C 1202-91. It was found that the corrosion rate of 30% PFA and 65% GGBS concretes was kept at a lower level after corrosion initiation, compared to the control specimens, presumably due to the restriction of oxygen and water access. However, it was less effective in increasing the chloride threshold level for steel corrosion. Hence, it is expected that the corrosion time for 30% PFA and 65% GGBS concrete containing recycled aggregate mostly equates to the corrosion-free life of control specimens. 相似文献
42.
Peter A. Hesbach Ann G. Kim Alexander S. P. Abel Steven C. Lamey 《Environmental monitoring and assessment》2010,168(1-4):523-545
Although many leaching methods have been used for various purposes by research groups, industries, and regulators, there is still a need for a simple but comprehensive approach to leaching coal utilization by-products and other granular materials in order to estimate potential release of heavy metals when these materials are exposed to natural fluids. A serial batch characterization method has been developed at the National Energy Technology Laboratory that can be completed in 2–3 days to serve as a screening tool. The procedure provides an estimate of cumulative metals release under varying pH conditions, and leaching the sample at increasing liquid/solid ratios can indicate the rate at which this process will occur. This method was applied to eight fly ashes, adapted to the acidic or alkaline nature of the ash. The leachates were analyzed for 30 elements. The test was run in quadruplicate, and the relative standard deviation (RSD) was used as a measure of method reproducibility. RSD values are between 0.02 and 0.70, with the majority of the RSD values less than 0.3. The serial batch leaching procedure was developed as a simple, relatively quick, yet comprehensive method of estimating the risk of heavy metal release from fly ash when it is exposed to natural fluids, such as acid rain or groundwater. Tests on a random selection of coal fly ashes have shown it to be a reasonably precise method for estimating the availability and long-term release of cations from fly ash. 相似文献
43.
K. Thomas Klasson Isabel M. Lima Larry L. Boihem Lynda H. Wartelle 《Journal of environmental management》2010,91(12):2466-2470
Increased emphasis on reduction of mercury emissions from coal fired electric power plants has resulted in environmental regulations that may in the future require application of activated carbons as mercury sorbents for mercury removal. At the same time, the quantity of poultry manure generated each year is large and technologies that take advantage of the material should be explored. The purpose of the work was to obtain preliminary data to investigate if activated chars made from different poultry manures could adsorb mercury from simulated flue gas. In laboratory experiments, activated chars made from chicken cake and litter removed mercury from the gas as well as a commercial alternative. It was also found that acid-washing these chars after activation may improve pore structure but does not influence the mercury removal efficiency. Activated chars were also made from turkey cake and litter. These raw materials produced activated chars with similar pore structure as those made from chicken manure, but they did not adsorb mercury as well. Acid-washing the turkey manure-based chars improved their performance, but this step would add to the cost of production. Preliminary evaluations suggest that unwashed activated chars may cost as little as $0.95/kg to produce. 相似文献
44.
Sexual cannibalism can occur before, during or after mating. Relatively few experimental studies have examined why there is
variation in the timing of sexual cannibalism. We examined the latency and number of attacks required for female spiders to
capture male spiders pre- vs. postcopulation. We also examined the effects of female mating status and hunger level on the
occurrence of pre- and postcopulatory cannibalism, which reflects the contribution of both relative capture success and female
motivation to cannibalize males. Precopulatory cannibalism occurred after a shorter interval and required fewer chases and
physical interactions for the female to successfully capture the male than was the case for postcopulatory cannibalism. Virgin
females were more likely to engage in postcopulatory rather than precopulatory cannibalism and mated females vice versa. Those
virgin females that did engage in precopulatory cannibalism had significantly lower body condition than virgin females engaging
in postcopulatory cannibalism. While precopulatory cannibalism occurred more quickly and required fewer attacks by females,
it comes at a potential cost of not mating with males. Hence, females are more likely to engage in precopulatory cannibalism
if they have already mated or, if virgins, if they have low body condition. These results indicate that the decision of when
to cannibalize males is dynamic and depends upon the relative value of a male as a mate versus a meal. 相似文献
45.
Joris Mergaert Caroline Anderson Ann Wouters Jean Swings 《Journal of Polymers and the Environment》1994,2(3):177-183
The microbial degradation of tensile test pieces made of poly(3-hydroxybutyrate) [P(3HB)] or copolymers with 10% [P(3HB-co-10%3HV)] and 20% [P(3HB-co-20%3HV)] 3-hydroxyvaleric acid was studied in small household compost heaps. Degradation was measured through loss of weight (surface erosion) and changes in molecular weight and mechanical strength. It was concluded, on the basis of weight loss and loss of mechanical properties, that P(3HB) and P(3HB-co-3HV) plastics were degraded in compost by the action of microorganisms. No decrease inM
w could be detected during the degradation process. The P(3HB-co-20%3HV) copolymer was degraded much faster than the homopolymer and P(3HB-co-10%3HV). One hundred nine microbial strains capable of degrading the polymersin vitro were isolated from the samples used in the biodegradation studies, as well as from two other composts, and identified. They consisted of 61 Gram-negative bacteria (e.g.,Acidovorax facilis), 10 Gram-positive bacteria (mainlyBacillus megaterium), 35Streptomyces strains, and 3 molds. 相似文献
46.
Analysis of bank erosion on the Merced River,Yosemite Valley,Yosemite National Park,California, USA 总被引:1,自引:0,他引:1
Channel changes from 1919 to 1989 were documented in two study reaches of the Merced River in Yosemite National Park through
a review of historical photographs and documents and a comparison of survey data. Bank erosion was prevalent and channel width
increased an average of 27% in the upstream reach, where human use was concentrated. Here, trampling of the banks and riparian
vegetation was common, and banks eroded on straight stretches as frequently as on meander bends. Six bridges in the upper
reach constrict the channel by an average of 38% of the original width, causing severe erosion. In the downstream control
reach, where human use was minimal, channel widths both decreased and increased, with a mean increase of only 4% since 1919.
Bank erosion in the control reach occurred primarily on meander bends. The control reach also had denser stands of riparian
vegetation and a higher frequency of large woody debris in channels. There is only one bridge in the lower reach, located
at the downstream end. Since 1919, bank erosion in the impacted upstream reach contributed a significant amount of sediment
(74,800 tonnes, equivalent to 2.0 t/km2/yr) to the river. An analysis of 75 years of precipitation and hydrologic records showed no trends responsible for bank erosion
in the upper reach. Sediment input to the upper reach has not changed significantly during the study period. Floodplain soils
are sandy, with low cohesion and are easily detached by lateral erosion. The degree of channel widening was positively correlated
with the percentage of bare ground on the streambanks and low bank stability ratings. Low bank stability ratings were, in
turn, strongly associated with high human use areas. Channel widening and bank erosion in the upper reach were due primarily
to destruction of riparian vegetation by human trampling and the effect of bridge constrictions on high flow, and secondarily
to poorly installed channel revetments. Several specific recommendations for river restoration were provided to park management. 相似文献
47.
E. Ann Clark 《Journal of Agricultural and Environmental Ethics》1988,1(4):275-289
Changes in global patterns of grain production have affected the profitability of commercial, cash-crop agriculture in North America. The current financial crisis has highlighted a perceived conflict between the priorities of (1) strengthening net farm profit, (2) maintaining the productive potential of the land base, (3) enhancing the health and cohesiveness of the agricultural community, and (4) addressing societal demands for safe foodstuffs. Reducing input costs by reducing the need for privately owned machinery can minimize the scale-dependence of agricultural practices, as illustrated with examples involving silage and intensively managed pasture in Ontario. This approach could improve farming opportunities for nontraditional, part-time farmers, and at the same time, create a niche for professional custom operators and managers. Enhancing the viability of nontraditional farm operations, a historically neglected component of the farming community, as well as commercial farms is viewed as one approach to sustaining and improving both the agricultural land base and the agricultural community. Applying resource-extensive rather than resource-intensive approaches to forage management reveals that these apparently divergent priorities are, in fact, interlocking pieces of the same puzzle. 相似文献
48.
Gregory M. Jue Sally Ann Shumaker Gary W. Evans 《Journal of environmental psychology》1984,4(4):337-345
In the present study we examined (1) community opinion of airport noise-abating alternatives and (2) the influence of perceived control on attitudes concerning noise-abatement policies and annoyance toward aircraft noise. We proposed that residents who perceive themselves as having little control over aircraft noise exposure would express higher levels of annoyance than residents who believe they have some degree of control. Furthermore, residents with low levels of perceived control would be less favorable toward proposed noise-abatement alternatives. Survey results collected from 239 households within the 65 CNEL contour of a community airport in Southern California support these hypotheses. Findings indicate strong public support for noise abatement and strong opposition to land-use alternatives. In addition, residents' perceptions of control in the airport planning and management process are significantly related to their annoyance with noise and their opinions about noise management policies. 相似文献
49.
Environmental planners often propose tourism as a means of financing programmes to protect significant environmental areas. Surveys of tourists can provide useful information about the significance of environmental problems, trade-offs among policy objectives, willingness to pay (WTP) for protection programmes and preferences for different payment mechanisms. In Khanh Hoa Province, the provincial People's Committee, the Ministry of Fisheries and the World Conservation Union are working to implement Viet Nam's first marine protected area (MPA) in Nha Trang Bay. This paper reports the results of a survey of local and other Vietnamese and foreign tourists to islands that will be included in the MPA. The majority of respondents thought rubbish on the beaches, water pollution and vendors on beaches were problems and that the MPA was a good idea. Foreign tourists were significantly more likely to perceive environmental problems than were Vietnamese tourists, and persons who agreed there were environmental problems were significantly more likely to support the concept of an MPA, despite the potential for possible economic effects with distributive consequences. WTP for protection was modest and positively correlated with education and income. Although foreign tourists were on average willing to pay more, a larger proportion of Vietnamese tourists were willing to pay some amount to support the MPA. Analyses indicate that changes in income and education expected with economic development will increase both awareness of problems and WTP for protection. The results of this analysis are both encouraging and cautionary. The need for an MPA is clearly recognized by most tourists, and most tourists are willing to pay small fees to support the MPA. Given that education has significant impacts on both perceptions of problems and WTP, educational programmes may be an effective strategy for managing the competing objectives of protection and use. 相似文献
50.
Recovery of temperate-stream fish communities from disturbance: A review of case studies and synthesis of theory 总被引:3,自引:0,他引:3
Naomi E. Detenbeck Philip W. DeVore Gerald J. Niemi Ann Lima 《Environmental management》1992,16(1):33-53
To evaluate the relative effect of autecologic factors, site-specific factors, disturbance characteristics, and community
structure on the recovery of temperate-stream fish communities, we reviewed case histories for 49 sites and recorded data
on 411 recovery end points. Most data were derived from studies of low-gradient third- or fourth-order temperate streams located
in forested or agricultural watersheds. Species composition, species richness, and total density all recovered within one
year for over 70% of systems studied. Lotic fish communities were not resilient to press disturbances (e.g., mining, logging,
channelization) in the absence of mitigation efforts (recovery time >5 to >52 yr) and in these cases recovery was limited
by habitat quality. Following pulse disturbances, autecological factors, site-specific factors, and disturbance-specific factors
all affected rates of recovery. Centrarchids and minnows were most resilient to disturbance, while salmonid populations were
least resilient of all families considered. Species within rock-substrate/nest-spawning guilds required significantly longer
time periods to either recolonize or reestablish predisturbance population densities than did species within other reproductive
guilds. Recovery was enhanced by the presence of refugia but was delayed by barriers to migration, especially when source
populations for recolonization were relatively distant. Median population recovery times for systems in which disturbances
occurred during or immediately prior to spawning were significantly less than median recovery times for systems in which disturbances
occurred immediately after spawning. There was little evidence for the influence of biotic interactions on recovery rates. 相似文献