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171.
172.
Jeff Rosenbloom Peter Mock H. J. Turin Peter Lawson Jess Brown 《补救:环境净化治理成本、技术与工艺杂志》1992,2(4):399-412
In 1981, the Arizona Department of Health Services (ADHS) discovered groundwater contamination by solvents and chromium at the Phoenix Goodyear Airport (PGA), just outside the city of Phoenix. ADHS and the U.S. EPA sampled the site for the next two years, finding that eighteen of their wells were contaminated with trichloroethene (TCE), six exceeding ADHS's action level of five micrograms per liter (μg/l). In 1983, the PGA site was added to the National Priorities List, and, in 1984, EPA began a $3 million remedial investigation, focusing on soils and groundwater. This article discusses how that investigation inspired the authors to develop a stream-lined evaluation method for PGA's volatile organic compounds (VOCs), the process for establishing VOC cleanup levels, and the $26 million of remediation work needed to be done at the site. The heart of this effort is a computer program called VLEACH, loosely standing for VOC-LEACHing, which anticipates the influence of VOCs on PGA's groundwater, even as remediation proceeds. 相似文献
173.
Eric C. Reichard L. Jeff Lefkoff 《Journal of the American Water Resources Association》1987,23(4):717-721
Knapp and Feinerman (1985) pose and solve a problem of steady-state allocation of ground water based directly on the underlying dynamic problem. Their dynamic steady-state formulation incorporates both the equations of transient ground. water flow and the discount rate. We wish to discuss two aspects of their analysis. First, we question their assertion that the computational advantages of the dynamic steady.state formulation will justify its substitution for the full transient problem. In fact, the dynamic steady-state problem will often be harder to solve than the properly formulated transient problem. Second, we argue that the dynamic steady-state is a concept that has limited applicability in ground-water management. In cases where the optimal steady state is indeed useful, the dynamic solution is often identical to the static solution. 相似文献
174.
Summary In experiments, blue-green chromis [Chromis viridis (Cuvier 1830)] were fed on either scattered or aggregated swarms of brine shrimp (Artemia sp.). Ten runs with each prey dispersion treatment were performed with shoals of one, two, five and ten chromis. The mean lag in reaching peak feeding rate for fish fed on aggregated prey was significantly shorter in the larger chromis shoals. In contrast, with the scattered treatment all such lags were similar and very short. As foraging proceeded, higher feeding rates were observed in the larger feeding shoals, regardless of prey dispersion. Prey capture success (i.e. the rate of retention of intercepted prey) declined with time, but was significantly higher in groups of ten fish. Two main conclusions emerge. Firstly, grouping facilitated initiation of feeding by individuals preying on concentrated swarms and reduced the delay in reaching a maximum feeding level. This may have been due to a suppression of the confusion effect through reduced reliance upon vigilance. Secondly, reduced vigilance allowed larger shoals of chromis to feed effectively over more extended periods. Trends of increasing shoal cohesion and decreasing prey retention rate with time were consistent with a postulated increase in antipredator vigilance with declining feeding motivation. 相似文献
175.
Parasitism at the Landscape Scale: Cowbirds Prefer Forests 总被引:3,自引:0,他引:3
Landscape-scale examination of parasitism patterns of Brown-headed Cowbirds ( Molothrus ater ) revealed heterogeneous parasitism rates across the mosaic of a forest and associated old-field communities. In a two year study in Dutchess County, New York, we found a significantly higher parasitism rate in the forest-interior community ( n = 301 nests; 17 species) than on the species in the adjacent and nearby old field and edge ( n = 328 nests; 15 species; 32.3% versus 6.5%; p < 0.0001). Cowbirds invaded a mature 1300-ha forest stand even when their traditional host species were available in adjacent old-field and edge habitats. The forest and old-field study areas were located in a 38,000-ha township with 55% forest cover and contained numerous agriculture, dairy, and horse farms that provided favorable habitat for cowbirds. Within-forest examination of parasitism patterns revealed four aspects of cowbird parasitism that contrasted with patterns described in other regions: (1) parasitism was concentrated significantly more often on ground- and low-nesting (nests ≤ 1 m) forest species than on medium- and high-nesting species (nests> 1 m; 35.01% versus 29.93%; p = 0.0393); (2) parasitism was not significantly greater on Neotropical migrant species than on short-distance migrants and residents; (3) the parasitism rate was not higher in nests close to edges; and (4) the parasitism level was low on certain forest species (such as Wood Thrush) that have experienced high parasitism levels in the Midwest. From a management perspective these data suggest that cowbirds exhibit regional differences in host and habitat use; the target host community of a particular cowbird population is unpredictable at the landscape scale; and a landscape scale should be used in designing cowbird studies to accurately assess local population dynamics. 相似文献
176.
177.
Predator evasion behaviour patterns of three populations of rainbowfish (Melanotaenia eachamensis) were compared. The populations differed in the level of complexity of their natural habitats and the type and extent of
predation. The predator recognition abilities of fish were assessed by exposing them to models differing in their degree of
predator realism. The availability of vegetated cover and the location of the models with respect to cover were manipulated.
Fish from Lake Tinaroo, a relatively open habitat containing numerous predators, showed strong changes in elective group size
(EGS) in response to the different models but did not rely on cover as a place of refuge. In contrast, Dirran Creek fish originate
from a small, fast-flowing, structurally complex stream lacking predatory fish species, and they showed little ability to
distinguish between the different models and responded to threat by spending longer in vegetated areas. Members of the Lake
Eacham captive stock increased their EGS in response to models representing low threat and with more threatening models increased
the amount of time spent in vegetated regions of the arena. The contrasting reactions to predatory threat displayed by these
populations highlights the need to use a number of different response indices when comparing the anti-predator responses of
different fish populations. These data suggest that the level of habitat complexity as well as prior predator experience influence
anti-predator responses of different fish popu-lations.
Received: 2 October 1996 / Accepted after revision: 27 March 1997 相似文献
178.
Odours from pulp mill effluent treatment ponds: the origin of significant levels of geosmin and 2-methylisoborneol (MIB) 总被引:2,自引:0,他引:2
Pulp and paper mills are well known for their sharp, sulphurous stack emissions, but the secondary treatment units also can be significant contributors to local odour. This study investigated the source(s) of earthy/musty emissions from a mixed hardwood pulp mill in response to a high local odour. Samples from five sites in the mill over five months were analyzed for earthy/musty volatile organic compounds (VOCs), examined microscopically, and plated for bacteria and moulds. In all cases, activated sludge showed substantial geosmin levels and to a lesser extent 2-methylisoborneol (MIB) at 2000-9000 times their odour threshold concentrations (OTCs). These VOCs were lower or absent upstream and downstream, suggesting that they were produced within the bioreactor. Geosmin and MIB were highest in late summer and declined over winter, and correlated with different operating parameters. Geosmin was most closely coupled with temperature and MIB with nitrogen uptake. Cyanobacteria were present in all sludge samples, but actinomycetes were not found. Gram-negative bacteria and one fungal species isolated from the bioreactor and secondary outfall tested negative for geosmin or MIB. We conclude: (i) geosmin and MIB contribute significantly to airborne odours from this mill, but are diluted below OTC levels at the river; (ii) these VOCs are generated by biota in the activated sludge; and (iii) cyanobacteria are likely primary source(s). The growth of cyanobacteria in activated sludge represents a loss of energy to the heterotrophic population; thus earthy/musty odours may represent a diagnostic for less than optimal conditions. 相似文献
179.
180.
Eddy J. Moors Annemarie Groot Hester Biemans Catharien Terwisscha van Scheltinga Christian Siderius Markus Stoffel Christian Huggel Andy Wiltshire Camilla Mathison Jeff Ridley Daniela Jacob Pankaj Kumar Suruchi Bhadwal Ashvin Gosain David N. Collins 《Environmental Science & Policy》2011,14(7):758-769
An ensemble of regional climate model (RCM) runs from the EU HighNoon project are used to project future air temperatures and precipitation on a 25 km grid for the Ganges basin in northern India, with a view to assessing impact of climate change on water resources and determining what multi-sector adaptation measures and policies might be adopted at different spatial scales.The RCM results suggest an increase in mean annual temperature, averaged over the Ganges basin, in the range 1–4 °C over the period from 2000 to 2050, using the SRES A1B forcing scenario. Projections of precipitation indicate that natural variability dominates the climate change signal and there is considerable uncertainty concerning change in regional annual mean precipitation by 2050. The RCMs do suggest an increase in annual mean precipitation in this region to 2050, but lack significant trend. Glaciers in headwater tributary basins of the Ganges appear to be continuing to decline but it is not clear whether meltwater runoff continues to increase. The predicted changes in precipitation and temperature will probably not lead to significant increase in water availability to 2050, but the timing of runoff from snowmelt will likely occur earlier in spring and summer. Water availability is subject to decadal variability, with much uncertainty in the contribution from climate change.Although global social-economic scenarios show trends to urbanization, locally these trends are less evident and in some districts rural population is increasing. Falling groundwater levels in the Ganges plain may prevent expansion of irrigated areas for food supply. Changes in socio-economic development in combination with projected changes in timing of runoff outside the monsoon period will make difficult choices for water managers.Because of the uncertainty in future water availability trends, decreasing vulnerability by augmenting resilience is the preferred way to adapt to climate change. Adaptive policies are required to increase society's capacity to adapt to both anticipated and unanticipated conditions. Integrated solutions are needed, consistent at various spatial scales, to assure robust and sustainable future use of resources. For water resources this is at the river basin scale. At present adaptation measures in India are planned at national and state level, not taking into account the physical boundaries of water systems. To increase resilience adaptation plans should be made locally specific. However, as it is expected that the partitioning of water over the different sectors and regions will be the biggest constraint, a consistent water use plan at catchment and river basin scale may be the best solution. A policy enabling such river basin planning is essential. 相似文献