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421.
We investigate the release of radioactive contaminants from Moruroa Atoll in a global high-resolution off-line model. The spread of tracer is studied in a series of simulations with varying release depths and time-scales, and into ocean velocity fields corresponding to long-term annual mean, seasonal, and interannually varying scenarios. In the instantaneous surface release scenarios we find that the incorporation of a seasonal cycle greatly influences tracer advection, with maximum concentrations still found within the French Polynesia region after 10 years. In contrast, the maximum trace is located in the southeast Pacific when long-term annual mean fields are used. This emphasizes the importance of the seasonal cycle in models of pollution dispersion on large scales. We further find that during an El Ni?o/Southern Oscillation (ENSO) event reduced currents in the region of Moruroa Atoll result in increased concentrations of radioactive material in French Polynesia, as direct flushing from the source is reduced. In terms of the sensitivity to tracer release time-rates, we find that a gradual input results in maximum concentrations in the near vicinity of French Polynesia. This contrasts the instantaneous-release scenarios, which see maximum concentrations and tracer spread across much of the South Pacific Ocean. For example, in as little as seven years radioactive contamination can reach the east coast of Australia diluted by only a factor of 1,000 of the initial concentration. A comparison of results is made with previous studies. Overall, we find much higher concentrations of radionuclides in the South Pacific than has previously been predicted using coarser-resolution models. 相似文献
422.
Richard Hill‐Rowley Thomas McClain Matthew Malone 《Journal of the American Water Resources Association》2003,39(1):99-111
ABSTRACT: This paper presents a methodology for preparing a static water level map using a sample of water level measurements obtained from the well log records of private wells that are finished in glacial drift. The test was conducted in Tyrone Township, located in east central Michigan. A variety of selection criteria were examined and the resulting maps were compared with a ground truth map that was prepared from water level measurements obtained in the field. The map prepared from a random sample of wells at a density of two points per section best approximates the ground truth map. Using a sample of records from the Michigan Statewide Groundwater Database to create static water levels that are used in community ground water vulnerability analyses will provide a more accurate map than using the complete dataset or other selection criteria based on temporal groupings or seasonality. 相似文献
423.
The Roles of Photooxidation and Biodegradation in Long-term Weathering of Crude and Heavy Fuel Oils 总被引:1,自引:0,他引:1
Roger C Prince Robert M GarrettRichard E Bare Matthew J GrossmanTodd Townsend Joseph M SuflitaKenneth Lee Edward H OwensGary A Sergy Joan F BraddockJon E Lindstrom Richard R Lessard 《Spill Science & Technology Bulletin》2003,8(2):145-156
Although spilled oil is subject to a range of natural processes, only combustion, photooxidation and biodegradation destroy hydrocarbons and remove them from the biosphere. We present laboratory data that demonstrate the molecular preferences of these processes, and then examine some oil residues collected from previously documented releases to confirm the important roles that these processes play in removing spilled oil from both marine and terrestrial environments. 相似文献
424.
Mark C. Scott Gene S. Helfman Matthew E. McTammany E. Fred Benfield Paul V. Bolstad 《Journal of the American Water Resources Association》2002,38(5):1379-1392
ABSTRACT: Streams integrate biogeochemical processes operating at broad to local spatial scales and long term to short term time scales. Humans have extensively altered those processes in North America, with serious consequences for aquatic ecosystems. We collected data on Upper Tennessee River tributaries in North Carolina to: (1) compare landuse and landscape geomorphology with respect to their ability to explain variation in water quality, sedimentation measures, and large woody debris; (2) determine if landscape change over time contributed significantly to explaining present stream conditions; and (3) assess the importance of spatial scale in examining landuse influences on streams. Stream variables were related to both landuse and landscape geomorphology. Forest cover accounted for the most variation in nearly all models, supporting predictions of nutrient enrichment, thermal pollution, and sedimentation caused by landscape disturbance. Legacy effects from past catchment disturbance were apparent in sedimentation measures. Nitrogen and phosphorus concentrations, as well as stream temperature, were lower where riparian buffers had reforested. Models of stream physicochemistry fit better when predictors were catchment wide rather than more localized (i.e., within 2 km of a site). Cumulative impacts to streams due to changes in landuse must be managed from a watershed perspective with quantitative models that integrate across scales. 相似文献
425.
We observe the behavior of 37 authors of shared (i.e., non‐commercial) software for the Apple Newton in terms of multiplex commitment (committed to multiple related targets) and the helping behaviors directed at these multiple related targets. The behavior of these shared software authors show a pattern of commitment to related targets consistent with our expectations of multiplex commitment and relationships to two helping behaviors (the number of shared software programs produced, and the degree of sacrifice expected with that shared software). The related targets of commitment were the users of the software, other shared software authors, and the newsgroup that served as the electronic social exchange system, but not the FTP site that enabled the exchange or the Listserv that served as an additional electronic social exchange system. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
426.
Robert G. Paterson Michael I. Luger Raymond J. Burby Edward J. Kaiser H. Rooney Malcom Alicia C. Beard 《Environmental management》1993,17(2):167-178
The EPA’s new nonpoint source pollution control requirements will soon institutionalize urban erosion and sediment pollution
control practices nationwide. The public and private sector costs and social benefits associated with North Carolina’s program
(one of the strongest programs in the country in terms of implementation authority, staffing levels, and comprehensiveness
of coverage) are examined to provide general policy guidance on questions relating to the likely burden the new best management
practices will have on the development industry, the likely costs and benefits of such a program, and the feasibility of running
a program on a cost recovery basis. We found that urban erosion and sediment control requirements were not particularly burdensome
to the development industry (adding about 4% on average to development costs). Public-sector program costs ranged between
$2.4 and $4.8 million in fiscal year 1989. Our contingent valuation survey suggests that urban households in North Carolina
are willing to pay somewhere between $7.1 and $14.2 million a year to maintain current levels of sediment pollution control.
Our benefit-cost analysis suggests that the overall ratio is likely to be positive, although a definitive figure is elusive.
Lastly, we found that several North Carolina localities have cost recovery fee systems that are at least partially self-financing.
This article is based on research by the authors for the North Carolina Department of Environment, Health and Natural Resources
(DEHNR). The views are those of the research team and do not necessarily reflect the position of DEHNR. 相似文献
427.
Richard H. Hosier Jill Boberg Matthew Luhanga Mark Mwandosya 《Natural resources forum》1990,14(2):143-154
Woodfuel balances are commonly used by energy planners in developing countries to determine the adequacy of woodfuel resources. Recently, critics have argued that wood balances are misleading in their simplicity, exaggerating both the severity of the woodfuel shortage and the need for planned interventions to solve that problem. This paper examines four different wood balances developed for Tanzania. While the four studies all indicate that areas with miombo woodlands are in the greatest wood surplus, the specific estimates for any given region may differ widely. Despite their shortcomings, energy planners need woodfuel balances to give an impression of the adequacy of woodfuel resources. However, if energy planning is to have any effect, these balances must represent the beginning, and not the end result, of the planning process. Planners must follow the wood-energy balance analysis with work utilizing local people to solve local problems. 相似文献
428.
Matthew L. Brooks 《Environmental management》1995,19(1):65-74
Human disturbance in the western Mojave Desert takes many forms. The most pervasive are livestock grazing and off-highway
vehicle use. Over the past few decades several areas within this region have been fenced to preclude human disturbance. These
areas provide opportunities to study the impact of human activities in a desert ecosystem. This paper documents the response
of plant and small mammal populations to fencing constructed between 1978 and 1979 at the Desert Tortoise Research Natural
Area, Kern County, California.
Aboveground live annual plant biomass was generally greater inside than outside the fenced plots during April 1990, 1991,
and 1992. The alien grassSchismus barbatus was a notable exception, producing more biomass in the unprotected area. Forb biomass was greater than that of alien annual
grasses inside the fence during all three years of the study. Outside the fence, forb biomass was significantly higher than
that of alien grasses only during spring 1992. Percent cover of perennial shrubs was higher inside the fence than outside,
while no significant trend was detected in density. There was als more seed biomass inside the fence; this may have contributed
to the greater diversity and density of Merriam's kangaroo rats (Dipodomys merriami), long-tailed pocket mice (Chaetodipus formosus), and southern grasshopper mice (Onychomys torridus) in the protected area.
These results show that protection from human disturbance has many benefits, including greater overall community biomass and
diversity. The significance and generality of these results can be further tested by studying other exclosures of varying
age and configurations in different desert regions of the southwestern United States. 相似文献
429.
Thomas R. Harris Matthew L. Rea 《Journal of the American Water Resources Association》1984,20(2):193-201
ABSTRACT: Recent growth in irrigated agriculture and metropolitan areas of the Western United States suggests that if growth continues, there will be a potential shortage in future water resources. Compound the expansion of agriculture and municipal demands with possible enaction of instream flow requirements, a method to allocate water among alternative economic sectors in the West is needed. In this study, an interindustry-linear programming model based on the 1972 national model format is used to allocate scarce water supplies among competing regional economic sectors. The shadow price of water and the sectorial value of water at different availabilities for each competing sector is derived. Also, economic sectors are ranked by value of water at different water availabilities. 相似文献
430.
Matthew F. Knowlton Mark V. Hoyer John R. Jones 《Journal of the American Water Resources Association》1984,20(3):397-408
Summer lake survey measurements of total phosphorus (TP) and chlorophyll a (CHLa) from 188 reserviors and natural lakes in the midwest were analyzed to determine the magnitude of major sources of variability. Median variance among replicate samples collected at the same location and time was about 7-8 percent of the mean for both TP and CHLa. Median observed temporal variability within summers was 27 percent of the mean for TP and 45 percent of the mean for CHLa. Median values of year-to-year variance in average TP and CHLa were 22 percent and 31 percent of the mean, respectively. A range of approximately two orders of magnitude was observed among individual estimates of variance in each of these categories. The magnitude of observed temporal variability was affected only slightly by variance among replicate samples on individual days and was weakly correlated with the length of time during which samples were collected from individual lakes. Observed temporal variation was similar between reservoirs and natural lakes when variances were calculated with logtransformed data. The magnitude of temporal and year-to-year variance can severely limit the power of statistical comparisons of TP and CHLa means, but has less effect on establishing relative rankings of lake means, Sources and relative magnitude of variability are important in the use of TP and CHLa data in regression models and in the planning of lake surveys and subsequent data analysis. 相似文献