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排序方式: 共有998条查询结果,搜索用时 250 毫秒
901.
Langan Simon Hodson Mark Bain Derek Hornung Mike Reynolds Brian Hall Jane Johnston Lynne 《Water, Air, & Soil Pollution: Focus》2001,1(1-2):299-312
Current legislation within Europe aimed at limitingecosystem damage resulting from inputs of atmosphericpollution is based on the critical load concept. Mineralweathering rates are central to the calculation ofcritical loads (acceptable levels) of acid deposition.The authors have undertaken a number of studies whichillustrate the complications and limitations inherent inpredicting mineral weathering rates and the implicationswhich these have for critical loads calculations andmapping. Calculated weathering rates and critical loadsfor two acid-sensitive parent materials (greywackes andgranites) are presented and are used to illustrate theimpact that uncertainty can have on critical loadexceedances. The results have obvious implications forportraying the uncertainties of critical loads to policy makers. 相似文献
902.
Brian E. Haggard Daniel E. Storm Emily H. Stanley 《Journal of the American Water Resources Association》2001,37(5):1291-1299
ABSTRACT: We examined the effect of a point source (PS) input on water chemistry and nutrient retention in Spavinaw Creek, Arkansas, during summer baseflows in 1998 and 1999. The nutrient uptake length (Sw) concept was used to quantify the impact of nutrient inputs in the receiving stream. We used an artificial injection upstream of the PS inputs to estimate background S and used the natural decline in nutrient concentrations below the PS to estimate the net nutrient uptake length (Snet). Sw for soluble reactive phosphorus (SRP) in the upstream reference section was O.75 km, but Snet ranged from 9.0 to 31 km for SRP and 3.1 to 12 km for NO3‐N in the reach below the PS. Snet‐SRP was significantly correlated with discharge whereas Snet‐NO3‐N was correlated with the amount of NO3‐N enrichment from the PS. In order to examine specific mechanisms of P retention, loosely exchangeable P and P Sorption Index (PSI) of stream sediments were measured. Sediments exhibited little natural P buffering capacity (low PSI) above the PS, but P loading from the PS further reduced PSI. Loosely exchangeable P in the sediments also increased three fold below the PS, indicating sediments removed some water column P. The physical process of flow and sediment sorption apparently regulated P retention in Spavinaw Creek, whereas the level of N enrichment and possibly biotic uptake and denitrification influenced N retention. Regardless of the mechanism, Spavinaw Creek demonstrated little ability to retain PS‐added nutrients because net nutrient uptake lengths were in the km range. 相似文献
903.
Rob de Loë Liana Moraru Reid Kreutzwiser Karl Schaefer Brian Mills 《Journal of the American Water Resources Association》2001,37(1):57-72
ABSTRACT: Demand side management is being used increasingly by Ontario municipalities as a way to improve the efficiency of water use, defer the costs associated with constructing new water treatment works, and minimize the environmental impacts associated with supplying water. A comprehensive survey of 153 Ontario municipalities was completed in mid‐1998. These ranged in size from small rural townships (with populations as low as 500 people) to the province's largest urban center, Metropolitan Toronto, with a population of approximately 2.5 million people. The questionnaire measured the use of six broad types of demand side measures, including water pricing and metering; municipal by‐laws (ordinances) that promote water conservation; operational and maintenance measures to reduce water losses and consumption; water‐saving plumbing fixtures and devices; public participation programs that encourage water conservation; and other measures, such as water audits. Additionally, the survey collected data on implementation barriers and opportunities. Since the last comprehensive Ontario survey, conducted in 1987 by Kreutzwiser and Fea‐gan (1989), there has been an increase in the use of basic tools such as metering and pricing, plumbing fixtures, and public participation programs. Additionally, new initiatives, such as water audits and computerized monitoring equipment, are being used. However, in many areas opportunities exist to make better use of demand side measures. Unfortunately, municipal capacity to do so often is constrained by (among other factors) limited finances, lack of political will, and public resistance. Demonstration of real cost savings to consumers, and the development of specific goals and objectives for demand side management programs, are two important steps needed to overcome these challenges. 相似文献
904.
A preliminary characterization of polynuclear aromatic hydrocarbons (PAH) in dichloromethane extracts of diesel exhaust particulates is described. Acid-base liquid-liquid partitioning followed by adsorption chromatography was used to isolate the PAH fraction. Compounds were identified primarily by the mass spectra of high-resolution gas chromatographic effluents. Three four-ring PAHs and their alkyl-substituted homologues were the predominant constituents. In addition, ultraviolet spectra of four high performance liquid chromatography-separated PAHs were superimposable with those of reference compounds leading to their unambiguous identification. These results show the advantage of using several complementary techniques for characterization rather than gas chromatrographapy-mass spectrometry alone. 相似文献
905.
Brian S. Nelson 《Behavioral ecology and sociobiology》2002,53(1):42-50
Eastern towhees, Pipilo erythrophthalmus, (Emberizidae, Passeriformes) in Florida estimate source sound-pressure level (SPL; i.e., sound amplitude) and often misjudge speaker distance in the field when vocalization source SPL is varied experimentally. Sound frequencies below ~3.5 kHz attenuate reliably with distance in comparison with higher sound frequencies in Florida scrub habitat. As a result, I predicted that towhees should use SPL as an auditory distance cue when they hear stimuli produced with sound frequencies below ~3.5 kHz but use another cue when they hear stimuli produced with sound frequencies above ~3.5 kHz. Subjects often misjudged speaker distance when approaching playbacks of SPL-altered stimuli produced with sound frequencies below ~3.5 kHz but rarely misjudged speaker distance when played SPL-altered stimuli produced with sound frequencies above ~3.5 kHz. I discuss the possibility that towhees employ a duplex sound localization strategy. 相似文献
906.
Statistical evaluation procedures for monitoring data at facilities permitted under the Resource Conservation and Recovery Act (RCRA) are frequently established before monitoring begins. Selecting the statistical method before background data have been collected often leads to the use of statistical procedures that are inappropriate for the actual monitoring data. Such was the case for unsaturated zone monitoring at a permitted land treatment unit in the Gulf Coast area of Texas. Due to the large number of “not detected” results in the background database for lysimeters, statistical evaluation procedures specified in the original RCRA permit yielded an artificially low standard deviation, resulting in background values that were strongly biased on the low side. An alternate statistical procedure based on probability plots was developed and was accepted by the state environmental regulatory agency. This technique, which has wide applicability for many types of environmental monitoring data, significantly reduced the chasing of false positives, thus saving potentially expensive investigations and remediations. 相似文献
907.
908.
909.
Ventilation requirements in occupied spaces have traditionally derived largely from odor control. The requirements have rested on the notion that an environment that seems subjectively acceptable to a visitor will in fact be healthful and comfortable for both visitor and occupant alike. Ventilation requirements have derived secondarily from criterion concentrations of notable contaminants (e.g., carbon dioxide). The present investigation looked again at both sensory (odor, irritation) and physical criteria of acceptability, paying particular attention to the difference between smoking and nonsmoking occupancy in a well-controlled environmental chamber. More than 200 persons (visitors) made judgments of odor intensity and acceptability under various conditions of occupancy (up to 12 nonsmoking occupants; a temperature of up to 25.5°C; up to 16 cigarettes smoked per hour). The results implied that under nonsmoking conditions and moderate humidity only about 7.5 cfm (3.8 L sec−1) of fresh air per occupant sufficed to satisfy visitors, but that under smoking conditions at least 5 times as much fresh air is necessary. Our estimate of ventilation requirements for smoking were derived in part from measurements of carbon monoxide and total suspended particulate (TSP) mass concentration. Levels of TSP achieved during realistic smoking and ventilation rates exceeded levels deemed acceptable outdoors. Surfaces in the chamber played an important role in the elimination of particles, presumably via adsorption. Use of an electrostatic precipitator could keep TSP levels under control. Nevertheless, it remains to be seen whether control of TSP will eliminate the need for enormous ventilation for odor control during smoking occupancy. 相似文献
910.