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21.
Regular fuel reduction burning is an important management strategy for reducing the scale and intensity of wildfires in south-west
Australian native forests, but the long term effects of this on tree and stand growth are not well understood. Five fire treatments,
including application of frequent and infrequent low intensity burns, and 25 years of fire exclusion, were applied to small
(4 ha) experimental plots in a low rainfall mixed jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) forest to investigate the effects of these treatments on tree stem diameter growth, stand basal area increment and tree
mortality. Mean tree stem growth measured over 20 years was lowest in the long unburnt treatment compared with the burn treatments,
although surface soil nutrient levels were generally higher in the unburnt treatment, suggesting these sites may be moisture
limited. There was no clear pattern of the effects of the burn treatments, including the number of fires and the interval
between fires, on tree stem growth, stand basal area increment, crown health or mortality. These factors were strongly influenced
by dominance condition, with dominant and co-dominant trees growing most and suppressed trees growing least and experiencing
the highest mortality levels. There was no evidence of deteriorating tree or stand health that could be attributed to either
regular low intensity burning or to a long period (25 years) of fire exclusion. 相似文献
22.
23.
Ilona Riipinen Jeffrey R. Pierce Neil M. Donahue Spyros N. Pandis 《Atmospheric environment (Oxford, England : 1994)》2010,44(5):597-607
The interpretation of thermodenuder (TD) data often relies on the assumption that thermodynamic equilibrium is reached inside the instrument. We modeled the evaporation of three organic aerosol types (adipic acid, α-pinene SOA and aged OA) inside a thermodenuder with a mass transfer model, and calculated equilibration time scales for these systems at realistic conditions. The equilibrium times varied from less than a second to several hours, decreasing with increasing aerosol concentrations, decreasing particle sizes, decreasing volatilities and increasing mass accommodation coefficients. The results indicate that generally TDs measure particle evaporation rates rather than equilibria, and time-dependent modeling of the evaporation is usually needed to interpret the data. Measurements at varying residence times and temperatures, on the other hand, are desirable to investigate the equilibration of the studied aerosol and decouple the kinetic effects from the effects caused by the thermodynamic properties of the aerosol. Organic aerosol is likely to be further from equilibrium under typical field conditions compared with laboratory data. When determining the aerosol properties from TD data, assuming incorrectly equilibrium results in under-prediction of the vaporization enthalpy of the evaporating species. Similar under-estimation is predicted if multicomponent aerosols are approximated with single-component properties. 相似文献
24.
25.
Gebbink WA Letcher RJ Burgess NM Champoux L Elliott JE Hebert CE Martin P Wayland M Weseloh DV Wilson L 《Environment international》2011,37(7):1175-1182
In the present study, we identified and examined the spatial trends, sources and dietary relationships of bioaccumulative perfluorinated sulfonate (PFSA; C(6), C(8), and C(10) chain lengths) and carboxylate (PFCA; C(6) to C(15) chain lengths) contaminants, as well as precursor compounds including several perfluorinated sulfonamides, and fluorotelomer acids and alcohols, in individual eggs (collected in 2008) from four gull species [glaucous-winged (Larus glaucescens), California (Larus californicus), ring-billed (Larus delawarensis) and herring (Larus argentatus) gulls] from 15 marine and freshwater colony sites in provinces across Canada. The pattern of PFSAs was dominated by perfluorooctane sulfonate (PFOS; >89% of ΣPFSA concentration) regardless of egg collection location. The highest ΣPFSA concentrations were found in the eggs collected in the urbanized areas in the Great Lakes and the St. Lawrence River area [Big Chicken Island 308 ng/g ww, Toronto Harbour 486 ng/g ww, and Ile Deslauriers (HG) 299 ng/g ww]. Also, eggs from all freshwater colony sites had higher ΣPFSA concentrations, which were significant (p<0.05) in many cases, compared to the marine sites with the exception of the Sable Island colony in Atlantic Canada off the coast of Nova Scotia. C(6) to C(15) chain length PFCAs were detected in the eggs, although the pattern was variable among the 15 sites, where PFUnA and PFTrA dominated the pattern for most colonies. Like the ΣPFSA, the highest concentrations of ΣPFCA were found in the eggs from Big Chicken Island, Toronto Harbour, Ile Deslauriers (HG), and Sable Island, although not all freshwater sites had higher concentrations compared to marine sites. Dietary tracers [δ(15)N and δ(13)C stable isotopes (SIs)] revealed that PFSA and PFCA exposure is colony dependent. SI signatures suggested that gulls from most marine colony sites were exposed to PFCs via marine prey. The exception was the Mandarte Island colony in Pacific British Columbia, where PFSA and PFCA exposure appeared to be via terrestrial and/or freshwater prey consumption. The same was true for the freshwater sites where egg SIs suggested both aquatic and terrestrial prey consumption as the source for PFC exposure depending on the colony. Both aquatic (marine and freshwater) and terrestrial prey are likely sources of PFC exposure to gulls but exposure scenarios are colony-specific. 相似文献
26.
Neil H. Coates 《Journal of the Air & Waste Management Association (1995)》2013,63(3):201-203
The Fourth International Conference on Fluidized Bed Combustion (FBC) was held at The MITRE Corporation in McLean, VA, December 9 to 11, 1975. With attendees from Great Britain, West Germany, Japan, Canada, and Sweden, the conference apparently fulfilled its international scope and intent. The objectives of the conference were to review the current state of technology in FBC, to promote technical information exchange on FBC and related areas, and to generate a useful technical information base for further FBC development. Throughout the conference, the goal of commercialization was repeatedly emphasized. Sponsored by the U.S. Energy Research and Development Administration (ERDA) and coordinated by MITRE, this meeting was the most comprehensive event in the seven year series of conferences on this subject according to attendees. ERDA, the government’s lead agency in FBC technology development, is the principal sponsor and coordinator of the National Fluidized Bed Combustion Program with the goal of advancing the commercialization time frame for FBC. Prior conferences in this series were hosted by the Environmental Protection Agency (EPA) at about two year intervals at Hueston Woods, Ohio. The last EPA conference was held in October 1972. 相似文献
27.
Andrea R. Ferro Neil E. Klepeis Wayne R. Ott William W. Nazaroff Lynn M. Hildemann Paul Switzer 《Atmospheric environment (Oxford, England : 1994)》2009,43(3):706-714
Residential interior door positions influence the pollutant concentrations that result from short-term indoor sources, such as cigarettes, candles, and incense. To elucidate this influence, we reviewed past studies and conducted new experiments in three residences: a single-story 714 m3 ranch-style house, a 510 m3 two-story split-level house, and a 200 m3 two-story house. During the experiments, we released sulfur hexafluoride or carbon monoxide tracer gas over short periods (≤30 min) and measured concentrations in the source room and at least one other (receptor) room for various interior door opening positions. We found that closing a door between rooms effectively prevented transport of air pollutants, reducing the average concentration in the receptor room relative to the source room by 57–100% over exposure periods of 1–8 h. When intervening doors were partially or fully open, the reduction in average concentrations ranged from 3% to 99%, varying as a function of door opening width and the distance between source and receptor rooms. 相似文献
28.
Neil L. Drobny 《Journal of the American Water Resources Association》1971,7(6):1180-1193
Applications of linear programming to water quality and water quantity problems are discussed, and a fairly comprehensive sample of recent literature in these areas is reviewed. Basic elements of linear programming are also discussed. Emphasis is placed on the elements of linear programming that make it a useful tool for analyzing water resource problems and the basic features of various water resource problems that render them amenable to meaningful analysis by linear programming. 相似文献
29.
Graduated licensing has been implemented in many U.S. states to reduce teenage driver crash involvement. The goal is to introduce teenagers gradually to driving before allowing full, unrestricted licensure. Tennessee, one of the states that introduced graduated licensing, implemented a program to influence both driving by teenagers during the learner stage and restrictions imposed by parents after licensure. In addition to a standard welcome letter, booklets and reminder cards were mailed to parents of teenagers who had just obtained their learner's permits. The booklets and cards were designed to assist parents in becoming more actively involved in their children's driving experiences. The effects of three different approaches (welcome letter only, letter plus booklet, and letter plus booklet plus reminder cards) on parental involvement, teenage crashes, and teenage citations were assessed based on telephone interviews with parents. Although the parents said the booklets and reminder cards were helpful and should continue to be sent to other parents, there were no discernible effects on teenage practice driving and reported parental involvement during the learner stage. Nor was there any measurable influence on restrictions imposed by parents after licensure. It is unknown whether the standard welcome letter affected parental involvement, but overall supervised driving exceeded the state requirements by a substantial margin. 相似文献
30.
Abstractions of surface and groundwater for irrigation in Scotland are currently subject to control in only two small catchments. Under the terms of the EU Water Framework Directive, it will be necessary to introduce new legislation to control abstractions elsewhere. To help in the development of appropriate policy for Scotland a study has been carried out to examine the significance of irrigation and the effectiveness of different types of control strategies in terms of the economics of potato cropping and stream hydrology in Scotland. This paper presents the findings of the hydrological study and highlights some of the spatial and temporal issues that need to be considered in the selection of control mechanisms, if they are to be successful in achieving objectives for environmental improvement.The study was focussed on two catchments in the east of Scotland, the Tyne and West Peffer. The effectiveness of several different abstraction control strategies was examined to see how stream flows in the catchment would be modified by their implementation. The results of the study demonstrated that the West Peffer catchment in particular is significantly affected by irrigation abstractions. Control mechanisms based on allowable monthly abstraction volumes and flow-based abstraction bans would be of considerable help in restoring stream flows to their natural levels, but would modify the hydrological regime in slightly different ways. A spatial analysis of stream flows demonstrated that implementation of controls based on a single monitoring point may be ineffective at maintaining acceptable levels of flow throughout the catchment and that this may require a tighter control at the monitoring point. 相似文献