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451.
452.
Harald Geiger Karl H. Becker 《Journal of the Air & Waste Management Association (1995)》2013,63(4):425-433
Abstract Based on exhaust gas analyses from the combustion of five different types of gasoline in a passenger car operated on a chassis dynamometer, box model simulations of the irradiation of exhaust/NOx /air mixtures using an established chemical mechanism for a standardized photo-smog scenario were performed. The fuel matrix used covered wide fractional ranges for paraffinic, olefinic, and aromatic hydrocarbons. Two fuels also contained methyl tertiary butyl ether (MTBE). The different O3 profiles calculated for each run were compared and interpreted. The O3 levels obtained were strongly influenced by the exhaust gas concentrations of aromatic and olefinic hydro-carbons. The higher exhaust content of these compounds caused higher O3 production in the smog system investigated. The conclusion of the present study is that the composition of gasoline cannot be taken directly for the estimation of the emissions’ O3 creation potential from its combustion. Variation of the dilution in the different calculations showed evidence for an additional influence of transport effects. Accordingly, further detailed exhaust gas analyses followed by more complex modeling studies are necessary for a proper characterization of the relationship between fuel blend and gasoline combustion products. 相似文献
453.
Davide Falchieri Karl Mierzejewski Steven Maczuga 《Journal of environmental science and health. Part. B》2013,48(4):535-548
Abstract The feeding behavior of gypsy moth larvae exposed to two pesticide deposits (Bt and carbaryl) on oak leaf disks was monitored to determine the relationships between its efficacy and application parameters (droplet density and pesticide concentration). A range of pesticide concentrations and droplet densities (from 9 to 149 droplets/cm2) was used to simulate high and low application rates produced by different methods of application in the field. The LD50 and the LC50, appeared to be affected by the spatial distribution of the deposit on the leaf surface. Both Bt and carbaryl showed a decreasing LD50 at increasing time after spray. The LD50 of Bt decreased from 14.1 BIU/liter to 3.1 BIU/Iiter between 48 and 144 hours after spray. The results show that feeding inhibition by Bt is more closely related to concentration than to droplet density and dose per unit area with the highest feeding inhibition occurring at 10 BIU/liter at 9 droplets/cm2. With carbaryl, an increase in both concentration and droplet density was necessary to cause a decrease in leaf area eaten by larvae. 相似文献
454.
Abundance of denitrification genes under different peizometer depths in four Irish agricultural groundwater sites 总被引:1,自引:0,他引:1
Maria Barrett Mohammad M. R. Jahangir Changsoo Lee Cindy J. Smith Niamh Bhreathnach Gavin Collins Karl G. Richards Vincent O’Flaherty 《Environmental science and pollution research international》2013,20(9):6646-6657
This study examined the relationship between the abundance of bacterial denitrifiers in groundwater at four sites, differing with respect to overlaying land management and peizometer depth. Groundwater was sourced from 36 multilevel piezometers, which were installed to target different groundwater zones: (1) subsoil, (2) subsoil to bedrock interface, and (3) bedrock. The gene copy concentrations (GCCs), as gene copies per liter, for bacterial 16S rRNA genes and the denitrifying functional genes, nirK, nirS, and nosZ, were determined using quantitative polymerase chain reaction assays. The results were related to gaseous nitrogen emissions and to the physicochemical properties of the four sites. Overall, nirK and nirS abundance appeared to show no significant correlation to N2O production (P?=?0.9989; P?=?0.3188); and no significant correlation was observed between nosZ and excess N2 concentrations (P?=?0.0793). In the majority of piezometers investigated, the variation of nirK and nirS gene copy concentrations was considered significant (P?<?0.0001). Dissolved organic carbon (DOC) decreased with aquifer depth and ranged from 1.0–4.0 mg l?1, 0.9–2.4 mg l?1, and 0.8–2.4 mg l?1 within piezometers located in the subsoil, subsoil/bedrock interface, and bedrock depths, respectively. The availability of increasing DOC and the depth of the water table were positively correlated with increasing nir and nosZ GCCs (P?=?0.0012). A significant temporal correlation was noted between nirS and piezometer depth (P?<?0.001). Interestingly, the nirK, nirS, and nosZ GCCs varied between piezometer depths within specific sites, while GCCs remained relatively constant from site to site, thus indicating no direct impact of agricultural land management strategies investigated on denitrifier abundance. 相似文献
455.
Kevin C. Bold Frederica Wood Pamela J. Edwards Karl W. J. Williard Jon E. Schoonover 《Environmental monitoring and assessment》2010,163(1-4):685-698
Road prisms, including cutbanks, road surfaces, and fillslopes, can be important contributors of sediment to streams in forested watersheds. Following road construction, cutbanks and fillslopes are often seeded, mulched, and sometimes fertilized to limit erosion and sedimentation. Assessing the success of vegetation establishment on cutbanks and fillslopes is a common task of forested land managers. This study developed and applied a photographic image analysis method to assess percent ground cover along an entire cutbank of a cut-and-fill haul road in the Monongahela National Forest in Tucker County, West Virginia. Variable-sized sections were employed to quantify the vegetative cover. Measurements obtained by this technique were similar to more commonly applied fixed-area plots, and it proved to be a useful tool for land managers who require a more repeatable quantification of ground cover than is possible through visual assessments. Cutbank slope and aspect also were analyzed to determine their potential impact on cutbank vegetation establishment. Slope was not a significant variable in explaining differences in vegetation cover; however, aspect did affect vegetation establishment. South-facing aspects had significantly lower percent vegetation cover than northeast, east, northwest, and north northwest aspects after the first year following seeding and throughout the entire study. Mean percent cover on the south-facing cutbanks was 32% over all time periods, compared to 60% to 73% for the other represented aspects. This result was expected since south-facing slopes generally are drier in the growing season and are subject to more freeze–thaw cycles in the winter. Timber felled onto the cutbank also decreased vegetative cover in the short term on north and north northwest aspects, but vegetation quickly became reestablished on these aspects with their favorable growing conditions. 相似文献
456.
457.
A study was conducted to evaluate the efficacy of PHOSter® technology for treating groundwater contaminated with trichloroethene (TCE) at Edwards Air Force Base, California. The technology consists of injecting a gaseous mixture of air, methane, and nutrients into groundwater with the objective of stimulating the growth of methanotrophs, a naturally occurring microbial group that is capable of catalyzing the aerobic degradation of chlorinated solvents into nontoxic products. Injection operations were performed at one well for a period of three months. Six monitoring wells were utilized for groundwater and wellhead vapor monitoring and for groundwater and microbial sampling. In the five monitoring wells located within 44 feet of the injection well, the following results were observed: dissolved oxygen concentrations increased to a range between 6 and 8 milligrams per liter (μg/L); the biomass of target microbial groups increased by one to five orders of magnitude; and TCE concentrations decreased by an average of 92 percent, and to below the California primary maximum contaminant level (MCL; 5 micrograms per liter [µg/L]) in the well closest to the injection well. © 2008 Wiley Periodicals, Inc. * 1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America. 相似文献
458.
Sabine Grundmann Ulrike Dörfler Bernhard Ruth Christine Loos Tobias Wagner Heidrun Karl Jean Charles Munch Reiner Schroll 《Water, Air, & Soil Pollution: Focus》2008,8(2):177-185
A recently designed two-chamber-lysimeter-test-system allows the detailed investigation of degradation, transport and transfer
processes of 14C-labeled substances in soil–plant–atmosphere-systems under outdoor conditions. With this test system it is feasible to distinguish
between 14C-emissions from soil surfaces and 14C-emissions from plant surfaces in soil monoliths under real environmental conditions. Special soil humidity sensors allow
the measurement of soil water content near to the soil surface, in 1 and 5 cm depth. The behavior of organic chemicals can
be followed for a whole vegetation period and a mass balance for the applied chemical can be established. Some selected results
of the herbicides isoproturon and glyphosate – using the two-chamber-lysimeter-test-system – are presented to demonstrate
its applicability for the identification and quantification of the processes that govern pesticide behavior in soil–plant-systems.
Mineralization of 14C-isoproturon was very different in four different soils; the mineralization capacity of the soils ranged from 2 to 60%. Leaching
of isoproturon in general was very low, but depending on the soil type and environmental conditions isoproturon and its metabolites
could be leached via preferential flow, especially shortly after application. For the herbicide 14C-glyphosate no accumulation of residues in the soil and no leaching of the residues to deeper soil layers could be observed
after three applications. Glyphosate was rapidly degraded to AMPA in the soil. Glyphosate and AMPA were accumulated in soy
bean nodules. 相似文献
459.
Duniway MC Karl JW Schrader S Baquera N Herrick JE 《Environmental monitoring and assessment》2012,184(6):3789-3804
Collection of standardized assessment and monitoring data is critically important for supporting policy and management at
local to continental scales. Remote sensing techniques, including image interpretation, have shown promise for collecting
plant community composition and ground cover data efficiently. More work needs to be done, however, evaluating whether these
techniques are sufficiently feasible, cost-effective, and repeatable to be applied in large programs. The goal of this study
was to design and test an image-interpretation approach for collecting plant community composition and ground cover data appropriate
for local and continental-scale assessment and monitoring of grassland, shrubland, savanna, and pasture ecosystems. We developed
a geographic information system image-interpretation tool that uses points classified by experts to calibrate observers, including
point-by-point training and quantitative quality control limits. To test this approach, field data and high-resolution imagery
(∼3 cm ground sampling distance) were collected concurrently at 54 plots located around the USA. Seven observers with little
prior experience used the system to classify 300 points in each plot into ten cover types (grass, shrub, soil, etc.). Good
agreement among observers was achieved, with little detectable bias and low variability among observers (coefficient of variation
in most plots <0.5). There was a predictable relationship between field and image-interpreter data (R
2 > 0.9), suggesting regression-based adjustments can be used to relate image and field data. This approach could extend the
utility of expensive-to-collect field data by allowing it to serve as a validation data source for data collected via image
interpretation. 相似文献
460.
Determining sources of dissolved organic carbon and disinfection byproduct precursors to the McKenzie River, Oregon 总被引:2,自引:0,他引:2
Kraus TE Anderson CA Morgenstern K Downing BD Pellerin BA Bergamaschi BA 《Journal of environmental quality》2010,39(6):2100-2112
This study was conducted to determine the main sources of dissolved organic carbon (DOC) and disinfection byproduct (DBP) precursors to the McKenzie River, Oregon (USA). Water samples collected from the mainstem, tributaries, and reservoir outflows were analyzed for DOC concentration and DBP formation potentials (trihalomethanes [THMFPs] and haloacetic acids [HAAFPs]). In addition, optical properties (absorbance and fluorescence) of dissolved organic matter (DOM) were measured to provide insight into DOM composition and assess whether optical properties are useful proxies for DOC and DBP precursor concentrations. Optical properties indicative of composition suggest that DOM in the McKenzie River mainstem was primarily allochthonous--derived from soils and plant material in the upstream watershed. Downstream tributaries had higher DOC concentrations than mainstem sites (1.6 +/- 0.4 vs. 0.7 +/- 0.3 mg L(-1)) but comprised < 5% ofmainstem flows and had minimal effect on overall DBP precursor loads. Water exiting two large upstream reservoirs also had higher DOC concentrations than the mainstem site upstream of the reservoirs, but optical data did not support in situ algal production as a source of the added DOC during the study. Results suggest that the first major rain event in the fall contributes DOM with high DBP precursor content. Although there was interference in the absorbance spectra in downstream tributary samples, fluorescence data were strongly correlated to DOC concentration (R2 = 0.98), THMFP (R2 = 0.98), and HAAFP (R2 = 0.96). These results highlight the value of using optical measurements for identifying the concentration and sources of DBP precursors in watersheds, which will help drinking water utilities improve source water monitoring and management programs. 相似文献