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91.
Peter J. Popp Gary A. Bishop 《Journal of the Air & Waste Management Association (1995)》2013,63(12):1463-1468
ABSTRACT The University of Denver (DU) has developed a new remote sensor for the measurement of mobile source nitric oxide (NO). This system is integrated with an existing infrared remote sensor and is capable of measuring carbon monoxide and hydrocarbons in addition to NO, at a rate of more than 1000 vehicles/hr. The detection limit on a low-emitting vehicle under typical measurement conditions is 24 parts per million NO (3σ). Measurements from this instrument correlated well in a side-by-side comparison with the previous NO remote sensor developed at DU, and we have used this study to confirm a suspected interference by aromatic hydrocarbons in the older instrument. The results of an extended field experiment using the new instrument, conducted in fall 1997, are also presented. The NO emissions of the fleet measured in this study (averaging 15.0 g NO/gal) exhibit a skewed distribution typical of mobile sources. This paper also describes the relationship between NO emissions and model year and NO emissions and vehicle acceleration, as measured by the new remote sensor. 相似文献
92.
The role of organic acids on surface water acidity as well as their buffering during anthropogenic acidification and subsequent recovery was studied in a field experiment on a total organic carbon (TOC)-rich stream draining the Svartberget catchment in northern Sweden. H(2)SO(4) was added to the stream to increase SO(4)(2-) concentration by 90 microeq l(-1) for 30 h. About 60% of the added H(+) was buffered by protonation of organic acids, another 20% was buffered by base cations released from the surface of the stream channel and only ca. 20% of the added acid remained unbuffered. TOC concentrations (27 mg l(-1)), and site density of carboxylic groups--8.6 microeq (mg TOC)(-1)--remained stable during the experiment. Two models of organic acid dissociation (a triprotic model and a monoprotic pH-dependent pKa model) were fitted to the experimental results. These models explained the observed variations in organic anions, but the model parameters were quite different from those reported by studies in Northern America and Central Europe. This experiment had substantially more buffering effect of TOC between pH 4.4 and 5.3, which is an environmentally important pH range. 相似文献
93.
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95.
Real-time control of aeration tank operation is key to high-efficiency pollutant removal and energy savings. One of the aims of this study was to examine the potential for using redox potential (oxidation-reduction potential [ORP]) to indicate wastewater quality online in aeration tanks treating medium (chemical oxygen demand [COD] of 70 to 150 mg/L) and low (COD of 15 to 30 mg/L) pollutant-concentration wastewaters. The field-scale data provide a good relationship between ORP values and nutrient removal along the length of the aeration tanks. The ORP values increased dramatically as organic matter was removed along the aeration tanks, indicating the improvement of the bulk liquor redox status. Dissolved oxygen higher than 1.0 mg/L was necessary for good biodegradation and improvement of the liquid redox status. Nitrification occurred at higher ORP values (380 to 420 mV) than was the case for organic substrate oxidation (250 to 300 mV). The microprofiles obtained from microelectrode measurements substantiate the heterogeneity of the microbial processes inside activated sludge flocs. Because of microbial oxygen utilization, the aerobic region in the activated sludge floc was limited to the top layer (0.1 to 0.2 mm) of the activated sludge aggregate present in medium-strength wastewater, with an anoxic zone dominating inside the flocs. When dissolved oxygen in the bulk water was higher than 4.0 mg/L, the anoxic zone inside the floc disappeared. At low wastewater pollutant concentrations, the ORP and dissolved oxygen inside the activated sludge aggregates were higher than those from medium-strength wastewater. The prospect of using ORP as an online control approach for aeration tank operation and the potential reasons for activated sludge floc size varying with pollutant strengths are also discussed. 相似文献
96.
Andrew J. Pemberton Lars J. Hansson Sean F. Craig Roger N. Hughes John D. D. Bishop 《Marine Biology》2007,153(1):71-82
Microscale genetic differentiation of sessile organisms can arise from restricted dispersal of sexual propagules, leading
to isolation by distance, or from localised cloning. Cyclostome bryozoans offer a possible combination of both: the localised
transfer of spermatozoa between mates with limited dispersal of the resulting larvae, in association with the splitting of
each sexually produced embryo into many clonal copies (polyembryony). We spatially sampled 157 colonies of Crisia denticulata from subtidal rock overhangs from one shore in Devon, England at a geographic scale of ca. 0.05 to 130 m plus a further 21
colonies from Pembrokeshire, Wales as an outgroup. Analysis of molecular variance (AMOVA) revealed that the majority (67%)
of genetic variation was distributed among individuals within single rock overhangs, with only 16% of variation among different
overhangs within each shore and 17% of variation between the ingroup and outgroup shores. Despite local genetic variation,
pairwise genetic similarity analysed by spatial autocorrelation was greatest at the smallest inter-individual distance we
tested (5 cm) and remained significant and positive across generally within-overhang comparisons (<4 m). Spatial autocorrelation
and AMOVA analyses both indicated that patches of C. denticulata located on different rock overhangs tended to be genetically distinct, with the switch from positive to negative autocorrelation,
which is often considered to be the distance within which individuals reproduce with their close relatives or the radius of
a patch, occurring at the 4–8 m distance class. Rerunning analyses with twenty data sets that only included one individual
of each multilocus genotype (n = 97) or the single data set that contained just the unique genotypes (n = 67) revealed that the presence of repeat genotypes had an impact on genetic structuring (PhiPT values were reduced when
shared genotypes were removed from the dataset) but that it was not great and only statistically evident at distances between
individuals of 1–2 m. Comparisons to a further 20 randomisations of the data set that were performed irrespective of genotype
(n = 97) suggested that this conclusion is not an artefact of reduced sample size. A resampling procedure using kinship coefficients,
implemented by the software package GENCLONE gave broadly similar results but the greater statistical power allowed small
but significant impacts of repeat genotypes on genetic structure to be also detected at 0.125–0.5 and 4–16 m. Although we
predict that a proportion of the repeat multilocus genotypes are shared by chance, such generally within-overhang distances
may represent a common distance of cloned larval dispersal. These results suggests that closely situated potential mates include
a significant proportion of the available genetic diversity within a population, making it unlikely that, as previously hypothesised,
the potential disadvantage of producing clonal broods through polyembryony is offset by genetic uniformity within the mating
neighbourhood. We also report an error in the published primer note of Craig et al. (Mol Ecol Notes 1:281–282, 2001): loci Cd5 and Cd6 appear to be the same microsatellite.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
97.
Summary The threat-sensitive predator avoidance hypothesis predicts that prey can assess the relative threat posed by a predator and adjust their behaviour to reflect the magnitude of the threat. We tested the ability of larval threespine sticklebacks to adjust their foraging in the presence of predators by exposing them to conspecific predators of various sizes and recording their foraging and predator avoidance behaviours. Larvae (<30 days post-hatch) displayed predator escape behaviours only towards attacking predators. At 3 weeks post-hatch larvae approached the predator after fleeing, a behaviour which may be the precursor to predator inspection. Larvae reduced foraging and spent less time in the proximity of large and medium-sized predators compared to small predators. The reduction in foraging was negatively correlated to the predator/larva size ratio, indicating that larvae increased their foraging as they increased in size relative to the predator. We conclude that larval sticklebacks can assess the threat of predation early in their ontogeny and adjust their behaviour accordingly.Correspondence to: J.A. Brown 相似文献
98.
Kevin Bishop 《Journal of Environmental Planning and Management》1992,35(1):63-76
In 1989 the Countryside and Forestry Commissions launched a national programme to create Community Forests on the fringes of major towns and cities in England and Wales. The assumption that such forests will be of benefit to the community at large was tested by means of surveys of two existing multi‐purpose woodlands adjacent to major conurbations. Contingent valuation, travel cost and time cost methods of environmental valuation were used to estimate the existing user benefits of the two woodlands for recreation. The study highlights weaknesses in the travel cost approach when applied to recreational facilities located near urban fringe areas which can be accessed on foot. The results of the two surveys are discussed and compared with similar results for more rural woodlands/ forests. The study suggests that on social grounds at least the concept of Community Forests should be pursued with recreation benefits alone exceeding management costs by a factor of three. 相似文献
99.
Co-occurring foundation species can determine biological community structure via facilitation cascades. We examined the density dependencies of facilitation cascades, including how the density of a basal foundation species influences the density of secondary foundation species, and how the density of secondary foundation species influences community structure. The system in which we assessed density dependencies was a temperate mangrove forest in which pneumatophores trap the fucoid alga Hormosira banksii and provide substrate for the oyster, Saccostrea glomerata. The alga and oyster in turn determine benthic community structure. In the field, algal biomass was positively correlated with pneumatophore density. Oysters, by contrast, were highly over-dispersed and correlated with the presence/absence of pneumatophores. Epifaunal abundance and species richness were positively correlated with algal and oyster abundance, but their effects were independent. The positive effect of pneumatophore density on epifauna was primarily an indirect effect of trapping more algae. Pneumatophores did not directly influence invertebrate communities. Experiments revealed that, at very low pneumatophore densities, algal retention was insufficient to facilitate epifauna above that found on pneumatophores alone. At higher densities, however, increasing the density of pneumatophores increased algal retention, and the density and diversity of associated invertebrates. Shading by the mangrove canopy reduced algal biomass but did not modify the density-dependent nature of the cascade. Our results extend facilitation theory by showing that the density of both basal and secondary foundation species can be critical in triggering facilitation cascades. Our study also reveals that, where foundation species co-occur, multiple, independent cascades may arise from a single basal facilitator. These findings enhance our understanding of the role of density-dependent facilitation cascades in community assembly. 相似文献
100.
Spatial and temporal variability of fish assemblages in Kuwait Bay was studied using the catch data acquired through monthly
otter trawl sampling from June 2002 through July 2004. We compared species composition using relative species density and
cluster analysis among different seasons (summer’02, summer’03, winter’03, and spring’04) and areas (center, south 1, south
2, west, north and east). Significant differences in total species, species richness (SR), diversity (H′), and fish abundance were tested among (between) different seasons and areas using analysis of variance (ANOVA) and Duncan’s
test. The results showed that the catches consisted of 80 species representing 41 families with Leiognathus bindus and Plicofollis tenuispinis dominating numerically. Spatially, species composition fell into three main areas: (1) east; (2) south 1 and south 2; and
(3) north, center, and west. Temporally, winter’03 and spring’04 were closely related, but we found low similarity between
the two summers and even lower similarity between the summers and other seasons, indicating high intra-annual variation. L. bindus was abundant in most of the areas except south 1, south 2 and the east area. Spatial changes of abundance of the two dominant
species showed a complementary trend. Where L. bindus was numerically high, P. tenuispinis was low, and vice versa. Significant lower total species number and SR were observed in south 2 than all the other areas
except the east, and significant higher fish abundance occurred in the summers than during the other seasons. Overall, it
was concluded that variation in fish assemblages was area dependent, while fish abundance was mainly influenced by seasonal
changes. 相似文献