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排序方式: 共有129条查询结果,搜索用时 31 毫秒
61.
Jack A. Stanford Edward B. Reed 《Journal of the American Water Resources Association》1974,10(3):470-477
ABSTRACT: A colonization basket sampling technique for quantifying macroinvertebrates in rubble bottom rivers is described. Basket samplers were compared to collections made using the Surber square foot sampler. Procedure for processing samples is described. Macrobenthos were more accurately quantified by basket samplers because both surface and subsurface habitats were sampled, no organisms were lost when samplers were removed from the river, substrata and associated fauna were retained for analysis, and the samplers were used efficiently in both pool and riffle areas. At the end of the colonization period the basket samplers contained one-half cubic foot of river bottom and macroinvertebrates spatially arranged within. 相似文献
62.
Keith V. Slack Rodger F. Ferreira Robert C Averett 《Journal of the American Water Resources Association》1986,22(2):237-248
ABSTRACT: Four different bottom-placed artificial substrates were compared with the Ponar grab for collecting benthic invertebrates. Artificial substrate samples of organisms were larger and more diverse than those of the grab. Barbeque Basket samplers caught the most taxa and individuals and Beak Trays caught the least. Chironomids and crustaceans were dominant in artificial substrate samples. Exposure habitat (left or right bank) determined taxa availability, whereas sampler design determined suitability for colonization by the taxa. Diversity for Beak Tray samples was lower than that for other artificial substrates but higher than for Ponar samples. The Barbeque Basket, Bull Basket, and Multiple Plate samples were taxonomically similar. Ponar samples were different, and Beak Trays were of intermediate similarity. As qualitative samplers, Barbeque Baskets were 63 percent efficient, followed by Bull Baskets (55 percent), Multiple Plates (48 percent), Beak Trays (38 percent), and Ponar Grabs (6–10 percent). Bull Baskets required the least and Beak Trays the most replicates to be within a preselected percentage error of the mean at the 95 percent probability level for numbers of taxa and individuals, and for diversity. Under conditions of the study, Bull Baskets ranked highest, followed by Barbeque Baskets and Multiple Plates, in selected performance criteria. Differences between grab and artificial substrate samples are explainable in terms of major riverine habitats and characteristics of the collection methods. 相似文献
63.
被动采集大气颗粒物样品的粒径分布特征 总被引:1,自引:0,他引:1
在可同时采集气态与颗粒态大气污染物的被动采样装置中放置涂有薄层凡士林的载玻片,用于采集大气悬浮颗粒物,利用粒度粒形仪分析样品粒径分布特征,并深入探讨风速以及采样罐外壁添加300目滤网(孔径50μm)对样品粒径分布的影响.结果表明,在室内静风与室外相对封闭的条件下,添加滤网可有效阻止50μm的粗颗粒组分进入采样罐;而在室外有风的条件下,添加滤网后仍有粗颗粒进入采样罐中,但进入概率与风速大小之间无关.观察粒径10μm以下颗粒的分布曲线,室内静风条件下得到的分布曲线与主动采样得到的结果极为类似.而在有风条件下,3~5μm的颗粒组分比重有所减少,6~9μm颗粒组分比重明显增加.上述问题在被动采样器的使用中需予以考虑,结合样点具体情况判断是否添加滤网. 相似文献
64.
醋酸乙烯作为重要的有机化工原料在扬州多家化工企业使用,在此针对醋酸乙烯的理化性质,采用便携式采样器采集气体样品,参考了EPA.625方法中采样罐采样热脱附气相色谱-质谱法进行分析,但是热脱附装置和采样罐价格昂贵.质谱分析时间较长.操作要求高.不便于常规监测分析,现采用活性炭吸附气相色谱分析醋酸乙烯。通过实验总结出一套采样时间短分析速度快.灵敏度高的快速分析方法.为环境监测工作中醋酸乙烯应急监测提供分析参考。 相似文献
65.
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67.
Frédériqu Larrarte 《Environmental Fluid Mechanics》2008,8(3):249-261
A precise determination of the pollutant loads processed through the sewer networks is required for legal, environmental and
management reasons. Such a determination requires a good evaluation of concentrations, which is not an easy task because samplers
or sensors can perform measurements in a cross-sectional area of only a few locations, and this local information must then
be extrapolated across the whole cross-sectional area of the sewer network. This latter step is problematical. A great deal
of attention must be given to suspended solids because they are prone to settle and display heterogeneous concentration patterns.
A two-dimensional sampler has been designed to measure the variation of suspended solids concentration throughout a cross-sectional
area. This paper presents the principles upon which the conception of this experimental device was based and the building
process. Experimental results are presented and discussed. 相似文献
68.
Measurement of nitrogen dioxide using passivediffusion tube over 22 months in Cambridge, U.K. areanalysed as a function of sampler exposure time, andcompared with NO2 concentrations obtained from aco-located chemiluminescence analyser. The averageratios of passive sampler to analyser NO2 at acity centre site (mean NO2 concentration 22 ppb)are 1.27 (n = 22), 1.16 (n = 34) and 1.11 (n = 7) forexposures of 1, 2 and 4-weeks, respectively. Modellingthe generation of extra NO2 arising from chemicalreaction between co-diffusing NO and O3 in thetube gave a ratio (modelled/measured) of 1.31 for1-week exposures. Such overestimation is greatest whenNO2 constitutes, on average, about half of totalNOx (= NO + NO2) at the monitoring locality.Although 4-week exposures gave concentrations whichwere not significantly different from analyserNO2, there was no correlation between thedatasets. At both the city-centre site and anothersemi-rural site (mean NO2 concentration 11 ppb)the average of the aggregate of four consecutive1-week sampler exposures or of two consecutive 2-weeksampler exposures was systematically greater than fora single 4-week exposure.The results indicate two independent and opposingsystematic biases in measurement of NO2 bypassive diffusion sampler: an exposure-timeindependent chemical overestimation with magnitudedetermined by local relative concentrations of NO andO3 to NO2, and an exposure-time dependentreduction in sampling efficiency. The impact of theseand other potential sources of systematic bias on theapplication of passive diffusion tubes for assessingambient concentrations of NO2 in short (1-week)or long (4-week) exposures are discussed in detail. 相似文献
69.
Scott A. Lecce 《Journal of the American Water Resources Association》2009,45(1):272-277
Abstract: This paper describes the construction and testing of a device for pumping water samplers that collects suspended sediment samples by moving the intake vertically to keep it at the same proportion of flow depth. The device uses a simple sprocket mechanism that can be mounted vertically on the downstream side of culverts and bridge pilings to protect against damage from floating debris during storms. Suspended sediment samples collected from an urban stream with the depth‐proportional device were compared with manual samples taken with a depth‐integrated sampler. Scatter in the relationship between pumped and manual samples (R2 = 0.76) are probably explained by horizontal variability in concentrations, poor mixing associated with lateral sediment inputs from construction site erosion, the downstream orientation of the intake, and the failure of the concentration at 60% of the flow depth to match the average vertical concentration. 相似文献
70.
Junxia Wang Maud Mercury Maurice Millet Michel Montury 《Environmental pollution (Barking, Essex : 1987)》2009,157(2):365-370
To estimate the atmospheric exposure of the greenhouse workers to pesticides, solid phase microextraction (SPME) was used under non-equilibrium conditions. Using Fick's law of diffusion, the concentrations of pesticides in the greenhouse can be calculated using pre-determined sampling rates (SRs). Thus the sampling rates (SRs) of two modes of SPME in the lab and in the field were determined and compared. The SRs for six pesticides in the lab were 20.4-48.3 mL min−1 for the exposed fiber and 0.166-0.929 mL min−1 for the retracted fiber. In field sampling, two pesticides, dichlorvos and cyprodinil were detected with exposed SPME. SR with exposed SPME for dichlorvos in the field (32.4 mL min-1) was consistent with that in the lab (34.5 mL min-1). SR for dichlorvos in the field (32.4 mL min−1) was consistent with that in the lab (34.5 mL min−1). The trends of temporal concentration and the inhalation exposure were also obtained. 相似文献