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61.
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无人机已被证明是适用于甲烷点源排放速率估算的一种新颖且有效的观测平台,然而对其估算的准确度与不确定度尚缺乏有效分析与量化。利用包含已知排放速率被动示踪物的大涡模拟,再现了1种强湍流混合环境下的甲烷羽流并对羽流进行了连续多次模拟飞行观测实验,通过逆高斯方法(IG)和质量平衡方法(MB)对排放速率进行了估算并量化了其准确度与不确定度,最后对不同的飞行时间安排及差异化的空间飞行策略进行了探究以提升估算效果。结果表明,对于研究所涉及的大气混合条件,通过IG和MB方法对多次模拟飞行估算的排放均值可达到既定排放值的95.3%和86.1%,不确定度为56.6%和56.9%;通过单架无人机多次重复飞行采样进行估算可显著降低不确定度,5次重复飞行可降至<30%;2架无人机在不同高度的同步飞行可使MB方法估算的不确定度降至35.2%~51.9%,IG方法则对该措施不敏感。研究仅考虑甲烷的传输扩散过程,结果也适用于其他被动示踪物的点源排放估算。 相似文献
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底泥是湖泊水库的重要组成部分,能够反映湖泊水库演化的历史过程.水体底泥污染已经成为世界范围内的一个环境问题.文章采用人工湿地控制(生态滤池)试验与野外布点调查取样相结合的方法,以芦苇(Phragmites australis Dar.Baiyangdiansis)为供试植物,系统地研究了白洋淀地区底泥现状和污染程度及在芦苇生境下其化学性质等所发生的一系列转化和演变情况,并针对芦苇对底泥的净化及受污染底泥异地的无害化处理进行了研究.结果表明:随着底泥用量的增加,芦苇的长势、生物量、株高等也增加.底泥用量大(3#池)则底泥中污染物含量动态变化明显.在一年的时间里,各滤池底泥中营养元素的含量总体趋势是降低的,其中以碱解氮降低幅度最大;有效态Cu的含量有所上升,有效态Zn、Cd、Pb含量变化幅度小,只是略微有所下降.因为芦苇生长带走了一部分有效态元素物质,底泥内各种元素总量有所降低,其有效态重金属含量变化不明显,只是略有下降,说明芦苇根系会影响底泥中重金属的存在形态. 相似文献
66.
Devlin JF Schillig PC Bowen I Critchley CE Rudolph DL Thomson NR Tsoflias GP Roberts JA 《Journal of contaminant hydrology》2012,127(1-4):3-14
Three projects involving point velocity probes (PVPs) illustrate the advantages of direct groundwater velocity measurements. In the first, a glacial till and outwash aquifer was characterized using conventional methods and multilevel PVPs for designing a bioremediation program. The PVPs revealed a highly conductive zone that dominated the transport of injected substances. These findings were later confirmed with a natural gradient tracer test. In the second, PVPs were used to map a groundwater velocity field around a dipole recirculation well. The PVPs showed higher than expected velocities near the well, assuming homogeneity in the aquifer, leading to improved representations of the aquifer heterogeneity in a 3D flow model, and an improved match between the modelled and experimental tracer breakthrough curves. In the third study, PVPs detected subtle changes in aquifer permeability downgradient of a biostimulation experiment. The changes were apparently reversible once the oxygen source was depleted, but in locations where the oxygen source lingered, velocities remained low. PVPs can be a useful addition to the hydrogeologist's toolbox, because they can be constructed inexpensively, they provide data in support of models, and they can provide information on flow in unprecedented detail. 相似文献
67.
Construction of six large dams and reservoirs on the Missouri River over the last 50–75 years has resulted in major landscape
changes and alterations in flow patterns, with implications for riparian forests dominated by plains cottonwood (Populus deltoides). We quantified changes in land cover from 1892–1950s and the 1950s–2006 and the current extent and age structure of cottonwood
forests on seven segments (two reservoir and five remnant floodplain) comprising 1127 km (53 %) of the unchannelized upper
two-thirds of the Missouri River. Riparian forest area declined by 49 %; grassland 61 %; shrubland 52 %; and sandbar habitat
96 %; while agricultural cropland increased six-fold and river/reservoir surface area doubled from 1892 to 2006. Net rates
of erosion and accretion declined between the 1892–1950s and 1950s–2006 periods. Accretion exceeded erosion on remnant floodplain
segments, resulting in declines in active channel width, particularly in 1950s–2006. Across all study segments in 2006, most
cottonwood stands (67 %) were >50 years old, 22 % were 25–50 years old, and only 10 % were <25 years old. Among stands <50 years
old, the higher proportion of 25–50 year old stands represents recruitment that accompanied initial post-dam channel narrowing;
while declines in sandbar and shrubland area and the low proportion of stands <25 years old suggest declines in geomorphic
dynamism and limited recruitment under recent river management. Future conservation and restoration efforts should focus both
on limiting further loss of remnant cottonwood stands and developing approaches to restore river dynamics and cottonwood recruitment
processes. 相似文献
68.
微波催化氧化修复技术处理有机氯污染土壤 总被引:1,自引:0,他引:1
采用微波催化氧化修复技术处理常州某农药厂有机氯农药污染场地和南通某化工厂有机氯污染场地土壤,考察不同参数条件下实验装置对污染土壤的处理效能。结果表明,在微波功率18kW、微波辐射时间20min、土壤处理量400kg/h、土壤含水率15%、活性炭添加量0.03kg/kg的最佳条件下,实验装置运行稳定,有机氯农药污染土壤中氯丹去除率可达70%左右;有机氯污染土壤中邻二氯苯、石油烃总量、1,2-二氯乙烷、苯酚去除率分别可达到99.98%、91.29%、98.52%、74.74%。研发的污染土壤微波催化氧化修复技术及实验装置对有机氯污染土壤的修复具有一定的普适性。 相似文献
69.
Tubifex tubifex metabolizes 2,4,6-trinitrotoluene (TNT) to 2-amino-4,6-dinitrotoluene (2ADNT) and 4-amino-2,6-dinitrotoluene (4ADNT). Elimination rates of metabolically-generated ADNTs are low compared to ADNTs absorbed directly from water, suggesting that metabolically-generated ADNTs may be bound or sequestered within tissue and therefore less available for elimination. A solid phase microextraction (SPME) technique was used to extract ADNTs from T. tubifex tissue to investigate the recalcitrance of metabolically-generated ADNTs. As SPME is a gentle, non-depletive, equilibrium sampling technique useful for measuring "available" organic compounds, we hypothesized that metabolically-generated ADNTs would be less extractable than absorbed ADNTs. T. tubifex were exposed to two scenarios to generate tissues containing absorbed ADNTs and metabolically-generated ADNTs. Tissue was then homogenized in a neutral buffer solution. Polyacrylate-coated (PA) SPME fibers were deployed and agitated in tissue homogenates to measure available ADNTs. Extractability of ADNTs from tissue containing metabolically-generated ADNTs was significantly less than expected: 50-60% based on the theoretical fiber-water partition ratio. Extractability of absorbed ADNTs was significantly higher (81-90%), and not significantly different than expected. The lower SPME extractability of metabolically-generated ADNTs may stem from the unavailability of metabolically-generated ADNTs sequestered in tissue or bound to tissue macromolecules during metabolism of TNT to ADNT. Tissue extractions using SPMEs may be able to estimate bound organic residues in tissue and serve to indicate the toxicological bioavailability of tissue-associated organic compounds. 相似文献
70.
P. N. Lahanas K. A. Bjorndal A. B. Bolten S. E. Encalada M. M. Miyamoto R. A. Valverde B. W. Bowen 《Marine Biology》1998,130(3):345-352
Migratory marine turtles are extremely difficult to track between their feeding and nesting areas, and the link between juvenile
and adult habitats is generally unknown. To assess the composition of a feeding ground (FG) population of juvenile green turtles
(Cheloniamydas Linnaeus), mitochondrial DNA control region sequences were examined in 80 post-pelagic individuals (straight carapace length = 31
to 67 cm) sampled in September 1992 from Great Inagua, Bahamas, and compared to those of 194 individuals from nine Atlantic
and Mediterranean nesting colonies. Evidence from genetic markers, haplotype frequencies, and maximum likelihood (ML) analyses
are concordant in indicating that multiple colonies contribute to the Bahamian FG population. ML analyses suggested that most
Bahamian FG juveniles originated in the western (79.5%) and eastern (12.9%) Caribbean regions, and these proportions are roughly
comparable to the size of candidate rookeries. These data support a life-cycle model in which individuals become pooled in
post-hatchling (pelagic) and juvenile (benthic) habitats as a consequence of ocean currents and movement among FGs. A substantial
harvest of immature turtles on their feeding pastures will influence the reproductive success of contributing nesting populations
over a wide geographic scale.
Received: 1 April 1997 / Accepted: 14 October 1997 相似文献