WAVE INDUCED FLOW AND TRANSPORT IN SEDIMENT BEDS1

ABSTRACT: The fate of contaminants in large water bodies is highly influenced by the transfer of flow and solutes across the water sediment interface. In this paper, an analytical model is presented where flow in both sediment bed and open channel is coupled at the interface through a boundary layer occupying the upper part of the sediment bed. The presence of this layer allows not only the capture of the inertia effects through a drag term in the generalized Darcy's equation, but also the specification of different soil parameters for the two porous zones. The flow is advective and driven by wave action along the water surface. The resulting system is solved for the pressure and flux in each sediment layer. The generated transport velocity fields are linked to a random walk simulation that is used to examine the trajectories of solute particles. Comparison of these trajectories against experimental tracer tests suggests a pattern very similar to the one attributed to the presence of surface mounds. The results clearly show the significance of the boundary layer and the drag term for soil with high permeability and the impact of both the thickness of the boundary layer and the length of the gravity wave relative to the depth of the water channel on the transport and exchange across the interface. The paper also examines the sensitivity of the mass exchange to the permeability of the two porous zones.     

长江三峡库区横向扩散系数研究初探

进行长江长寿段示踪剂岸边有限时段连续投放试验,求得横向扩散系数及其与流速、水深、流量、污染物浓度等关系。以长寿湖大沙坝河段为类比试验,预测得到三峡库区在90％保证率的最枯月流量下典型江段的横向扩散系数,并可用于库区的污染带计算。     

人工湿地水力停留时间分布模拟

将人工湿地视为在纵向分散活塞流反应器（PFD）的主流道上并联一个n级串联完全混合反应器（CSTRs）所组成的系统.在这一物理概念的基础上,推导了模拟人工湿地水力停留时间分布（RTD）的CSTRs＋PFD并联模型.模型所包含的4个参数（串联CSTRs个数n,串联CSTRs容积占系统总容积的百分数z,进入串联CSTRs的流量占总流量百分数f,PFD的分散数D）对RTD的峰值时间、峰值高度、平均停留时间、停留时间分布方差具有良好的调节作用.与传统模型相比,该模型能更准确地反映不同人工湿地的特征水流规律.模型采用基于流量的无量纲时间变量,可应用于非稳态变流量下人工湿地RTD的模拟.用前期示踪剂试验所获得的5条水平潜流人工湿地的RTDs对该模型进行验证,当这4个参数取值为z=0.41、f=0.57、n=3、D=0.667时,该模型计算所得RTD与实测RTDs拟合程度良好,较传统PFD或CSTRs模型能更好地反映该人工湿地RTD早期高峰、峰值集中、尾部倾斜拖长的流态特征.     

The field campaigns of the European Tracer Experiment (ETEX): overview and results

As part of the European Tracer Experiment (ETEX) two successful atmospheric experiments were carried out in October and November, 1994. Perfluorocarbon (PFC) tracers were released into the atmosphere in Monterfil, Brittany, and air samples were taken at 168 stations in 17 European countries for 72 h after the release. Upper air tracer measurements were made from three aircraft. During the first experiment a westerly air flow transported the tracer plume north-eastwards across Europe. During the second release the flow was eastwards. The results from the ground sampling network allowed the determination of the cloud evolution as far as Sweden, Poland and Bulgaria. This demonstrated that the PFT technique can be successfully applied in long-range tracer experiments up to 2000 km. Typical background concentrations of the tracer used are around 5–7 fl ?^-1 in ambient air. Concentrations in the plume ranged from 10 to above 200 fl/?^-1. The tracer release characteristics, the tracer concentrations at the ground and in upper air, the routine and additional meteorological observations at the ground level and in upper air, trajectories derived from constant-level balloons and the meteorological input fields for long-range transport models are assembled in the ETEX database. The ETEX database is accessible via the Internet. Here, an overview is given of the design of the experiment, the methods used and the data obtained.     

Pesticide dispersion by spraying under tropical conditions

Pesticide air pollution by spraying was evaluated under different temperature, humidity and wind climatic conditions in Brazil. Field experiments were performed with application towards the soil and in guava orchards, where spray dispersion was monitored by adding p-aminobenzoic acid (PABA), a fluorescent substance, as a tracer to the water contained in the spray tanks. Samples were collected with filter membranes (Whatman 180025), and the PABA was extracted from the filters by shaking with water in a Petri dish and measured in a spectrofluorometer. A spray aimed towards the soil with filters positioned on the ground and hung at different heights did not show different upward dispersion as observed when lateral pulverization was conducted. In this case, a tractor with a sprayer moved through a 3 m high and 6 m wide frame with filter membranes mounted at 60 cm intervals. Spray dispersion patterns were modified by guava leaf resistance. No influence of temperature and humidity was observed in this short-lived spraying process. Nevertheless, wind drift can occur during airborne dispersion and is an important pesticide pollution source which requires control. Droplets with PABA powered by assisted spraying upwards returned to the ground by gravity and, therefore, did not constitute a vertical source of atmospheric pollution.     

二恶英类物质检测分析技术进展

介绍了同位素稀释气相色谱质谱联用和生物快速检测法测定二恶英类化合物的技术进展,概述了国际通用的二恶英类标准分析方法体系,提出了各方法的适用范围,综述了我国二恶英类化合物分析研究现状并对我国二恶英分析检测提出了建议。     

现代受体模式评述

传统的数学受体模式可概括地分为两大类,即化学质量平衡法(CMB)和多元技术(MVT),CMB由于要求已知所求源的成分谱。从而在应用中受到限制。MVT以因子模式为中心,由于因子模式的本征向量解法求解不唯一或称误差太大,使得MVT给人一种人造数据的印象。近年来,元素示踪体系将受体模式的应用范围从城市尺度扩展到区域尺度,由于该体系经验性太强,未能得到广泛的应用。本文针对现代受体模式中存在的一些关键性问题作了系统的评述。      

A rapid isotope ratio analysis protocol for nuclear solid materials using nano-second laser-ablation time-of-flight ICP-MS

The analysis of the isotopic composition of nuclear or non-nuclear solid materials is performed in a variety of fields, e.g., for quality assurance in the production of nuclear fuels, as signatures in forensics, nuclear safeguards, and non-proliferation control, in material characterization, geology, and archeology. We have investigated the capability of laser ablation (New Wave Research, 213 nm) coupled to time-of-flight (TOF) ICP-MS (GBC OptiMass 8000) as a rapid analytical protocol for multi-isotope screening of nuclear and non-nuclear solid samples. This includes natural and non-natural isotopic compositions for elements including Cu, Zr, Mo, Cd, In, Ba, Ta, W, Re, Pt, Pb, and U, in pure metals, alloys, and glasses. Without correcting for mass bias (mass fractionation), an overall precision and accuracy of about 4% (1σ) can be achieved by minimizing the deposited laser power and thus fractionation (mass removal based on thermal properties). The precision and accuracy in combination with literally no or minimized sample preparation enables a rapid isotope screening of solid samples that is of particular interest to support nuclear forensic and safeguard analysis.     

垂直流人工湿地水力学特点对污水净化效果的影响

通过在污水中加入示踪剂,研究了人工湿地的水力学特点及其对污水净化效果的影响规律.结果表明,影响水力学各特点的主要原因是湿地植物根系所造成的物理学和生物学上的效应.水力学各特点与污水净化效果之间存在着密切关系:出水快、出水量大的系统具有较好的净化效果;除无植物系统外,停留时间较长的系统有较好的净化效果;容水体积大的系统净化效果也较好;水力负荷则主要通过影响其他各水力学特点而影响净化效果.结果表明,对水力学特点的优化将极大地促进污水净化效果的提高.     

煤炭的非传统稳定同位素研究进展

煤炭在世界各国的能源结构中都占有极其重要的地位,被工业界誉为“黑色的金子”。中国能源结构也以煤为主,煤炭资源的利用对人们的生产生活有着举足轻重的作用,其存放、运输和燃烧过程中向环境中排放大量有害、有毒物质,影响人体健康。非传统稳定同位素作为一种新兴的示踪剂,可以为上述过程提供示踪,逐渐在煤炭研究中得到应用。本文拟对煤炭研究中成熟的非传统稳定同位素（Li、B、K、Mo和Hg）的应用进行综述,包括不同地区煤中同位素特征以及煤中非传统稳定同位素在环境示踪方面的潜力。最后对煤中非传统稳定同位素前处理消解存在的问题、不同赋存状态、其他非传统稳定同位素和激光原位研究进行展望。