Obtaining species: sample size considerations

Suppose fish are to be sampled from a stream. A fisheries biologist might ask one of the following three questions: ‘How many fish do I need to catch in order to see all of the species?’, ‘How many fish do I need to catch in order to see all species whose relative frequency is more than 5%?’, or ‘How many fish do I need to catch in order to see a member from each of the species A, B, and C?’. This paper offers a practical solution to such questions by setting a target sample size designed to achieve desired results with known probability. We present three sample size methods, one we call ‘exact’ and the others approximate. Each method is derived under assumed multinomial sampling, and requires (at least approximate) independence of draws and (usually) a large population. The minimum information needed to compute one of the approximate methods is the estimated relative frequency of the rarest species of interest. Total number of species is not needed. Choice of a sample size method depends largely on available computer resources. One approximation (called the ‘Monte Carlo approximation’) gets within ±6 units of exact sample size, but usually requires 20–30 minutes of computer time to compute. The second approximation (called the ‘ratio approximation’) can be computed manually and has relative error under 5% when all species are desired, but can be as much as 50% or more too high when exact sample size is small. Statistically, this problem is an application of the ‘sequential occupancy problem’. Three examples are given which illustrate the calculations so that a reader not interested in technical details can apply our results.     

传统生存方式变迁对农村环境的影响

随着农村社会经济的发展,农户的生存方式开始逐步由传统的生存方式逐步转变为现代的生存方式。在具体的案例研究过程中,我们既可以看到传统生存方式的环境友好的一面,也可以看到传统生存方式变迁过程中农户经济行为变化对于农村环境的不利影响。与此同时,社会经济发展过程中,新的现代生产生活要素的介入,在不断使农户的生活逐步走向现代化的同时,也带来了种种环境问题。总之,农村环境问题的产生既有传统生存方式本身存在的问题,也来自于生存方式变迁过程中新的外部物质的介入,因此,对于农村环境的改善需要同时从这两方面着手,在改善农户生存方式的同时,更要从根本上控制外部的污染物质的介入。     

环境应急监测工作现状存在的问题及对策研究

近年来,各类突发性环境污染事故时有发生,造成生命、财产的巨大损失和生态系统的严重破坏,这一问题引起了世界各国的高度重视.由于突发性污染事故具有爆发的突然性.危害的严重性以及影响的广泛性和长期性等特点,采取切实有效的措施来预防这类事故的发生以及提高对事故处理处置应变能力,已经成为环境保护一项非常重要的工作,因此建立健全有效的环境应急监测系统,加强各级环境监测站应急监测能力建设,提高其应急监测能力,意义十分重大.环境应急监测对于防范突发性环境污染事故,在事前预防、事中监测、事后恢复的各个过程中起着极其重要的作用,环境应急监测已成为环境监测的重要组成部分.本文系统地分析了我国环境应急监测工作现状,针对实际工作中存在的问题,提出了解决对策.     

A hybrid method for inverse characterization of subsurface contaminant flux

The methods presented in this work provide a potential tool for characterizing contaminant source zones in terms of mass flux. The problem was conceptualized by considering contaminant transport through a vertical "flux plane" located between a source zone and a downgradient region where contaminant concentrations were measured. The goal was to develop a robust method capable of providing a statement of the magnitude and uncertainty associated with estimated contaminant mass flux values. In order to estimate the magnitude and transverse spatial distribution of mass flux through a plane, the problem was considered in an optimization framework. Two numerical optimization techniques were applied, simulated annealing (SA) and minimum relative entropy (MRE). The capabilities of the flux plane model and the numerical solution techniques were evaluated using data from a numerically generated test problem and a nonreactive tracer experiment performed in a three-dimensional aquifer model. Results demonstrate that SA is more robust and converges more quickly than MRE. However, SA is not capable of providing an estimate of the uncertainty associated with the simulated flux values. In contrast, MRE is not as robust as SA, but once in the neighborhood of the optimal solution, it is quite effective as a tool for inferring mass flux probability density functions, expected flux values, and confidence limits. A hybrid (SA-MRE) solution technique was developed in order to take advantage of the robust solution capabilities of SA and the uncertainty estimation capabilities of MRE. The coupled technique provided probability density functions and confidence intervals that would not have been available from an independent SA algorithm and they were obtained more efficiently than if provided by an independent MRE algorithm.     

江苏省重要生态功能保护区划分的问题及对策分析

江苏省重要生态功能保护区的划分,为实现社会经济和生态环境的协调发展奠定了良好基础。针对重要生态功能保护区划分过程中存在的各种问题,如划分区域分割、划分随意性大、禁止开发区少、管理不到位等,分别从技术层面和管理层面提出了相应的对策与建议,为重要生态功能保护区划分的完善和生态功能的充分发挥提供了可行方案。     

浅谈节约型城市的构建

构建节约型社会是实现城市可持续发展的必然要求。节约型城市的构建应通过转变经济增长模式、推行循环经济、加强节能科技的创新,发展替代能源,同时结合政策手段、宣传教育和法律手段来实现。     

新农村生活污水处理设施问题初探

农村生活污水无害化排放不仅是新农村建设的要求,也是改善农村居民生活环境的需要。本文分析了中国新农村生活污水部分处理设施存在的问题及原因,并针对新农村生活污水处理设施在工程设计、施工、监管和运行管理上提出了一些探讨性的建议,期望能为中国新农村污水处理设施的建设提供有益的参考作用。     

浅谈我国安全评价工作存在的问题及对策

针对我国目前安全评价工作中存在缺乏依法行政、评价标准不规范、管理不到位等问题和不足之处,提出了一些改进的建议和对策,以为企业实行安全生产目标管理提供科学标准以及为政府及行业实施宏观安全管理提供科学的依据。     

浅议曲靖市煤矿资源开发中的生态环境建设

通过调查,分析了曲靖煤矿资源开发中存在的主要环境问题,对加强矿区生态环境建设提出了措施和建议。     

清洁生产审核工作中几个问题浅析

介绍了长期从事清洁生产咨询和培训工作中常遇到的问题,并提出了看法。