What do significance tests really tell us about the environment?

Routine application of significance tests does not extract the maximum information from environmental data and can lead to misleading conclusions. Reasons leading to this are: a significant result can often be reached merely by collecting enough samples; a statistically significant result is not necessarily practically significant; and reports of the presence or absence of statistically significant differences for multiple tests are not comparable unless identical sample sizes are used. These problems are demonstrated by application to pH data for grazed and retired fields, and by discussion of significance tests used in recent US regulations for groundwater quality. The advantages of equivalence tests, where the tester must state the difference of practical difference, are discussed and applied to the field pH problem. We recommend that environmental managers and scientists pay more attention to statistical power and decide on what is a practical difference. Confidence intervals for the size of the differences, accompanied where necessary by equivalence tests, are the preferred means of addressing the question: “is there a difference of practical significance?”     

The reactions of paraquat and divalent metal ions with humic acid: Factors influencing stoichiometry 2

Abstract

Laurentide humic acid has been titrated with paraquat and with selected divalent metal ions. In some cases, the humic acid was spiked with one cation before titration with another one. Several equivalence points were determined for the binding of the divalent cations, including paraquat. Three equivalence points agreed well with values predicted from the acidic properties of the humic acid. Eight independent experiments gave nine replicate values for an equivalence point that corresponds to 79.2 mole % of the total pairs of carboxyl groups. It is postulated that this represents a large molecular weight or structural fraction of the humic acid. The remaining 20.8 mole % can either bind one divalent cation to two carboxylate anions or bind one divalent cation to one carboxylate anion, with another anion providing for charge balance. Aggregation ‐ disaggregation and dissolution ‐precipitation phenomena may determine which case prevails, and they in turn are sensitive to the chemical compositions of samples. It should be possible to develop analytical chemical methods for characterizing the stoichiometric properties of humic acid samples.     

石化化工建设项目环境影响评价技术要点

石化化工行业是国民经济的重要组成部分,同时具有工艺复杂,涉及大量危险化学品,环境风险高、危害大等特征,其环境影响评价技术难度较大。产业政策、规划符合性和总图布置、选址合理性;工程分析;环境风险评价;污染防治措施等内容是石化化工项目环境影响评价的核心。本文对这几个方面环境影响评价技术要点进行了系统总结,为今后相关项目环评工作提供借鉴和参考。     

Using biological data from field studies with multiple reference sites as a basis for environmental management: the risks for false positives and false negatives

Field surveys of biological responses can provide valuable information about environmental status and anthropogenic stress. However, it is quite usual for biological variables to differ between sites or change between two periods of time also in the absence of an impact. This means that there is an obvious risk that natural variation will be interpreted as environmental impact, or that relevant effects will be missed due to insufficient statistical power. Furthermore, statistical methods tend to focus on the risks for Type-I error, i.e. false positives. For environmental management, the risk for false negatives is (at least) equally important. The aim of the present study was to investigate how the probabilities for false positives and negatives are affected by experimental set up (number of reference sites and samples per site), decision criteria (statistical method and α-level) and effect size. A model was constructed to simulate data from multiple reference sites, a negative control and a positive control. The negative control was taken from the same distribution as the reference sites and the positive control was just outside the normal range. Using the model, the probabilities to get false positives and false negatives were calculated when a conventional statistical test, based on a null hypothesis of no difference, was used along with alternative tests that were based on the normal range of natural variation. Here, it is tested if an investigated site is significantly inside (equivalence test) and significantly outside (interval test) the normal range. Furthermore, it was tested how the risks for false positives and false negatives are affected by changes in α-level and effect size. The results of the present study show that the strategy that best balances the risks between false positives and false negatives is to use the equivalence test. Besides tests with tabulated p-values, estimates generated using a bootstrap routine were included in the present study. The simulations showed that the probability for management errors was smaller for the bootstrap compared to the traditional test and the interval test.     

建设项目环境风险防范措施评估要点探讨

简述了环境风险事故致因理论,提出了控制和消除人员的不安全行为、机(物)的不安全状态、环境的不安全条件以及管理的不安全缺陷等环境风险防范措施,为建设项目环境风险管理提供技术参考。     

森林水源涵养价值核算方法评述与实例研究

针对森林水源涵养价值内涵理解不同,不同方法核算结果差异迥然的现象,总结现有方法深入分析其内涵,并选取5种方法进行实例计算。结果表明:黄土高原区两个小流域方法间核算结果差异显著,其中以纸坊沟为例,综合蓄水能力法、当量法、水量平衡法Ⅰ及降水储存量法Ⅰ所得价值最高可相差1.5×10⁶元,而南方女儿寨小流域同比相差最高为2×10⁵元,且三个流域利用水量平衡法Ⅱ计算所得结果皆出现反常现象。分析表明:降水储存量法Ⅰ与水量平衡法Ⅰ内涵接近,反映实际水源涵养价值;综合蓄水能力法则反映潜在水源涵养价值,在干旱半干旱地区可能出现实际蓄水能力低于理论值,实际价值与潜在价值相差较大的情况;水量平衡法Ⅱ计算公式无法代表其所期望反映的内涵,建议选用土壤蓄水能力法替代。     

废水中有机碳的生物化学行为及TOC与BOD的互换

完成了若干废水的好氧和厌氧生化培养实验,结果证实了以下假定和推论:在好氧条件下,TOC和BOD均近似服从一阶动力学原理,并以遵守KTOC=KBOD的等效降解特征而相互等价。由等效耗氧原理推论了TOC与BOD的下述互换关系:BOD₅=α′·(TOC₀—TOC₅),实验测得不同废水的表现耗氧系数α′,值为1.45±0.15。在厌氧条件下,上述等价性和互换性均不成立。      

奈达翻译理论分析

翻译是一项十分复杂的工作.中外翻译理论界流派林立,成果颇丰.但由于这一语言现象涉及因素太杂,理论体系的构建难度较大.尤金·奈达在当代翻译理论界因其不断创新的意识而成绩斐然.本文旨在通过对奈达博士翻译理论的介绍和探究,来谈一些自己的认识和看法,从而在翻译教学中加以借鉴.     

Foreword

We provide an introduction to the volume The Arctic in the Earth System perspective: the role of tipping points. The terms tipping point and tipping element are described and their role in current science, general debates, and the Arctic are elucidated. From a wider perspective, the volume focuses upon the role of humans in the Arctic component of the Earth system and in particular the envelope for human existence, the Arctic ecosystems. The Arctic climate tipping elements, the tipping elements in Arctic ecosystems and societies, and the challenges of governance and anticipation are illuminated through short summaries of eight publications that derive from the Arctic Frontiers conference in 2011 and the EU FP7 project Arctic Tipping Points. Then some ideas based upon resilience thinking are developed to show how wise system management could ease pressures on Arctic systems in order to keep them away from tipping points.