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81.
Biodiversity surveys are often hampered by the inability tocontrol extraneous sources of variability introduced intocomparisons of populations across a heterogenous landscape. If not specifically accounted for a priori, this noisecan weaken comparisons between sites, and can make itdifficult to draw inferences about specific ecologicalprocesses. We developed a terrain-based, paired-sitesampling design to analyze differences in aquaticbiodiversity between streams draining eastern hemlock (Tsuga canadensis) forests, and those draining mixedhardwood forests in Delaware Water Gap National RecreationArea (USA). The goal of this design was to minimize variancedue to terrain influences on stream communities, whilerepresenting the range of hemlock dominated streamenvironments present in the park. We used geographicinformation systems (GIS) and cluster analysis to define andpartition hemlock dominated streams into terrain types basedon topographic variables and stream order. We computedsimilarity of forest stands within terrain types and usedthis information to pair hemlock-dominated streams withhardwood counterparts prior to sampling. We evaluated theeffectiveness of the design through power analysis and foundthat power to detect differences in aquatic invertebratetaxa richness was highest when sites were paired and terraintype was included as a factor in the analysis. Precision ofthe estimated difference in mean richness was nearly doubledusing the terrain-based, paired site design in comparison toother evaluated designs. Use of this method allowed us tosample stream communities representative of park-wide forestconditions while effectively controlling for landscapevariability. 相似文献
82.
空气质量周报二氧化硫采样过程影响因素的探讨 总被引:1,自引:0,他引:1
文章通过对空气质量周报连续采样过程有关影响因素进行探讨 ,分析了影响大气二氧化硫监测结果的一些原因或可能 ,首次对甲醛吸收液连续采样稳定性提出疑问 ,强调周报质量保证的重心要从实验室环节转到现场采样等环节上来 相似文献
83.
基于灰局势决策的火灾形势评价方法 总被引:1,自引:0,他引:1
简要介绍灰局势决策的基本原理。以灰局势决策的多目标方案选优思想为基础,运用灰局势决策中统一效果测度的计算方法,对火灾统计数字进行灰处理。通过对反映火灾形势的4项基本指数进行测度变换、测度运算等处理,将原先相对独立的统计数字统一到一个可以涵盖原有数据有效信息的单一测度之下,从而得到一个可以评价各参评时段之间相对火灾形势的综合指标,以此为依据实现了对火灾形势的综合评价。结合实例,具体说明基于灰局势决策的火灾形势评价方法的操作过程。 相似文献
84.
Brett B. Roper Jeffrey L. Kershner Eric Archer Richard Henderson Nicolaas Bouwes 《Journal of the American Water Resources Association》2002,38(6):1637-1646
ABSTRACT: The last few decades have seen an increased reliance on the use of stream attributes to monitor stream conditions. The use of stream attributes has been criticized because of variation in how observers evaluate them, inconsistent protocol application, lack of consistent training, and the difficulty in using them to detect change caused by management activity. In this paper, we evaluate the effect of environmental heterogeneity and observer variation on the use of physical stream attributes as monitoring tools. For most stream habitat attributes evaluated, difference among streams accounted for greater than 80 percent of the total survey variation. To minimize the effect that variation among streams has on evaluating stream conditions, it may be necessary to design survey protocols and analysis that include stratification, permanent sites, and/or analysis of covariance. Although total variation was primarily due to differences among streams, observers also differed in their evaluation of stream attributes. This study suggests that if trained observers conducting a study that is designed to account for environmental heterogeneity can objectively evaluate defined stream attributes, results should prove valuable in monitoring differences in reach scale stream conditions. The failure to address any of these factors will likely lead to the failure of stream attributes as effective monitoring tools. 相似文献
85.
The Seymour aquifer region of Texas has been identified as containing elevated levels of nitrate in ground water. Various state and federal agencies are currently studying policy options for the region by gathering more site-specific information. However, because of lack of sufficient information, cause and effect relationships between water quality and agricultural practices have not been well established for the region. Some recently available biophysical simulation models have impressive capabilities in generating large amounts of data on environmental pollution resulting from agricultural production practices. In this study, the data generated by a biophysical simulation model were used to estimate the nitrate percolation response functions for the Seymour aquifer region. Interestingly, nitrate percolation values obtained from simulation models often comprise acensoredsample because the non-zero percolation values are only observed under certain climatic events and input levels. It has been shown in the econometric literature that the use of Ordinary Least Squares (OLS) on censored sample data produces biased and inconsistent parameter estimates. Thus, a sample selection model was used in this study to estimate the response functions for nitrate percolation. The study provides some insight into the relationship between nitrate percolation and agricultural production practices. In particular, the study demonstrates the potential of selected design standards in minimizing agricultural nonpoint-source (NPS) pollution for the study area. 相似文献
86.
建立了水系沉积物中6种重金属分析的前处理方法,研究了样品粒径、消解前处理对测定结果的影响,对方法适用性作出评价,并对实际样品进行测定。结果表明:通过Hg元素含量的测定,粒径为0.147 mm的沉积物粒径可满足分析要求;采用微波-硝酸-盐酸-氢氟酸消解、ICP-MS法,对5种不同类型沉积物标准样品的6种重金属的测定结果显示,该方法精密度好、准确度高。利用建立的方法测定广西某河流湖库沉积物样品,6种元素测定结果 RSD为1.57%~11.1%,加标回收率大于74.4%。 相似文献
87.
在酸性介质中,痕量Hg(Ⅱ)能显著催化空气中的O2氧化K4[Fe(CN)6],生成蓝色化合物,反应对Hg(Ⅱ)为一级,催化反应的表观活化能为62.95kJ·mol-1.据此建立了测定痕量Hg(Ⅱ)的动力学分析法,测定条件为K4[Fe(CN)6]:1.4×10-3mol·L-1,[CH3COOH]:0.14mol·L-1,75℃.在此条件下,线性测定范围为0.02—0.70μg·ml-1.本法重现性好,常见共存离子中除Ag(I)严重干扰外,其余离子不影响测定.测定了水样及污泥样品中的Hg含量,结果满意 相似文献
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90.
随着固结时间的增加,试样逐渐变硬的硬化效应使软粘土的动剪切模量增大;同时,随着固结时间的增加,试样高度和直径明显减小的尺寸效应,也使软粘土的动剪切模量受到显著的影响。通过软粘土自振柱试验,分析了固结时间对软粘土的最大动剪切模量、动剪切模量比和试样尺寸的影响;根据自振柱试验的基本原理,分析了试样尺寸的变化对软粘土动剪切模量的影响;结合试验得到的固结时间和试样尺寸的关系,分析了固结时间通过试样尺寸对软粘土动剪切模量的影响。 相似文献