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Diatom-Based Stream Bioassessment: the Roles of Rare Taxa and Live/Dead Ratio

机译:基于硅藻的流生物评估:稀有分类群和活/死比的作用

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摘要

It is unclear whether accounting for the number of rare taxa or differentiating live (cells with visible chloroplasts) and dead (empty cells) diatoms would enhance the accuracy and precision of diatom-based stream bioassessment. My dissertation research examines whether the number of rare taxa and percentage (%) live diatoms can be used as indicators of human disturbance in streams/rivers. To address my objectives, I analyzed two datasets collected at different spatial scales. The large scale dataset was collected over the course of five years and included more than 1300 sites and over 200 environmental variables from 12 Western US states (US EPAu27s Environmental Monitoring and Assessment Program). The small scale dataset included 25 streams from the Oregon Coast Range. My findings revealed that rarity definition is important in bioassessment. Rural taxa richness (number of taxa with high occurrence and low abundance) was the only rarity metric that distinguished least disturbed (reference) sites from the most disturbed (impacted) ones. Neither of the other two rarity metrics, satellite (taxa with low occurrence and abundance) and urban (taxa with low occurrence and high abundance) taxa richness, was able to do that. Results from regression tree analysis revealed that rural taxa richness increased with human disturbance, but it was significantly higher at impacted sites only in the Mountains ecoregion (t-test, p0.05). Percentage live diatoms distinguished reference from impacted sites only in the Mountains ecoregion (t-test, p=0.02) and somewhat in the Plains (t-test, p=0.05). However, % live diatoms exhibited opposite patterns in the two ecoregions. They increased with disturbance in the Mountains and decreased in the Plains. The results from the small scale study in the Oregon Coast Range revealed similar species compositions between live and live+dead diatom assemblages (non-metric multidimensional scaling) and similar relationships with their environmental variables (linear fitting). Both assemblages correlated well with in-stream physical habitat conditions (e.g., channel dimensions, substrate types, and canopy cover). Both rural taxa richness and % live diatoms can be used as indicators of human disturbance in streams/rivers, especially in the Mountains ecoregion, dependent on specific assessment objectives.
机译:目前尚不清楚是否考虑稀有分类单元的数量或区分活的(具有可见叶绿体的细胞)和死的(空细胞)硅藻是否会提高基于硅藻的流式生物评估的准确性和准确性。我的论文研究检验了是否可以将稀有分类单元的数量和百分比(%)的活硅藻用作人类对河流/河流干扰的指标。为了实现我的目标,我分析了两个以不同空间比例收集的数据集。在过去的五年中收集了大规模数据集,其中包括来自美国西部12个州的1300多个站点和200多个环境变量(美国EPA u27的环境监测与评估计划)。小规模数据集包括来自俄勒冈海岸山脉的25条溪流。我的发现表明,稀有性定义在生物评估中很重要。农村分类单元的丰富度(发生率高而丰度低的分类单元的数量)是唯一可将受干扰最少的站点与受干扰最严重的站点区分开的稀有度。卫星(发生率和丰度较低的类群)和城市(发生率和丰度较高的类群)其他两个稀有度指标均无法做到这一点。回归树分析的结果表明,农村分类单元丰富度随着人为干扰而增加,但仅在山区生态区中受影响地区显着增加(t检验,p0.05)。仅在山区生态区(t检验,p = 0.02)和在平原地区(t检验,p = 0.05),活硅藻的百分比与受灾地区的参考有所不同。但是,在两个生态区域中,活硅藻的百分比显示相反的模式。它们在山区受到干扰而增加,而在平原则减少。俄勒冈海岸山脉小规模研究的结果表明,活的和活的+死的硅藻组合之间的物种组成相似(非度量多维标度),并且与它们的环境变量具有相似的关系(线性拟合)。两种组合都与河内物理栖息地条件(例如,河道尺寸,基质类型和冠层覆盖)密切相关。取决于特定的评估目标,农村分类单元的丰富度和活硅藻的百分比都可以用作人类对河流/河流特别是山区生态区的干扰的指标。

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