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161.
长湖浮游动物群落结构及其与环境因子的关系 总被引:2,自引:0,他引:2
为研究长湖浮游动物群落结构及其与环境因子间的关系,于2012年4月至2013年1月进行了4次调查采样。共鉴定出浮游动物67种(不包括原生动物),以轮虫种类为主(42种),其丰度与生物量均占据较大优势。浮游动物丰度的季节性差异显著,夏季最高(4412ind./L),冬季最低(831ind./L)。季节间的物种更替率大于59%,但优势种种类的季节变化不明显。优势种共8种,均为轮虫,萼花臂尾轮虫(Brachiouns calyciflorus)、针簇多枝轮虫(Polyarthra trigla Ehrenberg)是四个季节均出现的优势种,P.trigla Ehrenberg的优势度与出现频率均是各个季节的最大值,各季节这两种优势种的丰度和在总丰度的占比均超过59.13%。依据Shannon指数、Pielou指数、Margalef指数评价长湖水体处于中度污染,肥度指数评价长湖处于富营养状态。相关性分析、多元逐步回归方程、冗余分析的结果显示:水温是影响长湖浮游动物群落结构季节变化的关键因子;浮游植物表征含量chl a也是影响长湖浮游动物群落结构的关键因子,总氮、总磷通过影响浮游植物的群落结构间接地影响浮游动物的组成;能耐受较高p H的B.calyciflorus在长湖碱性水体中有较好的适应性;夏季马洪台区较低的溶解氧一定程度上限制了该区域轮虫的生长,总悬浮物通过降低溶解氧对浮游动物产生间接作用;化学需氧量对P.trigla Ehrenberg、螺形龟甲轮虫(Keratella cochlearis)等耐污种的影响较大,并对浮游动物的丰度产生正向作用。 相似文献
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韩玲 《地球科学与环境学报》2003,25(2):70-72
在遥感地学分析模型中,由于遥感信息模糊和不确定性的特点,其特征空间中的特征分布并不完全符合特定的高斯密度分布,而是分布形状各异,相互交错,用传统模型是很难获得特征的最优分布解的,而空间逐步寻优数据挖掘方法(SOMM)是在演化寻优理论的基础上,融合知识的参数化分布函数,来逐步分离特征空间,逐步降解的获得特征树状的层次结构。结合实例,用SOMM方法对遥感影像进行分类计算,并与传统的最大似然分类方法的分类结果进行了比较。 相似文献
165.
Preliminarystudyonthesealevelchangeanditslong-termprognosticmethodforShanghaiQinZenghao,LiYongping,DuanYihong(ReceivedNovembe... 相似文献
166.
Abstract A procedure to identify sets of operational rules for gated spillways for optimal flood routing management of artificial reservoirs is proposed. The flood retention storage of a dam having a gated flood spillway is divided into 15 sub-storages whose surface elevations are identified as critical levels. The most suitable operation set for the downstream conditions and for the dam can be chosen from many derived operation sets. The spillway gates are operated in an optimum way for any floods from very small magnitudes to the probable maximum flood (PMF), without having to forecast the actual magnitude of the incoming flood hydrograph. Decision floods are formed by dividing the PMF into 15 sub-hydrographs by 5 and 10% increments in the ranges 5–50% and 50–100% of the PMF, respectively. Many potential spillway gate openings from closed to fully open are chosen initially. As a result of a series of routing simulations of 15 decision floods, a set of 15 gate openings is determined such that all floods from very small magnitudes to the PMF may be routed without overtopping the dam crest. Next, a few more 15-stage operation rules are determined such that the gate openings of the initial stages are decreased as their critical levels are increased stepwise, with the objective of attenuating smaller floods more effectively and releasing higher outflows for larger floods close to and including the PMF. The developed model is applied to the Catalan and Aslantas dams in Turkey, both of which serve for flood mitigation as well as hydropower generation. Citation Haktanir, T., Citakoglu, H., and Acanal, N., 2013. Fifteen-stage operation of gated spillways for flood routing management through artificial reservoirs. Hydrological Sciences Journal, 58 (5), 1013–1031. Editor Z.W. Kundzewicz; Associate editor A. Montanari 相似文献
167.
The prediction accuracy of the traditional stepwise regression prediction equation (SRPE) is affected by the multicollinearity among its predictors.This paper introduces the condition number analysis into the prediction modeling to minimize the multicollinearity in the SRPE.In the condition number prediction modeling,the condition number is used to select the combination of predictors with the lowest multicollinearity from the possible combinations of a number of candidate predictors (variables),and the sel... 相似文献
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Øyvind Nordli Øyvind Lie Atle Nesje Rasmus E. Benestad 《Geografiska Annaler: Series A, Physical Geography》2005,87(3):431-445
By stepwise regression analysis the accumulation, ablation, and equilibrium line altitude (ELA) were modelled by circulation indices and spring‐summer temperature on six Norwegian glaciers (Ålfotbreen, Nigardsbreen, Rembesdalsskåka, Storbreen, Hellstugubreen and Gråsubreen). The circulation indices were derived from a gridded monthly mean sea level pressure (MSLP) data set, whereas temperature series were derived from instrumental and proxy data. Analyses showed that accumulation on the western glaciers was strongly related to western airflow perpendicular to the main mountain range releasing precipitation on the glaciers. No other airflow variable significantly improved the regression. For the continental glaciers, circulating air in connection with low pressure systems was also found to be important. This may explain the lack of synchronicity in the glaciers' development in southern Norway during the Holocene. Accumulation was better modelled using the MSLP data set than by using the North Atlantic Oscillation (NAO) index as predictor. The decadal variations of accumulation, ablation, and ELA were analysed by a Gaussian low pass filter. The well‐known abundant accumulation on Norwegian glaciers during the early 1990s turned out to be unprecedented during the entire series (since 1781), whereas the accumulation of the 1960s has not been lower since the early 19th century according to model results. Ablation increased significantly from the mid‐19th century to the 1930s. The ablation maximum during the 1930s has not yet been exceeded. Also the 1930s show extremely high ELA values. 相似文献