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991.
Altogether 64 predominantly biological traits were coded for more than 600 macroinvertebrate species from European rivers. The main question was: Are biological traits able to reflect “biological functionality” in large rivers and if so, is it possible to deduce an assessment system based on functionality? Analysis of the raw trait structure of all species indicates that these traits are not completely independent from their higher systematic units. To avoid mis-interpretations when judging from mixtures of habitats (β-biocoenosis) we used for our investigations only sample series from -biocoenosis, pre-tested by a mathematical criterion of homogeneity. Within -biocoenosis, traits are shown to be able to compensate for drastic changes with respect to species number and species composition along a river continuum, demonstrating their functional quality. Long-term changes in the trait and species structures of German waterways were studied using multivariate methods, based on an analysis of 142 sampling series. A shift from traits typical for K-strategists to traits typical for r-strategists was detected to be the main background variable. The rK-strategy is regarded as a true functional character of species. We calculated the relative positions of all trait-coded species on this rK-scale, and plotted the functional diversity of our samples against the structural diversity of the species from several river systems. Rivers extremely dominated by r-strategists show a deficit in functional diversity. Rivers dominated by K-strategists also show deficits, possibly in concordance with modern ecological theories such as the intermediate disturbance theory. The quantitative proportions of extreme r- to K-Strategists in -biocoenosis can be used as a general disturbance measure. 相似文献
992.
结合浙江省新昌县沃西大桥的施工实际,提出了挂篮放样方法,监测了挂篮在施工过程中的高程变化,确保了大桥施工的顺利进行。 相似文献
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During a one‐year period temporal and spatial variations in suspended sediment concentration (SSC) and deposition were studied on a salt and freshwater tidal marsh in the Scheldt estuary (Belgium, SW Netherlands) using automatic water sampling stations and sediment traps. Temporal variations were found to be controlled by tidal inundation. The initial SSC, measured above the marsh surface at the beginning of inundation events, increases linearly with inundation height at high tide. In accordance with this an exponential relationship is observed between inundation time and sedimentation rates, measured over 25 spring–neap cycles. In addition both SSC and sedimentation rates are higher during winter than during summer for the same inundation height or time. Although spatial differences in vegetation characteristics are large between and within the studied salt and freshwater marsh, they do not affect the spatial sedimentation pattern. Sedimentation rates however strongly decrease with increasing (1) surface elevation, (2) distance from the nearest creek or marsh edge and (3) distance from the marsh edge measured along the nearest creek. Based on these three morphometric parameters, the spatio‐temporal sedimentation pattern can be modelled very well using a single multiple regression model for both the salt and freshwater marsh. A method is presented to compute two‐dimensional sedimentation patterns, based on spatial implementation of this regression model. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
998.
Unsteady bedload transport was measured in two c. 5 m wide anabranches of a gravel‐bed braided stream draining the Haut Glacier d'Arolla, Switzerland, during the 1998 and 1999 melt seasons. Bedload was directly sampled using 152 mm square Helley–Smith type samplers deployed from a portable measuring bridge, and independent transport rate estimates for the coarser size fractions were obtained from the dispersion of magnetically tagged tracer pebbles. Bedload transport time series show pulsing behaviour under both marginal (1998) and partial (1999) transport regimes. There are generally weak correlations between transport rates and shear stresses determined from velocity data recorded at the measuring bridge. Characteristic parameters of the bedload grain‐size distributions (D50, D84) are weakly correlated with transport rates. Analysis of full bedload grain‐size distributions reveals greater structure, with a tendency for transport to become less size selective at higher transport rates. The bedload time series show autoregressive behaviour but are dif?cult to distinguish by this method. State–space plots, and associated measures of time‐series separation, reveal the structure of the time series more clearly. The measured pulses have distinctly different time‐series characteristics from those modelled using a one‐dimensional sediment routing model in which bed shear stress and grain size are varied randomly. These results suggest a mechanism of pulse generation based on irregular low‐amplitude bedforms, that may be generated in‐channel or may represent the advection of material supplied by bank erosion events. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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1 INTRODUCTION The transport of sediment in rivers with active floodplains is a two-dimensional process because the main channel and the floodplain can have very different transport capacities. Therefore, two-dimensional (2D) models are often used to simulate the streamwise and transverse variations of sediment erosion and deposition. Many 2D numerical models have been presented to simulate sediment transport in floodplains (James, 1985; Pizzuto, 1987; Howard, 1992; Nicholas and Walli… 相似文献
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