Blackfly communities from five German stream types out of two ecoregions (small and mid-sized siliceous gravel-bed mountain streams of the Central mountains, ecoregion 9, and organic type brooks, small and mid-sized sand-bottomed Central lowland streams of ecoregion 14) are compared. Ecoregional, as well as stream type-specific biocoenotic differences are discussed. The presence of Prosimulium sp. was restricted to mountain streams, whereas Simulium lineatum seemed to prefer mid-sized sand-bottomed Central lowland streams, and S. vernum showed a clear preference for Central lowland streams. An Index of Morphological Stress (IMS), derived from 22 geo-hydromorphological parameters recorded during sampling in the field, is presented. According to the IMS values, sites are divided into morphologically ‘unstressed’ sites (high or good morphological quality) and ‘stressed’ sites (moderate, poor or bad morphological quality), and biocoenotic differences of the two categories are discussed. Two stream types and the entire data set showed significantly higher numbers of taxa at ‘unstressed’ sites. Linear Multiple Regression (LMR) was used to identify geo-hydromorphological parameters that significantly explain the variance of the three most constant taxa, Prosimulium sp., P. hirtipes and Simulium sp. in the LMR model. 相似文献
Maximum likelihood supervised classifications with 1-m 128 band hyperspectral data accurately map in-stream habitats in the
Lamar River, Wyoming with producer's accuracies of 91% for pools, 87% for glides, 76% for riffles, and 85% for eddy drop zones.
Coarser resolution 5-m hyperspectral data and 1-m simulated multiband imagery yield lower accuracies that are unacceptable
for inventory and analysis. Both high spatial resolution and hyperspectral coverage are therefore necessary to map microhabitats
in the study area. In many instances, the high spatial resolution hyperspectral (HSRH) imagery appears to map the stream habitats
with greater accuracy than our ground-based surveys, thus challenging classical approaches used for accuracy assessment in
remote sensing.
Received: 9 April 2001 / Accepted: 8 October 2001 相似文献
The objective of this paper is twofold: 1) to validate the German stream typology for Schleswig-Holstein, and 2) to develop an assessment system for lake outlets. The German stream typology, based on a top-down analysis of geomorphological variables, was validated using biotic data of streams in Schleswig-Holstein, northern Germany. A null model analysis was conducted to test for differences between seven stream types (sand streams and rivers, gravel streams and rivers, partly-mineralic streams, limnic marsh streams, and lake outlets). The dataset compiled for the statistical analysis comprised 28 streams, 65 different sampling sites, 428 samples, and 296 taxa. The analysis confirmed all stream type except partly-mineralic streams, which showed faunal overlap with all types except gravel streams. Gravel streams were the most distinctive stream type. Lake outlets were shown to be a unique type, having a distinct macroinvertebrate fauna. Furthermore it was shown, that the species composition differed between lentic and lotic outlets. Canonical correspondence analysis of 19 investigated lake outlets revealed that characteristics of the lakes had only a minor effect on macroinvertebrate community structure.
The developed assessment system of lake outlets was based on the habitat association of 132 macroinvertebrate taxa. Taxa were allotted to five categories of lake outlet preferences depending on the results from ordinations, frequency tables and abundance distributions. A qualitative and a quantitative lake outlet index (LTI) were tested with independent data sets. The quantitative LTIquan proved to be more robust and only slightly affected by seasonal changes in the macroinvertebrate community composition. Assessments of lake outlets based on macroinvertebrates should be conducted in spring and autumn to reduce the risk of misclassifications, in particular, for boundary cases rated between good and moderate quality classes. 相似文献
The biotic composition, structure, and function of aquatic, wetland, and riparian ecosystem depend largely on the hydrological regime (Poff, N.L., Ward, J.V., 1990. Implications of streamflow variability and predictability for lotic community structure: a regional analysis of streamflow patterns. Can. J. Fisheries Aquat. Sci. 46, 1805–1818; Richter, B.D., Baumgartner, J.V., Wiginton, R., Braun, D.P., 1997 How much water does a river need? Freshwater Biol. 37, 231–249). Available flow data for many rivers in the world can be used to validate these ecological theories. There is a demand for studies that use hydrological indices to establish criteria, which serve to group together regime types at a local level. Once this has been done, these hydrologically similar groups can be used to identify communities of living organisms that are linked to specific aspects of the river's behaviour.
An approach to characterise flow regimes in the river network of the Tagus basin in Spain is presented. The river Tagus (río Tajo) is one of the seven major rivers of the Iberian peninsula. All hydrological data were acquired from the measurements made in the Tagus basin, at 25 gauging stations. Twelve variables were derived for each gauged site to describe variability and predictability of average streamflow conditions, and to describe the frequency, timing and intensity of high flow and low flow extremes.
A hierarchical clustering routine was used to identify similar groups of rivers as defined in terms of similar characteristics of their streamflow regime. The variables were also examined with simple correlations to determine if multicollinearity occurred, in order to reject redundant parameters or to identify similar behaviour trends between pairs of parameters. Some parameters have shown a tendency to increase or decrease along the east–west axis, suggesting that some of the studied characteristics may have a geographical cause.
Cluster analysis, with the values of the 12 parameters, reveals two main groups, each of which splits into two main subdivisions. One of these subgroups contains six rivers with similar characteristics, can be considered to be ‘classic regular rivers’, the stations in this first subgroup are mostly situated geographically close to each other. At the other end, we have found a subgroup, with a high variation of flows over the year and high flood flows; these rivers are highly irregular rivers with great changes. This regular–irregular gradient found between the groups is similar to that observed by others authors (Poff, N.L., Allan J.D., 1995. Functional organization of stream fish assemblages in relation to hydrological variability. Ecology 76, 606–627), and strong associations have been documented with compositions of populations and probably reflect differences in other similar important environmental factors. 相似文献
The grain-size distributions of bedload gravels in Oak Creek, Oregon, follow the ideal Rosin distribution at flow stages which exceed that necessary to initiate breakup of the pavement in the bed material. The distributions systematically vary with flow discharge and bed stress, such that at higher flow stages the grain sizes are coarser while the spread of the distribution decreases. A differential bedload transport function for individual grain-size fractions is formulated utilizing the dependence of the two parameters in the Rosin distribution on the flow stress. The total transport rate, which is also a function of the flow stress, is apportioned within the Rosin grain-size distribution to yield the fractional transport rates. The derived bedload function has the advantage of yielding smooth, continuous frequency distributions of transport rates for the grain-size fractions, in contrast to the discrete transport functions which predict rates for specified sieve fractions. Successful reproduction of the measured fractional transport rates and bedload grain-size distributions in Oak Creek by this approach demonstrates its potential for evaluations of transport rates of size fractions in gravel-bed streams. The approach will be useful in investigations of downstream changes in bed material grain-size distributions. 相似文献
A reply to Finlayson (1986) suggesting that the priority should be for more widespread measurement of dissolved organic matter, without the need for special equipment. The use of chemical oxygen demand is also clarified. 相似文献
Knowledge of the basic life history traits of an aquatic organism such as voltinism and growth patterns is a fundamental step in understanding its potential use as indicator taxon and how it adapts to its complex environment. The distribution and life cycle of the Maghrebian endemic Choroterpes atlas Soldán & Thomas, 1983 was studied over a two year period. Random forest classification indicated that the species occupied both permanent and intermittent streams with high water depth, large river bed width and strong water flow. Density-based clustering of body measurements allowed the identification of last-instar nymphs which exhibited a significant sexual dimorphism: F-0 females were significantly larger than corresponding males. In addition, size-frequency plots and generalized additive models indicated that C. atlas exhibited a multivoltine annual cycle with three overlapping generations. Nymphal growth of the first generation happened in winter and spring with emergence occurring in June/July. The second generation grew from June/July to September whereas the third generation was completed from August/September to November. GAMs also indicated that body size varied significantly between years. The large regional distribution, habitat requirement, and phenology of C. atlas may ideally complement the potential use of Ecdyonurus rothschildi as a useful environmental indicator for North African streams and rivers. 相似文献