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Natural variation of macrophyte vegetation of lowland streams at the regional level

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In the present study, we present a synopsis of two macrophyte surveys of physiographic units in northwest Germany carried out over one decade. Data were used to test a set of hypotheses on macrophyte distribution at the regional level. Rank-frequency curves resembled the broken stick model. Twenty-one species of the 59 most frequent species occurred at high frequencies above 15 percent. Helophytes made up a high percentage (12 of 21) of the frequent species. Phalaris arundinacea was the most frequent species in both sampling periods. Most species showed no considerable change in frequency over time, among them the core hydrophytes. Spatial variation of species frequencies among physiographical units showed a unimodal distribution in relation to frequency. Spatial variation of frequencies of functional groups was significantly lower. Most uneven distribution among physiographical units was found in cryptogams. DCA ordinations of physiographical units showed a spatial gradient from alluvial plains to higher grounds units, which remained constant over time. CCA ordination of physiographical units in relation to environmental parameters identified two main axes, an altitudinal gradient and an alkalinity gradient. Species composition of units corresponded to the main landscape pattern of alluvial plains, glacial lowlands, and higher grounds on Mesozoic rock. Species diversity showed a complex behavior. Diverse units were found both in alluvial plains and glacial lowlands of intermediate elevation. The study may help defining regionally differentiated reference states for stream management, benchmarking indicator scores of species and avoiding application of assessment methods outside their range of applicability.
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Chapter
The following plant groups are generally considered as macrophytes: macrophytic green, red and brown algae, stone worts, mosses and liverworts, and hydrophytic vascular plants (with the main growth forms of the submerged, floating leaved and free-floating plants) and helophytic vascular plants (incl. creeping and high-growing graminoids as well as dicotyledons). The sections of rivers where physical and chemical conditions allow the growth of macrophytes are called the “macrophyte region” (Roll 1938). They can also be considered as “macrophyte-dominated ecosystems” in the sense of den Hartog (1979). Macrophytes are connected to other compartments of the ecosystem in several ways (see Dahl & Wiegleb 1984): Besides phytoplankton and “Aufwuchs” algae, macrophytes are very important primary producers connecting the inorganic environment to the biotic community. The organic substances produced are mainly not used by herbivores but are transferred into the detritus food chain. Macrophytes are food and habitat for the macrofauna that shows many functional relations to the plants. Furthermore relations to epiphytic bacteria and algae as well as to the phytoplankton are evident. Macrophytes have a strong chemical effect on the water. Nutrient elimination from the water as well as nutrient pumping from the sediment into the water have been discussed. Furthermore, oxygen production and elimination of toxic substances and microbes are important. Macrophytes also have physical effects on the environment. Especially sediment stabilization, differentiation of the current velocity and the influence on the microclimate and on quantity and quality of the light consumption shall be mentioned.
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