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Riparian vegetation is a typical ecotone by its structural and functional position between the terrestial part of the watershed and the stream (Naiman, Decamps 1990). In consequence, the riparian zone forming an integrated component of stream ecosystems significantly determines the aquatic community. Macroinvertebrates are affected by defined variability of environmental factors. In streams under canopy: light access is reduced; summer temperatures are lower; shed leaves form the main source of energy; insects falling from the vegetation into the water create another source of food; roots from trees form shelter and strongly influence hydraulic patterns. As a result, many (micro) habitats can exist and persist. The relationships between the covered percentage of the riparian zone, hydraulic processes, POM retention and macroinvertebrate functional organization was analyzed. Riparian vegetation forms a buffer zone in agricultural landscape and thus prevents inflow of nutrients, but also of fine sediments. Clearing of riparian vegetation changes all these conditions, resulting in a totally different and less varied biocommunity. Examples are given from Poland and The Netherlands.
The effect of riparian ecotone functional complexity and stream hydraulics on an upland river ecosystem has been analysed. The amount of nutrients retained by the bottom sediment was lowest on a sandy substrate and highest in wetland bays. A stream bed covered by Berula erecta had about three times higher nutrient retentive capacity than did a sandy substrate. The trophic potential of CPOM, measured as total protein, was significantly correlated with the amount of deposited CPOM and depended on stream order. Macroinvertebrate biomass was highest at an intermediate riparian ecotone complexity with an adequate supply of organic matter and incident light. Fish biomass followed the same trend, being lowest in heavily shaded areas and in open channels without riparian vegetation, but highest in ecotones of intermediate complexity. These results indicate that the riparian ecotone structure and the heterogeneity of the stream channel may regulate biodiversity, productivity and nutrient retention in the fluvial corridor.
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