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Abstract

Abstract
In two small unpolluted streams the uptake of dissolved organic substances by suspended bacteria was investigated during one year. The uptake potential (V_max) of glucose (range: 0.04 - 16 µg glucose l⁻¹ h⁻¹) is similar to that in eutrophic lakes, that of acetate (range: 0.01 - 4.1 µg acetate l⁻¹ h⁻¹) seems to be a little smaller than in eutrophic lakes, whereas the concentrations of dissolved organic matter are mostly in a range of oligotrophic lakes. Factors which influence V_max are mainly the number of bacteria, the temperature, the stream discharge and the quantity and composition of of dissolved organic matter. With increasing stream discharge the specific uptake potential (uptake potential/number of bacteria) decreases. At the time of leaf fall an extraordinary high specific uptake potential was observed. The high values of V_max can be explained by permanent allochthonous input of bacteria and dissolved organic substances. The uptake kinetic parameters and their relationships to the number of bacteria, the temperature, the stream discharge and the quantity and composition of dissolved organic matter show that the allochthonous influence is stronger in the woodland stream Rohrwiesenbach than in the open grassland stream Breitenbach.