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Abstract
In 2 small unpolluted streams in eastern Hesse (Fed. Rep. of Germany) the number of suspended bacteria, counted by a membrane filter technique, was from June 1973 to August 1974 mostly in a range which is known from eutrophic lakes. In the Rohrwiesenbach, a woodland stream, the concentrations of bacteria (range at sampling station Rwb III: 0.4 - 9.2 * 10⁶ bact./ml, average: 3.1 * 10⁶) were similar to concentrations in eutrophic lakes during most of the year. The concentrations of bacteria in the Breitenbach, an open grassland stream, often reached the numbers in eutrophic lakes (range at sampling station Btb II: 0.5 - 2.7 * 10⁶ bact./ml, average: 1.2 * 10⁶).
Relationships between the number of bacteria and discharge were observed at 4 of 6 sampling stations, between the number of bacteria and temperature at 5 of 6 sampling stations. Under special consideration of these relationships the origin of suspended bacteria (the terrestrial environment or/and the stream itself) is discussed. The proportion of bacteria of allochthonous origin is supposed to be much higher in woodland stream sections (Rohrwiesenbach) than in open grassland stream sections (Breitenbach).
