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Abstract

To evaluate the role of bacteria in the food web of the Breitenbach, a small, unpolluted stream in West Germany, it is necessary to determine the bacterial production of the stream-bed sediments. It is in this enviornment that the greatest flux of matter occurs. For this purpose, the leucine incorporation method of KIRCHMAN et al. (1985) which had been developed for the measurement of protein synthesis in marine bacterioplankton, was evaluated for its applicability to stream-bed sediments. With some modifications, it was shown that the technique was suited for use with the various sediment types in the Breitenbach. Deviations from the original procedure included the use of higher ³H-leucine concentrations (about 100 µmol · l^-1), necessary for obtaining substrate saturation, and the processing of samples after treatment with boiling TCA. Samples, either sandy sediments or small stones, were filtered through membrane filters, rinsed, and then combusted in a biological oxidizer. The latter separated incorporated tritium from the sediment, thus avoiding quenching problems. First results have shown that, when expressed as a function of the particle surface area, much higher levels of activity were to be found in the coarse stony sediments. However, if expressed on the basis of sediment volume or stream-bed surface area, then higher activity levels were recorded for the sandy sediments. For the stream-bed as a whole, this means that by far the greater proportion of bacterial production occurs in these sandy areas. Small-scale variability in incorporation rates with depth was high in the sandy sediments, and appeared to be influenced by the distribution of particulate organic matter within the sediment. However, the differences in total bacterial production between entire sediment cores were only small. The hight rates of bacterial production that were measured could make a substantial contribution to faunal nutrition in the stream. The complete results will be published elsewhere.