Mycobacteria in runoff waters from natural and drained peatlands

To assess the effect of peatland type and of forest-drainage performed 30 y r earlier on the occurrence of mycobacteria in runoff-waters, the counts of culturable mycobacteria were followed during a snow-free season. Runoff-wa ters were from a natural and a drained peatland and each had a different nu trient status. Samples were collected in May, June, August, and October of 1992. Mycobacteria were isolated from all waters. The highest culturable co unts were detected in August (up to 7.3 x 10(3) CFU/L). The runoff waters f rom the two natural peatlands had similar median counts, whereas lowering o f the water table by drainage slightly increased the mycobacterial counts i n most cases. Changes in vegetation, such as a decrease in the coverage of Sphagnum species, or soil characteristics following drainage had little eff ect on the occurrence of mycobacteria in the runoff-waters, even though Sph agnum vegetation has been regarded as important for the growth of these bac teria. The counts of mycobacteria in the runoff-waters correlated with prec ipitation but not with air temperature. This indicates that the mycobacteri al growth took plate mainly in vegetation and soil, not in the runoff-water s. when total runoff during May to October nas taken into account, the leac hing rates of mycobacteria from all catchments were about 4 to 5 x 10(11) C FU km(-2). Thus drainage had a negligible effect on the leaching of mycobac teria from peatlands.