Suspended bacteria in calcareous and acid headstreams: abundance, heterotrophic activity and downstream change

SUMMARY. 1. Concentration of total suspended bacteria and heterotrophic activity (as turnover rate and turnover rate per bacterium for glucose assimilation by a trace-addition approach) were determined at distance intervals along four high-trophic-status calcareous headstreams in the Yorkshire Worlds and along four low-tropic-status acid headstreams in the Galloway Hills.
2. Mean concentration of suspended bacteria was marginally greater in the calcareous streams while turnover rate and turnover rate per bacterium were substantially greater.
3. Further determinations of heterotrophic activity (as turnover rate, turnover rate per bacterium, V_max and V_max per bacterium for glucose mineralization by a kinetic approach) supported the conclusion that heterotrophic activity was greater in the calcareous streams.
4. Mean cell volume of suspended bacteria, measured by electron microscopy, was found to be greater in the calcareous streams.
5. In the calcareous streams the concentration of total bacteria and turnover rate usually increased substantially, in a straight-line relationship, with distance downstream from the source. In the acid streams such downstream increase was less usual, the rate of increase per unit length of stream was less, curvilinear relationships were more frequent and on some occasions downstream decrease was observed.
6. The calcareous and acid streams thus formed two distinct groups on the basis of heterotrophic activity, cell volume and rate of downstream increase of suspended bacteria. This division was not necessarily caused solely by difference in pH but might be due to the combined effects of the many environmental variables which change in parallel with pH.