Bacteria in contrasting headwater streams
Suspended and epiphytic bacteria were studied in calcareous headstreams of the Yorkshire Wolds and in acid headstreams of the Galloway Hills. Mean concentrations of suspended bacteria were marginally greater in the calcareous streams, while heterotrophic activity was substantially greater. Mean cell volume was also greater. The concentration and activity of suspended bacteria in the calcareous streams usually showed linear downstream increase, while in the acid streams, the downstream increase was less, and was frequently not observed. In Mill Beck (a calcareous stream) it was found that the population of epiphytic bacteria near the source was easily sufficient to sustain the observed downstream increase in suspended bacteria. In Dungeon Burn (an acid stream) a substantial population of epiphytic bacteria was also found, but there was no downstream change in concentration of suspended bacteria; reasons are suggested for the apparent non-release of epiphytes in the Galloway stream. The mean volume of suspended bacteria in Mill Beck changed between the source and downstream limit of a vegetated section, to resemble that of epiphytic bacteria, suggesting that suspended bacteria were dislodged epiphytes. Estimates were made of the attachment rate of suspended bacteria to submerged vegetation in Mill Beck; daily attachment represented only a small proportion of the total standing crop of epiphytic bacteria. A further study in Mill Beck, over a Spring growing period, demonstrated a temporal change in the density of epiphytic bacteria, which was related to change in discharge and temperature. The results supported the suggestion that epiphytic bacteria might largely be the source of suspended bacteria in this headstream.