Epilithic bacteria in an acid and a calcareous headstream

Abstract

SUMMARY. 1. Environmental variables and epilithic bacteria on small stones were monitored during summer and winter in Burbage Brook and the River Lathkill, two headstreams in the Derbyshire Peak District.2. Burbage Brook was usually near‐neutral in summer, but acid in winter; the River Lathkill was circumneutral throughout the year.3. In summer, epilithic bacteria showed few between‐stream differences. In winter, however, total bacteria, colony‐forming units, per cent chromogenic colony‐forming units, per cent viable bacteria, Vmax for glucose mineralization and Vmax/bacterium were all significantly less in the acid Burbage Brook.4. Inhibition of epilithic bacteria in Burbage Brook was also observed when pH fell to a low level during a summer spate.5. Multiple‐regression analysis confirmed that epilithic bacteria were less successful at low pH but also suggested that pH was not the only environmental variable to influence epilithic bacteria. Especially notable were positive relationships with density of epilithic chlorophyll a and temperature in Burbage Brook and with chlorophyll a in the River Lathkill.