EPIPHYTIC BACTERIA DOWNSTREAM OF SEWAGE-WORKS OUTFALLS

Epiphytic microorganisms were investigated in two watercourses which w ere enriched by sewage-works effluent. These were a disused canal and a small stream in North-East England. Scanning electron microscopy, on the submerged macrophytes Callitriche sp. and Eloden canadensis, from the canal, demonstrated abundant epiphyton which was dominated by rod -shaped bacteria and pennate diatoms, especially Cocconeis sp. An in s itu counting technique showed that the density of epiphytic bacteria w as greater downstream of the sewage-works outfall on plants from both watercourses. The proportion of metabolically-active epiphytic bacteri a, and cell length of epiphytic bacteria, were determined on Callitric he in the small stream, and were greater downstream of the outfall. Th us increase in (1) the population density of epiphytic bacteria, (2) t he proportion of cells which were metabolically active, and (3) cell s ize, combined to increase the potential contribution of epiphytic bact eria to biopurification and downstream recovery. Epiphytic diatoms, in contrast to bacteria, apparently did not increase in abundance downst ream of the outfalls.