ACTIVITY AND ABUNDANCE OF BACTERIOPLANKTON IN 3 DIVERSE LOWLAND WATERCOURSES

The hypothesis that the activity and abundance of bacterioplankton wer e similar in two low-level fenland water courses, but were different f rom those in a high-level main river, was rejected. Mean values of V-m ax for glucose mineralization, V-max per bacterium, abundance of free- living and total directly counted bacteria, abundance of colony-formin g units and percentage of culturable bacteria were similar in the low- level Beverley and Barmston Drain and in the River Hull, but were less in the low-level Holderness Drain. The less favourable regime in the Holderness Drain was related to intermittently acid conditions. Tempor al variation by bacterioplankton in all three water courses was, howev er, also related to environmental variables other than pH, notably tem perature, chlorophyll, biochemical oxygen demand, current velocity, to tal suspended solids and particulate organic matter. The activity and abundance of bacterioplankton appeared to have increased in the River Hull between 1975-1976 and 1992-1994.