SEASONAL-CHANGES IN THE SANITARY BACTERIAL QUALITY OF WATER DRAINING A SMALL UPLAND CATCHMENT IN THE YORKSHIRE DALES

The faecal coliform concentration of overland flow and streamwater within a small catchment in the Yorkshire Dales was monitored over a 2 year period. Strong and consistent seasonal trends in bacterial concentration were found. During the height of summer (mid June to the end of August), faecal coliform concentrations in streamwater were found to be significantly higher than at other times of year. Consistently low concentrations were found during winter months. These trends closely followed those identified for semi-permanent overland flow, suggesting a direct causal link between streamwater quality and the bacterial concentration of overland flow entering the stream channel. The seasonal trends identified were explained with respect to long term changes in the size of the store of enteric bacteria existing in the surface soils of the catchment. Changes in land store size were related to seasonal changes in the frequency and amount of rainfall input to the catchment. The implications of the research findings for the management of upland catchments used for water supply or recreation are discussed.