Agricultural land-use effects on the indicator bacterial quality of an upland stream in the Derbyshire peak district in the U.K.

Concentrations of indicator bacteria – faecal coliforms (FC) and faecal streptococci (FS) – were monitored at stream and water inflow sampling sites over a 21 month period within a small upland catchment in north Derbyshire, England. Agricultural land-use within the catchment included rough, semi-improved and improved pastures for sheep grazing. During its passage through the catchment, the stream became significantly contaminated by faecal bacteria, suggesting the existence of a semi-permanent store of faecal bacteria in catchment soils, combined with hydrological transport mechanisms capable of moving bacteria from the land to the stream channel. Spatial changes in the bacterial quality of streamwater could be explained by the influence of a number of monitored water inflows to the stream, although a clear and consistent relationship between the bacterial quality of catchment waters and the intensity of adjacent agricultural land-use was not apparent. This is explained in terms of a trade-off between practices which allow land-use intensification and a consequent reduction in the potential for bacterial survival in soils and efficient hydrological transport via surface-water flows. A consistent seasonal pattern of bacterial concentration change was observed, with the highest concentrations occurring during summer months as stocking density increased and the bacterial land store recovered from high precipitation-related outputs during the winter. The extent of faecal bacterial contamination of the stream, particularly during summer months, may constitute a real health risk to recreational cavers using parts of the limestone karst system into which the stream drains.