Spatial and temporal bacterial quality of a lowland agricultural stream in northeast Scotland.

Stream water concentrations of the faecal coliform group of sanitary indicator bacteria were monitored in the Newmills Burn, a small agriculturally intensive tributary of the River Don in Aberdeenshire. The results indicated that during its passage through the catchment, stream water became significantly contaminated with faecal coliform bacteria from the main agricultural land use inputs of livestock grazing and organic waste applications. Point sources of faecal coliform bacteria in terms of farmyard runoff, however, also appeared to be important in contributing to the spatial pattern of contamination. Significant temporal variation was observed in response to the hydrological behaviour of the catchment. Higher flows and more frequent washout of stored bacteria in winter and spring months led to lower faecal coliform concentrations than were detected during the summer. Maximum faecal coliform concentrations were measured during rainfall events and the varying responses associated with these helped to identify the importance of different sources of bacteria in the catchment and the mechanisms transferring them. The overall impact on the water quality of the Newmills Burn was considered as having a potentially serious threat to the health of downstream recreational users of the River Don, as well as to the large proportion of the local population who rely on private water supplies.