The Effects of De-stocking on Microbial Delivery from Catchment Diffuse Sources in an Area Affected by Foot and Mouth Disease (the Caldew Study)

The virtual elimination of the principal point sources of human bacterial pollution through advanced treatment systems has not produced 100% compliance with microbial standards at all UK bathing water locations where they have been installed. This is partly explained by the existence of diffuse bacterial pollution derived from agricultural activities within catchments draining to the bathing zone. This pollution loading is highly episodic and driven by catchment hydrological dynamics producing a short term flush of faecal pollution early in the hydrograph event. Remediation of this diffuse pollution loading requires the type of upstream catchment management and control noted in the CEC Draft Bathing Water Directive (CEC, 2002) which suggest the implementation of Water Framework Directive (CEC, 2000) principles in the management of complex pollution sources . There is very little information on diffuse source microbial dynamics. In particular, the relative importance of different catchment microbial sources such as grazing animals, farm hardstanding areas, direct defecation in streams by livestock, farm waste spreading, small sewage treatment works, septic tanks and soakaways and combined sewage overflows. Thus, the policy maker has not, to date, been able to provide clear advice and guidance through codes of practice for the farming and contracting communities which would result in lowered faecal indicator loadings from diffuse sources to recreational waters. This opportunistic project was initiated by the Environment Agency, North West Region, to quantify the contribution of grazing animals to faecal indicator loadings in streams draining the Caldew catchment in Cumbria. Some sub-catchments of the Caldew were almost entirely de-stocked following the UK-wide outbreak of foot and mouth disease in 2001-2002. Water sampling programmes were undertaken by Environment Agency field officers to quantify the effects of de-stocked and re-stocked conditions within the Caldew catchment. Detailed sub-catchment data describing land use were acquired by ADAS and CREH have analysed the resultant data to provide a longitudinal comparison of water quality changes within the sampled sub-catchments and to place the Caldew data into the context of other ‘normally stocked’ UK catchment investigations. The Caldew subcatchments case study provides a unique illustration of the faecal indicator delivery from a principally grassland, UK catchment where the major sources of faecal indicators are livestock, wildlife and small sewage systems such as septic tanks and soakaways. In so doing, it provides a possible baseline scenario against which other pollution prevention strategies, such as the implementation of farm waste management plans, use of buffer strips, or de-intensification of farming, might be assessed.