Animal Waste, Water Quality and Human Health

Transport of microbial pollution in catchment systems 185measured against best management practices to reduce diffusesource contributions.(2) As the scale reduces, the policy questions focus on the impacts of specificon-farm interventions such as stock exclusion from stream banks, filterstrip width, installation of wetlands and farm dirty water containmentand disposal which are addressed in Chapter 6 of this book. It is at thisscale that the uncertainties and contradictions in much of the empiricaldata in this area become most problematic. This problem is present forall catchment modelling studies and scaling issues have beenextensively discussed for the nutrient parameters, see for exampleBrazier et al. (2005). The “flow connectivity simulation” as exemplifiedby Heathwaite et al. (2005) for phosphorus is likely to be an extremelyuseful approach and just as applicable to FIO transport modelling as tothe nutrient parameters. Where high connectivity has been observedlinking farmyard impervious surfaces in Scotland with adjacent streams,single steading areas have been shown to increase stream high flow FIOloadings by over 300% (Kay et al. 2003) in a catchment usedpredominantly for livestock rearing where 7 km 2 of the catchment wasabove the monitoring point. These, sub one km 2 effects can be the mostimportant factors in determining sub-catchment transport of FIOs butwould not be addressed where input data to GIS driven models usingexport coefficient remains at the one km 2 resolution.(3) The further development of existing process-based modelling approachesdeveloped in New Zealand (Collins, 2004), Canada (Jamieson et al.,2004a,b, 2005a,b), Australia (Ferguson et al. 2003a,b, 2005), the UnitedKingdom (Vinten et al. 2002, 2004a,b) and the USA (Bai & Lung 2005)is essential if model outputs are to inform the design of farm-scale (