Animal Waste, Water Quality and Human Health

198Animal Waste, Water Quality and Human Healthimplementation of POMs. For example, the Scottish Environment ProtectionAgency (SEPA 2009) identifies more than 30 specific BMPs for reducing FIOconcentrations in Scotland, but attenuation efficiency data (for E. coli) arepresented only for six: one is expressed quantitatively (74% reduction, based ona single study), whereas the others are simply rated as “high” or “medium”, withno source being cited. Similarly, Cuttle (2007) adopts an “expert judgment”approach (rather than citing actual empirical data) in assessing the BMPeffectiveness in England. To meet the requirement for empirical evidence toinform the design and implementation of POMs, the Centre for Research intoEnvironment and Health (CREH) is compiling a database on the effectiveness ofBMPs in attenuating the transport of livestock-derived pathogens withincatchments. This chapter presents a summary of the current database; assessesthe relative effectiveness of those BMPs for which attenuation data areavailable; examines the evidence relating to the impact of catchment-scaleimplementation of BMPs on water quality; and, identifies the major gaps in theevidence base that need to be targeted in future empirical studies.6.2 CATCHMENT DYNAMICS OF LIVESTOCK-DERIVEDPATHOGENS6.2.1 Hydrological pathwaysApart from direct voiding of faeces to streams or the possibility of manure enteringduring application to the land, microbial contamination of watercourses depends onthe transport of organisms, either independently or attached to particles of soil orfaeces, via hydrological pathways (Tyrrel & Quinton 2003). These range fromslow, diffuse soil seepage, through more rapid bypass flow through soils andartificial soil drainage, both of which have the capacity to carry significantmicrobial loads (Ross & Donnison 2003), to surface runoff from the land,including artificial surfaces (e.g. roofs, yards, tracks and roads) and theconveyance of contaminated water to watercourses via artificial drains. Rainfall issignificant in two ways: it enhances catchment connectivity (Heathwaite, Quinnet al. 2005) by activating potential pollutant flow paths that do not operate underdry conditions (surface runoff from ground surfaces, upstream extension of streamnetwork into source areas and sites of ephemeral flow, etc.); and it increases thevolumes of water flow and hence the capacity for pollutant transport throughoutthe hydrological system. Detailed reviews of these various transmission pathwaysand the microbial delivery to receiving waters from pastures are presented byHickey, French et al. (2002), Collins (2005), Oliver (2005), Collins (2007) andTyrrel & Quinton (2003), and are discussed further in Chapter 5.