Animal Waste, Water Quality and Human Health

200Animal Waste, Water Quality and Human Healthsewage treatment systems and their controlling factors (e.g. (Struck 2006))augment the database, it should be noted that the proportions of independent andparticle-attached pathogens and FIOs, the character of the particles present and,hence, their vulnerability to sedimentation and die-off, may differ significantlybetween livestock and sewage effluent. Boutilier et al. (2009), for example,report EC surviving longer in the treatment of effluent from a dairy farm than inthat of domestic wastewater.Accurate characterisation of the sources, source strengths and catchmentdynamics of agriculture-derived FIOs and pathogens, and of the effectiveness ofBMPs, is confounded by the sheer complexity of geographical (spatial) andtemporal factors that affect them. From the global scale down to the level ofindividual farm units there is very marked spatial variability in environmentalconditions (e.g. climate, topography, soils and hydrology) and in the nature oflivestock farming systems and management practices. Consequently, theempirical data are catchment- or site/farm-specific and therefore need to be usedwith caution when applied elsewhere.Equally important is the range of temporal variability, including seasonalpatterns in weather conditions, housing of livestock and the application ofmanure to land; diurnal patterns in certain operations, notably the daily washingof milking parlours and yards on dairy farms; and the episodic and variablenature of rainfall events. High-flow conditions following rainfall may at timesprovide elevated microbial fluxes within catchments. In the United Kingdom,concentrations and flow volumes both typically increase by an order ofmagnitude, leading to a 100-fold increase in catchment export coefficients (Kay,Crowther et al. 2008). At such times the effectiveness of certain BMPs is likelyto be compromised, for example, hydraulic residence time (HRT) within CWswill be reduced, with a greater likelihood of rapid by-pass flow, leading todiminished opportunities for die-off, predation and sedimentation (Werker,Dougherty et al. 2002, Edwards 2005, Kay 2005, Kay, Crowther et al. 2008).Water quality monitoring data are often biased towards low-flow conditions andmay provide an inadequate basis for characterising high-flow events. It should alsobe recognised that when longitudinal (before-and-after BMP adoption) studies areemployed at a catchment or field scale, then the results are likely to be confoundedby different antecedent weather conditions in the two sampling periods. Theassessment of the effectiveness of certain BMPs may be further complicated bya delayed response as a result of labile pollutant stores on ground surfaces andwithin the soil, as reported for nutrient attenuation in Sweden (Grimvall,Stålnacke et al. 2000). Individual catchment- and field-scale investigations ofBMPs must therefore be regarded very much as unique “case studies”. Incontrast, plot- and laboratory-scale (e.g. soil-box) investigations provide a better