Animal Waste, Water Quality and Human Health

Transport of livestock-derived pathogens within catchments 201basis for isolating the effects of different processes and controlling factors, but needto be used with care when scaling up to field and catchment situations. Someinvestigators (Miller, Lewis et al. 2007, Miller, Lewis et al. 2008), for example,note that there is a greater chance of channelized flow-reducing attenuationthrough an actual vegetated buffer strip (VBS) than through a plot- orlaboratory-scale VBS.6.4 OUTLINE OF PRESENT DATABASEThe present CREH database (which will be available in due course at http://www.ies.aber.ac.uk/en/research/groups/centre-research-environment-and-health)focuses on those BMPs (as identified in Table 6.1) for which microbial attenuationhas been quantified, and includes data for the full range of microbial parametersreported in the various studies. Representative data on the influent and effluentconcentrations of FIOs or pathogens, and attenuation rates (flux-based wherepossible) are presented in Table 6.2. In each case data have been reported for asingle parameter: EC or FC where possible, since these are the most commonlyreported parameters, or an alternative FIO/pathogen parameter if neither wasmeasured.Attenuation through an individual scheme (e.g. a CW) is conventionallyexpressed as either a reduction in flux (i.e. number per unit time) orconcentration of organisms. Flux data provide the best measure since they takeinto account any reductions in water flow, for example, reductions in surfaceflow through a system as a result of soil infiltration (Collins 2004, Roodsari,Shelton et al. 2005) and/or evaporation/evapotranspiration. Summary statisticsfor the attenuation data are presented in Figure. 6.2. These need to be interpretedwith some degree of caution since they include cases where the number ofindependent data sets and/or data values is very small (n < 10), attenuation datafor all the individual FIOs and pathogens reported (not just the parameters listedin Table 6.2), rates of attenuation in either microbial flux or concentration (withthe former being used where data permit), data with different levels ofaggregation, and all data irrespective of the study type (empirical field- orplot-based and modelling-based) or of conditions at the time of sampling (e.g.flow or season). Nonetheless, they provide a preliminary basis for assessing therelative effectiveness of the different measures. For consistency, all microbialconcentrations in the text are reported to two significant figures using thescientific notation and attenuation rates are expressed as log 10 reductions: log 10attenuations of 1.0 and 3.0 correspond with percentage reductions of 90.0 and99.9%, respectively.