Animal Waste, Water Quality and Human Health

186Animal Waste, Water Quality and Human Healthand wetland systems has also been intensively researched using jar scaleexperiments (Fontes et al. 1991), but field validation data are very sparse(Foppen 2006) preventing policy guidance on some potentially usefulremediation strategies such as unlined wetlands (Harrington et al. 2005).(4) The key model output required by the policy community is the “episodic”transport of FIOs during storm events (which is the key risk period forbathing water and shellfish non-compliance) but very few studies havemeasured FIO dynamics through events to facilitate model calibrationand validation (McDonald & Kay 1981). More commonly data havebeen collected through regular monitoring over periods of a year or more(Tong & Chen 2002) and researchers have sought to disentanglecomplex relationships by retrospective correlation analysis (Kim et al.2005). This will not uncover the most significant processes where theoriginal data are biased to low flow conditions because of the “regular”sampling regime and perhaps 95% of the transport flux occurs inrelatively short-term high-flow events which are “missed” by the samplingregime employed. This “episodic” transport is the condition found inlivestock farming areas where the zoonotic pathogen loadings originate.Thus, studies seeking to inform TMDL estimates or the design ofProgrammes of Measures should characterise both high- and low-flowwater quality which is logistically difficult but essential. Monitoring dataare generally not suitable for microbial transport model calibration.The reasonable assumption has often been made that FIOs associate with sedimentand sediment models can be employed to predict FIO flux, but very few studies havesought to understand how, or indeed whether, FIOs partition with differentsedimentary fractions and how particle size and mineralogy influence attachment,transport and survival in freshwater systems. The limited estuarine marine work inthis area may not be applicable to freshwater systems (Kay et al. 2005). A studyby Characklis et al. (2005) indicates that different microorganisms will havedifferent partition coefficients and that these may also vary with the compositionof the water matrix, for example between low-flow and high-flow events. Hence,extrapolation between FIO and multiple pathogen species will likely be inaccurateand the relationships will vary with composition of the water matrix.REFERENCESAitken, M., Merrilees, D. and Duncan, A. (2001). Impact of Agricultural Practices andCatchment Characteristics on Ayrshire Bathing Waters. Scottish Executive CentralResearch Unit, Edinburgh.