Animal Waste, Water Quality and Human Health

Transport of livestock-derived pathogens within catchments 2456.7 EVIDENCE OF THE EFFECTIVENESS OFCATCHMENT-SCALE BMP IMPLEMENTATION ONWATER QUALITYHitherto, the adoption of BMPs to address concerns about livestock-derived faecalcontamination of watercourses has generally been sporadic and typically confinedto a small proportion of farms and/or land area within catchments, therebyprecluding meaningful empirical investigation of changes in catchment-scalemicrobial fluxes. One notable exception was a 10-year (1987–96) longitudinalstudy in the Piedmont region of Virginia, USA, in which a 11.63 km 2 catchmentmonitored for two years prior to the introduction of BMPs (manure storage,streambank fencing, use of water troughs, etc.) and for seven years afterwards(Inamdar, Mostaghimi et al. 2002). While reductions in both FC and FSconcentrations were recorded at the main watershed outlet, no improvement wasdetected in certain subcatchments. Similarly equivocal results were reported forlongitudinal study undertaken of stream water quality in four catchments innorth and west Scotland (Kay, Wilkinson et al. 2005, Kay, Aitken et al. 2007).Here there was quite intensive targeted implementation of measures (streambankfencing or control of steading runoff) in selected sub-catchments, with a seriesof nearby ‘control’ subcatchments in which no measures were introduced. Thedata, which were seasonally adjusted to allow for the fact that the pre- andpost-remediation sampling had to be undertaken at different times of the year,indicate reductions in high-flow GM EC and IE concentrations of c. 0.52 log 10where the extent of new streambank fencing is >40% of streambank length(CREH 2006). In contrast, in the sub-catchments where the steading measureswere implemented, no improvement in water quality was detected.In other studies, models have been developed to predict the effects of particularBMPs upon water quality at the catchment outlet. Collins & Rutherford (2004),for example, developed a spatially distributed model using the WatershedAssessment Model (WAM; Bottcher, Hiscock et al. 1998) in which fluxes anddie-off of EC are simulated on a cell-by-cell basis across a catchment. Scenariomodelling, which was applied to steep hill-country catchments grazed by beefcattle and sheep (as compared to lowland pastoral landscapes in which dairycattle are dominant), predicted log 10 reductions in median EC concentrations of0.11 and 0.19 in two simulations of the effects of RBSs. Also, (McGechan, Lewiset al. 2008) have combined the MACRO model (to simulate transport from fieldsby surface runoff and macropore flow to field drains; (Jarvis 1994) with a channelnetwork model to simulate EC fluxes from catchments. The resulting model,which was calibrated and tested on a dairy farm in West Scotland, has been usedto investigate the effects of a range of BMPs during the summer grazing season: