Pathogen Pathways − Contamination of water bodies via artificial drainage
Executive summary
New Zealand dairy cattle are a large reservoir of Campylobacter jejuni, Cryptosporidium and Giardia. The spread of these pathogens from grazed areas to amenity, or potable, waters via discharge of surface runoff, or subsurface drainage, pose recognisable risks to the health of humans and livestock. However, there has been little research into the relationships between the occurrence of these pathogens in host dairy cattle, other potential hosts, transport vectors, and their survival in the agroecosystems associated with dairy farms.
The research objectives covered in this report were to quantify the relative importance of artificial drainage and surface runoff from grazed dairy pasture as pathogen transmission routes to surface-water bodies. It is important that the conclusions drawn here are kept in context: the experiments described below were conducted on a mole-pipe drained Pallic soil under grazed pasture at No.4 Dairy Farm, Massey University, under the weather conditions that prevailed between 25 September and 15 October 2003. In addition, the effect of both natural and simulated rainfall events were studied.
The main research findings reported are:
- Campylobacter was present in most cow dung spots, drainage and runoff samples collected during this study. The highest concentrations of Campylobacter in water (>103 organisms/100ml) were associated with drainage and runoff events occurring immediately (same day) after grazing. Such concentrations in drinking water can cause campylobacteriosis (Reid, 1991).
- Campylobacter concentrations in drainage and runoff declined with time (days) after grazing. However, lower numbers of organism were still present in drainage and runoff days and even weeks after grazing. The source of this ongoing contamination of water with Campylobacter could either be Campylobacter that has survived in old dung spots and the associated soil environment or come from other sources (eg. wild birds).
- In this study dung pats formed water-stable skins a day after grazing. Resampling of dung spots over a period of 9 days showed that Campylobacter survived under the skin of dung spots with no clear reduction in population levels over time. The formation of the water-stable skin on dung is believed to reduce the contamination of rainwater as it moved into and across the soil, reducing the Campylobacter concentrations in drainage and runoff water.
- In the cow dung spots and water samples collected in this study, there appeared to be no clear relationship between concentrations of Campylobacter and E. Coli, which is the common indicator species for faecal contamination of waters.
- Cryptosporidium and Giardia were not present in any of the dung spots sampled in this study. Also, Cryptosporidium was not present in surface runoff samples and only one drainage water sample contained oocysts. Giardia cysts were present in many of the drainage samples coming from both the recently grazed plots and plots that had not been grazed for up to 19 days. The soil, or old dung spots from previous grazings, and not fresh dung, was presumably the cyst source. Numbers of Giardia cysts were highly variable between plots and with time.
- The grazing on 25 September 2003 did not clearly elevate Giardia cysts numbers in either drainage or surface runoff. However, at the grazing on 7 October 2003, the highest levels of Giardia cysts recorded typically came from drainage and surface runoff water generated immediately after grazing.
Overall, this study shows that there is ongoing contamination of drainage and runoff water with Campylobacter from dairy pasture. The greatest contamination tended to occur when drainage and runoff events occurred immediately after pastures had been freshly grazed. Ultimately, the relative levels of contamination will depend on the level of shedding of Campylobacter in the dung of grazing cows, which previous studies have shown to be highly variable between cows and over time.
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