Dung – particularly in water – is bad news. Faecal bacteria and pathogens can cause disease in people. Faecal contamination is monitored using E. coli (Escherichia coli) as an “indicator” organism. E. coli is a type of bacteria commonly found in the guts of warm-blooded mammals (including people) and birds.
Where does excess E. coli in our waterways come from?
Common sources of E. coli bacteria include untreated human wastewater discharges, storm water run-off and animal waste. Faecal concentrations are typically higher in pastoral streams, but even near-pristine streams are not totally E. coli free because of contamination by birds and wild animals.
When comparing agricultural land uses, sheep and beef farming and dairy farming contribute similar E.coli loadings into waterways, despite the typically much higher stocking rates in dairy farms. This is because sheep and beef farming is generally carried out on steeper country and run-off from hill country is greater – as a proportion of a catchment – than from flat land. Surface run-off is usually the largest cause of E. coli contamination into receiving waterways.
Studies have found 5 sheep/ha can deliver up to 10 times the loading of E.coli/ha, compared with dairy cattle grazing at 3 cows/ha.
How to minimise faecal loss to waterways
- Control the grazing duration of pasture and fodder crops
- Winter stock off paddocks
- Keep stock out of waterways by improving on-farm infrastructure, such as reticulating stock water, improving stock crossings, planting shade trees away from water, and installing culverts or bridges at regular stock crossings
- Where landscapes allow, run tile drain outlet flows into wetlands or sediment traps prior to entering ditches
- Reduce stocking rates.
The best way to understand and manage faecal bacteria on farm is to develop a Farm Environment Plan specific to your property.
What is the impact of too much E. coli in water?
Excessive E. coli makes water unsafe to drink or swim in and can cause infections. Water is only deemed safe for drinking if there are very low concentrations of E. coli present.
When E. coli in rivers and lakes are detected above 550/100mL, health authorities put up signs stating that swimming or collecting shellfish is not recommended. When E. coli concentrations are high, other faecal pathogens (such as campylobacter) can also be present that might cause illness.
Watch
Dr Richard Muirhead at the B+LNZ Environment Conference 2017 discussing dung.
