Cleaner streams expected to benefit human health

Cleaner streams expected to benefit human health

Thursday, February 13, 2020

The good work deer farmers are doing to improve the health of their waterways is expected to have human health benefits.

“While there is a public focus on nitrogen, sediment is a more important issue for deer. Not only does it contain valuable topsoil, it contains faeces and phosphorus. Also, sediment can smother the streambed, making it inhospitable for much stream life,” says DINZ environmental stewardship manager Lindsay Fung.

“By fencing-off priority waterways, removing wallows that overflow into streams, installing sediment traps and wetlands and carefully managing winter grazing, we can improve waterway health.”  

He says there has only been limited research into the impact of deer farming on water quality. But it is well-known that harmful bacteria that can make people ill are found in the faeces of all farm animals, including deer.

“Ducks and other waterfowl also cause pollution and some animals carry more harmful bugs than others, but these are side issues. Our focus on keeping sediment out of waterways is the right one. Deer farmers who have been working on this for several years say they are getting great results – clean streams and a return of fish life.”

A joint ESR/Environment Southland study has shown that wildfowl are the biggest source of faecal pollution in 80% of Southland rivers sampled. Pollution from cows, sheep, deer and goats was present in about half the samples, with levels increasing after rain.

“Unfortunately this is not a get-out-of-jail-free card for farmers. That’s because ruminant faeces also contain disease organisms like campylobacter and salmonella and the parasite, cryptosporidium. All are human health hazards,” says Fung.

Environment Southland science manager and report author Dr Elaine Moriarty says the risk of becoming sick after swimming in a river that contains bird pollution is low, while the risk of swimming in a river with even a small amount of faecal pollution from humans or farm animals is very high.

The Southland study consists of five reports, one for each of the main Southland river catchments and one looking at faecal contamination in shellfish gathering areas.

AgResearch scientist Dr Richard Muirhead says the presence of E. coli bacteria, which originates in the gut, is used to indicate whether a waterway has been contaminated by faeces.

He says if animal droppings are still identifiable as faeces in the paddock they will contain E. coli.  When they are washed off pasture during rain the E. coli travels with them, contaminating any waterway they enter. Once in the waterway, the bacteria are slowly destroyed by sunlight and micro-organisms.

Most (but not all) strains of E. coli don’t pose a health risk in their own right. But because there is a clear correlation between ruminant E. coli and campylobacter (‘campy’) levels in NZ rivers and E. coli is easier to test for, this is what the official water quality guidelines are based on.

This does not mean there is a relationship between E. coli and campy at a farm level. In 2015, Moriarty and others tested 206 deer faecal samples in Canterbury and Southland, finding campy in only 13% of the samples. E. coli was present in all the samples. They also reported big variations (0-65%) in campy incidence between sampling dates.

The campy rates in this study were higher than similar studies of faeces from wild deer in Europe, but much lower than studies of campy in the faeces of other NZ livestock. The incidence of campy has been shown be as high as 81% in lamb faeces, 30% in sheep and 64% in cattle.

Most of the campy isolated in the deer study were types that are found in other farm animals. They are also known to cause illness in humans.

“Irrespective of the levels of campy, the practical solution for deer farmers is to continue their good work, focussing on those projects that have the greatest effect in terms of reducing the amount of sediment getting into waterways,” says Lindsay Fung.

Farmers wanting help with their farm environmental plans and tips on practical ways to reduce run-off, are encouraged by Fung to join a local Deer Industry Environment Group (DIEG). Each of these informal groups is made up of five to eight farms and has a focus on helping members write and/or implement their plans through a mix of mutual support and professional guidance.

Contact phil.mckenzie@deernz.org or tel 0274 997 809 for more information about your local group.