E Coli kite mark shows manure pollution risk

2 December 2008 by Tom Marshall

Researchers have created a system to help farmers and advisors recycle manure without risking pollution to nearby streams and rivers.

Muck spreading

Manure helps maintain the fertility of farmland. But when washed off the land and into rivers and streams by rainfall, it can carry bacteria such as E. Coli and threaten human health by contaminating irrigated crops or polluting bathing waters.

As well as these bacteria, it also contains high levels of nutrients and organic matter that can harm river ecosystems by over-fertilising plants and algae - a process known as eutrophication - and also by starving fish of oxygen.

The problem of faecal contamination of watercourses has been seen in the West Country, which has a large grassland-based livestock industry and many tourists. Several public beaches in the south west have recently failed to meet the requirements of the Bathing Water Directive, potentially harming the area's tourist industry.

A recent EU Directive, the Water Framework Directive, is coming into force soon, and will compel EU nations to account for the state of all their inland bodies of water, and eventually put them in good ecological order.

The upshot will be that farmers who don't keep the contaminated runoff from their land within strict limits will risk a fine. Other legislation, such as the Nitrates Directive, will also increase the pressure to stem the flow of polluted water.

An interdisciplinary team of researchers from Lancaster and Exeter Universities and North Wyke Research, an institute sponsored by the Biotechnology and Biological Sciences Research Council, has developed a tool to help farmers visualise and understand the risks of contamination. It uses a kite-shaped diagram to represent these risks.

"How can an individual farmer reduce the risk of polluting watercourses?" asks Dr Dave Chadwick from North Wyke Research, who led the project. "The kite risk-assessment tool is designed to help. It illustrates whether the farm is high risk, and how the farmer can apply his efforts most effectively and at least cost. So we expect it to be a particularly useful tool for farm advisors."

"This is only a first step," Chadwick explains. "We have also developed a cost-assessment tool that offers farmers a list of the methods they could use to reduce the risk of microbial pollution together with what each method would cost. At the moment we are trying to get follow-on funding to link this cost assessment to the kite risk assessment tool," he adds.

Making this link would allow farmers to determine the most cost-effective way to reduce risk of pollution by a given percentage, or target where best they can spend a fixed amount of money on pollution control.

The researchers based the kite risk assessment tool on visits to 77 farms in the Taw river catchment in North Devon, with long-term monitoring of around 10 of them. They looked at variables like the shape of the landscape and the number of grazing animals, and surveyed farmers' knowledge of the risk of pollution and attitudes to managing manure. They also tested water quality at fixed locations over several seasons.

Representing the risks

Using the data, the researchers came up with a kite-shaped model framework to represent the problem visually. Each point of the kite shape stands for one of the four variables that the researchers showed to be the crucial factors determining the risk of E. Coli pollution.

The first is the accumulated microbial burden on the land - this includes how densely the land is stocked with animals and how manure, whether in solid or slurry form, is managed. The second is the potential for run-off, including the presence of drains and landscape features like slopes and streams.

The third variable is farm infrastructure - for example, how much manure storage is there, are there livestock collection yards, and if so, how effective are measures to divert contaminated runoff from them into storage facilities rather than ditches and streams?

The final factor is the degree to which there are social and economic obstacles to change - for instance, have farmers had training in the risk of pollution, and can they afford to invest in better infrastructure to deal with manure?

Much depends on the individual farm. "We encountered some farmers who take a more laissez-faire attitude towards managing manure, but whose farms have a topography and infrastructure that gives them a lot of protection against the risk of microbial transfers to water," Chadwick explains. "But there were other farmers who were really on the ball and interested in the issue, but who have farms with features such as topography and soil type that mean they are at much greater risk of running into problems".

Kite concept diagram showing a 4-way graph plotting; obstacles to take action, runoff potential, infrastructure and E.coli burdon

These four factors, rated from 0 to 10, determine the shape of the kite by forming its four axes. So if a farmer's land is sloping and well-drained, with good potential for run-off, and has accumulated a large burden of E. Coli, but also has good infrastructure for manure storage, and there is plenty of money and training to enable change, the kite representing their situation will be elongated towards the bottom and left but shortened at the right and top (see picture).

The overall degree of risk of E. Coli contaminated runoff ending up in watercourses is represented by the colour of the whole shape, with red being the riskiest and green the safest.

Once a farmer's situation has been assessed, they can then take practical and targeted measures to reduce the transfer of polluted runoff if need be.

These measures could include ensuring clean water that falls on the roofs of farm buildings does not mix with water that's been contaminated by contact with manure, preventing soil compaction around water troughs or gates, establishing buffer zones between grazing animals or manure spreading and drainage ditches and other watercourses.

The researchers discovered, among other things, that untreated sewage from the farmhouse was a significant factor in the total amount of pollution in several cases. This was a surprise, and may highlight an area needing more research - human waste is potentially more dangerous to health than manure from animals.

Slurry conundrum

Another insight from the study is that injecting manure slurry into the soil may have disadvantages. This is a common practice in several European countries to reduce ammonia emissions and unpleasant odours.

Ammonia emission followed by deposition of nitrogen-rich rainfall can harm vulnerable ecosystems and cause loss of biodiversity. Until recently, Britain's anti-ammonia emissions regime has been relatively relaxed in most areas, but this could change and slurry injection is one method being considered to help meet potentially more stringent targets.

While slurry injection does indeed limit ammonia pollution by reducing the amount of slurry that is exposed to the air, other benefits include reduced risk of livestock being contaminated with potential pathogens whilst grazing, meaning that grazing stock could be let onto areas of pasture more quickly after slurry injection than after surface spreading of slurry.

But research from this latest project also showed that slurry injection causes more faecal bacteria to survive compared to surface spreading, as the bacteria are protected from UV light and desiccation.

The picture is complex. Although slurry injection causes greater persistence of bacteria in the slots, they are not necessarily at greater risk of being transported to watercourses. So, whilst ammonia pollution is a major problem, if injecting slurry into the soil can be done in a way that does not increase risk of polluted runoff, its ability to prolong the lives of harmful bacteria could be a price worth paying. Chadwick points out that more attention should be paid to such secondary effects of anti-pollution measures.

The project is part of the Rural Economy & Land Use Programme (RELU), a multi-disciplinary collaboration between the Economics & Social Research Council (ESRC), the Biotechnology & Biological Sciences Research Council (BBSRC) and NERC, with additional funding from the Scottish government and the Department for Environment, Food & Rural Affairs.

The programme aims to investigate the social, economic, environmental and technological challenges faced by rural areas.