When blood-red sludge broke through containment walls in the Hungarian town of Ajka in October 2010, the immediate concern was the safety of hundreds of nearby residents. In the end 10 people died from exposure and the toxic muck spilled into waterways, including the Danube, prompting alarms downstream.

Spills on the magnitude of the one at the Ajka alumina plant are relatively rare and industrial pollution in many European rivers has declined since the 1960s. Tougher treatment laws, international cooperation and EU policies like the 2000 Water Framework Directive and 2006 Groundwater Directive are credited with the improvements.

While factories were once the big concern, more attention is focusing on pollution from farming, which accounts for more than half of land use in the EU and is overall the biggest consumer of water.

Dietrich Borchardt is among those worried about agriculture’s effect on waterways.

“Acute industrial pollution is a rare case in Germany and even throughout Europe,” said Borchardt, who heads the Department of Aquatic Ecosystem Analysis at the Helmholtz Centre for Environmental Research in Germany. He attributes threats to “the excess rate of fertilisers”.

“What we call good agricultural practice today,” Borchardt said in a telephone interview, “from a water perspective is not a good practice.”

A leading pollution source

Fertilisers typically contain nitrogen, phosphorous, potassium and sulphur, nutrients that help ensure healthy crops and boost yields. Commercial fertilisers use a form of nitrogen – nitrates - while organic fertilisers such as manure also contain high levels of the compound. Nitrates quickly leach into the soil and wash into streams, lakes and aquifers.

The European Environment Agency (EEA), an EU body, identifies nitrogen runoff from fertiliser and manure as one of three main pollution threats in Europe, along with particulate matter from vehicle exhaust and ground-level ozone from industrial and auto emissions.

Globally, the UN Food and Agriculture Organisation identifies farming as a leading cause of groundwater pollution, producing three times the nitrogen emissions of industrial sources.

Health experts say high levels of nitrates can cause weakness and illness in children, the frail and pregnant women. Yet nitrates also have profound effects on ecosystems, promoting growth of algae that chokes off oxygen for fish and other marine life.

The WWF environmental group says agricultural runoff is the main cause of nutrient overload in the Baltic Sea, which along with other pollution and excessive fishing are blamed for depleting fish populations.

Farmers are not the only culprits. Combustion engines give off nitrogen emissions that pollute the air as well as groundwater, and nitrogen also contaminates water supplies from waste landfills and the sludge produced from sewage treatment.

Yet conservationists and researchers say farming practices pose another threat to groundwater through the use of chemicals to combat pests and bugs.

Pesticide threat

A recent study by Borchardt’s colleagues at  Helmholtz warned that pesticide contamination of European waterways will worsen in the decades ahead – especially in northern countries – as climates warm and insects migrate to areas once too frigid to populate. The researchers estimate that in the decades ahead, some 40% of Europe’s waterways will be degraded from pesticide use.

Acknowledging agriculture’s risks to water quality, the European Commission has proposed a set of measures to update its Nitrates Directive and fertilisers regulation. Its proposed reform of the Common Agricultural Policy (CAP) would give farmers cash incentives to rotate crops to reduce fertiliser use.

The Commission also wants to encourage farmers who use buffer areas that could protect streams and rivers from nitrate and chemical runoff. The proposals, if approved, would take effect in 2014. But the Commission’s ‘greening’ plan for agriculture is facing sharp criticism at a time of rising global demand for food and inevitable conflicts between conservation and production.

Farming and industry groups contend plant nutrition and protection are vital to meet the needs of rising demand, especially as the global population grows. How to balance food production needs and avert water scarcity will be among the challenges discussed during the World Water Forum in Marseille, 12-17 March, and the UN Conference on Sustainable Development in June.