Pollution in US rivers is widespread and will persist

If rivers are a nation's lifeblood, the US should be on the sick list. More than half of the country's streams and rivers are in a "poor condition" for aquatic life, according to a survey by the US Environmental Protection Agency.

The agency sampled nearly 2000 sites in 2008 and 2009, looking at factors such as physical disturbances, mercury in fish flesh, faecal bacteria and nutrients from fertilisers.

Nutrient pollution, which causes algal blooms that can deplete a river's oxygen, was the main problem: 40 per cent of rivers and streams were rated "poor" for their high levels of phosphorus and 28 per cent were given the same rating for excessive nitrate contamination. Nitrates are the more persistent contaminant as they leach into groundwater and from there into streams. A new study suggests nitrates will cause pollution for decades to come, even without further fertiliser use.

Phosphorus pollution is also a growing problem. Only 34.2 per cent of river stretches tested were rated in "good" condition for phosphorus, down from 52.8 per cent in 2004.

Unfortunately, not all farmers observe official guidance on fertiliser use. "If everyone followed it, things would probably be quite a bit better," says Neil Dubrovsky, a US Geological Survey hydrologist based in Sacramento, California.

Journal reference: Environmental Science & Technology, doi.org/kx2

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