A study conducted by the British Geographical Survey adds urgency to concerns about the potential for ammonium from historic landfill sites leaching into waterways.
The study, published in August in the journal Science and the Total Environment, found that more than 27 tonnes of ammonium leaches from an Oxford wetland into the Thames every year. Researchers studied the area around the Port Meadow landfill site, which lies on the banks of the Thames northwest of Oxford.
Un-lined landfill sites like this – of which there are believed to be thousands in the UK – present an obvious concern with respect to ammonium and other pollutants, but this is a rare attempt to quantify the problem, which could be a nation-wide issue.
During the study, researchers drilled a series of boreholes, taking regular water samples between May 2010 and August 2013, in the hope of gaining an estimate of the total amount of ammonium moving through the floodplain.
Researchers were able to discriminate between ammonium from its other principal source – bird droppings – and that from the landfill site by using isotopic analysis.
It also seems odd that the problem should seem to rear its head now. Daren Gooddy, one of the principal researchers with the BGS said: “We’ve been getting rid of waste for an awful long time.”
“Since Victorian times, we’ve been putting it into landfill and ad-hoc waste dumps on the edge of our towns and cities, often on the fringes of floodplains.”
“Collectively, this contribution to overall ammonium concentrations in rivers could be very high,” he said. “It’s something that really ought to be taken into account when we’re drawing up management plans for floodplains on the margins of towns and cities.”
It’s a problem Gooddy believes could be repeated across the developed world.
The issue of nutrient pollution of rivers and waterways has gained in urgency over the years, principally originating with fertilisers used in agriculture. Much of this makes it into waterways where it causes eutrophication, and development of algal blooms, which starve fish and other aquatic organisms of oxygen, and in some cases are actually poisonous.
Modern landfill sites tend to be lined with a layer of clay, which prevents anything leaking out.