Nitrate contamination of UK water 'may get worse' fear
There are no quick fixes for UK groundwater contaminated with nitrates and the worst is yet to come, scientists fear. Over the years, intensive agriculture has caused rising levels of nitrates in groundwater sites, say researchers from the University of Bristol.
It can take decades for reduced use of nitrates on land to show benefits in river and groundwater and things may get worse before they improve, they fear.
Head of research, Dr Nicholas Howden, who is Senior Lecturer in Water in the Department of Civil Engineering, says, "Balancing the needs for agriculture and clean groundwater for drinking requires understanding factors such as the routes by which nitrate enters the water supply and how long it takes to get there.
"Our results suggest it could take several decades for any reduction in nitrate concentrations of river water and groundwater, following significant change in land management practices."
The Bristol Univesity research, financed by the Natural Environment Research Council, examines the measurement of water quality in the Thames River basin since the 1870s and concentrated on the transportation of nitrates from land used for agriculture to the Thames water.
Researchers estimated how much nitrate leached from the soil to the groundwater after taking into account land use practices and an algorithm that calculated how nitrates would travel from the land to the water.
The quality of the Thames water, which is treated and supplied to millions for drinking water, has been recorded for 140 years, so is an ideal example for the study.
Levels of nitrates in the Thames doubled around World War II. They rose again in the 1970s and have remained high, despite the fact that nitrates use in agriculture has declined since then.
As nitrates can take decades to reach the river, the increase in concentrations from 1968-72 was caused by grassland ploughing in the Second World War, the researchers believe.
Co-author, Dr Fred Worrall, from the Department of Earth Sciences at Durham University, says: "The 60s and 70s saw a gradual intensification of food crop production and consequent nitrate release from the land. If your input is dispersed, your output is dispersed; if your input is sharp, your output is sharp. The aquifer is just transporting it; it's not processing it. The nitrate comes through as a pulse."
Fellow co-author, Professor Tim Burt in Durham University's Department of Geography, says, "You can work out the budget, and there is a phenomenal amount of nitrogen accumulating somewhere in the Thames basin. We don't know where and we don't know in what form, but it represents a potential legacy for a long time.
"The effects of land-use changes can take decades to filter through the river basin and this has major implications for policies to manage rivers."
Researchers hope the study, Nitrate pollution in intensively farmed regions: What are the prospects for sustaining high-quality groundwater?, will help planners follow practices that maintain water quality and agricultural production levels.
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