Study investigates whether groundwater is sustainable
Researchers in the United Kingdom have discovered that agriculture practices developed in the last century that gave food security a boost also contributed to increasing nitrate pollution in both surface water and groundwater. The study, presented in the journal Water Resources Research, evaluated water quality measurement over the last 140 years to track this problem in the Thames River basin. Led by the University of Bristol, researchers used a simple model that combined two key elements: an estimate of nitrate available for leaching triggered by land use and land management, and an algorithm to determine this leachable nitrate through to surface water or groundwater. The Thames River catchment is well suited for the purposes of this study: people have been checking the quality of the river's water for the last 140 years, and the region has undergone innovative agricultural development in the last century. Nitrate concentrations in the Thames swelled in the 1940s and then again some 30 years after. The concentrations have stayed at high levels, despite a drop in nitrate from inputs from agriculture from the 1970s to the early 2000s. Their data show that it takes time for nitrate to reach the river, and that the rise in nitrate concentrations in the late 1960s to early 1970s was triggered by the delayed groundwater response to ploughing of permanent grasslands during the Second World War. '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,' explains lead author Dr Nicholas Howden from the Department of Civil Engineering at the University of Bristol. '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.' For his part, co-author Dr Fred Worrall from the Department of Earth Sciences at Durham University in the United Kingdom 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.' Professor Tim Burt from the Department of Geography at Durham University, also one of the authors of the paper, 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.' A long-term vision for water quality remediation is needed if this problem is going to be solved. The team says there is no 'quick fix'. They also add that the worst may still be to come.For more information, please visit: University of Bristol:http://www.bris.ac.uk/Water Resources Research:http://www.agu.org/journals/wr/
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