Thames archive reveals long nitrate rise

Scientists have assembled a remarkable record of water quality in the Thames that stretches back over 140 years.The archive is thought to be the longest for any river in the world.Putting it together involved hunting down old paper documents detailing monthly water tests. Some of them even had to be retrieved from the US. The Bristol University-led team says the record provides a true baseline against which measures to keep the great river clean can now be judged.But it also illustrates just how intractable the issue of nitrate pollution has become. Over the 140 years of the new time series, this nitrogen component of river chemistry is seen to climb relentlessly. The pollution will almost certainly have altered the ecology of the river, shifting the balance of plantlife in the Thames."Generally, Thames water quality has been improving - the fish are returning," explained Bristol's Dr Nicholas Howden. "But the big challenge that remains is diffuse pollution, and the UK remains the global hotspot for nitrate flux. "We have the highest export for nitrate for any country in the world per capita or per land area, depending on how you want to express it. And some of the highest concentrations are coming out through the Thames."