Action needed to reduce nitrogen and phosphorus pollution in the Thames

In a podcast on the NERC Planet Earth website, Paul Whitehead from Oxford University and Mark Barnett from the Environment Agency comment on the pollution challenge of the river Thames. They explain why the river will fail to meet European Union standards unless action is taken by farmers to reduce fertiliser use and water companies cut the amount of phosphorus being discharged by sewage works.

“Nitrogen and phosphorus come from a range of different sources,” said Paul Whitehead, Professor of Water Science at the School of Geography and the Environment. For example, phosphorus comes through sewage works, from the soap we use in everyday in dishwashers and washing machines, as well as from agricultural and rural diffuse sources.

“They create eutrophic conditions in the river, where you get excessive blooms of algae and growth of unwanted plants” explained Paul. “It is possible to kill a river, meaning the oxygen levels in the river are reduced down to zero and fish and macroinvertebrates can’t survive.”

Mark Barnett, Catchment Coordinator for the Environment Agency said that although a lot of work has been done over the last few decades to reduce nitrates and phosphates, there is still quite a long way to go to meet European Union targets.

Climate change could have significant impacts on river pollution in the future as the distribution of rainfall changes, with more rainfall predicted in the winter and reduced rainfall and river flows in the summer. “This means that in the summer there will be less dilution of pollutants coming into the river system, so that could raise phosphorus levels, and in winter more nitrogen and phosphorus could be flushed out of the catchment into the river system,” warned Paul Whitehead.

Building riparian buffer strips is one measure that could be taken to cut down pollution levels – these are zones of land next to the stream channel which effectively act as a filter for the sediments and nutrients found in water running off the fields. There are also technologies available for removing phosphorus at sewage treatment works, enabling it to be recycled and sold back to farmers rather ending up in the river.

“I’m reasonably confident that things will improve” said Paul Whitehead. “They’ve improved massively over the last 50 years in the Thames so I’m sure that will continue. Technology is improving the whole time, the water companies are quite keen to actually extract phosphorus and sell it back to the farmers, it’s potentially a source of money for them and at the same time farmers want to use less and less fertiliser because it is more expensive.”

Listen to the Planet Earth podcast