Podcast: Why the River Thames faces a pollution crackdown

Floating mats of green algae in a river

Floating mats of green algae in a river

4 February 2014 by Richard Hollingham

This week in the Planet Earth podcast, Paul Whitehead of the University of Oxford and Mark Barnett of the Environment Agency explain why the UK's River Thames will fail to meet new pollution standards unless farmers and water companies take radical action.

To assist those who find text-based content more accessible than audio, a transcript of this recording is available below.

Richard Hollingham: This time in the Planet Earth podcast, what phosphorus nitrate pollution is doing to our rivers. I'm Richard Hollingham and I'm standing on the swollen banks of the River Thames at Wallingford in Oxfordshire, the water practically lapping at my feet, looking across the water to the flood planes, sodden fields and bare trees. Now, the river is certainly considerably wider than it would normally be and much faster flowing, but it does look pretty clean. That said, according to a recent study this waterway will fail to meet new pollution standards unless some radical action is taken by farmers to reduce the use of fertiliser and water companies cut the amount of phosphorous being discharged from sewage works. Well the scientist that has carried out this research is Paul Whitehead from the University of Oxford and I am also joined by Mark Barnett, a catchment coordinator for the Environment Agency. Now, Paul, you specifically studied phosphate and nitrate pollution in the Thames - what do these chemicals do to the river and where do they come from?

Paul Whitehead: Nitrogen and phosphorus come from a range of different sources. Phosphorous comes through the sewage treatment works, from in fact soaps that we use in our washing machines and our dishwashers and of course from humans as well and that ends up in the river system having been discharged from sewage treatment works.

Richard Hollingham: What does it do to the river?

Paul Whitehead: They create eutrophic conditions in the river, so that's where you get excessive blooms of algae in the river system, growths of unwanted plants. It is possible to kill a river and by that you mean that you've reduced the oxygen levels in the river down to zero where fish cannot survive and macro invertebrates can't survive.

Richard Hollingham: Now, Mark, we should say that UK rivers are a lot cleaner than they used to be?

Mark Barnett: Yes, they are. A lot of work has been done over the last few decades and the Thames in particular won an international award for the most improved river back in 2010 for phosphates work done to deliver European directives has seen great reductions in nitrates and phosphates as well.

Richard Hollingham: That said this river and other rivers around the country are not going to meet the European Union targets?

Mark Barnett: Yes. A lot of improvements have been made but there is still quite a way to go. The Water Framework Directives' target that we have to deal with at the moment, we are currently working internally and with partners to see what we can do to reduce them further.

Richard Hollingham: So, Paul, you looked at various scenarios of what you could do about this. What were you conclusions?

Mark Barnett: We concluded that it was necessary to remove some of the phosphorus coming out of the sewage treatment works and the private sources, also to reduce some of the phosphorus from the diffuse sources. So we looked at various measures like building riparian buffer strips around the-

Richard Hollingham: Sorry, a what?

Mark Barnett: A riparian buffer strip - that's a strip of land next to the stream channel where effectively it acts as a filter bed, so that the water running off the fields goes through that channel and essentially sediments will drop out within it, some chemical processing will happen such that the phosphorus will be absorbed onto the soils and nitrogen can denitrify in those buffer strips, so that's one approach that could be used to enhance the reduction of nutrients in catchments.

Richard Hollingham: What about improving the sewage treatment? A lot of the flow, not perhaps at this time of the year but at other times of the year in the rivers, is going through sewage treatment works. Wouldn't it be relatively straight forward to remove the phosphorus and remove the nitrates?

Mark Barnett: It's difficult to remove nitrates, surprisingly enough, but phosphorus is more possible; you can use chemical precipitation techniques to remove phosphorus at sewage treatment works. The technology is quite well known and in fact the precipitate that they extract is largely pure phosphorus. It can then be recycled and it can be sold back to the farmers, basically, so that you are making use of the phosphorus resource rather than putting it into the river system.

Richard Hollingham: And that is a point isn't it, that phosphorus in particular is useful stuff and relatively scarce?

Mark Barnett: Oh it's increasingly scare and they're talking about pig phosphorus, so in other words the sources of phosphorus in the world has reached a peak and it will only go down from now on, so that means that prices of phosphorus will go up and that will impact farmers. They have to use some phosphorus for fertiliser, application to grow crops and it makes some sense to actually try and recycle some of that phosphorus that is in the river and essentially sell it back to the farmers at a lower price.

Richard Hollingham: How do the effects of climate change come into this?

Mark Barnett: Well, climate change will have a big affect on UK rivers partly because there will be a change in the distribution of rainfall, so you might have increased rainfall in the winter and less in the summer and means that there will be lower flows in the rivers in the summer and that means there will be less dilution of pollutants coming into the river system, so that could raise phosphorus levels, for example, and in winter it could flush more nutrients, nitrogen and phosphorus out of the catchment into the river system. So those would have significant impacts on the river in the future.

Richard Hollingham: This is an issue isn't it, Paul. You can get a river so clean whether it's the Thames or another river in this country or elsewhere and then it's really hard to do the next step particularly when you've got agricultural areas, cities, towns, villages?

Paul Whitehead: That's certainly a major problem and it is quite easy to perhaps improve the quality by 70% or 80% but that last 20% is extremely difficult to meet because you're dealing with lot of different sources and trying to put control measures on all of them is an extremely difficult thing to do and quite a costly thing to do as well.

Richard Hollingham: So what will happen do you think over the next few years in terms of river quality?

Paul Whitehead: I'm reasonably confident that things will improve; they've improved over the last 50 years massively in the Thames so I'm sure that process 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. So the pressures are there for improvement, it's just a case of how you make those improvements.

Richard Hollingham: Paul Whitehead and Mark Barnett, thank you both and you can find more about this work on the Planet Earth online website. You can also find Planet Earth online on Facebook and Twitter and we will put some pictures of today's recording and actually a rather beautiful view from where we are standing. That's the Planet Earth podcast from the Natural Environment Research Council. I'm Richard Hollingham, thanks for listening.