The Planet Earth podcast - 'River Thames pollution, Arctic freshwater bulge'.
27 February 2012
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Sue Nelson:Hello, and welcome to the Planet Earth podcast. Today we're in London beside a stretch of water that is 215 miles long, beloved by artists and first crossed by a bridge built by the Romans 2000 years ago. It is, of course, the River Thames and I am here because of what can be found in the capital's famous waterway. There's also news from the natural world which includes a fossil cricket's love song and I'll also be popping into University College London to learn more about the huge body of fresh water recently discovered in the Arctic.
Dr Catherine Giles:It's over a 1000 kilometres across, so that's the distance between roughly, say, London to Venice, so it's quite a large area of the Arctic Ocean.
Sue Nelson:I'm beside a section of the River Thames near Waterloo Bridge which offers one of the best views of the City - St Paul's Cathedral in the distance on one side and on the other Big Ben and the Houses of Parliament.
50 years ago this river was so polluted it was considered biologically dead. Today, though, it is considered one of the cleanest rivers through a major city. Pollutants though such as nitrates harm newborn babies and trigger the rapid growth of algae in rivers killing fish and choking plants. As a result nitrates are removed from water supplies but even so the amount of nitrates in the River Thames has trebled since the 1930s. Scientists wanted to know why and so a team from the Universities of Bristol, Durham and Cranfield has been studying how nitrates move through the land to end up in rivers, springs and other sources of water. To do this they use a paper trail of archives containing records of water quality dating back 140 years, the longest continuous record of its kind anywhere in the world. To discuss what they wound I'm with two of the team members, Dr Nicholas Howden, a senior lecturer in water at the University of Bristol and Tim Burt, Professor Geography and Dean for Environmental Sustainability at Durham University. And I'm going to begin by asking you, Nicholas, where have these nitrates in the Thames come from?
Tim Burt:Well, a proportion of the nitrate in the Thames has come from sewage effluent discharges. That has largely been controlled in the last 20/30 years with lots of new treatment processes being put in place. A lot of that comes from point source discharges, so we can see them and we know where they are, we know who's discharging them and they've been largely cleaned up as they can be and regulated. The compartment that we've been mostly interested in looking at the diffuse sources - so those are the sources that are widely distributed throughout the Thames catchment and that's one of the largest catchments in the UK and it's some 10,000 square kilometres, so it's a very big area, and that is predominantly coming from our agricultural activity to grow food, so ploughing, fertilizing, use of animals and the natural processes of biological fixation and also some atmospheric deposition as well. So, it's a combination of factors that have come from our use and our more and more intense use of the river catchment from which all of this water drains to then end up in the Thames.
Sue Nelson:How does ploughing release more nitrates into the soil? Tim.
Tim Burt:Well ploughing mineralises organic matter, it basically aerates the soil and you get organic matter of being oxidised and that works through to first of all, sort of, ammonium salts and then though to nitrates. So it's the aeration of the soil. It's what, in a sense, ploughing is actually about turning organic matter into nutrients which can then grow crops.
Sue Nelson:So does this mean then that during World War II, for example, when everybody was being encouraged to 'Dig for Victory' and the records that you've been studying have gone further back in time than that, did you notice an accompanying spike in a way then of nitrate levels?
Tim Burt:Yes, we did. In fact in the first war as well, but the second world war in particular and there wasn't much use of fertiliser other than animal manures then, but the mere fact of ploughing and widespread ploughing, a huge increase in the area of land under the plough and that does show through. It showed through to an extent straight away, but it also showed through in a big delayed response which came several decades after the war. But, yes, you can definitely see a link between 'Food for Victory' and all those sorts of campaigns and the water quality in the Thames decades later.
Sue Nelson:I know that, Nicholas, one of the important things here is about when you saw the link as well. It took time to get those nitrates from the surrounding land into the River Thames.
Dr Nicholas Howden:Yes, that's right. So what we've tried to do is to estimate what the inputs were in any particular year and then we've used this long record of what was going on in the river to try and match the inputs to the outputs using a series of stores. So, in this case, two stores - one which is run off, so that's the water that hits the land and it makes it way to the river in that year and then there's a second store which is a ground water pathway and so the water that falls in any particular year takes nitrate with it and then it ends up in the river sometime later. In producing our model we allowed that delay time to vary up to a number of decades from zero to about 50 years or even more. And what we found was by using the estimated pattern of inputs that we come up by considering what fertilizers were used, how much ploughing there was, how many animals there were in any year. We were able to match that input to what we actually observed in the river and by doing that we can estimate what these different delay times are and how long it takes for something we do in, say, 1940, to reach the river. It turns out the answer is reaches us in about 1970 and the split is roughly 50:50. So a 50% of what goes onto the land comes out in that year and 50% is delayed by approximately 30 years.
Sue Nelson:That's incredible though isn't it - 30 years. I mean that's a real case of thinking about the future isn't it in terms of the effect of behaviour will have on the land and how it will effect nature around us.
Dr Nicholas Howden:Yes it is and we think it is very important because a lot of what we do we think that if it doesn't have an effect shortly after we've done it then it doesn't have an effect at all. Whereas in actual fact to deal with this problem we are going to have to think in terms of 50 year cycles, and that's because we're dealing with a natural system that has this natural time constant and it's very important that we start to understand this when we're setting policy objectives, when we're trying to understand how what we do now will effect the future. For example, a team in New Zealand have started to set travel times on their land around certain freshwater lakes and saying you can only have this much nitrate that you can use in this year, and once you've used it up you are on the 50 year travel time, it can't happen. You can't do anything else for a number of years. So, this sort of management strategy is being piloted and it's the sort of thing that we're going to have to think about if we want to reduce the levels to the land at the moment, so we can affect a 50% decrease in the run off. That's the maximum we could affect if we stopped everything now. Because 50% of it is still what's happened in the last three decades.
One of the very important things as well is that we talked about 'Dig for Victory' and that has an image of me going and digging up my garden. Just to put that into perspective - what we're talking about in the Thames catchment, as a whole, is a 30% change in the amount of arable land that there was. So we're not just talking about people digging us their gardens, we're talking about wholesale ploughing of every piece of grassland that there was more or less available for arable crops to be grown. So we're talking about a lot of land.
Sue Nelson:Behind you, at the moment, there's the potential of a land also being ploughed up but for building new houses particularly around the London area and the greenbelt area. How do you convince politicians then, Tim, that they have to look beyond the four years of their next voting terms of getting into parliament and think 30, 40, 50 years ahead - that's not going to be easy.
Tim Burt:It's not because I think the natural tendency is to look in political cycles and assume that any management policy and strategy will have a payback in time for the next election, and I think it will some very clear excited and selfless politicians to say this is a long term strategy and these are things we need to do over the longterm, and I think the nitrate pollution is just one aspect of that where we may be looking at long term ground water levels or long term changes in other parts of the system. But it is very difficult to get people to put in place strategies where the payback will be, you know, well after my time, probably and it may be our children or our grandchildren who see the benefit of strategies that are put in place now.
Sue Nelson:Nicholas Howden from the University of Bristol and the University of Durham's, Tim Burt. This is the Planet Earth podcast and as you can hear I've left the banks of the River Thames and have travelled just over a mile north to the Centre for Polar Observation and Modelling at University College, London. Recently British scientists discovered a dome of fresh water in the Arctic Ocean using two European space agency satellites and the lead author of the study was Dr Catherine Giles here at University College, London. First of all, Catherine, could you describe what this dome of water actually looks like?
Dr Catherine Giles:Well, if you're imaging you are looking down on the earth over the north pole and you can see the Arctic ocean, if you cast your eyes over to Canada, then go north of the Canadian coastline then you're in the Beaufort Sea, and in the Beaufort Sea there's a circulation system called the Beaufort gyre, so that's a rotating dome on water that rotates in clockwise direction and what we've seen from the satellites is that dome increasing in height. The area is about - well it's over 1000 kilometres across, so that's the distance between roughly, say, London to Venice, so it's quite a large area of the Arctic Ocean.
Sue Nelson:And when you say a dome, are we talking like a huge Millennium dome rising of water above the sea surface?
Dr Catherine Giles:I imagine it more like a contact lens rather than a Millennium dome, but it's still quite a large amount of water, it's about 8000 cubic kilometres of fresh water which is roughly about 10% of all the fresh water that's stored in the Arctic Ocean.
Sue Nelson:Now, did you have clues that there was this body of fresh water in among a salty ocean?
Dr Catherine Giles:Well yes. Measurements taken from ships and moorings have shown that there has been an increase in fresh waters, say, over the past 15 years or so. But it is really difficult to make measurements in the Arctic because of the cold, dark winters and the ocean itself is covered by a layer of frozen seawater so it makes it hard for the ships to break through. So this is why this satellite data is really useful. It helps to tie these snapshots of data taken from the ships and from the moorings to give us an idea of the overall picture of how the Arctic Ocean is changing.
Sue Nelson:Now you were using two European space agency satellites, the ERS2 and MV Sat which is sort of the double bus analogy always gets used on this, but it is a huge, huge environmental satellite. Were they both looking at the saltiness of the ocean or sea surface tide in order to work out that, hold on, we've got this enormous amount, and it is enormous, amount of fresh water in the Arctic?
Dr Catherine Giles:What these satellites do - we use an instrument on board them called a radar altimeter and what that does is measure the elevation or the height of a surface. Now, as I said, the Arctic Ocean is covered by a layer of frozen water known as sea ice but as the sea ice moves around it breaks up and it exposes bits of the ocean and the satellites are sensitive to those bits of the ocean, they can see them from space and we can measure how high they are. So, the data we're using is actually looking at changes in the sea surface height and from that combining it with data from another satellite called Grace which measures changes in mass we can estimate the change in the fresh water.
Sue Nelson:Now do you know how this body of fresh water came to be there in the first place, what caused it?
Dr Catherine Giles:Well it's well known that the Arctic Ocean gets fresh water from rivers running off into the ocean itself. So, again, if you imagine looking down over the top of the earth, over the North Pole the Arctic Ocean is surrounded by land - you've got the Russian side and then Canada and America and Greenland. Now, as we go into the summer the rivers on that land start to thaw and as they thaw that fresh water pours into the Arctic Ocean, so what we're seeing here is either that water being redistributed around the ocean or it being stored in the Arctic Ocean whereas it might have gone elsewhere, it might have actually left. Now that's not the only source of fresh water as the sea ice cover melts that can add fresh water to the Arctic and also changes in evaporation and precipitation can also change the amount of fresh water that's stored in the Arctic Ocean.
Sue Nelson:Is there a possibility that this fresh water could flow into other circulatory systems around the earth?
Dr Catherine Giles:Well, what we've seen in our data is that the fresh water that has been stored over the past 15 years that the winds seem to be controlling that storage of fresh water. So it's possible if the winds then change direction then that fresh water could be released out into the western Arctic, to the rest of the Arctic Ocean or beyond. And we're interested in that because changes in fresh water leaving the Arctic Ocean can influence the deep confection in the North Atlantic. Now, part of the reason that Northern European enjoys a relatively mild climate in the winter is because of heat transported by currents that are derived from the Gulf Stream. So this circulation system we call the global overturning circulation system, and that's bringing heat from lower latitudes up to the north in the ocean currents and as that water reaches the north it cools, it releases its heat to the atmosphere and the cooler water it then sinks and then more water moves up to take its place. Now, this is a density during the circulation. The water is sinking because it's more dense, so if you then add less dense fresh water from the Arctic possibly you could effect that circulation system and in the past we've seen than an amount of water of a similar size to this 8,000 cubic kilometres may have influenced this confection in the Labrador Sea which is one of the areas in the North Atlantic where you get this kind of overturning circulation. Whether that had an effect on our climate is something that we don't know.
Sue Nelson:Catherine Giles from the Centre for Polar Observation and Modelling at University College, London, thank you very much indeed.
And now for a round up of recent news from the natural world with Tamara Jones from Planet Earth Online. And we're going to begin with news of a songbird with quite an impressive range of flight.
Tamara Jones:It's pretty amazing this songbird. I mean it's quite a small bird - it's a northern [unclear 0:16:32.6] and it's about the size of a robin and researchers have attached minature tracking devices to them to find that their epic migrations are around about 30,000 kilometres every year. That's about 18,000 miles, that's a round trip and they're travelling from the Arctic to Africa all the way from, sometimes, Alaska, so you've got a sub-species that live in Alaska and you've got another sub-species that live in Eastern Canada and Greenland and Iceland and you might expect the Alaskan species to go down to California if they want, somewhere warm, but in fact they travel overland over Russia, over the Arabian Peninsula to get to Eastern Africa to find somewhere warm to spend the winter.
Sue Nelson:So what will the scientists do now?
Tamara Jones:The thing is the very fact that they know that they go to Africa and they don't go anywhere else, they don't go to North America suggests that we need to take that into account when it comes to conservation and making sure that these birds are okay.
Sue Nelson:Blue tongue virus now - now this is a virus that infects animals like cows, sheep and deer and in fact there was a outbreak in Europe in 2006 and there's been some progress, I believe, in terms of the spread of blue tongue.
Tamara Jones:Well that's right. Researchers have discovered that midges, tiny little insects, you know, the midges that bite you in Scotland in the summer, that they might expect that they just get blown around by the wind and they're just completely at the mercy of the elements, but in fact these midges can flow both upward and downwind and the midges actually carry the disease so the animals don't get the disease from each other and so this means that the researchers can find out a little bit more about how some of these outbreaks might spread in the future.
Sue Nelson:So that a sort of unexpected outcome there from such a tiny little insect in terms of the effect it is having on cattle and sheep, and we're going to end with, I think, quite an incredible story about the song of a fossil cricket.
Tamara Jones:This is an amazing story - it's gorgeous. These scientists have found that this fossil cricket - it's basically a cricket that lived a 165 million years ago actually made a sound very similar to the crickets that are alive today.
Sue Nelson:Which makes you immediately want to say, how on earth did they manage to work that out.
Tamara Jones:The only way they managed to work it out was that the fossil was so well preserved which meant that its wings were perfectly, perfectly preserves so they could figure out the noise that this cricket would have made when it rubbed one wing against the other.
Sue Nelson:I assume then one of the scientists must have the equivalent of a back catalogue of cricket noises and knowing how crickets make the noise normally which is, as you say, rubbing their wings together and are ridges of teeth. They can work out then that what the tone would be as well because not all crickets must make the same noise.
Tamara Jones:No, exactly, it depends on the number of teeth on one wing and the way it rubs it against the other plectrum on the other wing. So, these researchers they actually compared the shape of the wing and the shape of the teeth with crickets that are alive today to figure out exactly what sound it would.
Sue Nelson:Well I think we ought to have a listen then to what sound they've come up. [sound of cricket] That's incredible, so that's a recreated sound of a 160 million year old cricket sounding incredibly fresh but it's the tinkling sound that gets me, it's very clear and crisp. So that would have been heard in rainforests I assume.
Tamara Jones:That's what they say that the rainforests might have been quite dense so a single tone sound would have actually would have been projected a lot further than a kind of rasping sound that some crickets today use, so it would have been heard by the dinosaurs for sure.
Sue Nelson:Tamara Jones, thank you very much indeed. And that ends this edition of the Plant Earth podcast from the National Environment Research Council, and you can find out more about all of those stories and more on Plant Earth online. Don't forget to visit us on Facebook and do follow us on Twitter. I'm Sue Nelson, thanks for listening.