Water: Drips, Drains and Droughts

珊瑚礁生物多样性最丰富的生态系统the oceans. They make up less than 1% of area but host a quarter of all life. And this makes for a noisy atmosphere but within the past 5 years, they've become significantly more quiet. A group from the University of Exeter has been listening in to the lifebeat of the great barrier reef, and found that it’s about a quarter of the volume it used to be. And this is going to have a devastating knock on effect. Georgia Mills got the story from first author Tim Gordon.

蒂姆-珊瑚礁非常嘈杂的地方。它们是完整的of shrimps clicking their claws and fish chatting and chirping and whooping, and those sounds are used for all sorts of different things. Fish alarm call to warn each other about predators, they communicate with each other, they hunt together using sound. But what we’ve seen recently is that where we work on the Great Barrier Reef has been decimated by climate change. Tropical cyclones are happening more frequently and more strongly, and coral bleaching is wiping out whole areas of the ecosystem.

When we went back recently and listened again to some of the areas that we’d worked in five years ago, it broke our heart. What used to be a raucous symphony of noise from the whole orchestra of animals, is being silenced.

Georgia - Oh wow! And what kind of impact is this going to have?

Tim - It’s really sad in of itself to hear that degradation. But it’s more than that actually because the sound of a reef is really important for attracting fish to it. Fish start their lives as larvae out in the open ocean where they’re avoiding predators and eating plankton and then once they’ve developed into juvenile fish, they then hear their way back home again. They come and find a reef to settle on and they listen out from miles away in the open ocean to hear that reef.

现在我们做了一个实验表明,sound of reefs today, that new quieter degraded sound, is much less attractive to juvenile fish and fewer fish are able to hear their way home to it.

Georgia - How did you test that?

Tim - What we did is we built a lot of experimental replica reefs all around a bay and on some of the reefs we put loudspeakers playing the sound of healthy reefs from five years ago, and on some of the reefs we put loudspeakers playing the sound of today’s degraded reefs. What we found was that on the reefs that played today’s degraded sounds, we got 40% fewer fish settling to those reefs than the ones playing the sound of a healthy reef.

格鲁吉亚——正确的。So this is really making a big difference then in how many fish are coming back. What kind of a knock-on effect would that have on a reef?

Tim - It’s worrying because reefs really need their fish or the whole system starts to collapse. You see fish help with nutrient cycling, they keep food webs in balance, they form associations with anemones but, most importantly, they graze away this harmful macroalgae that tends to grow over degraded reefs. This stuff sort of like slimy seaweed and when corals die, it grows over the top of the whole thing and chokes the reef. It stops any new corals from settling, any new corals from growing back, and it really slows down recovery. If there are fish on reefs, they eat away at the algae; that clears bare patches and allows coral to grow back again. But if reefs don’t have healthy fish populations, they’re really stuck on what we call this ‘slippery slope to slime.’

Georgia - Is there anything that we can do about this?

Tim - Absolutely. I think it is crucial that we remember that there is still hope. There’s renewable energy technologies that are advancing all the time and emissions are falling as a result. In the UK, we’ve recently broke our record for the longest run without using coal power in the UK. Our Government's discussing plans to go carbon zero by 2050, so there is already progress in reducing our emissions. I just think it needs to happen faster.

Georgia - While we’re waiting, can we use your experiment method to lure the fish back in while we wait?

Tim - This definitely raises that possibility and that is research that we’re actively doing at the moment. There’s the possibility that we might be able to use sound to help with reef restoration. If we can attract fish in using loudspeakers, it might help reefs to rebound quicker. But, like we say, the most pressing issue really is reducing emissions because any restoration efforts that we can produce will only be feasible on small scales, and will only partially help to restore reefs. So if we’re really serious about protecting what is the most beautiful and most valuable ecosystem in the world, then we really need to start addressing our emissions more seriously.

Recently Avengers Infinity War hit cinemas, breaking all the records for a Superhero movie and taking over £29.4m in its opening weekend.. So, of course, Georgia Mills has taken the opportunity to brush up on some maths.

Georgia - Have you ever asked someone under the age of ten what they think the biggest number in the world is? The results are invariably amazing…

One thousand and one million hundred and three

One hundred and twenty nine billion and eighty three.

Ninety.

Eight million?

Seven.

Seven?

Yeah.

That’s quite a big number isn’t it?

Yeah.

Georgia - Thank you to Emma, Claire, Sarah and Jim for sending those in. And, to be fair to those kids, it’s kind of a trick question.

Eugenia - There is no biggest number in the world because if there were we could also add one and it would be bigger. So you might think that the biggest number in the world is ‘infinity.’

Georgia - This is Eugenia Cheng. She’s scientist in residence at the School of the Art Institute in Chicago and also the Author of Beyond Infinity.

Eugenia - Infinity is very large, but actually you don’t have to be that dumb not to understand it because it’s very difficult to understand. And although it’s something that you can think about, even when you’re a small child and you are having those arguments about who’s more right - “I’m infinity times right”! Actually, it took mathematicians thousands of years to pin down what infinity is in a way that actually stands up to logic.

One way you can describe infinity is you can simply say it is the quantity of whole numbers that exist. You might think that’s cheating because you haven’t said what it is, but mathematicians kind of like cheating. And then, there’s this funny thing you can do where you can actually make a bigger infinity. So, if someone says to you “oh, I’m right times infinity”, then you can beat them. Not that everything is about beating people. You can say “I’m right times two to the power of infinity”, and that’s actually bigger.

Georgia - But isn’t infinity already the biggest number? How can there be a bigger one?

尤金尼亚-这是个好问题。问题是那t if you use the fact that infinity is the absolutely biggest thing and then you work with it logically in mathematics, you very quickly find you can prove that everything equals zero, which is a bit of a problem. Because if everything equals zero, then there isn’t really anything in the world, and that’s okay in mathematics, you’re in the zero world, but it’s not a very interesting world to be inside. But, of course, there are other worlds in which everything doesn’t equal zero and that’s why we actually need higher and higher orders of infinity to avoid everything collapsing to zero.

Georgia - Infinity simply refuses to behave itself. Everything goes a little bit weird when you think about it. And a famous example of this involves an infinite hotel…

Eugenia - Oh yes. The Hilbert Hotel is one of the famous thought experiments involving infinity. Hilbert’s Hotel is an infinite hotel and the idea is that there is a room for every number 1, 2,3,4, 5, 6, and so on. Suppose your hotel is full and you’re the manager of the hotel and a new guest arrives, you could either turn the guest away - say “bye, no room at the hotel”. Or you could go ahh, but I could make some more money if I move everyone up one room. So the person in room 1 goes to room 2; the person in room 2 goes to room 3; the person in room 3 goes to room 4, and so on and there’s an infinite number of rooms, so you never run out of rooms. But now room one is empty so the new guest can move into room 1 so, miraculously, the hotel was full and now there’s a spare room and this is something you can’t do in a normal hotel.

In a finite hotel, if it’s full, it’s just full, but infinity is weird like that. It’s sometime called a paradox but there's nothing wrong with it, so it’s the type of paradox which doesn’t involve an actual fallacy, it just contradicts our intuition about the world, and that’s not wrong, it’s just that we’ve discovered something. So sometimes, when we're thinking about infinity, the idea isn’t exactly to understand infinity better, but it’s to shed light on our actual world. We also learn a lot about numbers that do come up in life by imagining what would happen if infinite things were true.

Georgia - This is quite mind blowing the whole idea, and I suppose our experience of the world is finite. I only have ten cakes or whatever, I’m never going to have infinity….

Eugenia - Poor you.

Georgia - Yes, it’s a real shame. I’ll never have infinite cakes. So I suppose it’s not surprising that well, to me at least, the whole idea is a bit like ‘pow’.

Eugenia - I think that’s right. But the funny thing is that although we don’t have infinite cakes, we do sort of have infinite pieces of cake. Because, if you cut your piece of cake in half, and then you take half of the rest, and half of the rest, and half of the rest, and so on. That’s what small children do to make their cake last forever or, at least, that’s what I did.

Georgia - So infinity is useful for me to decide that my cake is going to last forever, but is a useful concept in mathematics? Does it have any applications?

Eugenia - It’s the study of infinity that lead to the whole field of calculus, and calculus is all about things that continuously change. And it leads to things like differential equations, which are probably the most applied, the most applicable and used parts of mathematics and everything that’s around us. If you point at any object around you, there’s going to be tons of calculus that went into the making of it: from the electricity that was used to make it to the tools that were used to make it to the design, to the way it was shipped around the world - it’s everywhere around us.

Georgia - So infinity is all around us, but it still makes my head spin, and yearn for the simple days, when the highest number conceivable was “seven”.

Music:www.bensound.com

Turns out, our planet earth is a watery place, its in the ground, in our atmosphere and water covers 71 percent of the Earth’s surface. But our water supply never stays still, it’s moving from place to place all the time… and that’s thanks to something called the water cycle. Jonathan Bridge is a physical geographer at Sheffield Hallam University, who explained how it works...

Jonathan - It’s essentially the movement of water from place to place on the Earth’s surface and it’s easy to see that most of the water is in the oceans. The Sun then adds energy to the surface of the ocean and evaporates water, so it’s a sort of purifying process if you like. What’s held in the atmosphere is just the water molecules and those salt molecules or those salt ions are kept within the sea so, gradually, it became saltier over time. Then, when the atmospheric conditions are right, that water vapour then condenses and forms droplets, which fall as rain or snow or other types of precipitation.

Izzie - Something us brits know all too well! This heating and evaporating is all about transferring energy. It’s like when your body becomes too hot, sweat evaporates off of your body and carries the excess heat with it into the air. The same happens with the surface of the Earth. As water evaporates, heat is carried from the Earth’s surface into the atmosphere. Likewise, as rain falls down, heat can be transferred from the atmosphere back to the ground. But how are these all-important clouds formed?

Jonathan - The atmosphere exists at various different temperatures and pressures, and the ability of gas to hold water vapour in its gaseous form depends on the local temperature. As the air containing the water rises, it cools down and the water vapour loses its ability to exist in a gaseous form. So it starts to condense out and turn into tiny droplets of liquid water, so that forms clouds. And then, eventually, those droplets of water grow sufficiently large that they can’t be held up by the air any more and so they fall to Earth under gravity.

Izzie - Essentially, the rain falls to the earth’s surface and one of three things can happen.

Jonathan - If you’ve got a natural landscape with lots of vegetation: trees and plants and so on, then quite a large fraction of that rainfall is caught by the plants, either directly by falling on their leaves and being absorbed or it goes into the soil and then the roots immediately take that water back up. Maybe 40% of the rainfall is immediately recycled via the plants and then ends up being returned to the atmosphere by the process called ‘evapotranspiration,’ that is part evaporation and part transpiration which is the sort of plants’ breathing process if you like to think of it like that.

Izzie - Or option number two…

Jonathan - If it’s not caught by the plants then it can infiltrate into the soil, and into the underground into the subsurface. Some of it will go into the soil and be transferred and it can flow through the soil horizontally. Some of it flows vertically down into the deeper subsurface and eventually forms groundwater which is held in porous rocks, deep underground and that is a long term store. There’s some groundwater aquifers, some reserves of groundwater which is 30,000 years old, which are almost sort of fossils of water which fell a long long time ago. Other aquifers are much more shallow and their recharge rates, or their turnover rates are more rapid.

The final pathways is the most obvious one we think of when it rains, and that’s flowing over the ground’s surface. So overland flow which, eventually, runs into streams and rivers and lakes and forms the water we see on the land’s surface. In natural conditions, that might only be 10% of the total rainfall.

Izzie - And obviously, it’s call the water cycle for a reason. This surface water runs into rivers which combine to make bigger rivers and the bigger rivers run down to the sea, collecting salts and rocks with them as they go. And the process starts all over again.

Every situation across the world is different when it comes to water supply and treatment. There’s a rather lengthy process between turning on our taps and flushing the toilet. Long story short, water is taken from nearby rivers or ground water, thoroughly cleaned and sent to our taps. Once we’re done with it, we send it on down the drain for our waste water to be treated and then it’s released back out to the environment, and the process starts again. Izzie Clarke met with Regan Harris at Anglian Water’s sewage treatment site, to see it for herself. First stop: the gravity sewer, basically, the 18m drop above all of Cambridge city’s waste.

Sounds of rushing water

Izzie - It’s a long way down. Oh… that’s a smell

Regan - Yup, it’s stinky. From here, the sewage is pumped to essentially the first part of the treatment process and that is basically where we start to filter out all the solid stuff, all the rags and unflushable things that people put down the drain. We’re talking about things like wet wipes, sanitary products, cotton buds. They’re things Anglian Water always ask people not to put down the drain but, unfortunately, we still get a fair few of them that we need to take out first before we go on to clean the water any further.

Within our region alone, we’re looking at 800 tons of unflushables per day that we take out of used water. That’s why we're always asking people to only put the three Ps down the loo, so that’s pee, poo, and toilet paper, and it’s basically something that we need to try and avoid if we can.

Izzie - What happens to these unflushables that still make their way into this system?

Regan - Ultimately, they’re screened out here initially and then they do end up in landfill because there’s nothing else we can do with them. They can’t be recycled, they can’t be composted. Essentially, they are collected here, they’re screened off the water and they end up going to landfill which is why, again, it’s really important that people don’t do it.

Izzie - Shall we go and take a look at the next step? It’s like a conveyor belt of basically wipes, nappies, and other things really.

Regan - That’s it, exactly. These are the screens that essentially take out all the solid matter from the used water that comes to us, so it’s a vital part of the process really. This is the initial part of the water recycling process.

Izzie - So that’s the big unflushables out of the way. It was then onto the second part of the screening process, and the water was still looking rather murky at this point.

Regan - The next stage is that we wash all the grit and the little bits and pieces out from the water and they’re collected below us. We get all the runoff from the roads, so you can imagine when water runs off the road, it goes down the drain. All that contains grit and and all sort of other little stones and particles; they all get washed and separated off here. Interestingly, we also get the lovely little bits of sweetcorn and things like that, and also medication and stuff that people have flushed down the loo, so all that kind of bigger granular stuff is collected here.

Izzie - Oh my gosh, there is so much sweetcorn in that skip. I really wasn’t expecting to see that.

Once I’d recovered from the sheer amount of sweetcorn that gets filtered off, we skimmed pasted 5 massive concrete cylinders, otherwise known as primary settlement tanks. Here, the big solids in the water settle to the bottom of the
tank and are sucked away to be used as fertilizer for agriculture, and then we arrived at our fourth destination...

Regan - These are what we call our ‘sludge activation treatment’ part of the process essentially. What they are is four lanes of the used water; each lane holds about 6 million litres. And what we do here is pump in dissolved oxygen to aerate the water. This allows different bacterias to grow which actually eat the sewage and break it down. They’re the same sorts of bacteria that we have inside our own guts, and what we do is provide them with the perfect conditions to grow and multiply to help us break down the sewage. It’s a completely natural process and all we’re doing her is allowing something that’s natural to do its job and help us in the water treatment process.

Izzie - We can see these little whirlpools in front of us. Is that just the oxygen that’s being pumped in to help these little bacteria that live in this water to munch down on whatever is still left floating around?

里根-。我们泵的氧气the water allows the bacteria to flourish; that means they can munch on all the baddies that make sewage a pollutant, things like ammonia and phosphate as well. You can see actually, as the lane gets further and further away from us the water gets stiller, and that’s because as it moves along, the bugs are doing their job and taking out the baddies that we need them to. So by the end, you will see that the water is much cleaner and isn’t that different from what you’d see in your local river or stream.

Izzie - Because in front of us we’ve got a big algae - it’s almost like an algae pond really. Lots of movement and then yeah, you’re absolutely right, as it goes further on there’s not as much action.

Regan - No, exactly. And that’s because we’re nearly at the end of the treatment process now and the water’s nearly ready to go back to the river.

Izzie - We’re now finally at the final stage of our water treatment. Has there been solids in the water up until this very final stage?

Regan - Yes. Solids of varying degrees of sizes. We saw the big solids removed right at the beginning and then gradually, as the process goes on, it gets smaller and smaller and smaller until we’re here at our radial flow tanks, and this is the final stage before the water’s returned to the river. And essentially, what happens here is the water is allowed to settle here and then it overtops this little wier in front of us, and you can see the water’s really really clean at this point and it just traps and remaining solids in the water and they’re taken away and treated at the sludge treatment process.

Izzie - So this is pretty much the cleanest water we will see before it goes into a river really?

Regan - This is it. This is exactly how it goes back to the river, and you’ll find that the water that comes off of this treatment works is as clean, if not a little bit cleaner than what’s in the river already. We have tough environmental standards we have to comply by before we can put water back into the environment, and we’re absolutely committed to doing that and we’re regulated by the Environment Agency on it. Yeah, this is it, this is the final stage.

Izzie - But not drinking water though?

Regan - No. I don’t think you’d want to drink it, just as you wouldn’t want to have a glass of water out of your local river, but it’s definitely clean enough for the ducks and the fishes and any wildlife that’s flourishing in the River Cam nearby.

Izzie - Why is it important to take our sewage and treat it in this way that we’ve explored?

Regan - Well, it’s really important that we’re able to return water to the environment. Our role at Anglian Water is to balance the needs of our customers, so in terms of allowing people and businesses to have the water they need to do day to day washing, using their toilets. All of that stuff as well as supporting local business and the economy, but we can’t do that at the expense of the environment. So what we have to do is treat the water we use to a really high standard and then give it back because there is only a finite amount in the world that we can use.