Old mines leave behind a a pressing problem: Huge holes that make the landscape look like a chunk of swiss cheese. But in Germany, some scientists and city planners are turning these into lakes. The largest one will be the biggest artificial lake in Germany when it's done, with a shoreline of 26 kilometers or about 16 miles all around. But it's not as easy as simply filling the holes with water. It takes a LOT of research to get this science right. Interested in more environmental stories? Email us at [email protected]. We'd love to hear from you!Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.Learn more about sponsor message choices: podcastchoices.com/adchoicesNPR Privacy Policy
Chapter 1: What is the story behind Cottbus and lignite mining?
Hey, Shortwave. I come to you with a story. All right, let's hear it. So about two hours southeast of Berlin, there's a city called Cottbus. It's pretty small. About 100,000 people live there. For context, this is in eastern Germany, near the Polish border. And so historically, this part of Germany had a lot of lignite mining. This is a fossil fuel that is dark brown. It's soft.
It's kind of like an intermediate between hard coal and petroleum coke.
Oh, interesting. I've never heard of this. Okay, lignite.
Yeah, lignite. Then after the Berlin Wall fell in 1989 and Germany reunified East and West in the early 90s, a lot of mines in the former East shut down, mostly for economic reasons or they ran out of coal. Then there was this pressing problem.
There were a bunch of holes in the ground that used to be mines, but now looked like a landscape of Swiss cheese, which is not awesome aesthetically or safety-wise. And so the city of Cottbus has a really interesting plan. And One sweltering day in September, I went to go see one of these pits, 20 minutes east of the city.
Hello. It's great to have you here.
At the train station, I met up with Stefan Simonidis-Noak.
Here we are.
Stefan has lived in Cottbus for a long time. He works for the city council, and he's an urban planner working here.
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Chapter 2: How is a former mining pit being transformed into a lake?
Chapter 3: Who is leading the efforts to create the Cottbus Lake?
Stefan has lived in Cottbus for a long time. He works for the city council, and he's an urban planner working here.
Welcome to the Cottbus Lake.
Wait, did he just say lake? Uh-huh. Because, Emily, Stefan and his colleagues are turning this giant former mining pit into a huge lake. It'll be the biggest mining pit turned lake in... in all of Germany. It's even in the lake's name, Cottbusser Ostsee. In German, that literally means Cottbus East Lake, okay? But it's also a play on words that means Cottbus Baltic Sea.
And that is like the dream that Stefan and his colleagues are chasing. A mini Baltic Sea right near the city center. Yes.
I'm really a fan of the Baltic Sea and the shorelines and big sandy beaches. And we will have this here. The Kotlos Beach is a really huge one.
Well, today on the show, how? How do you get from a Swiss cheese landscape to the largest artificial lake in Germany?
I'm Emily Kwong. And I'm Willa Rubin. You're listening to Shortwave, the science podcast from NPR.
All right, Willa, so let's pick up where we left off. You get off the train and caught bus to see the lake.
What does it look like? Emily, this lake is huge. That was my first impression. But honestly, what really took me aback were all the birds.
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Chapter 4: What environmental research is involved in creating pit lakes?
Fascinating. Okay, walk me through this transformation process. How do you go about turning a pit mine into a lake?
Okay, so first, when you stop mining, groundwater starts to creep back up to the surface. And what do you mean by groundwater? Yeah, yeah, yeah. So when mines are operating, mines are kept super, super dry, and And all that groundwater, this is water that is normally below the surface of, in this case, lignite.
That groundwater is normally, when mines are operating, getting pumped out into local rivers. And it's being really closely monitored because, you know, no one wants mines to flood, especially when people are working in those mines. Absolutely not. Then when mining stops, that dewatering process also stops.
Then the groundwater is... rebounding, and the former mining hole becomes a lake.
Basically, they switch off some pumps, and then groundwater starts coming back into these pits.
Well, then that's it. Bada bing, bada boom. Isn't that easy? You just, like, stop mining, and it turns into a lake?
Like, kinda, sorta, not really. Oh. You start to get water filling up the pit, which is great, but a couple of problems. The first is that it can take many, many decades for all of the groundwater to come back on its own. That's problem number one. And problem number two is that the groundwater that is lying beneath the lignite, once it reaches the air, it is often incredibly acidic.
Because when that groundwater comes back up to the surface, it often comes into contact with oxidation products of pyrite. This is a shimmery, golden-looking mineral. Sometimes it's called fool's gold. And it can cause a lot of problems.
As long as this mineral is deep underground and has no contact with air and that means oxygen, everything is fine. But once it comes into contact with air, The oxidation is started.
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Chapter 5: How do groundwater dynamics affect the lake transformation?
Chapter 6: What are the future plans for the Cottbus Lake?
But these lakes are a beautiful piece of nature. And that is a very important driving force for me in my work. I want to keep them clean. I want to keep them in an ecologically healthy state so that both nature and we as humans can benefit from them.
He is super passionate about it, and he is one of the people who kind of wrote this playbook about how to turn a mining pit into a lake.
Fascinating. Okay, walk me through this transformation process. How do you go about turning a pit mine into a lake?
Okay, so first, when you stop mining, groundwater starts to creep back up to the surface. And what do you mean by groundwater? Yeah, yeah, yeah. So when mines are operating, mines are kept super, super dry, and And all that groundwater, this is water that is normally below the surface of, in this case, lignite.
That groundwater is normally, when mines are operating, getting pumped out into local rivers. And it's being really closely monitored because, you know, no one wants mines to flood, especially when people are working in those mines. Absolutely not. Then when mining stops, that dewatering process also stops.
Then the groundwater is... rebounding, and the former mining hole becomes a lake.
Basically, they switch off some pumps, and then groundwater starts coming back into these pits.
Well, then that's it. Bada bing, bada boom. Isn't that easy? You just, like, stop mining, and it turns into a lake?
Like, kinda, sorta, not really. Oh. You start to get water filling up the pit, which is great, but a couple of problems. The first is that it can take many, many decades for all of the groundwater to come back on its own. That's problem number one. And problem number two is that the groundwater that is lying beneath the lignite, once it reaches the air, it is often incredibly acidic.
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