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MLA Full: | "We Discovered a New Natural Cycle!" YouTube, uploaded by SciShow, 8 June 2024, www.youtube.com/watch?v=rtAIPn3V23U. |
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So we all know about the carbon cycle, and the water cycle, and maybe even the nitrogen cycle. But new research has figured out there's a salt cycle, too. Problem is, that same research has found that we already broke it. Here's what that means and how we can fix our broken salt cycle!
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Hosted by: Savannah Geary (they/them)
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Support SciShow by becoming a patron on Patreon: https://www.patreon.com/scishow
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Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever: Adam Brainard, Alex Hackman, Ash, Benjamin Carleski, Bryan Cloer, charles george, Chris Mackey, Chris Peters, Christoph Schwanke, Christopher R Boucher, DrakoEsper, Eric Jensen, Friso, Garrett Galloway, Harrison Mills, J. Copen, Jaap Westera, Jason A Saslow, Jeffrey Mckishen, Jeremy Mattern, Kenny Wilson, Kevin Bealer, Kevin Knupp, Lyndsay Brown, Matt Curls, Michelle Dove, Piya Shedden, Rizwan Kassim, Sam Lutfi
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Nature loves to do things in cycles.
You probably learned about some of them in school, like the water cycle, maybe the carbon cycle, and heck, maybe even the nitrogen cycle. What you probably can’t picture as a poster on your classroom wall is the salt cycle.
And that’s because we’ve just discovered it. And we’ve also already broken it. Yay.
In fact, humans are breaking the natural flow of salt by… a lot. And in order for us to understand what we’re breaking before we can fix it, let’s take a look at what the salt cycle even is, and why it matters. [♪ INTRO] First of all, we are not just talking about the salt on your kitchen table. Table salt, AKA sodium chloride, is just one kind of salt out there.
See, in chemistry, salts are combinations of a positive ion and a negative ion that come together to form a neutral compound. So for instance, your positive sodium ion meets a negative chlorine ion, and they pair up and make the salt on your potato chips. But you can also pair up two sodium ions with one sulfate ion, since that’s got a charge of minus two.
Or maybe that chlorine is more interested in doubling up and pairing with a magnesium ion. Point is, as long as the charges balance out, there are a bunch of different ways to group up some ions to form a salt. But when we’re talking about the salt cycle, the main players we’re interested in are sodium, potassium, calcium, magnesium, chloride, bicarbonate, and sulfate.
That being said, those ions won’t stick together forever. Throw them into some water and the polar water molecules pull the ions apart again, at least until they dry out and get stuck back together. So it makes sense that salt can go through natural cycles, if you think about it.
Salt can erode out of rocks, dissolve in water, and get washed out to sea. And once it’s there, it doesn’t have to stay there; salt can be blown back to land by the wind or deposited on the seafloor where it can eventually be lifted back up and out. There’s a bit more to it than that, but the general idea is that salt is pretty much always on the move.
Which actually makes it surprising that scientists didn’t think of it that way, at least not until pretty recently. Apparently the people who study salt levels in the soil and the people who study salt levels in freshwater don’t, like, talk to each other. And if you look at everything in isolation like that, you can miss big trends in how things are moving from place to place, and how that might be changing.
So in a 2023 paper, researchers connected those dots and made the case that the salt cycle belongs with the water cycle and all the other cycles we think about for how stuff moves around the planet. They also determined that like so many cycles before it, humans have screwed it up. We’re basically moving salts all around the cycle faster and at higher quantities than the natural processes can cope with, and the amount of stuff we actually use salts for is kinda staggering.
Consider mining – not just rock salt, but also stuff like potash that gets used for fertilizer, and materials for cement and concrete. And when we mine them out of environments, they’re… not there any more to erode out over time and slowly wash downstream. And then when that cement and concrete weathers, it erodes all those salts into the water and soil, but much faster than would have happened naturally.
Same with the fertilizer that we chuck into fields and then runs off into the environment. Salts are even used in cleaning supplies, like detergents, and they enter the environment via wastewater. Another big one is road salt.
We’re mining out rock salt, scattering it all over our roads, and never really cleaning it all up. Here in the US, it doesn’t seem like anyone bothers to limit how much road salt you use. At best they make polite suggestions.
That road salt can either get washed away by melting snow and ice, or just kind of sit there where it is and slowly soaks down into the soil. All of this essentially takes that weathering process and puts it on ultra fast-forward. So maybe you’re thinking, but Earth is surely very big.
And we humans are very small. Can we really be disrupting the salt cycle so much? Yes.
Yes we can. Estimates suggest that in the United States, just shy of 200 megatonnes of salt are washed into rivers and streams every year from natural, non-human related sources. But just road deicing alone produces 37.8 megatonnes of salt runoff.
Add in other sources like agriculture and you end up with 80-ish megatonnes of anthropogenic salts entering the freshwater system, so 40% of what Mother Nature was doing on her own. Asking the natural salt cycle to deal with that much salt is asking a lot. It’s not like we can just stop doing some of these things.
Food needs fertilizer, and I dare you to get anywhere here in Missoula in January without road salt. And before all you locals say that they don’t salt the road in Missoula. Yes, we do.
That is a myth. But it is worth understanding their impacts, including on ourselves. Salts blown by the wind can wreck soil fertility.
And since the wind can carry things a long way, the effects aren’t localized to whoever’s fault it was to start with. For example, a lake in Kazakhstan called the Aral Sea started drying up in the 1960’s, and by now it’s almost completely gone. Now, winds carry salt from the dried-up lake bed up to 500 kilometers away into neighboring Uzbekistan and Turkmenistan.
That has negative consequences for crops, wildlife, and human health all along the way. Or consider the effect on freshwater lakes, where a spike in chloride – especially from road salt – can signal a die-off of zooplankton and a corresponding algal bloom. That has negative consequences for commercial fishing, as well as the overall health of the lake’s ecosystem.
In 2022, researchers warned that current limits on chloride across North America and Europe aren’t strict enough to prevent this from happening. And we humans are not immune to the consequences of our actions. For instance, a lot of that salt ends up in our drinking water, and we can’t always filter all of it out.
And when we’re talking about sodium in particular, that can lead to high blood pressure, especially in pregnant folks. Saltier groundwater can even encourage radioactive elements to leach into the aquifers where we get our water… and I don’t think I have to explain to you why you don’t want radium in your drinking water. So, what can we do?
Well, it’s pretty early days for this research, like, it’s literally the same group of researchers in the same paper saying “There is a salt cycle!” and also “we broke it.” According to those researchers, we need a clearer understanding of human effects on salt transport so we can figure out what effective limits would be for curbing our salt use. It’s also vitally important to understand just how much salt we’re pumping into fresh water, because we… need that stuff. And we need more information on, and experts from, the global south to make sure we go about making change in an equitable way.
But I think it’s sort of cool that we’re still discovering big, planet-wide phenomena like this. I mean, there’s a whole global salt cycle and we just noticed? What else do we just not know about yet?
Hopefully, next time we discover a whole system about how our world works, we do so before we break the whole thing, and not after. [♪ OUTRO]
You probably learned about some of them in school, like the water cycle, maybe the carbon cycle, and heck, maybe even the nitrogen cycle. What you probably can’t picture as a poster on your classroom wall is the salt cycle.
And that’s because we’ve just discovered it. And we’ve also already broken it. Yay.
In fact, humans are breaking the natural flow of salt by… a lot. And in order for us to understand what we’re breaking before we can fix it, let’s take a look at what the salt cycle even is, and why it matters. [♪ INTRO] First of all, we are not just talking about the salt on your kitchen table. Table salt, AKA sodium chloride, is just one kind of salt out there.
See, in chemistry, salts are combinations of a positive ion and a negative ion that come together to form a neutral compound. So for instance, your positive sodium ion meets a negative chlorine ion, and they pair up and make the salt on your potato chips. But you can also pair up two sodium ions with one sulfate ion, since that’s got a charge of minus two.
Or maybe that chlorine is more interested in doubling up and pairing with a magnesium ion. Point is, as long as the charges balance out, there are a bunch of different ways to group up some ions to form a salt. But when we’re talking about the salt cycle, the main players we’re interested in are sodium, potassium, calcium, magnesium, chloride, bicarbonate, and sulfate.
That being said, those ions won’t stick together forever. Throw them into some water and the polar water molecules pull the ions apart again, at least until they dry out and get stuck back together. So it makes sense that salt can go through natural cycles, if you think about it.
Salt can erode out of rocks, dissolve in water, and get washed out to sea. And once it’s there, it doesn’t have to stay there; salt can be blown back to land by the wind or deposited on the seafloor where it can eventually be lifted back up and out. There’s a bit more to it than that, but the general idea is that salt is pretty much always on the move.
Which actually makes it surprising that scientists didn’t think of it that way, at least not until pretty recently. Apparently the people who study salt levels in the soil and the people who study salt levels in freshwater don’t, like, talk to each other. And if you look at everything in isolation like that, you can miss big trends in how things are moving from place to place, and how that might be changing.
So in a 2023 paper, researchers connected those dots and made the case that the salt cycle belongs with the water cycle and all the other cycles we think about for how stuff moves around the planet. They also determined that like so many cycles before it, humans have screwed it up. We’re basically moving salts all around the cycle faster and at higher quantities than the natural processes can cope with, and the amount of stuff we actually use salts for is kinda staggering.
Consider mining – not just rock salt, but also stuff like potash that gets used for fertilizer, and materials for cement and concrete. And when we mine them out of environments, they’re… not there any more to erode out over time and slowly wash downstream. And then when that cement and concrete weathers, it erodes all those salts into the water and soil, but much faster than would have happened naturally.
Same with the fertilizer that we chuck into fields and then runs off into the environment. Salts are even used in cleaning supplies, like detergents, and they enter the environment via wastewater. Another big one is road salt.
We’re mining out rock salt, scattering it all over our roads, and never really cleaning it all up. Here in the US, it doesn’t seem like anyone bothers to limit how much road salt you use. At best they make polite suggestions.
That road salt can either get washed away by melting snow and ice, or just kind of sit there where it is and slowly soaks down into the soil. All of this essentially takes that weathering process and puts it on ultra fast-forward. So maybe you’re thinking, but Earth is surely very big.
And we humans are very small. Can we really be disrupting the salt cycle so much? Yes.
Yes we can. Estimates suggest that in the United States, just shy of 200 megatonnes of salt are washed into rivers and streams every year from natural, non-human related sources. But just road deicing alone produces 37.8 megatonnes of salt runoff.
Add in other sources like agriculture and you end up with 80-ish megatonnes of anthropogenic salts entering the freshwater system, so 40% of what Mother Nature was doing on her own. Asking the natural salt cycle to deal with that much salt is asking a lot. It’s not like we can just stop doing some of these things.
Food needs fertilizer, and I dare you to get anywhere here in Missoula in January without road salt. And before all you locals say that they don’t salt the road in Missoula. Yes, we do.
That is a myth. But it is worth understanding their impacts, including on ourselves. Salts blown by the wind can wreck soil fertility.
And since the wind can carry things a long way, the effects aren’t localized to whoever’s fault it was to start with. For example, a lake in Kazakhstan called the Aral Sea started drying up in the 1960’s, and by now it’s almost completely gone. Now, winds carry salt from the dried-up lake bed up to 500 kilometers away into neighboring Uzbekistan and Turkmenistan.
That has negative consequences for crops, wildlife, and human health all along the way. Or consider the effect on freshwater lakes, where a spike in chloride – especially from road salt – can signal a die-off of zooplankton and a corresponding algal bloom. That has negative consequences for commercial fishing, as well as the overall health of the lake’s ecosystem.
In 2022, researchers warned that current limits on chloride across North America and Europe aren’t strict enough to prevent this from happening. And we humans are not immune to the consequences of our actions. For instance, a lot of that salt ends up in our drinking water, and we can’t always filter all of it out.
And when we’re talking about sodium in particular, that can lead to high blood pressure, especially in pregnant folks. Saltier groundwater can even encourage radioactive elements to leach into the aquifers where we get our water… and I don’t think I have to explain to you why you don’t want radium in your drinking water. So, what can we do?
Well, it’s pretty early days for this research, like, it’s literally the same group of researchers in the same paper saying “There is a salt cycle!” and also “we broke it.” According to those researchers, we need a clearer understanding of human effects on salt transport so we can figure out what effective limits would be for curbing our salt use. It’s also vitally important to understand just how much salt we’re pumping into fresh water, because we… need that stuff. And we need more information on, and experts from, the global south to make sure we go about making change in an equitable way.
But I think it’s sort of cool that we’re still discovering big, planet-wide phenomena like this. I mean, there’s a whole global salt cycle and we just noticed? What else do we just not know about yet?
Hopefully, next time we discover a whole system about how our world works, we do so before we break the whole thing, and not after. [♪ OUTRO]