WEBVTT
Kind: captions
Language: en
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]