TRASCRIZIONE 🔗
WEBVTT
00:00.000 --> 00:13.440
In my research travels, I've spent time in Alaska and witnessed the beauty of the land
00:13.440 --> 00:14.440
there.
00:14.440 --> 00:19.880
The mountains rise above the ground, forest and grasslands stretched to the skyline and
00:19.880 --> 00:22.560
rivers cut through the landscape.
00:22.560 --> 00:28.200
But what would you think if you were hiking there and came across a river that was orange
00:28.200 --> 00:33.620
with rocks along the bottom coated with something that looked like rust?
00:33.620 --> 00:38.400
Your first thought might be that there's a mine upstream, or maybe an industrial spill.
00:38.400 --> 00:44.440
But what you're witnessing isn't man-made pollution, instead it's coming from the ground
00:44.440 --> 00:45.440
itself.
00:45.440 --> 00:50.160
Today, we're going to talk about how climate change can alter something most of us would
00:50.160 --> 00:54.560
never think about, the chemistry of a river.
00:54.560 --> 01:06.200
Welcome back to the podcast, I'm Dr. Mac, and this is the Climate Translation.
01:06.200 --> 01:09.800
So what exactly is turning these rivers orange?
01:09.800 --> 01:15.040
The short answer is iron, or more specifically, the formation of rust.
01:15.040 --> 01:19.960
To understand how it gets into the water, we need to go underground.
01:19.960 --> 01:25.720
As much of Arctic Alaska, the ground remains frozen year after year.
01:25.720 --> 01:27.760
We call it permafrost.
01:27.760 --> 01:33.440
We've talked about it on the podcast before, particularly because frozen ground can store
01:33.440 --> 01:36.320
enormous amounts of carbon.
01:36.320 --> 01:41.280
But permafrost freezes more than soil and organic material.
01:41.280 --> 01:45.800
It also affects how water moves underground.
01:45.800 --> 01:50.640
Imagine a layer of permanently frozen ground beneath the surface.
01:50.640 --> 01:56.160
Rain and melting snow can soak into the upper soil during the summer, but that frozen
01:56.160 --> 01:58.840
layer acts like a barrier.
01:58.840 --> 02:02.880
Water can't easily travel deeper into the ground.
02:02.880 --> 02:06.520
But as the Arctic warms, that changes.
02:06.520 --> 02:12.560
The layer that thaws each summer can become deeper, in some places sections of the ground
02:12.560 --> 02:16.640
that were once frozen year round, remain thawed.
02:16.640 --> 02:23.280
Suddenly, water can reach rocks and minerals that it rarely interacted with before.
02:23.280 --> 02:27.280
And some of those rocks contain a mineral called pyrite.
02:27.280 --> 02:32.320
You may know pyrite by another name, Fools Gold.
02:32.320 --> 02:35.160
Pyrite contains iron and sulfur.
02:35.160 --> 02:41.320
And when it remains buried and isolated from water and oxygen, not much happens.
02:41.320 --> 02:45.440
But exposed it to both, and chemistry takes over.
02:45.440 --> 02:50.280
The pyrite begins to break down, and iron is released.
02:50.280 --> 02:56.240
Sulfur reacts with the water and
Load full transcript
oxygen to produce sulfuric acid, and that acidic water
02:56.240 --> 03:01.280
can dissolve additional metals from the surrounding rock.
03:01.280 --> 03:05.640
Scientists call this process acid rock drainage.
03:05.640 --> 03:09.480
If that sounds like a familiar process, there's a reason.
03:09.480 --> 03:16.200
The same basic chemistry can occur around mines when digging exposes sulfide-rich rock
03:16.200 --> 03:18.360
to air and water.
03:18.360 --> 03:24.000
But in these remote, Alaskan watersheds, nobody's digging mines.
03:24.000 --> 03:28.240
Thawing permafrost is providing the access.
03:28.240 --> 03:34.520
Groundwater moves through the newly thawed rock, picking up iron and sulfate and acid and
03:34.520 --> 03:40.840
other dissolved metals, and eventually emerges from the hillsides in small springs and
03:40.840 --> 03:42.320
seaps.
03:42.320 --> 03:48.840
That water then flows into nearby streams, and once the dissolved iron reaches the oxygen-rich
03:48.840 --> 03:52.680
water at the surface, it reacts again.
03:52.680 --> 03:54.840
The iron oxidizes.
03:54.840 --> 03:57.480
In other words, it rusts.
03:57.480 --> 04:03.040
Tiny iron-rich particles form in the water and then settle into the streambed, coating
04:03.040 --> 04:09.800
rocks with orange material, scientists are seeing across, for instance, the Brooks Range.
04:09.800 --> 04:15.160
It's very similar to what happens when you leave a piece of iron outside in the rain.
04:15.160 --> 04:18.000
The only difference here is the scale.
04:18.000 --> 04:22.920
Instead of rust forming on a nail or an old piece of metal, the chemical reaction is
04:22.920 --> 04:26.840
occurring across an entire watershed.
04:26.840 --> 04:30.800
And that orange color is really only the part that we can see.
04:30.800 --> 04:36.960
The same process can release metals such as zinc and nickel, copper, aluminum, manganese
04:36.960 --> 04:39.040
and cadmium.
04:39.040 --> 04:44.880
Some of these can become a bigger problem for aquatic life than the iron itself.
04:44.880 --> 04:50.160
So when scientists see a river turn orange, they're not just simply looking at a strange
04:50.160 --> 04:51.720
change in color.
04:51.720 --> 04:56.920
They're seeing evidence that the chemistry beneath the landscape has changed.
04:56.920 --> 05:01.800
And new research is showing that once those chemicals enter a river, they may travel
05:01.800 --> 05:07.640
much farther downstream than anyone initially expected.
05:07.640 --> 05:13.000
At first glance, this might seem like a very local problem, a small spring emerges from
05:13.000 --> 05:19.680
thawing ground, the water picks up iron in other metals, and a nearby creek turns orange.
05:19.680 --> 05:24.240
But then perhaps a few miles downstream, everything returns to normal.
05:24.240 --> 05:29.560
But new research suggests that the chemistry travels much farther than that.
05:29.560 --> 05:37.200
In September of 2026, a team led by Taylor Evinger and Jonathan O'Donnell with the US Geological
05:37.200 --> 05:44.920
Survey and several partner institutions published a study in the AGU Advances Journal examining
05:44.920 --> 05:49.960
six watersheds across Alaska's Brooks Range.
05:49.960 --> 05:55.760
The researchers collected water samples from places where acidic groundwater entered streams
05:55.760 --> 06:01.440
from affected tributaries and from larger rivers farther downstream.
06:01.440 --> 06:04.520
And the differences were striking.
06:04.520 --> 06:10.680
Some of the small seeps coming directly out of the ground were extremely acidic.
06:10.680 --> 06:17.800
They also contained much higher concentrations of sulfate and metals such as iron, aluminum,
06:17.800 --> 06:24.120
manganese, zinc, nickel, and cadmium than the nearby unaffected water.
06:24.120 --> 06:27.920
But then those streams flowed into larger rivers.
06:27.920 --> 06:32.880
He might expect some of the chemistry to be diluted and disappear, and some of it did,
06:32.880 --> 06:34.600
but not all of it.
06:34.600 --> 06:40.120
In the Salmon River watershed, researchers could still detect elevated levels of several
06:40.120 --> 06:48.240
metals more than 100 kilometers or 60 miles downstream from where the acidic water first
06:48.240 --> 06:50.320
entered the river system.
06:50.320 --> 06:57.920
In some cases, concentrations remained as much as 70 times higher than they had been upstream
06:57.920 --> 07:00.240
of the affected area.
07:00.240 --> 07:04.840
And that's important because the river did not necessarily look dramatically polluted
07:04.840 --> 07:07.200
that far downstream.
07:07.200 --> 07:13.160
The bright orange iron that we can see with our eyes is only one part of the story.
07:13.160 --> 07:18.600
Some metals remained dissolved in the water, others attach themselves to tiny particles
07:18.600 --> 07:24.040
and sediment, and both can continue moving down with the river.
07:24.040 --> 07:26.520
There was another interesting finding.
07:26.520 --> 07:32.200
Even though some of the small tributaries and seeps were extremely acidic, the larger
07:32.200 --> 07:37.000
rivers often did not become strongly acidic themselves.
07:37.000 --> 07:39.840
And the reason is because of buffering.
07:39.840 --> 07:45.840
Think about adding lemon juice to a large glass of water, and then also doing it to a teaspoon
07:45.840 --> 07:47.240
of water.
07:47.240 --> 07:53.600
The larger volume can absorb more of the acid without changing it dramatically.
07:53.600 --> 07:56.880
Rivers can do something similar, chemically.
07:56.880 --> 08:02.560
Certain minerals dissolved in water can neutralize some of the incoming acid, so the main river
08:02.560 --> 08:10.200
may maintain a fairly normal pH, even while carrying much higher concentrations of sulfate
08:10.200 --> 08:12.000
and metals.
08:12.000 --> 08:17.160
That means simply measuring acidity won't tell you the whole story.
08:17.160 --> 08:23.640
The researchers also found
evidence that some of the changes happened remarkably quickly.
08:23.640 --> 08:30.200
Water quality records from two watersheds showed major jumps in sulfate and zinc beginning
08:30.200 --> 08:33.440
around 2019 and 2020.
08:33.440 --> 08:39.120
Those changes followed an unusually warm and then snowy winter.
08:39.120 --> 08:43.920
And once the chemistry shifted, it persisted for several years.
08:43.920 --> 08:50.480
So what looked like a slow process with permafrost gradually thawing over decades could produce
08:50.480 --> 08:53.960
a much more sudden change in a river.
08:53.960 --> 08:59.240
One year the water chemistry may look relatively normal, and then a few years later an entire
08:59.240 --> 09:05.960
stretch of the watershed may be carrying metals that were previously locked underground.
09:05.960 --> 09:11.560
And once those metals begin moving downstream, the next question becomes unavoidable.
09:11.560 --> 09:15.960
What happens to the organisms that live in the water?
09:15.960 --> 09:21.640
Once the chemistry of a river changes, the organisms living in it have to respond.
09:21.640 --> 09:28.240
And in Arctic Alaska, one of the fish scientists are closely watching is the Dolly Varden.
09:28.240 --> 09:33.600
Dolly Varden are members of the salmon family, and like salmon they spend most of their
09:33.600 --> 09:39.680
lives in the ocean and then return to fresh water streams to spawn.
09:39.680 --> 09:45.240
That makes clean, cold river habitats extremely important.
09:45.240 --> 09:51.160
But rusting rivers can change that habitat in several ways at once.
09:51.160 --> 09:54.400
The most obvious problem is the metals.
09:54.400 --> 10:00.680
Some metals, including zinc, copper, aluminum, and cadmium, can become toxic to fish when
10:00.680 --> 10:03.480
concentrations become high enough.
10:03.480 --> 10:06.680
And acidity can make the problem worse.
10:06.680 --> 10:14.000
As water becomes more acidic, some metals become easier for aquatic organisms to absorb.
10:14.000 --> 10:16.960
But toxicity is only part of the story.
10:16.960 --> 10:19.800
Remember the orange coating we talked about earlier?
10:19.800 --> 10:23.360
That iron can settle into the stream bed.
10:23.360 --> 10:27.760
And for fish trying to reproduce, the stream bed is important.
10:27.760 --> 10:31.680
Dolly Varden lay their eggs in gravel.
10:31.680 --> 10:37.280
Water normally moves through the spaces between those rocks carrying oxygen to the developing
10:37.280 --> 10:38.760
eggs.
10:38.760 --> 10:45.040
But if iron-rich material begins coating and clogging those spaces, water can't circulate
10:45.040 --> 10:50.560
as easily, and that could reduce the oxygen reaching the eggs.
10:50.560 --> 10:56.280
The chemistry can also affect the smaller organisms living on the bottom of the river.
10:56.280 --> 11:02.280
Aquatic insects and other tiny animals make up an important part of the food web for
11:02.280 --> 11:03.760
fish.
11:03.760 --> 11:10.440
The
United States Geological Survey researchers have already found that orange streams tend
11:10.440 --> 11:17.400
to have a poorer habitat for these bottom dwelling organisms than nearby clear streams.
11:17.400 --> 11:21.000
So a river can change in several ways at once.
11:21.000 --> 11:22.960
The water chemistry can change.
11:22.960 --> 11:25.000
The stream bed can change.
11:25.000 --> 11:27.240
The food supply can change.
11:27.240 --> 11:34.240
And many fish avoid sections of water altogether if the conditions become stressful enough.
11:34.240 --> 11:40.480
In September of 2026, researchers published a study specifically looking at how much
11:40.480 --> 11:46.720
known Dolly Varden spawning habitat overlaps with these rusting rivers.
11:46.720 --> 11:52.560
They used decades of satellite imagery to track where streams had changed color, and then
11:52.560 --> 11:59.320
compare those locations with mapped spawning areas across Northwest Alaska.
11:59.320 --> 12:02.160
And the results were highly variable.
12:02.160 --> 12:05.200
Some rivers showed little or no overlap.
12:05.200 --> 12:07.480
Others showed much more.
12:07.480 --> 12:13.040
Across the entire region, the percentage of known spawning habitat affected in any given
12:13.040 --> 12:17.000
year ranged from 0 to 21%.
12:17.000 --> 12:22.400
In individual watersheds, the overlap was sometimes much greater.
12:22.400 --> 12:28.080
In the Wulik River, more than half of the mapped spawning habitats were affected
12:28.080 --> 12:29.680
during one year.
12:29.680 --> 12:34.860
In smaller streams, researchers found years when all of the mapped spawning habitat
12:34.860 --> 12:37.360
overlap with the degraded water.
12:37.360 --> 12:41.280
Now, it doesn't mean that all of the fish disappeared.
12:41.280 --> 12:44.400
And the researchers were careful to make that claim.
12:44.400 --> 12:50.120
The study measured the overlap between the degraded water and the spawning habitat.
12:50.120 --> 12:56.600
It did not measure how many fish survived or how many eggs successfully hatched.
12:56.600 --> 13:00.440
But it tells scientists where the risk may be the greatest.
13:00.440 --> 13:05.240
And that's important because these rivers are not just ecosystems.
13:05.240 --> 13:11.480
They also support fish that are important to local communities for substance and recreation.
13:11.480 --> 13:16.440
So the orange color may be the first thing people notice, but the deeper concern is what
13:16.440 --> 13:18.840
the color represents.
13:18.840 --> 13:24.400
The chemical change beginning underground can move into a stream, travel downstream, and
13:24.400 --> 13:30.320
settle onto the riverbed, and eventually reach organisms that depend on the river to
13:30.320 --> 13:32.720
reproduce.
13:32.720 --> 13:38.960
So if thawing permafrost due to climate change is helping to drive this process, does that
13:38.960 --> 13:43.120
mean every arctic river is going to turn orange?
13:43.120 --> 13:48.520
The short answer is no, geology is just as important as the climate.
13:48.520 --> 13:53.200
Warming can thaw the ground, it can deepen the layer that melts each summer, and it can
13:53.280 --> 13:56.480
open up new pathways for groundwater.
13:56.480 --> 14:01.000
But none of that automatically produces acid or releases metals.
14:01.000 --> 14:06.240
For that to happen, the right minerals have to be there in the first place.
14:06.240 --> 14:11.120
Think back to the pyrite we talked about earlier, if groundwater begins reaching rock that
14:11.120 --> 14:18.520
contains a lot of sulfide minerals, then oxygen and water can trigger those chemical reactions.
14:18.520 --> 14:23.640
Sulfuric acid can form, and iron and other metals can be released.
14:23.640 --> 14:28.880
But if the underlying geology is different, thawing permafrost may produce a completely
14:28.880 --> 14:32.520
different chemical response, or none at all.
14:32.520 --> 14:39.200
So climate change is not simply turning arctic rivers orange, it's changing the access.
14:39.200 --> 14:44.480
It's allowing water and oxygen to reach parts of the ground that were previously off
14:44.480 --> 14:48.000
limits, frozen off from the surface.
14:48.000 --> 14:51.360
What happens next depends on what is buried there.
14:51.360 --> 14:53.880
The landscape matters.
14:53.880 --> 14:58.040
Sometimes watersheds contain minerals that can neutralize the acid.
14:58.040 --> 14:59.360
Others don't.
14:59.360 --> 15:04.200
Some have large rivers that are capable of diluting incoming water.
15:04.200 --> 15:10.080
Others are just made up of small streams, where even one acidic seap can have a large
15:10.080 --> 15:11.560
effect.
15:11.560 --> 15:17.280
And groundwater doesn't move the same everywhere, it follows cracks and slopes and soil
15:17.280 --> 15:20.240
layers and underground channels.
15:20.240 --> 15:28.280
That means two neighboring valleys experiencing similar warming can respond very differently.
15:28.280 --> 15:32.960
Rivers and one may appear clear, while in the other they may begin changing color in
15:32.960 --> 15:35.040
just a few years.
15:35.040 --> 15:41.520
That's one reason scientists are trying to map where these vulnerable areas are located.
15:41.520 --> 15:46.520
Satellites can help identify streams that have changed from clear to orange.
15:46.520 --> 15:50.600
Aircraft and drones can survey remote watersheds.
15:50.600 --> 15:57.160
Scientists on the ground can collect water samples to measure the acidity, the sulfate concentration,
15:57.160 --> 16:00.040
the iron and other trace metals.
16:00.040 --> 16:06.640
And long-term monitoring stations can show when a river's chemistry begins shifting.
16:06.640 --> 16:09.840
Researchers are also looking beyond Alaska.
16:09.840 --> 16:15.840
Permafrost exists in enormous areas of Canada, Greenland and Siberia.
16:15.840 --> 16:20.800
And many of those landscapes contain similar mineral deposits.
16:20.800 --> 16:25.760
So one of the questions scientists are asking is whether the rusting rivers of Alaska are
16:25.760 --> 16:31.640
just a local oddity, or an early example of something we may begin seeing elsewhere
16:31.640 --> 16:33.640
across the Arctic.
16:33.640 --> 16:38.760
We don't know the answer yet, but the rapid change is already documented in parts of
16:38.760 --> 16:44.920
the Brooks Range, show just how quickly a watershed can respond if the right conditions
16:44.920 --> 16:46.480
line up.
16:46.480 --> 16:50.320
That might be the most surprising part of this story.
16:50.320 --> 16:55.320
Climate change is often described in terms of temperature, a warmer atmosphere, a warmer
16:55.320 --> 16:57.720
ocean and melting ice.
16:57.720 --> 17:01.840
But warming changes where water flows underground.
17:01.840 --> 17:08.360
It can expose minerals that were previously sealed away, in some cases, for millennia.
17:08.360 --> 17:12.280
And they can trigger chemical reactions that were largely dormant.
17:12.280 --> 17:18.000
And those reactions can then move from rock to groundwater to rivers and eventually to
17:18.000 --> 17:21.040
entire ecosystems.
17:21.040 --> 17:25.600
Climate change didn't create the iron, it didn't create the pyrite.
17:25.600 --> 17:27.280
That was already there.
17:27.280 --> 17:30.120
What it changed was the access.
17:30.120 --> 17:35.040
And sometimes unlocking something that's been frozen for thousands or even millions of
17:35.040 --> 17:49.120
years can completely change the river that's flowing above it.
17:49.120 --> 17:55.000
A river turning orange may look like a pollution story, but in Arctic Alaska, the source can
17:55.000 --> 17:58.080
begin at far beneath the surface.
17:58.080 --> 18:03.760
Thawing ground opens new pathways for water, water reaches minerals that were once frozen
18:03.760 --> 18:06.840
away and chemistry takes over.
18:06.840 --> 18:13.800
The effects can travel from rock to groundwater to rivers and eventually an entire ecosystem.
18:13.800 --> 18:17.840
While climate change does not create those minerals, it is changing the conditions that
18:17.840 --> 18:24.840
allow them to react and providing yet another example of just how complex the world is
18:24.840 --> 18:26.840
that we live on.
18:26.840 --> 18:30.720
I'm Dr. Mac and this has been The Climate Translation.
18:30.720 --> 18:34.960
If you have a question about the climate you've been too afraid to ask or if you have
18:34.960 --> 18:38.000
a differing opinion, I want to hear from you.
18:38.000 --> 18:41.480
I can use your viewpoints in future episodes.
18:41.480 --> 18:46.240
You can reach me at theclimatetranslation at gmail.com.
18:46.240 --> 18:47.080
I'll see you next time.