A walk through
stories of change
As the seasons change,
our environments do too.
Learn about how seasonal changes
impact different elements:
atmosphere, temperature, precipitation, snow, permafrost, lakes, growing season, and the tree line.
Browning of lakes
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Immersion
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Discovery dive
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Local evidence
Wow, those peaks are so high!
Mountains surround you, and there are no trees up here to protect you from the strong winds.
It looks like the Arctic. Let’s wander a bit further.
Taiga : Northern regions that are covered with coniferous trees, and experience lots of rain and snow
Tundra : Earth’s northernmost biological region, where the land is frozen and trees can’t grow
Hiking down was a good idea. You can see more clearly now—is that a lake you spot from afar?
Let’s hurry, it’s starting to rain heavily.
It’s much warmer here than it was up in the mountains.
(+1°c = +7% more moisture in the atmosphere. The hotter it gets, the more precipitation the environment will experience, including snow, hail, and rain.)
The ground doesn’t seem very stable here, but it looks rich in nutrients! Browning and greening are happening at the same time… How mysterious.
As the permafrost thaws, plants can grow deeper roots, so the tree line moves north: into the tundra. That’s called “Arctic greening.” But the increasing shrubbery and rising tree line are collapsing at the same time. This is due to the instability of the newly unfrozen soil, and the effect is known as “browning.”
You’ve made it to the lake. Let’s go swimming!
But the water is strangely dark and looks more brown than blue… You can’t see what’s beneath the surface. Are you sure you want to venture in?
Sunlight is necessary even to underwater life, but the light rays keep getting blocked by leaves, sticks, and other products of runoff.
You decided to face your fears and jump in!
Welcome to the lake. The water features lots of big algae and plants thanks to the penetrating light, and the fish seem happy here.
The deep wedge in the rocky ground is called permafrost: soil that has been frozen for a long time. Due to multiple factors, some of which you witnessed on your way down—like warmer temperatures, and increased precipitation—permafrost is thawing. When permafrost thaws, the ground becomes unstable and vegetation can collapse. This results in streams of carbon-rich water filled with debris like branches, leaves, and soil, flowing into the lake, while the wind carries other natural debris into the water. Now the water has begun browning, too!
- Let’s dive in, and explore the carbon cycle!
- It has multiple steps that I repeat over and over
- Sedimentation : As I sink into the water, I bring outside carbon with me—like little leaves and sticks that were stuck to my body before I jumped in!
- Burial : I take a little break at the bottom, enjoying the view.
-Decomposition: Then I go back up for air, but usually leave some carbon behind. So I gather some more, and I’m ready for another jump!
The high-latitude lake water is far from empty—it’s home to lots of living organisms. Some are invisible to our eyes, like tiny fish (zooplankton), small algae (phytoplankton), or little remains of birch trees (organic carbon). Some are easily visible, like the larger fish: click on them to learn who they are!
They all coexist in the food web. In browning lakes, populations of organisms that need sunlight to survive, like algae and aquatic plants, are dwindling. This makes it hard for fish to eat, and hide from predators. Like humans, fish can only thrive under certain conditions. (For example, they need sufficient oxygen, safe temperatures, and abundant food.) But just like us, fish have unique tastes and sensibilities. The lake has recently become home to fish species that enjoy nutrient-rich environments, and recently moved in from elsewhere. (Maybe they migrated toward this newly carbon-heavy body of water on their own, or perhaps they were released into the water by humans, for fishing purposes.) Other fish are threatened by their new world—all of a sudden, the lake too warm for them and their eggs to survive, and they struggle to find food in the dark. They might start dying off, or migrating elsewhere, as a result.
Look at which fish live in which conditions. Hot and cold water contain different oxygen levels, and therefore, different types of fish. Fish usually prefer the warmest and most oxygenated layer of water. As the lake gets browner, this phenomenon will increase, and fish habitats will continue to shrink. Old species will disappear (for example, arctic char), and only the newer, or better-adapted species will survive (like pike or perch).
A column of lake water has a top part, or “pelagic zone,” where most of the food web lives, and a bottom, or “benthic” layer, which contains the most waste; mostly dead algae and plants.
- Fish are the lake residents with which we humans are most familiar
- Be it swimming for fun, or fishing to feast, we encounter them a lot.
- But as lake water gets browner and warmer, lakes’ ice cover changes.
- So our winter activities like skating or skiing are impacted, too !
Have you heard of lapplandsmästerskapet? It’s an ice fishing competition here on Torneträsk that brings together people from all over Scandinavia, each aiming to catch the biggest fish. It used to be held each May, but due to the changing ice cover of the lake, it must now take place in April: lakes are clearly changing.
arctic char (salvelinus alpinus): loves the cold winter, but struggles in the heat
average size / 30 - 50 cm
pike (esox lucius): enjoys a warm bath—even big predators like luxury
average size / 40 - 60 cm
perch (perca fluviatilis): is able to find food in the dark!
average size / 10 - 25 cm
brown trout (salmo trutta): has trouble seeing where it’s going, making it easy prey
average size / 30 - 50 cm
arctic salmon (salmo salar): can live in the salty ocean, fresh rivers, and fresh lakes, but brown water? No thanks!
average size / 70 - 100 cm
barbel (barbus barbus): is a culinary archaeologist; will always dig for food!
average size / 40 - 60 cm
minnow (phoxinus phoxinus): has a tiny body but a big appetite, adapting its prey as needed
average size / 4 - 8 cm
grayling (Thymallus thumallus): is social among fellow grayling, but is not a team player when it comes to other species
average size / 30 - 50 cm
During winter, food is rarer and the lake temperature is generally quite low—but it’s a bit warmer at the bottom, so fish tend to move low and slow. During summer, the food is back and the temperatures are warmer at the top, so fish move up and get around.
Sweden’s surface is 9% lake, which shows how important lakes are to the country’s environment.
The Arctic, known for its negative temperatures most of the year, hosts quite a few of Sweden’s lakes. Scientists have been studying them closely since 1913, allowing us to see what’s been happening to these precious ecosystems over the past hundred-plus years.
Here is what a typical high-latitude lake looks like.
- The vegetation, composed of birch and wild grass, is slowly moving north (this, again, is called “Arctic greening”) but collapses frequently, too (also known as “browning”).
- The area is quite rocky, as the lake sits on a bed of rocks.
- Organic matter is transported into the lakes by runoff from higher lakes, precipitation, thawed permafrost, and wind.
Summer to autumn
To see how the lake changes, switch between seasons and compare throughout the years. Click on the ice cover for flat charts to appear.
Compare when the ice formed and how long it stayed each year.
Ice forms, creating oxygen bubbles. The longer it sticks around, the more algae will grow on it!
Winter to spring
All of this data is collected thanks to scientists’ fieldwork, as they sample the water at all points of the year and in any weather!
Compare when the ice broke, and how thick it got each year.
Ice breaks in crystals and almost never gets past a meter thick, but it’s enough to hold a truck!