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The 4 tiers of a lake ecosystem

Tuesday, September 8

A lake ecosystem is as complicated as it is beautiful. Here are the top three things you should know about how the tiers of the ecosystem work:

  • Producers take energy from the sun, or natural chemical processes, and use it to make energy.
  • Big consumers are often specialized in how and what they eat, with some having large mouths to easily scoop up small fish and others with down-facing jaws used for sucking up meals of algae and invertebrates.
  • Decomposers do the dirty work of converting feces, dead organisms and other detritus into energy and nutrition for themselves and those that eat them.

As a lake ages, these producers, consumers and decomposers serve different purposes. Here are the three key stages a lake enters and leaves as it changes over time:

  • Oligotrophic lakes are young lake ecosystems that tends to have clearer water, minimal plant growth, less mucky sediment at the bottom, and fewer large producers like fish.
  • A mesotrophic lake is a middle-aged lake ecosystem that is fed more nutrients and has greater plant production.
  • A eutrophic lake is an old lake ecosystem that typically holds shallow, murky water. The shallow water is warmed more easily by the sun. It also produces more plant growth and algae.

The fundamentals of a lake ecosystem

When an organism fits seamlessly into its ecosystem, it is considered native. For example, monarch butterflies consume milkweed as caterpillars and then consume nectar and disperse pollen as adults. Shelf mushrooms live on the sides of decaying wood and assist in breaking down the dead tree into energy and nutrients. Opossums eat anything they can easily put in their mouths, especially ticks. All of these species are native to northern Indiana and are important parts of a lake ecosystem.

Native: Plants and animals that grow naturally or have lived for a long time in a certain region. Native plants and animals tend to be self-sustaining and already adapted to the region they’re in. For instance, native plants can survive dry and rainy seasons better than non-native plants.

Another important aspect of lake ecosystems is their dependence on dissolved oxygen. After oxygen enters water, it changes form and becomes dissolved oxygen. Fish can draw it in through their gills, and aquatic plants can draw it up through their roots and release it into the air and water. It is essential to all forms of aquatic life, although some do not need as much as others to survive.

Every native organism has a niche, and every niche exists on a level of the ecosystem. Each level contains an extremely diverse group of organisms, and though we talked about some of our favorites, and about the aquatic food chain as a whole, here are some examples of the four broad levels of a lake ecosystem.

The primary producers

Producers comprise the base of the food chain. They take energy from the sun, or natural chemical processes, and use it to make energy.

Many producers, like trees and duckweed, do not actively move. Some, like cyanobacteria (known as blue-green algae) move up and down but not much more. Sometimes, though, there are producers that are truly mesmerizing to watch.

One the Lilly Center team has observed under a microscope is called a euglenoid. Its name means it is “like a euglena”. Euglena are microscopic free-swimming organisms that, in this case, use photosynthesis to gain the energy to swim in their graceful spiral motion.

The little consumers

There are countless kinds of zooplankton! They are fundamental to a lake ecosystem because they serve as food for other growing organisms, like fish. Zooplankton are also excellent indicators of the health of the water they live in. As the Environmental Protection Agency (EPA) describes, “The effects of environmental disturbances can be detected through changes in species composition, abundance and body size distribution.”

Here is one of our favorites: the rotifer. The best way to envision a rotifer is as an itty-bitty lake Roomba. Rotifers swim around at high speed using their tail (or tails) as a paddle and their mouth as a vacuum, hoovering up algae and tiny protozoa as they go along their busy microscopic lives.

The big consumers

Anything that moves and can be seen with the naked eye consumes other organisms, too. This group of consumers is likely the most well-known group, as it contains everything from smallmouth bass to crawfish and even to mussels. Big consumers are often specialized in how and what they eat, with some having large mouths to easily scoop up small fish and others with down-facing jaws used for sucking up meals of algae and invertebrates.

The decomposers

This group is diverse and pretty hard to find. They do the dirty work of converting feces, dead organisms and other detritus into energy and nutrition for themselves and those that eat them. Although these little creatures often go unnoticed, they are always there, doing the job we are so glad we do not have to do.

Every level of a lake’s ecosystem does a unique and important job in protecting and prolonging native species and the habitats they live in. There’s a direct benefit for us, too: When the lakes are healthy, so are property values, family memories, local businesses, farms and more.

How does a lake ecosystem change over time?

Aging is a natural process ─ in both humans and lake ecosystems! Although they do not retire from a full-time job or grey hair, lakes and their inhabitants change in several ways while aging. Our actions can either speed up or stabilize the process.

What is an oligotrophic lake?

An oligotrophic lake is a young lake ecosystem that tends to have clearer water, minimal plant growth, less mucky sediment at the bottom, and fewer large producers like fish. Fewer nutrients are in the water, which means there is less algae and weeds.

What lives in an oligotrophic lake?

Oligotrophic lakes tend to be deeper and therefore colder than older lakes. Cold water also holds more dissolved oxygen than warm water, so the ecosystem is perfect for fish species that prefer this kind of chilly, highly oxygenated water.

An oligotrophic lake is oxygen-rich but has too few nutrients to support many forms of life. Even so, the dissolved oxygen is used in plant and algae production. As the plants and algae decay, sediment slowly builds in the bottom of the lake. It is broken down by bacteria, which also use dissolved oxygen.

What is a mesotrophic lake?

A mesotrophic lake is a middle-aged lake ecosystem that is fed more nutrients and has greater plant production. Sediment accumulates on the bottom, which makes the lake shallower and warmer overall. More algae is produced because of the increased nutrients, which can lead to a less-clear lake with a greenish tint. 

But that does not mean the lake is unhealthy! The ecosystem of a clear lake (like an oligotrophic lake) has fewer weeds and plants, but it also has a limited food web and few aquatic organisms. A healthy, balanced mesotrophic lake is home to a wide variety of fish, crustations, reptiles, plants and more. 

What lives in a mesotrophic lake?

The ecosystems of many lakes in Kosciusko County are mesotrophic. They are home to blue gill, sun fish, perch, catfish, bass and more. They are also known for turtles and crayfish. Mesotrophic lakes are shallower than oligotrophic lakes, though, so they host fewer cold water fish. More plants are visible, too.

In a mesotrophic lake, dissolved oxygen is used and produced by virtually every form of life in the lake, from producers to decomposers. If the production of dissolved oxygen is outpaced by the use of dissolved oxygen, a lake ecosystem will slowly tilt toward eutrophication.

What is eutrophic lake?

A eutrophic lake is an old lake ecosystem that typically holds shallow, murky water. The shallow water is warmed more easily by the sun. It also produces more plant growth and algae. The lake is in the process of filling itself in with sediment (like decaying leaves, organisms and aquatic plants) and will eventually become home to many types of wetland plants and animals.

What lives in a eutrophic lake?

For a while, a less-eutrophic lake might hold common, hardy fish like bass and pike. It will also become home to a large variety of semiaquatic plants and critters. But as it ages, it slowly becomes anoxic, either forcing out or suffocating fish and other dissolved oxygen-dependant critters. As this happens, the work of decomposers speeds up. More decay leads to feet of mucky sediment that is nutrient-dense and perfect for wetland plants. Eventually, the lake will become a marsh, bog, fen or some similar type of wetland.

How can I stop my lake from eutrophicating?

It is important to remember that this is a normal process. All natural lakes are living, breathing ecosystems. Left by themselves, they will become wetlands over the course of hundreds of years. 

What we do can cause the lake to age more quickly or more slowly. Notice that nutrients are a prime cause of quicker lake aging. More nutrients lead to more algae, plant and weed growth. When those die off, they produce (you guessed it) more nutrients! Nutrients come in many forms, but here are examples of ones we can help keep out of our lakes:

  • Fertilizer used for landscaping or crops
  • Soil from eroding shorelines
  • Leaves and other lawn debris
  • Anything that is not naturally occurring, like household chemicals

Try reducing the use of lawn fertilizers, and preventing soil erosion by landscaping with native plants. You can also compost yard waste rather than allowing it to enter a local lake or stream. These small changes will help keep lake ecosystems healthy for generations to come!


Article written by Abby Phinney and Jed Harvey, Lilly Center staff.