Everything you want to know about lake Succession!!
Freshwater lakes, in principal, are ephemeral. As a system they are created, they age, and they die, in a predictable pattern. This process of aging is what we call succession. Many palustrine systems like freshwater marshes and bogs are simply really old lakes and ponds. Lake succession is mainly driven by the input of organic matter and sediment into the lake system. As the lake fills up, it looses water and becomes a new type of system.
Watch a short overview Video from Untamed Science
Birth of a Lake
Lakes are born in many different ways. Receding glaciers can leave large depressions in the landscape which can quickly be filled with water and glacial out-wash. These types of lakes are called kettle lakes. Crater lakes are formed in the middle of a volcanic depression or the crater left by an asteroid collision. If the meandering pattern of a river pinches off it can leave an oxbow lake, a stagnant body of water in the depression of a former flowing river.
If you think you've noticed a pattern here you're not crazy. Lakes are born in topographical depressions and filled with water. The speed at which the lake ages and goes through its stages of succession depends on the amount of water, nutrients and sediment being put in or taken out of it.
Filled in and Dried up: Bogs
Water loss and sediment fill are a main ingredient in lake succession. In the northern latitudes, kettle lakes dominate and sphagnum moss is the most common ground cover surrounding them. Sphagnum is wonderfully absorbent and is able to hold about one pound of water to every ounce of dry sphagnum. As the sphagnum grows around the edges of a lake, it quickly absorbs some of the water; this then creates more room for more moss to grow and so on until the entire 'lake' is covered in sphagnum. Over time, the layers of sphagnum moss decay to form peat layers. This lake can then be called a peat bog. Some bogs in the Denali National Park in Alaska can have over 20 ft of peat below the bog!
Bogs have very acidic soil and water. Because most decomposers cannot survive in such acidic soil, bogs can be rich with well preserved animal and plant remains. The acidic soils will also stunt the growth of trees and only allow for certain specially adapted plants to grow there. *The acidic nature of sphagnum moss makes it a great antiseptic and bandage in survival situations* Bogs are normally formed in higher altitudes where they are not fed by underground springs of water. If they are fed by underground springs then they are called fens. Because fens are not as dry as a bogs, they can remain in the late stages of succession for a very long time.
A second way lakes can go through succession is through a process called eutrophication. This happens when nutrients are washed into the lake from the surrounding area, or watershed. Nutrients can include animal waste and fertilizers, which scientists call nitrates, and eroded inorganic material called phosphates.
Along with oxygen, nitrates and phosphates are requirements for life, especially plants. As more and more nutrients are washed into the lake, the more plants, like algae, are able to grow and reproduce. The more algae that grows, the cloudier, murkier and greener the water gets. Algae goes through photosynthesis like all plants, breathing in carbon dioxide and breathing out oxygen to form sugars. Initially, the amount of algae in the water increases the amount of oxygen available to other animals. Unfortunately, everything that lives has to die. When the algae dies it sinks to the bottom of the lake and decomposes. Along with sediment being washed into the lake from the surrounding area, the dead plant and animal material decomposes to from soil. The decomposers responsible for breaking down the dead organisms breathe oxygen. So, too much algae in the water can actually decrease the amount of oxygen, which can decrease the amount of living things that are able to live there.
This can get kind of confusing, all you have to do is remember the book If you give a mouse a cookie. Its a little silly, but just remember, every time you give the lake something its going to want something else. If you give a lake some nutrients, its probably going to want to grow some algae. If it grows some algae, it will probably want some oxygen to wash them down. Decomposition that happens deep in the soil without oxygen can smell really bad, like rotting eggs, because the bacteria that break it down use other gasses instead of oxygen to breathe. Just try digging your hand into some pond muck, YUM! Eutrophication happens slower in big lakes and lakes that don't get many nutrients washed into them. Lakes that are in the beginning stages are called Oligotrophic, and lakes at the end stages are called Eutrophic.
Death of a Lake
The two processes that have been described here are not the only ways a lake can go through succession, and many times it is a combination of the two. A bog can go through eutrophication, and a eutrophic lake can become a bog. It all depends on the living (biotic) factors involved. The size of the lake can also effect how fast it ages. Lake Michigan is still oligotrophic despite being around for thousands of years. Eventually though, sediment from various sources will fill in a lake and most of the water will leave it, if there is not a source feeding it. When this happens the lake is essentially 'dead' and all that remains are traces of a once thriving ecosystem.