How a Lake Becomes a Bog

This is a satellite photo of the area in Wisconsin where I live, courtesy of Google Maps. You can see why it’s called “Land O’ Lakes” (no relation to the butter, though we sometimes call the abandoned lumber mill on the edge of town “the butter factory” to confuse people). We also have a lot of bogs. These two facts are not unrelated.

These are kettle lakes that were formed by retreating glaciers 10,000 years ago. Many of them have Sphagnum moss growing around their edges. Sphagnum is amazingly absorbent, holding up to twenty times its dry weight in water, and the mats it forms eventually grow thick enough that they act as a substrate for a whole community of other plants we associate with bogs – leatherleaf, wild blueberry and cranberry, orchids, carnivorous plants like pitcher plant and sundew, and many more.

Slowly the lake fills with sediment, and the sphagnum eats away more and more at its edges, growing thicker and absorbing more water as it does. As the lower layers of spagnum die, they decompose very slowly due to anaerobic (oxygen-poor), acidic conditions, so that over time you get rich, moist deposits of peat. Below is an old lake on this property that’s been almost completely bog-ified, with only a small area of open water left in the middle.

Eventually the sphagnum and peat build up to the point where they can even support trees, mostly tamarack and black spruce.

This is all just one more example of the powerful process of ecological succession – one natural community transforming into another through time.