What Is a Bog? (Definition, Benefits & Facts)

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What Is a Bog? (Facts & Information About Bogs & Bogland)

The Great Kemeri Bog in Latvia
Latvia’s Great Kemeri Bog spans over 12,000 acres and is around 8,000 years old. Photo by GRID-Arendal / CC BY-SA 2.0

“Bog” is, unfortunately, a blanket term that is often applied to any wetland or marginal environment, resulting in a great deal of confusion as to what exactly a bog is. Is it a wetland, any wetland? Is it any pond or lake margin? And what are bog plants – are they just plants that grow in wet environments?

The answer to these are: yes, a bog is a type of wetland, but it is not any wetland, nor is it simply the edge of any waterbody, and bog plants are those that are found specifically in bogs, suited particularly to the parameters created by these environments.

More specifically, a bog is a type of freshwater environment with nutrient-poor, non-draining or poorly draining soils with an acidic pH that is most often between 3.5 and 5 depending on the exact location, underlying soils, and plant species composition, though some transitional bogs can have a pH closer to 6. Their soils are usually peaty, spongy, and the water is obtained purely from precipitation rather than fed by groundwater or another water source, making them ombrotrophic.

How Are Bogs Created?

sphagnum moss in a bog
Thick, pillowy peat mosses, like this sphagnum, characteristically blanket most bogs. Photo by Katja Shulz / CC BY-SA 2.0

Bogs are formed in existing depressions created by glacial retreat, outwashes, kettle and pothole depressions, and glacial lakebeds. These areas naturally have acidic, low nutrient conditions, and over time as they fill with plant matter, rainwater, and snowmelt it creates a thick, peaty bottom that gives rise to a multitude of very well-adapted plants and organisms. Over hundreds or even thousands of years, a bog is formed. Sometimes, sphagnum mosses form first over dry land, inhibiting moisture and rain from evaporating and over time creating a bog.

Bogs can exist within the entire depression, or just make up a portion of it – in the latter instance, you might see a wetland or lake with a dense mat of mossy, shrubby vegetation floating atop it or at its edge. This floating mass is a bog, and is more often to be transitional with a mildly acidic (almost neutral) pH than bogs that make up the entire area, which are often quite acidic.

Why Are Bogs Important?

Perhaps one of the most critical roles played by bogs is that they act as a sponge that soaks up rainwater, snowmelt, and runoff, thus preventing flooding and helping to cycle pollution runoff. They also function as carbon sinks; as decay occurs so slowly in bogs, they are able to hold onto mass amounts of carbon dioxide, thus preventing it from being released into the atmosphere. In fact, IUCN reports that “peatlands [like bogs] are among the most valuable ecosystems on earth…[and] are the largest natural terrestrial carbon store.” Yearly, bogs and other peatlands store more carbon dioxide than all other ecosystem types worldwide combined.

bog turtle in a bog
Bogs provide critically important food and habitat for a variety of wildlife, including the critically endangered bog turtle (Glyptemys muhlenbergii). Photo by Patrick Randall / CC BY-NC 2.0

They are most often dominated by plants that thrive in acidic, low-nutrient conditions, such as sphagnum and other peat mosses, various blueberry species, cranberries, heaths, pitcher plants, orchids, pickerelweed, and are almost always surrounded by trees. The most usual trees found around bogs are often stunted (less than 6 feet tall) due to the nutrient-poor soils and include buttonbush, black spruce, tamarack, jack pine, white pine, and occasionally red maple in more southern bogs.

Bogs are naturally very nutrient poor, and as such the plants found in these wetland types are adept at either surviving off of very little nitrogen, or fixing their own. Due to a lack of water flow and the thick vegetation that decays very slowly, there is very little oxygen, either. Though few animals live in bogs (with the exception of some turtles and frogs), many animals depend on them for survival. Moose, rabbits, hares, beavers, many birds, muskrats, bears, foxes, and many others feed readily on the vegetation and insects found in and around bogs, particularly the nutrient-dense berries produced by heaths like blueberries and cranberries.

Are There Different Types of Bogs? (List of Bog Types)

Yes, there are several! We’ll break them down briefly below.

Raised Bog

A raised bog with grasses and trees in Corlea, Ireland
Raised bogs don’t often have much standing water, and have more sedges and trees than other bogs. Photo © N Chadwick (cc-by-sa/2.0)

Raised bogs, simply put, look, well, raised. Their vegetation and decaying matter have built up enough to give them a rather domed appearance. They tend to have more shrubs, small trees, and grass and sedge species than other bogs.

Blanket Bog

a blanket bog in the mountains of Ireland
Blanket bogs are somewhat rare and incredibly important, but more common in the cool, maritime mountains of Ireland. Photo by Forestry and Land Scotland

Blanket bogs exist in more mountainous, highland locations, and are so named because the bog and its vegetation appear to “blanket” a consecutive area of valleys, hills, and portions of the lower mountains. These highland areas experience high rainfall but low evapotranspiration, which allows the bog to form not only over singular depressions, but rolling, hilly land as well.

String Bog

a string bog in Goose Bay, Canada
A bird’s-eye view of a string bog spanning from Goose Bay to Nain in Canada. Photo by George Shepherd / CC BY-NC 2.0

String bogs span a swath of landscape, interspersed with low sort of islands of land that dot the connected bogs. The elevated “islands” have woodier vegetation, like heath shrubs and small trees, while the low portions are dominated by mats of mosses, sedges, and the like.

Cataract Bog

Cataract bogs are not technically bogs, but rather are fens because they are formed from fresh, flowing water. We’re including it anyway, as these systems are often referred to as bogs. They’re formed by some type of permanent flowing water feature, like a stream or small creek, flowing over (or under) a rocky, acidic outcropping. Over time, the stream erodes at the rock, creating a depression that eventually becomes separate from the stream. This forms a cataract bog over many, many centuries.

Quaking Bog

Quaking bogs are the ones we talked about briefly in the “How Are Bogs Created?” section. This type of bog forms in or on the edge of a waterbody like a lake, and forms a several foot deep floating layer of sphagnum and other thick vegetation, known as a “bog mat.” These bogs can be dangerous, because they look solid and as though they can be walked on. Sometimes they can be, but there is a risk of breaking through the vegetation and dropping into deep water or muck and having a very hard time getting out. These also feel as though they are shaking or quaking when walked on, hence their name!

Valley Bog

Valley bogs, as the name implies, form exclusively in wet valleys after a layer of peat has gradually built up along its bottom. These are also known as “mire valleys.”

Transitional Bog

Transitional bogs, also known as mesotrophic bogs, aren’t as nutrient poor or acidic as other bogs, and as a result tend to have a bit more plant and animal diversity. The soils they are formed in contain moderate amounts of nutrients, which result in a bog that is only slightly acidic as opposed to very acidic.

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