THE BOG GUIDE
Geology, Hydrology, and Chemistry
Field guides don't typically feature abiotic factors of an environment since it is something you generally don't 'see'. In a typical bog however, you are indeed witnessing earth science at work. Consequently, geologic processes tend to take particularly long periods of time to manifest themselves, so it worth cross-referencing this with the Anthropology section for a comparison of timescales.
This page gives brief overview to how chemistry of soils and the movement of freshwater determine every biotic (living) aspect of the Caribou Bog.
While a fen is part of a peatland bog, it can appear as a forest as shown here. Deciduous trees dot the landscape but are nowhere as prevalent as conifers, which thrive in at least partially acidic soil. Below the fen is a water table that forms a moat around the edge of the fen.
Raised sections of the bog create perceptual islands where the typical acidity is not as prevelent, allowing trees to grow to a comparably impressive height in the center of the bog.
Anoxic conditions create an acidic environment where conifers tend to thrive above other plants in the bog section. Below the conifers are specially adapted plants that handle these conditions better than these trees.
This is the gradient. To the left is the fen and to the right is the bog. Is it clear that underlying hydro-geology of the soil is the result of the steep decline in tree height, brought about by extreme acidity. Note stunted tree growth compared to others.
A handful of peat.
Image Courtesy: Dirtdoctor.com
What is a Bog?
A bog is a type of wetland that has peat, which is partially decayed plant matter. The Caribou Bog in particular has two subsections to its peat wetland: a fen and a bog. The bog is defined by extremely acidic soil whereas the fen is comparably alkaline. In addition, groundwater moves from the bog to the fen. This, coupled with the geology and chemistry of the soil, determines what grows in the Caribou Bog.
How Does a Bog Form?
The short answer is glaciers. The long answer is almost 25,000 years long.
Before the last ice age, Caribou Bog was likely a large forested hollow (a valley without a stream). This hollow would've been deforested by encroaching glacial action and would have covered the bog with a sheet of ice over a mile and a half thick (!) that extended from the North Pole down to Long Island and Cape Cod. When the glaciers retreated (melted), ice from the glacier was caught in the deep hollow that would become Caribou Bog. This ice was caught, broken off and isolated, eventually melting to form a lake. So by 11,000 years ago, Caribou Bog was merely a lake from ice melt.
Forests grew around the shoreline and aquatic plants colonized the lake. As time went on, trees and aquatic matter died and fell into the lake but never fully decomposed due to lack of oxygen in the lake. This anoxic environment in the water is the process driving the formation of peat (Note: When peat is compressed for millions of years it becomes coal!). Plant matter would die, settle at the bottom, and then accumulate for thousands of years, essentially filling the lake.
The filling of this lake continued until the peat, acting like a sponge, absorbed lake water, filled in the lake entirely and became saturated. Excess water fell underground into a water table that is the old lake bed. The result is continued formation of peat, continually rising at the center. At this point, the lake gradually became an acidic environment and became a raised bog.
Geology & Geography
As the Caribou Bog assumed its eventual shape, the dynamic process of earth sciences and chemistry unfolded.
The aforementioned partially decayed plant matter creates an acidic environment where peat forms. The acidity is in part accelerated by tannic acid, which is derived from tannin. You may have heard of tannin before--it exists in principally in oak trees, acorns, and fir trees among other plants and helps them defend against fires and infections, among many other purposes. Tannin is an organic compound whose is acidic nature is due to having a high amount of hydrogen in it. The process of dying trees falling into water and leeching tannin, coupled with an already-anoxic environment drives the acidic environment of Caribou Bog.
Recall that as plant matter decayed in the ancient lake, it gradually replaced the surface water with itself and created a lakebed-shaped water table below. When the plant matter becomes peat, it accumulates on top of itself and creates a raised or dome bog. Raised portions exhibit a less acidic environment and create perceptual islands where trees grow taller. These islands are generally at the center of bogs.
Hydrology & Geography
While basic geography formed out of the ancient lakebed, the movement of water changed drastically and ultimately now define the Caribou Bog.
Recall that peat is an absorbent material that holds water like a sponge. For thousands of years, the continued formation of peat took up all the ancient lake's water until excess fell out into a water table at the bottom of the lake. Just like rivers, groundwater moves from high to low (though at a painfully slower rate). As peat accumulated to a peak at the center, groundwater moves from high, the 'peat peak' to low, the surrounding area, beyond the ancient shoreline. The groundwater moves "downhill" underground until it spills into the fen and forms a moat around the edge of it. At this point, the water has lost its acidity and is somewhat alkaline by comparison.
At the center of the bog, however, the water is extremely acidic. These conditions create an challenging environment for plants to grow. As a result, There is a gradient in height of trees from the upland, to the fen and to the bog. As you approach the center of the bog, the trees decrease in height from over 100 feet to nearly 1 foot. This extreme gradient is the product of extreme acidity in the bog and less acidity in the fen.
The Product
After thousands of years of 'peatbuilding', the two distinct parts of the peatland bog emerge: the fen and the bog. The underground movement of water from mounting peat moves toward the fen. Groundwater from the uplands moves downward into the fen as well. The product is a forested wetland with trees and understory with shallow roots. Springs and occasional ponds rise in the fen and drain it, eventually joining other river systems.
The rising peat at the center of the bog creates a raised landmass over the original water of the lake that is extremely acidic and poor in nutrients. It is fed only by rainwater and houses plants that are specially adapted to the environment. This is the bog. Anything not specially adapted, such as the Black Spruce, will have stunted, erratic growth.
The Gradient & Miscellaneous
This aforementioned gradient is a perfect display of hydro-geologic gradient of acidity. Recall that bogs are the ancient lakebed and fens are between there and the upland. Where the fen meets the bog is where a shoreline most likely was. This gradient is a visual to where a acidity drastically increases.
Confused? That's ok. Bog chemistry and earth science is not easy to grasp without a visual. Here are some helpful links to understand this bog formation process:
Raised Bog Formation (Youtube)
Formation and Types of Peatlands
Sources:
1. "Formation and Types of Peatlands." Formation and Types of Peatlands. Bard Na Mona, n.d. Web. 22 Nov. 2016.
2. "What Is Peat?" What Is Peat? International Peatland Soceity, n.d. Web. 22 Nov. 2016.
3. Cannas, Antonello. "Department of Animal Science - Plants Poisonous to Livestock." Cornell University Department of Animal Science. Cornell University, n.d. Web. 22 Nov. 2016.
4. Peat Bog Formation.wmv. Dir. Melissa Grima. Peat Bog Formation.wmv. Youtube, 25 Mar. 2012. Web. 22 Nov. 2016.