Monday, January 03, 2011
Earth is a rocky planet—a peculiarly watery one—spinning around a relatively huge, hot, radiating ball of thermonuclear plasma. How water got here and why it hasn't boiled off and blown away to a colder region in our solar system is somewhat of a mystery to scientists; though they're coming up with some plausible theories. Man is a terrestrial chordate, whose niche is dry land. But this niche, nevertheless, is dependent on the water cycle for its wellbeing; weather, rain, rivers, streams give vitality to a place that would otherwise be dryer than desert. Popular media reports, give us the impression that the carbon cycle and man's activities are the major factors controlling weather and whether the arctic regions stay as they are, advance, or retreat. In reality, carbon dioxide is only a factor. There are other factors and other cycles; for example, Milankovitch cycles, a theory that describes the collective effects of changes in our planet's movements upon the climate. This theory is not yet completed, but it is an exceedingly interesting idea, one that would help explain some of the glacial and interglacial activity here on our cozy little rock in space.
Caught up in a triune relationship between sun, water, and land, the best representatives of this confluence are wetlands; in my opinion anyway they are. This is where it all happens: water, land, sky congregate at these mires; life and death coexist and complement one another; time, schedules, governments, wars, and WikiLeaks seem rather unimportant here. By definition wetlands are areas that are inundated by water at a frequency and duration sufficient to support a prevalence of water loving plants typically adapted to waterlogged soils. Wetlands generally include swamps, marshes, bogs, and the like.
But what are swamps, marshes, and bogs really? A basic way to differentiate them is that swamps are wetlands with trees, marshes wetlands with grasses, and bogs are peatlands—dominated by mosses. But I prefer to think of wetlands in terms of their purpose. At the seaside, grassy marshes act as an interface between land and sea. They shield the land from any tempest forming out at sea, they protect fragile ocean ecosystems from the land, toxic runoff from watersheds, for example. Tidal salt marshes are one of the most productive ecosystems on earth. I really don't understand why man hasn't tapped into that yet. Swamps, on the other hand, are more closely associated with rivers. They function like reservoirs during floods and act like filters, absorbing excess water, storing it, purifying it, and slowly release it back to the main course on its journey back to the sea. Bogs are peatlands, and there are several peatland types, the two main ones are bogs (rain fed, acidic peatlands) and fens (peatlands fed by surface or groundwater), but what peatlands do ecologically is a bit ambiguous. While swamps and marshes are associative, bogs are loners, cool, foreign places, best appreciated when by oneself, when one seeks remoteness and solitude. Some bogs gives one a sense of foreboding and they don't give away their secrets or their water up lightly. In northern Europe, heaths (bogs) were where society's outcasts lived, these folks were known as bogeymen and heathens.
Given the right conditions peatlands develop by two different but related processes, lakefill and paludification. The later can result from altering drainage—beaver dams are an excellent example of paludification. My interest, in this column, is with the former type, the lakefill type; these are the bogs associated with the before said Milankovitch cycles. Their usefulness is more difficult to understand than swamp or marsh, which have district ecological usefulness, whereas the bog-type wetland seems to be more of a geophysical process. Marshes and swamps are ecosystems tangent to ocean and drainage, bogs are best thought of as part of the aging process of lakes and ponds. Bogs of this type are mostly found in the Northern Hemisphere, in a broad belt that includes the central and southern regions of the boreal forests and the northern parts of the deciduous forests of Russia, Canada, northern Europe and the United States.
The last glacial period is sometimes confused as the last ice age, though the ice age is still here, going strong. To throw out a metaphor, one could say that we are currently enjoying a warm day in the middle of winter. But on a much colder day we had this glacial period dubbed the Wisconsin Glacial. And my photos here represent evidence left behind, when the Wisconsin Glacial retreated north aways, about 10,000 years ago. Kettle Lakes: These are formed by blocks of ice that are separated from the glacier by either the ice retreating or by blocks calving off the glacier itself. Under certain conditions these blocks of ice become partially buried in meltwater sediments. Over time the blocks melt completely, leaving behind these kettle hole lakes.
Sometimes along or near a kettle lake one finds odd hills called kames, which are mounds of gravel and sand that were deposited by meltwater. Kettle lakes thus have a glacial origin, born and abandoned by an icy mother and destined to end their life as a bog, done in by sphagnum moss.
Eventually the bog becomes so filled in by sphagnum that it can no longer support itself or retain water to the degree it could when it was younger, and it becomes land again—land that is as it was before the glacier ever arrived, becoming meadow or forest. This process of aging we call succession; thus many northern bogs are simply really old ponds and lakes. How it happens: amazingly absorbent sphagnum can hold about a pound of water for every ounce of moss. As the sphagnum grows around the lake's edges, it absorbs the lake water making more room for more moss to grow, this cycle repeats itself until the entire lake is covered in sphagnum. Young bogs are fun to explore because when walking across them you are literally walking on water. There is no clear definition what is water and what is land. These bogs are often called quaking bogs because they tremble and shift under your weight when you walk over them. Over time, the layers of sphagnum moss decay to form layers of peat and the lake is turned into a peat bog. Sphagnum mosses release hydrogen ions into the lake turning the water acid.
Most decomposers cannot survive such acidic conditions; in some acidic bogs plant and animal remains often never decay completely. In addition, these acidic soils stunt the growth of trees and only allow for certain specially adapted plants to thrive there. Thus a strange mix of plants live in the bog, and botanist are one of the few people who truly appreciate them. Cranberries and blueberries from the arctic tundra flourish hand-in-hand with orchids and carnivorous plants like sundews and pitcher plants, from the tropics.
Posted by Wayne Ferrier at 12:03 AM | Permalink