Geology is all around us, scarcely thought of as we go about our lives. Yet, it affects everything we do as a civilization, as a society and as individuals. While barely appearing to change from day to day, it works to alter the course of evolution. Preserving a record of creatures and landscapes both ancient and forgotten, the story of our past is written in stone and waiting to be read. I offer a view of how I see our world and its inhabitants, both past and present, as seen through my lens.
Sunday, June 12, 2011
Walking on Water at the Philbrick-Cricenti Quaking Bog: Part I - Geology and Plant Successions
The Philbrick-Cricenti bog has a deceptively firm appearance.
WELCOME TO A “QUAKING” BOG
If you’d like to walk on water, the opportunity awaits you at the 36.2 acre, Philbrick-Cricenti Bog of rural New London in southern New Hampshire. Formed by arctic plant species that grew across the top of a glacial pond, a living mat of sphagnum moss and sedge, dwarf spruce and tamarack now literally floats on 20 feet of murky water. Walking a squishy trail that feels like a wet sponge, you can venture out to the middle of this ancient pool on a floating carpet of vegetation over an open body of water, hear its distinctive sound, and feel the unmistakable bounce of a quaking bog.
The bog appears to have solid ground, but don’t be fooled. Step on it, and you’ll sink into a springy-spongy-bouncy-soggy mat of plant life. Your safe walk across the bog is made possible on a trail of wooden, boardwalk-like planks. If you leave the walkway, you’ll risk the fate of wandering livestock and wildlife such as the horse, cows and deer supposedly at the bottom of the pond. You could become a "human pickle" as one blogger so aptly phrased it. What looks like solid ground is surely a trap for the unwary and careless. But don’t be deterred. It’s a wonderful other world!
WHAT IS A WETLAND?
Bog. Marsh. Playa. Moor. Peatland. Swamp. Muskeg. Schwingmoor. Quagmire. Pothole. Fen. Carr. Pocosin. Mire. Flark. Wet meadow. Vernal pool. These are all terms used to describe types of wetlands, and they’re not all the same. Most people, including myself, tend to use many of these terms interchangeably, but there are major differences. Wetlands are low-lying ecosystems that are saturated with water at or close to the surface, but they differ due to variations in hydrology, soils, chemistry, wildlife and vegetation. Wetlands have plant and animal communities that are highly diversified and well adapted to a waterlogged environment.
WETLANDS ARE NOT WASTELANDS
Wetlands provide habitats for an incredibly wide variety of plants and animals. They are also important because they filter out impurities in water, recharge ground water supplies, provide trace elements, transform nitrogen into less harmful forms (dentrification), and prevent flooding by acting as a spongy-reservoir. Wetlands are a source of cranberries and wild rice, provide diverse recreational opportunities and are a cultural link for many people. Recently, bogs have been recognized for their role in regulating global climate by storing large amounts of carbon in peat deposits.
Despite their value, wetlands have historically been equated as wastelands. Tragically, wetlands are often filled in and obliterated, permanently lost to residential, industrial and agricultural use. Amazingly, over half of the wildlife species currently listed as endangered or threatened depends on wetlands for part of their lifecycle. Wetlands, and bogs in particular, are truly unique communities that take thousands of years to form and can be irreversibly destroyed in an instant, all too often in the name of progress.
FOUR TYPES OF WETLANDS
Wetlands are not necessarily wet year-round. Some are only seasonably wet. They are transitional areas between aquatic and upland ecosystems. The most common types of wetlands are swamps, marshes, fens and bogs, each possessing a unique ecosystem.
Diagram of a woody swamp, a grassy marsh, and a peatland fen or bog (Modified from National Geographic, March 1987)
Swamps are wetlands dominated by woody trees (coniferous and/or deciduous) and tall shrubs (such as willows, dogwood and alder). The ground is underwater either all or most of the time, fed by precipitation, by floods from lakes and streams (limnogenous), and groundwater discharge (topogenous). Swamps may dry out completely during the summer, but their substrate is usually continuously waterlogged. Their waters are circum-neutral to moderately acidic and show little deficiency in mineral nutrients and oxygen. Swamps can be alluvial, non-alluvial or tidal.
Marshes are seen near ponds, lakes and coasts, and are under water most of the time. Coastal marshes may increase and decrease in size with the tides, and can be small or huge (such as the Everglades). Marsh vegetation typically consists of herbaceous, non-woody plants (such as cattails, bulrushes, reeds, grasses and sedges). In the open water of marshes, floating and submerged plants can be found (such as water lilies and pondweeds). Marshes can be freshwater, saltwater or brackish.
Fens have soils consisting of peat, and therefore, are peatlands like bogs. Like a bog, they receive their water from rainfall (ombrotrophic) but also from groundwater discharge or seepage (soligenous) from adjacent uplands (minerotrophic). Therefore, fens typically have more nutrients than bogs, and the water is less acidic. Typical vegetation includes sedges, mosses, grasses, reeds, low shrubs, tamarack, white cedar, sundews, pitcher plants, and orchids, making them more species-rich than bogs.
A bog is a peatland, like a fen, consisting of a poorly-drained, low-lying area that receives its water from rainfall but almost certainly fed somewhat by runoff and seepage. Because a true bog has no outlet or inlet, the Philbrick-Cricenti bog is actually considered a poor fen, since it has an outlet that ultimately discharges to nearby Little Sunapee Lake. Being fed by rainfall makes a bog inherently nutrient- and mineral-poor, both of which are needed for plant growth. The bog’s ecosystem is said to be oligotrophic (as opposed to being eutrophic), meaning it offers little to sustain life. But don't be deceived; the bog is teaming with life!
Cross-sectional view of a kettle hole bog (Modified from National Geographic, March 1987)
Bogs have a surface carpet of moss and sedge, an underlying layer of spongy, partially decomposed peat, and stunted Black Spruce trees. The physical environment of a bog, being highly acidic, low in oxygen, and low in minerals and nutrients, places enormous demands on its vegetation that has responded with a high degree of diversification and specialization. Peatlands are the only ecosystems in which the plants play such a large role in controlling their physical environment. Mosses and sedges can change the water chemistry, which, in turn, can alter its plant and animal life.
A typical block of Sphagnum moss from a bog contains plants that are adapted to its deceptively hostile environment. They include the thick, waxy leaves of leatherleaf (1) and bog rosemary (2), the orchid arethusa (3), grasslike-sedges (4), the carnivorous bryophytes such as the pitcher plant (5) and sundew (6), Labrador tea (7), cranberry (8), and lilies such as Solomon's seal (9). (Modified from National Geographic Magazine, March 1987)
WHERE DO BOGS TYPICALLY FORM?
Bogs, like wetlands in general, occur in areas of depressed topography. In northern latitudes, the ideal landscapes for bogs to develop are in glacial tills and glaciolacustrine clay deposits that are poorly drained. Hence, bogs are common in colder, glaciated northern states (especially Maine, Vermont, Wisconsin, Michigan and Minnesota) and Canada. In New England, northern-type bogs, such as the Philbrick-Cricenti, are characterized by species of the boreal zone or taiga, and are found principally in western Massachusetts and Connecticut. The climax trees (trees that make up a mature and self-sustaining forest as opposed to pioneer trees that are first to colonize) are Black Spruce and Tamarack. By contrast, southern-type bogs are characterized by species of the southeastern coastal plain such as the Atlantic White Cedar and rhododendron, and are found principally in eastern Massachusetts, eastern Connecticut and Rhode Island.
HOW DOES A BOG FORM?
Bogs are prevalent in glaciated regions of North America and Eurasia where kettle hole-depressions in glacial till were created by large blocks of ice abandoned by the retreating continental ice sheets. Kettle lakes, without an inlet or outlet, formed within the depressions created by the buried ice. Such was the case at the end of the Wisconsinan Episode, the most recent glacial advance of the mile-thick Laurentide Ice Sheet at the end of the “last Ice Age” about 18,000 years ago. Note that not all bogs were formed by glaciers. A poorly drained lakebed or depression has the potential to fill and sustain under the right conditions.
It is unknown why some kettle lakes become bogs, but small, deep lakes are more suitable than large, shallow ones. Larger lakes allow circulation to occur more freely ensuring adequate oxygen for decomposition. In a small lake with less circulation, the rate of decomposition is not nearly as complete, being an anaerobic environment. Organic matter is deposited faster than it is broken down. Also, bogs develop in depressions typically where most of the water comes from precipitation rather than from groundwater runoff. As a result, the bog water is mineral-poor (soft) and acidic, further enhancing partial decomposition.
THE BOG MAKER...
Sphagnum moss is the dominant plant in the bog’s ecosystem and has a high capacity to retain water. This not only serves to maintain wet conditions but reinforces the anaerobic conditions that are favorable to the bog’s development. In addition, sphagnum moss has a high “cation exchange capacity.” This means that it removes mineral cations (Ca++ and Mg++) from the water, and in turn, gives off hydrogen ions. This further reduces the pH to between 3.0 and 5.0, comparable to that of acid rain. Acid conditions slow decomposition even further and encourage peat accumulation, a thick layer of decomposing vegetation.
FROM POND TO BOG...
The Philbrick-Cricenti bog has been forming for 10,000 years! The process of bog creation from a lake or pond begins at the periphery as vegetation flourishes, first grass-like sedges, and later sphagnum moss, leatherleaf and Labrador tea. This creates a vegetation succession from the outer to the inner bog. The already cooler microclimate is further aided by an insulating layer of moss, which along with the other plants, forms a floating, vegetative mat upon the waters of the bog. As mentioned, bogs are generally not connected to rivers and streams, and receive their water from rainfall which creates stagnant conditions in the bog. This circumstance results in water chemistries that are low in nutrients and low in oxygen. These conditions create a habitat that relatively few types of plants will tolerate.
THE BOG MAT…
Sphagnum moss grows with new layers growing on top of older dying layers. The result is the accumulation of peat, brownish-black layers of compressed, partially and slowly decomposing remains of dead plants which have accumulated on top of each other within the subsurface. Peat consists of sphagnum moss along with the roots, leaves, flowers and seeds of heathers, grasses and sedges. It’s 90% water and 10% solid plant material. Peat is actually a precursor to coal, and when dried and burned, is an energy source. The severe shortage of nutrients creates an impoverished environment for further plant growth. Slowly, the developing bog mat encroaches upon the open water at the center of the bog, as the accumulating peat layers grow thicker beneath the mat. Woody shrubs become more common.
Eventually, all open water may be eliminated by the ever-advancing, ever-consolidating bog mat. The mat continues to grow in thickness until it becomes grounded to the sediments at the bottom of the lake. The vegetation develops and flourishes in concentric zones as the ecosystem of the bog slowly evolves. A variant called a "raised" bog has grown so much that the surface actually is elevated compared to the surrounding habitat.
As the basin of the bog fills in, shrubs and trees invade the floating mat from the periphery. The end product in all cases is a mature, bog forest dominated by trees adapted to water-logged, peaty soils such as spruce or cedar. This entire process can take thousands of years to complete. It has been estimated that the Philbrick-Cricenti bog is about 13,000 years old. Bogs are dated by studying core samples and analyzing their stratigraphy, since surface vegetation is a poor indicator of bog formation and succession. The actual history of a bog lies well below the surface in the layers of accumulating peat. In this manner, only can the true history of the bog’s development be revealed.
MY WALK ON WATER THROUGH THE PHILBRICK-CRICENTI BOG
On a sunny, late May afternoon, while visiting my daughter’s school in southern New Hampshire, we took a detour to visit the Philbrick-Cricenti bog in rural New London. A mile-long network of trails all on wooden planks runs through this remarkably beautiful, kettle-lake bog and provides a “safe path over a floating mat of tundra plants” on which to walk. Courtesy of the New London Conservation Commission, an informational display greets all visitors offering them a detailed brochure and map of the bog, which is marked by numbered signs that refer to the brochure.
Walking on the boards, we entered a deciduous, wooded region of Red Maples (Acer rubrum) and Royal Ferns (Osmunda regalis), which was the location of the shore line of a 25-acre pond at the end of the glacial period. Both of these plants are common and widespread, and very much at home in the extreme moisture and increased acidity conditions of the bog.
The former lake bottom was about 5 feet below at this point. We encountered hordes of ravenous mosquitoes, so we quickened our pace to the open areas of the bog.
Still in the woods but close to the open area of the bog, the Royal Ferns transitioned to majestic colonies of tall Cinnamon Ferns. The Cinnamon Fern (Osmunda cinnamomea) is called a “flowering” fern, because its golden color appears as if it’s in flower. The flowers are actually the sporangia, which are the spore-forming portion of the plant. This is a temperate-zone, deciduous fern. Its genus is known in the fossil record back to the Triassic Period. Ferns have been around for more than 300 million years, reaching their zenith during the Carboniferous Period. A group of seed ferns evolved that gave rise to the flowering plants of today. Fern terminology: the frond is the “leaf” that contains the “seeds” or spores on the frond’s underside, and the rhizome is the “stem.”
A majestic Cinnamon Fern
Close to the bog-proper as the acidity increases, deciduous Red (Swamp) Maples were replaced by coniferous Black Spruce (Picea mariana), typical of northern-type bogs. Recall that southern-type bogs are associated with Atlantic White Cedar.
Walking on the wooden planks, you can literally feel the ground move beneath your feet, the source of the term “quaking bog.” It's an experience you'll never forget!
Out on the open bog mat, we've left the tall maples and spruce behind us. The floating mat of vegetation that covers the bog is comprised of many plants, but the "bog maker" is a mix of Sphagnum moss and sedge. Sphagnum moss (Sphagnum rubellum) is a member of the phylum Bryophyta, a group of plants that does not flower, produce fruits, seeds or cones, but does produce spores. They were possibly the first land plants. Sphagnum moss can retain 20 times its own weight within its cells. Most plants that we think of are vascular with internal tubes for transporting food and water, but moss has poorly developed tubes, being a non-vascular plant.
A close up of the mat of Spagnum moss and sedge, and a little of the underlying brown, decomposing peat.
Interestingly, plant roots that require oxygen for respiration are immensely disadvantaged by the anaerobic conditions in the peat. Most of the bog plants maintain all their roots within the live moss and perhaps a few centimeters of the peat to take advantage of the aerobic zone above the water level.
On a historical note, because of its ability to soak up blood and its relative freedom from bacterial contamination, Sphagnum was used as a surgical dressing during World War I. Native Americans used Sphagnum moss to diaper their infants, attesting to its "cleanness" and absorbancy. Lastly, a distinction should be made between the American usage of ‘sphagnum peat moss’ and the British ‘sphagnum peat.’ The former refers to the live moss growing on the bog that is often used as a soil conditioner, and the latter, the decaying matter underneath is used as a source of fuel when dug from a peat bog.
Bog sedge (Carex paupercula), along with Sphagnum moss, are the first to grow out over the water and form the floating, bog mat. It is a plant that resembles grass and is well-adapted to wetlands. Water chestnut, papyrus and cottongrass are types of sedge. Grass-like sedge grows with binding roots that produce new plants. The stem of sedge is triangular in cross section, and its leaves are spirally-arranged in three ranks, while grasses have alternate leaves forming two ranks. Remember this jingle in order to tell sedges from similar plants: "Sedges have edges, rushes are round, grasses have joints from the top to the ground." This being my first visit to a bog, I anticipated a foul odor from decomposing plants and water stagnation, but everything smelled fresh and clean. The air of the open bog was still and quiet, as scores of dragonflies darted just over head foraging for insects. No mosquitoes were encountered on the bog, perhaps thanks to the dragonflies. Many such bog dragonflies (such as the Boghaunter) are endangered because of habitat destruction from urbanization and pollution, the unfortunate fate of many wetlands as well.
We carefully walked on the planks for safety and to not damage the delicate plant life underfoot. However, my daughter couldn’t resist the temptation to test the waterlogged-sponginess of the bog mat. It's quite amazing!
The plantlife of the bog is arranged in concentric, vegetational zones. A progression of plant succession can be seen in the photo (below). It was taken from near the center of the bog, which is the earliest stage of zonation. The photo looks outward towards the Upland Border of coniferous trees such as Black Spruce. Absent in the periphery is a marginal Moat (Lagg) Zone, a marshy zone of open, shaded water with little vegetation. A moat is largely the result of increased decomposition due to elevated nutrient levels from upland runoff. A Tree Zone of Tamarack and Black Spruce, as the dominant trees, is next with several shrubs in the understory. Sphagnum is present but often with a different growth color than in open areas of the mat. Closer to the center of the bog is the Shrub Zone, where the dominant vegetation growing on the mat includes heath shrubs such as leatherleaf, bog laurel and bog rosemary. We are standing within the open, sun-bathed Sedge Zone that blankets the entire bog. Sedges form a matrix of rhizomes and roots that trap debris and provide support for the bog moss. Cottongrass also occurs. These species form the floating mat of the bog. Notice the occasional tamarisk and spruce that punctuate the central portion of the bog. The Open Water Zone, the earliest stage of succession, is absent at Philbrick-Cricenti. Typically, bogs have very little open water.Classically, the succession of plants will progress to the conversion of the bog to a mature forest and a terrestrail habitat.
The succession of plants over and within the bog, called a hydrarch succession, occurs over a long period of time. The first biotic community to develop is called a pioneer community, and its species, pioneer species. The pioneer community is replaced by another community, and so on, as the vegetation progresses over the bog. Eventually, a climax community forms of stable, self-perpetuating species that are in harmony with the physical environment.
View from the center of the bog outward showing concentric, vegetational zonation and succession
Along the path, tamaracks and spruce are stunted in their growth due to the poor nutrient content of the bog's soil. In the open bog mat, many of the trees have a bonsai-like appearance. Many of the Black Spruce are more than 60 years old.
Here's a miniature spruce that looked like a bonsai-tree.
At one stop on the boardwalk, my daughter checked the depth of the bog with a 10 foot-long pole. The bog brochure states that the official depth is 20 feet.
My congratulations to the Town of New London and its Conservation Commission for protecting and educating everyone about this invaluable natural resource.
Please visit my next post for Part II of "Walking On Water at the Philbrick-Cricenti Quaking Blog." I'll investigate more of the plantlife growing on the bog mat.