When a Bog Is Not a Bog

May 01, 2009
Michael Alcamo
Trail Walker


When a Bog Is Not a Bog



A swamp (above) is different from a bog, fen, or marsh. Photo: Bridge and Tunnel Club

by Michael Alcamo

Not far off the bright red line that marks the Long Path on the map for Schunemunk Mountain (West Hudson Trails, map 114), you'll see a small patch of wavy blue lines  indicating "swamps and wetlands." Usually we hikers avoid wetlands. Yet they are among our most important ecosystems and can be quite interesting for their diversity.

Wetlands typically fall into one of four categories: bog, fen, marsh, or swamp.

A bog (called a mire in certain areas) is a wetland that generally is cut off from flowing water. Bogs receive their water primarily from precipitation, augmented in some case by groundwater seepage. Water outflow is generally as seepage to groundwater, not to an exiting stream. Owing to the lack of water circulation, bogs are low in oxygen; and owing to the chemical actions initiated by sphagnum mosses, which find bogs to be friendly habitat, bogs are quite acidic. For these reasons fish do not thrive and waters are quite clear. You may, however, find in bogs carnivorous plants, like pitcher plants and sundews, which derive nutrients from eating insects rather than drawing them from soil. Mammals such as beaver and muskrat also do well in bogs.

Because of the bog's high acidity (which discourages bacterial growth), plants and animals decompose very slowly in it. This organic matter instead builds up and forms peat, which, given enough time, will become a coal deposit. (Peat is useful itself as a fuel, though, and it's estimated that 94 percent of the original bogs in the United Kingdom have been "mined" for peat.)

A fen, by contrast, is a wetland with a watercourse. Though the wetland may look like a bog, somewhere water will be flowing-even if ever so slightly-bringing oxygen and nutrients to the area. Fens are described as either "rich" or a "poor" depending on the degree of water circulation and therefore nutrients. The more water flow, the richer the fen. The nutrients permit the growth of abundant plant life, including grasses and sedges. A fen can, in fact, resemble a meadow. Mosquitoes, dragonflies, and horseflies are very common in fens, as are as the birds and mammals that eat them.

Then, there is the marsh, a transitional environment between land and permanently aquatic environments. A marsh is characterized as a wetland intermittently or continuously flooded with water, generally not deep, and dominated mainly by soft-stemmed plants like grasses and sedges. A marsh can be salty, fresh, or brackish. Marshes are vital ecosystems, serving as breeding grounds for a diversity of animal life that benefit from the protection of the slow-moving, nutrient-rich water.

Lastly, there are swamps. These too are intermittently flooded areas, but usually dominated by woody vegetation, such as trees and woody bushes. Swamps can be fresh or saline and are generally seen as deeper than marshes. Because water moves through both a swamp and a marsh, acidity is minimized and oxygen levels are generally high. Therefore marshes and swamps do not accumulate peat deposits and do permit the growth of fish.

Interestingly, Black Rock Forest in Orange County, NY, includes a feature once known as Barton's Swamp, through which some water runs. Ecologist and historian Neil Maher has written that the Barton family mined and sold peat from this "swamp" in the late 19th century*. In today's terms, it would not be classified as a swamp at all, but probably as a fen.

Then of course, there is Barton Swamp on Schunemunk Mountain, the one marked by those wavy blue lines mentioned at the start of this article. It lies in the trough between the mountain's two ridges, with the Long Path on the western ridge and the Jessup Trail on the eastern ridge. Between these two ridge trails, runs the Barton Swamp Trail. But is that wetland really a swamp? I recall moving water, and the map indicates the Baby Brook coursing downhill from its vicinity. I remember as well the predominance of woody trees, and no sphagnum or peat accumulation. Therefore my guess: it really is a swamp. But what a good excuse to get out and see it again to make sure!


* Black Rock's Hidden Past  

Michael Alcamo is a naturalist, Trail Conference member, and frequent contributor to this newsletter. He is also a member of the Mid-Hudson Chapter of the Adirondack Mountain Club.