The Potomac Heritage Trail and the Evolution of the Nation
The following is adapted from Dr. Philip W. Ogilvie's 1997 paper on the PHT corridor, articulating the significance of the corridor in our Nation's evolution and the associated ecological and economical changes.
A Corridor between East and West
An anchor in the ever-changing context of the Potomac is George Washington's vision of the River as "the great avenue into the Western Country." The Potomac provided the central hub in the life of our Nation's first president. He was born and died on its banks, he surveyed much land within the basin, and his calling as a military leader came on the river and in defense of the Potomac Country for the British Crown. Washington used the River as a highway from the eastern settlements to the wilder west, and it provided food, income, and power for many. Washington himself owned about 12,000 acres of land in scattered locations.
The theme of an east-west corridor links the history, transportation and technology of the Potomac River corridor. Prior to the European invasion, land transportation in the Potomac region was largely by trail, usually the improved trace of a game trail. Large mammals, especially bison and elk during historic times, picked routes that used the least energy and, over the years, the passage of animals engraved trails in the landscape. People followed these trails and the resulting paths became the established routes of travel.
Transportation by waterway was unreliable at best. Whenever paddlers encountered an obstruction they would have to carry their crafts around the obstructions. But as General Washington recognized, the Potomac represented more than an avenue west--it also represented resources and water power. The River has provided a rich fisheries resource, remarked upon by Captain Henry Fleet in 1631. Washington harvested the river to feed his establishment fish, both fresh and salt, to sell and to fertilize his fields. The shad population in the River may be taken as an example of a fairly typical change in abundance overtime. Washington harvested a seemingly unlimited population of shad and, in the 1832 harvest, 22,500,000 were taken. A century of overfishing, obstacles to upstream migration, and pollution have resulted in reducing the shad population to the status of threatened. Today, however, American shad reintroduction is described as a success story.
European colonists recognized the vast potential of waterpower by adopting water laws, including mill seat rights, as some of their first legislation. As long as the Europeans remained confined to the Tidewater, there were very few sites with enough feet of fall to power a water mill. Wind and tidal mills predominated during this period, but as settlement expanded into the Piedmont mill-seats became an important aspect of land grants. The individual mill evolved in two ways: Many started as saw mills and produced lumber until the area was cleared; and either seasonally or sequentially, they were used to mill grain, plaster, bone, wool, paper as well as used for cutting stone.
Ecology, Economy and Change
The Potomac Basin has been shaped and reshaped greatly through time as ecosystems have been changed gradually by each resident human society over the last 14,000 years. A slow deterioration, due primarily to the activities of man, has more recently turned into a rapid destruction of habitat coupled with industrialization and over-population. The tides are slowing turning in the other direction, however; for the past 50 years there has been a steady, but slow, repair of natural ecosystems. Today we live in an ever-threatened, fragile and still-recovering structure.
For example, the recent efforts to bring back American shad, a species once economically important, have been successful, but only to a point. The numbers of shad are growing but it is still unlawful to catch and keep shad.
Today there is greater interest in ecology than ever before, but the idea lingers that ecology is a subject important only in the biological sciences. Other groups do include the effects of humans as an innate part of ecology; in the social sciences, however, ecology is viewed as if humanity were the only agent responsible for change.
The effects of time, as another major factor in ecological change, is consistently minimized or ignored by many. In 1886, William Morris Davis of the Pennsylvania Geological Survey published a paper called, "Rivers and Valleys of Pennsylvania." This paper, with a few corrections, is still very applicable today despite its age. There are four major physical factors continuing to shape rivers today:
The formation of wind and water gaps by erosion
The headwater migration of divides
The adjustment to stream structure
Scientists think that many millions of years ago a super continent, called Pangea, began to break apart to form the modern continents. The topographic changes occurring after the continental split have resulted in the present Chesapeake Bay and Potomac River basin:
• A huge meteorite impacted the earth at what is today the mouth of the Chesapeake Bay, creating a giant crater and further affecting the direction of flow of the proto-rivers (rivers before the Potomac's existence).
• The westward erosion of the headwaters of the ancient Potomac captured other drainage systems, such as the Shenandoah, and thus increased the size of the basin.
• The Potomac River's flow and flooding wore down the heights of the uplifting plateau, resulting in sedimentation and water and wind gaps--spaces eroded from mountains; examples include the Gap in the Blue Ridge where the Potomac and the Shenandoah rivers converge.
Everyday Ecology in the Potomac Basin
The Potomac River corridor can be divided into six physiographic sections: the sediment-covered Coastal Plain, divided from the Piedmont by the fall line; the ancient crystalline rock of the Blue Ridge; the Great Valley, from the Shenandoah Valley south of the River to the Cumberland Valley north of the River; the rippled Ridge and Valley portion of the Appalachian Highlands; and the eastern front of the Allegheny Plateau.
Traveling through these regions is a vast window into geology and geomorphology--the study of the earth's physical makeup and the earth's physical changes, respectively. And this opportunity is a primary reason that Congress authorized the Potomac Heritage National Scenic Trail.
The rock cycle is demonstrated in many places, but nowhere as graphically as Sideling Hill along Interstate 68 in Washington County, Maryland. From the side of the mountain one sees the different levels of rock and deposits and the curvature that sugggests the movement of the earth's plates. We go back in time when studying the rocks of the basin and, fortunately, can also retreat in time by visiting some very special ecosystems. Fossils and pollen allow us to reconstruct the changes in environment over time until the archaeological record begins in the late Pleistocene era.
We still have remnants of ice age ecosystems in the basin today. These are probably best described as "muskegs," an Algonquian word meaning "trembling earth." Locally they are called quaking bogs, glades, swamps, marshes and bogs. Muskegs are at high enough altitudes (ca. 1,000 meters) for frosts to occur in summer, acting as a natural "refrigerator." Cranesville Swamp in Garrett County, Maryland, is a good example. Many arctic plants and animals have their southern-most distribution in these muskegs.
During the most recent inter-glacial period, about 100,000 years ago, there were great bald cypress swamps along the Potomac, and the stumps still show up in excavations in Washington, D.C. While cypress swamps are rare in the Potomac basin, a cypress marsh may be reached by canoe in Pohick Bay Regional Park in Fairfax County, Virginia.
As the continental ice sheet withdrew, a new ecosystem of plants and animals came into play. This complex included caribou and muskoxen as well as several now extinct large ice age mammals. There were few populations of humans at that time in the area, and except for hunting larger mammals, humans probably had little effect on the ecosystem at that time. Over time the area grew into a deciduous forest similar to what we see today, but the trees grew in greatly different proportions to each other.
Many plants have become less prominent since the Pleistocene era. For example, the chestnut and the American elm were two primary tree species hat have been all but wiped out. Some birds have been eliminated including, the passenger pigeon, the Carolina parakeet and the ivory-billed woodpecker. Bison, elk, wolves and mountain lions all used to roam the Potomac basin but are now gone. Game fish and shellfish that provided a commercial fishery, such as sturgeon, shad, striped bass and oysters, have been reduced in numbers and not longer profitable.
In contrast, there are some native species that are more numerous today. The effects of invasive plants, microbes and animals have all had a huge effect on the ecology, including the impacts of humans. Indigenous people, for example, would burn the undergrowth to prevent catastrophic fires. Europeans suppressed semi-controlled burns, resulting in years of fuel buildup, which could lead to devastating fires. As land was used for agriculture and urbanization, natural communities were eliminated and, with industrialization and chemical agriculture, the Potomac River became polluted.
Fortunately, there has been progress in reclaiming the health of the Potomac and some other rivers. A new environmental awareness has led to a cleaner Potomac and better conservation practices; we face many challenges while maintaining hopeful prospects for the future.