The word "ecology" comes from the Greek language and means "the study of households." We can think of the natural world as divided into a variety of households, each containing a number of living things as well as non-living things, such as soil, water, air, and a variety of chemical elements. This is much like domestic households that contain both people and the things necessary to support their lives. Each natural household is known as an ecosystem, a term that reflects the many activities and interactions that regularly take place between its living members and the chemical and physical features of their environment.

      Ecosystems can be as small as a rotting log or as large as an ocean. The Amazon rain forest is an ecosystem, as is Antarctica. It is often convenient to identify small ecosystems that exist within larger ecosystems, such as an ocean tide pool or a forest glade.

      The Chesapeake Bay is certainly an ecosystem. Accordingly, an understanding of the Bay involves a close look at the biology of the Bay's 2,700 species of living things, its geological characteristics, chemical components, and their patterns of interactions. Because we are also a significant part of the Bay ecosystem, our role must also be taken into consideration if we are to gain a complete understanding of the Bay's ecology.

The Estuary Ecosystem

      With few exceptions, brooks and streams join major rivers that eventually reach the ocean. An estuary is a partly enclosed body of water where fresh water from a river meets ocean salt water and the two mix. The Chesapeake Bay is the nation's largest estuary, receiving salt water from the Atlantic Ocean and fresh water from more than 50 rivers and innumerable smaller tributaries.

      Because estuaries receive constantly varying amounts of salt water and fresh water from tides and rainfall, they act as large mixing areas. Nutrients vital to plant and animal life drain from the land and reach estuaries where they are used by these living resources. The chemical, physical and biological elements of river and sea unite to create these unique estuarine ecosystems.

      Because salt water is heavier than fresh water, estuaries like Chesapeake Bay contain two layers: a saltier layer that lies on the bottom and a freshwater layer above. Mixing occurs where the two layers meet. Further mixing takes place as a result of wind, tides, temperature changes and rainfall.

      The waters of the Chesapeake are saltiest near the mouth of the Bay and gradually become fresher northward. The force of the earth's rotation makes salt water accumulate on the Eastern Shore, so water tends to be saltier on the eastern side of the Bay at any latitude. Overall, however, the proportions of fresh and salt water in the Bay depend largely on the amount of rainfall that flows out of the Chesapeake's major rivers. During a wet year, the entire Bay will be somewhat fresher than normal, and conversely, a dry year will result in higher-than-average salinities. Salinity is one of the most important physical features in determining what lives in a particular part of the Bay, so plant and animal populations in the Bay differ north to south, west to east, and from year to year. Temperature and bottom sediment also determine the distribution and abundance of organisms.

      Estuaries teem with a variety of plant and animal life. The constant movement of the tides sweep away wastes and circulates nutrients and food, providing a favorable situation for sedentary animals such as oysters and clams. Estuaries are important nursery grounds for fish. Indeed, many kinds of aquatic animals spend some portion of their life cycles in estuaries. The enormous biological productivity of estuaries is reflected in their immense commercial importance. The Chesapeake Bay, for example, is the source of fish and shellfish industry worth over $850 million each year.

The Watershed

      A thorough examination of Chesapeake Bay ecology includes not only the body of water itself, but also the entire drainage area, referred to as the Bay watershed. The Chesapeake Bay watershed includes all the land from which water drains right into the Bay or into one of its tributaries. Water which falls onto land outside the Chesapeake Bay watershed will drain into some other body of water - Delaware Bay, the Ohio River, the Atlantic Ocean, or any number of streams or lakes.

      The Chesapeake Bay watershed is huge. It extends from the south of the Bay in southern Virginia near Norfolk to the headwaters of the Susquehanna River in New York and west to the middle of Pennsylvania. It encompasses 64,000 square miles of land and is the largest watershed on the eastern seaboard of North America.

      Why is the size of the Chesapeake's watershed important? Because anything capable of being carried by rainwater, whether it be gasoline, used oil or pesticides, paint, or fertilizer, can eventually enter the Bay. For example, a particularly rainy season in the Bay watershed will result in a greater amount of fresh water coming into the Bay, by way of the many rivers and tributaries. This will decrease the Bay's salinities. A spill of toxic chemicals from a factory can have effects for almost 200 miles. Fertilizers and topsoil from farms can enter rivers during heavy rains, and eventually end up in the Bay. In fact, all of the natural fluctuations in weather, plus the activities of the 13 million people who inhabit the Chesapeake Bay watershed, will have some sort of effect on the Bay's ecology.

Evolution of a Watershed

      The Chesapeake Bay is a geological result of the last Ice Age. As the glacier that covered much of North American melted some fifteen thousand years ago, sea level rose, flooding the lower Susquehanna River basin and creating the Chesapeake Bay. With the exception of the portion that was originally the Susquehanna River channel, the Chesapeake Bay is relatively shallow. The old river bed itself is the current deep Bay channel.

      The bulk of the watershed was originally forested. Trees play several roles in maintaining a healthy watershed. They buffer heavy rainfall which otherwise pelts the earth, causing soil to wash away. Trees absorb and evaporate large amounts of water during the growing season, thus reducing flood potential. As people moved into the watershed and cleared trees from the land, there has been a substantial increase in soil erosion, flooding and the delivery of sediment, nutrients, and other materials into the major tributaries of the Bay.

Life in the Chesapeake

      Most of the living things in the Chesapeake Bay are much too small to see with the naked eye. Microscopic plants and animals, known as plankton, are perhaps the most important species in the Bay. Without them, no other animals would be able to survive. Why? Because all living animals in an ecosystem need energy in the form of food. Plants and animals continuously circulate energy in a complex network called a food web. Plants capture energy from sunlight and use it to manufacture food in the unique process of photosynthesis. The smallest plants in the Bay, called phytoplankton, float freely near the surface of the water where sunlight is plentiful. Animals called zooplankton, which also drift in the Bay currents, feed on phytoplankton, as do many other invertebrates, including the early stages of mollusks, crabs, and even some fish species. Small animals, in turn, provide food for somewhat larger animals. Animals such as adult striped bass, ospreys, and people consume the largest animals in the Bay. Through the food web, all animals the Bay ecosystem ultimately depend on the abundant supply of phytoplankton, and rooted submerged aquatic vegetation.

      Energy in an ecosystem recycles when a plant or animal dies. Various kinds of decomposers, organisms such as bacteria, feed on dead material and animal wastes. As plants capture new energy from the sun and decomposers return nutrients to the ecosystem, organisms in the food web thrive.

      It is not unusual for a food web to undergo temporary disruptions such as forest fires, floods, and droughts. Ecosystems are normally able to recover from these disruptions after some time. When man-induced disruptions are added to the ecosystem on top of the stresses that already exist, the ecosystem's ability to bounce back diminishes. Unlike the proverbial camel, whose back will break under a large enough load of straw, stressed ecosystems don't simply collapse. Instead, they gradually degrade, changing in numerous small ways to endure the range of assaults on them. Over a long period an ecosystem loses its original character altogether, and consequently, loses many of the plants and animals that once inhabited it.

      Currently, scientists are worried about water pollution and the health of the Chesapeake Bay ecosystem. This is the threat that the Chesapeake Bay, as well as the plants and animals that live in its waters and on its shores, now faces.

Habitat

      An animal's habitat is the place where it lives, finds food, defends itself from predators, finds a mate and reproduces. Most animals confine their activities to a particular kind of habitat where they are most successful at fulfilling their needs. For example, ospreys live adjacent to the Chesapeake Bay because it offers an adequate food source (fish) and good nesting sites. Likewise, oysters populate areas where there is a suitable flow of oxygen-filled water, an abundant supply of plankton to serve as a food source, and a hard surface to settle on.

      Animals differ in their ability to adapt with change. Some species of animals are able to adapt to changes by their habitats or food sources easily. Raccoons, for example, survive equally well eating fish from a river or table scraps from garbage cans. Many animals, however, do not adapt well to change. Degradation of a species' habitat can result in a decrease in the animal's population or extinction of that species in the area.

      Many plant and animal species have suffered from habitat destruction in the Chesapeake Bay. The canvasback duck no longer winters on the Bay in its former abundance because its primary food sources, the aquatic plant known as wild celery, has become too scarce to support large flocks. Other species of submerged aquatic vegetation have also declined precipitously over the past 20 years. The canvasbacks that still winter on Chesapeake Bay have resorted to eating small clams. Redhead ducks, on the other hand, have suffered much because they depended on a diet of underwater grasses. Oyster populations are down because of poorly oxygenated water and a lack of clean, hard surfaces on which their young can settle. Areas of the Bay around Baltimore and Norfolk support little or no bottom life. Loss of wetlands and degradation of water quality throughout the Bay have reduced plant and animal diversity and abundance. Each minor change has had its impact; the cumulative effects of these changes has been devastating.

Toxic Materials

      A toxic substance is a poison. Almost any substance can be toxic at high enough levels. Toxic materials enter the Bay from a variety of sources, most commonly industrial discharges and sewage outflow. In limited quantities, incoming fresh water and outgoing tides dilute and remove these harmful chemicals. The current rate of toxic input into the Chesapeake Bay, however, far exceeds its ability to eliminate it. As a result, toxic substances collect in the sediments on the Bay's floor and slowly enter the food web.

      A classic example of the impact of toxic materials on animals in an ecosystem is the case of DDT, widely used after World War II as an insecticide. When animals contaminated with DDT were eaten by other animals, toxic effects spread far beyond insects. DDT accumulated in the tissues of certain birds, such as the peregrine falcon and bald eagle, causing their eggshells to be thin and, consequently, to break in the nest. For several years, few offspring were produced. After DDT was banned from use in the United States in 1972, peregrine falcon, osprey and bald eagle populations have gradually recovered.

Excessive Nutrients

      Unlike a toxic chemical that can actually kill plants and animals directly, nutrients alter living populations in the Bay by stimulating algal growth. Plants make their own food from sunlight, carbon dioxide, water and essential nutrients such as nitrogen and phosphorus. When nutrients are absent or low, plant growth is minimal. This is why farmers put fertilizers containing the important nutrients nitrogen, phosphorus, and potassium, on agricultural crops. Use of fertilizers results in larger yields.

      Unfortunately, excess nutrients promote the growth of plants in the Bay, too. Algae are microscopic plants that usually occur (as phytoplankton) near the water's surface. Abundant growth of algae can give the water a cloudy green color or can grow as "slime" on rocks or pilings. Fertilizers wash off cropland and residential lawns into the Bay, providing the nutrients enabling algae to reproduce at overwhelming rates. As algae cloud the water, they prevent sunlight from reaching the Bay floor, causing rooted aquatic plants to die. Decomposing algae use up much of th water's oxygen supply, which in turn stresses fish and other animals in the Bay, especially oysters and clams.

Our Role

      People affect every aspect of the Bay ecosystem. We alter its chemistry by pouring our wastes into it. We change its geological features by dredging channels, filling wetlands, and speeding shoreline erosion. We harvest its fish, shellfish, and waterfowl in huge quantites. In short, we affect the entire ecosystem every day through countless commercial and recreational activities.

      The human population of the Bay watershed continues to grow and is projected to be 15 million by the year 2000. Everyday activities of each of the watershed's inhabitants, such as flushing toilets and fertilizing gardens, combine to place enormous stresses on the Bay. As the chief source of disruption, human activities threaten the Bay's health and future productivity more than any other organism or natural force.       Ironically, we are the only creature in the Bay ecosystem that can control the impact we have on the Bay. It is critically important that man act as a responsible steward of the Bay and as advocates for those species of living things that suffer from our careless actions. Only through becoming aware of our dependence on the Bay and vigilant of our responsibility for it will we be able to maintain it in the years ahead.

      Each person in the Chesapeake Bay area can help restore the Bay. What about you? You can start by learning more about he Bay's problems and their causes and taking action to change those aspects of your own lifestyle that have adverse effects on the Bay's well-being. Take Pride in Chesapeake Bay - its fish, its wildlife, and its future.

      The Chesapeake Bay is the largest estuary in North America. Its waters provide food and habitat for an abundance of fish and wildlife. It serves as a highway for commerce, a playground, a storehouse of food, and a home for the 13 million people who live in its vast watershed. But in recent years the Chesapeake has become less able to support the fish and wildlife it once did. Increasing amounts of excess nutrients, sediment, and toxic substances are causing serious ecological problems in the Bay. Studies show alarming declines in species of fish and wildlife and in the habitat available to them.
      The U.S. Fish and Wildlife Service is one of many Federal, State, and local agencies and private organizations engaged in the Chesapeake Bay restoration program to reverse the damage already done, to arrest further degradation and to restore the Bay - as nearly as time, technology and resources allow - to its former productivity.
      As one of the primary Federal stewards of the nation's living natural resources, the U.S. Fish and Wildlife Service provides leadership in habitat and wetlands protection, fish and wild life research, technical assistance, and in the conservation and protection of migratory birds, anadromous fishes, certain marine mammals, and threatened and endangered species. The Service also manages more than 430 Wildlife Refuges and 70 National Fish Hatcheries across the country, including several in the Bay area.