Freshwater Environments Watersheds, Pond Succession, Wetlands

From outer-space, the earth looks like it is covered with veins and arteries, similar to our bodies.

Although there are many rivers and streams, these sources of running water account for a very small portion of the earth's total surface, just 0.3%.

Watershed A watershed describes an area of land that contains a common set of streams and rivers that all drain into a single larger body of water, such as a larger river, a lake or an ocean.

Watershed Scientific Concepts Surface runoff is important to aquatic ecosystems, since the water running off the land eventually supplies these systems. Water, though, is not the only thing that runs off the land. Water also carries water pollutants and soil, and both are deposited into aquatic ecosystems.

Watershed Scientific Concepts Not all water runs off the surface of the land. Some of the water soaks into the ground through the soil and underlying rock layers—a process known as infiltration. When infiltration occurs, some of the water returns to the surface, while the rest remains below as groundwater.

Streams and Rivers The journey from stream to ocean begins in our backyards and farms. Precipitation comes down, literally, everywhere—in various forms. It may rain, hail, snow or sleet. Water not absorbed by roots enters the ground water supply by infiltration. Most water runs off the surface, down a hill and eventually into a river. Ditches and small streams, which may be dry when it does not rain, can quickly fill up with water when it does finally rain.

When Rivers Run Into the Ocean Where rivers meet the ocean is called the mouth of the river. Soil and dirt carried by these rivers is deposited at the mouth, and new land is formed. The new, soil-rich land is known as a delta..

The Nile River is the longest and probably the most famous river in the world. As it flows toward the Mediterranean Sea from the mountains of central Africa, it grows in size. The Nile Delta is a very large and impressive sight. It is home to some of the most productive agricultural land in the Middle East.

Lakes A lake is a large body of fresh water. Lakes can range in size from small ponds to huge bodies of water such the Great Lakes in the U.S. Lakes and rivers are closely tied. Since both rivers and lakes are freshwater and flow in and out of each other, they share similar characteristics and many species reside in both habitats.

Ponds A geological event, such as a glacier or sink hole, can create a pond. Ponds are nothing more than shallow lakes where water collects and light can penetrate to the bottom. If left alone, ponds will fill in with dirt and debris until they become land. It often takes hundreds of years for a pond to be transformed from a body of clear water into soil.

The Four Stages of Pond Succession 1)As a pond develops seeds are flown in by birds and land animals come to inhabit the pond. These are the pond pioneers. 2) As more creatures arrive the debris on the bottom increases. Pondweed, and other submergent vegetation, appears and soon grow all along the bottom.

The Four Stages of Pond Succession 3) Emergents then appear on the edges of the pond. Over time, sometimes hundreds of years, as ponds plants grow, die and decompose, layers of debris build up. These layers of decaying matter raise the pond floor over the years.

The Four Stages of Pond Succession 4) After some time, the pond floor is close enough to the bottom that emergents can grow all the way across the floor. When this happens, the ponds becomes a marsh. Many interesting creatures can reside in the shallow muddy waters of marshes. (Marshes can be created in other ways also.)

The Four Stages of Pond Succession The marsh continues to fill in with dirt and debris. Eventually trees grow in the water. It is now a swamp. Over time, the swamp may dry out. Land that was once a pond, may become a forest or grassland.

Wetlands Fresh water wetlands are found all over the world in lowland areas or along rivers, lakes, and streams. Some wetlands are temporary and seasonal, they occur for a few weeks at a time and then disappear until they are refilled with water. Other wetlands are always under water.

What Are Freshwater Wetlands The term "wetlands" encompasses a wide variety of aquatic habitats including swamps, marshes, bogs, prairie potholes, flood plains, and fen. Natural wetlands are lands which, due to geological or ecological factors, have a natural supply of water—either from tidal flows, flooding rivers, connections with groundwater, or because they are perched above aquifers or potholes.

What is a marsh? A freshwater marsh is an inland area inundated with 1–6 feet (33–200 cm) of water, containing a variety of perennials (mostly grasses), forbs (flowers), and bushes, rather than trees, as in swamps.

What is a swamp? Swamps are slow moving streams, rivers or isolated depressions that host trees and some shrubs.

What is a bog? A bog is a peat-accumulating wetland. Some shrubs and evergreens grow in bogs, as do mosses. Most water comes from precipitation. There is usually no direct inflow or outflow of water.

What is a prairie pothole? A prairie pothole is a wetland area found in the northern Great Plains. These shallow or bowl- like depressions have variable wetness. They are often used for breeding by birds. Prairie potholes are not wet year-round.

What is a riparian marsh? Marshes that occur along rivers are called riparian marshes. These marshes serve two ecological roles: to absorb excess water when river levels are high and to release water when river levels are low. These balancing forces help prevent floods and droughts.

However, for the past 100 years mankind has straightened and deepened rivers in order to make them more accessible for commerce. The unfortunate side effect is the loss of riparian marshes. Today, very few riparian marshes are left. Some scientists believe that the great Mississippi River flood of 1993 was worsened, in part, by the loss of these wetlands.

The Role of Wetlands in an Ecosystem Wetlands prevent flooding by holding water much like a sponge. By doing so, wetlands help keep river levels normal and filter and purify the surface water. Wetlands accept water during storms and whenever water levels are high. When water levels are low, wetlands slowly release water.

Erosion Control Looking at pictures of deltas, one can tell that rivers deposit a lot of sediment into the ocean. The sediment is from top soil that has been eroded and washed away. Emergents (plants firmly rooted in the muddy bottom but with stalks that rise high above the water surface) are able to radically slow the flow of water. As a result, they counter the erosive forces of moving water along lakes and rivers, and in rolling agricultural landscapes.

Wetlands and Water Purification Wetlands also clean the water by filtering out sedimentation, decomposing vegetative matter and converting chemicals into useable form. The ability of wetlands to recycle nutrients makes them critical in the overall functioning of earth. No other ecosystem is as productive, nor as unique in this conversion process.