River

Rivers and streams have a unique ecological system, far different from stable bodies of water such as lakes or ponds. Probably their most noticeable feature is constant motion. Probably their most noticeable feature is constant motion. Rivers are always traveling, usually in one general direction and this affects the life within them.

Not only is the water in a river always moving but there are great differences in the speed of this movement. A stretch of water may be slow, meandering section, a lake that's almost closed off from the rest of the river, a run of rapids and waterfall, or quiet backwaters. One reason for this is the natural geoligical formation of the river valley. Water will tumble quickly downhill or cliff while it will wander more slowly across a wide flat plain.

Plants and animals living underwater must constantly adapt to the movement of the waters. Sometimes they cling tightly to underwater rocks. At other times they have to swim upstream most of the time just to stay in the same place, like Alice in wonderland. This does not mean that a rivers an unfriendly environment. Many plants and animals thrive under just such unstable conditions.

Rivers and streams provide various habitat or living areas, along any one section. Some habitats may consist of fast-moving water rapids and riffles. Other habitats may be quiet, fairly stationery pools. . River animals may live in more than one habitat. For instance, a trout may spend most of its time deep in shady pool, move to another part of stream for feeding and use yet another area for spawning. A healthy stream needs certain conditions in order to sustain life. It must have adequate nutrients or food. But it can't have too much, which can cause excess of growth and choke the stream. A healthy stream must also have sunlight, which is necessary for the process of photosynthesis. It must have temperatures that are warm enough h for plants and yet cool enough for fish. It must have unpolluted water and an adequate oxygen supply. Most of these conditions are interdependent.

Seasonal changes in the level and width of a river can greatly disturb its ecology. flooding usually happens during the spring thaw. When the snow melts, a gentle mountain. Stream can become a range a cascade of icy water. A heavy rainstorm can change a lazy river into a swollen and dangerous one. Such transformations an occur overnight. When faced with such unexpected force and violence, many animals and plants are ripped from their habitat and swept downstream. Sometimes they survive , but often, particularly in the case of plant life, they are destroyed.

Much vegetation is swept away by floods, and more is killed by the prolonged submersion. On the other hand, nothing that requires substantial water all through the year can survive along a stream which contains water for only six to nine months. Most rivers rarely experience such extremes in water level, but most do vary by few feet during the year. If the banks of the river are steeply sloped, damage is usually minimal. But if the river is situated along a relatively flat plain, even a few feet can cause enormous damage. The flatter the terrain, the farther the water will spread during any flooding. not only do floods damage homes and threaten plant and animal life, but they also cause serious erosion as they wash away irreplaceable topsoil from the banks another characteristics of rivers and streams is their constant mixing or turbulence. Waters toss, turn, and pick up solids and move them along downstream. They exert a force against any life in the water, which means that every spot along the river is constantly changing. Such changes are in sharp contrast to a lake, in whish the plants and some animas can remain in the same spot for months.

Instability is the key word in describing rivers and streams, because these bodies of water are never inactive or dormant unless dried up. Instability causes hardship for living things both in and along the banks of these rivers and yet many species of life thrive in just such a situation. Oxygen is needed by almost all animals and plants for survival and the constant mixture and movement of the water enables it to capture large amounts of oxygen from the air. Thus streams are oxygen rich bodies of water, while small lakes or ponds are often oxygen poor and cannot as easily support life.