10-3 Flowing-Water Ecosystems Examples are rivers, streams, creeks and brooks. All refer to water that flows over land. Most aboveground freshwater environments with moving water are all referred to as streams by scientists.

Stream Organisms These organisms are adapted to the flow of the stream in which they live. Some insect larvae have hooks that allow them to hold on to plants. Others have suckers to hold on to rocks and things. A lot of trout and salmon have adapted to live in streams. Salmon live in oceans but return to upstream for reproduction purposes. Sometimes dams block their way back upstream.

Stream Organisms

Stream Flow Most streams begin at high altitude and flow downhill from mountain tops because of gravity. Most start from melting snow. Streams usually flow towards oceans. The “source” or “head” is where the stream begins.

Stream Flow At the head of a stream, water flow is fast and cold and full of oxygen. As it flows downhill, it slows down. As it flows it picks up sediments (small particles that settle to the bottom of a body of water). Sediments provide place for plants to anchor their roots. Plants growing further cause the stream to slow down. This then allows phytoplankton to grow and provides food for consumers.

Sedimentation and Erosion These cause a stream to change its course over time naturally. As a stream meanders, erosion takes place along the fast-flowing outer edge of the stream. The inner edge of the stream moves more slowly depositing sediment there. The stream becomes increasingly curved with time.

Human Impact on Streams Dams made to form reservoirs. Dams formed to channel water for irrigation. These acts result in flooding and water shortages which affect the aquatic life in the stream.