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Biological Monitoring

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Stream habitat

 

Healthy streams support aquatic life. Most organisms adapted to live in streams need cool, clean water with a high content of oxygen and adequate food sources to survive. Stream organisms also need diverse habitat. These characteristics are obtained if a stream system has certain components.

 

Vegetation along the sides of streams (called the riparian area) shades creeks to keep temperatures cool. Riparian vegetation stabilizes the banks, helping to control erosion of sediment into the water. Sediment in a creek is considered a pollutant since it kills many of the organisms in the water by smothering them. Sediment can also inhibit creek creatures´ ability to find food. Leaf litter from the riparian area feeds many aquatic invertebrates; invertebrates, in turn, are eaten by organisms like birds, frogs, and fish that are higher up in the food chain.

 

Streams with fast flowing waters usually have sufficient amounts of dissolved oxygen for stream inhabitants. As the water cascades down slopes and over boulders and rocks in the stream, oxygen from the air enters the stream system. Cool water can hold more oxygen than warmer water, so cool streams will be better able to support aquatic life.

Stream organisms need to have places to hide from predators, forage for food, reproduce, and rest. Streams with diverse habitat will meet these needs. Diverse habitat is provided by structures in the stream like large logs, tree roots, boulders, and undercut banks. Stream bottoms in healthy creeks have a mixture of substrate materials including sand, gravel, cobble, boulders, and bedrock. Fine sediment covering the stream bottom over large areas are a sign that excess sediment is entering the stream system. It is also important that a stream have varying depth regimes, including deep pools and shallow areas.

 

Human activities can negatively impact stream habitat. Streams are diverted, dammed, and straightened. Removal of vegetative cover and disturbance of the soil cause erosion of sediment into creeks. Water diversions upstream result in lower flows, and consequently, water with higher temperatures. Runoff from farms, homes, livestock, industry, and roads may carry heavy nutrient loads and chemical pollutants into stream waters. Once creeks are impaired, restoration projects and land management changes may help restore balance to the system.