Stream Anatomy — Riparian zone

The strip of land adjacent to a natural water course such as a river or stream is called the riparian zone. The vegetation within this zone provides a source of energy (e.g. fallen leaves) and physical habitat. Vegetation also moderates the amount of sunlight reaching the stream and traps sediment runoff from the surrounding landscape. Plants also absorb and slow runoff which helps reduce stream flashiness. A "flashy" stream has rapid changes in flow during runoff events, high peak discharges, low baseflows (during dry spells), and often high concentrations and transport of nonpoint pollutants. Increases in impervious areas in urbanized areas increase the flashiness of streams. In its natural condition most of the rain would soak into the ground before seeping into the stream and so the flow would increase more slowly and not reach as high a value. This means less erosion from bank cutting and less material washed in directly. It also means that groundwater inputs are more steady throughout the year, so there is more water in the stream for longer periods during dry periods and droughts. Reduced flows, in turn, lead to much higher temperatures and lower oxygen concentrations.

The distribution and characteristics of the vegetative communities are determined by climate, water availability, topographic features, and physical and chemical properties of the soil. The quantity and quality (species composition) of the terrestrial vegetation can directly affect stream channel characteristics. Root systems in the streambank bind soil particles slowing erosion and the creation of undercut banks. Trees and small shrubs growing on the stream bank are a source of organic matter for aquatic insects and other small organisms to eat and woody debris that provides habitat for them as well as fish, amphibians, reptiles, birds and mammals. Vegetative communities with high species diversity tend to support more terrestrial and aquatic animal diversity than communities with few species. Riparian vegetation also serves to shade much of the water from direct sunlight, and its removal can lead to increased temperature stress for fish.

Miller Creek in Duluth is federally listed as "impaired" because of high temperatures in summer. Hundreds of trees have been planted in the past 10-12 years to try and shade the creek in the Miller Hill Mall area. Similarly, the Weber Stream Restoration Initiative sponsored a streamside tree planting effort in 2006 for upper Amity Creek. All of the creeks that we monitored in the Duluth area had extended periods during summer 2006 with temperatures exceeding values known to cause acute stress to trout. You can view these data with our interactive data visualization tool by clicking here.

Duluth is located in the North Shore region of the Northern Superior Uplands Division of Minnesota.   Check out the MN DNR description of this area.