Three Boquet landowners receiving streambank erosion control projects this year have all agreed to establish stream-side buffer zones. The three landowners will receive assistance with these plantings from the U.S. Fish & Wildlife Service's "Wildlife Partnerships" program. Why are vegetated buffer zones so important? Because they make streambanks more stable, help control pollution to the river, and optimize habitat conditions for aquatic plants and animals.
Trees and woody vegetation draw water from the streambanks, helping to dewater the banks and improve their stability. Vegetation also protects streambanks from the raw and erosive power of rivers flowing at high velocities, or from ice flows during spring melts.
Fine sediments can be a serious pollutant in water bodies because they can harm or destroy small aquatic insects and smother fish eggs. But sediments play another pollutant role. Excess nutrients, such as phosphorus, attach to sediments. When sediments are swept off the land into a river by rain or snow melt, so is the phosphorus. Vegetation planted along the tops of streambanks hinder this run-off. The speed of water flowing over the land is reduced by the many obstructing plants. Then the soil structure, made more porous with vegetation and its litter, acts as a filter to trap the sediment. Excess phosphorus from farmland is reduced because about 85% of available phosphorus is bonded to the sediment soil particles. Vegetation, particularly treed vegetation, traps the phosphorus laden sediment, retains it, then takes it up in the plant tissues.
The vegetated buffer also transforms or converts toxic chemicals due to the bacteria and fungi in the decaying organic debris. Microbial decomposition, oxidation, reduction, hydrolysis, solar radiation, and other bio-degrading forces at work in the soil and vegetated litter of a buffer area change harmful residues like pesticides and herbicides into non-toxic compounds.
A treed buffer zone also provides food and energy to aquatic life. In the Boquet's shaded upland reaches, probably 75% of the organic food base is supplied by the detritus (fruit, twigs, leaves and insects falling from the vegetation) and dissolved organic compounds. Bacteria, fungi, and aquatic insects - like the macroinvertebrates we studied in our kick net samples - feed on the detritus and are, in turn, eaten by larger aquatic animals and fish. Thus, the food chain of the river system is dependent upon treed buffer areas.
Of course, water temperature is also greatly controlled by vegetation. Although the groundwater and springs that provide most of the Boquet's base flow remain fairly constant in temperature throughout the year, direct sun for extended periods of time can raise the water temperature above what can be tolerated by trout, salmon, and other fish. Leaf canopy is necessary to filter and shade the river from excess solar radiation.
Lastly, treed buffer zones actually control the amount of food available to aquatic animals. If there weren't debris dams from fallen trees and branches, stream-side vegetation would be quickly washed downstream without contributing to the food chain. Debris dams hold the detritus long enough for it to be processed and eaten by the macroinvertebrates. Only a permanent, mature treed buffer zone can contribute the amount and size of debris needed for a stable river ecosystem.
So, BRASS is grateful to the landowners for their cooperation and to the U.S. Fish & Wildlife Service for their participation.