One of the primary functions of a shoreland buffer zone is
filtration of sediments from runoff waters. According to a study in the
Journal of Environmental Quality (Cooper 1993), in terms of volume,
sediment is the largest pollutant of streams and rivers. The addition of
sediments to a river or lake can block light needed for plant
photosynthesis, and can smother life on the bottom, such as fish eggs,
clams, and insects that are a crucial component of the food web.
Sediments also can carry contaminants such as phosphorous and
agricultural chemicals into surface waters. Native vegetation
within shoreland buffer zones act as a natural filter to trap sediments
contained in runoff waters before they reach lakes and rivers.
In the mid 1990s Panuska, of the Wisconsin Department of Natural
Resources, studied the differences in the amounts of runoff and
sedimentation at various levels of shoreland development. His computer
modeling work compared two 20,000 square foot areas. The first site was
a typical maple-beech forest. The second site was a developed property
containing a home (3,350 square feet), a paved driveway (770 square
feet) and a groomed lawn around the property. Both sites had the
same slope (6%). The results illustrated that the runoff volume on the
developed site was five-fold greater than on the vegetated maple-beech
forest site. Additionally, the runoff from the developed site
carried seven times the phosphorous load and 18 times the sediment load
compared to the runoff from the undeveloped site. This study illustrates
the potential impact of shoreland development on water quality.
In addition to filtering sediments, shoreland buffer zones also
serve to stabilize shoreland banks, reducing bank erosion. The
roots of the trees, shrubs, and ground cover plants help stabilize
shorelines. These roots add structure to soils as well as increase water
infiltration. The net result is a reduction in bank erosion and an
increase in water quality. The vegetation also aids in slowing down the
speed of the runoff water. By slowing down the velocity of runoff
water, the coarser sediment particles settle out on land prior to
reaching the water.
The literature is filled with different recommended buffer zone
widths to maximize sediment removal. Recommendations range from 15
feet to 100 feet. One literature review (Desbonnet et al. 1994) found
that the optimal width was 82 feet. It is clear that the State defined
width of 35 feet will have a positive impact on reducing sediments
entering our lakes and rivers, but a larger buffer would be better.
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