A prime example of a streamside buffer and how it functions.
About Forest Buffers
Although we may not realize it, we use many types of buffers every day; From the paper filter for our coffee maker that prevents grounds from getting into our coffee, to the insulation in our home that protects us from cold and heat, to the umbrella we may use to keep us dry on rainy days, we use many things to "buffer" or protect us.
Trees are often used as buffers where there are conflicts in adjoining land uses. Trees planted along busy highways create both a visual and noise buffer for nearby neighborhoods. Trees and forests often surround schools, parks and recreational areas to create a comforting environment. In fact, one of the best ways to protect the Anacostia River watershed and the Chesapeake Bay is to plant and conserve trees as forest buffers along their banks and shorelines.
Streamside or riparian (derived from a Greek word meaning "on or near the shore") are one of the most effective and least expensive ways to protect the Anacostia River and its tributaries. Riparian buffers filter sediment and pollutant runoff from non-point sources such as streets, storm drains, and parking lots, and provide extensive root systems that "lock" soil particles together, slowing erosion.
The organic layer on the riparian forest floor is made up of leaves, twigs and fallen logs create a natural "sponge" that stores water and nutrients, and converts fertilizers and pollutants into environmentally-safe compounds that can be absorbed by trees and vegetation. In addition, riparian forests shade streams and cool water temperatures, providing a desirable habitat for entire ecosystems of macroinvertebrates, fish, and mammals.
The 3-Zone Buffer System…
The Maryland Department of Natural Resources - Forest Service promotes the establishment of a 3-zone buffer system to protect the Anacostia watershed and other tributaries of the Chesapeake Bay. In an ideal setting, the 3-zone buffer system provides all of the benefits that the forest has to offer; an effective buffer against non-point source pollution, habitat for fish and wildlife, areas for recreation, and a renewable source of forest products. Let's take a look at how the 3-zone buffer system works:
Zone 1 is located directly on the stream or shore portion, stretching upland from the edge of the water. The primary purpose of this zone is to stabilize the stream bank and provide habitat for aquatic organisms. The roots of trees and shrubs in zone 1 "lock in" soil to resist erosion caused by flowing water.
Roots and fallen logs slow stream flow and create pools that form unique "microenvironments" that support species of macroinvertebrates that are different from those found in riffles caused by rocks only a few feet away. This creates greater biodiversity in the stream ecosystem.
The leaf canopy found in zone 1 provides shade that controls water temperature and provides food sources for aquatic life. Maximum summer temperatures of a non-forested stream may be 10-20 degrees warmer than a forested stream.
This is very significant as a 4 to 10 degree change in water temperature can alter the life history characteristics of macroinvertebrates that form an important part of the food chain.
Located immediately upslope from zone 1, the primary function of zone 2 is to remove, transform, or store nutrients, sediments, and pollutants flowing over the land surface or in groundwater. Debris from trees such as leaves, twigs and branches slows and traps sediments from runoff, allowing time of nutrients to infiltrate into the ground where they can be stored and "used" by trees.
In areas where shallow groundwater flows through the root zones of trees, large amounts of nitrates can be removed before water enters the stream. Up to 90% of nitrates can be removed by plant uptake and the denitrification of soils, and studis have shown that zone 2 can remove 50% to 80% of the sediment in runoff from upland fields. Zone 2 can also be a "managed forest" providing firewood and important forest products, while still protecting zone 1 and the stream.
Located immediately upslope of zone 2, zone 3 contains grass filter strips or other control measures to slow runoff, filter sediment and chemicals, and allow water to infiltrate into the ground. Zone 3 acts to spread out the flow of water and prevents runoff from adjacent land uses from eroding channels into the buffer.
Studies show that grass filter strips can remove 50% or more of sediment runoff and nutrients such as phosphorous. Over time, the efficiency of grass strips decreases as deposited sediments smother grass. Periodic maintenance is required to remove sediments, establish vegetation, and remove channels. In urban areas like the Anacostia watershed, stormwater control devices like street drains and sediment control ponds may be common in zone 3.