Riparian: Relationship Between Riparian Corridors and Aquatic Ecosystems
Numerous studies have shown the benefits of a buffer zone between land use activities and a stream. These riparian buffer zones (RBZs) provide for the filtering of silts, sediments, and pollutants before they enter our streams and rivers (Newbold 1980, Wenger 1999). The leading causes of water quality impairment in Ohio are land use and disturbances such as development in ecologically sensitive areas, poor agricultural management practices, increases in impervious surfaces, modification of stream channels and removal of the riparian corridor (Ohio EPA 2000). Surface water runoff is trapped and filtered by the plants within the riparian corridor. The root tips of riparian trees and shrubs come into contact with the water table to filter nitrogen and phosphorus and utilize these nutrients.

Most of the literature on this topic has recommended minimum widths for these buffer zones based on pollutant or sediment filtration by riparian vegetation. For example, Castelle (1994) found that the relationship between sediment removal and the buffer width is non-linear and that disproportionately wide buffers are required to remove the most sediment. In order to increase the sediment removal level from 90% to 95%, the buffer width would have to rise from 100.1 feet to 200.1 feet.

Wenger (1999) suggested that while narrower buffer widths are effective for short-term sediment trapping, much wider buffer widths would be needed for the long-term retention of sediment. He concluded that the minimum width for adequate control of sediment is 30 feet, but the intensity and duration of the activities beyond the RBZ must be considered when regulating their size.

In addition to sediment removal, the trees in a riparian corridor make a canopy that shades the water and moderates its temperature. Such temperature moderation indirectly affects the levels of algae, macroinvertebrates, and certain types of fish. A canopied stream has a cooler temperature and less light but more heterotrophic or non-living organic matter. Fallen leaves or leaf detritus are an especially good example of a heterotrophic energy source. Bacteria and detritivores (eaters of plant detritus) break down such coarse and fine particulate matter, and then they become part of the food chain. In some streams, the energy brought from these exterior sources into the stream exceeds the energy created by the photosynthesis in algae (Allan 1995). This means that without an adequate corridor of trees along our streams, the food chain breaks down.

Streams without a forest canopy harbor a different kind of aquatic community than shaded streams. Sunlight raises the temperature of the water and encourages algae growth, which in turn fosters only certain macroinvertebrate communities. This leads to more of a monoculture in the fish and macroinvertebrate communities and threatens the diversity of the ecosystem.
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