4.2 Aquatic Communities
integrity because of the loss of riparian bufers and related increases in sediment, bank erosion, and stormwater runof containing sediment and other potentially toxic materi- als. Erosion and the resultant sedimentation are the largest sources of nonpoint source pollution in this system. Livestock access to streams contributes heavily to bank erosion, sedimentation, and nutrient input. Timber harvests and poorly constructed and main- tained timber roads are additional sources of erosion if proper controls are not used and maintained. An increase in impervious surfaces due to roads, parking lots, homes, and businesses increases the amount and speed of runof being delivered into aquatic systems. Decreased groundwater recharge between storms due to impervious surfaces leads to a decrease in stream base fows. Runof from urban areas often contains higher concentrations of nutri- ents (such as nitrogen and phosphorus), sediment, metals, hydrocarbons, and microbes. Exotic and Invasive Species. Exotic species invasion is a concern, with the Asian Clam, and Rusty and Virile crayfsh having been collected in both cool and coldwater streams. Asian Clam populations have increased signifcantly in recent years and are extremely abundant in certain large rivers such as the Little Tennessee River. Tese may have nega- tive efects on native species, such as competition for space and resources. With increases in water temperature, some invasive species may move into these coldwater habitats. Invasive plants in the riparian area (such as Japanese Knotweed) can have negative impacts on stream systems by creating a monoculture with poor nutrient inputs, reducing bank stability, and allowing too much sunlight to infltrate, resulting in warmer stream temperatures. Other invasive species, such as the exotic pest Hemlock Wooly Adelgid, may be a signifcant factor in coldwater stream communities because of the important role that hemlock plays in these riparian areas. If hemlocks are removed from the system, nutrient inputs and temperature regimes may be disrupted, which would in turn disrupt aquatic organism life cycles and cues. Clearing and Snagging. Clearing removes standing trees and riparian vegetation from streambanks and snagging removes woody debris (logjams, snags, mid-channel bars) from within streams. Tese measures are often taken to lower stream discharge volume and improve drainage, especially in urban areas. Direct efects are the physical alteration of the habitat while indirect efects include changes in fuvial processes (Cobb and Kaufman 1993) . Riparian vegetation is critical to the overall stream and streambank stability and modera- tion of water temperatures. Lack of riparian vegetation or inadequate forested bufer widths can cause streambank erosion and sedimentation. In addition to stabilizing streambanks, riparian vegetation serves as nutrient input to the stream community, flters pollutants, and helps regulate stream temperature by providing shade. Lack of sufcient vegetation
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2015 NC Wildlife Action Plan
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