4.2 Aquatic Communities
and stream fow and thermal regimes may have a more signifcant infuence on fsh occur- rence and abundance. Termal Stratifcation and Algal Blooms. Termal stratifcation is rare in warmwater streams due to the mixing efect of fows and lack of sufcient depth. During periods of low water fow and little wind, deeper pools within a river may become stratifed with little or no vertical mixing. Under these conditions DO levels in the deeper water may be depressed and become unsuitable for many aquatic organisms. Algal blooms in the surface water can exacerbate DO depletion and result in local degradation of water quality. Such condi- tions are temporary and are readily alleviated by increased water fow or increased wind velocity. In Coastal Plain streams, stratifcation may occur due to saltwater intrusion occurring as a subsurface density fow. Te denser saltwater does not mix with the less dense fresh water and as a result the water column becomes stratifed. Oxygen depletion as well as toxic bacterial and algal blooms can be associated with this type of event, often leading to signif- icant mortalities within the aquatic community. Invasive Species. Warmwater streams provide pathways for invasion by nonnative species. In the absence of obstructions such as dams, culverts, waterfalls, etc., invasive species can travel long distances within a system and establish viable populations within the main stem river as well as tributaries. Once in a river system, invasive species are difcult, if not impossible, to eradicate or even control. Water Quality. Warmwater streams typically occur at lower altitudes with a relatively moderate topography. Tus the adjacent land is more likely to be used for purposes such as residential development industry, commerce, and agriculture. All of these are sources for discharges of various chemicals into the river, which can moderately or substantially afect biological communities. Te moderate temperature regime of these waters often acceler- ates biological activity promoted by inputs of organic compounds resulting in degraded water quality. Sedimentation is particularly problematic in warmwater streams. Development of riparian and adjacent areas can accelerate erosion and relatively low stream gradients can pro- mote the deposition of eroded sediment within the stream channels. Sedimentation can decrease the depth, increase water temperatures, and decrease the biological productivity of afected waters. Rivers fowing through or near urban and suburban areas may receive products from sewage treatment plants, such as incompletely processed pharmaceuticals, that can afect the production of hormones in aquatic fauna.
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2015 NC Wildlife Action Plan
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