Water Quality of the Ozark Plateaus, Arkansas, Kansas, Missouri, and Oklahoma, 1992-95
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Habitat characteristics can affect biological communities in many different ways. For example, trees along streambanks provide shade, erosion protection, and leaf litter to a stream. These factors often affect the density and diversity of fish (p. 16-17), aquatic insects, and algae.
Several factors can affect aquatic habitats, which then affect biological communities. Many habitat characteristics appeared to be influenced more by basin size than by land use.
Physiography, geology, basin size, and land use are among the factors that can affect aquatic habitats. Most habitat characteristics appeared to be more influenced by basin size than by land use (Femmer, 1997). Sites with larger basins tend to be wider, deeper, more sinuous streams with greater water velocity and larger canopy angles. Sites with smaller basins tend to have steeper basin and stream gradients.
Small streams in agricultural areas generally have fewer trees and other woody plants in the riparian zone than do small streams in forested areas. This results in more sunlight reaching the streams in the agricultural areas. More sunlight and the higher nutrient levels probably result in faster growing attached algae in these streams.
Cleared pastureland commonly extends to (or nearly to) streambanks in agricultural areas, resulting in narrow or absent riparian vegetation zones. Small streams in agricultural basins generally had lower mean woody-plant densities than small streams in forested basins (Femmer, 1997). Small streams in agricultural basins also generally were more open to sunlight because of larger canopy angles than small streams in forested basins. More sunlight and higher nutrient levels (p. 6) in streams in agricultural areas probably result in faster growing attached algae in these streams.
Compared to smaller streams, larger streams are wider and have gravel bars extending farther from the edge of water to the streambanks. Therefore, larger streams in forested and agricultural basins tend to be more separated from their riparian zones.
Small streams in agricultural areas commonly have a narrow (or absent) band of riparian trees.
Small streams in forested areas generally have a wider band of riparian trees. Here an overhead canopy shades much of the stream.
Larger streams often are more open to sunlight--either because of wide gravel bars or simply because the streams are wider.
Habitat characteristics that seem to differ between agricultural and forested sites (Femmer, 1997), but are not the result of agricultural activities, include water velocity, sideslope gradient, and flood-plain width. Some characteristics that may be influenced by land use are canopy angle (discussed above), channel width, and channel sinuosity. Mean channel width and mean channel sinuosity both tended to be greater at agricultural sites.
A study (Brown and Lyttle, 1992) of several instream (between the banks of streams) gravel-mining sites on streams in the Arkansas part of the Ozark Plateaus indicated that stream channels were altered as pools became shallower and larger and riffles were less frequent downstream from the mining sites. Game-fish biomass and abundance of game fish and silt-sensitive fish were lower at and downstream from these sites than at upstream reference locations. On the basis of Arkansas Game and Fish Commission data, Arkansas State University (1996) reported similar differences in fish communities in gravel mining areas of the Spring River in northeastern Arkansas. Brown and Lyttle (1992) also reported differences between benthic invertebrate (animals such as bottom-dwelling insects) communities at mining sites and communities at reference locations. Kanehl and Lyons (1992) reported similar physical and biological effects in other streams of the United States.
The severity of the effects of gravel mining on streams probably is dependent on several factors. These factors include hydrology, channel shape, and gravel removal methods and related activities.
Petersen, J.C., Adamski, J.C., Bell, Davis, J.V., Femmer, S.R., Freiwald, D.A., and Joseph, R.L., 1998, U.S. Geological Survey Circular 1158, on line at < URL:http://water.usgs.gov/pubs/circ1158>, updated April 3, 1998
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Last modified: 4/3/98