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<br />60 <br /> <br />than in nearby shaded (28 C) areas (Karr and Gorman 1975). Burns (1.972) <br />observed a water temperature incre8se of 20 F following riparian canopy <br />removal during road construction. <br />Species with lower temperature optimUlns may be unable to conlplete life <br />cycle requirements when exposed to increased temperatures. Community <br />structure may change with resident species being replaced by species less <br />desirable but more tolerant of increased temperatures. <br /> <br />Riparian Zones Trap Sediment <br /> <br />Plant nutrients such as phosphorus and nitrogen lnay attach to sediment <br />particles during surface runoff from agricultural wat,ersheds. Therefore, <br />riparian zone vegetation forms a type of entrapment buffer ~one and <br />filtering system for sediment and debris be,tween the terrestrial and <br />aquatic zones. The extent of entrapment depends on sE~veral variables such <br />as runoff ...ater depth relative to vegetation height, :Length and slope of <br />vegetated area, vegetation characteristics, size and distribution of <br />incoming sediments, application rate of water, and slelpe distance between <br />sediment origin and vegetation (Karr and Schlosser 19i'8). Up to 54 percent <br />reduction in stream sediment loads have been reported when overland water <br />flow depths are much less than grass height (Mannering: and Johnsoll 1974). <br /> <br />Several workers have reported that (1) efficiency of reducinl~ sediment <br />bads varies >rith the type of vegetlition with efficient species rE~moving 50 <br />percent of the initial sediment, (2) an inverse relationship exists between <br />length of vegetation required to re~ove a given percentage of sediment and <br />the particle size, (3) the rate of sediment deposition in the vegetation is <br />constant over a range of lower slopes, but depositioll declines after a <br />critical slope is reached, and (4) ...hen vegetation is clipped or flow depth <br />is great enough to submerge the vegetation, "filtering" efficiency <br />ultimately declines to zero (Taylor 1947, W:llson 1967, Trollner et at. <br />1973, Trollner et al. 1975, Trollner and Kayo 1976). <br /> <br />Riparian Zone Vegetation <br /> <br />Location, structural components and spE~cific functions of the <br />components of riparian vegetation are summarized and illustrated in Table 1 <br />(Meehan et al. 1977). Although this structural and functional summary was <br />proposed for a coniferous forest stream ecos:ystem in the Pacific northwest <br />it generally applies to other geographical areas as weH. <br /> <br />functionally, above Iround and above channel ripaz:ian vegetation: <br />(1) forlll8 a canopy of'sb8de in lower order Stta.IDS that: controls water <br />temperature and lialts in.tren primary production, (2)' 18 . 80urce of <br />large and fine plant detritus~ and (3) is a source of t:errestrlal Insect <br />'life. Large debris (l..~'ii:ee"'lalls, branches) derive~1 fro. riparian <br />vegetation that enters' till!' aquatic zone: (1) controls routing of ..ater and <br />sediment, (2) shapes habitat such as pools and riffles, (3) provides <br />habitat cover (shelter), and (4) forms substnte for biological ac1:ivity. <br />',\Roots located in the riparian zone: (1) increase stream-bank stability, <br /> <br />\ <br />,~- <br />_...~.- <br />