Laserfiche WebLink
<br />~\ <br />;; <br /> <br />marsh ecosystem processes makes it essential to conduct studies of the influence of flood flows <br />on riparian and marsh communities and bacl...water ecology in close concert with <br />geomorphological studies. Coordination of geomorphological and ecological studies will include <br />both timing and location. <br /> <br />Wetland and Riparian Vegetation <br /> <br />Obiectives <br />The objectives of this part of the study are to monitor and. where possible, model the <br />impacts of planned flooding and changes in geomorphology on wetland and riparian vegetation <br />area, patch distribution, cover and composition, and processes of vegetation loss and recovery. <br />We anticipate a planned high-flow experimental release from Glen Canyon Dam will have <br />predictable, minor and short-term impacts on the existing dynamic condition of wetland and <br />riparian vegetation. Loss of wetland and riparian vegetation to scour will be a function of stage, <br />geomorphic location, and life-history strategy (specifically root architecture). Site stability will <br />be positively correlated with above-grolDld cover, stem density and root density, negatively <br />correlated with velocity, and will be non-linearly, negatively correlated with the size of reach <br />deposited sediment in various geomorphic settings. Recovery of vegetation will be a function of <br />life history strategy (vegetative versus seed-based reproduction), stage and geomorphic location. <br />We expect Colorado River streamside vegetation will rapidly redevelop following the <br />experimental flood. ' <br /> <br />J nstification <br />Flooding is an essential. ubiquitous and natmal process in fluvial ecosytems. As a form <br />of disturbance, flooding alte1'S landforms by scouring and reworking sediments, and killing or <br />damaging established riparian vegetation (White 1979, Sousa 1984, Pickett and White 1985, <br />Stevens and Waring 1985). These changes exert direct and indirect impacts on fluvial . <br />sediments, processes, and aquatic and wetland/riparian assemblages (ponamperuma 1984, <br />Kozlowski 1984, Pens 1984, Stevens and Waring 1985, Gore and Pens 1989, Schmidt and Graf <br />1990). Overall, flooding effects on riparian plant assemblages are predicted to increase with <br />increased flooding intensity (sensu Connell 1978), and therefore with the magnitude of <br />discharge. <br />The diversity of sessile organisms, such as wetland and riparian plant species, are <br />influenced by interactions between disturbance (Connell 1978) and productivity gradients that <br />interact with life-history parameters (Huston 1979, 1994). Stevens and Waring (1985) and <br />Stevens (1989) examined flood-related distribution of riparian vegetation in the Colorado River <br />and its tnbutaries in Grand Canyon. From studies of the 1983 high flows, they showed that <br />flood-related mortality differed markedly between riparian plant species on the basis of <br />architecture and growth strategies. Mortality of shallow-rooted taxa in fine-grained <br />environments was attributed to scour, while deeply rooted taxa in debris fan environments <br />perished through drowning. Clonal woody species suffered extensive rarnet mortality, but <br />considerably less genet loss, as compared to all oth~r wetland and riparian species. <br />Productivity is strongly correlated with moisture availability in arid-land riparian <br /> <br />14 <br />