Recent vegetation changes and their relationship to beach soil dynamics along the Colorado River through Grand Canyon

Scala, John Richard, Environmental Sciences, University of Virginia
Howard, Alan, AS-Environmental Sciences (ENVS), University of Virginia
Mills, Aaron, AS-Environmental Sciences (ENVS), University of Virginia
Kochel, R. Craig, AS-Environmental Sciences (ENVS), University of Virginia

The controlled releases emanating from Glen Canyon Dam to the Colorado River in Grand Canyon have permitted the establishment of spatially diversified plant populations on fluvial sediments. Reworked deposits modified by daily flow fluctuations display the most marked recent increases in vegetation density and species diversity. Intermediate terrace deposits primarily influenced by eolian transport also exhibit recent colonization, although not as pronounced. Pre-dam high terraces have remained relatively unchanged during the post-dam period with little alteration in community composition.
Laboratory analyses of beach soils located within the three zones suggest possible physical and chemical "preferences" by surface vegetation. Sandbar willow appears restricted to moist, sandy, near shore environments. Pure stands of arrowweed are generally found on coarse grained, macro-nutrient poor eolian sediments. Saltcedar is somewhat ubiquitous in distribution, however, it develops into dense thickets on soils with a loamy texture and a relatively high base cation content. Pre-dam high terrace deposits dominated by mesquite are the oldest in the canyon, exclusively fine grained and generally rich in base cations.
The sedimentological-vegetational interaction resembles a positive feedback relationship. The establishment of seedlings and subsequent growth aids deposition and stabilization of fluvial sediments which in turn augments further riparian colonization.
A future assessment of vegetation changes and sediment dynamics along the Colorado River corridor of the Grand Canyon is now entirely different from what was thought six months ago. The unparalleled post-dam releases during the summer of 1983 will undoubtedly redistribute sediments and scour riparian communities. It will be months before the severity of this impact can be assessed, however, the next few years will likely reveal rapid colonization of scoured fluvial deposits and the reestablishment of a dense and diverse riparian community.

MS (Master of Science)
Plants -- Effect of water levels on -- Arizona -- Grand Canyon

Imperfect: leaves 8 and 57 wanting.

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