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Show surface flows in streams where it dominates the bank vegetation. In addition, litter from tamarisk is known to hinder competition from other plant species by causing an accumulation of salts at the soil surface. These impacts could be significant if the plant invades the smaller canyon riparian zones. The effect of tamarisk is also a subject needing further study at Glen Canyon. Tamarisk along the lakeshore is still becoming established; it has not yet formed stable ecosystems. These communities will probably attain some importance as insect and wildlife ( particularly bird) habitat in the future, and already offer habitat for fish during high water. Tamarisk transpires great quantities of water into the atmosphere; significant water losses from the lake could occur as the vegetation matures, and these would be reflected in either lower releases from the dam or lower storage. At some lakes in the Southwest tamarisk has been actively controlled by herbicides or anti- transpirants as a means of " water salvage" on an experimental basis. This has not yet been suggested at Glen Canyon, but it could become an issue in future years. III. H. 2. Management alternatives. Alternative A: No action At present, no management programs are aimed specifically at riparian communities in the NRA. Impacts to these sensitive ecosystems are considered in environmental compliance programs under the wetlands protection requirement and other guidelines, and riparian zone protection is incorporated into park management programs for minerals and grazing. However, the key resource to protect in preserving riparian communities is water. Information is needed on the hydrodynamics of riparian zones in the park to diagnose threats. Under Alternative A this lack of information would continue. Alternative B: Articulate a management policy to protect riparian resources ( preferred alternative) Under this alternative park management would adopt a policy giving high priority to inventorying, quantifying, and protecting riparian water sources. This policy would pertain to natural communities and natural waters of the NRA and not to the relationship between the reservoir and tamarisk, an exotic plant. Such action would provide guidance for protecting riparian waters from depletion by competing uses such as grazing and mineral leasing. The policy would further require the quantification and maintenance of minimum instream flows before such competing uses are approved, and would require the prevention of water quality degradation in riparian areas. This policy would be consistent with the conservation of existing water rights for NRA purposes and with existing regulations controlling water quality degradation. 41 |
