Evaluation of Invasive Species Management Strategies and Technologies for Protection of Drawdown Zones in Annually Drafted or Drought-Affected Reservoirs
Exposed drawdown zones of numerous reservoirs throughout the Western United States are adversely impacted by encroachment and establishment of invasive plant species during periods of seasonal or annual drafting or recedence during extended drought, particularly salt cedar (_Tamarix spp._).
What are the best management strategies and technologies for control of invasive species in light of:
* Prescribed reservoir hydrographic protocols
* Invasive species colonization and infestation dynamics
* Exposed soils, geologic substrates and site predisposition to invasion
* Semi-aquatic environmental constraints on use of weed control measures
This proposal addresses activities to develop partnerships and increase involvement of water users and suppliers to:
* Expedite application of research on drawdown zone stabilization
* Coordinate research across agency, commercial, and private stakeholders in cost-effective pursuit of site protection during extended drawdown events
Need and Benefit
Reclamation operates and maintains numerous multi-purpose reservoirs throughout the Southwestern United States. Many of these reservoirs are currently experiencing adverse environmental and ecological impacts to shoreline drawdown zones as a result of extended drought progressively and perennially lowering water levels. Exposure of bare shoreline soils below high-water line (BHWL) during these drawdown events greatly increases frequency and severity of weed infestation problems, particularly from aggressive, perennial species such as salt cedar (_Tamarix spp._), Canada thistle (_Cirsium arvense_), and knapweeds (_Centaurea spp._). Prescribed annual or seasonal drafting protocols for hydroelectric generation, flood storage, maintenance of downstream fisheries minimum flows or conservation pools, and other purposes also exacerbate these problems.
Invasive species growth on exposed shorelines poses severe risk for new or increased dissemination of weed seed and other reproductive propagules to surrounding landscapes and ecosystems, including ecologically sensitive riparian sites along reservoir tributaries. Lacustrine fisheries habitat within littoral (shallow) zones is also adversely impacted by erosion loss or wave-induced diffusion of shoreline substrate fines, thereby favoring or shifting plant establishment and composition during drawdown events toward aggressive annual (ruderal) or perennial invasive species with germination and dormancy strategies highly adapted to such altered soil environments. Subsequent increase of dead, decomposing weed biomass contributes to aquatic eutrophication in littoral shoreline habitat.
Effective strategies for addressing these invasive species management concerns have not been developed or refined to-date, in part because of the perceived ephemeral nature of reservoir drawdown events. In light of longer-term impacts resulting from recent extended drought and/or longer drafting periods, these strategies are particularly needed in terms of:
* Scientific soundness of treatment approache
* Correlation to reservoir hydrologic dynamics (i.e., treatment windows, treatment residuals in soils, etc.)
* Development of rapid-response shoreline revegetation protocols for use during drawdown events, utilizing inundation-tolerant desirable species to stabilize the site and minimize weed colonization
* Assessment of predisposition of certain reservoir locations or soils to weed infestation in relation to regional weed population pressure, topographically influenced microclimate, and transportation vectors. Evaluation of herbicide chemistry in relation to physical leaching or retention properties in exposed shoreline soils altered by long-term inundation and wave action has not been studied. Similarly, uncertainty as to site classification in reservoir drawdown zones by State agencies responsible for implementation and monitoring of aquatic versus nonaquatic labeled application of herbicides also suggests the need for research that will not only determine best management practices in light of environmental constraints but also refine and codify permissible herbicide products within these zones. Involvement and commitment of resources from these State agencies with other agencies, cooperators, and research collaborators to address this lack of appropriate strategies and technologies is a prime thrust of this Science and Technology (S&T) Program research project.
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