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Invasive species, Aquatic ecology -- Research -- United States, Environmental monitoring -- Pacific Northwest


A survey of aquatic plants in a selected Corps of Engineers reservoirs in Oregon was conducted. Cottage Grove, Dorena, Fern Ridge, Dexter and Willow Creek Reservoirs contained abundant aquatic plants. Potamogeton pectinatus and Potamogeton epihydrous were the most common native plant species. Myriophyllum aquaticum and Potamogeton crispus were the most widespread nonnative plants. Species richness in the reservoirs was correlated with trophic status and basin morphology. Shallow reservoirs that included extensive areas of nutrient-rich sediments that were historic flood plain soils supported the greatest biomass and number of species. Mesotrophic reservoirs had lower species diversity. Oligotrophic reservoirs with steep basin morphology, nutrient-poor sediments, and large water level fluctuation did not support aquatic vascular plant populations.

An aquatic plant management program should be developed for the reservoirs. The program should focus on preventing introduction and spread of invasive aquatic plants and on rapid response procedures for new infestations. Those reservoirs that currently support aquatic macrophyte communities may be most susceptible to invasion and rapid spread of new introductions, however, even reservoirs that are currently free of aquatic plants may be invaded.

Early detection is critical to effective implementation of rapid response procedures for invasive aquatic plant control. Annual survey of the most productive reservoirs is recommended to document introduction of new species. Plant community composition changes during the growing season, and multiple surveys during the growing season are preferred over one-time visits.

Management of established populations of invasive species in the reservoirs will be difficult. Where invasive plant abundance is limited in area and number management activities may be implemented to slow dispersal and perhaps eradicate the plants. Integrated pest management procedures should be followed to ensure effective and economical aquatic plant control.


Report was produced for US Army Corps of Engineers Portland District Office

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