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Distribution and Management of Invasive Aquatic Plants in the Ross Barnett Reservoir, MS

Cox, M. C., Wersal, R. M., & Madsen, J. D. (2009). Distribution and Management of Invasive Aquatic Plants in the Ross Barnett Reservoir, MS. Aquatic Plant Management Society Annual Conference. Milwaukee, WI.

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Invasive Aquatic Plant Distribution and Management in the Ross Barnett Reservoir Michael C. Cox, Ryan M. Wersal, and John D. Madsen; GeoResouces Institute, Mississippi State University, Box 9652 Mississippi State, MS 39762-9652, Encompassing 13,400 hectares (33,000 acres) just north of Jackson, Mississippi, the Ross Barnett Reservoir is the largest man-made impoundment in Mississippi. Maintained by the Pearl River Valley Water Supply District (PRVWSD), the reservoir is the primary potable water supply for the City of Jackson. Three invasive aquatic plant species that have caused major problems are waterhyacinth (Eichhornia crassipes (Mart.) Solms.), alligatorweed (Alternanthera philoxeroides (Mart.) Griseb.), and hydrilla (Hydrilla verticillata L.F. Royle). Waterhyacinth and alligatorweed have been under active management for almost a decade, primarily through the use of systemic herbicides, resulting in a significant decrease in their occurrence in the Ross Barnett Reservoir. Hydrilla was first observed in the Reservoir in 2005 and has since been aggressively managed with the systemic herbicide fluridone and the contact herbicide endothall. As a result of the 2005 survey, it was estimated that hydrilla could encompass over 2,800 hectares (7,000 acres) of the Ross Barnett Reservoir if control techniques and continued assessments were not implemented. The PRVWSD has begun to develop a long term strategic management plan to address the growth and spread of these species. To ensure that these management techniques are successful, surveys of the littoral zone plant community have been conducted since 2005 to monitor and record changes in the occurrence of plant species as well as to assess management techniques. There a total of 26 aquatic or riparian species. The native plant American lotus (Nelumbo lutea Willd.) was the most observed species, increasing in occurrence from 17% to 25% from 2005 to 2008 respectively. All non-native species, alligatorweed, waterhyacinth, hydrilla, parrotfeather (Myriophyllum aquaticum (Vell.) Verdc.), and brittle naiad (Najas minor All.) had an occurrence below 10% across all years. Alligatorweed was the most commonly observed invasive species. Reductions in the presence of alligatorweed and waterhyacinth in the Ross Barnett Reservoir can be attributed to the aggressive management of these species. Hydrilla has been reduced to less than 100 acres, indicating that fluridone treatments were generally successful. However, scattered plants and possible overwintering by root crowns suggest rigorous surveying and monitoring is needed to ensure successful management of hydrilla.

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