Assessing the Aquatic Plant Community within the Ross Barnett Reservoir, Mississippi

Alligatorweed, waterhyacinth, and hydrilla are three nonnative aquatic species of concern in the Ross Barnett Reservoir near Jackson, MS. Point-intercept surveys were conducted on the reservoir from 2005 to 2010 to monitor native and nonnative species' distributions and assess herbicide treatment efficacy across the reservoir. Foliar applications of 2,4-D, glyphosate, imazapyr, and diquat were made during summer months for emergent and free-floating vegetation, whereas submersed applications of liquid copper and granular fluridone were applied in spring and late summer for subsurface hydrilla populations. American lotus is the native species that has been observed the most throughout the survey years, with occurrence frequencies averaging between 17 and 27%. Alligatorweed populations significantly decreased from 21% in 2005 to 4% in 2006; however, they consistently increased in the next 4 yr to 12% occurrence in 2010. Waterhyacinth occurrence has remained relatively constant over the study period, averaging below 10% occurrence. Hydrilla was discovered in the reservoir in late 2005 and has remained below 2% in frequency of occurrence since 2006. Suppression of these nonnative species has been attributed to rigorous monitoring and herbicide applications conducted on the reservoir since 2005. A logistic regression model indicated that as native species richness increased, the likelihood of a nonnative species occurring also increased.Nomenclature: Alligatorweed, Alternanthera philoxeroides (Mart.) Griseb., American lotus, Nelumbo lutea Willd., hydrilla, Hydrilla verticillata (L. f.) Royle, waterhyacinth, Eichhornia crassipes (Mart.) Solms.Management Implications: This research was conducted over a 6-yr time span to assess long-term management techniques for tracking the distribution and monitoring the control of several invasive aquatic plant species. In addition, this research was designed to determine the impact on the composition of the native plant community within this reservoir. A point-intercept survey of the entire Ross Barnett Reservoir was conducted each year using point locations at 300-m intervals within a grid system established by geographic information system (GIS) across the reservoir. Each year (2005 to 2010), these locations were surveyed for all plant species present. Aquatic herbicides were the primary method used for nonnative plant management in the reservoir over the previous 6 yr. By comparing how often each plant species occurred over consecutive years, we determined how effective our management program was. A logistic model was also utilized to decipher the effects of native species richness on the likelihood of nonnative species invasion. This model showed that a greater native species richness favored nonnative species establishment. We concluded that our herbicide applications were effective in reducing nonnative plant coverage; however, source plant populations upstream of the reservoir were likely supplying propagules capable of producing future populations throughout the reservoir. Employing an Early Detection and Rapid Response program based on results gathered from the logistics model could significantly reduce nonnative plant establishment by defining locations that are more favorable or susceptible to invasion, based on native species richness at that particular location. Integrating a prevention program in addition to effective postestablishment practices such as herbicide applications is the most effective way to reduce invasive plant establishment and spread.