Managing the Invasive Cyanobacterium Lyngbya wollei in a Southeastern USA Reservoir: Evaluation of a Multi-year Treatment Program

Lyngbya wollei is a filamentous cyanobacterium that causes numerous adverse impacts in reservoirs and lakes, such as toxin production, harboring fecal bacteria, devaluing property, impeding navigation/recreation, and degrading wildlife habitat. This study assessed a chemical treatment program in a Southeastern USA reservoir using a chelated copper formulation (Captain (R) XTR) in combination with diquat dibromide (Tribune (R)) over 2 years. The treatment program consisted of multiple applications during the summer and fall months. Overall, biomass decreased significantly (alpha = 0.05) in the two treated coves, by 97 and 80%, whereas L. wollei increased significantly (alpha = 0.05) in the untreated reference cove, by 25,127%. During the study, the quantity of algaecide applied was decreased in one of the treatment coves to adjust for the reduction in L. wollei biomass, as well as reduction in treated area, as part of an adaptive management strategy. The measured exposure demonstrated the residence time of the copper algaecide was short, with most of the copper dissipating in hours, which was attributed to sorption to L. wollei, sediments, and dilution. The biomass monitoring procedure, used transects spaced in 150 m intervals and sampled algae at 0-2 m, 5-7 m, and 10-14 m distances from shore, was effective at discerning changes in L. wollei biomass in the treated and untreated coves. This study indicated that the treatment program was effective for reducing L. wollei biomass and demonstrated the utility of the surveying technique to implement adaptive management of this filamentous cyanobacterium.