Combination Of Reservoirs Research Articles

Risk evaluation of cyanobacteria-dominated algal blooms in a North Louisiana reservoir

Cyanobacteria blooms may produce toxins thatare harmful to invertebrates and fishinhabiting aquatic systems. The objectives ofthis risk evaluation were: (1) to investigatethe potential toxicity (i.e., adverse effectsof cyanobacteria on the survival, reproduction,and behavior) of Lyngbya-dominated algalblooms from a North Louisiana reservoir to Daphnia magna and Pimephales promelas;and (2) to develop mitigation strategies forthis cyanobacteria infestation using physicaland chemical methods. Survival and reproductionof D. magna populations significantlydecreased after exposure to reservoircyanobacteria collected in spring in comparisonwith populations of test organisms exposed toeither Chlorophyta species or a combination ofreservoir cyanobacteria and Chlorophytaspecies. In April 1998, reservoir cyanobacteriaalso elicited a significant avoidance reactionby juvenile P. promelas (20–30 d).However, cyanobacteria collected in August andDecember (1997) did not cause adverse effectsfor either D. magna or P. promelasin terms of survival, reproduction, orbehavior. A physical control method, loweringthe water level of the reservoir (i.e.,drawdown), was simulated in the laboratory for8, 20, and 35 d. After re-saturation of algalpopulations with nutrient enriched medium, theyrecovered to 132.9, 129.4, and 23.7% oforiginal chlorophyll a concentrations,respectively. Herbicide application resulted in>78% decrease in chlorophyll aconcentration of reservoir cyanobacteria by7-d after initial herbicide application. Todecrease risk(s) of Lyngbya-dominatedcyanobacteria and maintain seasonal control inthis reservoir, drawdown in conjunction withherbicide application or recurrent herbicideapplication is recommended prior to onset ofcyanobacteria proliferation.