The effect of ultrasound for algae growth control on zooplankton

Abstract

The use of ultrasound (US) to control algal growth in natural water bodies raises concern about the undesirable effects of US on non-target organisms. In this study a lab-scale experiment was performed to evaluate the effects of low-power US to counteract algal growth on adult and juvenile Daphnia magna. The 48-hour experiment was conducted in a 200 L glass aquarium with three fish nets, each filled with five D. magna. Each net was inspected for immobilized D. magna on different times during ultrasonication; additionally, basic physical-chemical parameters were measured. The results showed that tested low-power US device had no acute effect on the mobility of adult or juvenile D. magna, since after 48 h of ultrasonication 87% and 82% of adult and juvenile organisms remained mobile, with the same or higher percentage of mobile D. magna in the control groups. Additionally, no statistically significant effects were noticed on the measured physico-chemical parameters. However, when applied for algae control in field conditions, US is in operation constantly or at least for a long period of time (several weeks or months); therefore, the effect of long-term exposure to ultrasonication on zooplankton should be tested to ensure that US devices are safe for zooplankton.