Sound field and water quality in reservoirs using ultrasound as a management strategy to control cyanobacteria blooms

Ultrasound is an emerging technology for managing cyanobacteria harmful algal blooms (cHABs). This study characterized the sound field and water quality spatially at five field sites. Based on data from multiple sampling locations within a reservoir, the ultrasound signal attenuates exponentially with distance and the attenuation coefficient in the reservoirs is about ten times greater than pure water. The sound attenuation coefficients did not vary with frequency bandwidth or with turbidity, phycocyanin, temperature, or wind speed. Only chlorophyll-a had a positive relationship with the attenuation coefficient in the low frequency bandwidth. No statistically significant variation in the sound level was found when varying the measurement depth and ultrasound source depth, indicating that the sound field is even at the measured depths and ultrasound transducer configurations. Water quality paired with sound levels and compared to control reservoirs without ultrasound did not reveal significant differences in any of the reservoirs tested, suggesting there is no effect of ultrasound in the evaluated reservoirs. This field evaluation of ultrasound confirmed previous work indicating that cavitation, gas vesicle collapse, and critical structural resonance are unlikely to affect cHABs at the sound pressures and frequencies measured in the field.