Whether water exchange is an effective solution for emergency mitigation of algae bloom

Addressing harmful algal blooms(HABs) through water exchange remains an unresolved challenge, and there is no clear consensus on the optimal approach for effectively restraining the proliferation of algal cells. This study aimed to investigate the impact of water quality, exchange rate, and timing on the growth of algal cells in the Niuweiling Reservoir, with the aim of unveiling an effective water exchange strategy for mitigating HABs in natural water systems. The results indicate that, the growth rate of algal cells can be reduced to 38.3 mu g center dot L-1 center dot d-1, with Class III water exchange, in contrast to an increase to 47.4 mu g center dot L-1 center dot d-1 observed with Class V water exchange. This suggests that HABs can be mitigated by implementing clean water exchange, although the accumulation of nutrients from poor-quality water may still trigger HABs. Additionally, initiating water exchange with clean water at a high exchange rate during the early stages was more effective in mitigating HABs. Conversely, a high exchange rate and early exchange with poor-quality water increases the risk of HABs. To elucidate the mechanism underlying HAB mitigation via water exchange, we present an illustration of the impact of water exchange from an upper river or reservoir on algal cell growth. This study provides a theoretical foundation for devising water-exchange strategies to combat HABs in natural water bodies.