Using flocculation and subsequent biomanipulation to control microcystis blooms: A laboratory study.

Area of Science:

• Environmental Science
• Aquatic Ecology
• Ecotoxicology

Background:

• Microcystis harmful algal blooms (HABs) pose significant ecological and environmental challenges due to their frequent occurrence and persistence.
• Chemical flocculation is a common method for HAB mitigation, but high dosages of flocculants like polyaluminum chloride (PAC) can harm aquatic ecosystems.
• There is a need for sustainable and ecologically safe methods to manage HABs.

Purpose of the Study:

• To investigate a novel approach combining reduced PAC dosage with Daphnia magna (D. magna) for effective and ecologically sound HAB removal.
• To assess the impact of this combined method on algal removal efficiency and the survival and proliferation of D. magna.
• To establish a sustainable strategy for mitigating Microcystis blooms.

Main Methods:

• Microcystis HABs were treated with varying dosages of PAC.
• The effects of PAC on D. magna mortality and algal removal were evaluated.
• D. magna were introduced after flocculation with a reduced PAC dosage (15 mg/l) to assess their grazing efficiency and impact on residual algae.

Main Results:

• A high PAC dosage (30 mg/l) achieved >95% algae removal but caused 90% D. magna mortality.
• A reduced PAC dosage (15 mg/l) achieved >90% algae removal and allowed D. magna to thrive, increasing their density by 40-fold and body size.
• The combined approach facilitated sustainable removal of HABs by enabling D. magna to graze on residual algae.

Conclusions:

• Combining a reduced PAC dosage with D. magna biomanipulation provides an effective and environmentally friendly strategy for HAB removal.
• This method mitigates risks associated with high flocculant dosages, promoting ecosystem health.
• The study demonstrates a viable approach for sustainable management of Microcystis blooms.