Carbon dioxide infusion reduces invasive mussel biofouling (quagga mussel; <i>Dreissena rostriformis bugensis</i>) in raw water systems

The efficacy of carbon dioxide (CO₂) to reduce biofouling by quagga mussels (<i>Dreissena rostriformis bugensis</i>) in raw water systems was investigated. Experiments were conducted in a mobile laboratory located at Bureau of Reclamation Davis Dam Hydropower Facility and supplied with raw water from Lake Mohave, a reservoir of the Colorado River, USA. Incoming water was split between five chambers, each infused with CO₂ at a different rate. Raw reservoir water containing quagga larvae (veligers) was mixed with CO₂ chamber outflows and delivered to tanks containing settlement plates. Two experiments were conducted. Experiment 1 tested continuous infusion at target concentrations of 30, 45, 60, 75, and 100 mg L⁻¹ dCO₂ (dissolved CO₂). Experiment 2 evaluated intermittent infusion schedules: 24 h on/off with 50, 75, and 100 mg L⁻¹ dCO₂ and 24 h once/week with 100 mg L⁻¹ dCO₂. In Experiment 1, the percent settlement decreased with mean CO₂ concentration, ranging from 5.0% to &lt; 0.1% in 28.7 and 92.2 mg L⁻¹ dCO₂, respectively. In Experiment 2, the efficacy of 24 h on/off at dCO₂ &gt; 72.2 mg L⁻¹ was similar to continuous treatment. The least effective treatment was 24 h once weekly at 95 mg L⁻¹ dCO₂. These results demonstrate that CO₂ treatment may reduce mussel biofouling in raw water systems.