The efficacy of carbon dioxide (CO2) to reduce biofouling by quagga mussels (Dreissena rostriformis bugensis) 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 < 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 > 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.
Keywords: Aquatic invasive species; carbonic acid; dreissenid; veliger settlement.