The partitioned aquaculture system: impact of design and environmental parameters on algal productivity and photosynthetic oxygen production

Abstract

Fish production in pond culture systems is often limited by the dissolved oxygen (DO) concentration. Algal productivity greatly impacts the DO concentration but is difficult to control in traditional pond systems. The partitioned aquaculture system (PAS) was designed to increase fish production in pond systems by increasing net oxygen production through management of algal productivity and biomass concentration. This initial research was conducted to establish algal productivity and biomass levels in the PAS as a function of algal cell retention time, nutrient addition rate, water depth, and mixing and to characterize the photosynthetic oxygen production rate as a function of solar radiation. In order to focus on algal productivity, an inorganically fertilized PAS without fish was operated for this study. Algal productivity in the PAS was greater for the cell retention time of 1.2 days than 2.5 days, greater for external inorganic carbon addition rates of 0.6 and 1.2 mmol/l per day than for 0 mmol/l per day addition rate, greater for the water depth of 34 cm than 66 cm, and greater for the water velocity of 12.5 cm/s than 3.1 and 6.2 cm/s. Algal productivity rates of 5–10 g C/m 2 per day were achieved. Algal culture composition was impacted by inorganic carbon addition. Over a 2-year period, the algal culture was composed primarily of blue–green algae (Cyanophyta) when no external inorganic carbon was added, and green algae (Chlorophyta) at external inorganic carbon addition rates of 0.6 and 1.2 mmol/l per day. The maximum gross photosynthetic oxygen production rate at 20°C was found to be 0.096 mg O 2/mg TSS per hour for predominantly blue–green algal cultures and 0.14 mg O 2/mg TSS per hour for green algal cultures. Corresponding maximum algal specific growth rates, calculated using a literature value for algal cell composition, were 0.077 and 0.12/h for blue–green and green algae, respectively.