Date of Award
Doctor of Philosophy (PhD)
Division of Agriculture (SAFES)
Fish production in pond culture systems is often limited by the dissolved oxygen (DO) concentration. Algal biomass and productivity, which greatly impact the DO concentration, are difficult to control in traditional pond systems. The Partitioned Aquaculture System (PAS) was designed to increase fish production by managing algal productivity and DO through control of algal cell retention time, water depth, and mixing. The objectives of this study were 1) to determine impact of culture conditions on algal productivity, 2) develop a model of algal productivity and diel DO levels, and 3) to predict the maximum fish production attainable with the PAS.
For this study, algal cell retention time was controlled through continuous discharge of the culture. Algal productivity was calculated from algal biomass (measured with 0.45 µm filters), retention time and water depth. Oxygen production and respiration rates were measured using in-pond incubations.
Algal species composition was dependent on the inorganic carbon content of the culture water. The algal culture was comprised primarily of blue-green algae (Cyanophyta) at 0.7 mmol/1/d inorganic carbon addition rate, and green algae (Chlorophyta) at 1.1 and 1.8 mmol/1/d addition rates.
Algal productivity was 1.2 times greater for the 1.1 and 1.8 rates than for the 0.7 mmol/1/d inorganic carbon addition rate; 1.2 times greater for the 0.34 m than the 0.66 m water depth; 1.5 times greater for the 0.125 m/s than for the 0.0313 and 0.0625 m/s water velocity; and 1.3 times greater for the 1.2 day than the 2.5 day retention time.
Maximum oxygen production rates of 0.11 and 0.12 mg Oifmg TSS/hr were achieved for blue-green and green algal cultures, respectively. Maximum DO concentrations of 25 -30 mg/1 were routinely observed.
The algal productivity and DO model constructed for the PAS incorporates an inhibitory light model for light-limited algal growth and the Monod model for carbon-and nitrogen-limited growth. Steady state and dynamic simulations of the DO profile as a function of the design and environmental conditions closely matched the observed values. Maximum fish production of 10,000 kg/ha is predicted for light-limited cultures ~n the PAS operated at 0.0313 m/s water velocity, 20 hour retention time and 0.6 m water depth.
Drapcho, Caye M., "Modeling of Algal Productivity and Diel Oxygen Profiles in the Partitioned Aquaculture System" (1993). All Dissertations. 3455.