Phosphorus dynamics modeling and mass balance in an aquaponics system

Aquacultural effluents are rich in P, a growing concern worldwide for potential environmental pollution. Thus integrating aquaculture with agriculture, e.g. aquaponics, shows promise to enhance nutrient and water use efficiency and overall environmental sustainability. The present study was carried out to quantify a P flow, P mass balance, and evaluate P removal efficiency by hydroponic lettuce integrated with tilapia aquaculture. Also, a phosphorus dynamics simulation model was developed to be a decision support system for phosphorus management. 15 tilapia juveniles (20 g) and four 15-day-old lettuce seedlings comprised each aquaponics experimental unit (n = 3). At days 0, 7, 14, 21 and 28 after transplanting, water samples were taken from each aquaponics biofilter to determine the reactive and total concentration of phosphorus. The P dynamics model was validated by comparing predicted to observed values of dissolved P over time. The linear regression equations between predicted and measured values were compared with the 1:1 line for statistically significant differences (p < 0.05) in slope and intercept values. The adequacy of the model was determined by testing if intercept equals zero and slope equals one separately using the one sample Student t-test. Comparison of simulated and measured values of dissolved P dynamics showed a good fit around the 1:1 line with the slope (b = 1.005) and intercept values (a = 0.0189) being not statistically different (p > 0.05) from 1.0 and 0, respectively. The assimilation of P in the fish and plant components comprised 71.7% of the total P input, indicating high P utilization by the system. The P dynamics model predicted the behavior of dissolved phosphorus in aquaponics systems, which can be used to determine adequate fish:plant ratios, maximize P use efficiency and minimize waste. The overall high P utilization by fish and plants identified in this study showed that aquaponics is an excellent tool for recycling phosphorus while yielding a high-quality crop.