Phosphorus dynamics modeling and mass balance in an aquaponics system B.S. Cerozi ⁎, K. Fitzsimmons Department of Soil Water and Environmental Science, The University of Arizona, P.O. Box 210038, Tucson, AZ 85721-0038, United States abstract article info Article history: Received 21 January 2016 Received in revised form 23 January 2017 Accepted 30 January 2017 Available online xxxx Aquacultural effluents are rich in P, a growing concern worldwide for potential environmental pollution. Thus in- tegrating aquaculture with agriculture, e.g. aquaponics, shows promise to enhance nutrient and water use effi- ciency 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 manage- ment. 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 b 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 N 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 sys- tem. 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. © 2017 Published by Elsevier Ltd. Keywords: Phosphorus Nutrient dynamics modeling Mass balance Integrated agriculture-agriculture Aquaponics 1. Introduction With the prospects of an increasing world population and the neces- sity to raise food production, phosphorus (P) represents a critical nutri- ent to a growing agriculture industry. Phosphate rock has been the exclusively viable source of phosphorus in the manufacturing of phos- phate fertilizers (Morawicki, 2012). Mining and processing phosphate rock are highly energy intensive processes requiring energy worth N 70,000 BTU per ton of ore (U.S. DOE, 2002) that potentially result in a broad range of adverse environmental effects. P fertilizer supplies will be affected by rising feedstock prices, and by challenges to access to more fossil fuel and phosphate rock reserves. In the future, the extrac- tion of low-grade phosphate ores will necessitate additional beneficia- tion processes, which might increase production costs (Heffer and Prud'homme, 2013) and greenhouse gasses emissions (Bojarski et al., 2008). The use of agricultural wastes as an alternative to the overdepen- dence of synthetic fertilizer production for a worldwide supply of P shows promise and is being re-examined (Cordell et al., 2009). Aquacul- tural effluents are known to be rich in dissolved and suspended solids that contain mainly phosphorus (P) and nitrogen (N), generated from fish excretion, feces and uneaten feed (Summerfelt and Clayton, 2003). These P wastes released by aquaculture operations are a growing concern worldwide due to their potential of environmental pollution (Chowdhury et al., 2013). Hence, integrating aquaculture with existing irrigated farming systems has the potential to enhance productivity, water use efficiency and overall environmental sustainability (Ingram et al., 2000), reduce use of pesticides and chemical fertilizers (Rejesus et al., 2013), promote ecological and social benefits (Halwart et al., 2003), and maximize farm production without increasing water con- sumption (McIntosh and Fitzsimmons, 2003). Aquaponics, an example of integrated aquaculture-agriculture, is the combination of recirculating aquaculture and soilless vegetable produc- tion in a closed-loop system. Aquaponics has received considerable at- tention due to system's capability to raise fish at high density, sustain adequate water quality, minimize water exchange, and produce a Agricultural Systems 153 (2017) 94–100 ⁎ Corresponding author. E-mail address: bcerozi@email.arizona.edu (B.S. Cerozi). http://dx.doi.org/10.1016/j.agsy.2017.01.020 0308-521X/© 2017 Published by Elsevier Ltd. Contents lists available at ScienceDirect Agricultural Systems journal homepage: www.elsevier.com/locate/agsy