Marine shrimp recirculating aquaculture systems are densely stocked to ensure they are economically feasible. With intensive feed inputs and repeated water use, contaminants such as nitrogen, phosphorus, and heavy metals, including copper, chromium, cadmium, iron, manganese, nickel, zinc, and lead, can a ccumulate. Such issues have been shown to negatively affect shrimp production. The purpose of this two-month-long decoupled aquaponics trial was to evaluate Spartina alterniflora production and water remediation effectiveness in reused, brackish shrimp water.
Four plants were floated on rafts in each of 24, aerated buckets (18.9-L ) that were randomly assigned to one of six treatments (four replicates per treatment). T he 2 x 3 factorial design consisted of two sources of water ( clean, artificial saltwater [SW] or reused water [RW] from a 19-m3 biofloc raceway) and three levels of fertilizer application (no fertilizer [NF] , fertilizer [F] , and fertilizer plus nitrate [FN] . A standard hydroponics fertilizer was applied in the F and FN treatments, and s odium nitrate was used in the FN treatments to examine what effect excess nitrate may have on plants . T emperature, pH, salinity, and DO data were collected 3 times per week; dissolved NO3, NO2, NH3 PO3 , and K concentrations were measured on ce per week and plant performance (number of leaves and stems, dry and wet weight of stems and roots, number of dead leaves and stems, leaf c hlorophyll c oncentration index and plant height) were determined at the beginning and conclusion of the trial. Changes in plant performance were analyzed using a two-way (two by three factor) analysis of variance (ANOVA) while the other parameters were analyzed using a two-way repeated-measures ANOVA.
There was a significant (P>0.05) differences in pH, salinity, and DO across treatments. The SW Source water had significantly greater mean ± SD shoot dry weight (SW: 10.068 ± .415; RW: 8.514± .415; P=0.01) and number of leaves (SW: 51.3 ± 1.940; RW: 41.9 ± 1.9; P=0.001). Fertilizer type had a significant effect on the number of leaves (FN: 50.6 ± 2.39; F: 42.0 ± 2.35; P=.012), dry root weight (NF: 3.731 ± .225; F: 3.026 ± .225; P=.029), and number of dead leaves (FN: 22.30 ± 1.38; F: 17.34 ± 1.36; P=.038). These results suggest that S. alterniflora performs best in clean saltwater compared to reused shrimp culture water. Plants have a variety of effects on water quality, and the plants do respond to excess dissolved nutrients, which is a common characteristic of reused water. Further research is needed to examine what components of reused water could be changed to facilitate better plant production and remediation potential.