Improving Plant Health Through Nutrient Remineralization in Aquaponic Systems

Abstract

The exploitation of readily bioavailable fish excreta as a source of plant nutrients lies at the cornerstone of aquaponics farming. Research on nutrient cycling in aquaponic systems has devoted considerable attention to the plant uptake of dissolved nutrients in fish excreta, however, the integration of particulate-bound nutrients into downstream hydroponic farming has remained elusive. The high amount of organic carbon present in fish sludge may lead to biofouling if directly incorporated into hydroponic circulation systems, reducing the utility of incorporating fish solids on a large scale. In this study, we implemented a novel treatment system capable of reducing the carbon and nitrogen load of fish solids to produce a liquid fertilizer for a downstream hydroponics unit. Lettuce (Lactuca sativa) fertilized with exclusively a commercial nutrient solution, the biofilter effluent (coupled aquaponic system), effluent from the solids treatment system, or the latter two combined were grown in nutrient flow technique gutters downstream of a recirculating aquaculture system stocked with rainbow trout (Oncorhynchus mykiss). While crop yields were lower for the aquaponic treatments compared to lettuce grown in a commercial nutrient solution, plant sap analysis demonstrated a contrasting picture with respect to internal nutrient concentrations. Lettuce grown in the commercial hydroponic solution were deficient in several mineral nutrients (Mg, Ca, Na, and Si) nor did they have higher iron concentrations despite the significantly higher EDTA-chelated aqueous iron (460 × greater than other treatments) in the nutrient solution. Nutrient uptake in the rhizosphere was not investigated on a molecular level, although stunted rhizosphere growth in the commercial nutrient solution control suggests a weakened capacity for nutrient uptake in comparison to other treatments. Alongside the remineralization of micronutrients, the solids treatment system addressed the common issue of excess carbon leading to biofouling via a total suspended solids reduction of 87.27% ± 9.95 during the coupled aquaponics cultivation period. Ultimately, these data lead to two important conclusions. Firstly, optimizing nutrient bioavailability is not synonymous to increasing the presence of a nutrient in the water column. Secondly, estimating ideal nutrient solution concentrations involves both preventing nutrient blocking and improving bioavailability.

Plants Dictate Root Microbial Composition in Hydroponics and Aquaponics

“…Future studies must likewise determine whether aquaponic facilities benefit from sterilization, or whether the co-cultivation of plants and fish in an environment promoting diversity leads to a more resilient facility-wide microbiome. Secondly, in line with previous work on the relationship between aqueous nutrient concentrations and plant health ( Lobanov et al, 2021 ), more research is needed to determine whether a greater focus on maintaining plant health as opposed to only maximizing yield will lead to more disease-tolerant crops, and ultimately more productive crops.…”

“…The above trends indicate community consolidation in our system, suggesting that prioritizing plant health metrics will likewise reduce the potential for disease. We have recently demonstrated that trace nutrients are not taken up by plants proportionally to their external aqueous concentrations ( Lobanov et al, 2021 ), which suggests that fundamental issues such as plant nutritional needs should be prioritized. Given the slow growth requirements of k-strategists [e.g., anammox ( Laureni et al, 2015 ; Zhang et al, 2017 ; Zielińska et al, 2018 ), archaea ( Seyler et al, 2014 ; Bartelme et al, 2017 )], system-wide maturation of the microbial population may take months or years ( Savidov and Brooks, 2004 ).…”

Potential of Bacterial Strains Isolated from Coastal Water for Wastewater Treatment and as Aqua-Feed Additives

“…The toxicity of the forms of ammonia (NH 3 ) increases with water pH (the ammonia/ammonium ratio increases at pH 7 and above), which is one of the reasons for the importance of pH control in aquaculture. Aquaculture systems including autotroph biofloc technology (ABFT) [19], biofloc technology (BFT) [70], recirculating aquaculture systems (RAS) [71], and integrated multi-trophic aquaculture (IMTA) [72] systems such as aquaponic systems [73], constructed wetlands [74], integrated marine systems [75], high-rate algal ponds [76], periphyton systems [77], and partitioned aquaculture systems [78] aim mainly to remove nitrite-N (NO 2 -N) and ammonia (NH 3 ). Therefore, the four strains used in this study can be utilized in aquaculture, as they were shown to be excellent in their water-quality-improvement utilities.…”

Utilization of Sludge from African Catfish (Clarias gariepinus) Recirculating Aquaculture Systems for Vermifiltration

“…With the current state-of-the-art, only the dissolved nutrients from the process water are being used for plant cultivation; however, some nutrients are often lacking in this solution [14]. Further, if directly transferred into the hydroponics system, the significant amount of organic carbon inside the solids may lead to biofouling, clogging, and undesired oxygen depletion in the system [15].…”