Epsilon Archive for Student Projects

Abstract

Aquaponic systems are increasingly recognized as sustainable alternatives to conventional agricultural systems, offering enhanced resource efficiency in terms of both water and nutrients. However, key factors that could further improve the productivity and resilience of these systems, such as improved nitrification, remain largely underexplored. This dual case study primarily investigated the effects of bacterial inoculation with two strains of Pseudomonas fluorescens on nitrogen dynamics in a coupled aquaponic system, while also examining the relative amount and distribution of microbial communities across system compartments. Water samples used in this study were collected from the fish tank and the biofilter at different time points and inoculated under controlled conditions. The two strains were originally isolated from a recirculating aquaculture system at Gårdsfisk located in Kristianstad, Sweden. Concentrations of ammonium, nitrite, nitrate and total inorganic nitrogen (TIN) were measured over two consecutive weeks to examine nitrogen transformations and assess overall nitrification activity. Bacterial inoculation resulted in significantly increased nitrate and TIN production in biofilter water relative to controls. In contrast, these effects were not consistently observed in fish tank water, where nitrification activity was presumed low. Analysis of culturable microbial groups revealed significant differences in microbial community structure between system compartments, however interpretation of these results was limited. Overall, the results indicate that the influence of P. fluorescens on nitrogen dynamics is strongly context dependent and likely mediated through indirect mechanisms such as enhanced mineralization or synergistic interactions with already existing nitrifying autotrophs. While the findings of this study suggest potential benefits of inoculating with P. fluorescens during biofilter establishment, further controlled studies are required to evaluate its applicability and consistency across varying water conditions.