An aquaponic (AP) system combines a recirculating aquaculture system (production of aquatic animals, mostly fish) with a hydroponic system (production of plants) and recycles water and nutrients between these two main components. Nutrient-rich water from the aquaculture component is directed to the hydroponic component and provides nutrients for plant growth, while nutrient-poor water is returned back to the aquaculture component. One of the key nutrients in AP is nitrogen, which is introduced into the nitrogen cycle of the system via fish feed and subsequent fish excreta. Ammonia and nitrite are both harmful to fish. The transformation between these forms as well as the production of nitrate are mediated by bacteria. Other components of the AP, such as the biofilter, solids removal unit, settler, sump, piping, as well as their physicochemical conditions, further affect microbial community and nitrogen dynamics. The spatial distribution of microbial communities and the dynamics of the nitrogen cycle in an AP system are poorly understood.
This project aims at quantifying nitrogen fluxes between different components of the AP system as well as quantifying the nitrogen losses from the system. In addition, microbial communities that are involved in the nitrogen cycle will be characterized. The main forms of nitrogen in all AP system components (fish feces, fish tank, biofilter, solids removal unit, digester, sump, piping, and rhizosphere) will be quantified. Bacterial community composition and function will be described with a metagenomics approach and by using quantitative PCR for specific populations of bacteria involved in N-cycling. Finally, nitrogen fluxes among system components will be traced using a 15N isotope in order to parametrize the nitrogen dynamics in the system.