A Study of Nitrogen Dynamics in an Integrated Stellate Sturgeon and Spinach Aquaponic System with Different Crop Densities

Abstract

Introduction. Obtaining and maintaining a healthy, productive aquaponic system requires intensive scientific research, monitoring and also adjustments, when necessary. Aims. To quantify the nitrogen budget for a stellate sturgeon - spinach integrated LECA grow bed aquaponic system, where three plants densities were used. Materials and Methods. The experiment was made in triplicate, using a 12 aquaponic units LECA grow bed aquaponic system. Three crops densities were used (V1 - 59crops/m2, V2 - 48crops/m2 and V3 - 39crops/m2 and V4 - no crops, only with LECA grow bed). Fish were were fed with 41% brute protein feed, at an average feeding ratio of 1.75% of total biomass. Water samples were taken and analysed by using photometric methods (Merck kits). The stellate sturgeon meat, spinach and also faeces nitrogen content was determined by Kjeldahl method. Results. Differences between the removal rates for each of the three variants of tested crops densities were significant higher (p<0,05) at V1 compared to V3 and also higher at all three variants comparing them to the control variant. The amount of ammonium removal rates from biofilter and LECA grow bed was significant (p<0,05). Also, differences between spinach nitrogen composition from V3 compared to V1 were found significant higher (p<0,05). The nitrogen content from fish meat and fish faeces was found to be within normal limits, appear also in the literature. Conclusion. Considering the nitrite and nitrate concentrations, only spinach grown in aquaponic conditions, as presented above, at densities of 59crops/m2, is marketable. In addition, it can be concluded that spinach growth in LECA grow bed aquaponic systems have a higher nitrogen content, comparing with the one growth using floating rafts technique.