Obtaining and maintaining a healthy, productive aquaponic system requires intensive scienti ic research, monitoring and also adjustments, when necessary. To quantify the nitrogen budget for a stellate sturgeon-spinach integrated LECA grow bed aquaponic system, where three plants densities were used. The experiment was made in triplicate, using a 12 aquaponic units LECA grow bed aquaponic system. Three crops densities were used (V1-59crops/m 2 , V2-48crops/m 2 and V3-39crops/m 2 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. Differences between the removal rates for each of the three variants of tested crops densities were signi icant 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 bio ilter and LECA grow bed was signi icant (p<0.05). Also, differences between spinach nitrogen composition from V3 compared to V1 were found signi icant higher (p<0.05). The nitrogen content from ish meat and ish faeces was found to be within normal limits, appear also in the literature. Considering the nitrite and nitrate concentrations, only spinach grown in aquaponic conditions, as presented above, at densities of 59crops/m 2 , 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 loating rafts technique.
Ranunculus rionii and Ceratophyllum demersum develop aquatic dense stands, which lately started to represent a major ecological concern for all the ponds and/or lakes in Romania. The potential relationships between the phytochemical compounds detected in these plant extracts (acids, phenols, heterocycles, alcohols, hydrocarbures) and the allelopathic properties against Gram positive and Gram negative bacterial strains and microalgal cultures were investigated and discussed in the current study. The untargeted solid phase micro extraction (SPME) GC/MS analysis performed on the dried plants incubated for 25 min at 50°C showed that phenols are the major constituents of the volatile fingerprint with a relative peak area higher than 13%, namely: 2,6 bis(1,1-dimethylethyl)-4(1-oxopropyl) phenol and phenol, 3,5-bis (1,1-dimethylethyl). The inhibition effects ex situ of the analyzed extracts suggest that aquatic macrophytes may excrete inhibitory substances and show allelopathic inhibitory potential against certain bacterial strains and on: Rhizoclonium hieroglyphicum and Microcystis aeruginosa cultures.
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