Duckweed Lemna minor (Liliopsida, Lemnaceae) as a natural biofilter in brackish and fresh closed recirculating systems
Journal Title: Aquaculture, Aquarium, Conservation & Legislation - International Journal of the Bioflux Society - Year 2012, Vol 5, Issue 5
Abstract
This study attempted to assess the potential use of common duckweed Lemna minor as natural biofilter in brackish closed recirculating systems of 4 g/L salinity and to evaluate the effect of salinities in the ranges of 1-7 g L-1 on the duckweed’s ammonium NH4+1 uptake. Furthermore the possibility of nitrification as a second mechanism of nitrogen removal in closed recirculating systems was investigated. Three closed recirculating systems each having 20 mixed Oreochromis niloticus were used. Duckweed L. minor and fresh water were added in system 1, fresh water only in system 2, and duckweed with brackish water in system 3. Ammonium NH4+1 and nitrate NO3-1 were tested periodically in each system during a 1.5 month period. Another three experiments were run in parallel using aquariums incubated with 60.00 g fresh weight L. minor at salinities in the ranges of 1-7 g L-1for two weeks. Aquariums were exposed directly to sunlight in experiment 1 and 3, and were placed in the dark in experiment 2. The nitrogen source in experiment 1 and 2 was 100 mg L-1 of NH4Cl, and 280 mg L-1 of NH4Cl in experiment 3. NH4+1 and NO3-1levels were monitored as above. L. minor managed to reduce the average NH4+1 levels to 0.5 mg L-1, 0.43 mg L-1 below the standard recommended levels in both brackish and fresh water systems, respectively. Ammonium NH4+1 uptake was coupled with nitrate NO3-1 uptake under favorable conditions of sunlight. Salinity in the ranges from 1-7 g L-1 enhanced ammonium NH4+1uptake (r = 0.8819, p = 0.023) without affecting nitrate NO3-1 uptake or any observed mortality of the duckweed. Nitrification was a second mechanism of nitrogen removal in a closed recirculating system, but it was affected by salinity and light. Average ammonium NH4+1 of 51.8 mg L-1 was toxic to L. minor and death was observed within a week in experiment 3. The duckweed L. minor was an efficient natural biofilter in both brackish and fresh water closed recirculating systems
Authors and Affiliations
Mutaz Al-Qutob, Tharwat Nashashibi
Keywords
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