The Efficiency of Aquatic Macrophytes on Nitrogen and Phosphorous Uptake from Pond Effluents in Different Seasons
Lilian Kalengo 1  
,   Hailong Ge 1  
,   Nannan Liu 1  
,   Zhijian Wang 1  
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Southwest university, School of Life Science Institute of fisheries and aquaculture Room 107 Tiansheng Road no.2
Lilian Kalengo   

Southwest university, School of Life Science Institute of fisheries and aquaculture Room 107 Tiansheng Road no.2
The present study investigated the efficiency of four aquatic macrophytes; Lemna spp, Pistia stratiotes, Ipomoea aquatica and Eichhornia crassipes on Nitrogen and Phosphorous utilization from aquaculture effluents concerning seasonal changes and biomass production. These nutrients in excess affect fish health and cause eutrophication in water bodies hence affects the ecosystem. Aquatic macrophytes were planted in tanks filled with effluents from carp pond and other tanks were left without plants and served as control/algal treatment. Water samples were collected weekly for analysis of total nitrogen (TN), ammonia-nitrogen (NH3-N), nitrate-nitrogen (NO3-N), total phosphorus (TP) and ortho-phosphate (ortho-P). Results show that average water temperature raised from 12.2 ± 0.21°C in winter to 32.0 ± 0.4°C in summer with no significant difference (p>0.05) between treatments and pH was neutral in winter and slightly alkaline in the other seasons. Seasonal changes had impact on macrophytes biomass accumulation with the highest in spring for Lemna spp (91.3%), followed by P. stratiotes (81%) and in summer, E. crassipes (64%). Autumn and winter had the lowest biomass accumulation and I. aquatica had the lowest in all seasons. For each season, nutrients concentration decreased with no significant difference (p>0.05) between treatments. Average NH3-N removal efficiencies were higher during summer and autumn followed by spring and lowest in winter for all treatments. NO3-N and TN decreased significantly from highest in summer to lowest in winter in all treatments. Ortho-P removal efficiency was slightly higher than TP and decreased from highest in spring to the lowest in winter (91.4% to 7.8%, control/algae; 90.3% to 8.4%, E. crassipes; 86.2% to 8.3%, Lemna spp; 82.5% to 10.8%, P. stratiotes). Chlorophyll a concentration was higher in Lemna spp (62.2μg/L) and control/microalgae treatments (59.3μg/L) indicating that there was probably microbial community that contributed to nutrients utilization. Aquatic macrophytes in association with microalgae were responsible for Nitrogen and Phosphorous removal. Seasonal temperature change affects growth and nutrients uptake of aquatic macrophytes. Decrease in temperature reduce the efficiency of nutrients removal and biomass production. For an effective N and P removal from pond effluents in a given season, selection of a proper aquatic macrophyte must be kept into consideration with regards to given season.