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The Efficiency of Aquatic Macrophytes on the Nitrogen and Phosphorous Uptake from Pond Effluents in Different Seasons

Kalengo Lilian, Ge Hailong, Liu Nannan, Wang Zhijian

Journal of Ecological Engineering

2021

Vol. 22, nr 8

75--85

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 aquacultural effluents concerning seasonal changes and biomass production. These nutrients in excess affect fish health and cause eutrophication in water bodies, hence affecting the ecosystem. Aquatic macrophytes were planted in tanks filled with the effluents from carp pond and other tanks were left without plants, serving as control/algal treatment. The 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). The 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 whereas 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 values in all seasons. For each season, the 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 the highest in summer to the lowest in winter in all treatments. The ortho-P removal efficiency was slightly higher than TP and decreased from the 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). The chlorophyll a concentration was higher in Lemna spp (62.2 μg/L) and control/microalgae treatments (59.3 μg/L) indicating that there was probably microbial community that contributed to nutrient utilization. Aquatic macrophytes, in association with microalgae, were responsible for the nitrogen and phosphorous removal. Seasonal temperature change affects the growth and nutrients uptake of aquatic macrophytes. A decrease in temperature reduces 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 taken into consideration with regards to a given season.