Purification effects of Myriophyllum elatinoides Gaudich and Ipomoea aquatica Forsk in simulated pond culture tail water

【Objective】 To explore the adaptability of Myriophyllum elatinoides Gaudich and Ipomoea aquatica Forsk to aquaculture tail water with different nitrogen and phosphorus levels under floating environment culture conditions, as well as the nutrient uptake and removal effects of nitrogen and phosphorus, and to provide reference for promoting the promotion and application of the two plants in pond culture tail water treatment.【Method】M. elatinoides Gaudich and I. aquatica Forsk were selected as test plants. Three groups of low(A), medium(B) and high(C) with total nitrogen(TN) and total phosphorus(TP) concentrations of 5, 10, 15 mg/L and 1, 2, 3 mg/L were set to simulate aquaculture tail water respectively. The biomass, nitrogen, phosphorus accumulation and nitrogen, phosphorus removal capacity of the two plants at 42 d were compared.【Result】 M. elatinoides Gaudich continued to grow for 42 d in groups A, B and C. Its 42 d net biomass, nitrogen and phosphorus accumulation increased with the increase of growth time and water nitrogen and phosphorus concentration, and the maximum appeared in group C. I. aquatica Forsk grew normally for 28 d in groups A, B and C, its 42 day net increased biomass and nitrogen and phosphorus accumulation decreased with the increase of nitrogen and phosphorus concentration in water, and the maximum values appeared in group A. During the experimental period of 42 d, M. elatinoides Gaudich had the highest removal rates of ammonia nitrogen(NH₄⁺-N), TN, active phosphorus (SRP) and TP. The removal effect of nitrogen and phosphorus increased with the increase of nitrogen and phosphorus concentration, and the removal ability of ammonia nitrogen was the strongest, and the maximum value appeared in group C. The nitrogen and phosphorus removal efficiency of I. aquatica Forsk decreased with the increase of nitrogen and phosphorus concentration in water, and the plant growth and removal capacity decreased after 28 d. The contribution rate of nitrogen and phosphorus uptake by plants showed that the contribution rate of nitrogen and phosphorus uptake by M. elatinoides Gaudich ranged from 33.65% to 99.82%, which was higher than 2.34%-62.21% of I. aquatica Forsk. Under the experimental conditions, the adaptability of the two plants to the simulated aquaculture tail water with A, B and C nitrogen and phosphorus levels was the best for M. elatinoides Gaudich, followed by I. aquatica Forsk. Plant absorption was the main way for M. elatinoides Gaudich to remove nitrogen and phosphorus from water.【Conclusion】M. elatinoides Gaudich has a wide range of nitrogen and phosphorus adaptation, which is manifested as high nitrogen and phosphorus, and its adaptability, growth and water purification ability to water nitrogen and phosphorus levels is better than that of I. aquatica Forsk, which can be used for long-term purification of tail water from pond aquaculture in southern China, and the application potential is better than that of I. aquatica Forsk. The growth of I. aquatica Forsk and the removal effect of nitrogen and phosphorus in water decreased with the increase of nitrogen and phosphorus concentration in water body, and it should be harvested regularly when applied to the treatment of tail water of pond aquaculture in summer and autumn to ensure the purification effect.