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The extracts of three emergent macrophytes (Acorus calamus, Oenanthe javanica, and Sagittaria sagittifolia) were tested to study their allelopathic activities on unicellular Microcystis aeruginosa, Anabaena flosaquae, Aphanizomenon flosaquae, and natural phytoplankton assemblages. The 72 h EC₅₀ of the most active extracts were measured. The results demonstrated the obvious species-specific activities of macrophytes on algae. Anabaena flosaquae and Aphanizomenon flosaquae was sensitive to the three macrophytes extracts, while unicellular M. aeruginosa was only sensitive to A. calamus and O. javanica extracts under the extracts concentration of 100 mg·L⁻¹. Only the extract of A. calamus roots showed high growth inhibition on the natural phytoplankton assemblages in Dianchi Lake (Microcystis water bloom). The 72 h EC₅₀ of A. calamus roots hexane extract on unicellular M. aeruginosa was 13.59 mg·L⁻¹, while that on natural phytoplankton assemblages was 48.75 mg·L⁻¹. These results demonstrated that the growth inhibitory activities of allelochemicals on unicellular M. aeruginosa cannot instead of the efficacies for controlling Microcystis bloom completely. And according to the different sensitivities of Microcystis species, the colonial Microcystis strains or natural Microcystis bloom will be proposed as the target organism when searching for Microcystis bloom control.
To obtain sustainable aquaculture, developing appropriate treatment processes for wastewater is essential. In this study, two three-stage hybrid wetland systems were configured to treat aquaculture effluent. The two systems added with or without artificial aeration were operated under a high HLR (8.0 m/day) with a short retention time (0.96 h). By the results, COD could be effectively removed by both the systems, and it had been significantly enhanced by continuous aeration (air:water ratio being 7.5:1). For nitrogen (N) compounds, NH4+-N concentration of outflow compared to the inflow was elevated in most cases under the nonaerated condition, but an opposite trend was observed for the aerated state, which indicated that dissolved oxygen (DO) required for nitrification in the natural bed was more insufficient at the high organic loading rate. TN mass removal was efficient without aeration, but it significantly declined after enhancement, possibly due to the resuspension of trapped organic N promoted by the strong airflow. The artificial aeration also significantly improved the treatment performance on phosphorus. By canonical correspondence analysis (CCA), the first-order removal rate constants of various pollutants were significantly correlated to the measured environment of the inflow. Under the high constant HLR accompanied by low DO, pollutant loading rate became the first dependent factor on removal rate for such a rapid filtration system.
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