Purifying Effect Of Ecological Floating Bed To The Source Water Quality

Nowadays, the problem of lake-eutrophication was very serious in China, and scientists focused on the improvement of water quality for water source. As one of concerned technologies used to improve the source water quality home and abroad, the ecological floating-bed has advantages such as easy to operate, and without environmental risk and secondary pollution. But most applied floating-beds are single plants foating-beds at present. Therefore, it has important theoretical and practical significance to study the combined floating-bed technology of plants and aquatic animal for improving the source water quality in eutrophic lake.In this study, the purification and mechanism of ecological floating bed were studied by growing plants individually, the combination of floating-bed plants and scraping feeding Bellamya aeruginosa, and the combination of floating-bed plants, filter-feeding fishes (Hypophthalmichthys molitrix) and scraping feeding Bellamya aeruginosa through laboratory and outdoor field test. In order to provide basis for the application of aquatic animal and plant combined floating-bed, the growth characteristics of each unit in ecological floating bed were observed, and the effect on physical and chemical indicators of water quality and the coupling effect between organisms were analyzed. The results showed that:By growing floating-bed plants individually, the purification effects on eutrophic water bodies were significant. The purification effect on nitrogen and phosphorus by cultivating Eichhorinia crassipes individually was best, Canna indica secondary, Arundo donax var. versicolor worstly. The capability of Eichhorinia crassipes for increasing dissolved oxygen was better than the other two species. It was proved that Eichhorinia crassipes was the optimal plant to reduce nitrogen and phosphorus in eutrophic water bodies.Among the three combinations of Eichhornia crassipes and Bellamya aeruginosa, Canna and Bellamya aeruginosa, Arundo donax var versicolor and Bellamya aeruginosa, the combination of Eichhorinia crassipes and Bellamya aeruginosa had the highest purification effect on total nitrogen, ammonium nitrogen and nitrate nitrogen in eutrophic water, which reduced total nitrogen in eutrophic water by 71.94%(from 8.34 mg/L to 2.34 mg/L), ammonium nitrogen by 85.31%(from 4.56 mg/L to 0.67 mg/L), and nitrate nitrogen by 59.66%(from 3.52 mg/L to 1.42 mg/L). The combination of Eichhorinia crassipes and Bellamya aeruginosa and the combination of Canna indica and Bellamya aeruginosa had similar effect on total phosphorus in eutrophic water, and both reduced the average concentration of total phosphorus in eutrophic water by 85.29%(from 0.34 mg/L to 0.05 mg/L). There were very significantly positive correlations between the removal of total nitrogen and total phosphorus by combined floating-bed and the increased biomass of floating-bed plants[r=0.895**(P<0.01);r=0.95**(P<0.01)]. And there were significantly positive correlations between the decrement of total nitrogen concentration by combined floating-bed and the increased biomass of Bellamya aeruginosa (r=0.785**, P<0.05). The purification effect on eutrophic water bodies by the ecological floating-bed was better than that by cultivating floating-bed plant individually. The results proved that there was coupling effect between plants and Bellamya aeruginosa.In the application of that ecological floating-bed composed of plants, Hypophthalmichthys molitrix and Bellamya aeruginosa improved the simulative water quality of Chaohu Lake, the removal efficiency on chlorophyll, total nitrogen and ammonium nitrogen in eutrophic water were significant by each treatment compared with control group, as well as nitrate nitrogen and total phosphorus. And the difference of removal efficiency on the eutrophic nutritional index in eutrophic water was very significant between different treatments(P<0.01). The combined ecological floating-bed of Eichhorinia crassipes, Hypophthalmichthys molitrix and Bellamya aeruginosa had the highest purification effect on chlorophyll, total nitrogen, ammonium nitrogen, nitrate nitrogen, and total phosphorus in eutrophic waters, which reduced chlorophyll in eutrophic water by 71.04%, total nitrogen by 51.17% and ammonium nitrogen by 65.10%, nitrate nitrogen by 57.26% and total phosphorus by 72.80%. There were significantly positive correlations between the reduction amount of nitrogen and phosphorus by combined floating-bed and the increased biomass of floating-bed plants [r=0.973*(P<0.05); r=0.979*(P<0.05)], as well as the reduction amount of nitrogen and phosphorus by ecological floating-bed and the increased biomass of Hypophthalmichthys molitrix [r=0.983*(P<0.05);r=0.963*(P<0.05)]. Hypophthalmichthys molitrix and Bellamya aeruginosa improved the purification effect on nitrogen and phosphorus of the floating-bed to eutrophic water bodies (The latter is higher), and they both removed phytoplankton effectively. Eichhorinia crassipes had the highest contribution rate for nitrogen and phosphorus. Meanwhile, Eichhorinia crassipes and Alternanthera philoxeroides both had higher biomass and better purification effect in the combined floating-bed ecological system of plant and filter-feeding fishes and scraping feeding Bellamya. All results proved that the combination builded artificially with plant, filter-feeding fishes and scraping feeding Bellamya had better purification effect on pollutants, and improved water quality and optimized ecological system environment. And in this symbiotic system, they could play their ecological functions adequately. Based on all results, it was an environment-friendly and effective method to deal with eutrophic water using bioecological combination, and there was coupling effect among floating-bed plant, filter-feeding fishes and scraping feeding Bellamya.