Study On The Reduction Of Algal Bloom And Migration Of Nitrogen And Phosphorus Under The Cooperation Of Fish Filter-feeding And Plant Purification

In order to study the cyanobacteria blooms and eutrophication status in Lake Chaohu,and to provide technical support for its remediation,an year-long field investigation on the water environment was carried out in the whole lake.Simultaneously,an enclosure experiment was carried out in the northwestern area of the lake to reduce cyanobacteria blooms by the cooperation of fish filter-feeding and plant purification.The migration and transformation of nitrogen and phosphorus in the water-sediment system was also studied during the process.The main results are as follows:(1)The nitrogen concentration in the water in summer was significantly lower than that in winter in Lake Chaohu,while the phosphorus concentration is higher than that in winter.The western part had significantly higher concentrations of nitrogen and phosphorus than the eastern part.The northwestern area had the highest concentrations of nitrogen and phosphorus and the most serious status of cyanobacteria blooms.(2)Under the synergistic of silver carp filter-feeding and plant purification,the biomass of cyanobacteria and the suspended solids can be significantly reduced.The transparency of the water was greatly improved.The remediation effect is more obvious under the high silver carp stocking density of 80g/m3.(3)Under the synergistic of silver carp filter-feeding and plant purification,the water quality could be greatly improved.The concentrations of total nitrogen,total phosphorus and phosphate in the water decreased significantly at both the densities of 80g/m3 and 40g/m3.(4)Under the synergistic of silver carp filter-feeding and plant purification,the contents of ammonia nitrogen and phosphate in the sediment interstitial water both decreased obviously,which suppressed the release of nitrogen and phosphorus from the sediment and reduced the internal loadings in the water.(5)Under the synergistic of silver carp filter-feeding and plant purification,the content of nitrate nitrogen in sediment has increased.An obvious transformation of Fe-P to Al-P and Ca-P was discovered.These transformation was beneficial to suppress the release of nitrogen and phosphorus from the sediment.To sum up,under the synergistic of silver carp filter-feeding and plant purification,the cyanobacteria bloom in water was rapidly reduced.The water quality was also significantly improved because of the significantly decrease of nitrogen and phosphorus concentrations in the water.In addition,the release of nitrogen and phosphorus from the sediment was suppressed and the internal loadings were reduced.These results indicate that the synergistic of silver carp filter-feeding and plant purification was adaptable for the remediation of eutrophication in Lake Chaohu.