The Construction Of Microcosm And The Migration And Transformation Of Nitrogen And Phosphorus With Silver Carp And Bighead Carp As The Core

In order to solve the problems of lake eutrophication causing the disorder of the water ecosystem,this study use the combination of Plagiogathops micrloepis Bleeker(Xenocypris microlepis),Hypophthalmichthys molitrix(Silver carp),Aristichthys nobilis(Bighead carp),and Daphnia magna in the simulated eutrophic water colume.The purpose is to further improve the detrital ecological chain and food web,and take this as the core build a micro universe.This study research the law of nitrogen migration and transformation by using stable isotope technology.This study also research the effect of temperature and disturbance on the microcosm and the migration and transformation of phosphorus.Finally,this study prov ide a reference for the actual ecological regulation of water bodies.The main conclusions of this study are as follows:(1)Study on the mechanism of ingestion and digestion of Microcystis by Xenocypris microlepis.Temperature improves the ability of the carp to ingest and digest cyanobacteria by increasing the activity of digestive enzymes in the intestines of the carp,and the proportion of Bacillus and Methylobacterium.When the ingestion digestibility in the 30°C group reached the highest values,the protease activity,amylase activity and cellulase activity in the intestine also reached the highest value,as well as the proportions of Methylobacterium and Bacillus also reached 15.5%and 12.6%,respectively.(2)Study on the establishment of microcosms and the migration and transformation of nitrogen.The addition of Xenocypris microlepis,Silver carp,Bighead carp and Daphnia magna in the microcosmic structure has obvious joint control effects on water quality,and significantly reduces the concentration of nutrients in the water and the density of Microcystis in the water,as well as increasing the proportions of Novosphingobium,Gemmobacter and Pseudomonas in the sedimentary facies.At the end of the experiment,the concentration of TN?TP and algae cell density in the Xenocypris microlepis,Silver carp,Bighead carp and Daphnia magna groups reached 1.613 mg/L,0.093 mg/L and 2.113×10⁶cell/L,respectively,which were lower than other experimental groups.The migration and transformation pathways of nitrogen in the microcosm are:13.80%of ¹⁵N remained in the sedimentary facies in the form of algae debris and fish feces;26.42% of ¹⁵N is converted to ¹⁵N-NH₄⁺and ¹⁵N-NO₃^-exists in the water phase through the ammonification of microorganisms;25.34%of ¹⁵N is absorbed by Microcystis and remained in the biological phase in the food web;36.12%of ¹⁵N removed from the system by microbial action.(3)The effect of temperature and disturbance on the microcosm.Disturbance and high temperature cannot affect the reduction of nutrient concentration in the microcosmic water body,nor can it cause the continuous proliferation of Microcystis,but the intermittent disturbance makes the number of Microcystis higher than that of each group.At the end of the experiment,the low-temperature intermittent disturbance group reached 6.01×10⁷cell/L,which was much higher than the other groups,and the high temperature would further reduce the density of Microcystis.(4)The migration and transformation law of phosphorus in the microcosm.The inorganic phosphorus and organic phosphorus in the sedimentary phase will migrate to the water phase under the action of anaerobic environment and phosphate solubilizing bacteria;the phosphorus in the water phase will be absorbed by Microcystis,and part of it will enter the organism through the food web,and part of it will return to the sedimentary facies.This migration and transformation law of phosphorus reduces the content of phosphorus in the sedimentary phase and promotes the cycle of phosphorus.Increasing temperature will promote the migration of phosphorus to the water phase.Continuous disturbance will cause the phosphorus in the sedimentary phase to migrate to the water phase in the form of particulate phosphorus.Intermittent disturbance will cause the particulate phosphorus in the water phase to migrate back to the sedimentary phase and be fixed.