Study On Stochastic Model Of Lake Eutrophication

There are two stable states in lake ecosystems.One is oligotrophic lakes and other eutrophic lake.The oligotrophic lake ecosystems are those in which there are fewer nutrients(mainly refers to the nitrogen,krypton,phosphorus)with clear water quality and relatively few phytoplankton on the surface of the lake;the opposite is eutrophic lake ecosystem.In this thesis,we focuses on the steady state and phosphorus cycle of the ecological system of Tai lake.When the environment parameter changes,the transitions between two stable states will occur.With the increase of parameter perturbation,the transition between the two states becomes more intense.These phenomena present a bistable dynamic mechanism between poor nutrition and eutrophication.In this article,first,we considers the noise on the influence of the ecological system.Secondly,the formation mechanism of three forms of phosphorus salt,gran-ular phosphorus,water-soluble phosphorus and phosphorus in algae is considered.Thus,a typical non-linear dynamic model of phosphorus cycle in single-layer box is established.Then the stability of lake ecosystems and the effects of three forms of phosphorus kinetic are analyzed from the point of view of numerical analysis.The three forms of phosphorus in lakes are analyzed in detail,that is,the exchange of phosphorus between lakes and the outside world is considered,and the conversion of phosphorus between lakes is also considered.There are many random disturbances in the phosphorus cycle of lakes.These can be regarded as Gauss white noise in mathematical models.The main disturbances are seasonal,wind and hydraulic scouring.According to the characteristics of periodic variation of these factors,the disturbance is regarded as a factor of periodic variation.The validity of the model is verified by comparing the simulation results with the measured results in 2014 and 2015.