| As an important part of the ecosystem,wetlands provide necessary services for the stability of the ecosystem and human life.Relevant researches on the environmental dispersion of pollutants in wetlands,especially for the prediction of the location of pollution zones and the diffusion patterns of pollutant clouds after pollution occurs in wetlands,can provide a basis for ecosystem risk assessment and the formulation of pollution control policies.Thus,analyzing the environmental dispersion within wetland flows is of great significance for protecting the ecosystem.Based on Taylor’s dispersion theory and porous media theory,considering the influence of different complicated boundary conditions on the dispersion of wetland pollutants,an analytical study of the environmental dispersion in wetlands is conducted.According to different boundary conditions,different analytical methods are extended to solve analytical solutions of pollutant concentration distribution in different wetland models,and the influence of wind stress and different absorption intensities on the two-dimensional spatial distribution of pollutant concentrations in wetlands is discussed.In this paper,three analytical methods have been extended to analyze the environmental dispersion of pollutants within wetlands in order to adapt to different wetland models under complicated boundary conditions.The extended A-G method is used to solve the two-dimensional spatial concentration distribution of pollutants within a single-layer wetland under wind stress.Impact of wind stress on environmental dispersion in a three-layer wetland is explored based on the Gill’s expansion theory.And the environmental dispersion coefficient in three-layer wetlands is given through the analytical method.Based on the multi-scale method,two-dimensional spatial distribution of pollutant concentrations in wetlands with the first-order absorption boundary at the bottom are obtained.And two-dimensional pollutants concentration distributions in wetlands under the combined effect of wind stress and first-order absorption boundary are studied with the multi-scale theory.In addition,the effect of wind,and first-order absorption boundary on the diffusion of pollution in wetlands are also discussed.The analysis in this paper shows that with the existence of the wind stress and the bed absorption boundary,the two-dimensional spatial concentration distribution in the wetland is significantly impacted by wind and the bed absorption.Wind stress affects the two-dimensional spatial concentration distribution of pollutants in wetlands by changing the vertical velocity structure.The impact on pollutant concentration distribution depends not only on the strength of the wind but also by the wind direction.The bed absorption can lead the changes of the total solute mass,then pollutant is reduced by the bed absorption.Under the effect of downstream wind,the gradient of concentration distribution in the vertical direction decreases with the increase of wind strength,and the diffusion range of pollutant clouds will be wider;the situation would be different under the effect of upstream wind,the concentration gradient of pollutant clouds in the vertical direction shows a increasing trend at first and then decreasing with the gradual increase of wind force.When the wind strength is weak,the diffusion of pollutant clouds in the longitudinal direction is more narrow than in the windless state,it would be more concentrated near the pollution source,when the wind strength reaches a certain value,the concentration gradient of pollutant clouds in longitudinal would be smaller than that with the absence of wind,and the diffusion range of pollutant clouds in the longitudinal direction is larger than that in the windless state.Under the effect of the absorption boundary,the diffusion range of the pollutant concentration in the wetland is smaller than that without the absorption boundary.The centroid of the cloud approaches the surface layer with the increase of the absorption intensity.In summary,different analytical theoretical methods for wetland models under different boundary conditions are give in this paper.The environmental dispersion is systematically analyzed in wetland flows,and the pollution environmental dispersion in different wetland models under the influence of complex boundary conditions is solved.Analytical solution for the spatial distribution of the two-dimensional concentration,the contaminant cloud and the influence of complex boundaries on pollutant dispersion are discussed. |
