Research On The Effect Mechanism Of Water-Sediment-macrophyte Interaction On Water Quality

The process of nutrients release at the water-sediment interface has significant impact on water quality and water environment ecosystem.The research of internal nutrient release and nutrient migration-transformation under the interaction of water,sediment and aquatic macrophytes is of utmost importance for controlling internal pollution and eutrophication in water environment.In this paper,combined with the results of laboratory experiments and field monitoring,a coupled and dynamic water-sediment-macrophyte ecosystem model was proposed.This model was applied to simulate nutrient release from sediment and nutrient migration and transformation in Baitan Lake and Jinshan Lake.The contents and achievements of the paper are as follows:(1)The characteristics of nutrient release from sediment and its influence factors,water ecosystem models were reviewed.Considering the need to study the impact of nutrients release at the water-sediment interface on water quality,this paper summarized the problems and demands in the research region of the nutrient release at the water-sediment interface and its influence mechanism on water quality.At present,it is urgent to focus on the effect and the dynamic mechanism of internal release at the water-sediment interface on water quality.(2)The internal release characteristic of nutrients at the water-sediment interface affected by disturbance and aquatic macrophytes were studied.The release fluxes of N and P in the static condition were lower than that in the disturbance condition.The greater the disturbance intensity,the larger the release fluxes of nutrients were.Affected by aquatic macrophytes,the TN and TP concentrations in surfacicl sediment decreased.Aquatic macrophytes have a positive impact on the concentrations of TN and TP in surfacicl sediment.The N and P in sediment showed obvious stratification characteristics.The release fluxes of N and P at the watersediment interface decreases and the release were inhibited under the effect of aquatic macrophytes growth.Aquatic macrophytes can indirectly regulate internal N and P release fluxes at the water-sediment interface by affecting dissolve oxygen(DO)concentration in water and TP concentration in sediment.(3)Through field monitoring,the forms of nutrients in water and sediment and the vertical characteristics of sediment nutrients were analyzed.The spatio-temporal distribution of physical and chemical characteristics,different forms of nitrogen(N)and phosphorus(P)concentrations shows obvious difference.The concentrations of nutrients in sediments generally showed a decreasing trend with increasing sediment depth,and the variation accorded with the exponential equation,showing obvious stratification characteristics.(4)Combined with the characteristic of nutrients transport and transformation among water,sediment and macrophyte,a coupled and dynamic water-sediment-macrophyte ecosystem model was developed.The physical migration and diffusion,biochemical reaction of nutrients affected by aquatic macrophytes were taken into account in this model.This model can quantify the physical mechanism and process of nutrients transport and transformation among water,sediment and aquatic macrophytes.(5)The spatio-temporal distribution and the release flux of nutrients in Baitan Lake was estimated by the proposed model.The estimated values were compared with the measured data in Baitan Lake,and the average relative errors were below 10 %.These overall resulted in a good fit of simulated and observed data,indicating a good method performance.Nitrogen and phosphorus release fluxes of Baitan Lake basin were the smallest in Spring and the largest in Summer and Winter.N and P deposited to sediment in Spring,while N and P released from sediment to water in Summer and Winter.In the whole year,sediment N and P released to water.(6)Different forms of nutrients and their spatio-temporal distribution under the interaction of water,sediment and aquatic macrophytes in Jinshan Lake were simulated by the proposed model.The estimated values were compared with the measured data,and the average relative errors were below 15 %.These overall resulted in a good fit of simulated and observed data,indicating a good method performance.The concentrations of inorganic nutrients in pore water of the surfacial sediment is significantly higher than that in water,and the Jinshan Lake is significantly polluted by internal pollution.The concentrations of organic nitrogen and phosphorus in Jinshan Lake was higher than that of inorganic nitrogen and phosphorus.The concentrations of nutrients during the growth of aquatic macrophytes was lower than that during the decay of aquatic macrophytes.