Study On Small Urban Shallow Lake Inner Pollution Source And Environmental Dredging Depth

Taken lake Xuanwu in Nanjing-a small urban shallow lake as the research object, Analysed the physical and chemical character of the surface sediments of Xuanwu lake. Simulated the indoor release nitrogen and phosphorus experiment from the surface sediments under difference condition that effect inner pollution source. Researched the mechanism of different factor such as temperature, dissolved oxygen, oxidation-reduction potentials, pH value, disturb, algae and chironomid effect on the release nitrogen and phosphorus from the lake sediment, the release flux of nitrogen and phosphorus from the lake sediment are summarized through the simulated experiment of pole-core sample in Xuanwu lake, and ration study on the relationship between releasing rate coefficient and factors(temperature, dissolved oxygen, pH value) are also taken on, revised the traditional sediment-water interface exchange flux calculation formula of nitrogen and phosphorus.This paper also studied the mechanism of temperature, pH value, sediment grain size, disturb intensity effect adsorption-desorption on ammonia and phosphate from the lake XuanWu sediment. Meanwhile researched kinetics mechanism that ammonia and phosphate adsorbed and desorbed from lake XuanWu sediment. Explored Henry isotherm adsorbed phosphate model, Freundlich isotherm adsorbed phosphate model and Langmuir isotherm adsorbed phosphate model, studied the probability density distributing function of sediment phosphorus contamination adsorption capacity under the Henry, Freundlich, Langmuir adsorption kinetics pattern.Establish the hydrodynamics mathematic model of lake Xuanwu, studied field of inflow-outflow with 180 kilo ton per day and current driven by stead East wind, West wind, South wind, North wind, Southeast wind, Northwest wind, Northeast wind, Southwest wind respective. Moreover simulated field of the admixture flow driven by the 6m/s eight stead different direction wind respective with 180 kilo ton per day. Established,researched and developed a plane depth-averaged 2D flow-water quality-sediment pore water pollution coupled model (FQSC2DM) based on the hydrodynamic characteristic of lake Xuanwu. Compare and choose the better project that pump water into lake Xuanwu 180 kilo ton per day from water supply factory using this model. Simulated results match the measured data very well, the conclusion was adopted by public utility bureau of Nanjing city.Determined the sediment environmental dredging depth is 25 centimeter in lake circumference, 15 centimeter in lake center through long-term nitrogen and phosphorus release indoor experiment and computing release flux using pore water model. Educed the environment-al dredging depth criterion and erect the cleanup sediment method which aim at phosphorus release based on phosphorus forms change pre-release and post-release from the sediment. Confirmed the sediment environmental dredging depth is 25 centimeter in lake circumference, 12．5 centimeter in lake center through phosphorus forms determinateness method, which match the conclusion that drawn from long-term nitrogen and phosphorus release experiment very well. The study provides a new approach and a practical model for sediment environmental dredging depth determinateness in the shallow lake.