The Application Study On The Modelling Total Phosphorus Input And Water Quality Response In Lake Yangzonghai

On the basis of firstly modeling total phosphorus input and water quality response and calculating the environmental capacity for total phosphorus of Lake Yangzonghai,this paper analyzing the sources of total phosphorus and the change pattern of total phosphorus concentration.The result is found to be quite consistent with the monitoring data.The model can be used as a tool for controlling the total phosphorus and the lake water quality.The research combined the remote sensing,geographical information system (GIS)and the Universal Soil Loss Equation(USLE)to estimate the non-point pollution load from the agricultural land,counting the point source load by discharging reporting forms and monitoring.It is found by the research that the total load of total phosphorus going to the lake from the catchment was 107.7 tons in 2004, among which 86 percent from non-point source and 14 percent from point source. Non-point source pollution load was mainly from the soil loss as a result of land use in the catchment.Point source pollution load came from cattle and fowl breeding(44 percent),fishery(24 percent),domestic pollution(20 percent)and the channeling water(12 percent).The analysis of water resources in Lake Yangzonghai catchment shows that the amount of water resources in the basin varies largely from year to year.The annual amount of water going to the lake is 47.73 million cubic meters,with the maximum 96.5 million cubic meters and the minimum 17.63 million cubic meters.The water amount of the driest year is only 20 percent of that in the wettest year.Consequently, it is vital to control the water use and to main tern the balance of water demand and water supply in the basin so that a stable environmental capacity of the lake can be maintained.The lake is in the process from the oligotrophic state to the mesotrophic state at present.The concentration of total phosphorus in Lake Yangzonghai was between 0.017 mg/l and 0.031mg/l,with an average value of 0.021 mg/l,showing a declining trend from year 2000 to year 2005.Because the average concentration of total phosphorus is fluctuating near the warning line of eutrophication,the lake is facing the threat of eutrophication now.The relation between total phosphorus input and water quality response established by zero dimension lake water quality model,with 15 percent relative error, can be used for the control of the total phosphorus and the water quality management of the lake.Prediction by the model shows that it is very effective to improve the water quality of the lake by reducing the load input.The concentration of total phosphorus changes with the load reduction almost at same proportion.So,it is the best way to control the water pollution by reducing the external load input.The environmental capacity of Lake Yangzonghai changes with its volume.The environmental capacity for total phosphorus in terms of average volume of the driest months in last ten years is 149 tons.Compared with the present load input,it is larger than the present load input.But because the seasonal change of both the environmental capacity and the external load input is not synchronous and even,the concentration of total phosphorus occasionally goes higher than the water standard.It is necessary to control the total phosphorus load input according to the environmental capacity change in terms of month or season to maintain the water quality to meet the standard continuouslySince the pollution of Lake Yangzonghai is mainly from agricultural source,main efforts should be taken to control the phosphorus from the non-point pollution.The measures includes formulating the master plan of land use in the basin as soon as possible,optimizing the industry structure and layout,promoting water-saving agriculture,remediation the soil loss by integrated way,setting up a buffeting belt around the lake,purifying the channeling water before it getting to the lake,the population control etc.Aiming at the point source load control,the measures to be taken includes the sewage insect ion around the lake,the sewage treatment plant in the southern town,restricting the growth of cattle and fowl breeding and fishery.The new ideas in this paper are as follows:It is the first time for Lake Yangzonghai to establish the relation between the total phosphorus input and water quality response.The proceeding is leading in the study of Lake Yangzonghai. It is creative to analyze the change pattern of total phosphorus concentration based on environmental capacity calculation.The research approach to combine the remote sensing,geographical information system(GIS)and the Universal Soil Loss Equation(USLE)together to estimate the non-point pollution load from the agricultural land is quite practical and creative.