Lake Basin Land-use Change And Lake Water Quality Relationship Studies

As a kind of resources, lakes are important to the socio-economy. At present lakes of our country are polluted seriously by human activities, which lead to the change of land use and then the change causes the change of lake water quality. It has a theoretical and practical significance to explore the influence which the change of land use makes to the lake water quality. The change of land use affects lake water quality in two ways of point-source pollution and nonpoint-source pollution. Usually point-source pollution can be more easily prevented and controlled through relevant laws and regulations. Presently, point-source pollution of lake Erhai is not much, and nonpoint-source pollution has the main effects on lake Erhai water quality. Therefore, with the application of remote sensing and GIS technology, with the aid of the SWAT model,taking 1990,2001 and 2006 phase remote sensing image as the foundation, adopting DEM data, soil data, rainfall data, basin slope length, slopes and other data, this thesis takes lake Erhai as an example, and researchs the change of lake water quality influenced by the change of lake Erhai basin land use, and take the nonpoint-source pollution as a research object.The pollution loads by nitrogen and phosphorus primarily. The main research contents of this paper are as follows:1. Firstly we make pretreatment to the original images of in 1990,2001 and 2006 and join them together with ERDAS software.Then we cut remote sensing images according to Lake Erhai basin range, so get remote sensing images of Lake Erhai basin. In ArcGis9.2 working platform, and combining the GPS records of field investigation, GIS data information, we establish interpretation template, In ArcGIS9.2 working platform,we digitize remote sensing images of Lake Erhai basin,and then perform visual correction. Through grid inspection, overall accuracy classification results is for 0.801. It satisfies the classification requirements of remote sensing image land use, then gets three issues status charts of the land use.2. With the multiple rainfall figures of Lake Erhai basin, we get 1990,2001 and 2006 three years contour of the precipitation by kriging interpolation method in ArcGIS9.2 platform, and cut out the soil type map of Lake Erhai basin from national soil map according to erhai location roughly, then classificate soil maps again according to the river boundary segmented basin and to SWAT model requirement.3. In ArcGIS9.2 working platform, we make data format and projection transformations on DEM and land use to make all spatial data have the same geographic coordinates and projection. We make pretreatment as filling to DEM etc, then make convergence analysis, generate river network, and divide sub-basin according to DEM processed in AVSWAT2.0.0 platform, finally we get relevant information of Lake Erhai basin.4. With the application of spatial data processed, watershed meteorology, fertilizer and other data in ArcGIS9.2 working platform, we make analog output of nitrogen and phosphorus in basin in AVSWAT2.0.0 platform, then we get total nitrogen and total phosphorus load in 1990,2001 and 2006. Through the values of water quality, we calibrate total phosphorus and total nitrogen of river channel output files on SWAT model. Overall, the model simulation results are basically reasonable, can be used to nonpoint source pollution analysis for Lake Erhai.5. We set up different scenes of land use change, then we simulate and get the total nitrogen and phosphorus load in AVSWAT2.0.0 platform after land use change.6. we get the total nitrogen and phosphorus load data according to 1990,2001 and 2006 three years of land use change data, and analyze effects which the change of land basin use makes to water, combining with the result of nitrogen and phosphorus load produced by different scenes setted of land use change.7. Finally, this article puts forward some measures to the reasonable utilization of land source of Lake Erhai basin and gives some suggestions for reducing Lake Erhai eutrophication, such as watershed land use planning and lake planning etc. It initiates for reasonable planning of Lake Erhai and provide reference methods for the followed-up work.