Analyzing The Impact On The Changes Of The Key Elements Of Surface Cover In Dianchi Lake Basin On The Water Quality Of Dianchi Lake In Recent 30 Years

Land use/land cover change?LUCC?directly affects the cyclic processes of surface materials and energy,and has an important impact on climate change and regional ecological environment.With the rapid development of social economy,the problem of non-point source pollution of water body is becoming more and more prominent,and non-point source pollution caused by the change of surface factors such as forest land,cultivated land,wetland,impervious surface,etc.,is the main source of pollution affecting the quality of water in land use/land cover change?LUCC?..Over the past 30 years,with the rapid development of the economy and the continuous promotion of urbanization,the key elements of the surface cover of the Dianchi Lake Basin has changed greatly.At the same time,water quality deteriorated seriously in Dianchi Lake,cyanobacteria and blooms erupted frequently,and the water quality of Dianchi Lake was the inferior Class V for 20 consecutive years.So,the extraction of the key elements information of the surface cover and changes of the Dianchi Lake basin in the last 30 years and its influence on the water quality in Dianchi Lake are the main research content.Using Landsat remote sensing image data as data source,through the visual interpretation method,index method and decision tree method to extract the key elements information of the surface cover of Dianchi Lake Basin,the change characteristics of land cover in Dianchi Lake basin in recent 30 years were analyzed by means of land cover change amplitude,land cover dynamic model and transfer matrix.The change of water quality in Dianchi Lake was analyzed with the Mann_Kendall mutation analysis model.Finally,the correlation between the key elements of the surface and the water quality index of Dianchi Lake basin is discussed with the method of statistical analysis and spatial analysis.It provides beneficial suggestions for the ecological balance in the Dianchi Lake Basin,the Dianchi governance and the urban planning of Kunming and the rational use of the land.The preliminary conclusions of this paper are as follows:?1?Significant changes in the key elements of the surface cover of the Dianchi Lake basin in recent 30 years.Among them,the area of impervious surface has increased rapidly.In 1989,the impervious surface coverage rate was only 5.14%.In2016,the impervious surface coverage rate reached 20.58%;The area of cultivated land increased first and then decreased.The area of cultivated land reached the maximum in 1998,and then decreased year by year.The area of forest land was increasing,compared with 1989,the coverage rate of forest land area increased by about 10%in 2016.The wetland area has been growing continuously since 2010.The undulation of unused land area fluctuates greatly,but it has a tendency to decrease greatly on the whole.The area of the water body is the smallest,and the proportion of the area has been maintained at about 10%-11%.?2?From the perspective of the transfer of the key elements of the surface cover,the most of the transfer area is cultivated land and unused land;The areas with the largest increase in area are forest lands and impervious surfaces.From the direction of the transfer,the unused land has mainly turned to forest land,cultivated land and impervious surfaces,and the cultivated land has mainly turned to forest lands and impervious surfaces.From the perspective of the spatial differences in the transfer,the transfer of unused land to cultivated land mainly occurs in the northern area of the Panlong River basin,the northernmost part of the Dianchi Lake basin;The transfer of unused land to impervious surfaces mainly occurred in the eastern and northeastern parts of Dianchi Lake;the transfer of cultivated land to the impervious surface mainly occurred in the urban area of Kunming City in the northern part of Dianchi Lake.?3?the pollution of water quality in Dianchi is serious,and it has been the inferior Clsaa V water quality for the last 20 years,which belongs to the moderate and severe eutrophic lake.It was found that the distribution of chlorophyll a in water was related to the distribution of impervious surface and cultivated land.The change of COD_Mn,BOD₅,TP and TN in Dianchi water quality in recent 30 years has been monitored and analyzed by Mann-Kendall mutation.It is found that except for the monotonous increase of TN concentration,the other indexes all increase or decrease.The water quality of most sub-basins deteriorated during 1998-2013,and improved slightly in 2016.?4?The correlation between forest land,cultivated land,wetland,impervious surface and water quality is significant,among which,forest land and wetland are negatively correlated with water quality,and the cultivated land and impervious surface are positively correlated with water quality.And this correlation is most significant in the two-scale range of 1000m and sub-basin.It can be seen that the key elements of the surface of rivers and lakes near the shore zone has a greater impact on water quality.