| As a city in South China at the junction of Jiangsu,Zhejiang and Anhui provinces,Liyang has been developing rapidly since its establishment of a county-level city,and the process of urbanization is advancing rapidly.At the same time,the water environment in Liyang is deteriorating,the harmonious development of human and nature has been broken,and the sustainable development of the economy is facing a serious threat.During the process of urbanization,the dramatic change of urban land use and the abrupt change of underlying surface structure directly affect the quality of urban water environment.Under this background,it is particularly important to analyze and study the intensity of land use change and understand the advantages and disadvantages of water environment evolution.Through exploring the coupling relationship between land use change and water environment evolution,it can provide a certain basis for the sustainable development of economy and society and the protection of water environment in future cities.Taking the basin of Liyang Danjinlicaohe as an example,based on the DEM elevation data of 1989,2003,2012 and 2016,the water quality monitoring data of four routine monitoring sections of Liyang Danjinlicaohe in 2012,the water quality monitoring data and the field investigation data,this paper used various tools such as ArcGIS,ENVI,SPSS,Canoco,Google Earth and WINQSB flexibly,used the research methods such as geography,environment,statistics and ecology to study the change of land use,the evolution of water environment and the coupling relationship in Liyang Danjinlicaohe basin.(1)The range of the basin was defined by DEM elevation data and remote sensing image,and the water system map was generated by ArcGIS,and corrected them by Google Earth and visual interpretation of remote sensing.The water system characteristics and water system structure parameters were calculated and analyzed after the classification of water system by Horton method.The results show that the water system structure is deteriorating with the urbanization,and the water system density,the water surface rate and the development coefficient of the river network are in the downward trend.According to the water quality of rivers,evaluated the water quality from 2012 to 2016 by using the single index evaluation method.The results showed that the most serious indicators were ammonia nitrogen,total nitrogen and total phosphorus.The comprehensive evaluation of water quality is carried out by the Nemerow index method.It is found that the overall water quality was still not optimistic and the water quality fluctuates obviously,but the change trend of water quality has improved in recent years.(2)Using ENVI and ArcGIS to extract land use information from TM remote sensing images.According to the extraction information,the analysis results show that the land use types,such as cultivated land,water body and woodland,were in a continuous downward trend,down 6.98%,6.79% and 1.17% respectively in 2016 compared with 1989.The area of construction land continued to rise,reaching 5426.42 hectares in 2016.By using the entropy of land use information and the evaluation method of the balance degree of land use,it is found that the degree of land use equilibrium in the study area has fallen from 0.8649 in 1989 to 0.8606,and the land use structure was deteriorating,which is not conducive to the sustainable development of the city.(3)Through the definition of 500 meters,1000 meters,1500 meters and 2000 meters buffer zones,the characteristics and changes of land use in different buffer zones were analyzed,and a coupling analysis was made on the change of land use and the evolution of water environment.Using RDA redundancy sorting analysis,construction land is negatively correlated with dissolved oxygen and positively related to petroleum.In the 2000 meter buffer area,the construction land is positively correlated with the permanganate index and the chemical oxygen demand.In addition,the correlation between construction land and permanganate index,ammonia nitrogen,chemical oxygen demand,total nitrogen and other water quality indicators increased positively in the urban area.There is a negative correlation between cultivated land and dissolved oxygen,which is positively correlated with ammonia nitrogen,total nitrogen and total phosphorus,but the influence of cultivated land on the index of permanganate index and chemical oxygen demand is strengthened in the buffer range of 1000 meters in urban area.There is a positive correlation between water and chemical oxygen demand,and there is a negative correlation between water and total phosphorus in the 1000 meter buffer zone,and the dilution and degradation of phosphorus in the water body is strengthened.There is a negative correlation between forest land and water quality indicators.The larger the forest area is,the better the water quality is,but the correlation is not obvious due to the limited woodland area.The water system structure changes caused by land use change also have a certain influence on water quality.The correlation between the changes of water system structure characteristics and water quality is tested by Pearson correlation test.The results show that the correlation of dissolved oxygen and petroleum and water system structure is more significant.(4)Using the target programming model,the land use pattern in the basin was optimized on the basis of economic development,planning restriction,minimization of the contribution value of land use pollution and the maximization of the balance of land use.After the optimization measures were adopted,combined with the preliminary analysis of pollution sources,corresponding measures of point source control and point source control were put forward. |
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