Research On The Relationship Between Landscape Pattern And Hydrology And Water Quality In Yongding River Watershed Based On HSPF Model

In 2005,General Secretary Xi Jinping put forward the concept that"lucid waters and lush mountains are invaluable assets",and the Sixth Plenary Session of the 19th Central Committee of the Communist Party of China pointed out that we should focus on the construction of ecological civilization and take major steps to promote the construction of a beautiful China.The Yongding River is a natural corridor running through the Beijing-Tianjin-Hebei ecological function zone,and it is the focus of the first breakthrough in the ecological field of regional coordinated development.It is of great significance to strengthen the ecological environment protection of the Yongding River.However,affected by climate change and human economic and social activities,the Yongding River Basin is facing problems such as lack of water resources,serious shortage of ecological water in the river,poor water quality in some sections,declining water environment carrying capacity,and ecosystem degradation.The evolution law of landscape pattern can explain the impact of human activities on land use changes and river hydrology and water quality.Therefore,comprehensively consider the relationship between human activities,land use,water resources,and water environment in the Yongding River Basin to conduct landscape pattern changes and river basin hydrology.The research on the relationship between water quality is of great significance.Based on RS and GIS,the research researches the changes of land use/landscape pattern in the basin,establishes the HSPF hydrological model,simulates the runoff and water quality of the basin,and sets up different land use and climate evolution scenarios to explore The evolution of watershed runoff and water quality under different conditions was analyzed,and point out the relationship between watershed landscape pattern and hydrology and water quality and the main conclusions of this study are as follows:（1）The research on the change of land use area in the river basin,the dynamic degree of single land use and the land use transition matrix found that:from 1995 to 2018,the area of forest land and construction land in the river basin continued to increase,the area of cultivated land and water area showed a phenomenon of decrease first and then increase.The area of unused land increased first and then decreased.The fastest area of change was construction land,followed by forest land.Mutual transformation occurred various land use types,which was mainly reflected in cultivated land,forest land,grassland and construction land.Among them,cultivated land is mainly converted into forest land,grassland and construction land;forest land and construction land are mainly converted from cultivated land and grassland.The Fragstats4.1software was used to research the changing characteristics of the landscape pattern in the watershed.The results showed that the fragmentation and complexity of the watershed landscape decreased.At the same time,the distribution of the landscape tended to be uniform,the connectivity continued to decrease.With the growth of population and the improvement of urbanization level,the degree of aggregation and connection of construction land is on the rise.Affected by the centralized water delivery and ecological water replenishment in recent years,the landscape dominance of water areas exceeded that of cultivated land and reached the highest level in 2018.（2）The HSPF hydrological model is used to simulate the runoff and water quality of the watershed,with 2014-2016 as the regular period,and 2017-2018 as the verification period for parameter calibration and verification.The simulation results show that the relative error（Re）between the measured value and the simulated value of annual runoff is controlled within 10%;the Nash coefficient（Ens）of the monthly runoff simulation rate is about 0.7 in both regular and verification periods,and the correlation coefficient（R）is both at 0.9 about.The relative error（Re）between the measured value and the simulated value of water quality is controlled at about10%,and the Nash coefficient（Ens）and the correlation coefficient（R）are about 0.7 and 0.9,respectively.The simulation results are generally in line with the variation trend of the measured values.（3）According to the parameters that have been calibrated,different land use scenarios and climate scenarios are set up to simulate runoff and water quality.The results show that the water conservation capacity of cultivated land is greater than that of forest land and grassland.Land use scenario one（L1）and scenario The second（L2）runoff is reduced by 19.39m~3/s and28.87m~3/s compared with the baseline scenario（L0）,respectively;the pollutant concentration is L1>L2>L0,indicating that the intensification of human activities will affect the water quality of the river and the existence of forest and grass.It will have a certain purification effect on the water body.Climate change scenario one（C1）increased runoff by 4.74m~3/s,while scenario two（C2）decreased by 7.58m~3/s,indicating that the increase in rainfall and temperature had opposite effects on runoff;COD concentrations C1>C2,NH₃-N and TP concentration C2>C1,indicating that COD is less sensitive to temperature than NH₃-N and TP.（4）The results of Pearson correlation analysis and redundancy（RDA）analysis show that:at the landscape level,the reduction of the complexity of landscape shape and the increase of landscape aggregation can promote runoff,and the reduction of landscape fragmentation is beneficial to the runoff.Reduce the concentration of COD.At the type level,the decrease in the number of cultivated land patches and the intensification of human activities are not conducive to the generation of runoff,while the decrease in the number of water patches,the decrease in the degree of fragmentation of forest land and the increase in the degree of connection are conducive to the formation of runoff.The increase of grassland landscape aggregation degree and the increase of landscape dominance,aggregation degree and connection degree of construction land will cause the decrease of COD concentration;the connection degree of unused land will increase,and the concentration of NH3-N will decrease;the aggregation degree of water area will increase.An increase in the TP concentration is caused,and an increase in the degree of aggregation in the unused land results in a decrease in the TP concentration.