[Effects of Land Use Composition and Landscape Pattern on River Water Quality at Multi-temporal and Spatial Scale in...

Due to the heterogeneity of the natural environment， there are also differences in the impact modes between land use and water quality in different regions. Exploring the impact of land use on water quality is of great significance for the restoration and protection of water environments. Based on water quality monitoring data and land use data in the Yangtze River Basin （Chongqing Section）， this study extracted the land use composition and landscape pattern at three spatial scales： sub-basin， the 500 m riparian buffer zone， and the 1 000 m river reach buffer zone. Combined with the latest territorial spatial planning of Chongqing， the study area was divided into four regions （the central urban area Chongqing municipality， new area for the central urban， urban agglomeration in the Three Gorges Reservoir area in northeast Chongqing， and urban agglomeration in the Wuling mountainous area in southeast Chongqing）， and the effects of land use characteristics on riverine water quality were quantitatively discussed by using redundancy analysis methods. The results showed that：① The overall water quality of the rivers in the study area was better in the dry season than in the rainy season. The water quality in the central urban area Chongqing municipality was the best， while that in the new area for the central urban area was the worst. Total nitrogen was the main water pollutant in the study area. ② The explanatory power of land use on river water quality was stronger in the dry season than in the rainy season， and the magnitude of the difference varied with the spatial scale： the 1 000 m river reach buffer zone > the 500 m riparian buffer zone > sub-basin. ③ The impact of land use on river water quality was most significant in the central urban area Chongqing municipality. The correlation between land use and water quality was the highest in the 1 000 m river reach buffer zone in the central urban area Chongqing municipality， while in other regions， it was in the 500 m riparian buffer zone. ④ Farmland was the "source" landscape for river water quality. Forest and grassland， while functioning as "sinks" for intercepting and absorbing pollutants， were also "sources" of pollutants in the central urban area Chongqing municipality. Grassland was also a major source of nitrogen nutrients in the urban agglomeration in the Wuling mountainous area in southeast Chongqing. The impact of construction land on water quality showed duality in the central urban area Chongqing municipality. Edge density（ED）was positively correlated with the concentration of water pollutants， aggregation index（AI）was negatively correlated with the concentration of pollutants， and the correlation between the largest patch index（LPI）and the Shannon's diversity index （SHDI）and pollutant concentration varied by region. The impact of land use on river water quality varied by season and region. Therefore， it is necessary to optimize the landscape structure based on local conditions， especially for human activities near rivers， and formulate measures to reduce pollutant emissions to improve river water quality.