Abstract: Identifying the impacts of landscape pattern on surface water quality and its characteristic scale is a hot and crux in the field of water environment research. In this study, the Lashihai watershed in northwest Yunnan Province was taken as the research area, and 50 water sample points were taken as the centers. With an interval of 50 m, landscape type composition and 10 landscape pattern indices of five buffer zones between 50 to 250 m were calculated, and their correlations with the total phosphorus and total nitrogen contents of water body were analyzed to identify the characteristic scale of the impact of landscape pattern on water quality. The results showed significant differentiation of watershedscale landscape pattern between mountainous areas and dam areas. The bufferscale landscape pattern index of water sample points changed significantly in the 100 m buffer zone. The average concentrations of TP and TN were 0.12 mg·L^-1 and 1.61 mg·L^-1 respectively, with a trend of continuous enrichment from upstream to downstream and an obvious spatial difference of pollution degree among the sampling points. Surface water TP concentration was higher in grassland adjacent to water body, and TN concentration was higher in the forest in the mountainous area. When the buffer zone of the water sample point was 100 m, the correlation between the landscape pattern and the surface water quality parameters was the highest. The TP concentration was significantly positively correlated with patch density, edge density, landscape shape index, landscape split index, and Shannon diversity index. Therefore, we should focus on the grassland in the dam area and the landscape pattern within 100 m around the Lashihai Lake to improve surface water quality.

Key words: Lashihai watershed, landscape pattern, characteristic scale, water quality, plateau lake