云南拉市海流域景观格局对地表水质的影响及尺度识别

Effects of landscape patterns on surface water quality and its characteristic scale in the Lashihai watershed of Yunnan Province

识别景观格局对地表水质的影响及其特征尺度是水环境研究领域的热点和难点。本文以滇西北拉市海流域为研究区,以50个水样点为中心,按照50 m的间距,计算其50~250 m的5个缓冲区的景观类型组成和10种景观格局指数,并与水体总磷、总氮进行相关性分析,识别景观格局对地表水质影响的特征尺度。结果表明:流域尺度景观格局具有山区-坝区显著分异特征,水样点缓冲区尺度景观格局指数在100 m缓冲区时出现明显变化;总磷和总氮平均浓度分别为0.12 mg·L^(-1)和1.61 mg·L^(-1),具有自上游向下游不断升高的趋势,样点间的污染程度空间差异明显;邻近水体的草地的地表水总磷浓度较高,山区林地的地表水总氮浓度较高;水样点缓冲区100 m时其景观格局与地表水质参数相关性最高,其中总磷浓度与斑块密度、边缘密度、景观形状指数、景观分裂指数和香农多样性指数呈显著正相关。因此,应重点关注坝区草地和拉市海周边100 m内的景观格局,以改善地表水质。

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 watershedscale landscape pattern between mountainous areas and dam areas.The bufferscale 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.