赤水河流域中上游坡地景观特征对河流水质的影响

The effects of sloping landscape features on water quality in the upper and middle reaches of the Chishui River Watershed

在喀斯特地区,较大的地表坡降和坡地开发强度导致承载在地表景观上的污染物因地势和降水加倍迁移到河水中。以赤水河流域中上游为研究区,分别在全子流域、子流域坡地、子流域陡坡地三个层面上提取景观结构、景观开发强度和景观格局指数,研究各级坡地景观特征对水质的影响。结果表明:(1)与总林地相比坡林地对水质潜在的"汇"作用更加显著;占总耕地面积不足1/7的陡坡耕地、却对河水中总磷(TP)和氨氮(NH3-N)浓度大小贡献显著(相关系数为0.608和0.614)。(2)景观开发强度与各水质污染物指标呈现显著而稳定的正相关性,相关系数最高达0.960,它比单个景观对水质指标更具解释能力。(3)斑块形状复杂度、景观多样性、景观分离度均与水质污染物指标呈高度或显著正相关,且随着地形坡度的增大,水质污染物指标对景观散布与并列指数(IJI)和农香多样性指数(SHDI)越来越敏感。故减少对坡地尤其是陡坡地景观的不当人为干扰,对喀斯特地区流域水质保护有重要意义。

This study, with the sampling cases of the upper and middle reaches of the Chishui River Watershed in the karst region of southern China, attempts to examine the response mechanism of water quality variables to sloping landscape elements, which include landscape structure, landscape development intensity and landscape pattern, respectively extracted from three aspects of the whole sub-watershed, sloping land and steep land of the sub-watershed. The GIS spatial analysis and statistical analysis are employed based on Landsat80LI data and the water quality monitoring data during the plentiful water season and the withered water season from 2012 to 2013. There are three sub-sections in this study. One is the relationship between landscape structure and water quality. The data analysis results indicate that the landscape structure of sloping land and steep land has significant effect on the water quality of the river. Compared with the total woodland, the slope woodland has more significant positive effect on water quality. The percentage of steep slope cropland area has significant positive correlations with total phosphorus （TP） and ammonia nitrogen （NH3-N） （the correlation coefficients reach 0.608 and 0.614）, which shows that the percentage of steep slope cropland area has significant negative effect on water quality. The second is the relationship analysis between landscape development intensity and water quality. The indicators, which have a significant and stable positive correlation （the highest correlation coefficient is 0.960）, show that the landscape development intensity is more explicable to the water quality variables than any other single landscape composition. The last is the relationship analysis between sloping landscape pattern and water quality. The water quality is affected by complexity of the patch, isolation and diversity of landscape in this region. It is also found that the water quality variables have become increasingly sensitive to the Interspersion and Juxtaposition Index （UI） and the Shannon Diversity Index （SHDI） with slope degree increase. Therefore, more restrictions should be present to curtail land clearing on steep hills, and to keep away disturbance and destruction from human on the sloping land, especially on the steep land. It is significant to protect water quality in the karst area.