长江上游坡地景观特征对河流水质的影响

The influence of sloping landscape features on riverine water quality in upper Yangtze River

景观组成及景观格局特征决定了污染物的来源和地表景观的拦截消纳潜力,地表坡降会加剧土壤侵蚀,坡地景观特征是影响河流水质的重要因素。研究基于长江上游重庆段2015年水质监测数据和30 m空间分辨率土地利用数据,提取河岸带100 m、200 m、300 m、500 m、1000 m和子流域6种空间尺度上景观格局和景观组成,并进一步将景观组成分为总地类、缓坡地类和陡坡地类三种不同坡度尺度,再采用相关分析和冗余分析(RDA)等方法定量探讨了坡地景观特征(坡地景观组成、景观格局)对河流水质的多时空尺度影响。结果表明:坡地景观特征对2015年长江上游重庆段河流水质的影响具有空间尺度效应;坡地景观特征对河流水质的影响在河岸带尺度强于子流域尺度,其中关键尺度为河岸带100 m至300 m,最有效尺度为河岸带200 m。坡地景观特征影响水质的季节差异随空间尺度不同而变化,在河岸带100 m至300 m尺度为汛期强于非汛期,在河岸带1000 m尺度相反,在子流域尺度无季节差异。建设用地面积比与溶解氧(DO)和高锰酸盐指数(COD)正相关,耕地面积百分比与氨氮(NH^(+)_(4)-)参数正相关,两者为水质污染“源景观”,且缓坡耕地对水质的解释率高于总地类耕地;林地与水质参数呈负相关,对缓解水质恶化具有积极作用;集聚度(COHESION)、聚合度(AI)指标与NH^(+)_(4)-N参数及斑块密度(PD)、边缘密度(ED)与DO、COD_(Mn)参数均呈正相关。在集水区尤其是河岸带300 m范围内,严格把控建设用地污水收集与处理,种植河岸带防护林,采取横坡耕种方式,并通过优化景观结构(如种植植物篱)以增强景观拦截力以减少污染物的集中输出,从而改善河流水质。

Landscape compositions and patterns determine the sources of pollutants and the potential in interception and absorption of the surface landscape.Meanwhile,the surface slope will aggravate soil erosion.Therefore,the sloping landscape characteristics are important factors affecting riverine water quality.Based on the water quality monitoring data of the Chongqing section of the upper Yangtze River in 2015 and land use data with a spatial resolution of 30 m,this study firstly extracted landscape patterns and compositions at six scales:100,200,300,500 and 1000 m river buffers and sub-watershed.We further classified the landscape compositions into three different slope scales(i.e.,total land class,gently sloping land class and steep sloping land class).Furthermore,correlation analysis and redundancy analysis(RDA)were used to quantitatively explore the multiple spatial and temporal impacts of sloping landscape features.The results showed that:(1)the influence of sloping landscape features on riverine water quality exhibited a spatial scale effect.The influence was stronger at the riparian scale than the sub-basin scale with the conditions of key scale ranging from 100 m to 300 m in the riparian zone,and the most effective scale of 200 m riparian.(2)The seasonal differences in riverine water quality affected by sloping landscape features varied with the spatial scale.The flood season was stronger at the 100 m to 300 m riparian scales than the non-flood season,and the opposite in the 1000 m riparian scale,whilst,there was no seasonal difference at the sub-basin scale.(3)The ratio of construction was positively correlated with dissolved oxygen(DO),permanganate(COD)parameters,and the percentage of cultivated field was positively correlated with ammonia nitrogen(NH^(+)_(4)-),both of which were“source landscapes”of water quality pollution.The explanation rate of sloping cultivated land on water quality was higher than that of total land type cultivated land.Forest was negatively correlated with water quality parameters,which had a positive effect on mitigating water quality deterioration.(4)The patch cohesion index(COHESION)and aggregation index(AI)were positively correlated with NH^(+)_(4)-,while patch density(PD)and edge density(ED)indicators were also positively correlated with DO and COD_(Mn).In summary,strengthening sewage treatment technologies for urban,planting protective forests in the riparian zone,adopting cross-slope farming and optimizing the landscape structure can enhance the absorption of pollutants and effectively prevent the concentrated output of pollutants within the watershed(especially within 300 m riparian zones),which is of great significance to the prevention and control of water pollution in rivers.