基于冗余分析的成都市府河缓冲带土地利用对水质的影响

土地利用是影响河流水环境质量的重要因素之一。然而,大型城市河流缓冲区的土地利用类型及组成对河流水质的影响方式仍不清晰。选取成都市中心城区的府河及其支流作为研究对象,设置17个水质监测断面,于2018年1月—2019年12月对COD_Mn、NH₄⁺-N和TP 3个水质指标开展连续监测。同时,还获得了相同时段内的降水数据和基于高分卫星(GF-1)影像解译的土地利用数据。在此基础上,利用空间分析以及冗余分析方法,探讨河岸缓冲区内土地利用结构、组成对府河及支流水质的影响。研究结果表明:选取河段从上游到下游的COD_Mn、NH₄⁺-N和TP浓度均呈增加趋势,这3类污染物在上游第一个监测断面浓度依次为1.73、0.26、0.06 mg/L,到下游最后一个监测断面浓度为2.59、0.97、0.15 mg/L。相对于干流,府河支流污染物浓度无明显空间分布特征。从时间上看,6—9月水体中各污染物浓度相对较高。基于冗余分析的结果发现,在河段2 000 m缓冲区范围内的土地利用类型对水质的影响最明显,校正后的解释度达57%,表明河段内污染物质主要源于此区域。该范围内,建设用地与其他生产用地可能是COD_Mn与NH₄⁺-N的主要源区,农业用地是TP的主要来源,生态用地对于COD_Mn与NH₄⁺-N具有一定的吸收分解作用。但是,研究区生态用地以园林绿化用地为主,需要施用磷肥,可能成为水体TP的重要贡献源。因此,合理规划河流2 000 m缓冲范围内的建设用地与生态用地比例,控制园林绿化用地的施肥用量,是保障成都市城市河流水环境安全的重要途径。

Impacts of Land Use in Riparian Buffer Zone on Water Quality Based on RDA Model in Chengdu City

Numerous studies highlight the importance of water quality through land use. However,the scope of river buffer zones, the type of land use within the buffer zone,and the impact of its composition on the river''s water quality in the different river segments of metropolitan cities are rarely considered. In this study,we collected the water quality parameters (COD_Mn, NH₄⁺-N and TP) of the Fuhe River and its tributaries every month from 17 river segments located in the downtown area of Chengdu City from 2018 to 2019. Similarly,we collected precipitation data and the land use data interpreted by GF-1 satellite imagery in the same period. Then we uesd the spatial analysis and the redundancy analysis to explore the relationships between land use types and water quality indices in different buffer areas. The concentrations of TP,COD_Mn, and NH₄⁺-N gradually increased from the upper to lower reaches of the study area. The concentrations of the three types of pollutants in the first monitoring section (upstream) were 1.73,0.26 and 0.06 mg/L, while the concentrations in the last monitoring section (downstream) were 2.59, 0.97 and 0.15 mg/L,respectively. Compared to the main stream, tributaries had no obvious distribution characteristics. Regarding the temporal scale,the concentration of pollutants in the river was relatively high from June to September,possibly due to the summer monsoon rainfall,which has gathered pollutants from nearby water-flowing slopes. The spatial redundancy analysis found that the land use practice and characteristics within the buffer zone of 2000 meters in reach had the most obvious impact on water quality, with a corrected interpretation of 57%, indicating that the pollutants in the river mainly came from this area. Particularly, construction land and other commercial land might be the main sources of COD_Mn and NH₄⁺ -N,whereas agricultural land was the main source of TP. In addition,ecological land played some role in the uptake and decomposition of COD_Mn and NH₄⁺ -N. However, ecological land in urban may be a TP pollution source, which requires the use of a large amount of phosphorus fertilizer for landscaping. Therefore, it is necessary to balance the proportion of construction land and ecological land within the 2000 m riparian buffer zone and control the amount of fertilizer applied to the landscaping,which is an important way to improve water quality in Chengdu.