小流域农业面源污染阻力评价及"源-汇"风险空间格局

识别评价影响农业面源污染的"源-汇"风险格局,对小流域的农业面源污染防治规划有着重要的现实意义,为此,该文以三峡库区典型农业区王家沟小流域为研究区,借助最小累计阻力模型评价小流域农业面源污染阻力和识别"源-汇"风险。首先,通过土地利用解译数据确定"源"地的分级,在获取地形、距离、土地利用和氮磷等自然影响因子的基础上,构建氮和磷的阻力基面评价指标体系,并测算氮、磷和总阻力面,以此判定影响小流域农业面源污染的阻力空间分布趋势;同时借助阻力阈值,对阻力面进行等级划分,以此识别影响库区小流域农业面源污染的"源-汇"风险格局。结果表明:1)影响农业面源污染的不同阻力因子,其空间分布存在明显差异,由此奠定了阻力基面的空间异质性;阻力基面反映了影响三峡库区小流域农业面源污染的"源-汇"景观空间差异,表现为"源"景观类型的阻力基面小于"汇"景观类型;氮和磷的阻力面总体上围绕"源"地向外呈现不断增大的空间变化特征;2)划定了影响王家沟小流域农业面源污染的"源-汇"风险区:极高风险区(0.297 7 km~2)高风险区(0.154 4 km~2)中风险区(0.147 5 km~2)低风险区(0.147 4 km~2)极低风险区(0.016 0 km~2);影响整个小流域农业面源污染的"源-汇"风险偏高,但小流域内仍有一定范围的低风险区,能确保流域内的氮磷流失得到有效拦截。研究结果有助于从影响农业面源污染的"源-汇"景观和空间阻力角度识别评价"源-汇"风险格局,为科学防范和治理农业面源污染提供决策依据。

Resistance evaluation and "source-sink" risk spatial pattern of agricultural non-point source pollution in small catchment

Abstract: It has important practical significance for the prevention and control planning of agricultural non-point source pollution in small catchment by identifying and evaluating "source-sink" risk pattern impacting agricultural non-point source pollution. Therefore, in this paper, a case study was carried out in a small catchment named Wangjiagou, which located in the typical agricultural region of the Three Gorges Reservoir Region, and the minimal cumulative resistance model (MCR) was used to evaluate resistance and identify "source-sink" risk of agricultural non-point source pollution. At first, the source lands were divided into 6 grades by processing and analyzing on the land use data. Secondly, the resistance base surface impacting the agricultural non-point source pollution was constructed based on the selection of main natural influence factors, including topography factors (relative elevation and slope), land use factors (source-sink landscape type and vegetable interception index), hydrological factors (flow length and topographic wetness index), soil factors (soil loss vertical distance index and soil erosion intensity), nitrogen and phosphorus factors (nitrogen input and phosphorus input). Thirdly, MCR model was applied to obtain nitrogen, phosphorus and total resistance surface, respectively, and by which spatial distribution trend of resistance were identified. In the end, according to the resistance threshold, "source-sink" risk pattern was classified. The results showed that: 1) There were obvious difference among the spatial distribution of different resistance factors impacted on agricultural non-point source pollution, which established the foundation for spatial heterogeneity of resistance base surface. Resistance base surface reflected the spatial difference of "source-sink" landscape in the small catchment in the Three Gorges Reservoir Region, with the resistance base surface value of "source" landscape smaller than that of "sink" landscape. The obvious characteristic of resistance surface was that resistance surface changes were mainly influenced by spatial distance, and the value of resistance surface was smallest in the buffers located at the source lands, while the value was bigger and bigger as the distance was far from the source lands. 2) The MCR model was applied to classify "source-sink" risk pattern in the small catchment into 5 grades, including extremely high risk zone (0.297 7 km2), high risk zone (0.154 4 km2), medium risk zone (0.147 5 km2), low risk zone (0.147 4 km2) and extremely low risk zone (0.016 0 km2), which indicated that there was a high risk trend of "source-sink" risk pattern, while there were still a certain range of low risk areas in the small catchement, which can ensure the effective interception for nitrogen and phosphorus loss. The results are helpful to evaluate the risk degree and rank of non-point source pollution produced by "source-sink" landscape from the angle of resistance surface, and can provide the policy-making basis for preventing and controlling agriculture non-point source pollution scientifically.