土地利用变化影响的灞河流域潜在非点源污染风险时空变化特征

Spatial and temporal variations of non-point source pollution risk affected by land use changes in Bahe River Basin

流域内土地利用方式改变引起非点源污染源的时空变化,已显著影响地表、地下水环境质量。以人类活动影响强烈的灞河流域为例,采用改进后的潜在非点源污染指数模型(PNPI),探讨近20年半干旱区城市型河流土地利用变化影响下的流域潜在非点源污染风险时空变化特征及其主导因素。结果表明:灞河流域主要土地利用方式为林地与耕地,共占流域面积的85%。1995-2015年间西安实施区域融合发展战略,河流下游平原区城镇用地扩张近4倍,侵占大量原有草地与耕地;基于Quantile分类法,将研究区潜在非点源污染风险值划分为极低、低、中等、高和极高等级,区域流域内潜在非点源污染风险呈现两极分化现象,即人类活动影响区的非点源污染风险增强,极高风险区迅速扩张,同时上游水源区的非点源污染风险降低;近期,西安市城镇化的快速推进是流域极高潜在非点源污染风险区域迅速扩张的主要原因。

The spatiotemporal variations of non-point source pollution from land use changes have significantly affected the surface water and groundwater quality of the basin.In this paper,Bahe River Basin,strongly affected by human activities,is chosen as an example,and the improved potential non-point source pollution index(PNPI)model was used,to quantitatively analyze the spatiotemporal variations and the main factors of potential non-point source pollution(PNP)risk affected by land use changes in arid area cities in the latest 20 years.The results showed that the main land use patterns in the Bahe River Basin were forest land and cultivated farmland,accounting for 85%of the total basin area.Urban area in the lower reaches of the river basin expanded nearly four times,encroaching on a large number of original grassland and cultivated land due to the strategy of regional integration development in Xi’an from1995 to 2015.The Quantile classification method was applied to divide the PNPI risk grades into extremely low,low,medium,high and extremely high levels.The extremely high-risk area expanding rapidly as the urbanization in middle and lower reaches of the study watershed,while that the risk level of PNP reduced in the upstream after the water environmental protection measures.Urbanization in Xi’an City is the main reason for the rapid expansion of PNP areas with extremely high risk in the Bahe River Basin.