丹江口水库核心水源区化肥施用分布特征及其环境风险评价

Characteristics of Chemical Fertilizer Application and Environmental Risk Assessment in the Core Water Source Area of the Danjiangkou Reservoir

丹江口库区是南水北调中线工程的核心水源区,全面认识库区农业化肥施用的空间分布差异及对生态环境的潜在威胁,是加强化肥施用风险管控的前提。运用化肥污染环境风险评价模型,以十堰市为例,对各县(区、市)2020年主要农作物化肥施用特征和环境风险进行定量分析和评价。结果表明:十堰市2020年主要农作物化肥施用总量达8.97万t,且以复合肥为主,其中玉米和薯类是化肥施用总量最多的两种作物,二者的综合施用量达到全市化肥投入总量的50.37%,其次为小麦和油菜,稻谷、花生和豆类的化肥施用量占比相对较小。十堰市化肥施用存在明显的空间异质性,其中郧阳区和竹山县是化肥投入量最大的两个地区,而张湾区和茅箭区是化肥投入量最小的两个地区;各地区间化肥在农作物上的分布特征不尽相同,大致可分为小麦—玉米轮作体系主导型、玉米‖薯类间作体系主导型和玉米—油菜轮作体系主导型3种类型。十堰市单位播种面积平均化肥施用强度为343.07 kg·hm^(-2),超出我国生态县建设制定的化肥施用标准(250 kg·hm^(-2)),是发达国家化肥施用环境安全标准上限的1.52倍,且区域间存在差异。十堰市多数地区化肥施用风险程度处于中等风险水平,但竹山县和张湾区已进入重度风险状态。十堰市整体化肥施用的风险指数达0.697,尚处于中等风险水平,但存在演变为重度风险的隐患,其中氮肥和磷肥的施用风险程度整体已进入重度风险水平,钾肥施用伴随的环境风险整体处于中等风险的较低水平。水源区化肥施用负荷过高是多种因素相互作用造成的,相关部门应根据不同地区化肥负荷来源,从施肥技术、政策引导、机制激励、观念更新等方面采取有效措施,实现化肥“减施增效”和环境风险“可防可控”的双重目标。

Danjiangkou reservoir area was the core water source area of the middle route of the South-to-North Water Transfer Project,It was the premise to strengthen the risk control of chemical fertilizer application to comprehensively understand the spatial difference of chemical fertilizer application and its potential threat to ecological environment.This paper used environmental risk assessment model to evaluate the environmental risk of chemical fertilizer application of main crops in different areas of Shiyan city in 2020.The results showed that the total amount of chemical fertilizer applied to main crops reached 8.97×10~4 t in 2020 and compound fertilizer was the largest type.The comprehensive fertilizer application amount of corn and potato accounted for 50.37% of the total input of the city,which were the largest fertilizer consumption crop type.wheat and rapeseed followed,while rice,peanuts and pulses accounted for a relatively small proportion.The environmental risk of chemical fertilizer application among demonstrated significant different patterns of spatial distribution in Shiyan.The two areas with the largest amount of fertilizer input were Yunyang and Zhushan,while the two smallest were Zhangwan and Maojian.The distribution characteristics of chemical fertilizer on crops were not consistent in different regions,which could be roughly divide into three types:wheat-corn rotation system dominant type,corn+potato intercropping system dominant type and corn-rape rotation system dominant type.The average intensity of fertilizer application per unit sown area in Shiyan city was 343.07 kg·hm^(-2),which had exceeded the standard of fertilizer application for China’ ecological county constructions(250 kg·hm^(-2)) and was 1.52 times of the upper limit of environmental safety standard of fertilizer application in developed countries.The risk level of fertilizer application in most areas of Shiyan were “medium”,but it has entered serious state.in Zhushan and Zhangwan.The overall risk index of fertilizer application was 0.697,which was still at the medium risk level,but there were hidden dangers that might change into severe risk.And the environmental risk of nitrogen fertilizer and phosphate fertilizer application had entered a severe risk level,while it was at a lower level of medium risk of potassium fertilizer.Excessive intensity of chemical fertilizer application in the water source area was caused by a wide range of sources.The relevant government departments should take effective measures based on the load sources of fertilizer in different regions from the aspects of fertilization techniques,policy guidance,mechanism incentive and concept renewal,so as to achieve the dual goals of “reducing fertilizer application and improving efficiency” and “preventing and controlling environmental risks” simultaneously.