全域尺度的农田面源污染对水环境质量的影响分析

Effects of Nonpoint Source Pollution on Water Environmental Quality at National Scale

【目的】探究全域尺度的农田面源污染对水环境质量的影响。【方法】基于我国多年化肥施用量、农田氮磷面源污染排放系数和农业用水量等数据,采用统计分析方法,分析了农田面源污染及其对地表水质量的影响。【结果】化肥施用量从2015年开始下降,至2019年氮肥和磷肥施用量分别降低了13.7%和9.1%;农业用水占比从2012年开始下降,2019年降低了2.2%;2007—2017年期间,农田氮污染排放系数从5.7%降低至2.4%,农田磷污染排放系数从0.9%降低至0.5%;地表水环境质量显著改善,2018年较2009年河流Ⅳ+Ⅴ类水质占比降低了40.8%,劣Ⅴ类水质占比降低了71.5%。全域尺度的农田面源污染防治取得了巨大成效,农作物产量不减反增。我国农田尾水属于劣Ⅴ类水质,对地表水环境质量的潜在影响较大,尤其在局部地区或部分流域段。【结论】从全域尺度看,农田面源污染总磷(TN)和总氮(TP)对地表水环境质量的整体影响较少,2017年开始,呈显著降低趋势。农田面源污染的关注重点应转移到局部地区和部分流域段,以逐步提升地表水环境质量。

【Background and objective】Non-point pollution from farmland(NPF)is the main source of pollutants in surface water in China and has received attention.the progress achievements of water pollution control effects and surface water environment obvious improvements had been carried out in recent years,which involve“Three Rivers”(the Huai River,Liao River and Hai River),“Three Lakes”(the Tai Lake,Dian Lake and Chao Lake),the Songhuajiang River,three Gorges Reservoir Region,the upper and middle Yellow River,the water resource and waterline basin of South to North water diversion project.The monitoring sections ofⅠ-Ⅲriver quality had been improved by 18%,and that of interior classⅤriver quality had been reduced by 15%in the last 10 years,the total surface water quality has improved significantly.As President Xi Jinping pointed out,agricultural development should not only put an end to new accounts owed by the ecological environment,but also gradually repay the old accounts,and fight a tough battle against agricultural non-point source pollution.Prevention and control of agricultural non-point source pollution is an important way to realize high quality agricultural development and water environment quality assurance.【Objective】The fundamental status of China’s large agricultural country is to maintain a relatively high level of fertilizer application and a higher ratio of agricultural water for a long period of time,so national food and other agricultural products security could be guaranteed.However,the problems from NPF should be paid a close attention.【Method】Based on the data of fertilizer application amount,emission coefficient of nitrogen and phosphorus non-point source pollution,agricultural water consumption,and the quality of farmland tail water and the influence on surface water quality were analyzed.【Result】The ratio of fertilizer application was decreased after 2015,in which nitrogen fertilizer and phosphorus fertilizer were reduced 13.7%and 9.1%in 2019,respectively.Agricultural water use decreased after 2012,in which the ratio of agricultural water was reduced by 2.2%in 2019.From 2007 to 2017,the emission coefficient of farmland nitrogen pollution was reduced from 5.7%to 2.4%,and the emission coefficient of farmland phosphorus pollution was reduced from 0.9%to 0.4%.The environmental quality of surface water had been improved significantly,in which the ratio of classⅣ+Ⅴof river water quality was reduced by 0.8%and interior classⅤwas reduced by 17.4%in 2018,compared to that in 2009.NPF control has achieved a great progress and crop yields continue to increase.Agricultural tail waters all belong to interior classⅤ,which have a potential effect on surface water quality,especially in some local areas or parts of basin.【Conclusion】On a national scale,effects on surface water quality of total nitrogen and total phosphorus pollution from NPF are limited and they showed a significant decreasing trend after 2017.The keys in NPF should pay attention to some local areas and river basins,so surface water environmental quality can gradually improve.