基于同位素示踪方法的东江流域氮素分布特征和来源解析

Characterization of nitrogen distribution and source analysis in the Dongjiang River basin based on isotope tracing method

为了探明东江流域氮素污染现状及氮素污染来源,在东江流域设置31个采样点位,于2020年枯水期(1月)和丰水期(7月)进行水体样品和主要污染源样品的采集及检测,结合氮氧双稳定同位素及SIAR模型,绘制典型污染源的δ^(15) N、δ^(18) O特征分布图并估算其贡献率,定量分析识别氮素来源,从而对东江流域的氮负荷进行更加有效地控制.结果表明:①东江流域氮素污染以支流区最为严重,其次为源头区,这两个区域的水质均达到地表水环境质量标准(GB3838-2002)氨氮浓度的Ⅲ类水平,相比之下,上游区、中游区污染较轻,且氨氮浓度能达到地表水环境质量标准的II类水平.②东江流域氮素以硝态氮为主要赋存形态,枯水期、丰水期各研究区域内硝态氮占总氮的比例分别为43.29%~74.83%、65.51%~80.08%.③东江流域枯水期生活污水是主要的污染来源,贡献率为44.45%~61.39%,丰水期降雨径流是主要的污染来源,贡献率为36.67%~46.11%,究其原因跟流域内不同水文期降雨量大小和河道水量有关.④氮素浓度在丰水期和枯水期之间存在明显差异,且从2009年至今,水体氮素污染程度呈现加重趋势,建议通过测土配方,因地制宜地使用化肥、农家肥,将产生的生活污水、养殖废水等收集集中处理等措施,提高污水处理率,减轻东江流域氮素污染负荷.

In order to investigate the status of nitrogen pollution and its sources in the Dongjiang River basin,water samples and major pollution sources samples were collected from 31 sampling sites in the basin during the dry(January)and wet(July)seasons in 2020.Based on the analysis of nitrogen and oxygen dual stable isotope and SIAR models,the characteristic distribution ofδ^(15) N andδ^(18) O of typical pollution sources were mapped and their contribution rates were estimated.The sources of nitrogen pollution were then identified by quantitative analysis,with the aim to more effectively manage and control nitrogen pollution in the Dongjiang River basin.The results showed that:①Nitrogen pollution in the Dongjiang River basin was most serious in the tributary area,followed by the source area,though the water quality in these two areas reached the class Ⅲ level of ammonia nitrogen concentration on basis of the surface water environmental quality standard(GB3838-2002).The upstream and midstream areas,which were less polluted,could reach the class II level of ammonia nitrogen concentration by the surface water environmental quality standard.②Nitrogen in the Dongjiang River basin was dominated by nitrate nitrogen,which accounted for 43.29%~74.83%and 65.51%~80.08%of the total nitrogen in the study area during the dry and wet seasons,respectively.③The pollution was mainly originated from domestic sewage in the Dongjiang River basin during the dry season,with a contribution rate of 44.45%~61.39%,while rainfall runoff was the main source of pollution during the wet season,with a contribution rate of 36.67%~46.11%.The difference of sources was attributable to precipitation and river flow during different hydrological periods in the basin.④There was a significant difference for nitrogen concentration between dry and wet seasons,and until now from 2009,the nitrogen pollution of water bodies showed an aggravating trend.It is recommended to improve the sewage treatment capacity and reduce the nitrogen pollution load in the Dongjiang River basin through measures such as soil testing,using chemical and agricultural fertilizers according to local conditions,and collecting and centralizing the generated domestic sewage and farming wastewater for treatment.