沉积盆地地下水无机氮来源示踪及其演化模式

Sources tracing and evolution model of inorganic nitrogen of groundwater in sedimentary basin

以我国沉积型盆地三江平原的典型农业区抚远地区为例,采用水化学法和GIS技术分析区域水化学成因作用及无机氮素的污染特征,利用氮氧双稳定同位素分布特征及稳定同位素解析模型(SIAR)确定氮素来源及各污染源贡献比,基于对影响氮素浓度变化的多项因素的认识,建立区域氮素的水化学演化模式.结果表明:研究区地下水中氨氮超标率为56.52%,毫克当量百分数平均值占无机氮总量的55.50%,是地下水无机氮素中污染影响程度最大的指标;土壤有机氮、厩肥污水和氨态化肥是径流补给区氮素的主要污染来源,各污染端元贡献比由大到小依次为40.49%、30.24%和29.27%.地下水补给区是氨氮污染最重的区域,排泄区是硝酸盐氮污染相对严重的区域,氧化还原条件是影响氮素浓度的关键因素;在氮素的时空演化过程中,除二级阶地仍保持天然水化学状态外,一级阶地和漫滩区的氮素浓度均有不同程度的升高.

Based on Fuyuan area in Sanjiang Plain,a typical agricultural area of a sedimentary basin,the study analyzed the regional hydrochemical effect and inorganic nitrogen pollution characteristics with the hydrochemical methods and GIS technology.The nitrogen source and contribution ratio of each pollution source were determined through the distribution characteristics of nitrogen,oxygen bistable isotopes and stable isotope analysis model(SIAR).With the understanding of affecting factors on the changes of nitrogen concentration,the regional hydrochemical evolution model of nitrogen were established.These results showed that 56.52%of groundwater had ammonia nitrogen concentration exceeding the standard rate in the study area and the average milligram equivalent percentage accounted for 55.50%of the total inorganic nitrogen,which was the most important index of groundwater inorganic nitrogen pollution.Soil organic nitrogen,manure sewage and ammonia fertilizer were the main sources of nitrogen pollution in the runoff recharge area,and the contribution ratios of each pollution source was 40.49%,30.24%and 29.27%respectively in descending order.The groundwater recharge area was the most polluted area of ammonia nitrogen,while the discharge area was the relatively serious pollution area of nitrate nitrogen.The redox conditions were the key factor affected the nitrogen concentration.In the process of spatial and temporal evolution of nitrogen,the nitrogen concentration in the first terrace and floodplain area increased in varying degrees except the natural hydrochemical state in the second terrace.