丹江流域典型农田包气带-含水层中硝酸盐氮还原过程及其影响因素

Vertical Distribution of Nitrogen Reduction Process and Its Influencing Factors at a Typical Farmland Vadose Zone-Aquifer System in Danjiang River Basin, China

探究硝酸盐氮在农田土壤包气带-含水层中的迁移转化过程对地下水硝酸盐氮污染防治具有重要意义.该研究在丹江流域河南段典型农田采集了12个不同深度(0~42.5m)的包气带土壤和含水层沉积物样品,对氮素与抗生素的浓度水平、硝酸盐氮还原过程的潜在速率及其相关功能的基因丰度进行了系统测定.结果表明,TOC、NO_(3)-N和TP浓度在包气带土壤和含水层沉积物中具有显著差异;83种目标抗生素中仅检出7种,在包气带和含水层中的浓度范围分别为0.01~115.20ng/g和0.01~2.50ng/g;3种磺胺类抗生素浓度随深度递减,2种大环内酯类抗生素浓度随深度增加.厌氧氨氧化和反硝化是浅层包气带(0~0.8m)中硝酸盐氮还原的关键过程,平均贡献率分别为53.9%和26.4%;深层包气带(0.8~6.0m)则以硝酸盐异化还原成铵为主导,对硝酸盐还原的贡献率达93.1%;含水层沉积物中最主要的硝酸盐氮转化过程是反硝化,贡献率为50.5%.氮转化过程速率与其相应功能基因的垂向分布特征一致.进一步发现抗生素浓度是影响农田包气带-含水层接续系统中硝酸盐氮转化过程的主要因素,NO3-N浓度与DEN过程功能基因丰度显著正相关,磺胺胍(SGD)与硝酸盐氮还原过程显著正相关,而脱水红霉素(AETM)则表现出显著负相关关系.该研究为深入揭示包气带-含水层接续系统中硝酸盐氮还原过程提供了有力支撑.

It is of great significance to explore nitrate migration and transformation process in vadose zone-aquifer for the nitrate pollution control in groundwater.In this study, 12 vadose zone soil and aquifer sediment samples from different depths(0~42.5m) were collected at a typical farmland in Danjiang River Basin.Concentrations of nitrogen, antibiotic, rates of dissimilatory nitrate reduction processes, and abundance of related functional genes were analyzed.Concentrations of TOC,NO_(3)-N,and TP in the vadose zone soil and aquifer sediment showed significant differences.Seven of 83 investigated antibiotics were detected with concentration in the range of 0.01~115.20 and 0.01~2.50 ng/g for vadose zone soil and aquifer sediment, respectively.Besides, results showed that anaerobic ammonium oxidation(ANA) and denitrification(DEN) were the key processes for the nitrate reduction in the shallow vadose zone, with an average contribution of 53.9% and 26.4%,respectively.While the dissimilation and reduction of nitrate to ammonium(DNRA) accounted for 93.1% of total nitrate reduction rate in the deep vadose zone.In aquifer sediments, denitrification(DEN) was the most important nitrogen conversion pathway(50.5% on average).Vertical distribution of functional genes shared the same patterns as their corresponding nitrate reduction processes.Furthermore, antibiotics showed significant influence on nitrate reduction processes, in which sulfaguanidine(SGD) was positively correlated with the nitrate reduction process, while anhydroerythromycin(AETM) demonstrated significantly negative correlation.Among physiochemical parameters, only NO3-N was positively correlated with the abundance of functional genes of DEN.This study is vital to revealing the nitrate reduction process in the vadose zone-aquifer system.