设施农业区地下水系统中赤霉酸降解及其与三氮转化约束机制研究

Gibberellic acid and nitrogen are over applied at facility agriculture area, the higher solubility of gibberellic acid would lead to its weak adsorption and strong migration in soil, followed by its intensive degradation. Moreover, this degradation process maybe complicated by the unstable chemical form of gibberellic acid, and also affected by the transformation of three-nitrogen. Therefore, it is critical to expose this degradation mechanism and investigated the fate of gibberellic acid under those complex environments. Considering the dry-wet cyclic environment in soil and aerobic-anaerobic-aerobic alternate in groundwater and eutrophic conditions at facility agriculture area after the intermittent irrigation, batch-type experiment is conducted in this project to monitor the degrading byproducts and final products of gibberellic acid in soil and groundwater under different dry-wet conditions at facility agriculture area, then analysis the influence of pH, dissolved oxygen, salinity, nitrate, ammonium, phosphate and pesticide (glyphosate) on the degradation of gibberellic acid and screening the key factors, and understanding the degradation pathway and mechanism of gibberellic acid. Meanwhile, the dynamic simulation experiment is also employed to investigated the mutual restrain mechanism between gibberellic degradation and three-nitrogen transformation in groundwater system under the intermittent irrigation and eutrophic conditions at facility agriculture area, and characterize the fate of gibberellic acid in groundwater under the complex environment at facility agriculture area. Finally, provide theoretical support for control and eliminate the potential threat of gibberellic acid on groundwater system security!

赤霉酸农药和氮肥在设施农业区被大量过度施用，且赤霉酸高溶解度会造成其在土壤中的弱吸附和强迁移并伴随强烈降解，而其不稳定化学形态会使这一降解过程复杂化并受三氮转化的约束，揭示此降解机理并探讨设施农业区地下水系统中复杂环境下赤霉酸归趋具有重要理论实际意义。本项目针对设施农业区间歇性灌溉下土壤中常出现的干湿交替和地下水中常出现的好氧-厌氧-好氧交替及富营养特点，通过静态批实验解析设施农业区不同干湿条件下土壤和地下水中赤霉酸降解的中间产物和终产物，分析pH、溶解氧、盐分、硝酸盐、铵盐、磷酸盐和农药（草甘膦）对赤霉酸降解的影响并筛选特征影响因子，阐明赤霉酸降解途径及机理。同时，通过动态模拟实验研究设施农业区地下水系统中间歇性灌溉和富营养条件下赤霉酸降解与三氮转化的约束机制，刻画设施农业区地下水系统中复杂环境下赤霉酸归趋，为控制和消除赤霉酸对地下水系统安全的潜在威胁提供理论支撑！

作为一种新型微毒农药，赤霉酸（GA3）在设施农业区被广泛、大量施用。而且，通过课题组已有研究发现GA3在多种典型土壤及矿物上的吸附较弱，仅在水铁矿上表现出特异性吸附，使其极易向地下水迁移并威胁地下水安全！另外，GA3在迁移过程中极易发生水解反应和生物降解，并可能受到地下水环境特别是三氮转化的影响。为此，本项目针对设施农业区地下水系统中GA3的降解及其与三氮转化的相互影响，开展了室内批试验和柱试验研究，并通过反应动力学模型和HYDRUS模型进行了数值模拟。结果表明：GA3在水铁矿上的吸附行为主要受反应体系pH的影响：当2.9<pH≤8.0时，主要形成可逆性较强的外圈络合物；当2.4≤pH≤2.9时，主要形成可逆性较弱的内圈络合物。但是，GA3在水铁矿上反应前4 h内以吸附作用为主、4 h后转化作用占主导，其与水铁矿表面≡Fe-OH21/2+形成的外圈络合物是转化产物的前驱体。同时，GA3在水溶液和三种典型土壤中的降解均符合准一级动力学模型，在pH=2–8的水溶液中其半衰期为16.1-24.6 d，在三种典型土壤中其半衰期为1.8-14.1 d。另外，GA3迁移过程中三种典型土壤基本没有吸附作用，三种典型土壤对GA3的迁移均无阻滞作用，且氨氮、硝氮、正磷酸盐、草甘膦对GA3的吸附与迁移均无影响。然而，GA3迁移过程中驯化的GA3降解菌群的添加可以显著提升GA3的降解速率。其中，在加有降解菌群的水溶液中GA3（<500 mg/L）于144 h内可降解95%以上，在加有降解菌群的三种典型土壤中GA3（100 mg/kg）的半衰期为4.2-5 d。最后，本项目通过建立多步反应动力学概念模型和数学模型，精细刻画了GA3在Fh-H2O界面上的吸附和转化过程，并通过Hydrus-1D模型模拟并预测了GA3在土壤中的迁移过程，为控制GA3对地下水系统安全的潜在威胁提供了理论支撑！