三峡库区消落带土壤有效态As(III)和As(V)迁移转化及释放机理

After water impoundment of the Three Gorges Reservoir (TGR), the pollution of heavy metals in water-level-fluctuating zone (WLFZ) has drawn particularly great research attention from environmental scientists. However, few researchers focused on geochemical behaviors of Arsenic (As) in the WLFZ of TGR, especially for transfer and fate of the labile As(III) and As(V) during periodic dry-wet cycles. This program takes As(III) and As(V) in WLFZ of TGR as a research object to investigate the transportation and transferring mechanism of labile As(III) and As(V) in TGR WLFZ with the help of the sediment sampling and laboratory simulation experiment. The program will use the different advanced analysis techniques (DGT, DET, HPLC-ICP-MS, XANES). The aims of this program are: (1) to identify the spatial distribution and labile As in WLFZ in flood season and non-flood season and establish the geochemical baseline of As; (2) to clarify the underlying mechanisms, release kinetics, potential influencing factors and migration of labile As(III) and As(V) at the sediment-water interface; (3) to explore the two-dimensional spatial distribution pattern and transportation and transferring mechanism of labile As(III)和As(V) in WLFZ soil profiles; (4) to reveal to the translocation and transformation process and the source transferring process of labile As(III)和As(V) in the WLFZ under the influence of anti-season water transfer driven mechanism. This program will provide a new method for the transportation and transferring mechanism of different valence state of metals during periodic dry-wet cycles. The program also provides a scientific basis for assessing the environmental release risk of heavy metals in TGR WLFZ.

三峡水库蓄水后，消落带土壤重金属污染及其潜在释放风险问题倍受关注。然而，消落带周期性干湿交替条件下砷的地球化学行为研究较少，尤其是不同价态有效态砷的迁移转化和释放机理尚不清楚。本项目以有效态三价砷和五价砷为研究对象，将野外采样和室内模拟实验结合，综合利用原位采样和物理化学形态分析技术，识别淹没期和出露期三峡库区消落带土壤（沉积物）中有效态三价砷和五价砷的空间分布规律，建立三峡库区消落带土壤中砷的地球化学基线；阐明淹没时有效态三价砷和五价砷在沉积物-上覆水界面的归趋演变、释放动力学及主要控制因素；探索沉积物剖面有效态三价砷和五价砷的二维空间分布规律和迁移转化机理；揭示反季节调水驱动机制对消落带土壤中有效态三价砷和五价砷迁移转化的影响机制及源汇转化过程。课题成果为周期性干湿交替下不同价态有效态金属的迁移转化机理提供新思路，为科学评价三峡库区消落带土壤中重金属对水环境产生的环境风险提供科学依据。

三峡水库蓄水后，消落带土壤重金属污染及其潜在释放风险问题倍受关注。然而，周期性干湿交替条件下，消落带土壤中不同价态有效态砷（As）的迁移转化和释放机制却鲜有报道。本项目以有效态As(III)和As(V)作为研究对象，运用野外调研和室内模拟相结合的研究方法，开展了三峡水库消落带土壤中As的迁移特征和影响机制等相关研究。研究结果如下：建立了基于梯度扩散薄膜原位采样技术和高效液相色谱-电感耦合等离子体质谱仪的As(III)和As(V)原位价态分析方法以及As价态的液相色谱-原子荧光光谱联用技术；三峡水库干流消落带土壤中有效态As(III)和As(V)的浓度高于支流；消落带土壤固相的再供给能力相对较小，与As(V)相比，土壤固相对As(III)的补给能力较大；消落带土壤孔隙水中的As是有效态As的主要供给来源，且在土壤有机质竞争吸附占主导与铁锰氧化物结合态As解离作用的共同影响下，同时促进了孔隙水中As(III)和As(V)的释放；与2019年相比，2020年消落带土壤砷的入库量增加了1.84倍，流域降雨量、土壤侵蚀量、流域径流量的增长是引起2020年砷入库量增加的主要原因；消落带土壤中有效态As(III)和As(V)的迁移转化主要受到微生物介导下的氮、碳、锰的生物地球化学过程的影响；与自然（高温淹水-低温落干）相比，反自然（低温淹水-高温落干）情境下，因As迁移转化引起的生态环境风险相对更小。本项目建立的原位As价态分析方法为今后多价态元素环境行为的研究提供了技术支撑；形成的三峡水库消落带土壤中有效态As(III)和As(V)的迁移转化机理加深了对As环境地球化学行为的认识，为保障三峡水库水质及水生态安全提供理论依据。