酸雨区污染农田土壤重金属面源输出季节特征及驱动机制

It is of most importance and the key scientific issue to reveal the seasonal variation of heavy metals non-point exports and that driving mechanisms. This research plans to carry out a 3 consecutive years in-situ monitoring experiment by runoff plots and small watershed hydrological processes observation in a typical small agricultural watershed presenting typical heavy metals (Pb，Cd，As) contamination problems. This research emphatically tend to elucidate the seasonal variation patterns of available heavy metals, normal soil physiochemical characteristics, and rainfall parameters by 3-year continuous field measurement and dynamic monitoring. Research plan to monitor the non-point export concentrations and intensities of heavy metals during the natural acid rainfall runoff processes, and to evaluate the coupling relationships between heavy metals non-point exports with soil, landuse and precipitation group factors through multivariate statistical analysis using PCA, CCA as data mining methods. And to investigate the relationships and interaction mechanisms between “precipitation-soil-runoff” continuum. Then to quantify the contribution rates of factors for metals non-point exports and clarify the key impact factors, and then importantly reveal that driving mechanism. Research also attdempt to establish heavy metals non-point source pollution estimation model using EPR data mining techniques through the integration of 3 years monitoring data sets of both runoff plots and small watershed outlet, in order to provide scientific basis for heavy metals non-point source pollution control and receiving water security early warning and risk diagnosis of Xiangjiang River basin.

典型酸雨区污染土壤重金属面源输出的特征及其驱动机制是重金属污染风险控制亟待解决的关键科学问题。本研究选取湘中典型重金属复合污染农业小流域为实验场，通过连续3年的原位动态监测，分析土壤有效态重金属含量、理化性状、降雨等参数的季节性特征，采用PCA、CCA等多元统计方法阐明重金属面源输出与土壤、用地类型、降雨等集团因子的耦合关系，探讨“降雨-土壤-径流”三者间内在关联与作用机理，揭示关键驱动因子并揭示其驱动机制。整合径流小区与小流域3年的监测数据尝试建立重金属面源污染定量估算方法。研究成果可为湘江流域重金属污染治理、水系水质安全预警与风险诊断提供科学依据。

研究于湘江中下游典型Cd超标农业小流域中选取稻田、旱作蔬菜地、丘陵林地3类主要用地类型，分析不同用地类型Cd活性的季节变化特征及其与土壤基本理化参数的关联。原位监测结果显示，研究区为典型酸雨区，雨水pH值呈现冬、春季节低于夏、秋季。稻田土壤总Cd含量显著高于旱作蔬菜地，菜地显著高于林地，3种用地类型土壤总Cd含量季节特征相似，均为夏秋季节略低于冬春两季。3种用地类型Cd有效态季节变化与总Cd含量无明显的相关性，稻田土壤有效态Cd质量浓度在5-9月份的作物生长季明显低于其他月份，而菜地和林地则恰好相反。稻田土壤Cd有效性的最关键影响因子为Eh，呈显著正相关，与土壤pH负相关，菜地土壤与土壤TOC明显负相关，而林地土壤Cd有效性与水溶性有机碳、TOC呈现明显的正相关关系。研究显示，径流水相溶解态Cd浓度呈明显的季节性差异，春季显著高于夏季，雨水pH值可显著影响土壤溶解态Cd向径流水相迁移，与径流水相溶解态Cd浓度呈负相关关系。同一降雨事件产汇流过程监测结果显示，稻田径流水相溶解态Cd浓度显著低于旱田和荒草地，旱田与荒草地Cd面源输出负荷显著高于水稻田，由于降雨量差异，3类土地利用类型溶解态Cd面源输出负荷的季节性规律不明显。自然降雨过程，稻秆和豆秆生物炭添加均可显著降低溶解态Cd、Pb、Zn面源输出负荷，但均增加了溶解态As面源负荷，因此可能增加地表受纳水体水环境As超标风险。