摘要:农田系统是温室气体N2O的主要排放源，目前对酸性矿山废水（acid mine drainage，AMD）灌溉影响下，农田土壤剖面N2O的来源识别、转换机制及其控制因子缺乏深入研究。本文选择广东省大宝山矿区下游沿岸水稻田和甘蔗田两种典型农田，针对酸性矿山废水灌溉区（上坝村）和天然来水灌溉区（连心村），对土壤理化性质、重金属含量及包气带N2O浓度、同位素特征值进行了测定，定量计算了硝化和反硝化作用对土壤中N2O的贡献比和N2O转化为N2的还原比，评价了其相关影响因素。结果表明：在AMD影响下，灌区农田土壤剖面N2O浓度均高于同种作物类型天然来水区土壤，同种灌溉处理下甘蔗田土壤N2O浓度高于水稻田。甘蔗田表层土壤（0~30 cm）反硝化作用对N2O产生量的贡献比高于硝化作用，约71.29% N2O由反硝化作用产生。AMD灌区甘蔗田土壤剖面中N2O还原成N2的比例随深度增加逐渐减小，在N2O浓度峰值处仅有15.54% N2O被还原成为N2，而天然来水区N2O还原成N2的平均比率高达49.80%。这表明较弱的土壤N2O还原能力导致较高浓度的N2O残留在土壤中。相关性分析表明，AMD灌溉通过改变上坝村土壤的pH、重金属含量、含水率从而改变了土壤N2O的来源途径及还原能力。组合同位素特征值溯源法有效地揭示了农田土壤N2O的来源和AMD灌区土壤的潜在生态风险，为日后的治理修复工作提供了科学依据。
关键词:同位素特征值/
N2O/
酸性矿山废水灌溉/
硝化作用/
反硝化作用/
红壤区
Abstract:Acid mine drainage (AMD) is mostly untreated or not up to standard level before directly drained into rivers for irrigation, causing severe pollution of agriculture eco-environments. Metal pollution had been widely reported in extensive fields including the red soil region in South China. As we have known, N2O emitted from agricultural systems was one of the important causes of global greenhouse effects. However, there has been poor knowledge of potential changes in N2O evolution in polluted fields. In this study, four agricultural soil profiles from sugarcane and paddy fields were used to track the changes in N2O emission and sources of heavy metal polluted soils irrigated with AMD (Shangba Village, Wengyuan County, Guangdong Province) and then compared with unpolluted soils irrigated with natural water (Lianxin Village, Wengyuan County, Guangdong Province). The physical/chemical parameters and contents of heavy metals in the soils, N2O concentration and stable nitrogen and oxygen isotope compositions were analyzed to determine the contribution of nitrification and denitrification of N2O and the reduction ratio of N2O. Our results showed that there was slightly higher N2O concentration of the same crop in AMD irrigated area than in unpolluted soil irrigated with natural water, and higher soil N2O concentration in sugarcane fields than in rice fields. The production of N2O from denitrification was 71.29%, which was higher than that from nitrification in surface soil (0-30 cm) in sugarcane fields in areas irrigated with AMD. N2O reduction ratio in the soil profile in AMD irrigation area decreased gradually with increasing depth. There was only 15.54% N2O reduction to N2 at the peak of N2O concentration. However, the average ratio of N2O reduction to N2 in sugarcane fields irrigated with natural water was as high as 49.80%. Limited N2O reduction led to high levels of N2O residues in the soil. Studies showed that AMD irrigation changed the production and release of N2O by changing pH, heavy metal content and moisture content of agricultural soils. N2O production and reduction studies carried out using combined nitrogen and oxygen isotope compositions clarified potential risks of irrigated agricultural soils with AMD. This provided the scientific basis for future restoration works in polluted soils.
Key words:Isotopic signature/
Nitrous oxide/
Acid mine drainage irrigation/
Nitrification/
Denitrification/
Red soil region
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