灌溉水净化耦合稻田土壤阻控措施对稻米Cd的累积减低效果

Effects of irrigation water purification coupling with paddy soil Cd resistance measures on the reduction of Cd accumulation in rice

减低农田重金属输入是保障农业安全生产的关键措施之一。基于广西大环江流域重金属污染来源及灌溉水超标现状调研,选定典型Cd超标的大环江流域环江段,构建沉砂池+3级人工湿地系统对灌溉水进行净化,同时设置稻田土壤添加熟石灰、生物炭等阻控措施处理,旨在探明灌溉水净化耦合土壤阻控措施对典型污染区水稻Cd积累的联合减低效果。结果表明:研究区灌溉水中Cd浓度波动较大,监测期间(2020年4—11月)湿地系统入水总Cd最高浓度为8.38μg·L^(-1),最低为2.15μg·L^(-1),经系统净化后,总Cd浓度由入口的5.88±3.27μg·L^(-1)下降至0.69±0.35μg·L^(-1),其中沉砂池降Cd效果不明显,第一级人工湿地降Cd效率最高,系统对Cd的总去除率达88.3%,出水符合农业灌溉用水标准;稻米Cd含量分析结果显示,相比单一灌溉水净化对照灌区,添加熟石灰、生物炭以及熟石灰+生物炭3种钝化处理分别可降稻米Cd含量9.2%、1.5%和20.0%,单一石灰处理优于生物炭处理;灌溉水净化耦合钝化材料处理与当地常规水稻生产相比,稻米Cd的降低率最高达45.8%。可见,污染区灌溉水经人工湿地系统净化后,结合土壤Cd钝化阻控措施,减少了稻田土壤系统Cd输入量,有效降低了稻米中Cd的累积,提升了典型污染区稻米生产安全系数。研究结果可为南方Cd污染稻田的安全生产提供数据支撑与实践参考。

Reducing heavy metal inputs is one of the key measures for the safety of agricultural production.We investigated heavy metal pollution sources and excessive irrigation water status at watershed scale in a typical Cd polluted Huanjiang section of Great Huanjiang River Basin.We purified irrigation water by the grit chamber and 3-level constructed wetland system,and simultaneously coupled with adding slaked lime and biochar materials into paddy soil as Cd activity control measures.The main objective of this study was to understand the combined reduction effects of Cd contaminated irrigation water purification with soil Cd activity control on Cd accumulation in rice.Results showed that Cd concentration in irrigation water displayed obvious fluctuation during April to November 2020,with the maximum and minimum inflow concentration of 8.38 and 2.15μg·L^(-1)into the constructed wetland system,respectively.The mean Cd concentration declined from 5.88±3.27 to 0.69±0.35μg·L^(-1)after purification through the constructed wetland system,while no reduction effect was observed in the grit chamber process.The best Cd removal result was observed in the first-class wetland,the total Cd removal rate of the wetland system reached 88.3%,and the effluent water quality satisfied the irrigation water standard.The addition of hydrated lime,biochar and lime plus biochar reduced Cd accumulation in rice grain by 9.2%,1.5%and 20.0%,respectively,compared to the single irrigation water purification treatment.Single lime treatment with the same addition amount performed better than biochar treatment.The reduction rate of Cd in rice grain under the treatment of irrigation water purification coupled with passivation materials reached 45.8%compared with the local traditional rice production mode.Therefore,irrigation water purification by constructed wetland system,combined with soil Cd activity control,could effectively reduce Cd input into the paddy soil and Cd accumulation in rice,and thus effectively improved rice production security coefficient.The results can provide scientific support and practical reference for the safety production of Cd-contaminated rice fields in southern China.