Dry-wet cycling and soil moisture are key factors affecting cadmium (Cd) remediation in soils by biochar; however, their long-term effects on the transport of Cd between soil and biochar, Cd fraction distribution, and Cd potential risks are still unclear. To reveal the long-term Cd remediation mechanisms and potential risks in soil under biochar treatment, 180 days of artificial dry-wet cycling was conducted at four soil moisture levels (40 % θs, 60 % θs, 80 % θs, and 100 % θs; θs, saturated water content, W/W) based on local meteorological data to simulate 30 years of natural dry-wet processes. The results showed that Cd adsorbed by biochar in soils during long-term ageing first underwent rapid adsorption (over 0–5 years of simulated ageing), then equilibrium stabilization (over 5–20 years of simulated ageing), and finally slight re-released (over 20–30 years of simulated ageing). Compared with the total Cd adsorbed by biochar in the 20th year of simulated ageing, Cd adsorption by biochar accounted for 85.28 %, 14.72 %, and −3.22 % during 0–5, 5–20, and 20–30 years of simulated ageing, respectively, in the soil at 100 % θs. Similarly, the available Cd slightly increased in 20–30 years of simulated ageing. The greater the soil moisture was, the more effective the adsorption and immobilization of Cd by biochar. At the 20th year of simulated ageing, the Cd adsorption by biochar at 100 % θs was 1.51 times that at 40 % θs; the available Cd in the soil with biochar at 100 % θs was 0.91 times that at 40 % θs. The contribution of nonmineral components in biochar to Cd adsorption was greater in 0–1 years of the simulation, but the contribution of mineral components dominated and slightly decreased during 1–30 years of the simulation. This study highlighted that biochar was fairly effective in the long-term remediation of Cd in contaminated soils, but there was some risk of Cd activation in the later stages due to the ageing of biochar. Agricultural irrigation management has a significant effect on the long-term effectiveness of biochar remediation of Cd pollution. To prevent Cd reactivation, a high field moisture level is recommended, and excessive dry-wet cycling should be avoided through water management practices such as frequent irrigation with small amounts of water.

中文翻译：

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不同土壤含水量下干湿循环下生物炭应用土壤中Cd的长期修复机制及潜在风险


干湿循环和土壤水分是影响生物炭土壤中镉 （Cd） 修复的关键因素;然而，它们对 Cd 在土壤和生物炭之间的运输、Cd 馏分分布和 Cd 潜在风险的长期影响仍不清楚。为了揭示生物炭处理下土壤中 Cd 的长期修复机制和潜在风险，在四个土壤水分水平（40 % θs、60 % θs、80 % θs 和 100 % θs;θs，饱和含水量，W/W）下进行了 180 天的人工干湿循环，以模拟 30 年的自然干湿过程。结果表明，在长期老化过程中，生物炭在土壤中吸附的 Cd 首先经历了快速吸附（超过 0-5 年的模拟老化），然后是平衡稳定（超过 5-20 年的模拟老化），最后是轻微的再释放（超过 20-30 年的模拟老化）。与模拟老化第 20 年生物炭吸附的总 Cd 相比，在 100 % θs 的模拟老化 0-5、5-20 和 20-30 年模拟老化期间，生物炭对 Cd 的吸附分别占 85.28 %、14.72 % 和 -3.22 %。同样，在 20-30 年的模拟衰老中，可用 Cd 略有增加。土壤水分越大，生物炭对 Cd 的吸附和固定效果越好。在模拟老化的第 20 年，生物炭在 100 % θs 下对 Cd 的吸附是 40 % θs 时的 1.51 倍;使用 100 % θs 的生物炭的土壤中的有效 Cd 是 40 % θs 的 0.91 倍。在模拟的 0-1 年中，生物炭中非矿物成分对 Cd 吸附的贡献更大，但在模拟的 1-30 年中，矿物成分的贡献占主导地位并略有下降。 本研究强调，生物炭在污染土壤中对 Cd 的长期修复相当有效，但由于生物炭的老化，后期存在一些 Cd 激活的风险。农业灌溉管理对生物炭修复 Cd 污染的长期有效性具有显著影响。为防止 Cd 重新激活，建议使用高田间水分水平，并应通过水管理措施（例如经常用少量水灌溉）避免过度的干湿循环。