Since the 1950s, nearly 80% of wetlands in the Sanjiang Plain have been converted into paddy fields. The conversion might affect the solubility and mobility of soil iron, influencing the export of iron into the Amur River and the primary production of the Okhotsk Sea. However, information regarding long-term studies of the spatiotemporal dynamics of soil iron after cultivation is limited. In this study, six regions, including 18 plots in the Sanjiang Plain, were selected as sampling sites covering natural wetlands and paddy fields with planting ages of 2, 5, 11, 18, and 25 years after conversion from the wetland. Samples were collected at six different depths (0–10, 10–20, 20–40, 40–60, 60–90, and 90–120 cm) analyzed for water-soluble ferrous iron (Fe[II]), water-soluble iron (Fe_w), complex iron (Fe_p), amorphous iron oxides (Fe_o), free iron oxides (Fe_d), and total iron (Fe_t) and six soil physicochemical characteristics. Two years after the conversion of wetlands to rice fields led to an immediate decrease in Fe(II), Fe_w, Fe_p/Fe_d, and Fe_o/Fe_d, while the Fe_p and Fe_o contents decreased at 5 years. Both the concentrations and stocks of soil Fe_t increased gradually during the first 18 years. The findings in the Sanjiang Plain suggest that the function of wetlands after conversion as a source of iron might decrease with increasing time, with potential ecological effects on the neighboring marine environment. Recently initiated wetland restoration would protect the land ecosystems in the Sanjiang Plain and promote the future sustainability of the Amur Basin.

中文翻译：

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三江平原湿地转化对土壤铁的时空动态

1950年代以来，三江平原近80%的湿地已转为水田。转化可能会影响土壤铁的溶解度和流动性，影响铁向阿穆尔河的出口和鄂霍次克海的初级生产。然而，关于耕种后土壤铁时空动态的长期研究的信息是有限的。本研究选取三江平原18个样地6个区域作为采样点，覆盖自然湿地和水田，种植年龄分别为2、5、11、18和25年。在六个不同深度（0-10、10-20、20-40、40-60、60-90 和 90-120 厘米）收集样品，分析水溶性亚铁 (Fe[II])、水-可溶性铁（Fe _w）、复合铁（Fe_p )、无定形氧化铁 (Fe _o )、游离氧化铁 (Fe _d ) 和总铁 (Fe _t ) 和六种土壤理化特性。湿地转稻田两年后，Fe(II)、Fe _w、Fe _p /Fe _d和Fe _o /Fe _d立即下降，而Fe _p和Fe _o含量在5 年时下降。土壤 Fe _t的浓度和储量在最初的 18 年中逐渐增加。三江平原的研究结果表明，转化后的湿地作为铁源的功能可能随着时间的延长而减弱，对邻近的海洋环境具有潜在的生态影响。最近启动的湿地恢复将保护三江平原的土地生态系统，促进阿穆尔盆地未来的可持续发展。