作者：Ren, X., Yu, R. & Mi, Y.

Elucidating organic matter sources in lakes during the frozen period (FP) is crucial for understanding carbon and nitrogen cycling in global cold-region lakes. However, limited information exists on the sources and differences between suspended particulate organic matter and sediment organic matter in lakes during the FP. This study examined the stable carbon (delta 13C) and nitrogen (delta 15N) isotopic compositions of organic matter in suspended particulates and sediments from Daihai Lake to investigate the sources and implications of organic matter during the FP (January). Organic carbon in suspended particulates and total nitrogen in suspended particulates ranged from 0.45 to 1.22 mg/L and 0.08 to 0.20 mg/L, respectively, while organic carbon in sediments and total nitrogen in sediments ranged from 3.57 to 14.90 g/kg and 0.44 to 1.68 g/kg, respectively. Based on organic index (OI) and organic nitrogen (ON), suspended particulates (OI: 0.10 mg/L; ON: 0.12 mg/L) were slightly contaminated, whereas sediments (OI: 13.13 g/kg; ON: 1.08 g/kg) were heavily contaminated. The suspended particulate organic matter exhibited mixed source signatures, with exogenous inputs (sewage: 27.9% and soil: 22.2%) and endogenous production (phytoplankton: 25.8%). In contrast, sediment organic matter was predominantly exogenous inputs (soil: 40.3% and sewage: 26.6%). This discrepancy highlights a key process in organic matter transport and transformation under ice-covered conditions: phytoplankton-derived organic matter underwent preferential degradation during sedimentation, whereas terrestrial organic matter was more readily deposited and preserved. Notably, significant nitrogen isotope fractionation during sedimentation indicates that preferential mineralization of organic nitrogen and denitrification played key regulatory roles in the nitrogen cycling. The findings highlight the need to prioritize controlling exogenous organic matter inputs to lakes to ensure sustainable ecosystem.

阐明冰冻期湖泊有机质来源，对于理解全球寒区湖泊的碳氮循环至关重要。然而，关于冰冻期湖泊中悬浮颗粒态有机质与沉积物有机质来源及其差异的信息十分有限。本研究通过分析岱海悬浮颗粒物和沉积物中有机质的稳定碳（δ¹³C）和氮（δ¹⁵N）同位素组成，探究了冰冻期（1月）有机质的来源及其环境意义。悬浮颗粒物有机碳和悬浮颗粒物总氮含量范围分别为0.45至1.22 mg/L和0.08至0.20 mg/L，而沉积物有机碳和沉积物总氮含量范围分别为3.57至14.90 g/kg和0.44至1.68 g/kg。基于有机指数（OI）和有机氮（ON）评价，悬浮颗粒物（OI：0.10 mg/L；ON：0.12 mg/L）呈轻度污染，而沉积物（OI：13.13 g/kg；ON：1.08 g/kg）则呈重度污染。悬浮颗粒态有机质表现出混合来源特征，包括外源输入（污水：27.9%；土壤：22.2%）和内源生产（浮游植物：25.8%）。相比之下，沉积物有机质则主要来自外源输入（土壤：40.3%；污水：26.6%）。这一差异揭示了冰封条件下有机质迁移转化过程中的一个关键环节：浮游植物来源的有机质在沉降过程中发生了优先降解，而陆源有机质则更易沉积并保存。值得注意的是，沉降过程中显著的氮同位素分馏表明，有机氮的优先矿化与反硝化作用在氮循环中发挥了关键的调节作用。这些发现强调了优先控制湖泊外源有机质输入，以确保生态系统可持续性的必要性。

（来源：Journal of Hydrology 2026  DOI: 10.1016/j.jhydrol.2026.135094）