Zhao Chu, Yang Guangrui, Meng Lize, Chen Heran, Li Shuaidong, Chen Farong, Bian Zihao, Chen Jiaming, Zhou Jian, Jiang Qihao, Huang Tao, Yang Hao, Huang Changchun
State Key Laboratory of Climate System Prediction and Risk Management, Nanjing Normal University, Nanjing 210023,PR China; Key Laboratory of Virtual Geographic Environment/Jiangsu Centre for Collaborative Innovation in Geographical Information Resource Development and Application/Jiangsu Provincial Key Laboratory of Materials Cycling and Pollution Control, Nanjing Normal University, Nanjing, 210023, PR China; School of Geography, Nanjing Normal University, Nanjing 210023, PR China.
School of Environmental Science, Xiaozhuang University, Nanjing 211171, PR China.
Water Res. 2025 Jul 28;287(Pt A):124312. doi: 10.1016/j.watres.2025.124312.
Frequent extreme climate events are restructuring riverine carbon cycles dominated by dissolved inorganic carbon (DIC). However, the variability of dissolved organic matter (DOM) induced by rainstorm and its linkage to riverine DIC dynamics remain unclear, limiting an in-depth understanding of carbon transport and fate across the river-ocean continuum. This study employed Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with stable carbon and water isotope tracing techniques to investigate DOM-DIC interactions in the Yangtze River. Results demonstrated that organic matter constituted a major DIC source, contributing 13.52 ± 1.66% and 23.15 ± 3.27% of total DIC during normal (May) and rainstorm (September) periods in 2021, respectively. Extreme precipitation events (>150 mm·day) elevated dissolved organic carbon (DOC) concentration and the biological transformation index (I) of DOM, while reducing molecular mass and double-bond equivalents (DBE) compared to the normal condition. During the rainstorm period, DOC concentration and I values progressively declined downstream with increasing distance from the precipitation core, while molecular mass and DBE increased, contrasting with the spatially homogeneous DOM distribution characteristic of the normal period. Rainstorm enhanced terrestrial organic matter inputs, increasing DOC concentration and enriching low-molecular-weight, highly saturated CHO and CHON compounds. These synergistic effects accelerated DOM biodegradation to organic-sourced DIC (DICoc). Structural equation modeling further confirmed that extreme precipitation primarily promoted DICoc production through stimulated DOM biodegradation rather than photochemical oxidation. Storm events mobilized protein-like compounds from residential wastewater, while elevated water temperatures and nutrient levels collectively enhanced DOM biodegradability. Conversely, rainstorm-induced turbidity plumes suppressed photodegradation of terrestrial aromatic humic substances. Our findings highlight that precipitation-driven DOM loading and molecular transformations significantly accelerate biogeochemical carbon cycling.
频繁的极端气候事件正在重塑以溶解无机碳（DIC）为主导的河流碳循环。然而，暴雨引起的溶解有机物（DOM）的变异性及其与河流DIC动态的联系仍不明确，这限制了对碳在河流 - 海洋连续体中的传输和归宿的深入理解。本研究采用傅里叶变换离子回旋共振质谱（FT - ICR MS）结合稳定碳和水同位素示踪技术，研究长江中的DOM - DIC相互作用。结果表明，有机物是主要的DIC来源，在2021年正常时期（5月）和暴雨时期（9月）分别占总DIC的13.52±1.66%和23.15±3.27%。与正常情况相比，极端降水事件（>150 mm·天）提高了溶解有机碳（DOC）浓度和DOM的生物转化指数（I），同时降低了分子量和双键当量（DBE）。在暴雨期间，DOC浓度和I值随着离降水核心距离的增加而在下游逐渐下降，而分子量和DBE增加，这与正常时期DOM在空间上均匀分布的特征形成对比。暴雨增强了陆地有机物的输入，增加了DOC浓度，并富集了低分子量、高饱和度的CHO和CHON化合物。这些协同效应加速了DOM向有机源DIC（DICoc）的生物降解。结构方程模型进一步证实，极端降水主要通过刺激DOM生物降解而非光化学氧化来促进DICoc的产生。暴雨事件调动了生活废水中的类蛋白质化合物，而水温升高和营养水平共同提高了DOM的生物降解能力。相反，暴雨引发的浊流羽抑制了陆地芳香族腐殖物质的光降解。我们的研究结果强调，降水驱动的DOM负荷和分子转化显著加速了生物地球化学碳循环。
