Global warming has intensified the distinction between dry and wet seasons in monsoonal climates. The synergistic effect of high temperatures and rainfall during the wet season promotes the release of endogenous nitrogen (N) and eutrophication within lake ecosystems. However, the seasonal variations in sediments N speciation and bioavailability, and their intrinsic connection to release potential, remain unclear. This study employed sequential extraction method and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) to characterize extractable N (Ex-N) in Erhai Lake sediments during dry and wet seasons. The results indicated that ion-exchangeable organic form N (IEF-ON) serves as a substrate for microbial mineralization, with the highest proportion of protein-like substances (26.2%). The influx of N-containing polysaccharides and poly-N glycoproteins during the wet season further increased its bioavailability. Algal-derived N exists as the weak acid-extractable organic form N (WAEF-ON), which has the highest lipid proportion (11.7%) and the lowest double bond equivalent (DBE) values. Overall, elevated water temperatures and N input during the wet season accelerate both the mineralization rate of organic N (ON) and the content of labile N components. This potentially triggers a "priming effect" that could further activate the refractory N components in the sediments. Additionally, the wet season reduces sediment pH and redox potential, making WAEF-ON and strong alkali-extractable form N (SAEF-N) more labile and susceptible to release. This study reveals the adverse effects of seasonal variations on N sequestration in lake sediments, complicating the control of endogenous pollution release under the backdrop of climate change.

中文翻译：

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季节性水文变化影响氮形态并提高高原湖泊沉积物的生物利用度


全球变暖加剧了季风气候中旱季和雨季的区别。雨季高温和降雨的协同作用促进了湖泊生态系统内源性氮 （N） 的释放和富营养化。然而，沉积物 N 形态和生物利用度的季节性变化，以及它们与释放潜力的内在联系，仍不清楚。本研究采用顺序提取法和傅里叶变换离子回旋共振质谱 （FT-ICR MS） 对洱海湖沉积物中旱湿季节可萃取氮 （Ex-N） 的表征。结果表明，离子可交换有机形式 N （IEF-ON） 是微生物矿化的底物，蛋白质样物质的比例最高 （26.2%）。湿季含 N 多糖和多 N 糖蛋白的涌入进一步提高了其生物利用度。藻类衍生的 N 以弱酸可萃取有机形式 N （WAEF-ON） 存在，其脂质比例最高 （11.7%） 和最低的双键当量 （DBE） 值。总体而言，雨季水温升高和氮输入加速了有机氮 （ON） 的矿化速率和不稳定氮组分的含量。这可能会触发“启动效应”，从而进一步激活沉积物中的难降解氮成分。此外，雨季降低了沉积物的 pH 值和氧化还原电位，使 WAEF-ON 和强碱可萃取形式 N （SAEF-N） 更不稳定且更容易释放。本研究揭示了季节性变化对湖泊沉积物中氮封存的不利影响，使气候变化背景下内源性污染释放的控制复杂化。