Climate change is melting glaciers and altering watershed biogeochemistry across the globe, particularly in regions dominated by mountain glaciers, such as southeast Alaska. Glacier dominated watersheds exhibit distinct dissolved organic matter (DOM) characteristics compared to forested and vegetated watersheds. However, there is a paucity of information on how stream DOM composition changes as glaciers retreat and terrestrial ecosystem succession ensues. Importantly, it is unclear over what timescales these transformations occur. Here, we used bulk, isotopic and ultrahigh resolution molecular-level techniques to assess how streamwater DOM composition evolves in response to glacier retreat and subsequent terrestrial ecosystem succession. For this, water samples were collected from eleven streams across a chronosequence spanning a temporal gradient 0 to ~ 1400 years since glacier retreat in coastal, southeast Alaska. During the first ~ 200 years since glacier retreat, stream DOM showed marked and consistent changes in bulk, isotopic, and molecular-level composition. In particular, there was a decreased relative abundance (RA) of ancient, energy-rich (e.g., elevated aliphatic contribution), low aromaticity (e.g., low SUVA₂₅₄ and AI_mod) DOM and an increased RA of soil and vegetation derived aromatic DOM (e.g., more depleted δ¹³C, elevated condensed aromatic and polyphenolic contribution) that had a modern radiocarbon age. After ~ 200 years of ecosystem development, DOM composition was comparable to that observed for other temperate and arctic forested watersheds without permafrost influence. These results underscore the timelines on which glacier retreat may have substantial impacts on watershed biogeochemistry and coastal ecosystems that receive DOM from these rapidly changing landscapes.

气候变化正在融化全球的冰川并改变流域生物地球化学，特别是在以山地冰川为主的地区，如阿拉斯加东南部。与森林和植被流域相比，冰川主导的流域表现出明显的溶解有机质 (DOM) 特征。然而，关于流 DOM 组成如何随着冰川退缩和陆地生态系统演替而发生变化的信息很少。重要的是，尚不清楚这些转变发生的时间跨度。在这里，我们使用本体、同位素和超高分辨率分子级技术来评估河流 DOM 组成如何随着冰川退缩和随后的陆地生态系统演替而演变。为了这，自阿拉斯加东南部沿海冰川退缩以来，跨越时间梯度 0 到 ~ 1400 年的时间序列从 11 条溪流中收集水样。在冰川退缩后的前 200 年里，河流 DOM 在体积、同位素和分子级组成方面表现出显着且一致的变化。特别是，古老的、富含能量的（例如，脂肪族贡献增加）、低芳香性（例如，低 SUVA₂₅₄和 AI _mod ) DOM 和土壤和植被衍生的芳香 DOM 的 RA 增加（例如，更耗尽的 δ ¹³ C，增加的浓缩芳香和多酚贡献）具有现代放射性碳年龄。经过大约 200 年的生态系统发展，DOM 组成与在没有永久冻土影响的其他温带和北极森林流域中观察到的组成相当。这些结果强调了冰川退缩可能对流域生物地球化学和沿海生态系统产生重大影响的时间表，这些生态系统从这些快速变化的景观中接收 DOM。