Autochthonous dissolved organic matter (Auto-DOM) produced by a biological carbon pump using dissolved inorganic carbon (DIC) from carbonate weathering plays an important role in carbon cycling within inland waters. However, little is known regarding how environmental conditions impact the composition and fate of organic matter, especially in surface waters of the semi-arid Loess Plateau, which is enriched in DIC by significant carbonate weathering. To obtain novel insight, we combined hydrochemistry, isotopic composition (δ2H, δ18O, and δ13CDIC), Rayleigh fractionation model, optical spectroscopy (absorbance and fluorescence), and Fourier transform ion cyclotron resonance mass spectrometry measurements to elucidate how primary production and hydrology impact the composition of DOM and the stability of the resulting Auto-DOM throughout the river–reservoir–wetland aquatic continuum of the Bahe River in the carbonate-mineral-rich semi-arid Loess Plateau where carbonate weathering is significant. The Rayleigh fractionation model results indicated that watershed DIC is primarily consumed through aquatic primary production rather than CO2 degassing. Further investigation revealed that primary production and evaporation co-occurred in this watershed. With the enrichment of the stable water isotope δ2H, the relative abundances of the allochthonous compounds decreased and the relative abundances of the autochthonous substances increased, suggesting that the terrestrial signal of riverine DOM decreased while autochthonous production increased along the flow pathway. In addition, associations between optical and molecular characteristics among DOM samples from different water bodies revealed that the stability ratio (Fmax(C2/(C2 + C4))) of Auto-DOM to the ratio of carboxylic-rich alicyclic molecules showed a consistent trend, suggesting that phytoplankton-derived and biomineralized C2 compounds are potentially recalcitrant DOM in inland waters. We conclude that hydrology and primary production affect the source, composition, and, potentially, the stability of DOM in DIC-enriched surface waters of the semi-arid Loess Plateau, which may lead to a more humic-like DOM composition in inland water and export this lower bioavailability DOC to the ocean in the long term.

中文翻译：

---

半干旱水生连续体中溶解有机物组成和稳定性的水文和初级生产控制的多重示踪证据


生物碳泵使用碳酸盐风化产生的溶解无机碳 （DIC） 产生的本土溶解有机物 （Auto-DOM） 在内陆水域的碳循环中起着重要作用。然而，关于环境条件如何影响有机物的组成和归宿，人们知之甚少，尤其是在半干旱的黄土高原的地表水中，该高原通过显着的碳酸盐风化作用富含 DIC。为了获得新的见解，我们结合了水化学、同位素组成（δ2H、δ18O 和 δ13CDIC）、瑞利分馏模型、光谱学（吸光度和荧光）和傅里叶变换离子回旋共振质谱测量，以阐明初级生产和水文如何影响 DOM 的组成以及由此产生的 Auto-DOM 在整个富含碳酸盐矿物的半干旱地区巴赫河河流-水库-湿地水生连续体中的稳定性黄土高原，碳酸盐风化作用显著。Rayleigh 分馏模型结果表明，流域 DIC 主要通过水生初级生产而不是 CO2 脱气来消耗。进一步的调查表明，初级生产和蒸发同时发生在该流域。随着稳定水同位素δ2H的富集，异质化合物的相对丰度降低，土生土长物质的相对丰度增加，表明河流DOM的陆地信号减弱，而沿流路土生土长的产生增加。 此外，来自不同水体的 DOM 样品之间的光学和分子特征之间的关联表明，Auto-DOM 的稳定性比 （Fmax（C2/（C2 + C4））） 与富含羧基的脂环族分子的比率呈一致的趋势，表明浮游植物衍生和生物矿化的 C2 化合物是内陆水域潜在的顽固 DOM。我们得出结论，水文和初级生产会影响半干旱黄土高原富含 DIC 的表层水中 DOM 的来源、成分和潜在的稳定性，这可能导致内陆水域的 DOM 成分更像腐殖质，并将这种较低的生物利用度 DOC 长期输出到海洋。