Amazon rivers and flooded areas can be categorized into three types of water: white, black, and clear. These categories present unique physical–chemical characteristics that influence the characteristics and distribution of sedimentary organic matter (SOM). A geochemical assessment of the short sedimentary cores of four floodplain lakes within the Brazilian Amazon basin was performed. Two black, one white, and one clear-water floodplain lakes were selected to evaluate the variability of OM composition based on aliphatic biomarker and carbon isotopic ratios, as proxies for an enhanced methane cycle, anoxia, and to determine the origin of predominant aliphatic biomass. Gas chromatography was coupled to flame ionization detection (GC–FID), mass spectrometry (GC–MS) and combustion-isotope ratio mass spectrometry (GC–C–IRMS). These were used to determine aliphatic biomarker ratios, for quantification, and to measure carbon isotopic compositions. The TOC content was inversely proportional to the expected OM productivity; one black water (low OM productivity) presented the highest TOC content, and white water (high productivity) presented the lowest. Also, clear water lake (intermediate productivity) presented TOC content between the other lakes. Based on n-alkane proxies and profiles, as well as bacterial and plant-derivative terpene distribution, we observed a mostly terrigenous contribution for the black and clear water lakes (allochthonous SOM), as well as a prevalence of aquatic organisms in white water lake (autochthonous SOM). Only in the most superficial section of the white water lake, was intense OM degradation substantiated with n-alkanes showing an even-short-chain predominance, indicative of OM cycling. Also, for one black water lake, we detected depleted n-alkane and diploptene δ¹³C values (–42‰) associated with methanotrophic archaea and higher relative concentrations of des-A-triterpenes commonly associated with anoxic sedimentation. Based on these data, the influence of water-type on the SOM composition was verified. The approach helps to understand the application of n-alkane proxies to differentiate Amazonian environments.

亚马逊河流和洪水泛滥的地区可分为三种类型的水：白色、黑色和清澈。这些类别呈现出影响沉积有机质 (SOM) 特征和分布的独特物理-化学特征。对巴西亚马逊盆地内四个漫滩湖泊的短沉积岩心进行了地球化学评估。选择了两个黑色、一个白色和一个清水泛滥平原湖泊来评估基于脂肪族生物标志物和碳同位素比率的 OM 组成的变异性，作为增强的甲烷循环、缺氧的代理，并确定主要脂肪族生物量的来源. 气相色谱与火焰电离检测 (GC-FID)、质谱 (GC-MS) 和燃烧同位素比质谱 (GC-C-IRMS) 联用。这些用于确定脂肪族生物标志物比率、用于量化和测量碳同位素组成。TOC 含量与预期的 OM 生产率成反比；一种黑水（低 OM 生产力）的 TOC 含量最高，而白水（高生产力）的 TOC 含量最低。此外，清水湖（中等生产力）呈现出其他湖泊之间的 TOC 含量。基于正构烷烃代理和概况，以及细菌和植物衍生物萜烯分布，我们观察到黑水和清水湖（异地 SOM）的主要陆源贡献，以及白水湖中水生生物的普遍存在（本土SOM）。仅在白水湖的最表层部分，强烈的 OM 降解证实了正构烷烃显示偶数短链优势，表明 OM 循环。此外，对于一个黑水湖，我们检测到耗尽的正烷烃和双萜 δ ¹³C 值 (–42‰) 与甲烷营养古菌相关，而脱-A-三萜的相对浓度较高，通常与缺氧沉降相关。基于这些数据，验证了水类型对 SOM 组成的影响。该方法有助于理解正烷烃代理在区分亚马逊环境中的应用。