Organic and inorganic geochemical analyses on sediments from Preto Lake, a central Amazon basin floodplain water body, were used to document hydrological changes of the Solimões River during the late Holocene. Between 3600 and 400 cal yr BP, Preto Lake received smectite-rich sediment from the Solimões River, with high concentrations of Al (~ 53 × 103 ppm) and Si (~ 210 × 103 ppm). The high detrital input suggests there was a direct connection between Preto Lake and the main river channel. High river inflow maintained lake stage and was responsible for the contribution to sediments of phytoplankton-derived organic matter. Low sediment organic carbon concentrations characterized this period (mean ~ 3.8 wt%), probably because of dilution by river-borne lithogenic matter. Although the river inputs remained high, abrupt increases in TOC content around 1800 and 1200 cal yr BP suggest brief increases in fluvial nutrient supply to Preto Lake. During the last 400 cal yr, substantial declines in smectite (mean 40%), Al (~ 29 × 103 ppm) and Si (138 × 103 ppm) suggest the establishment of a semi-isolated lake, with reduced river inflow. A large proportion of C3-plant-derived organic matter, supplied by runoff from the kaolinite-rich watershed, was observed during this period, and was accompanied by high autochthonous primary production, driven by development of an aquatic macrophyte community. This change in sediment organic matter source accounted for the greater TOC content (~ 20%) of sediments deposited during this period. Although Holocene climate change was an important control on fluvial sediment supply to upper and lower Amazon Basin floodplain lakes, sedimentation processes in Preto Lake can also be linked to changes in the river’s course. The transition to a semi-isolated lake could have been a consequence of lateral and vertical sediment accretion, which formed a natural levee that blocked fluvial input to Preto Lake.

中文翻译：

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气候和水文控制对亚马逊洪泛区湖的全新世晚期沉积物供应

对来自亚马逊盆地中部洪泛区水体 Preto 湖沉积物的有机和无机地球化学分析被用来记录全新世晚期 Solimões 河的水文变化。在 3600 和 400 cal yr BP 之间，Preto Lake 接收了来自 Solimões 河的富含蒙脱石的沉积物，其中含有高浓度的铝（~ 53 × 103 ppm）和硅（~ 210 × 103 ppm）。高碎屑输入表明普雷图湖和主要河道之间存在直接连接。高河流入流维持了湖泊水位，是对浮游植物衍生有机物沉积物的贡献。这一时期的特征是沉积物有机碳浓度低（平均约 3.8%），可能是因为河流中的成岩物质稀释了。尽管河流输入量仍然很高，TOC 含量在 1800 和 1200 cal yr BP 左右突然增加表明 Preto Lake 的河流养分供应短暂增加。在过去的 400 cal yr 中，蒙脱石（平均 40%）、Al（~ 29 × 103 ppm）和 Si（138 × 103 ppm）的显着下降表明半孤立湖泊的建立，河流流入量减少。在此期间观察到由富含高岭石的流域径流提供的大部分 C3 植物来源的有机物质，并伴随着受大型水生植物群落发展驱动的高本地初级生产。沉积物有机质来源的这种变化导致在此期间沉积的沉积物的 TOC 含量更高（约 20%）。尽管全新世气候变化是控制亚马逊河流域上下游泛滥平原湖泊河流沉积物供应的重要因素，普雷图湖的沉积过程也可能与河道的变化有关。向半孤立湖泊的过渡可能是横向和纵向沉积物堆积的结果，沉积物形成了天然堤坝，阻止了河流输入到 Preto 湖。