Spatial and seasonal contrasts of sedimentary organic matter infloodplain lakes of the central Amazon basin

[摘要] In this study, we investigated the seasonal and spatial pattern ofsedimentary organic matter (SOM) in five floodplain lakes of the centralAmazon basin (Cabaliana, Janauaca, Canaçari, Mirituba and Curuai) whichhave different morphologies, hydrodynamics and vegetation coverages. Surfacesediments were collected in four hydrological seasons: low water (LW),rising water (RW), high water (HW) and falling water (FW) in 2009 and 2010.We investigated commonly used bulk geochemical tracers such as the C : N ratioand the stable isotopic composition of organic carbon (δ¹³C_org). These results were compared with lignin phenolparameters as an indicator of vascular plant detritus and branched glyceroldialkyl glycerol tetraethers (brGDGTs) to trace the input of soil organicmatter (OM) from land to the aquatic settings. We also applied thecrenarchaeol as an indicator of aquatic (rivers and lakes) OM. Our datashowed that during the RW and FW seasons, the surface sediments wereenriched in lignin and brGDGTs in comparison to other seasons. Our studyalso indicated that floodplain lake sediments primarily consisted ofallochthonous, C₃ plant-derived OM. However, a downstream increase inC₄ macrophyte-derived OM contribution was observed along the gradientof increasing open waters – i.e., from upstream to downstream. Accordingly, weattribute the temporal and spatial difference in SOM composition to thehydrological dynamics between the floodplain lakes and the surroundingflooded forests.

[学科分类] 地球化学与岩石