Sediment composition and depositional environments in tropical Lake Sentani, Papua Province, Indonesia

Tropical Lake Sentani in the Indonesian Province Papua consists of four separate sub-basins and is surrounded by a geologically  diverse catchment. Also, strong morphological differences between the sub-basins result in a unique water column structure for each basin, ranging from fully mixed to meromictic. We characterized the surface sediment (upper 5 cm) of the lake’s four sub-basins based on multivariate statistical analyses (Principal Component Analysis, hierarchical clustering) of major element compositions obtained by X-ray Fluorescence (XRF) scanning. Three types of sediment are identified based on distinct compositional differences between rivers, shallow/proximal and deep/distal lake sediments. The different sediment types are mainly characterized by the amounts of organic carbon (TOC) and sulfur on one side and elements associated with siliciclastic rocks (Ti, Al, Si, K) on the other. Our study shows large spatial heterogeneity within the lake’s sub-basins that is mainly caused by catchment geology and topography, river runoff as well as the bathymetry and the depth of the oxycline.The samples from rivers and river mouths are dominated by siliciclastic elements and linked with coarser grain sizes as well as an abundance of mafic rock fractions or carbonates, depending on catchment geology. The sedimentary environment also controls the behavior of Fe and Mn, as these elements change from a positive correlation with siliciclastic elements in river samples to a negative correlation in the lake, indicating a more redox-sensitive behavior. These highly variable conditions make Lake Sentani a natural laboratory, with its different sub-basins representing different depositional environments under identical tropical climate conditions