Sedimentology and microbiology of Lake Sentani, Papua Province, Indonesia – A multidisciplinary study of a tropical lake system under increasing anthropogenic stress

Lake Sentani consists of  four interconnected sub-basins with different water depths and water column characteristics, ranging from fully mixed to permanently stratified. Its catchment is comprised of highly diverse lithologies, ranging from mafic and ultramafic rocks to clastic sediment and carbonates, so each sub-basin receives a distinct sediment input. Lake Sentani is also influenced by anthropogenic activity due to the growing population around the lake, potentially leading to local eutrophication. Due to its unique characteristics, we investigated the effects of catchment lithology and water column structure on sediment composition. We also investigated microbial community composition and diversity in surface sediments across Lake Sentani as well as in the partially ephemeral tributary rivers and the river mouths, which form the connection between riverine and the lacustrine habitats.

Using multivariate statistical analyses of mineralogical and major element compositions obtained by X-ray diffraction (XRD) and X-ray Fluorescence (XRF) analyses we could identify three main types of sediment based on distinct compositional differences between rivers, shallow/proximal and deep/distal lake sediments. There is large spatial heterogeneity within the lake’s sub-basins that is mainly caused by catchment geology and topography, river runoff as well as bathymetry and the depth of the oxycline.The different sediment types are mainly characterized by the amounts of organic carbon (TOC) and sulfur as well as elements associated with siliciclastic rocks (Ti, Al, Si, K). Depending on the sedimentary environment, the redox-sensitive elements Fe and Mn change from a positive correlation with siliciclastic elements in river samples to a negative correlation in the lake.

Using 16S rRNA based analyses to investigate microbial community structure and diversity, we detected highly diverse microbial communities across the different lake basins and catchment river sediments, suggesting a wide variety of biogeochemical processes taking place. The molecular biological data broadly agree with the sedimentological differentiation of the sediment into three major groups, but they also provide a different perspective on the biogeochemical processes in the lake. However, our study also suggested increased anthropogenic stressors impacting the microbial community, most probably caused by population growth and urbanization, especially along the northern and northeastern parts. River and river mouth sediments, particularly from these more urbanized areas, were enriched in microbial taxa frequently associated with eutrophication and affiliated with human waste and industrial pollution.Our study highlights the value of multi-disciplinary datasets for a holistic lake management under increasing anthropogenic stress.