Geochemical Characteristics of Sediment in Tropical Lake Sentani, Indonesia, Are Influenced by Spatial Differences in Catchment Geology and Water Column Stratification

Abstract

Physical and (bio)chemical processes in the catchment as well as internal lake processes influence the composition of lacustrine sediments. Lake internal processes are a consequence of reactions and fluxes between sediment, porewater and the water column. Due to its separation into four interconnected sub-basins, Lake Sentani, Papua Province, Indonesia, is a unique tropical lake that reveals a wide range of geochemical conditions. The highly diverse geological catchment causes mineralogical and chemical differentiation of the sediment input into each sub-basin. Also, strong morphological differences between the sub-basins result in a unique water column structure for each sub-basin, ranging from fully mixed to meromictic. Given the strong differences in sediment composition and bottom water chemistry among the four sub-basins, Lake Sentani offers a unique chance to study multiple lacustrine systems under identical climate conditions and with a common surface water chemistry. We used sediment cores and water samples and measured physicochemical water column profiles to reveal the geochemical characteristics of the water column, the sediment and pore water for all four sub-basins of Lake Sentani. The chemical composition of the sediment reveals differentiation among the sub-basins according to their sediment input and water column structure. Catchment lithology mainly affects overall sediment composition, whereas pore water chemistry is also affected by water column structure, which is related to basin morphology and water depth. In the meromictic sub-basins the bottom water and sediment pore water appear to form a single continuous system, whereas in those sub-basins with oxygenated bottom water the sediment-water interface forms a pronounced chemical barrier.

Deciphering the source contribution of organic matter accumulation in an urban wetland ecosystem

“…The alkaline pH of sediments may also be attributed to the microbial activity, predominantly sulfate reduction and ammonification (Zhang et al, 2008). The EC of aquatic sediments is influenced by various factors including the geology of the catchment areas, rate of chemical weathering, and mineralization of OM (Bhateria & Jain, 2016; Nomosatryo et al, 2021). Higher values of EC at some depths of the sediment core are attributed to the high concentration of ions released from the decomposition and mineralization of domestic wastes and OM.…”

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

“…Our own depth soundings at every sampling location revealed maximum depths of 42, 12, 30 and 43 m, for sub-basins 1 to 4, respectively. In a recent study, Nomosatryo et al (2021) presented physicochemical properties of the water column, measured at or close to the deepest parts of each basin. In short, the upper 10 m of the water column in all four basins is well mixed, below this depth dissolved oxygen (DO) decreases more or less rapidly and becomes fully depleted in sub-basins 1 and 4, in sub-basin 3 DO just reaches depletion at the sediment-water interface, and shallow sub-basin 2 remains fully oxygenated.…”

“…The recent study of Nomosatryo et al (2021) presents geochemical depth profiles of sediment cores from each sub-basin, showing clear compositional differences between sites and with depth, and each sub-basin shows distinctly different trends. The present study focuses just on the sediment surface, albeit in higher spatial resolution.…”

“…Many of them showed that lateral heterogeneity can severely complicate reconstructions of paleoenvironmental conditions based on long sediment cores. In Lake Sentani Nomosatryo et al (2021) sampled the water column and took sediment cores in the deepest part of each sub-basin. Their results showed that climatic and hydrological changes are recorded in sedimentary sequence.…”