Long-term dynamics of organic matter inputs in sediments of Lake Balkhash, arid Central Asia: Coupled climate and anthropogenic influences

Abstract

Lake sediments as reservoirs of organic matter (OM) play crucial roles in the carbon burial and carbon cycle on the regional and global scales. However, the long-term history and patterns of sedimentary organic matter (SOM) inputs from various sources and its response to multiple drivers are not well constrained. Here, we demonstrated variations in the source and composition of SOM and the potential regulating factors using the multi-biomarker (n-alkanes, fatty acids, and alcohols) signatures in a core span the last ∼ 250 years from Lake Balkhash. The highest Paq (proportions of aquatic macrophytes) and relatively low short-chain lipid contents in sediments before 1860 CE indicate the dominant OM inputs from aquatic macrophytes and minor inputs from microalgae. This can be attributed to the humid conditions during the late Little Ice Age (LIA). The decreased Paq and the highest CPIH (carbon preference index for high molecular weight) in sediments deposited in 1860 ∼ 1930 CE revealed considerably elevated OM inputs from emergent plants coeval with declined aquatic macrophytes contributions. This pattern of OM inputs was likely caused by large variables of water levels during the climate transition period, promoting the growth of emergent plants and inhibited aquatic macrophytes. In sediments from 1930 ∼ 2016 CE, much higher terrestrial OM inputs and prevailing microalgal OM inputs were reflected by the highest principal components of each source, whereas the lowest Paq indicates minimal OM inputs from aquatic macrophytes. These changes were probably caused by intensification of anthropogenic perturbations, e.g., land reclamation, promoting more terrestrial OM and nutrients transported into the lake. These findings suggested that SOM inputs are highly linked to lake environmental changes and can be profoundly influenced by climate variability and anthropogenic activities, which provides insights into patterns of carbon burial and carbon cycle in lake-catchment systems in arid regions.