An Investigation into the Changing Pattern In Schizothorax fish abundance with pollution load in Dal Lake through an Interface of Environmental DNA and Dating Methods

Abstract

Understanding long-term environmental changes and historical distribution patterns of native fish species is vital for developing strategies to preserve their biodiversity and maintaining ecological balance in freshwater environments. However, lack of detailed historical data on fish populations in lakes presents various challenges which hinders accurate quantification, and the understanding of how anthropogenic fingerprints affect their temporal distribution. Tracking such quantitative fluctuations of fish populations is essential for reconstructing the complex dynamics of lake systems, as fish species play an essential role across multiple trophic levels. To address this knowledge gap, present study employed a multi-dimensional approach involving next-generation sedDNA sequencing, optically stimulated luminescence (OSL) dating, pollution proxies, and time series forecasting to reconstruct the historical distribution of Schizothorax species in Dal Lake, a Himalayan freshwater lake, over the past ~3700 years. Temporal dynamics of Schizothorax species were investigated alongside the influence of pollution and geochemical changes on its distribution patterns within lake. The results revealed that sedDNA concentration and Schizothorax abundance peaked ~727 years before present (BP) and sharp decline was observed beyond ~765 years BP extending down to the deepest layers of core corresponding to the age up to ~3719 years BP. Taxonomic analysis identified Schizothorax richardsoni, Schizothorax oconnori, Schizothorax esocinus, Schizothorax plagiostomus, Schizothorax labiatus and Schizothorax lissolabiata as dominant fish species while as Schizothorax niger, Schizothorax prenanti, Schizothorax argentatus, Schizothorax progastus, Schizothorax nukiangensis and Schizothorax curvilabiatus exhibited fluctuating distribution patterns within the sediment layers of the lake. Diversity indices showed significant variation within depth of core with highest species diversity observed around ~2002.5 years BP and low diversity ...