Distribution Characteristics of n-alkanes in the Sediments of Lake Gaoyou and Implication of Regional Environmental Evolution During the Past 140 Years

<p indent="0mm"> Lake Gaoyou, a crucial regulating reservoir for the South-to-North Water Diversion Project (Eastern Route), has experienced significant environmental changes in its watershed under intense anthropogenic disturbances. This study investigated the evolution of aquatic vegetation and watershed environments in Lake Gaoyou over the past <sc>140 years</sc> by analyzing the distribution characteristics of <italic>n</italic>-alkanes in sediment cores using ²¹⁰Pb dating, combined with total organic carbon (TOC), total nitrogen (TN), and C/N molar ratios. The results indicated that sedimentary organic matter in Lake Gaoyou primarily originated from terrestrial higher plants, aquatic macrophytes, and non-photosynthetic bacteria. The ecological evolution of the Lake Gaoyou region over the past <sc>140 years</sc> can be divided into three distinct phases: (1) before 1952, the aquatic vegetation index (P_aq) and (<italic>n</italic>-C₂₇+<italic>n</italic>-C₂₉)/(<italic>n</italic>-C₃₁+<italic>n</italic>-C₃₃) ratio suggested dominant organic matter contributions from aquatic macrophytes and terrestrial woody plants, reflecting low nutrient levels and minimal anthropogenic impacts; (2) phase of 1952 to 2010, a marked decline in P_aq and (<italic>n</italic>-C₂₇+<italic>n</italic>-C₂₉)/(<italic>n</italic>-C₃₁+<italic>n</italic>-C₃₃) indicated severe degradation of aquatic macrophytes, likely driven by intensified agricultural activities, hydraulic engineering, and aquaculture practices; (3) since 2010, rapid increases in TOC and TN, alongside rising trends in P_aq and (<italic>n</italic>-C₂₇+<italic>n</italic>-C₂₉)/(<italic>n</italic>-C₃₁+<italic>n</italic>-C₃₃), demonstrated partial ecological recovery attributed to restoration measures such as returning farmland to forests, returning aquaculture areas to lakes, and returning polders to lakes. On this basis, the evolution process of aquatic vegetation in eastern China was further compared, and the evolutionary stages of large-scale aquatic vegetation in different types of lakes and their response mechanisms to human activities were revealed, which provided a theoretical basis for the protection and restoration of regional lake ecological environment.