Diverse effects of climate changes and anthropogenic activities on sedimentary nitrogen isotope (δN) in lakes across different regions of China since the late Holocene.

Nitrogen plays a vital role in the Earth's systems. Nitrogen isotopes have been widely used in environmental and climatic research. Various biogeochemical processes and nitrogen sources contribute to the sedimentary organic matter. Therefore, environmental implications of sedimentary nitrogen isotope (δN) require further investigation. In this study, we report and compile the δN records from eight lakes in China influenced by either climate changes or anthropogenic activities since the late Holocene to determine the major forcing factors of δN. Our results showed that: (1) During the late Holocene, lacustrine δN was mainly regulated by natural climate changes, such as temperature, precipitation, or both as anthropogenic activities were weak. (2) The impact of gradually increasing anthropogenic disturbances on δN in the different lakes varied. Globally, the declining lacustrine δN values could be attributed to atmospheric reactive nitrogen deposition. However, on the regional catchment scale, the increased δN values in lakes may be related to increased nutrient input and higher primary production caused by increased anthropogenic activities, whereas the rapid decline of δN values in lakes is possibly related to more nutrient input and N-depleted organic matter input resulting excessive anthropogenic activities. Our study suggests that the impact of anthropogenic activities on lake ecosystems gradually increased in recent decades, and the amplitudes in variations of δN values in some lakes exceeded those during periods of weak anthropogenic disturbances. If not properly managed, anthropogenic disturbances may outweigh nature (i.e., temperature, precipitation) as the leading cause of lake ecosystem changes in the future.