Holocene pollen records from a large shallow lake in East Asia: Complexity of climate changes, environmental variations, and human activities

Abstract

The lack of consecutive Holocene sedimentary records in large shallow lakes poses a significant challenge for attaining a comprehensive understanding of long-term correlations among climate and environmental changes, as well as human activity worldwide. This paper presents detailed pollen records from a typical open Lake Baiyangdian which helped to reconstruct multiple environmental processes and human activities in North China during the Holocene, and to detect the complexity of the reconstruction results. The Baiyangdian area experienced a gradual expansion of wetlands since the early Holocene which then transformed into vast delta swamps due to the Holocene transgression of the Bohai Sea. The subsequent regression resulted in the degradation of the swamps and the formation of grassland 6,500–4,500 cal yr BP. The area quickly became a shallow lake after 4,500 cal yr BP, and then gradually expanded with the strengthening of river processes. The relatively warm mid-Holocene climate significantly accelerated the emergence of agriculture, notably the slash-and-burn cultivation after 6,500 cal yr BP, and the continuous intensification of agricultural activities after 4,000 cal yr BP. Human activity became a significant factor of the environmental change in the Baiyangdian Lake region since 2700 cal yr BP. Our results indicate that the Holocene pollen records from large shallow lakes are often complicated by sedimentary processes and human activity, and should be carefully considered when reconstructing past climatic and environmental changes.