Characteristics and environmental significance of organic carbon deposition in Baiyangdian Lake, China, 1969–2020

Abstract

Lake sediments provide a basis for ecological information that can reconstruct the history of a lake ecosystem and clarify the carbon sink process. We combined chronological information relating to sediment cores in Baiyangdian Lake with the history of human activities, to examine the influence of the natural environment and human activities on the humification of organic carbon. This analysis revealed the evolution of the ecological environment in the lake over the past 50 years. The results showed the average deposition rate of sediments to be 0.957 cm/a; with the total organic carbon and total nitrogen contents of sediments ranging from 14.32 to 333.19 g/kg and from 0.95 to 26.90 g/kg, respectively. The δ13C values ranged from −13.04 ‰ to −29.07 ‰, while the δ15N values ranged from −1.43 ‰ to 8.37 ‰. The fulvic acid carbon (FAC) content ranged from 0.52 g/kg to 14.21 g/kg, and the humic acid carbon (HAC) content ranged from 1.67 g/kg to 23.82 g/kg. The HAC/FAC value gradually increased as the sediment deepend. The results of each index in the sedimentary column, combined with the dating information, allowed us to conclude that, from 1969 to 1985, human activities had little effect on the lake, and the source of organic carbon and the humification process remained stable. During this period, the water purification function of the lake continued to improve. From 1985 to 2014, the surrounding economy developed rapidly, resulting in significant changes in the lake's ecological structure and the distribution of lake plants. Serious eutrophication occurred, leading to increased pollution Between 2014 and 2020, the lake protection measures implemented achieved initial positive results. During the period, the source of organic carbon and the humification process stabilized, eutrophication was alleviated, and the burial and fixation of organic carbon gradually reached a healthier state.