Chronological records of sediment organic carbon at an entrance of Dongting Lake: Response to historical meteorological events.

ABSTRACT

Lake sediments are the products of soil erosion and are strongly influenced by climate variability, particularly extreme meteorological events. Sediment organic carbon (SOC) can reflect environmental changes that affect sediment transport. However, the response of SOC chronological records to major meteorological events is relatively unknown. This study explored the chronological regularity of SOC and verified its variations using major historical meteorological events. Based on three sediment profiles with a depth of 230 cm at the Yuan River entrance to the West Dongting Lake (Hanshou entrance), the SOC chronology was reconstructed by employing the sedimentation rates calculated by 137Cs and 210Pb. The sedimentary environment then was interpreted via comparisons and quantitative analysis. The grain distribution and the S-shaped distribution of SOC reflected the general deposition regularity of organic carbon in lake sediments, which gradually stabilized with depth. The average sedimentation rates based on 137Cs and 210Pb were 1.310 and 1.319 cm a-1, respectively. Accordingly, SOC records covered the past 76 years via dating (0-100 cm), during which the SOC content first increased and subsequently stabilized. By comparing the data with the occurrence of 11 major historical meteorological events, we found that SOC generally increased after these events. Moreover, the frequent occurrence of meteorological events stabilized the SOC content. Severe floods had a greater impact on SOC content than severe droughts, causing SOC to change by up to 20.24% and 8.77%, respectively. Our findings suggest that major historical meteorological events can verify SOC chronological records, thereby highlighting their significant impacts on organic carbon variations in sediments.