Records of human-induced changes in sedimentation and carbon sequestration in Dalian Bay, north China

Abstract

To study human-induced changes in sedimentation and carbon sequestration over the last 100 years in Dalian Bay (a typical coastal sea in North China), three sediment cores from different locations (C1, C2 and C3) were collected and the chronologies of their depths were evaluated from a radionuclides-based approach. Sedimentation rates (mass accumulation rates) over core depths were calculated based on 210Pbex chronologies, with maximum values of 8.69 kg m−2·yr−1, 5.65 kg m−2·yr−1 and 8.47 kg m−2·yr−1 for C1, C2 and C3, all appearing at the top layer. Distinct increases in sedimentation rates since the 1980s were observed. Correlations between increasing sedimentation rates and decreasing sea areas of Dalian Bay after 1980 verified the influence of human activities on the sedimentary processes. The range of ratios on total organic carbon to total nitrogen (TOC/TN) and isotopic composition of carbon (δ13C) in the sediment was 9.44–17.9 and −22.81‰ to −24.46‰ respectively. Sedimentary organic carbon (SOC) in Dalian Bay showed characteristics of significant terrestrial input, while also being influenced by marine input. The carbon sequestration potential in Dalian Bay's sediment, based on the sequestration rate of SOC (SR-SOC), showed pronounced increase over time, especially since the 1980s. Primarily driven by sedimentation rate, the carbon sequestration potential was dominated by natural processes before 1980. Since then, it came under significant influence from human activities, and this trend grew more intense after the year 2000. Ecosystem service values from carbon sequestration were assessed, and the values' slower increase was the combined result of Dalian Bay's increased SR-SOC and decreased sea area.