Source and sequestration of sediment organic carbon from different elevation zones in estuarine wetland, North China.

Estuarine wetland plays an important role in regulating global carbon cycle due to high terrestrial carbon input and burial. However, it is unclear how the source and sequestration of sediment organic carbon (SOC) in estuarine wetlands changes under the anthropogenic impact in the past century. In this study, combining parameters of TOC/TN ratios, δC, δN and Pb-chronology, temporal trends of SOC source and sequestration flux in Liaohe estuarine wetland were studied. The results showed that the source of organic carbon in Liaohe estuarine wetland was dominated by terrestrial input (contribution >60 %). Due to vegetation, TOC in shallow reed marsh was significantly higher than that of bare beach and subtidal flat. Affected by elevation, the sediment mass accumulation rate (MAR, kg·m·yr) showed differences in reed marsh (C1), bare beach (C2) and subtidal flat (C3), which were 6.57, 13.56 and 13.25 respectively in the past century. MAR fluctuated over time, it showed an overall increasing trend, especially since the 1980s. Correspondingly, the sequestration flux of SOC (SF-SOC, g·m·yr) showed an overall increasing trend with average of 82.84 (reed marsh), 151.93 (bare beach) and 123.71 (subtidal flat). Comparing to TOC, the higher MAR had a more distinct effect on carbon sequestration in Liaohe estuarine wetland. The difference in sedimentation rate and carbon sequestration are linked to the changes in sediment flux of riverine input and land utilization in the catchment area due to human activities in recent decades, including the construction of reservoirs, dams and local ditch wharf.