Long-term fate of rapidly eroding carbon stock soil profiles in coastal wetlands

Marsh edge erosion is one of the major causes of land and associated carbon loss in wetland-dominated coastlines. Assessing carbon stocks and understanding fate of eroding carbon is an essential component of wetland carbon budget. This study aims to understand the vertical soil carbon profile of an eroding marsh and potential mineralization of carbon in estuaries. Eleven soil cores (similar to 2 m deep) were collected from the edge of four highly erodingmarsh sites and three cores from the estuarine bottom (similar to 50 cm deep). Coreswere sectioned into 10-cm intervals and analyzed for total, labile and refractory carbon, carbon density, select enzyme and microbial activities, and organic and inorganic phosphorus forms. The total carbon, labile carbon, and carbon density increased with depth at all sites. The carbon density at 1-1.5 m deep (0.04 +/- 0.003 g cm(-3)) was significantly higher (p < 0.0001) than the top 1 m soil (0.032 +/- 0.002 g cm(-3)), indicating the need for considering deeper carbon profile for blue carbon stock assessment. The age of the carbon at the estuarine bottom was 388 +/- 84 years before present (ybp) indicating the recently eroded wetland carbon is not reburied in the estuary. Significant anaerobic microbial activity was present at all the soil depths suggesting high potential of mineralization of eroded carbon in the aerobic estuarinewater. The coastlines experiencing high relative sea-level rise at present or coastlines that are projecting high sea-level rise in the near future are susceptible to losing an enormous amount of previously sequestered carbon over a relatively short period of time. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study found that in highly eroding marsh areas, the carbon density in the soil increased with depth, highlighting the need to consider deeper layers for blue carbon stock assessment. At the estuarine bottom, the age of the carbon was 388 +/- 84 years BP, indicating that recently eroded wetland carbon is not reburied in the estuary.