Saltmarsh Carbon Stock Changes under Combined Effects of Vegetation Succession and Reclamation

Abstract

Blue carbon ecosystems have been widely recognized for their carbon sequestration function to mitigate climate changes. However, both natural processes (e.g., interspecific competition) and human activities could alter the ability of blue carbon storage. To clarify the impacts of vegetation succession and reclamation on carbon stock changes, field investigation and laboratory analysis were conducted in a saltmarsh within Hangzhou Bay. Remote sensing data indicated a zonation pattern: the exotic species Spartina alterniflora encroached into the native species Scirpus mariqueter at a rate of 3.51 km2 a−1, but S. mariqueter expanded to the front bare mudflat at a rate of 2.51 km2 a−1. The carbon stock (1 m in depth) was found to be 85.37 Mg C ha−1 for the exotic species, 56.52 Mg C ha−1 for the native species, and 39.78 Mg C ha−1 for the bare mudflat. The carbon burial rate varied among 3 habitats, from 0.63 Mg C ha−1 a−1 in the bare mudflat to 1.39 to 1.59 Mg C ha−1 a−1 in the vegetation sites. Within the study area, vegetation succession contributed an additional 4,858 Mg of organic carbon between 2017 and 2020 to the carbon pool. The organic carbon content of the reclamation site showed a considerable reduction, from 8.51 g kg−1 to 3.34 g kg−1 after 2 years of reclamation, resulting in an emission of 21.61 Mg C ha−1. Overall, the vegetation succession increased the carbon stock of the region while reclamation caused a net carbon loss in the saltmarshes. These findings can enrich the cognition to promote blue carbon management in coastal zones.