Divergent response of blue carbon components to wetland types and hydrological effects in typical estuarine wetlands of Jiaozhou Bay, China

As ecosystems subject to periodic tides, estuarine wetlands have a significant capacity to sequester carbon over time. Understanding the distribution patterns of soil carbon components and identifying the key factors influencing these patterns are key to gaining insight into the function of "blue carbon" in coastal wetlands. To clarify the response of soil carbon components to wetland types and hydrological effects in estuarine wetlands, the typical estuarine wetlands in Jiaozhou Bay, China were selected as the study area, and the soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), soil inorganic carbon (SIC) and dissolved inorganic carbon (DIC) under different wetland types and hydrological effects were investigated. The results showed that the SOC, SIC, and MBC contents were significantly influenced by the wetland types. The SOC and MBC contents were as follows: mudflat (GT) > Phragmites australis wetland (PA) > Suaeda salsa wetland (SS). The overall content of SIC was highest in PA, followed by GT and SS. Hydrological effects had significant influence on the soil MBC, DOC and DIC contents. With the increase hydrological effects, the soil MBC content decreased by 38.89%-72.22%, while the DOC and DIC contents increased by 15.13%-19.89% and 13.41%-86.70%, respectively. The results of the correlation analysis and structural equation model indicated that wetland types and hydrological effects directly or indirectly (through changes in soil pH, bulk density, water content, and salinity) drove the changes in soil carbon contents in estuarine wetlands. Altogether, our findings implied that the alterations of wetland types and hydrological effects will affect the blue carbon function of estuarine wetlands. In the future, for accurate assessment of a blue carbon budget for estuarine wetlands, the differences in wetland types and hydrological effects of different areas should be considered.