Effects of water and salinity regulation measures on soil carbon sequestration in coastal wetlands of the Yellow River Delta

Water and salinity regulation measures have been widely taken to restore the ecological structures and functions of degraded coastal wetlands. To investigate the effects of different water and salinity regulation measures on soil carbon stocks in coastal wetlands, soil samples were collected to a depth of 50 cm in four types of wetlands (i.e., restored tidal salt marshes (RTSM, covered with Suaeda salsa) and degraded tidal salt marshes (DTSM, bare land); freshwater restored wetlands (FRW) and degraded wetlands without freshwater inputs (DWFI), covered with Phragmites australis) during the period from August to October in 2015 in the Yellow River Delta, China. Our results showed that the mean values of total carbon (TC), soil organic carbon (SOC), readily oxidizable organic carbon (ROOC) and dissolved organic carbon (DOC) were higher in restored wetlands (e.g., RTSM and FRW) than those in degraded wetlands (e.g., DTSM and DWFI). Along the whole soil profile, TC, SOC, ROOC and DOC were higher in RTSM soils than those in DTSM soils except for TC and SOC in the 0-10 cm soils and DOC in the 40-50 cm soils. FRW soils contained higher TC, SOC, ROOC and DOC than DWFI except for DOC in the 0-10 cm soils. Soil TC density (TCD), SOC density (SOCD), ROOC density (ROOCD) and DOC density (DOCD) in the top 50 cm soils in restored wetlands were higher compared with degraded wetlands. Multivariate analysis showed that soil carbon was significantly influenced by EC, soil base cations and anions (e.g., K+, Ca2+ Cl- and SO42-), pH, TN, C/N ratio, bulk density (BD) and soil texture (p < 0.05). The findings of this study indicated that these two water and salinity regulation measures are effective in increasing soil carbon stocks of coastal wetlands.