Soil organic carbon content and stock in wetlands with different hydrologic conditions in the Yellow River Delta, China

Abstract

Freshwater influenced wetlands (FIW), wetlands impacted by both freshwater flooding and underground seawater (MIW) and seawater influenced wetlands (SIW) were chosen as sampling sites to investigate the variations in the soil organic carbon content and stock in wetlands with different hydrologic conditions in the Yellow River Delta, China. The results showed that a salinity gradient developed as the hydrologic conditions ranged from freshwater to seawater. In 0–50 cm soils, the mean values of soil organic carbon (SOC), microbial biomass carbon (MBC) and readily oxidized organic carbon (ROOC) were higher in FIW and SIW than those in MIW, while the dissolved organic carbon (DOC) showed a higher mean value in MIW. Along the 0–50 cm soil profile, SOC, MBC, ROOC and DOC decreased as the soil depth increased in FIW and SIW. However, in MIW, soil carbon initially decreased and then increased later. The annual mean values of SOC in 0–50 cm soils were 6.87 g/kg in FIW, 4.92 g/kg in MIW and 5.42 g/kg in SIW, respectively. The soil organic carbon density (SOCD) values for FIW, MIW and SIW were 4.55, 3.26 and 3.84 kg C/m2, respectively. Correlation analysis revealed that SOC, ROOC and DOC were significantly negatively correlated with soil pH, bulk density (BD), sand content, and the C/N ratio, and positively related with water content (WC), silt content, and TN (p < 0.05). However, MBC showed a significantly negative relationship with EC, salt ions content, pH, BD and the C/N ratio, and a significantly positive correlation with TN (p < 0.05).