The distribution of soil dissolved organic carbon in wetlands under different hydrological conditions in the Yellow River Delta

The typical coastal wetlands including flooded freshwater-restored Phragmites australis wetland (FPW), nonflooding Phragmites australis wetland (NPW), tidal Phragmites australis wetland (TPW) and tidal Suaeda salsa wetland (TSW) were selected as sampling sites to investigate the concentration and distribution of soil dissolved organic carbon (DOC) in wetlands under different hydrological conditions．Soil samples up to a depth of 25 cm were collected in triplicates in October and December, 2018, and in April, 2019 to determine soil DOC and soil properties．DOC in soils from NPW was found to be higher than in soils of other three types of wetlands, with a maximum value of 18.54 mg·kg⁻¹ in the winter．Mean values of soil DOC in TSW, NPW, FPW and TPW were found to be 7.75 , 16.03 , 9.07 and 9.40 mg·kg⁻¹, respectively during 3 sampling seasons．Along 0-25 cm soil profile, DOC showed a generally decreasing trend in soils of four wetlands, with higher values in 0-5 cm soil．Principal component analysis (PCA) and correlation analysis showed that soil salt ions and soil texture were the main factors affecting soil DOC．Three dimensional (3D) fluorescence spectroscopic analysis indicated that DOC in soils of four wetland types all originated from various sources．Contributions of internal source and external input to soil DOC under different hydrological conditions were found to be quite different．