Abstract
This study was carried out in three kinds of salt marshes according to the vegetation covers, including Phragmites australis salt marsh (PSM), Suaeda salus salt marsh (SSM) and Tamarix chinensis-Suaeda salus salt marsh (TSSM). We applied allometric function, exponential function and logistic function to model the depth distribution of the SOCv and SOCc for each salt marsh, respectively. The results showed that the exponential function fits the depth distribution of the SOCv more well than other two functions. The SOCc can be fitted very well by all three functions for three salt marsh (Adj. R2 > 0.99), of which the allometric function was the best one. The mean topsoil concentration factors (TCFs) of three salt marshes were beyond 0.1, which means the SOC enrichment in surface soils due to plant cycling, but TCFs in PSM were significantly higher than those in SSM (P < 0.05). Nearly 30% of SOC was concentrated in the top 20 cm soils. The results of general linear model (GLM) suggested that four soil properties (soil water content, pH, soil salt content and silt+clay) and their interactive effects explained about 80% of the total variation of SOC stock in the top 20 cm soils and the 20–100 cm soil layers.
Highlights
This study was carried out in three kinds of salt marshes according to the vegetation covers, including Phragmites australis salt marsh (PSM), Suaeda salus salt marsh (SSM) and Tamarix chinensis-Suaeda salus salt marsh (TSSM)
A decreasing trend was observed along the soil profile according to the mean values of soil organic carbon (SOC), with the exception of the 40–60 cm soil layer, which was more similar to the soil salt content (SSC) trend
Our study showed that nearly 30% of the SOC was concentrated in the soil surface (0–20 cm) of the coastal salt marshes of the Yellow River Delta (YRD) (Fig. 5)
Summary
This study was carried out in three kinds of salt marshes according to the vegetation covers, including Phragmites australis salt marsh (PSM), Suaeda salus salt marsh (SSM) and Tamarix chinensis-Suaeda salus salt marsh (TSSM). Exponential function and logistic function to model the depth distribution of the SOCv and SOCc for each salt marsh, respectively. The SOC stocks in coastal salt marshes could be underor overestimated as a result of large uncertainties[7]. Under the influence of hydrological fluctuations, vegetation succession and burial processes, the SOC in salt marshes typically have a large spatial variation. Several models have been applied to describe and extrapolate the SOC content[16], and the exponential functions might be most widely used in modelling the vertical SOC distribution[14] due to its mathematical simplicity and its apparent similarity to the SOC decline with the soil depth[15] It remains unknown whether the exponential function could be fitted to the vertical SOC distribution in salt marshes.
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