Effects of multi-temporal environmental variables on SOC spatial prediction models in coastal wetlands of a Chinese delta

Mapping soil organic carbon (SOC) distributions in coastal wetlands plays an important role in assessing ecosystem services and investigating the global carbon cycle. Little research has explored the effects of environmental variables with seasonal variations on digital soil mapping (DSM). Our research utilized machine learning methods and established multiple prediction models of SOC based on multi-temporal data from dry and wet seasons, and mono-temporal data from April. The results showed that the relationships between SOC and environmental variables in different months varied significantly in coastal wetlands of the Yellow River Delta (YRD). In general, the environmental variables in the wet season showed stronger correlations and higher importance scores with SOC compared with those in the dry season. In addition, SOC prediction models in wet season and April had stronger prediction performance compared with those in the dry season. As a result, data fusion of multi-temporal data did not necessarily contribute to the model performance enhancement. Relative homogenous soil-landscape attributes and spectral characteristics in dry season could not accurately explain the strong spatial variation of SOC in this area, and it might be the major reason that caused the stronger model performance of soil prediction models in wet season than those in dry season. Therefore, the accurate spatial prediction of soil properties requires the characterization of the seasonal dynamics of soil-landscape relationships. In general, the findings of this research demonstrated that seasonal variation of environmental variables should be considered in the establishment of a DSM model in coastal wetland.

Automated summary

This research examined the effects of environmental variables with seasonal variations on digital soil mapping (DSM) in coastal wetlands. Machine learning methods were used to establish multiple prediction models of soil organic carbon (SOC) based on multi-temporal data. The results showed significant variations in the relationships between SOC and environmental variables in different months. The environmental variables in the wet season had stronger correlations and higher importance scores with SOC compared to the dry season. Furthermore, the prediction models in the wet season and April had stronger performance than those in the dry season. This study highlights the importance of considering seasonal variations in the establishment of a DSM model in coastal wetlands.