Spatial distribution exploration and driving factor identification for soil salinisation based on geodetector models in coastal area

Soil salinisation, as a serious environmental problem, has received widespread attention worldwide. Accurately and quantitatively identifying the driving factors of soil salinisation is difficult because of its complicated driving theory. Groundwater and soil problems should be considered in coastal sponge construction because of the complexity of geological conditions and the particularity of the water cycle. On this basis, the salinisation degree, spatial distribution, drivers and their quantitative relationship in Zhuanghe were respectively analysed using statistical method, interpolation analysis, geodetector model and data-fitting method. Zhuanghe is one of the pilot areas of China's coastal 'Sponge City'. Multisource data on factors, such as climate, geosciences and human activities, which cause soil salinity, were comprehensively collected. Five discrete methods were used to optimise the continuous data of the geodetector model to ensure the best-quality modelling results. The driving factors were also explored. Results show that the underground aquifers in coastal areas were affected by seawater intrusion. The groundwater depth was also shallow in some coastal areas. Furthermore, the soil pH and salt content in coastal areas were higher than those in inland. Differences in the optimisation methods and the number of layers for various factors, which exhibited a remarkably impact on the model results, were also observed. Natural break was superior to other methods for most factors. Groundwater depth and salt concentration were the dominant factors for soil salinisation in the study area. The interaction between factors was almost the bi- and nonlinear-enhance effects; the interaction between groundwater depth and Cl-water(-) or M played a leading role in salinisation. The groundwater depth should be maintained below 3.48 m through the establishment of a binary nonlinear model to ensure that groundwater and soil are unaffected. The findings of this study are of substantial help for relevant workers and have a remarkable guiding significance for the construction of coastal sponge cities.