Distinguishing the determinative landscape factors influencing the spatial variation of soil quality in Chongming Island, China

Soil quality of coastal wetlands plays an important role in maintaining biological productivity, improving environmental quality, and promoting plant and animal health. Landscape pattern is the major factor affecting variations in soil quality of coastal wetland. However, the influence of landscapes on spatial variations in soil quality has not been fully explored in coastal wetlands with highly fragmented landscapes. Here, we established a composite indicator of soil quality of coastal wetland, used a series of analysis methods to explore the spatial characteristics of soil quality of coastal wetland and the intrinsic relationships between soil quality and landscape factors, and quantified the landscape factors affecting the spatial variation of soil quality. Chongming Island, a typical estuarine island coastal wetland in China, was selected as the study area. The results showed that coastal wetland soil quality had distinct spatial variations, and significant correlations were observed between soil quality indicators and landscape factors. Key landscape factors, including distance to coastline (DTC), distance to human-related landscape types (DTH), number of landscape types (NLT), natural index of landscape (NIL), number of landscape patches (NLP), total edge of landscape patches (TELP), net primary production (NPP), normalized difference vegetation index (NDVI), soil salinity index (SSI), and normalized difference build-up and bare soil index (NDBSI), were identified and quantified at the optimal spatial evaluation units. Among the landscape types, woodlands and farmlands showed better soil quality and landscape conditions in coastal wetlands. Among the landscape pattern factors, landscape function factors, rather than composition and structure factors, had a greater impact on the spatial variation of coastal wetland soil quality. The soil quality was good at positions with high DTC and NDVI and low DTH and SSI. These findings highlighted that landscape factors NDVI (19.93%), SSI (15.93%), DTC (15.28%), and DTH (11.16%) contributed the most to the spatial variation in soil quality on Chongming Island. This study reveals the intrinsic correlations between soil quality and landscape, and provides a reference for maintaining the coastal wetland ecosystems.