Comprehensive assessment of soil quality for different wetlands in a Chinese delta

Soil quality is usually considered a powerful tool to reveal soil degradation status and wetland ecosystem health. It is insufficient to reflect actual soil quality based on soil fertility or heavy metal pollution assessment, respectively. A comprehensive assessment was performed to combine soil fertility and heavy metal contamination together, on the basis of 13 soil physical, chemical, biological indicators and six heavy metals, in the Pearl River Delta of China including urban river wetland (URW), ditch wetland (DW), riparian wetland (RiW), and reclaimed wetland (ReW). The moderate fertility level was observed according to the minimum data set, including total nitrogen (TN), microbial biomass carbon (MBC), total phosphorus, total potassium, sand, and salinity. DW soils had significantly higher soil fertility index values than RiW and ReW soils. Low TN, soil organic carbon (SOC), MBC levels, and sandy loam texture revealed potential chemical, biological and physical degradation risks, especially for ReW. In addition, wetland soils were heavily contaminated by heavy metals, particularly for Cd, according to Nemerow Pollution Index. URW soils exhibited significantly higher pollution levels than ReW soils. According to the methodology of comprehensive assessment, soil quality belonged to moderate and low grades because of severe heavy metal pollution, following with moderate nutrition level. Consequently, pollution treatment, fertility (e.g., SOC, N, P, and K), and soil texture improvement are crucial to improving soil quality, preventing further degradation and promoting ecological conservation and sustainability of coastal wetlands in the Pearl River Delta.