Evolution of multi-element coupling and geochemical behavior in dryland and paddy soils along a 3000-year...

This study investigated a 3000-year soil chronosequence in the Yangtze River floodplain to evaluate the enrichment, dispersion, correlations, and coupling of 40 elements in both dryland and paddy soils. Of these, 31 elements showed enrichment trends, whereas nine displayed dispersion trends. Positive correlations among elements weakened with reclamation duration, reaching their lowest point at 2000 years. Over the course of reclamation, the multi-element coupling index (MEC) and weighted multi-element coupling index (WMEC) peaked at 160 years and declined to their lowest values at 2000 years in both land-use types. Under the combined influence of factors such as nutrient availability, moisture conditions, and redox dynamics, dryland soils exhibited higher MEC and WMEC than paddy soils under the identical reclamation duration. Partial least squares path modeling (PLS-PM) indicated that clay content, bulk density (BD), and soil organic carbon (SOC) are the primary factors driving the WMEC. This study reveals the evolutionary trends of multi-element coupling and geochemical behavior in soils under long-term coastal wetland reclamation, providing a scientific foundation for environmental management and the safe use of land in coastal wetland ecosystems.