Heavy metal accumulation, geochemical fractions, and loadings in two agricultural watersheds with distinct climate conditions

The main aim of this study was to explore the effects of climate conditions on the transport and transformation of heavy metals. Sedimentary geochemical analysis and watershed modeling were used to investigate the distinctions between heavy metal pollution under different climate conditions. The results showed that the average concentrations of Cu, Cd, and Pb in sediments of the subtropical watershed (36.64, 0.60, and 133.69 mg/kg, respectively) were higher than those of the temperate watershed (26.58, 0.19, and 23.17 mg/kg, respectively) because of surface runoff-induced heavy metal loadings under higher precipitation. Also, the labile fractions, which mainly originated from anthropogenic sources, showed higher percentages in the subtropical watershed (67.84-91.33%), thereby indicating that the transport of heavy metals was promoted by surface runoff. Moreover, higher percentages of acid-soluble fractions of Cu and Pb (23.55-33.60%) in the subtropical watershed suggested that higher temperatures accelerated the transformation of heavy metal fractions, thus contributing to the transportation of heavy metals. Overall, climate conditions were the dominant factors for the differences between the subtropical and temperate watersheds. The results of this study suggest that the effects of climate conditions on the transport, enrichment, and bioavailability of heavy metals are of great significance. Such effects should therefore be the focus of future studies.