The relationships between fractal parameters of soil particle size and heavy-metal content on alluvial-proluvial fan

The particle size distribution (PSD) of soil is an important factor in determining heavy-metal content, mobility, and transformation. One method of describing the soil PSD is applying fractal theory. This study explored the use of fractal theory to characterize soil PSD in the alluvial-proluvial fan located downstream of the Yangshuo lead-zinc mine. The relationships between fractal parameters of soil PSD and heavy-metal content were analyzed. The results showed that soil in front of the mountain (FM) had higher clay content than soil on the mountain slope (MS) or in the middle of the alluvial-proluvial fan (MF). Among the different sections of the alluvial-proluvial fan, MS had the largest capacity dimension D(0), information dimension D(1), correlation dimension D(2), single fractal dimension D, spectral width Δα, and D(1)/D(0), whereas MF had the greatest symmetry degree Δf. Soil of MS had the highest ω (Cr) and ω (Fe), while FM had the highest ω (Zn), ω (Mn), ω (Pb), ω (Cu), ω (As), ω (Sb), and ω (Cd). Fractal parameters of soil PSD and soil mechanical composition were significantly correlated, while both variables were correlated with heavy-metal content. Fractal parameters can be used to indicate heavy-metal content when heavy metals migrate due to migration of particle size. This study thus introduces an empirical method for evaluating heavy-metal content in soil and analyzing the mechanisms of their migration, making a strong contribution to developing strategies that limit heavy-metal pollution.