The effect of soil chemical properties and ecological implications on the distribution of heavy metals in different types of peatland

Abstract

Due to their sorption properties and high organic matter content, peatlands play an important role in the retention of pollutants, including heavy metals. This study aimed to assess the extent and level of heavy metal contamination in different types of histosols (fibric, hemic and sapric) found Polish peatlands. It was hipothesised that differences in peatland type, reflected in the degree of organic matter decomposition and chemical composition, would significantly influence the accumulation levels and geochemical behaviour of heavy metals. The study examined the chemical properties and heavy metal content of three peatland soil types across 277 systematically distributed sampling plots in Poland. From each plot, composite soil samples were collected at a depth of 0–15 cm and analysed for pH, total carbon and nitrogen, and exchangeable cations (Ca²⁺, Mg²⁺, K⁺, Na⁺), and heavy metals (Cd, Co, Cr, Cu, Ni, Pb, Zn) using standardised laboratory procedures. The geo-accumulation index (I_geo) was applied to assess pollution intensity relative to regional geochemical backgrounds. Multivariate statistical techniques and spatial analysis were employed to identify patterns in soil chemistry and contamination. The results revealed significant differences in chemical properties between peatland types. Fibric histosols exhibited the lowest pH and the highest organic carbon content and C/N ratio, indicating a lower degree of decomposition. In contrast, sapric histosols exhibited a higher pH value, elevated levels of base cations (particularly Ca²⁺ and Mg²⁺), and more advanced organic matter mineralisation. Concentrations of heavy metals (especially Cd, Cr, Cu, Ni, and Zn) were generally highest in sapric histosols, particularly in southern Poland. The geo-accumulation index (I_geo) showed that sapric histosols were more contaminated than fibric and hemic types, with the highest I_geo values observed for cadmium and chromium. Spatial analysis revealed that the most polluted areas, as defined by the I_geo classification, were concentrated in the industrialised southern and south-western regions of Poland. These findings confirm that both natural and anthropogenic heavy metal accumulation are strongly influenced by peatland type and location. Statistical analysis showed strong correlations between metal content and pH, as well as cation concentrations (Ca²⁺, Mg²⁺, K⁺ and Na⁺). The distinctiveness of the chemical and metal composition of different peatland types highlights the importance of considering soil type and parameters when assessing environmental risk. This study provides new insights into the distribution of heavy metals in Polish peatlands and their association with histosol type and soil chemical properties. It demonstrates that the peatland type significantly influences the accumulation and spatial distribution of heavy metals in soil, with sapric histosols showing the highest levels of contamination. These results emphasise the significance of peat decomposition stage, pH and base cation content in determining heavy metal retention.