How the Physical and Chemical Properties Affect the Heavy Metal Content in Surface Water in Different Types of Peatlands

ABSTRACT Only ~3% of the global land surface is covered by peatlands, yet more than one‐third of global soil carbon is stored in these ecosystems and contaminant filtration can be provided. The extent to which peat humification (Fibric–Hemic–Sapric) is linked to dissolved heavy metals in peatland surface waters has remained poorly quantified at a national scale. Synoptic sampling was used to maximise spatial coverage. Consequently, spatial patterns were described for late‐summer conditions. A nationwide late‐summer survey of 233 peatland sites across Poland was conducted, and basic water chemistry together with dissolved trace metals (Cd, Cr, Cu, Ni, Pb, Zn, Fe and Mn) was quantified. Two contrasting hydrochemical regimes were identified. Higher and markedly more variable concentrations of Cd, Cu, Pb and Zn were observed in acidic, organic‐rich Fibric waters, whereas enrichment in Fe and Mn was more often observed in minerotrophic Sapric waters. Across all sites, trace‐metal concentrations were negatively associated with pH, while Fe and Mn were positively associated with conductivity and bicarbonate, consistent with stronger groundwater influence in minerotrophic settings. Screening against EU and Polish water‐quality criteria was performed and indicated that exceedances of regulated trace metals were mainly clustered along the Baltic coast and in the Upper Silesian region. Protection of ombrotrophic bog hydrology and management of groundwater inputs to fens are therefore recommended to sustain peatlands' metal‐retention functions.