Contaminated sediment dynamics in peatland headwater catchments

Abstract

Despite substantial research into Pb storage in peatlands, formal description of the mechanisms of contaminated sediment mobilisation is limited. This study explores the controlling factors of contaminated sediment dynamics in an eroding peatland in the Peak District National Park, UK. This study uses the Pb contamination stored near the peat’s surface as a fingerprint to trace contaminated sediment dynamics in three severely degraded headwater catchments. A field portable XRF analyser was used across a range of catchment surfaces to examine patterns of contaminant storage and release. Lead concentrations varied greatly over a small spatial scale. Erosion is exposing high concentrations of Pb on interfluve surfaces (up to 1660 μg g−1), and substantial amounts of reworked contaminated material (up to 1010 μg g−1) are stored on other catchment surfaces (gully walls and floors). A variety of factors have been shown to significantly control Pb release and storage in this environment, including wind action, aspect, and gully depth. Vegetation also plays an important role in retaining sediment-bound heavy metals within contaminated peat catchments. This study provides the first comprehensive overview of the mechanisms controlling Pb release and storage in degraded peatlands. Previous assessments of Pb fluxes may have underestimated contaminant export from severely degraded systems. Wind has also been identified as an as yet unaccounted for vector for heavy metal transport in peatland environments.