The role of Sphagnum decomposition in metal accumulation and release in peatlands (SMAP)

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Peatlands have the potential to retain and store large amounts of major and trace elements. Due to atmospheric deposition, trace elements from natural or anthropogenic sources reach the surface of ombrotrophic peatlands (bogs). After their deposition as solutes or particles, major and trace elements can be retained through plant uptake, physical entrainment or complexation by organic matter at different stages of decomposition. Due to its extreme sensitivity to trace metal accumulation, Sphagnum sp. (the dominant species in boreal peatlands) can effectively take up and retain soluble cations of trace elements (e.g., Cu+2, Hg+2, and Pb+2). Dissolved organic matter produced in peatlands can be mobilized and act as a major carrier of metal transport from peatlands to fluvial systems. Hydrologic conditions – heavy rain events preceded by dry conditions – are known to determine metal export from peatlands. Due to these conditions, the hydrological connectivity in the aerated part of peatlands is stimulated, connecting the pools of previously mobilized metals. However, less well known are the role of Sphagnum sp. degradation for the uptake and release of trace elements in the surface of the peatlands and the effects of seasonal and climatic changes on degradation. Based on in vitro Sphagnum decomposition and metal uptake experiments, the proposed study (SMAP) intends to determine to what extent the decomposition process of Sphagnum litter – i.e., the preferential degradation and transformation of more labile compounds and the selective preservation of more resistant compounds – affects the release of different trace elements to the hydrological system or their retention in the peat deposit. This research is expected to disentangle the role of the first stages of peat formation for the accumulation and release of metals during peat accretion. In addition, the expected results will improve our understanding of the crucial step of metal-signal formation, which will lead to the re-evaluation of the current use of peat records as palaeo-archives for historical atmospheric metal deposition.