Influence of depositional mobility (downwashing) on the accumulation of atmospherically supplied elements in peat cores: an experimental approach

Abstract: The potential influence of downwashing on atmospherically deposited elements is of rare focus compared with other geochemical processes related to peat. Downwashing may cause a rapid downward movement of atmospherically supplied elements before they bond to the peat organic substrate and thus reduce the reliability of age-depth models that rely on atmospherically supplied radioisotopes (e.g. 210Pb, 241Am, 137Cs). However, the existence of downwashing has not been directly tested, and to which depth the deposited element can be washed down is not fully understood. To address the question of downwashing, an experiment was set up to mimic wet deposition by applying a CuBr2 solution during a three-week period in peat cores collected from Rödmossamyran. Through this, the experimental results clearly supported the existence of downward mobility. Added Cu2+ could be measured to a depth of 10 cm, similar to previous studies based on Be and Pb. As a similar metal to Cu, the age-depth model based on 210Pb dating could underestimate the ages to some extent without consideration of downwashing.