Weathering release and ecosystem retention of trace metals along a 127-yr glacial retreat soil chronosequence.

Glaciers are retreating worldwide, exposing fresh substrates that undergo primary soil and vegetation development. Glacier retreat chronosequences provide unique settings to study trace metal sources (lithogenic vs. atmospheric) and their redistribution during early ecosystem development. Along the 127-yr Hailuogou Glacier retreat chronosequence, we analyzed the vertical metal distribution in soil to distinguish rock- and atmosphere-derived trace metals, and quantified fast- and slow-reacting mineral pools and their release rates in a laboratory weathering experiment to assess the metal availability for redistribution. We calculated total trace metal stocks in the upper 10 cm of mineral soil, organic layers, and above- and below-ground vegetation compartments (leaves, branches, bark, wood and roots). Our results indicate that Co, Cu, Ni, U and V mainly derived from the parent material, whereas Cd, Pb, and Zn originated from atmospheric inputs, with initial carbonate weathering contributing to Cd and Zn release. Weathering released trace metals from labile primary minerals abundant in younger soils, while vegetation establishment and organic layer formation enhanced trace metal accumulation. However, this accumulation did not compensate for the substantial leaching losses, which accounted for 39 - 49% of the initial stocks, except for Pb and Cd, whose atmospheric inputs offset losses, resulting in their long-term retention within the ecosystem. The dynamic interplay of weathering, atmospheric inputs and plant-driven redistribution in this young ecosystem reflect a rapid responsiveness of trace metals to environmental changes. The observed dynamics at decadal scale challenge the view that trace metals are generally little reactive in ecosystems.