Climate-driven enrichment of pollutants in peatlands

Peatlands play an important role for global carbon dynamics, acting as a sink or source depending on climate. Such changes imply a series of additional effects because peatlands are also an important reservoir of atmospherically derived pollutants. Using a multiproxy approach (non-pollen-palynomorphs, delta N-15, C/N, Se, Br, I, Hg, Ti), we show a relationship between climate (wetter-drier) and peat decomposition, which affected element concentrations in a Spanish bog during the last 5500 years. Changes in superficial wetness played a critical role in the cycling of elements coupled to carbon dynamics. Dry phases caused increased peat mineralisation, resulting in a 2-3 times increase in concentrations of the analysed elements independent from atmospheric fluxes. Under the present trend of climate change large areas of northern peatlands are expected to be severely affected; in this context our findings indicate that the increase in carbon release, which leads to an enrichment of elements, may enhance the export of stored contaminants (Hg, organohalogens) to the aquatic systems or to the atmosphere.