Pore-water indicators of rainwater-dominated versus groundwater-dominated peat bog profiles (Jura Mountains, Switzerland)

Abstract

The dominant inorganic anions and cations, and dissolved organic carbon have been measured in the pore waters expressed from peat cores taken from two Sphagnum bogs in the Jura Mountains of Switzerland: Étang de la Gruyère (EGr) consists of > 6 m of peat representing more than 12,000 yr of peat formation while at La Tourbière de Genevez (TGe) ∼ 1.5 m of peat have accumulated over the past 5,000 yr. The pore-water analyses of the core taken at EGr show that the first 100 cm of the core are influenced only by atmospheric inputs. The pH of the pore waters is constant (3.9 ± 0.1) with depth. Relative to the average composition of rainwater in this area, Na + is enriched throughout the pore-water profile, K + is neither enriched nor depleted, Mg 2+ is significantly depleted in the deeper pore waters and Ca 2+ strongly depleted throughout the profile. The dominant process affecting the cations in these waters is ion exchange, with the peats behaving like a simple cation exchanger with ion preference decreasing in the order Ca 2+ > Mg 2+ > H + > K + ⪢ Na +. In contrast, at TGe the pH increases from pH ∼4 at the surface to pH 5 at 80 cm. The Cl − and K + concentrations are up to 10 times higher than rainwater values because of mixing of the bog pore water with nearby groundwaters. The Mg 2+ and Ca 2+ concentrations increase with depth to concentrations up to 10 times higher than rainwater values, mainly because of the increasing importance of mineral dissolution within the profile.