EFFECTS OF SCALE ON MINERAL SOLUTE TRANSPORT IN CIRCUMBOREAL PEAT LANDFORMS

Mineral solute fluxes between raised bogs and fens in northern peatlands are complex, and largely depend on scale. In this study we test the hypothesis that the mobilization of solutes in peat underlying small ovoid bog islands mirrors that found under large raised bogs. We examined solute mobilization in a synoptic survey of porewater geochemistry along a transect consisting of a large raised bog, fen, and two ovoid islands within the Glacial Lake Agassiz Peatlands (GLAP), MN. We collected porewater samples at 0.5 m depth intervals from the water table to the underlying mineral soil and analyzed them for concentrations of major basic cations (Ca²⁺, Mg²⁺, Na⁺, K⁺), pH, and specific conductance (SC).

The greatest and smallest base cation concentrations occurred in the fen peat (mean SC 344 μS/cm) and at the bog crest/lower bog slope (mean SC 143 and 139 μS/cm), respectively. Base cation concentrations varied little with depth at the fen throughout the mid-peat profile (1.5-3.0 m), suggesting solutes are transported into the fen by means of lateral porewater flow. The bog crest and lower bog slope peat had relatively dilute solute profiles, indicating porewater flushing by vertical advection of recharge. Base cation concentrations at the upper bog slope (mean SC 263 μS/cm) and the ovoid islands (mean SC 274 and 303 μS/cm) showed marked curvilinear increases in concentration-depth profiles below 2 m, a characteristic of vertical advection-diffusion. Our results suggest the upper bog slope and ovoid islands behave as groundwater recharge areas that maintain similar geochemical profiles due to comparable advection-diffusion dynamics at the peat-mineral interface.