Centimeter-scale characterization of biogeochemical gradients at a wetland–aquifer interface using capillary electrophoresis

Steep biogeochemical gradients were measured at mixing interfaces in a wetland–aquifer system impacted by landfill leachate in Norman, Oklahoma. The system lies within a reworked alluvial plain and is characterized by layered low hydraulic conductivity wetland sediments interbedded with sandy aquifer material. Using cm-scale passive diffusion samplers, “peepers”, water samples were collected in a depth profile to span interfaces between surface water and a sequence of deeper sedimentary layers. Geochemical indicators including electron acceptors, low-molecular-weight organic acids, base cations, and NH 4 + were analyzed by capillary electrophoresis (CE) and field techniques to maximize the small sample volumes available from the centimeter-scale [...]