Land Cover Controls the Export of Terminal Electron Acceptors from Boreal Catchments

NO3, Mn, Fe, and SO4 act as terminal electron acceptors (TEAs), modifying mineralization pathways and coupling biogeochemical cycles. Although single TEA concentrations and fluxes have been intensively studied, the factors regulating the simultaneous fluxes and molar ratios of TEAs are poorly elucidated. We studied the mean concentrations, exports, and molar ratios of TEAs from 27 boreal catchments differing in land cover (percentage of agricultural land, peatland, forest, and built-up area) during the years 2000-2011. TEA exports and molar ratios were strongly controlled by land cover and only a little by atmospheric deposition. Fields produced the highest export of TEAs, particularly NO3. Peatland was linked to low NO3 and SO4, but high Fe exports. NO3, Mn, and Fe exports from forests were low, SO4 having proportionally the highest export. Together, the percentages of field and peatland predicted 93, 80, 75, and 67% of the variation in the export of NO3, Mn, Fe, and SO4, respectively. The variable export of TEAs having different availability and physical behavior may create different premises for anaerobic mineralization in downstream systems, which adds a new dimension to the link between terrestrial system, land use, and environmental problems, such as eutrophication and climate change.