Distribution and biological cycle of iron in freshwater peatlands of Sanjiang Plain, Northeast China

Iron cycling in wetlands is important because it plays an important role in interactions among wetland soils/sediments, plants and microorganisms. The seasonal variation of iron (Fe) distributed in two freshwater peatland ecosystems dominated by Calamagrostis angustifolia (CA) and Carex lasiocarpa (CL), was observed in Sanjiang Plain of Northeast China. The compartmentalization of the Fe cycle including storage in the atmosphere, litter, soil, and above- and below ground plant material was determined. The results showed that the Fe input from rain was 0.06 g m− 2 a− 1, and the total Fe mass in the peatland ecosystem was 5.18 × 103 for CA and 1.40 × 103 g m− 2 for CL. The major Fe pools were soils (98.6% and 97.1% for CA and CL, respectively). The Fe fluxes between each compartment resulted in the increase of the belowground Fe pool and decrease of the litter Fe pool currently both for CA and CL. CL has greater uptake coefficient (0.024) and cycle coefficient (0.034), but smaller use coefficient (0.58) than that of CA (0.02, 0.006, and 0.77, respectively). Peatland conversion for agriculture affected the former natural Fe cycle processes and mass balance to a certain extent in long term, because the Fe assimilated by soybean and rice are less than that of CA and CL, and cannot return to soils from harvesting. Drainage and ditch excavation for agricultural conversion caused considerable Fe loss via aqueous movement, so that Fe was likely lost and transported downstream by these ditch networks.