Dissolved Iron and Organic Matter in Northern Peatlands

Concentrations of dissolved (passing through aerobic filtration) iron and organic carbon (DOC) were determined in water samples collected from subarctic fens near Schefferville and boreal bogs near Sept-Iles, northern Quebec. Total iron and DOC concentrations averaged 19.3 and 1.2 mg/L, respectively, for all the samples analyzed and were weakly negatively correlated. The bog waters were higher in DOC and lower in total iron than the fen waters. Subsurface samples from the fens, underlain by iron-rich materials, showed increased iron concentrations, whereas the bogs, underlain by iron-poor materials, did not. Differences in the DOC: iron ratios can be explained by the different pathways of water and sources of DOC and iron in the two types of peatland. Reaction of the peat water samples with o-phenanthroline suggests both organically complexed and fine colloidal and dissolved forms of iron. The continuous variation method showed that peak absorbance occurs at DOC: iron ratios of 6:1 to 8:1, suggesting that all but the subsurface fen samples contained organic matter complexes that were undersaturated with respect to iron.