Seasonal Variations of Dissolved Iron Concentration in Active Layer and Rivers in Permafrost Areas, Russian Far East

Dissolved iron (dFe) in boreal rivers may play an important role in primary production in high-latitude oceans. However, iron behavior in soils and dFe discharge mechanism from soil to the rivers are poorly understood. To better understand iron dynamics on the watershed scale, we observed the seasonal changes in dFe and Dissolved Organic Carbon (DOC) concentrations in the river as well as dFe concentration in soil pore waters in permafrost watershed from May to October. During snowmelt season, high dFe production (1.38-4.70 mg L-1) was observed in surface soil pore waters. Correspondingly, riverine dFe and DOC concentrations increased to 1.10 mg L-1 and 32.3 mg L-1, and both were the highest in the year. After spring floods, riverine dFe and DOC concentrations decreased to 0.15 mg L-1 and 7.62 mg L-1, and dFe concentration in surface soil pore waters also decreased to 0.20-1.28 mg L-1. In late July, riverine dFe and DOC concentrations increased to 0.33 mg L-1 and 23.6 mg L-1 in response to heavy rainfall. In August and September, considerable increases in dFe concentrations (2.00-6.90 mg L-1) were observed in subsurface soil pore waters, probably because infiltrated rainwater developed reducing conditions. This dFe production was confirmed widely in permafrost wetlands in valley areas. Overall, permafrost wetlands in valley areas are hotspots of dFe production and greatly contribute to dFe and DOC discharge to rivers, especially during snowmelt and rainy seasons.