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

Abstract

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.

Northern High-Latitude Organic Soils As a Vital Source of River-Borne Dissolved Iron to the Ocean

“…High-latitude river systems transfer large amounts of dissolved iron, that is, iron-bearing humic substances (SAHLs) from land to sea. These unique substances have been shown to contribute significantly to relieving iron deficiency in coastal regions and shelf seas as well as in surface waters of the open Arctic Ocean and the northern North Atlantic Ocean, thereby supporting the oceanic sink for anthropogenic CO 2 . ,,− …”

Impact of permafrost degradation on the extreme increase of dissolved iron concentration in the Amur River during 1995–1997

“…Given the high correlation coe cients between annual/late summer dFe concentration and Ta with a lag of 8 years, we infer that increased dFe discharge likely lasted for 1-2 years. In addition to input of groundwater rich in dFe, summer rainfall is also considered to increase dFe concentration in rivers 17,49 . However, there was no signi cant correlation between the individual measurements of the Amur River discharge and dFe concentration in late summer (Fig.…”

“…active layer thickness peaks in September 17 . Dissolved iron was measured by the colorimetric method with 1,10-phenantroline, which was applied to water ltered through Whatman GF/F lters (0.7 µm) and acidi ed to pH < 2 with HCl (Russian international technical standards 52.24.358-2006) 57 .…”

“…Its high biological productivity is partly a result of the abundant dFe derived from the forests and wetlands in the Amur River basin [12][13][14] . According to previous studies, the extensive wetlands in the lower Amur basin 15,16 and the permafrost wetlands in the middle Amur basin 17 are important sources of dFe for the Amur River. However, little is known about the mechanisms of dFe discharge to the Amur River, especially in terms of long-term changes in dFe concentration.…”

Insights into Organic Carbon, Iron, Metals and Phosphorus Dynamics in Freshwaters

“…Extending the knowledge of river water chemical composition in Siberia, Tashiro et al [4] studied watershed-scale iron dynamics, and coupled the seasonal changes in Fe and dissolved organic carbon (DOC) concentrations in the tributaries of the Amur River basin. They demonstrated that permafrost wetlands in valley areas act as hotspots of dissolved Fe production and greatly contribute to Fe and DOC discharge to rivers, especially during snowmelt and rainy seasons.…”