Importance of Permafrost Wetlands as Dissolved Iron Source for Rivers in the Amur-Mid Basin
Y. Tashiro1,2*, M. Yoh3, V. P. Shesterkin4 , T. Shiraiwa5, T. Onishi6, D. Naito7,8*
1United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, Tokyo 1838509, Japan,2Institute for Space–Earth Environmental Research, Nagoya University, Aichi 4648601, Japan, 3Emeritus professor, Institute of Agriculture, Tokyo University of Agriculture and Technology, Tokyo 1838509, Japan, 4Khabarovsk Federal Research Center of the Far Eastern Branch of the Russian Academy of Sciences, Institute of Water and Ecology Problems (FEB RAS), Khabarovsk 680000, Russia, 5Institute of Low Temperature Science, Hokkaido University, Hokkaido 0600819, Japan, 6Faculty of Applied Biological Sciences, Gifu University, Gifu 5011193, Japan,7Center for International Forestry Research (CIFOR), Bogor 16115, Indonesia, 8Faculty/Graduate School of Agriculture, Kyoto University, Kyoto 6068502, Japan
*Current Affiliation
Corresponding author: Yuto Tashiro (tassy40y@gmail.com)
Key Points:
Abstract
Dissolved iron (dFe) transported by the Amur River greatly contributes to phytoplankton growth in the Sea of Okhotsk. Nevertheless, there has been little research on the dFe source of rivers, especially in the Amur-Mid Basin which is situated in a sporadic permafrost area. In the Amur-Mid Basin, permafrost generally exists under wetlands in the flat valley, and these permafrost wetlands could be a dFe source of rivers. To asess the importance of the permafrost wetlands as a dFe source, first we made a landcover map with high resolution of 30 m using Landsat-8 data and a machine learning technique (decision tree analysis). As a result of decision tree analysis, three normalized indices (normalized diference vegetation index, normalized difference soil index, and normalized difference water index) and slope enabled us to classify landcovers into three vegetation types: wetland, forest, and grassland. Using this landcover map, we investigated the coverages of the permafrost wetland in the sampled watersheds and examined the correlation with river water chemistry (dFe, dissolved organice carbon: DOC, and electrical conductivity: EC). As a result, dFe and DOC concentrations showed a clear positive correlation (dFe:r2 = 0.66, DOC: r2 = 0.46) with the coverage of permafrost wetlands, while EC showed a negative correlation with those (r2 = 0.45). These findings are the first to demonstrate the direct evidence about the importance of permafrost wetlands to supply dFe and DOC to rivers in the Amur-Mid Basin.