Mapping of Permafrost Wetland Using Satellite Data and Its Importance on Dissolved Iron Concentration in Rivers, Russian Far East

Abstract:

The Sea of Okhotsk is known as one of the world's richest marine ecosystems. This is because large amount of iron, an essential nutrient for the growth of phytoplankton, flows out of wetlands in the Amur River basin and supports to high primary productivity. Many studies paid attention to high dissolved iron (dFe) concentration in the Amur river and its availability in the Sea of Okhotsk. However, there is little understanding of iron behavior in active layer and the discharge mechanism from soil to rivers in permafrost watershed. In the mid-Amur basin, permafrost exists under wetlands which is seen in flat valleys, and we observed that dissolved iron production occurred from August to September. This suggests that permafrost wetlands in valley areas play an important role in dFe discharge to rivers.

In the present study, we attempted to clarify the correlation between the dissolved iron concentration in rivers and the distribution of permafrost wetlands in the Tyrma region of mid-Amur basin by using satellite data. Determining the distribution of permafrost wetlands was performed in the software QGIS. Using the Landsat-8 satellite data, we calculated a normalized difference vegetation index (NDVI) and a normalized difference soil index (NDSI). Then, these values were summarized for typical vegetation types of permafrost wetlands, forests, and grasslands based on the local ground truth. As a result, these vegetations can be distinguished under the conditions of NDVI and NDSI. Based on these two values, the distribution of permafrost wetlands in the whole Tyrma region was extracted.

We calculated area of the extracted permafrost wetlands in catchment area of 24 rivers in the Tyrma region, which we sampled and measured dFe concentration. The permafrost wetlands area / catchment area ratios and dissolved iron concentrations in the rivers showed a clear positive correlation. This result indicates that the permafrost distribution created using GIS is reliable, and the distribution of permafrost wetlands is highly effective to explain the variation in dissolved iron concentrations in the rivers. To our knowledge, this is the first time to discover the direct correlation between the permafrost distribution and dissolved iron concentration at the watershed scale.