09:15 〜 09:30
[ACC25-02] 衛生画像解析および現地植生調査から推定されるアムール川中流域の永久凍土分布
キーワード：永久凍土、リモートセンシング、湿地
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. In late 1990s, dissolved iron (dFe) concentration in the Amur river and its main tributaries increased dramatically. The reason for this is still unclear, but one possible reason may be permafrost degradation due to unusual high air temperatures in the late 1990s in Russian Far East. To consider this possibility, it is needed to understand iron dynamics in permafrost areas and reveal the permafrost distribution in Russian Far East.
In the present study, we attempted to clarify the permafrost distribution in the Tyrma region of mid-Amur basin by using satellite data (Landsat-8) and conducting local field research. Tyrma is located in approximately 270 km northwest of Khabarovsk in the Russian Far East. Mean annual air temperature is −1.96 ℃ and annual precipitation is 654.6 mm.
Using the Landsat-8 satellite data, we calculated a normalized difference vegetation index (NDVI) and a normalized difference soil index (NDSI). Both values were summarized for typical vegetation types of wetlands, forests, and grasslands based on the local ground truth in the Tyrma region. In addition, we conducted cross-sectional field research in wetlands to confirm that permafrost continuously exists under wetlands. Landform, vegetation, soil condition, groundwater level, and permafrost existence were investigated by crossing wetland in valley area from near river to hillslope.
The range of NDVI and NDSI summarized for wetlands, forests, and grasslands were clearly different. Based on NDVI and NDSI, landcover distribution of wetlands, forests, and grasslands were extracted in the whole Tyrma region (Figure). Local field research revealed that permafrost continuously exists under wetlands, and the top layer of permafrost was confirmed at 60~80 cm depth. Therefore, permafrost will exist with high probability under the extracted wetlands in Fig.1 (Red area). Furthermore, we found that the greater the permafrost distribution area in catchment area, the higher dFe concentration in rivers, suggesting that permafrost existence strongly affects dFe discharge from land to river.
In the present study, we attempted to clarify the permafrost distribution in the Tyrma region of mid-Amur basin by using satellite data (Landsat-8) and conducting local field research. Tyrma is located in approximately 270 km northwest of Khabarovsk in the Russian Far East. Mean annual air temperature is −1.96 ℃ and annual precipitation is 654.6 mm.
Using the Landsat-8 satellite data, we calculated a normalized difference vegetation index (NDVI) and a normalized difference soil index (NDSI). Both values were summarized for typical vegetation types of wetlands, forests, and grasslands based on the local ground truth in the Tyrma region. In addition, we conducted cross-sectional field research in wetlands to confirm that permafrost continuously exists under wetlands. Landform, vegetation, soil condition, groundwater level, and permafrost existence were investigated by crossing wetland in valley area from near river to hillslope.
The range of NDVI and NDSI summarized for wetlands, forests, and grasslands were clearly different. Based on NDVI and NDSI, landcover distribution of wetlands, forests, and grasslands were extracted in the whole Tyrma region (Figure). Local field research revealed that permafrost continuously exists under wetlands, and the top layer of permafrost was confirmed at 60~80 cm depth. Therefore, permafrost will exist with high probability under the extracted wetlands in Fig.1 (Red area). Furthermore, we found that the greater the permafrost distribution area in catchment area, the higher dFe concentration in rivers, suggesting that permafrost existence strongly affects dFe discharge from land to river.