10:45 AM - 11:00 AM
[ACG43-06] Global assessment of dissolved iron concentrations and fluxes in rivers
★Invited Papers
Keywords:Dissoved iron, Wetland, Redox reaction
The transport of iron from terrestrial to marine regions is an important process in the global surface iron cycle. Iron is transported to the oceans via rivers, lakes, and the atmosphere as dissolved iron that is gradually solubilized in soil and bedrock, which are large iron pools, or as suspended iron that is transported by soil particles themselves, and as aerosols that originate on land. While 50-90% of the iron in rivers is removed from water bodies by coagulation and precipitation in brackish water, it is also known that an iron transport mechanism exists in the ocean, and it is estimated that rivers account for about half of the iron originating from terrestrial sources. Therefore, it is essential to clarify the mechanisms of iron formation in rivers and to accurately evaluate iron concentrations and fluxes in order to obtain comprehensive understanding of the iron cycle. In this study, we focused on dissolved iron, which is considered to be mainly utilized by phytoplankton, and conducted a global evaluation of dissolved iron concentrations and fluxes in rivers. Based on the obtained results and previous findings on the mechanism of dissolved iron formation, future prospects are discussed.
The GEMStat data were used as the dissolved iron concentrations, and 277 watersheds with an area of 1,000 km2 or more were selected for the analysis because they did not show a significant increasing or decreasing trend and had more than 30 time series data points for the period 1990-2020. Correlation analysis and multiple regression analysis were conducted to examine the dominant factors determining dissolved iron concentrations in each watershed. The data set was constructed from 34 soil types from the Harmonized World Soil Database (HWSD), 12 land use types from the Global 1-km Consensus Land Cover, topographic indices from the HydroSHED (15-second resolution) dataset, and temperatures from the CRU TS4.05 dataset (15-second resolution). CRU TS4.05 (0.25-degree resolution) was used for meteorological conditions. The watershed boundaries of each dissolved iron observation site were determined using the HydroSHED (30 s resolution) flow direction data.
The results obtained are as follows. First, it was found that dissolved iron concentrations can be roughly classified according to Köppen's climatic classification, which was calculated based on meteorological conditions. The concentrations were 0.05±0.05 mg/L in the cold zone, 0.14±0.22 mg/L in the subarctic zone, 0.08±0.09 mg/L in the temperate zone, 0.06±0.06 mg/L in the tropical zone, and 0.02±0.02 mg/L in the dry zone, indicating that rivers with relatively high concentrations of dissolved iron were distributed in the subarctic and temperate zone, and in particular, rivers with relatively high concentrations in the The rivers with relatively high dissolved iron concentrations are distributed in the subarctic and temperate zones, with many rivers in the subarctic zone having high concentrations of dissolved iron. Further detailed investigation revealed that Gleysol, Histosol, and topographic indices were found to be significantly positively correlated with dissolved iron concentrations. All of these factors are consistent with biogeochemical mechanisms of dissolved iron formation and are also consistent with our analysis on dissolved iron concentration of Japanese rivers. We developed a regression equation to quantitatively express dissolved iron concentrations using these factors as variables and estimated global dissolved iron fluxes using the obtained regression equation and annual runoff estimated from CRUTS4.05. This is believed to be the first case where dissolved iron fluxes were estimated on a global scale for an individual river. However, the data used in this study include few river data from the Asian region, leaving a void of riverine dissolved iron concentration data.
The GEMStat data were used as the dissolved iron concentrations, and 277 watersheds with an area of 1,000 km2 or more were selected for the analysis because they did not show a significant increasing or decreasing trend and had more than 30 time series data points for the period 1990-2020. Correlation analysis and multiple regression analysis were conducted to examine the dominant factors determining dissolved iron concentrations in each watershed. The data set was constructed from 34 soil types from the Harmonized World Soil Database (HWSD), 12 land use types from the Global 1-km Consensus Land Cover, topographic indices from the HydroSHED (15-second resolution) dataset, and temperatures from the CRU TS4.05 dataset (15-second resolution). CRU TS4.05 (0.25-degree resolution) was used for meteorological conditions. The watershed boundaries of each dissolved iron observation site were determined using the HydroSHED (30 s resolution) flow direction data.
The results obtained are as follows. First, it was found that dissolved iron concentrations can be roughly classified according to Köppen's climatic classification, which was calculated based on meteorological conditions. The concentrations were 0.05±0.05 mg/L in the cold zone, 0.14±0.22 mg/L in the subarctic zone, 0.08±0.09 mg/L in the temperate zone, 0.06±0.06 mg/L in the tropical zone, and 0.02±0.02 mg/L in the dry zone, indicating that rivers with relatively high concentrations of dissolved iron were distributed in the subarctic and temperate zone, and in particular, rivers with relatively high concentrations in the The rivers with relatively high dissolved iron concentrations are distributed in the subarctic and temperate zones, with many rivers in the subarctic zone having high concentrations of dissolved iron. Further detailed investigation revealed that Gleysol, Histosol, and topographic indices were found to be significantly positively correlated with dissolved iron concentrations. All of these factors are consistent with biogeochemical mechanisms of dissolved iron formation and are also consistent with our analysis on dissolved iron concentration of Japanese rivers. We developed a regression equation to quantitatively express dissolved iron concentrations using these factors as variables and estimated global dissolved iron fluxes using the obtained regression equation and annual runoff estimated from CRUTS4.05. This is believed to be the first case where dissolved iron fluxes were estimated on a global scale for an individual river. However, the data used in this study include few river data from the Asian region, leaving a void of riverine dissolved iron concentration data.