The relationships between the river water chemistry and the wetland coverage are shown in Figure 7. Riverine dFe and DOC concentrations clearly increased with the wetland coverage (dFe:r2 = 0.66, DOC: r2 = 0.46). In contrast, riverine EC exponentially decreased with wetland coverage (EC: r2 = 0.45). In addition to these findings, we found that riverine dFe concentration had a strong positive correlation with DOC concentration (r2 = 0.63), and a negative correlation with EC (r2 = 0.74). Since EC is an index showing how much dissolved ion components are present in the water, these results strongly suggest that wetland (Mari ) supplies dFe- and DOC-rich and mineral-poor groundwater to rivers (see Discussion 4.2).