Relationships Between Floodplain Topography, Peat, Soil Moisture, and Alder Growth over a Decade After River Meandering Restoration in the Kushiro Wetlands, Hokkaido, Japan

This study aimed to identify the predominant factors that are important for environmental sustainability in wetland restoration in the Kushiro Wetlands, Hokkaido, Japan, where a nature restoration project was implemented over a decade ago. Field surveys of topography and vegetation, as well as laboratory soil tests, were conducted in the meandering-restored section of the Kushiro River, where alder trees have flourished, and in the reference section, where wetland grasslands have been maintained. We then applied correlation analysis to the data to examine the relationship between the peat soil characteristics and alder tree size. The results showed a significant positive correlation between organic matter and the water content ratio in all the survey sections (correlation coefficient: 0.88; p -value < 0.05). The reference section had 24.1 ± 11.1% organic matter, indicating well-developed peat with sufficient moisture retention, while the re-meandering section had 13.1 ± 3.8%, indicating underdeveloped peat with limited moisture retention. Furthermore, no correlation was found between the relative elevation and water content ratio (correlation coefficient: −0.01; p -value > 0.05), nor was there any difference in nutrient concentrations between the survey sections. Therefore, it is possible that the difference in alder tree sizes between the sections depended on the soil moisture retention capacity based on the degree of peat soil development. These results suggest that peat soil restoration is crucial in human sustainable development for suppressing alder proliferation and restoring original peat grasslands.