Analysis of Environmental Purification Effect of Riparian Forest with Poplar Trees for Ecological Watershed Management: A Case Study in the Floodplain of the Dam Reservoir in Korea

The Total Nitrogen(T-N) and Total Phosphors(T-P) contents in the soils of three riparian forests with poplar trees were compared with the surrounding cultivated and uncultivated lands. Three key results were obtained by analyzing poplar tree volume and the T-N and T-P content in the plant body. First, in soil surveys covering 36 points, the T-N and T-P content in the riparian forests were 0.064% and 0.036%, respectively, whereas in non-riparian forests, they were 0.147% and 0.101%, respectively. The two areas had significantly different T-N and T-P values. Within the non-riparian-forest category, the T-N and T-P content in cultivated land was 0.174% and 0.103%, respectively, showing significant differences from riparian forest values. When comparing riparian forests and uncultivated land, the T-N contents were not significantly different (p > 0.113), but the T-P content of 0.095% showed a significant difference (p < 0.006). Second, the total poplar tree volumes of the riparian forest test sites 1, 2, and 3 were 466.46 m3, 171.34 m3, and 75.76 m3, respectively. The T-N and T-P accumulation per unit area was the largest in site 1, at 497.75 kg/ha and 112.73 kg/ha, respectively. The larger the tree volume, the larger the T-N and T-P accumulation in the plant body, and the lower the T-N and T-P content in the soil. Third, analyzing the T-N and T-P removal rate in relation to the environmental conditions of the riparian forests showed that site 3 had the smallest total poplar tree content, and the T-N and T-P accumulation per unit area (ha) was also relatively low at just 56% and 68% of the average value. The main causes of this outcome are thought to be the differences in environmental conditions, such as the crop cultivated before poplar planting began and the terrain. The research results verify that riparian forests with poplar trees reduced T-N and T-P content in the soils. The growth of poplar is expected to increase the removal of T-N and T-P from the soil and contribute to the reduction of various nonpoint source pollution flows into rivers and lakes and to the purification of soil in flooded areas. Therefore, riparian forests can act as a form of green infrastructure and as a system to remove nonpoint source pollution in ecological watershed management.