Large weir construction causes the loss of seasonal habitat in riverine wetlands: a case study of the Four Large River Projects in South Korea

摘要

From 2009 to 2012, South Korea carried out national-wide construction projects in four rivers; sixteen large-weirs were constructed to control flood risk and to secure water resources. Environmental impact assessment of the weir construction evaluated conditional changes by comparing post-survey records with pre-construction periods. However, the ecological assessment for the weir construction in a long-term perspective has been still limited. In this study, we compared the long-term dynamics of riverine habitat in two construction sites (Nakdong River and Geum River), and one reference site (Seomjin River) in South Korea using 33-years database of satellite imagery. We classified 30 m-grid riverine habitats into three temporal types (i.e., permanent water, seasonal water, and non-flooded habitat) based on annual flooding frequency and its temporal trend was compared. After weirs construction, the area of permanent water was increased (Nakdong R.: +36.0%, Geum R.: +10.9%); seasonal habitat and non-flooded habitat were decreased (Nakdong R: -36.5% and -37.4%; Geum R: -22.9% and -28.2%, respectively). And annual flux of habitat transitions into different habitat types has been decreased only in weir construction sites. Among different habitat transition categories, habitat change into permanent water was the highest during the weir construction periods. Our long-term analysis of riverine habitat can be used to understand temporal changes and recovery after weir construction and channel dredging.