Analyzing the Effect of River Ecosystem Fragmentation by Bridges on Changes in the Wintering Population of Whooper Swans (Cygnus cygnus): Targeting the Nakdong River, Busan

Abstract

Background and objective: Fragmentation of river ecosystems is expected to affect biodiversity loss, but bridge construction is proceeding without consideration in urban areas. This study was conducted to determine the effect of internal environmental factors and river ecosystem fragmentation caused by bridge construction on the population of wintering whooper swans (Cygnus cygnus) in the Nakdong River of Busan Metropolitan City, a key wintering site for whooper swans.Methods: To compare the wintering population according to the distance between bridges, we surveyed and analyzed the current status of the population by period, distance between bridges, and land cover. One-way ANOVA and post-hoc test were conducted to confirm whether the differences in the environmental factors of the wintering sites, such as the distance between bridges, land cover status, and the number of wintering individuals, were statistically significant.Results: 83.6-94.7% of the wintering population in the lower Nakdong River were observed in Sec. 2 (Nakdong River Estuary Bank-Seobusan Nakdong River Bridge, 5.3 km) and Sec.4 (Gamjeon-Iron Bridge-Nakdong River Hwaengdansugwan Bridge, 3.6 km). As for the distance between the feeding and resting places of whooper swans and the bridges, whooper swans used the waterside and wetlands at an average distance of 1,147.5 m (10.9-2,611.2 m) from the bridge.Conclusion: Considering the weight of male swans and the presence of young individuals, as well as disturbance factors such as the noise and speed of vehicles crossing the bridges, it is necessary to maintain at least a 4 km distance between bridges for stable wintering. In addition, since fragmentation of river ecosystems has been confirmed to have an adverse effect on biodiversity, it would be desirable to keep the ecosystem intact and connected.