Ecological effects of daylighting and plant reintroduction to the Cheonggye Stream in Seoul, Korea

Seoul's Cheonggye Stream Reconstruction Project removed the concrete road surface that had covered the stream basin for decades to allow sunlight to the stream, reconstructed the stream's channel, restored the surface flow of water by pumping water from the river's downstream to its upstream area, and reintroduced riparian vegetation. Although the project did not fulfill the conditions of ecological restoration, there were a few ecological effects that this project brought. The reconstructed Cheonggye stream has enhanced species diversity and decreased the percentage of exotic species compared to an unrestored urban stream. Also, the species composition of the reintroduced riparian vegetation of the Cheonggye stream has since grown to more closely resemble the natural reference streams, whereas dissimilar to the degraded urban reference site. The re-established vegetation has attracted numerous animal species, and thereby increasing the size and diversity of the biota from 17 species before reconstruction to approximately 400 species. Consequently, the naturalness of the reconstructed Cheonggye stream, as indicated by morphological and ecological characteristics, has improved markedly. In addition, the reconstruction project also improved the water quality, as reflected by the biochemical oxygen demand (BOD). But the restoration of the Cheonggye stream is still underway and several requirements still need to be met to fully actualize true restoration. First, the river zone should be extended and linked to the surrounding terrestrial ecosystems to create an ecological network based on ecological information from the reference area. Second, more diverse microhabitats should be created within the waterway to support greater biodiversity. Flooding during the rainy season produces various microhabitats and human assistance can aid this natural occurrence. Finally, species composition and its spatial arrangement were focused on landscaping during the reconstruction; this approach should be changed to reflect the principles of ecological restoration.