Nakdong estuary barrage and reclamation project: Preliminary results of the botanical, macrozoobenthic and ornithological studies

Abstract

The Nakdong Estuary Barrage and Reclamation Project has been investigated by studies on the vegetation, macrozoobenthos and birds in the Nakdong river delta, Republic of Korea. This study deals with the preliminary results, obtained during October to November 1983, while the environmental impacts of the barrage were being discussed. The total biomass of Scirpus triqueter, the estuary's most important foodplant for waterfowl ( mainly for swans), was assessed at approximately 38·3 tonnes dry wt. Of this amount only the roots and rhizomes (9·6 tonnes dry wt) are expected to be consumed by birds. Aquatic weeds in the nearby fresh Jukrim branch provided another food source (5·8 tonnes dry wt). The wintering waterfowl also used other feeding areas such as farmland and freshwater impoundments—almost all herbivorous birds participated in nightly feeding migrations. At 12 stations, spread over 20·5 km 2 of intertidal flats of the estuary, a total of 40 macrozoobenthic species were found. Crustaceans dominated with 19 species, while molluscs and polychaetes were represented by 11 and 10 species, respectively. For all stations together an average biomass of 14·6 g ash-free dry wt (ADW) m −2 (range 3·1–51·9 g) was calculated, dominated by molluscs with 9·5 g, while the share of crustaceans and polychaetes was only 2·9 g and 2·2 g, respectively. In terms of weight, the bivalve Corbicula japonica was dominant with an average of 4·4 g ADW m −2. During three censuses 10 000 waders and 25 000 to 30 000 waterfowl were counted. Among them were two species not recorded before in Korea: the ruff and the canvasback. Of all nonpasserines the wigeon (with a peak of 6800) and the dunlin (with a peak of 9100) were most numerous, while the ducks proved to be the most dominant (64%) group of birds. In the beginning of October the wader density in the estuary amounted to 5·2 birds ha −1 intertidal area exposed at low tide.