The Effect of an Estuarine Barrage on Biogenic Silica flux in Nakdong River estuary

Abstract:

During the last 100 years, the patterns and amount of fresh water and materials load from the land into estuaries have changed due to anthropogenic developments. BSi (Biogenic Silica; a main component of diatom frustules) flux from the land is especially known to be affected by such developments. Two estuarine barrages were constructed around Nakdong River estuaries (Noksan dam in 1934 and Nakdong estuarine barrage in 1987) and abrupt change of BSi flux is expected. To determine effects of dam constructions, we have analyzed BSi concentration, water content, grain size, ignition loss and radioactive isotope using sediment cores from two stations (ND1 and ND2) at Nakdong estuary. BSi concentration, water content and ignition loss of ND1, located near West Nakdong River, are 0.17-2.63%, 11.76-36.0% and 0.4-5.8% respectively and those of ND2, which has relatively high accumulation rate, are 0.85-2.17%, 15.53-31.98% and 1.4-4.19% respectively. Decrease of BSi flux is quite clear in ND2, however, not in ND1 which has low accumulation rate. The reduced BSi flux might be responsible for the recent dinoflagellates dominance over diatom in the nearby coastal areas.