Environmental Characteristics of the Diatom in the Trench Sediments Around Bangudae Petroglyphs, Ulsan

Diatoms were studied from the trench sediments around Bangudae petroglyphs in order to better understand the depositional\ environment before and after the construction of Sayeon dam in Ulsan. There were no diatoms produced from the sediments before the dam construction while the diatoms were produced from the sediments (depth of trench 228 cm) after the construction of the dam. Seventy-five species of diatoms of 27 genera were identified in the trench sediments. The number of diatom valves per gram of dry sediment ranged from 0.2-5.8810(5)g(-1). Four diatom assemblage zones were identified according to the frequency of critical taxa as follows: assemblage zone I, from 228 to 150 cm; assemblage zone II, from 150 to 122 cm; assemblage zone III, from 122 to 62 cm; and assemblage zone IV, from 62 to 0 cm. In addition, based on the environmental indicator species, an analysis was carried out to measure eutrophication, acidity and CI- value. Results of the eutrophication and CI- values were as follows. Based on the lower 74 cm horizons, the degree of eutrophication middle-high to CI- values were lower, upper horizons appeared to eutrophication in the low, and CI- values were high. Acidification from low horizons of 122 cm showed a neutral-alkaline degree whereas it exhibited acid in the upper part. In particular, regarding nutrients (TP and TN), the index taxa showed a higher TP value at 175 cm while higher TN value at 62 cm.