Abundant and diverse palynofloras and diatoms have been recovered from Trench BH-4 of Isanpo area, Ilsan located in river-mouth of the Han River. These terrestrial and marine derived assemblages reflect that the paleoenvironmental changes have occurred during the past 2300 years. Erected pollen zone (2 pollen zones and 4 pollen subzones) and diatom zone (2 diatom zones and 6 diatom subzones) indicate that depositional environments have changed from estuary to lowland fluvial plain about 1800 C-14 yr BP. During 2300 similar to 1800 C-14 yr BP, Pollen Zone I and Diatom Zone I, elevation 3.31-2.74 m, are characterized by the abundance of hyposaline marine-brackish dinoflagellates and diatoms together with freshwater algae indicating an estuary surrounded by mountain-slope on which mixed coniferous-deciduous broadleaved vegetation forest flourished under wet, warm Temperate climatic conditions. On the other hand, Pollen Zone II and Diatom Zone II, elevation 3.72 similar to 3.36 m, are dominated by only freshwater diatoms and common freshwater algae without marine taxa of dinoflagellates and diatoms. These assemblages refer to be lowland fluvial plain that there were river or small ponds since about 1800 C-14 yr BP. Sterilized mountain soil conditions, caused by human activity such as deforestation and cultivation, accelerate an expansion of coniferous vegetation forest replacing the former mixed vegetation forest. The human impact is indicated by the occurrences of cultivated plants, Gramineae, Zea and Fagopyrum combined with synanthropogenic habitats of Ambrosia and Artemisia.
