The Secret of the Ancient Reservoir Revealed by Diatom Fossils

Diatoms are organisms that belong to phytoplankton. They make up more than 80% of phytoplankton and have chloroplast which performs photosynthesis. Its cell wall is made of hard glass components.

Diatoms are found in wetland sediments, which are very important research materials for understanding past environmental changes or predicting future environmental changes.

Gonggeomji is an ancient reservoir that is known as one of the three major reservoirs of the Samhan, Korea's ancient kingdom. In the encyclopedia of the Joseon Dynasty, the circumference of Gonggeomji is recorded as 8.6km, slightly longer than the Upo Wetland, the largest wetland in Korea.

However, there was a question about when Gonggeomji was formed.  NNIBR studied wetland sediments and diatoms of the reservoir to find out the age of Gonggeomji through records of organisms that lived in the past.

Analyzed the sediment, diatoms are found abundantly in the strata that were deposited 500 to 4,000 years ago. A total of 159 diatoms, including Genus Navicula and Genus Cocconeis, which are commonly found in freshwater, were found to have inhabited the reservoir.

The 32 species of diatoms are attached algae that mainly live by attaching to bedrock, gravel, and the surface of living organisms in water. Genus Gomphonema, Genus Cymbella, and Unotia were confirmed to have been included. 

Based on the results, it was revealed that the Gonggeomji was formed as a natural wetland about 10,000 years ago and then reformed as a reservoir about 1300 to 1400 years ago. Moreover, it was seen that the water level was the highest in the late Joseon Dynasty.