Ages and Loads of Riverine Carbon of the Five Largest Rivers in South Korea

Abstract:

Understanding the quantity and quality of riverine carbon is crucial to predict the changes of the regional carbon cycle and to efficiently manage drinking water quality. We investigated both the loads and ages of carbon exported by the five largest rivers in South Korea using seasonal sampling and dual carbon isotope analysis for 2012 – 2013. Annually a total of 581 Gg of carbon (DIC, DOC, and POC combined) was transported to the ocean through the five rivers, releasing 7.6, 1.7, and 0.8 g-C m-2 yr-1 of DIC, DOC, and POC, respectively, which accounted for 80%, 14%, and 6% of the annual loads of riverine carbon, respectively. About 37-45% of annual riverine DIC loads, 37-51% of DOC loads, and 33-47% of POC loads were released from the basins during the summer monsoon (June – August) indicating strong effects of precipitation in the riverine carbon export. Modern to ~1,020 years old carbon was released from the five river basins. The δDI¹³C and ΔDI¹⁴C showed a negative correlation in each river whereas no consistent correlation was observed between δDO¹³C and ΔDO¹⁴C, suggesting a large variation in DOC sources. Riverine POC load increased sharply after a typhoon and ΔPO¹⁴C was higher in summer than winter in the five rivers. The results suggested that both quantity and quality of riverine carbon released from the five largest basins could be strongly influenced by the Asian monsoon climates and that relatively young dissolved carbon could be predominantly released as the intensity and frequency of storms increase.