Loads and ages of carbon from the five largest rivers in South Korea under Asian monsoon climates

Abstract

Understanding the quantity and quality of riverine carbon is crucial to predict the changes in the global carbon cycle and to efficiently manage drinking water quality. We investigated the loads and 14C ages of carbon exported by the five largest rivers in South Korea using water samples collected seasonally along with daily water discharge data in 2012–2013. A total of ~581 Gg-C was discharged by the five rivers annually, releasing 7.9, 1.5, and 0.6 g-C m−2 yr−1 of DIC, DOC, and POC, respectively, from the river basins. About 30–50% of annual riverine carbon loads were released during the summer monsoon period (June-August) indicating strong effects of precipitation on the riverine carbon loads. Modern to old (up to 1020 ybp) carbon was released from the five river basins. The Δ14C ranged from −88.7 to 26.9‰ for DIC, −124.3 to 0.8‰ for DOC, and −125.5 to 35.1‰ for POC, demonstrating dynamically changing sources of riverine carbon. The Δ14CDIC, Δ14CDOC, and Δ14CPOC were the most enriched during the summer in almost all river systems, indicating that relatively young carbon is exported in summer although old carbon is released in the other seasons. The chemical weathering of both silicates and carbonates by CO2 was a dominant process to generate riverine DIC, while the contribution from C3 plants was dominant for riverine DOC. The results suggest that both loads and ages of riverine carbon could be strongly influenced by the Asian summer monsoon.