Evolution of sedimentary organic matter in a small river estuary after the typhoon process: A case study of Quanzhou Bay

Extreme weather events occur frequently under global warming scenarios and have an important impact on the global carbon cycle. Compared to large rivers, small rivers are more sensitive to extreme weather events (such as typhoons). This paper reports the results of a study carried out in the Quanzhou Bay to explore the evolution of small river estuarine sedimentary organic matter after typhoon process using measurements of the grain-size, total organic carbon (TOC), total nitrogen (TN) and δ¹³C of surface sediment samples collected 2-3 days and a month, respectively, after typhoon Matmo landing in 2014. The results show that the contents of TOC and TN in the sediments, which gradually decrease from the estuary to the outer sea of Quanzhou Bay, decreased approximately 13% and 16%, respectively, a month later compared with 2-3 days after typhoon landing. The significant decrease occurred in the Jinjiang River estuary and along the South Channel of Quanzhou Bay, while the North Channel and Luoyangjiang River estuary retained high levels of TOC and TN. The results of δ¹³C values and TOC/TN ratios show that the organic matter in the sediment of the Quanzhou Bay was a mixture derived from C₃ terrestrial plants and marine algae. The terrestrial organic matter was mainly deposited in the Jinjiang River estuary 2-3 days after typhoon landing and then spread along the tidal channel to the outer sea a month later. It indicates that the hydrodynamic forces stirred sedimentary organic matters that were input and settled during typhoon, and transported later along the North and South Channel to the outer sea. Some of those organic matters were accumulated in the North Channel during the transport process. The results provide significant meaning for the carbon cycle and material flux study on the coastal and margin seas.