The Effect of Yellow River Water and Sediment Regulation on the Flux of Particulate Organic Carbon to the Sea

The Yellow River is one of the world's rivers with the greatest sediment load. Since 2002, the Water-Sediment Regulation Scheme (WSRS) has been implemented, creating artificial flood peaks in a short period. This has significantly altered the hydrological processes and seasonal rhythms in the lower Yellow River, ultimately affecting the transport of sediment and particulate organic carbon (POC) to the sea. We used the measured data of water and sediment and the previously published data on the POC content in the Yellow River to reconstruct the POC flux into the sea and in the mainstream of the Yellow River since the implementation of WSRS. We to analyzeal how WSRS and climate change affect the transport of POC in the Yellow River. The results show the Xiaolangdi Reservoir WSRS significantly changes the POC transport pattern. The peak POC transport flux now occurs in June-July. During the June-July regulation period from 2002 to 2023, the average annual POC transport flux reached 269 kt/a, making up 58% of the annual total. In the non-regulation period (August—next May), the reservoir retention cuts off the sediment and organic carbon transport from the middle to lower reaches, reducing the lower reaches POC transport flux. Lijin Station non-regulation period average POC transport flux was just 214 kt, much lower than Tongguan Station in the same period, which was 776 kt. Different regulation stages show different POC transport in the lower reaches. In 2020, the sediment-regulation stage accounted for 85.6% of the total regulation period flux, the key time for POC transport. Climate fluctuations and WSRS jointly influence the changes in POC flux to the sea. Climate-driven variations in basin precipitation determine the availability of water resources for reservoir regulation, which in turn affects the exchange and transport of POC in the reservoir areas and downstream channels.