[Effect of Water and Sediment Regulation on the Transport of Particulate Organic Carbon in the Lower Yellow River].

Both natural processes and human activities in river basins have important impacts on the transport of riverine organic carbon (OC). Better understanding of the riverine OC transport processes is critical for the studies of global carbon cycling. Suspended particulate matters collected from the Lijin Station in the lower Yellow River during the water and sediment regulation ( WSR) period in 2012 (19 June-20 July) were analyzed for grain size, particulate OC (POC) and stable carbon isotopic ratios (delta13C) to investigate-the sources, composition, abundance of POC and the effect of WSR on the transport of POC. The results showed that the WSR in 2012 could be divided into two stages according to the variation of water and sediment discharges: the water-release stage (WRS) and the sediment-release stage (SRS). Variations of the water discharge, sediments, POC and delta13C in these two stages reflected the impacts of WSR on the sources of particulate matters and associated OC. The water discharge in the WRS stage was the highest (4270 m3 x s(-1)), and the sediments scoured from the riverbed in the lower reaches were the major source of suspended particulate matters in this stage, therefore the particles were characterized by relatively coarse grain size (13.9 microm in average of median grain size), low POC (avg. 0.38%) and relatively enriched and constant delta13C (-24.2% per hundred +/- 0.3% per hundred), probably because POC in the sediments scoured from the riverbed had old radiocarbon ages and high degradation. The suspended particulate matters in the SRS stage were mainly derived from the upstream reservoirs and flushed riverbanks due to local rainstorm, and the POC age was relatively young, thus this stage was characterized by high concentration of suspended particulate matters (up to 17.8 kg x m(-3)), fine particles (5.9 microm in average of median grain size), high POC (avg. 0.50%), and depleted and varied delta13C values (-24.8% per hundred +/- 0.6% per hundred). Variation of daily POC flux had similar pattern with sediment discharge, and the total POC flux during the water and sediment regulation period was 1.13 x 10(5) tons, accounting for 12% of the total POC flux in 2012. Compared with previous years, the total water discharge during the WSR period in 2012 has increased, while the total sediment flux and POC flux have reduced. In general, WSR played an important role on the transport of POC in the Yellow River. And furthermore, there was significant difference in the sources, composition and transport of POC in different stages of WSR.