Accretion rate and controlling factors of carbon and nutrients during coastal wetland evolution in Yellow River Delta

Core ZK4 with a shallow depth of 28.3 m was drilled in the Yellow River Delta in 2007. Samples from the core were used in the laboratory to make detailed sedimentological observations and perform analysis of water content, organic carbon (Corg), total carbon (TC), and nutrient compositions. According to the stratigraphic analyses of core ZK1, seven sedimentary environments were recognized, and the historical evolutions of coastal wetlands were revealed. Chronologies, sedimentation rates and carbon accretion rates of the environments were revealed from AMS¹⁴C dating method, historical records of the Yellow River diversions, and comprehensive analyses by means of historic geography and sedimentary geology. The results show that total carbons, organic carbons and nutrients (except for element S) are all in good linear correlations, the accretion rates of Corg, TC, N and P have very significantly positive correlations with sedimentation rates shown as R>0.89, p<0.01, and the sedimentation rates are the main factor controlling accretion rates of Corg, TC, N and P. Although Corg concentrations are low (<1%) in the modern Yellow River Delta sediments, the high sedimentation rates have made the average accretion rate of Corg in the sediments come up to 2878.23 g/(m²·a), much higher than the values in other high-Corg wetlands in the world, and thus the modern Yellow River Delta can be considered to be a very good carbon sink due to its high sedimentation rate.