3D particulate organic carbon(POC) field in the Changjiang River Estuary(CRE) - Riverine Carbon Flux

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Research Background

Rivers serve as crucial conduits that interconnect the carbon reservoirs of terrestrial ecosystems and marine ecosystems. Annually, approximately 400 Tg C (teragrams of carbon) of terrestrial organic carbon are transported to the ocean by rivers. This organic carbon flux consists of 60% dissolved organic carbon and 40% particulate organic carbon. Remarkably, ten major rivers worldwide account for approximately 40% of the total organic carbon flux transported to the sea. Notably, among these rivers, the Yangtze River, ranking as the third largest river globally and the largest in Asia, plays a pivotal role in conveying terrestrial organic carbon into the East China Sea. Similarly, the Pearl River, exhibiting the second largest annual runoff in China, serves as the primary conduit for terrestrial organic carbon transport into the South China Sea. Collectively, the Yangtze River and Pearl River contribute to around 60% of China's particulate organic carbon (POC) flux. The substantial amount of POC transported to marginal seas exerts a significant influence on the carbon balance within these regions. Moreover, the deposition and subsequent oxidation and decomposition of POC in marginal seas lead to the consumption of dissolved oxygen and the deterioration of water quality.

To address the estimation of POC flux into the sea, this study introduces a novel approach that combines remote sensing and high-resolution spatial-temporal models. This methodology offers a promising avenue for estimating POC flux and other substances within complex estuarine environments, presenting a valuable tool for assessing the flux of POC into the sea.

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Figures

Fig.1 Monthly climatological normal of surface POC concentration in the Pearl River Estuary from 2001.01 to 2016.12
Fig.2 Comparison between POC concentration on 2016.03.08 derived from numerical model and remote sensing data(GOCI)

Scientific Progress

POC flux refers to the total amount of POC passing through a section in a certain period. The unit is kiloton (kt). The dataset has a high spatial resolution of 500 m × 500 m, covering the Changjiang River Estuary (CRE) and its adjacent waters from July 2011 to June 2018. Compared with the in-situ POC flux data (the product of the in-situ POC concentration and the in-situ river discharge) at Xuliujing Hydrological Station, the Root Mean Square Deviation of the data set is 0.16 g/(s · m²), and the Average Relative Deviation is 28.13 %.

The dataset is a POC flux estimation model based on the combination of GOCI remote sensing data and the FVCOM three-dimensional (3D) hydrodynamic-sediment model. The monthly POC flux of each grid point is calculated. FVCOM model uses the predicted tide obtained by the eight main tides from a 1/30 ° tidal model of the China Sea in the OTIS (OSU Tidal Data Inversion) model on the open boundary as the tidal forcing. Daily discharge and monthly mean TSM at Datong Hydrological Station from July 2011 to June 2018 was used as the river forcing and was derived from the Changjiang Water Resources Commission and the China River Sediment Bulletin. The sea surface wind field was obtained from the European Centre for MediumRange Weather Forecasts (ECMWF), which was used as the wind forcing in the FVCOM. Assuming that the sediment concentration profile distribution in the CRE is similar to the POC profile distribution, the sediment concentration profile distribution simulated by FVCOM is combined with the sea surface POC concentration inversion by GOCI to obtain a 3D distribution of POC concentration in the CRE. Combined with the 3D flow field simulated by FVCOM, the POC flux is calculated. The method not only makes full use of their advantages but also reduces the uncertainty of independent estimation results when these two methods are utilized individually. It provides a new insight for estimating the POC flux and other substances flux in complex estuaries.

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References

Wang, Zhihong, Yan Bai, Xianqiang He, Bangyi Tao, Teng Li, Xiaoyan Chen, Tianyu Wang, and Fang Gong. 2021. “Estimating Particulate Organic Carbon Flux in a Highly Dynamic Estuary Using Satellite Data and Numerical Modeling.” Remote Sensing of Environment 252. https://doi.org/10.1016/j.rse.2020.112116.

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