Carbon System Simulation in the Pearl River Estuary, China: Mass Fluxes and Transformations

Abstract

A carbon cycle model is built to describe the behavior of carbon materials in the Pearl River Estuary (PRE), China. The distributions and transformations of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and particulate organic carbon (POC) are simulated in the water column and sediment for the year 2006. The terrestrial carbon input is the dominant factor that determines the seasonal variation of carbon, while physical and biochemical processes contribute to the spatial‐temporal circulation of carbon. The simulation results reveal that the PRE acts as a net source for atmospheric CO2 throughout the year, and it buffers the export of DIC from the river and sediment to the adjacent system via the DIC consumption by primary production. As a consequence of biochemical processes, the PRE exports more organic carbon to the sediment and adjacent marine ecosystems than the amount that it receives from upstream river reaches. POC burial in sediment and refractory DOC export to the adjacent marine ecosystems are the main carbon fixation pathways in the PRE. The total amount of carbon fixation in PRE is estimated 6.92 × 1010 mol C year−1. Carbon fixation analysis shows that (1) 20.4% of the POC deposited into sediment is fixed through burial, while the remaining continues to participate in the circulation of carbon materials, and (2) the combined effects of river discharge and monsoon dominate the amount and direction of refractory DOC exports.

Seasonal and Spatial Controls on the Eutrophication‐Induced Acidification in the Pearl River Estuary

“…The in situ data including salinity, temperature, nutrients, organic carbon, DO, pH and TA at different depths were collected by the State Oceanic Administration of China from July 15 to August 24, 2006 and from December 3, 2006 to January 20, 2007 in the PRE and its adjacent coastal area (Wang et al., 2017; H. Zhang & Li 2010). The carbon cycle component of our model has been extensively validated in previous studies (Liang et al., 2020; Ye et al., 2021), and the model skill in simulating key carbon cycle dynamics in PRE is comparable with the modeling studies conducted in other regions (Fitzpatrick, 2009; Kwiatkowski et al., 2014; Sohma et al., 2018). Therefore, this study focuses on the validation of the modeled distribution of DO, pH and TA.…”

Spatial and temporal variability of <i>p</i>CO<sub>2</sub> and CO<sub>2</sub> emissions from the Dong River in south China

“…The CO 2 emissions from the Dong River were higher in the wet season than in the dry season. This seasonal pattern is similar to that observed in the Xi and Daning rivers (Yao et al, 2007;Ni et al, 2019) but different from that observed in the Jinshui River in the upper Yangtze River, where pCO 2 is high in winter and low in summer (Luo et al, 2019), although all four rivers are in the East Asian Monsoon climate region. The seasonal differences in CO 2 emissions are largely caused by the pCO 2 variability, which in turn is regulated by external carbon inputs, internal production of CO 2 (Yao et al, 2007), and the dilution effect caused by precipitation (Johnson et al, 2007).…”

“…The seasonal differences in CO 2 emissions are largely caused by the pCO 2 variability, which in turn is regulated by external carbon inputs, internal production of CO 2 (Yao et al, 2007), and the dilution effect caused by precipitation (Johnson et al, 2007). For rivers where pCO 2 is lower in summer than in winter, the dilution effect overrides the effect of increased carbon inputs and internal CO 2 production (Luo et al, 2019). In contrast, for rivers like the Dong River, although the dilution effect remains, increased CO 2 inputs and metabolism are more significant factors in controlling its pCO 2 , thus leading to higher summer pCO 2 .…”

“…In addition, different rivers in this region may have contrasting trends in CO 2 dynamic due to different underlying controlling factors. Some rivers have the highest CO 2 efflux in the wet season (Li et al, 2013;Le et al, 2018;Ni et al, 2019), while others have the highest CO 2 efflux in the dry season (Luo et al, 2019), suggesting that an increase in the wet season runoff can have two distinct consequences. On the one hand, recent studies have indicated that the increased runoff could enhance external carbon inputs and thus CO 2 emissions (Hope et al, 2004;Johnson et al, 2008).…”

Inter-annual Variability of the Carbonate System in the Hypoxic Upper Pearl River Estuary in Winter

“…Viewing the entire PRE, Guo et al (2008) reported the seasonal variability of carbonate parameters in the main channel of the estuary based on field observations from 2000 to 2005; Liang et al (2020) simulated the spatial distributions of carbonate parameters in the summer and winter of 2006. In the hypoxic upper PRE, Guo et al (2008) found that both DIC and total alkalinity (TA) showed large seasonal variations, with much higher values in winter (>3000 µmol kg −1 ) than in summer (<1700 µmol kg −1 ).…”