Xiao Kai

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  • Article
    Submarine groundwater discharge in the northern Bohai Sea, China: Implications for coastal carbon budgets and buffering capacity
    (American Geophysical Union, 2022-07-20) Zhang, Yan ; Zou, Changpei ; Wang, Zhaohui Aleck ; Wang, Xuejing ; Zeng, Zhenzhong ; Xiao, Kai ; Guo, Huaming ; Jiang, Xiaowei ; Li, Zhenyang ; Li, Hailong
    Submarine groundwater discharge (SGD) has been widely recognized as an important source of dissolved nutrients in coastal waters and affects nutrient biogeochemistry. In contrast, little information is available on SGD impacts on coastal carbon budgets. Here, we assessed the SGD and associated carbon (dissolved inorganic carbon [DIC] and total alkalinity [TA]) fluxes in Liaodong Bay (the largest bay of the Bohai Sea, China) and discussed their border implications for coastal DIC budget and buffering capacity. Based on 223Ra and 228Ra mass balance models, the SGD flux was estimated to be (0.92–1.43) × 109 m3 d−1. SGD was the largest contributor of DIC, accounting for 55%–77% of the total DIC sources. The low ratio (<1) of SGD-derived TA to DIC fluxes and negative correlation between radium isotopes and pH in seawater implied that SGD would potentially reduce seawater pH in Liaodong Bay. Combining the groundwater carbon data in Liaodong Bay with literature data, we found that the SGD-derived DIC flux off China was 4–9 times greater than those from rivers. By analyzing the TA/DIC ratios in groundwater along the Chinese coast and related carbon fluxes, SGD was thought to partially reduce the CO2 buffer capacity in receiving seawater. These results obtained at the bay scale and national scale suggest that SGD is a significant component of carbon budget and may play a critical role in modulating coastal buffering capacity and atmospheric CO2 sequestration.
  • Article
    Editorial: Advances in understanding lateral blue carbon export from coastal ecosystems
    (Frontiers Media, 2022-10-27) Xiao, Kai ; Chen, Nengwang ; Wang, Zhaohui Aleck ; Tamborski, Joseph James ; Maher, Damien Troy ; Yu, Xuan
    ‘Blue Carbon’ refers to the carbon captured by the coastal systems or ocean and was coined about a decade ago (Nellemann et al., 2009), emphasizing the carbon sequestration capacity of coastal vegetated ecosystems (e.g., macroalgae/kelp, seagrass beds, saltmarshes, and mangroves). These blue carbon systems only cover <0.1% of the ocean area, but may account for >50% of the carbon storage in marine environments, representing a large carbon sink comparable to the global river input (Alongi, 2014). The fluxes of terrestrial-derived carbon including dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and particulate organic carbon (POC) transported through surface river runoff to the ocean were well known and quantified (Ludwig et al., 1996; Regnier et al., 2022). However, increasing evidence suggests that tidal exchange dominates the transport of significant dissolved carbon from coastal ecosystems to adjacent estuarine and shelf waters (e.g., Maher et al., 2013; Tait et al., 2016; Wang et al., 2016; Chen et al., 2021). This mechanism is commonly named as carbon ‘outwelling’ or lateral carbon export (e.g., Teal, 1962; Odum, 1968; Wang and Cai, 2004; Sippo et al., 2017; Cabral et al., 2021; Santos et al., 2021; Tamborski et al., 2021).