Greenhouse gases emissions and dissolved carbon export affected by submarine groundwater discharge in a maricultural bay, Hainan Island, China

Greenhouse gases (GHG) emissions in coastal areas are influenced by both mariculture and submarine groundwater discharge (SGD). In this study, we first conducted a comprehensive investigation on carbon dioxide (CO2) and meth-ane (CH4) emissions affected by SGD in a typical maricultural bay in north-eastern Hainan Island, China. A radon (Rn-222) mass balance model revealed considerable high SGD rates (179 +/- 92 cm d(-1)) in the bay, and the fluxes of SGD-derived dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) were 150.36 and 3.65 g C m(-2) d(-1), respectively. Time-series measurement results, including those for Rn-222, CH4, CO2, and physicochemical param-eters, indicated that GHG dynamics in the maricultural bay mainly varied with tidal fluctuations, and isotopic evidence further revealed that acetate fermentation was the main mechanism of methanogenesis in the maricultural waters. The water-air fluxes in the maricultural area were 1.05 +/- 0.32 and 9.49 +/- 3.96 mmol m(-2) day(-1) for CH4 and CO2, re-spectively, implying that Qinglan Bay was a potential source of GHG released into the atmosphere. At the bay-scale, the CO2 emissions followed a spatial pattern, and the CH4 emissions were mainly affected by mariculture. The high CH4 emissions in the maricultural waters caused by maricultural activities, SGD, high temperature, and special hydrol-ogy resulted in the formation of the CH4-dominated total CO2-equivalent emissions model. Our study highlights the importance of considering the link between SGD and GHG emissions in maricultural bays when constraining global GHG fluxes.

Automated summary

This study investigated greenhouse gas emissions in a maricultural bay in north-eastern Hainan Island, China, and found that both submarine groundwater discharge and mariculture activities influenced the emissions. The emissions varied with tidal fluctuations and the main mechanism of methane emissions was acetate fermentation. The study highlights the importance of considering the link between submarine groundwater discharge and greenhouse gas emissions in maricultural bays when constraining global greenhouse gas fluxes.