4:00 PM - 4:15 PM
[ACG40-08] Tidal-driven high CO2 evasion from mangrove swamp to the air and adjoining waters over spring-neap tidal cycles in the estuary of Fukido River, Ishigaki Island
Keywords:Mangrove, Carbon cycling, CO2 flux, Dissolved inorganic carbon, Partial pressure of CO2 , Total alkalinity
Although mangrove habitats are limited in sub-tropical and tropical areas, mangrove ecosystems account for annually approximately 15% of buried carbon in the ocean. They play an important role as blue carbon ecosystems that uptake atmospheric CO2. It is known that plenty of inorganic carbon runoffs to mangrove surrounding waters during an ebb tide. However, the comprehensive understanding of the dissolved inorganic carbon (DIC) cycle between soil, water, and air is still insufficient especially in the mangrove forests in Japan located at the northern limit of habitats in the Indo-Pacific region.
In this study, we measured CO2 flux between soil and air during the dry period and between soil and water during the wet period on Rhizophora stylosa swamp and, set up mooring systems for measuring pCO2 in water and air in front of the mangroves in the estuary of Fukido River, Ishigaki Island, Okinawa, Japan. Moreover, we conducted water sampling in the mangrove forest and the adjacent waters during ebb tide to quantify the CO2 evasion rate from the mangrove swamp to the adjoining waters and air.
The CO2 flux from soil to air during the dry period was within the previously reported values varied from 0.98 to 8.53 mmol/m2/h. However, the CO2 flux from soil to water during the wet period increased exponentially from flood tide to ebb tide, it reached a maximum of 38.1 mmol/m2/h. The mean CO2 fluxes between water and air measured by the bulk formula method were varied 0.33 mmol/m2/h, 0.02 mmol/m2/h, 0.06 mmol/m2/h, and 0.36 mmol/m2/h during thr former flood, later flood, former ebb, and later ebb tide periods, respectively. The 222Rn, a tracer for porewater, increased rapidly during the later ebb tide, suggesting that a large proportion of the increased pCO2 during low tide was due to DIC discharge through porewater. However, during the observation period, the maximum CO2 flux between water and air was only 1.19 mmol/m2/h, indicating that the DIC evasion rate from the soil to the air and adjoining waters was limited. Although DIC concentrations in the mangrove adjoining waters were extremely high, the pCO2 values during ebb tide in the adjacent seagrass meadow and coral reef zone were almost the same as those in the offshore water, suggesting that the effect of the high pCO2 water runoff to the adjacent waters was limited.
In this study, we measured CO2 flux between soil and air during the dry period and between soil and water during the wet period on Rhizophora stylosa swamp and, set up mooring systems for measuring pCO2 in water and air in front of the mangroves in the estuary of Fukido River, Ishigaki Island, Okinawa, Japan. Moreover, we conducted water sampling in the mangrove forest and the adjacent waters during ebb tide to quantify the CO2 evasion rate from the mangrove swamp to the adjoining waters and air.
The CO2 flux from soil to air during the dry period was within the previously reported values varied from 0.98 to 8.53 mmol/m2/h. However, the CO2 flux from soil to water during the wet period increased exponentially from flood tide to ebb tide, it reached a maximum of 38.1 mmol/m2/h. The mean CO2 fluxes between water and air measured by the bulk formula method were varied 0.33 mmol/m2/h, 0.02 mmol/m2/h, 0.06 mmol/m2/h, and 0.36 mmol/m2/h during thr former flood, later flood, former ebb, and later ebb tide periods, respectively. The 222Rn, a tracer for porewater, increased rapidly during the later ebb tide, suggesting that a large proportion of the increased pCO2 during low tide was due to DIC discharge through porewater. However, during the observation period, the maximum CO2 flux between water and air was only 1.19 mmol/m2/h, indicating that the DIC evasion rate from the soil to the air and adjoining waters was limited. Although DIC concentrations in the mangrove adjoining waters were extremely high, the pCO2 values during ebb tide in the adjacent seagrass meadow and coral reef zone were almost the same as those in the offshore water, suggesting that the effect of the high pCO2 water runoff to the adjacent waters was limited.