Highlights
- Total groundwater alkalinity export is 54% of the natural alkalinity input to the ocean
- Groundwater dissolved inorganic C export is 83.4% of dissolved C export
- Warming will decrease future groundwater dissolved inorganic C export by 9.02%–28.91%
- Tidal wetlands buffer ocean acidification by exporting alkalinity
Science for society
Marine ecosystems are vulnerable to ocean acidification, which results in the release of CO2. Tidal wetlands can export dissolved carbon via groundwater, ultimately buffering the oceans from acidification. Understanding the magnitude of groundwater dissolved carbon (including dissolved inorganic carbon) discharge from tidal wetlands is thus crucial for sustainable ocean management. Our study collects global data and estimates the groundwater dissolved carbon exported from tidal wetlands. The amount of dissolved carbon exported via groundwater represents 30.9%–53.6% of terrestrial dissolved carbon and largely increases the CO2 buffering capacity of coastal waters. Our study predicts that global warming will decrease groundwater dissolved inorganic carbon export and dampen the buffering capacity of tidal wetlands for ocean acidification. Our study highlights that tidal wetlands are significant contributors to the carbon budget and are natural solutions to ocean acidification.
Summary
Ocean acidification is a grand challenge to sustainable ocean management. Tidal wetlands are distributed from the polar to the tropical domain and provide unique ecosystem services such as groundwater carbon export. The carbonate and bicarbonate of exported dissolved carbon represent total alkalinity and buffer ocean acidification. However, the magnitude and variability of the dissolved carbon discharge from groundwater to the coastal ocean are poorly understood. Here, we estimate groundwater dissolved carbon and total alkalinity discharge by combining data from 337 locations in tidal wetlands. The average annual groundwater total alkalinity and dissolved carbon discharge in global tidal wetlands reach 16.2 (0.1–77.9) and 20.1 (0.1–96.6) Tmol, respectively, of which 83.4% is exported as dissolved inorganic carbon (DIC). Future groundwater DIC discharge decreases by 9.02%–28.91% due to increasing evapotranspiration, changing rainfall regimes, and relative sea level rise. Our study suggests that tidal wetlands export over 30% of terrestrial dissolved carbon to the coastal ocean.
Ouyang X., Maher D. T. & Santos I. R., in press. Climate change decreases groundwater carbon discharges in global tidal wetlands. One Earth. Article.
