Submarine Groundwater Discharge Strengthens Acidification in the Coastal Semi-Closed Bays

Abstract

Coastal ocean acidification is a worldwide problem associated with anthropogenic activity and climate change. In this study, a close relationship between submarine groundwater discharge (SGD) and coastal ocean acidification in Hong Kong's coastal waters is discovered. We for the first time evaluated the direct influence of SGD on seawater pH decline. Results show that SGD can contribute to up to 48% of seawater pH variation among terrestrial water input, air-sea CO2 exchange, photosynthesis/respiration, and bay-open water exchange in semi-closed bays through direct input of carbonate species. Local air-sea CO2 exchange has negligible influences on the seawater pH. In the semi-closed bay areas, SGD and aerobic respiration are major contributors to seawater pH variation but in areas with open space, the exchange process with open waters is more important. In addition to the direct input of carbonate species (total alkalinity and dissolved inorganic carbon), SGD also influences the seawater pH via considerable nutrient loadings. The findings highlight the importance of the investigation and management of groundwater to alleviate the fast coastal ocean acidification.