Impact of land-based freshwater inflows on coastal ocean acidification in the Arabian Sea

Coastal ocean acidification is a growing global concern, especially in densely populated regions where terrestrial inputs complicate its dynamics. Unlike the open ocean, coastal waters are heavily influenced by freshwater inflows. This study investigates the impact of riverine and groundwater inputs on seawater pH variability in the coastal Arabian Sea. River discharge leads to greater pH reduction during the monsoon (0.170 ± 0.021), while groundwater, despite its high alkalinity, causes a stronger decline in the non-monsoon season (0.296 ± 0.036) due to elevated pCO₂ levels (27,318 ± 5076). Groundwater alone accounts for 85 % of the freshwater-induced pH drop. The effect of atmospheric CO₂ exchange is negligible, as the region remains a perennial CO₂ source throughout the year. These findings highlight the need to account for coastal biogeochemical processes, particularly aerobic respiration and photosynthesis, in acidification assessments. Understanding these drivers is critical for managing coastal acidification under increasing anthropogenic pressures and climate-driven changes in freshwater inputs.