Supporting data set for article 'Groundwater-derived carbon promotes hypoxia, acidification, and coral reef demise in a large tropical estuary'

Submarine groundwater discharge (SGD) can carry substantial quantities of dissolved carbon from coastal aquifers into estuarine waters. However, its importance on estuarine carbon budgets is frequently neglected. Here, we resolve SGD and dissolved carbon budgets in the Pearl River Estuary (PRE), the largest estuary in Southern China surrounded by the world’s largest urban conglomerate. Results show that broadly-defined SGD contributed ~90% to the dissolved inorganic carbon (DIC) sources of the PRE exceeding riverine loads by 2–4 times. Moreover, SGD contributed 20-70% of the dissolved organic carbon (DOC) fluxes. SGD transports DIC at levels exceeding total alkalinity (TAlk) by 2.7–7 times, leading to acidification of nearshore waters. The groundwater pCO₂ was 10–36 times higher than that in estuary water. DOC mineralization derived by SGD can cause a decrease in estuary seawater pH by 0.04–0.16 and further increase bottom seawater CO₂ concentrations by 6.0–90.0 μmol L^-1, potentially affecting local coral populations. This process also can reduce bottom seawater oxygen levels by 12.0–150.0 μmol L^-1 and fuel the development of hypoxic zones. Overall, SGD regionally enhanced bottom water hypoxia and seawater acidification, creating challenging conditions for coral reef survival in an already stressed ecosystem. SGD should be considered when constructing carbon and ecological assessments at the land-ocean continuum.