Submarine groundwater discharge (SGD) significantly impacts biogeochemistry in most coastal waters. This study explored the temporal variations and hydrographic proxies of SGD based on investigations in the Pearl River estuary (PRE) using ²²⁶Ra and ²²⁸Ra as SGD tracers. The flux of SGD was significantly higher in summer than in winter and decreased in general during the last two decades. The carbon and nutrient fluxes via SGD were 10-25% equivalent as the riverine fluxes and affected their addition/removal processes in the estuary. The flux of SGD had a positive response to river discharge, implying a connection between surface runoff and shallow aquifers. Furthermore, the flux of SGD had significant negative correlations with the return flow factor and flushing time. Our results indicate that river discharge, flushing time and return flow factor may serve as hydrographic proxies of SGD in the PRE and potentially be applicable in parameterization of SGD in numerical models.

submarine ground, Pearl River Estuary, proxy, radium