Sea surficial waves as a driving force that enhances the fresh shallow coastal groundwater flux into the oceans

Submarine groundwater discharge (SGD) is a process through which groundwater and solutes are transferred from coastal aquifers into the oceans. Generally, the SGD is composed of two basic components: (1) fresh groundwater, FSGD; and (2) recirculated seawater, RSGD. Radon, a naturally occurring geochemical tracer, is a useful tool to evaluate the SGD in coastal areas. This study aims to evaluate the impact of wind waves on each components of submarine groundwater discharge. We monitored temporal fluctuations of seawater 222Rn concentration at Shiranui and Minamata bays, where elevated seawater 222Rn concentration spatial distribution observed during our previous studies. The measurements were conducted in coastal seawater where the connected coastal aquifer water table is very shallow. Additionally, a seawater model was applied to evaluate the seawater 222Rn concentration that originates from rivers in the study area. The 222Rn inventory in the study area implies that the groundwater advection is one of the major sources of 222Rn in the seawater. The obtained dataset suggests that the seawater 222Rn concentration increases, but the salinity decreases during windy periods. This means that more fresh groundwater contributes to dilute the recirculated seawater (RSGD) during windy conditions. Therefore, when the sea is windy and seawater waves propagate onshore, the fresh groundwater flux may increase where shallow coastal aquifers exist.