Estimation of submarine groundwater discharge and associated nutrient fluxes in eastern Laizhou Bay, China using 222Rn

Abstract

Summary There is increasing evidence that the inputs of nutrients to the Bohai Sea are closely related to submarine groundwater discharge (SGD). In this study, the naturally occurring isotope of radon ( 222 Rn) was used as a tracer to assess SGD in eastern Laizhou Bay. The 222 Rn concentration during a tidal period was measured continuously and a mass balance model that included atmospheric loss, tidal effects, mixing loss, diffusion from sediments, and SGD was established. The model budget indicated that 222 Rn flux attributed to SGD accounted for 58.3% of the total tracer input to the study area. The time-series of 222 Rn revealed that the SGD flux ranged from 6.64 to 7.21 cm d −1 , with an average of 6.93 cm d −1 , in September 2014. The estimated SGD flux is reasonable compared with those previously estimated in other studies by direct measurement methods, hydrogeological simulation and geochemical tracers. This result, as well as the current understanding of nutrients dissolved in groundwater, confirms the importance of SGD in delivering nutrients to Laizhou Bay and possible impact on marine ecological environment.