『Abstract
　Pore water radon (²²²Rn) distributions from Indian River Lagoon, Florida, are characterized by three zones: a lower zone where pore water ²²²Rn and sediment-bound radium (²²⁶Ra) are in equilibrium and concentration gradients are vertical; a middle zone where ²²²Rn is in excess of sediment-bound ²²⁶Ra and concentration gradients are concave-downwards; and an upper zone where ²²²Rn concentration gradients are nearly vertical. These ²²²Rn data are simulated in a one-dimensional numerical model including advection, diffusion, and non-local exchange to estimate magnitudes of submarine groundwater discharge components (fresh or marine). The numerical model estimates three parameters, fresh groundwater seepage velocity, irrigation intensity, and irrigation attenuation, using two Monte Carlo (MC) simulations that (1) ensure the minimization algorithm converges on a global minimum of the merit function and the parameter estimates are consistent within this global minimum, and (2) provide 90％ confidence intervals on the parameter estimates using the measured ²²²Rn activity variance. Model estimates of seepage velocities and discharge agree with previous estimates obtained from numerical groundwater flow models and seepage meter measurements and show the fresh water component decreases offshore and varies seasonally by a factor of nine or less. Comparison between the discharge estimates and precipitation patterns suggests a mean residence time in unsaturated and saturated zones on the order of 5 to 7 months. Irrigation rates generally decrease offshore for all sampling periods. The mean irrigation rate is approximately three times greater than the mean seepage velocity although the ranges of irrigation rates and seepage velocities are the same. Possible mechanisms for irrigation include density-driven convection, wave pumping, and bio-irrigation. simulation of both advection and irrigation allows the separation of submarine groundwater discharge into fresh groundwater and (re)circulated lagoon water.

Keywords: radon; radium; submarine groundwater discharge; subterranean estuary; pore water model; Indian River Lagoon; non-local exchange』

1. Introduction
2. Materials and methods
3. Results
4. ²²²Rn transport model
　4.1. Conceptual model and solution
　4.2. Model performance
5. Discussion
　5.1. Advection rates
　5.2. Comparison between ²²²Rn model based advection rates and other techniques
　5.3. Irrigation
6. Conclusions
Acknowledgements
Appendix A. Supplementary data
References