| Water column and sediment samples collected from Newport Bay, CA, were analyzed for radium and radon during February, April, August, and October, 2004 to quantify ground water discharge and benthic exchange. In-situ fluxes measured with chambers were enhanced from diffusive fluxes by factors of 1.5, 2.3, and 4.5 for Ra-224, Ra-223, and Rn-222, respectively, showing that isotopic flux enhancements correlate with increasing scale length as a result of irrigation. Budgets constructed for each isotope established an upper limit for ground water discharge of 0.09 +/- 0.14 m3/s in April and 0.12 +/- 0.17 m3/s in August, less than 4% of fresh water input. Tidal pumping supplied fluxes of Ra-223 and Ra-224 ∼2.5 times that of diffusion and irrigation. Transport models were constructed to evaluate mixing and potentially localized inputs. The predicted diffusivity was 85-145 m 2/s, indicating that mixing may be driven by two-layer flow, rather than diffusive exchange of eddies. |
