224Ra, 228Ra, and 226Ra in Winyah Bay and Delaware Bay

The first 224Ra (tsub(1/2)=3.64 days) measurements from mixing zones of estuarine systems are presented for the Pee Dee River-Winyah Bay and Delaware Bay Estuaries. High-resolution gamma-ray spectrometry was used to determine 224Ra, 228Ra (tsub(1/2)=5.7 years), and 226Ra (tsub(1/2)=1622 years) activity ratios. Desorption and diffusion from suspended and bottom sediments contributes to the non-conservative increases of the three isotopes in each systems. In Delaware Bay 224Ra concentrations were nearly constant over the 2.5% to 15% salinity range where two turbidity maximum zones are located. 228Th scavenings onto the suspended particles in the turbid zones may supply a regenerative source of 224Ra in this system. Samples collected on the ebb and flood tide from a salt marsh along Delaware Bay have a 5-fold increase in 224Ra from flood to ebb and 3- and 2-fold increases for 228Ra and 226Ra respectively, indicating salt marshes are another source of radium to estuarine waters. (orig.)