Transfer rates of dissolved tracers through estuaries based on 228Ra: A study of Long Island Sound

Using 228Ra (half-life = 5.7 y) we have determined the transfer rate of water as the carrier of tracers (dissolved substances) into Long Island Sound from its western boundary. The primary sampling was done in the summer of 1991, with additional sampling of surface waters in the winter and summer of 1992 and the summer of 1993. The (228Ra/226Ra) activity ratio was determined by γ-spectrometry of Mn-coated fibers through which sea water was passed. An independent measurement of 226Ra activity per liter of sea water via scintillation counting of 222Rn was made at each sampling site. Based on the 228Ra concentrations in Long Island Sound water, water from the western boundary (off Randalls Island near the connection of the East River with the sound) and shelf water entering the sound from the east together with the measured flux of 228Ra from Long Island Sound sediments, we can determine the transfer rate of water from the East River to Long Island Sound during the summer of 1991. This value was between 0.40 × 1014 l y−1 and 1.1 × 1014 l y−1, depending on the 228Ra flux from sediments used. The corresponding residence time of water in Long Island sound was between 166 and 63 days.