TRANSFER RATES OF DISSOLVED TRACERS THROUGH ESTUARIES BASED ON RA-228- A STUDY OF LONG-ISLAND SOUND

Using Ra-228 (half-life = 5.7 y) we have determined the transfer rate of water as the carrier of tracers (dissolved substances) into Long Is land 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 (Ra-228/Ra-226) activity ratio was determined by gamma-spectrometry of Mn-coated fibe rs through which sea water was passed. An independent measurement of R a-226 activity per liter of sea water via scintillation counting df Rn -222 was made at each sampling site. Based on the Ra-228 concentration s in Long Island Sound water, water from the western boundary (off Ran dalls Island near the connection of the East River with the sound) and shelf water entering the sound from the east together with the measur ed flux of Ra-228 from Long Island Sound sediments,: we can determine the transfer rate of water from the East River to Long Island Sound du ring the summer of 1991. This value was between 0.40 x 10(14) l y(-1) and 1.1 x 10(14) l y(-1), depending on the Ra-228 flux from sediments used. The corresponding residence time of water in Long Island sound w as between 166 and 63 days.