Geochemical cycling in the Hooghly estuary, India

U–Th decay series isotopes, δ 18O and Si measurements in the river estuarine waters and sediments of the polluted Hooghly estuary as well as the surface waters of the Bay of Bengal, its high salinity end member, are reported. Dissolved Si indicates that there are probably two mixing regimes, dissolved U behaviour is nonconservative and δ 18O behaves conservatively in the overall estuarine region. Isotopes of reactive elements, viz. 234Th and 210Po, are removed from the estuarine waters in