Behaviour of trace metals in the anoxic environment of Veraval harbour, India

The purpose of the present study is to investigate the behaviour of trace metals in anoxic environment. Water column of the harbour was found to be anoxic (DO < 0.2 mg l− 1) with high concentration of NH4+-N (av. 459 ± 21 μmol l− 1) and H2S (av.73 ± 2.5 μmol l− 1) irrespective of season and tide. High concentrations of Fe, Mn in bottom water indicated that Fe, Mn were diagenetically mobilized under the anoxic conditions prevailing in the harbour. In harbour sediments significant correlation of metals with TOC and TS indicated their diagenetic immobilization in anoxic environment. Fe was positively correlated with TS suggesting FeS formation in anoxic condition. TOC/TN ratio of sediments was higher (16 ± 5.2) than the normal marine planktonic sediments suggesting an increased burden of terrestrial carbon in the harbour. A sediment core collected 10 km away from the shore indicated build-up of trace metals in recent years, showing diagenetically upward movement of metals.