Total dissolved inorganic carbon and physicochemical characteristics of surface microlayer and upper mixed layer water from Lagos Lagoon, Nigeria

The carbonate and physicochemical characteristics of the surface microlayer and upper mixed layer of a tropical coastal lagoon were investigated. Data on the physicochemical parameters generally indicated a moderately polluted ecosystem. The influence of the ocean environment over the Lagoon system was evident by elevated salinity levels. The mean total dissolved inorganic carbon (DIC) for the surface microlayer (SML) and subsurface water (SSW) samples were 2626.6 and 2550.9 µmol/kg SW respectively. The dominant inorganic form of DIC in the lagoon water samples was HCO₃^- with a calculated average abundance >95.4% in the SML and >94% in the SSW. The bicarbonate species derived abundance varied between 1.6% (SML) and 8.4% (SSW), while the aqueous carbon dioxide were generally low in percentages ranging from 0.4 in SSW to 1.5 in SML water samples. In general, the occurrence of the carbonate species was in the order HCO₃^- > CO₃^2- > CO₂. Results showed that total alkalinity (A_T) was relatively greater than the DIC. Long term monitoring studies in the coastal lagoon systems is needed to understand the coastal water chemistry and pollution status.