Diurnal variation in physical-chemical properties and primary production in the interconnected marine, mangrove and freshwater biotopes of Kakinada coast, Andhra Pradesh, India

Diel and tidal changes in water temperature, salinity, dissolved oxygen, and nutrients (phosphate, nitrite, nitrate, ammonia) and primary production were studied in 3 interconnected biotopes (freshwater, marine and mangrove brackish water) of the Kakinada coastal zone, Andhra Pradesh, India. In the marine environment salinity was higher than in the mangrove waters. In both biotopes salinity showed a bimodal type of oscillation. Dissolved oxygen content was high in mangrove waters during the day but decreased during the night. Concentrations of phosphate, nitrite and nitrate were similar in the mangrove and bay water or slightly higher in the bay water depending on the tide. Levels were higher in the mangrove water at high tide indicating that some nutrients were imported to the mangrove environment by tidal movement. This phenomenon was not observed during the day. The concentration of ammonia was relatively high in the mangrove. Gross and net primary production in the mangrove water was 4 times higher than in the marine biotope.