Carbon Uptake Rates in the Cochin Estuary and Adjoining Coastal Arabian Sea

Carbon uptake rates in a tropical eutrophic estuary (Cochin estuary) and the adjacent coastal Arabian Sea were measured for the first time using ¹³C-NaHCO₃ labeling technique. The rates in the estuarine water (pre-monsoon 3.0-20.4; monsoon 2.55-12.4; post-monsoon 3.1-16.3 μmol C 1⁻¹ h⁻¹) were significantly higher than the coastal locations (pre-monsoon 0.02-0.1; monsoon 0.13-3.1; post-monsoon 0.007-0.032 μmol C 1⁻¹ h⁻¹). The measured primaiy productivity in the estuary was relatively higher at mesohaline locations influenced with lateral inputs and TN:TP close to the Redfield ratio (16:1). It suggests that in nutrient replete tropical systems, TN:TP plays a major role in controlling the primary productivity rates. The primaiy productivity data from the coastal Arabian Sea suggests the effect of estuarine discharge on the carbon uptake rate at nearshore regions and ability of anthropogenic inputs to modulate the coastal biogeochemistry.