Estimation of primary productivity (modified light and dark bottle oxygen method)

This method is based on the estimation of dissolved oxygen in the water samples (ml/l) by Winkler’s method. Three BOD bottles are used for this purpose. The DO content in the initial (I), Dark (D) and Light (L) bottles with a capacity of 125 or 250 ml after specific incubation period are utilized to calculate the primary productivity. The incubation period various with the nature of water sample such as 3.0 hours for sea water whereas 2.5 hours for shallow estuarine water. The incubation is done in light for the same in ‘L’ bottle and in dark ‘D’ bottle, while sample in I bottle is fixed by winkler ‘A’ and ‘B’ at the initial stage of experiment. Gross Primary (Photosynthetic) Production (GPP) is determined by using L-D values extrapolated for 12 light hours of the day. Net Primary (Photosynthetic) Production (NPP) of oxygen is obtained from either L-I or 0.8 (L-D) value ( calculated for 12 light hours of the day) whichever comes closer to (but less than) L-D value. If the L-I value falls much below 0.8 (L-D) value, it indicates that bacterial interference ( other biochemical oxidation process ) is more in the water samples. At times, L-I value exceeds L-D value. In such cases , 0.8 (L-D) value should be taken into account to assess NPP.