GHG emissions from algal facultative ponds under tropical conditions

96Full scale experiments were designed to enhance understanding of daytime and night-time variations of CH₄, CO₂ and N₂O levels in an algal facultative pond (AFP) under tropical conditions. The results showed that the AFP was a net source of CH₄ during both daytime (2,466.8±989.8 mg CH₄m^-2 d^-1) and night-time (2,254±1,152.5 mg CH₄m^-2 d^-1). The variations in CH₄ emissions were influenced by environmental factors and physicochemical parameters such as ambient temperature and total nitrogen (r²=0.52; p<0.05). For CO₂ emissions, a strong influence of the photoperiod was observed. During the daytime, the AFP served as a CO₂ sink (-743±847.5 mg CO₂ m^-2 d^-1) while at night-time it served as a CO₂ source (2,497±1,334.8 mg CO₂ m^-2 d^-1). CO₂ production in the AFP was correlated positively to COD, and negatively to pH and DO. The significant difference between daytime and night-time CO₂ reflected changes in algal photosynthesis and heterotrophic respiration. N₂O fluxes from the AFP during daytime (-0.95±2.7 mg N₂O m^-2 d^-1) and night-time (3.8±7 mg N₂O m^-2 d^-1) showed significant differences. By regression analysis, N₂O fluxes showed a positive correlation with NO^- ₃ N, and TKN, and negative correlation to DO and COD.