• The nitrate removal rate ranged between 1 942 to 3 628 kg nitrate-N Ha^-1 year^-1.
  
• The highest nitrogen removal rate was found at the sites with higher nitrogen concentration and organic matter content in the soil.
  
• Nitrous oxide was used by the bacteria when the nitrate was depleted from the groundwater.
  
• The methane productions increased with a decreasing nitrogen concentration.

• Higher source of nitrogen will not increase the rate of removing nitrogen compounds at a certain depth.
  
• Nitrate removal capacity and GHG production was found to be limited by the amount and the quality of organic matter in the soil.
  
• The bacteria activity under no oxygen condition seems also to be regulated by other environmental variables, such as the quality of the water.

• Dissimilatory nitrate reduction to ammonia (DNRA) was occurring beside denitrification.

The results we found in this study could help to achieve a better restoration of wetlands in the future. In order to have a better nitrogen removal with low greenhouse gas emissions from the wetlands.