Carbon Sequestration Potential of Constructed Wetlands Used for Wastewater Treatment

Wetlands present an important opportunity for carbon sequestration and greenhouse gas offsets by virtue of their potential for restoration using known and innovative land management methods, because inherently they are highly productive and accumulate large below-ground stocks of organic carbon. Wetlands are major carbon sinks. While vegetation traps atmospheric CO2 in wetlands and other ecosystems alike, the net-sink of wetlands is attributed to low decomposition rates in anaerobic soils. Carbon fluxes and pool sizes vary widely in different wetlands. Recently, artificially created constructed wetlands used to treat wastewater has been in common usage in Europe, USA and developed Asian countries for ecosystem-based eco-technology. Thus, waste water treatment and protecting these wetland bodies clearly represent an immediate and large opportunity for enhancing terrestrial carbon sequestration too. Experiments were conducted to measure the rate of photosynthesis in the key planted macrophytic plant species of the constructed wetland: the Phragmites karka (Reed grass, the local plant species) using the Li-Cor 6400. The uptake of carbondi-oxide by the plants could be measured at different CO2 levels in the atmosphere. It was found that the reed grass shows maximum photosynthesis at levels as high as 500 ppm of CO2. Thus, it can prove ideal for plantation at industrial sites emitting higher concentration of CO2, capable of treating the wastewater, thus purifying water as well as fixing CO2 and thus purifying ambient air in the industrial campus. Further it was found that the constructed wetlands have a good capacity to maintain the organic stocks in its medium as well at the anchoring gravel medium and the floor. Present study focused on the ‘subsurface flow constructed wetlands’ that have a smaller water column around the anchoring gravel bed as compared to the natural systems. Hence they have a greater carbon sequestration potential when compared to the natural systems. Constructed wetlands are a wise option to treat industrial waste waters efficiently when compared to the energy intensive conventional (engineering-based) treatment plants. Moreover they not only help to develop green belt around the industry but also serve to absorb the atmospheric carbon in a beneficial manner. The present study focuses on the carbon sequestration potential of two constructed wetlands. KeywordsConstructed wetlands, Organic carbon, sequestration, wastewater, treatment plants,