This chapter critically reviews recent literature on carbon storage and fluxes within natural and constructed freshwater wetlands and specifically addresses concerns of readers working in the field of applied science. The purpose is to review and assess the distribution and conversion of carbon in the water environment, particularly within constructed wetland systems. A key aim is to assess if wetlands are carbon sinks or sources. Carbon sequestration and fluxes in natural and constructed wetlands located around the world are assessed. All facets of carbon (solid and gaseous forms) have been covered. Conclusions are based on these studies. Findings indicate that wetlands can be both sources and sinks of carbon, depending on their age, operation, and the environmental boundary conditions such as location and climate. Suggestions for further research needs in the area of carbon storage in wetland sediments are outlined to facilitate the understanding of the processes of carbon storage and removal and also the factors that influence them. This timely chapter should help engineers to make the right decisions when designing wetlands taking climate change into consideration.
