Greenhouse Gases Emissions of Constructed Wetlands: Mechanisms and Affecting Factors

Constructed wetlands (CWs) widely applied for wastewater treatment release significant greenhouse gases (GHGs), contributing to global warming. It is essential to characterize the comprehensive source-sink effects and affecting factors of GHGs in CWs, offering references and guidance for designing and operating CWs to better control GHG emissions. However, current reviews focus on individual GHG emission mechanisms. With the aid of the Web of Science Core Collection database, the relevant literature on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions in CWs after 2010 was collected and organized. As highlighted in the review, CWs can produce and transmit these GHGs into the atmosphere, forming sources of GHGs and sequestration CO2 through plants photosynthesis, forming sinks of GHGs. Their overall performance depends on many factors. Hybrid CWs, Cyperus papyrus, Cyperus alternifolius, and Iris pseudacorus, adsorption substrates like Fe-C, low temperatures, and a C/N ratio of five are beneficial for GHG mitigation in CWs. Future studies should focus on in-depth research into the mechanisms and overall source-sink benefits of plants and microorganisms in relation to GHGs. This review provided a comprehensive understanding of the emission mechanisms and affecting factors of the major GHGs in CWs, bridging the research gap in this field, helping researchers to clarify the context, and providing valuable in-sights for further scientific investigations.