Are different configurations of pilot-scale constructed wetlands carbon sources or carbon sinks?

[Geoengineering News]

https://link.springer.com/article/10.1007/s11783-026-2158-0

Authors: Yichu Wang, Hao Qin, Tao Liu, Tao Lang, Sihan Li, Zihang Zhang, Shuhao He & Yi Chen 

20 January 2026

Abstract

Constructed wetlands (CWs) are gaining recognition as important carbon sinks, subject to factors such as system design and vegetation. However, the effect of configuration on carbon emissions in CWs remains inadequately understood. We constructed three configurations of CWs, free-water surface flow (FWS), horizontal subsurface flow (HSSF), and vertical subsurface flow (VSSF), to assess contaminant removal performance and carbon emissions. Higher removal efficiencies for NH4+-N, NO3−-N and COD were observed in HSSF (72.06%, 60.90%, and 70.01%) and VSSF (75.18%, 48.94%, and 69.47%) compared to FWS (64.89%, 35.50%, and 58.83%). FWS exhibited the highest CH4 emissions (1.59 mg/(m2·h)) and lowest CO2 emissions (−176.26 mg/(m2·h)) due to a greater abundance of Methanobacterium and plant biomass. Higher N2O emissions were observed in VSSF (0.33 mg/(m2·h)) compared to FWS (0.18 mg/(m2·h)) and HSSF (0.12 mg/(m2·h)). In general, the majority of carbon was buried in substrate (55.53%–64.50%), followed by plants (24.90%–40.84%) and wastewater (4.05%–14.08%). Carbon budget estimation showed that all CWs exhibited characteristics of carbon sinks. FWS exhibited the highest annual net carbon sink capacity at 4.78 kg CO2-eq/(m2·yr), followed by VSSF and HSSF at 2.81 and 2.54 kg CO2-eq/(m2·yr), respectively.

Source: Springer Nature Link