The Impact of Pulsing Hydrology and Fluctuating Water Table on Greenhouse Gas Emissions from Constructed Wetlands

Intermittent loading is often used in constructed wetlands (CW) to improve water purification capacity, however, little is known of its impact on greenhouse gas (GHG) emissions.. We studied GHG fluxes in three CWs for municipal wastewater treatment in Estonia: the hybrid CW in Ko had an intermittently loaded (8-10 pulses a day) vertical subsurface flow (VSSF) filter and a horizontal subsurface flow (HSSF) filter with stable water level (10 cm below the surface), the HSSF filter in Kodijarve with higher (42 cm) but more fluctuating water level (from 5 to 75 cm) in inflow and lower (52 cm) but stable water level (30-70 cm) in outflow, and the HSSF filter in Paistu with fluctuating water table (0-70 cm). Intermittent loading enhanced N2O emissions from the VSSF filter in Ko and the inflow parts of the HSSF in Kodijarve. Due to higher organic loading rates in the inflow part of the HSSF in Kodijarve and in the VSSF filter in Ko, the fluctuating water table/intermittent loading did not influence the CO2 and CH4 fluxes. The lower water depths in Paistu resulted in higher CO2 and N2O, and lower CH4 emissions relative to other systems.