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 Kõo 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 Kodijärve 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 N 2 O emissions from the VSSF filter in Kõo and the inflow parts of the HSSF in Kodijärve. Due to higher organic loading rates in the inflow part of the HSSF in Kodijärve and in the VSSF filter in Kõo, the fluctuating water table/intermittent loading did not influence the CO 2 and CH 4 fluxes. The lower water depths in Paistu resulted in higher CO 2 and N 2 O, and lower CH 4 emissions relative to other systems.