Diurnal cycling of dissolved gas concentrations in a willow vegetation filter treating landfill leachate

Membrane inlet mass spectrometry (MIMS) was used to monitor continuously and simultaneously the concentrations of dissolved gases (O2, CO2, CH4), in the willow root zone at the laboratory scale, and within the treatment bed of a willow vegetation filter treating leachate at a landfill site in mid Wales. These results demonstrate that willows are able to release oxygen into the root zone which accumulates during daylight. Diurnal cycles of oxygen, carbon dioxide, and methane were observed, whereby CO2 and CH4 varied reciprocally in relation to O2. The intensity of these cycles appeared to be related to light intensity and temperature. Oxygen was shown to fluctuate between completely anaerobic and fully aerated (300 μM), between day and night in sunny conditions.