Diurnal variation of methane and nitrous oxide fluxes from a constructed wetland with emergent macrophytes
(English)Manuscript (preprint) (Other academic)
In order to obtain valid integrated estimates of annual fluxes of gases like methane and nitrous oxide using daytime measurements, it is essential to know their diurnal variations. Therefore, this study was done to supplement measurements of the daytime emission of these two gases from a constructed wetland in southern Sweden. The wetlandconcerned is a pilot scale system of ponds designed to reduce nitrogen levels in the wastewater from a neighbouring sewage treatment plant before it is released into a nearby river. Measurements were made during three occasions spread over the I998 and I999 growth seasons in order to cover young, mature and early senescent phases of the plants present (Typha latifolia L. and Lemna minor L.). Care was taken to capture the morning peaks in gaseous emissions (if present) that have been reported to occur sometimes. The rates of methane emission showed minor diurnal variations, which correlated with fluctuations in carbon dioxide assimilation rates together with wind speed (R2 = 0.55), supporting the hypothesis that pressurised ventilation of plants is involved in the fluxes. Only once was any indication of a morning peak in the methane emissions observed. Nitrous oxide emissions were also correlated with the wind speed (R2 =o.8o), so nitrous oxide was likely transported in the same manner. A conceptual model is presented, accounting for the effects of several importantvariables, such as production, consumption and different gaseous transport mechanisms,that explains the small diurnal variations observed in the methane emissions. The emission rates of the two gases rarely followed the same pattern, and sometimes even had reversed trends. The relatively small diurnal variations could be largely ignored, because of the much larger variations in daytime rates observed over the seasons due to a range of other factors.
Social Sciences Interdisciplinary
IdentifiersURN: urn:nbn:se:liu:diva-79119OAI: oai:DiVA.org:liu-79119DiVA: diva2:538341