Controls of methane oxidation in dry streambeds

Despite advances in understanding methane dynamics in dry inland waters, the potential of dry riverbeds to act as sinks of methane, as soils do, and the controlling factors remain unclear. Here, we tested three main factors controlling methane oxidation in soils and freshwater ecosystems in sediments from a dry riverbed (decreasing in modulation degree): gravimetric water content (GWC), temperature, and light quality and intensity. We measured the rates of potential methane oxidation (PMO) along a gradient of GWC (1%, 5%, 8%, 10%, and 100%), temperature (10 ºC, 20 ºC, and 30 ºC) and light (in darkness, at photosynthesis-limiting (i.e., green) and photosynthesis-promoting (i.e., grow) light). Our results revealed that dry streambed sediments have the potential to oxidize methane. GWC, as the major controlling factor, followed a nonmonotonic function, with the highest PMO of around 5% GWC. As the secondary control, temperature affected PMO from dry sediment only but not from 100% GWC sediment. PMO was the lowest at 10 ºC and highest above 20 ºC. Interestingly, light reduced PMO by 3–6× compared to dark conditions, and grow light reduced PMO by ~2× compared to green light. Our results indicate that there will be day–night and seasonal variations in methane oxidation from dry riverbeds as a function of temperature, GWC and light, and between reaches, depending on the canopy cover and associated riverbed shading. Overall, our results highlight the potential of dry riverbeds to act as sinks of methane from the atmosphere.