Diel Cycling of Methane in Arctic Ponds

The importance of freshwater ecosystems in the arctic carbon cycle is often neglected. Lakes and ponds across the arctic, in particular, can be major contributors to total methane emissions. The magnitude of emissions from a given water body depends on a variety of physical and biogeochemical processes, many of which are driven by sunlight. One of these processes is photodegradation, which is the breakdown of complex organic molecules into simpler, often more labile forms by sunlight., Photodegradation may increase the availability of organic carbon for microbes, and therefore enhance the productivity of methanogens, significantly impacting the magnitude and form of carbon emissions. We explored the relationship between diel light cycles, carbon lability and CH4 emissions in several small arctic ponds in the Yukon-Kuskokwim Delta . We collected water and dissolved gas samples from three, medium sized ponds several times over the course of the solar cycle on two days in early July. In addition, methane fluxes were measured several times on each day from a single pond using an LGR ultraportable gas analyzer. . Samples were analyzed for dissolved organic carbon (DOC) concentration, as well as composition using Specific Ultraviolet Absorbance (SUVA) to estimate lability of DOC. Results show substantial variation in CH4 concentration and SUVA over the course of 24 hours. In addition, we found a strong correlation between CH4 concentrations and SUVA, suggesting a relationship between lability and CH4 production. Finally, we found substantial variation in CH4 emissions within each day and between the two days that suggest sunlight intensity and wind speed interact to drive CH4 emissions. . These results highlight the potential importance of small-scale temporal variation in physical drivers, and their interactions with microbial communities, in determining patterns of greenhouse gas emission from small ponds and their potential response to future climate changes.