Exploring the Sources of Unexpected High Methane Concentrations and Fluxes From Alpine Headwater Streams

Abstract

AbstractThe dynamics of methane generation and evasion from well‐oxygenated, oligotrophic streams have been traditionally neglected. We estimated evasion of methane and assessed its sources and production pathways using a stable isotope approach in 16 oxygen‐rich and C‐poor (dissolved organic carbon: 55.32 ± 57.56 μmol/L) Alpine headwater streams. Methane was often supersaturated relative to the atmosphere (0.093 ± 0.179 μmol/L). Fluxes (0.87 ± 1.34 mmol·m−2·day−1) were unexpectedly high and comparable to those from high‐latitude lakes and reservoirs. Our findings suggest that methane in the streambed was largely produced from carbon dioxide reduction, whereas acetoclastic pathways and major deliveries from adjacent soils, assessed from a mass balance, may have contributed to stream water methane. This study sheds new light on high‐alpine streams as a hitherto unaccounted source of methane to the atmosphere.