Author: Gerard  Rocher-Ros,  Postdoc (Umea university)

Description:
Running waters evade large amounts of CO₂ to the atmosphere, with a flux four times larger than the carbon (C) export to the oceans. Yet, the magnitude of global CO₂ evasion from streams and rivers remains uncertain, partly due to the large temporal variability of CO₂ concentrations in the water. Here, we present the first global compilation of high temporal resolution CO₂ data from 52 sites, to show that CO₂ evasion from streams displays a consistent pattern with, on average, night-time rates 0.53 g C m^-2 d^-1 (14%) larger than those during the day. This day-night difference likely emerges from CO₂ fixation by photosynthesis during the day and consistent with this, we show that canopy cover of the stream (shading) is the main driver regulating variation in diel patterns among sites. Further, because current global estimates rely on discrete CO₂ samples taken during daylight hours, these fail to account for time windows with higher fluxes. If the patterns revealed in this study are general, then we are currently underestimating global CO₂ evasion from running waters, with night-time evasion rates that could account for an additional 1.21 (CI=0.38-2.0) Pg C yr^-1 emitted to the atmosphere.

Category: Scientific Program Abstract > Special Session > SS27 Aquatic greenhouse gas dynamics in the face of global change