Evaluating stream CO<sub>2</sub> outgassing via drifting and anchored flux chambers in a controlled flume experiment

Abstract. Carbon dioxide (CO2) emissions from running waters represent a key component of the global carbon cycle. However, quantifying CO2 fluxes across air–water boundaries remains challenging due to practical difficulties in estimation reach-scale standardized gas exchange velocities (k600) and water equilibrium concentrations. Whereas craft-made floating chambers supplied by internal sensors promising technique estimate rivers, existing literature lacks rigorous comparisons among differently designed deployment techniques. Moreover, as now uncertainty k600 estimates chamber data has not been evaluated. Here, these issues were addressed analysing results flume experiment carried out Summer 2019 Lunzer:::Rinnen – Experimental Facility (Austria). During experiment, 100 runs performed using two different designs (namely, standard flexible foil with an external system sealing) modes (drifting anchored). The various combinations discharge channel slope, leading variable turbulent kinetic energy dissipation rates (1.5×10-3<ε<1×10-1 m2 s−3). Estimates line (4<k600<32 s−3), general increase for larger rates. gave consistent patterns response changes slope and/or flow rate. acoustic Doppler velocimeter measurements indicated limited turbulence induced on field (22 % ε, theoretical 5 k600). was then estimated generalized likelihood (GLUE) procedure. Overall, moderate high, enhanced high-energy set-ups. For anchored mode, deviations between 1.6 8.2 m d−1, whereas significantly higher values obtained drifting mode. Interestingly, (+ 20 %) compared chamber. Our study suggests that design might be useful techniques enhance robustness accuracy low-order streams. Furthermore, demonstrates value analytical numerical tools identification accurate estimations velocities. These findings have important implications improving greenhouse reaeration waters.