Water-air-CO2-flux changes after damming rivers loaded with suspended basaltic particles

Contributions of CO2 emissions from reservoirs to the atmosphere are continuously increasing with rising energy demand. Therefore, it is important to quantify the emissions and define the rate determining mechanism of CO2 fluxes in man-made reservoirs. Here we present results from two reservoirs in Iceland over a total time span of 16 years. The partial pressure of CO2 within the Ha<acute accent>lslo<acute accent>n reservoir, fed by glacier meltwater loaded with suspended basaltic particles, was considerably less than the CO2 pressure of the atmosphere during the years 2008-2013. The specific CO2 uptake from the atmosphere into Ha<acute accent>lslo<acute accent>n was estimated at 121 +/- 67.9 gCO2 m- 2 yr during the 6 months ice-free period or 5000 t annually. The uptake rate was governed by the CO2 gradient across the water-air-interphase and windspeed but less by temperature. However, temperature will affect water-rock interactions and sub-zero temperature can result in ice cover, terminating water-air interactions. Atmospheric CO2 concentration dictates the maximum upper limit of the CO2 influx rate at fixed wind speed. The downstream mixing of Ha<acute accent>lslo<acute accent>n reservoir water with the CO2 emitting Lagarfljo<acute accent>t reservoir lowered the CO2 emissions from Lagarfljo<acute accent>t from 5335 t CO2 yr- 1 to 1670 t CO2 yr- 1 after the damming. This study shows that dissolution of basalt in glacier melt waters leads to direct CO2 uptake from the atmosphere, which can potentially be utilised for future carbon removal from the atmosphere.