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

Abstract

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 Hálslón 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 Hálslón was estimated at 121 ± 67.9 g_CO2 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 Hálslón reservoir water with the CO₂ emitting Lagarfljót reservoir lowered the CO₂ emissions from Lagarfljót 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.