Quantified Carbon Dioxide Removal from an Alkalinity Addition Field Trial in the Kvina River, Norway

River alkalinity enhancement (RAE) is a carbon dioxide removal (CDR) approach in which alkaline minerals are added to rivers to accelerate weathering reactions that neutralize acidity and increase alkalinity export to the ocean. Although river liming is widely used to mitigate acidification, it has not been quantified as a CDR approach. Here we report results from a 98-day RAE trial in the Kvina River, Norway, conducted within an existing liming programme. The trial increased the existing pH from 6.0 to 6.8 by adding an additional 1 480 t of calcite. CDR was quantified by comparing the increase in alkalinity export at the river mouth relative to a limed control site. The trial generated 250 ± 30 tonnes carbon dioxide equivalent (t CO2e) of gross CDR, corresponding to a gross efficiency of 0.17 ± 0.02 t CO2e per t calcite and 54 % of the theoretical maximum CDR. Apart from phosphate, no other nutrients, trace metals, or indicators of an adverse water-quality impact increased significantly. These findings provide field-scale evidence that modestly increasing pH targets at existing liming facilities can increase alkalinity export and generate quantifiable CDR under site-specific hydrological, feedstock, and lifecycle conditions.