Considerable carbon dioxide emissions from groundwater over-exploitation in the North China Plain

This study compiled hydrogeochemical data from 6202 groundwater sampling sites across the North China Plain (NCP), being sampled between 2007 and 2010. This dataset comprises 4454 points in shallow aquifer and 1748 points in deep aquifer, which were used for the analysis of the quantitative calculation of CO2 emissions induced by groundwater over-exploitation in the NCP. These datasets revealed elevated HCO3- concentrations in the groundwater within the study area. Coupled with severe local over-exploitation, these have resulted in CO2 emissions from groundwater depletion and groundwater extraction reaching 0.53 Tg/yr and 4.03 Tg/yr, respectively. These values accounted for around 9% and 39% of the total CO2 emissions from terrestrial waters in the NCP, far exceeding the average proportion of groundwater CO2 emissions to total terrestrial water CO2 emission in China (<1%) and globally (∼1%). Additionally, shallow aquifers were found to emit significantly more CO2 than deep aquifers, contributing about 83% of the total emissions.