Diverse drivers of long-term pCO(2)increases across thirteen boreal lakes and streams

Understanding the mechanisms driving carbon dioxide (CO2) concentrations in inland waters is important to foresee CO(2)responses to environmental change, yet knowledge gaps persist regarding which processes are the key drivers. Here we investigated possible drivers across 13 Swedish lakes and streams where the partial pressure of CO2(pCO(2)) has increased over a 21-year period. Overall, we could not identify a single dominating mechanism responsible for the observedpCO(2)increase. In the 8 lakes, we found thatpCO(2)increased, driven either by a possible dissolved organic carbon (DOC) stimulation of microbial mineralization or by water color primary production suppression. In streams, the dominating mechanism for apCO(2)increase was either a change in the carbonate system distribution or a possible nutrient-driven decrease in primary production. This is the first study to demonstrate and explain consistent positivepCO(2)temporal trends in freshwater ecosystems, and our results should be taken into account when predicting future emission of CO(2)from inland waters.