Groundwater Discharge Drives Ebullitive and Diffusive CO 2 Emissions With Limited CH 4 Flux in a Typical Karst Spring

Abstract Groundwater discharge is a critical yet overlooked driver of carbon emissions from aquatic ecosystems. Despite this significance, its direct natural outlets, springs, remain unquantified carbon emission hotspots. Here, we investigated a representative bubbling karst spring (Pearl Spring, China) to disentangle how groundwater discharge controls ebullitive and diffusive emissions of CO 2 and CH 4 . High‐resolution dissolved gas monitoring showed that groundwater discharge elevated surface water CO 2 concentrations two orders of magnitude above atmospheric equilibrium, while CH 4 levels remained low. The ebullitive gases were composed predominantly of entrapped air (N 2 : 85%, O 2 : 10%), yet were markedly enriched in CO 2 (91×) and 4 He (5×) relative to atmospheric concentrations, indicating subsurface gas origin and additions to an air‐derived matrix. Flux measurements revealed extremely high ebullitive (2,238–3,667 mmol m −2 d −1 ) and diffusive (319–718 mmol m −2 d −1 ) CO 2 emissions, which were nearly two orders of magnitude above global averages for total CO 2 emissions from lakes and reservoirs, while CH 4 emissions were minor. These results suggest that springs can be previously underrepresented, ebullition‐dominated CO 2 hotspots, emphasizing their importance in terrestrial‐to‐atmosphere carbon transfer and regional to global carbon budgets.