Contribution of LGD source carbon to the carbon emission of eutrophic steppe lakes in northern cold and arid regions

Lake groundwater discharge (LGD) represents a critical but underappreciated source of greenhouse gases in lacustrine systems, though its governing mechanisms and quantitative significance are not yet clearly defined. This investigation focuses on Hulun Lake, a representative eutrophic lake in China’s cold-arid northern regions, through integrated analysis of stable isotope signatures (δ13C-CO2, δ13C-CH4, δ13C-DIC). We employed 222Rn mass balance modeling and greenhouse gas flux quantification to assess LGD’s contribution to CO2 and CH4 emissions. Results demonstrate elevated carbon component concentrations in groundwater relative to surface waters (DOC: groundwater 1755.50 μmol/L vs. lake water 1480.00 μmol/L vs. river water 933.25 μmol/L; DIC: groundwater 5089.00 μmol/L vs. lake water 7311.00 μmol/L vs. river water 3345.75 μmol/L). Groundwater exhibits higher mean dissolved greenhouse gas concentrations compared to lake water (CO2: 2.300 vs. 0.458 μmol/L; CH4: 0.029 vs. 0.027 μmol/L). Isotopic evidence confirms hydrological connectivity between groundwater and lake systems. Quantitative analysis reveals LGD accounts for 14.7 % of lacustrine CO2 emissions and 12.3 % of CH4 emissions. These findings establish LGD as a critical regulator of carbon biogeochemical cycling in lake ecosystems, necessitating its systematic integration into regional carbon budget assessments. The demonstrated significance of LGD in carbon dynamics underscores its essential consideration in regional and global carbon cycle models.