Quantitative identification of carbon source and sink changes caused by carbonate weathering and anthropogenic acid (HNO₃ and H₂SO₄) in karst river in northern China is of great practical significance for promoting “carbon peaking and carbon neutrality” in China. In this study, the surface water of Yufu River, a typical karst river in northern China, was conducted in the dry season of 2019. The hydrogeochemistry and isotopic tracer methods (δ₁₅^N_NO3, δ₁₅^N_NH4, δ₁₈^O_NO3 and δ^₁₃C_DIC) combined with Bayesian isotope mixing model (Simmr) and hydrochemical balance method are employed. The sources of river nitrate are quantitatively identified, and the impact of H₂CO₃, HNO₃ and H₂SO₄ on carbonate weathering and CO₂ carbon sink are quantitatively estimated. The results show that: the combined Simmr model of the hydrochemistry, hydrochemistry, δ^₁₅N_NO3, δ^₁₅N_NH4, δ^₁₈O_NO3 reveal that the main sources of riverine nitrate in Yufuhe River watershed are soil nitrogen (34.6~39.3%) and ammonium fertilizer (27.7~39.9%), followed by nitrate fertilizer (9.5~16.7%). The contribution proportions of sewage manure (7.1-12%) and atmospheric precipitation (4.4-7.5%) are relatively low. The ion ratios and δ^₁₃C_DIC reveal that HNO₃ and H₂SO₄ produced by anthropogenic activities are significantly involved in the carbonate weathering. The estimation of CO₂ consumption by hydrochemical equilibrium method is JYC > YFR > JXC > EXR; The amount of CO₂ released by sulfuric acid and nitric acid on carbonate weathering is EXR > JXC > JYC > YFR and EXR > JXC > YFR > JYC, respectively. The net CO₂ consumption in the Yufu river watershed is JYC (+0.26 mmol/L), YFR (+0.01 mmol/L), JXC (-0.81 mmol/L) and EXR (-2.13 mmol/L), respectively. JYC and YFR show karst carbon sink effect, while JXC and EXR mainly show carbon source effect. Thus, anthropogenic acids formed by intensive agricultural application of reducing nitrogen fertilizer and sulfur fertilizer are significantly involved in carbonate weathering, which is an essential factor resulting in the weakening of river carbon sink effect in karst areas in northern China. This study provides a crucial scientific basis for the construction of river carbon cycle models and the accurate assessment of basin carbon sinks in northern China or temperate karst areas.