Major ion chemistry, chemical weathering and CO2 consumption in the Songhua River basin, Northeast China

Abstract

A detailed analysis of the major ion chemistry, chemical weathering and CO2 consumption was conducted in the Songhua River basin, which is the largest basin with a draining area of 557 thousand km2 in Northeast China. The dataset used in this study included major ion concentrations came from 56 hydrological stations from the year of 1962 to 1984. The median of the total dissolved solid concentration of the Songhua River was 104.8 mg/L, about two times higher than the global average (65.0 mg/L), but lower than that of other Chinese Rivers. Prevalent ions were Na+, Ca2+ and HCO3 −, and the average Ca2+/Na+ and Mg2+/Na+ molar ratios were 0.70 and 0.42, which were close to silicate weathering end-member. Long-term trend analysis by seasonal MK test showed that from 1962 to 1984, Ca2+, Na+ + K+ and HCO3 − were significantly increasing, and the increasing rates calculated by linear fit slopes for Ca2+, Na+ + K+ and HCO3 − ions were 0.22, 0.63 and 2.35 mg/year, respectively. An inverse model showed that the dissolved loads primarily came from rock weathering (91.5 %), including silicate weathering (66.4 %) and a small portion from carbonates (16.1 %) and evaporites (9.0 %). Other origins consisted of anthropogenic inputs (5.3 %) and atmospheric inputs (3.2 %). Average silicate and carbonate weathering rates were estimated as 4.03 and 1.76 t km−2 year−1, and CO2 consumption rates of silicates and carbonates were 17.1 × 104 and 1.85 × 104 mol km–2 year−1, respectively. These results are consistent with the lithologies of the study area, which mainly consisted of silicate rocks.