Major ion chemistry in the headwater region of the Yellow River: impact of land covers

Abstract

Research on the ionic chemistry of rivers and weathering types provides the basis for elucidating the dynamics of river chemistry and exploring carbon cycling in river systems. There is a lack of water chemistry study in the river systems in the Tibet Plateau, especially in the streams/rivers flowing from and through glaciers and permafrost. Samples in the rivers flowing through different land covers (lakes, glaciers, permafrost, grasslands, peatlands) were collected in different months (April, June, August and October) in 2016, covering various hydrological regimes. The temporal and spatial dynamic variations of major ions and the underlying causes were explored. The results revealed that in the headwater region Ca2+ and HCO3− were the dominant ions, derived primarily from the dissolution of carbonatites and evaporates. However, the concentrations of ions from different land covers were vastly different.The high concentrations of Na+ and K+ in the lakes sample were mainly affected by evaporation and precipitation. The acid deposition caused by atmospheric pollutants resulted in high concentration of SO42− in glacial and permafrost streams. K+ concentration was high in the grassland region with frequent agricultural activities such as the planting and fertilization of highland barleys that applied nitrogen and potassium fertilizers. Although Total Dissolved Load (TDS) was higher for the lakes and streams/rivers from glaciers and permafrost, and its average (287.28 ± 40 mg/L) over the headwater region was lower than that in the middle and lower reaches of the Yellow River because of low temperature. The current study provided the basis of and reference for the overall water chemistry characteristics and carbon cycling processes of the entire Yellow River.