Hydrochemical Characteristics and Controls of Runoff at the Headwaters of the Urumqi River, Eastern Tianshan Mountain
天山乌鲁木齐河源区径流水化学特征及影响因素分析

Glacierised alpine basins present an ideal environment for studying interactions between water and rock, since chemical weathering rates are generally high and anthropogenic impacts are often minimal. Studies on glacier hydrochemistry are still at an initial stage in China, with less data being published on glacierized catchments. An analytical study of hydrochemical characteristics and controls of the proglacial streams at the headwaters of the Urumqi River were carried out in this study. Over the period from May 2006 through April 2008, a 2-year continuous precipitation and runoff samples were analyzed for major cations (Mg2+, Ca2+, Na+, and K+) and anions (SO42-, NO3- and Cl-), pH, electrical conductivity (EC), and total dissolved solids (TDS). Results reveal that Ca2+and Na + were the dominant cations, and HCO3- and SO42- were the dominant anions in precipitation. The anions and cations in the streams were dominated by Ca2+, HCO3-, and SO42-. Extensive interactions between meltwater and soil and chemical denudation of mineral solutes contributed much to the stream water, resulting in a higher solute concentration in streams than in precipitation. The average pH value in runoff was alkaline (7.67, 8.08, or 8.47), whereas in precipitation the average PH value was close to neutral (6.73). TDS and EC values in runoff samples in a descending order were the Zongkong station, Glacier No.1 station, and Empty Cirque station. The peak TDS value at Glacier No. 1 station was highest, with large magnitude for TDS values. The TDS yield in runoff was controlled by diurnal discharge at different scales at the three hydrological stations. It was concluded that the major origin of ions in runoff was weathering of rocks. Based on ion ratios and piper trilinear nomograph, main processes controlling the water chemistry were found to be carbonate weathering, pyrite weathering, and feldspar weathering in rocks. Ca2+and HCO3- were the dominant cation and anion during the carbonate weathering process. Contribution proportions of local precipitation to the solute at Glacier No.1, the Empty Cirque, and Zongkong station, based on the seawater correction approach, were 4.91%, 9.10%, and 5.42%, respectively. A new calculation also suggested that cation denudation rates were 18.1 t·km-2 a-1 and 12.3 t·km-2 a-1 at Glacier No.1 station in 2006 and 2007, respectively.