J. Hydrology, V 172, p 209-229, 1995

Controls on the Major Ion Chemistry of the Urumqi River, Tian Shan, PR China

Mark W. Williams
Department of Geography and Institute of Arctic and Alpine Research University of Colorado Boulder, Colorado 80309

Daquing Yang and Fengjing Liu
Lanzhou Institute of Glaciology and Geocryology Lanzhou, Gansu, PR China 730000

John Turk
USGS Water Resources Division Denver, CO

John Melack
Department of Biological Sciences University of California Santa Barbara, CA

Abstract:

Water and snow samples were collected in May of 1990 and 1992 in headwater basins and along a longitudinal transect of the Urumqi River, located in northwestern China. Surface waters were dominated by CA and HCO3 at all sites. Maximum measured SO4 concentrations in surface waters were 550 ueq/L and were balanced by CA and HCO3; pH was slightly alkaline at all locations. Several independent analyses each concluded that the solute compositon of surface waters was dominated by dissolution of rocks with rapid weathering kinetics, such as calcite and dolomite. Preliminary analysis of stable sulfur ratios in headwater basins shows S34 values of +6.8 for snow and +3.3 for surface waters. Changes in the S34 value of surface waters with increasing basin area were variable, suggesting changes in the stable sulfur ratios of source materials. The large amounts of HCO3 and base cations at all sites indicates that the Urumqi River is not sensitive to acidification from atmospheric deposition.


Figure 1: Topographic map of the Dry Cirque. Snowpit locations for chemical samples are designated by diamonds. The gaging station is marked with a square. Contour interval is 25 m.


Figure 2: Concentrations of selected ions in the outlet stream of the Dry Cirque, May 13 to May 19, 1990. Solute concentrations were inversely related to discharge. Discharge was separated into snowmelt or new water and subsurface or old water for the period May 13 to May 19 using Si as a tracer.


Figure 3: Longitudinal transect for temperature and selected solutes along the Urumqi River in May of 1990.


Figure 4: Log of the ratio of the ion activity product (IAP) to saturation product (KT) for calcite, dolomite, and gypsum, as a function of basin area for the Urumqi River.