| This study presents a complementary geochemical and isotopic database (Ca2+, Mg2+, Na, K+, HCO 3--, SO42--, Cl --, trace elements and isotopes of H, O, C, S and Sr) for water samples from the Indus River Basin. These results, as well as published data for precipitation and river discharges were used to address the following aspects of the Indus River Basin: (1) water budget, annual solute fluxes, and denudation rate; (2) whether the summer monsoon or delayed runoff from winter precipitation dominates the discharge of the Indus and where does the water vapor for precipitation originate; (3) what are the sources and processes that control the distribution of solutes; (4) estimate the contribution of major ions to river water from carbonate and silicate weathering.;The long-term mean annual precipitation water flux into the Indus River Basin is 398 km3. Based on major ion chemistry of rain and snow, the annual precipitation flux of Total Dissolved Solids (TDS) to the Indus River Basin is ∼ 844,400 tons. The Indus River annually transports ∼ 18 million tons of TDS that translates into a chemical denudation rate of 21 tons km--2.;Oxygen and deuterium isotopes in the Indus River at Sukkur barrage for the Water Year March-94 to February-95 define the relationship deltaD = 7.5 (delta18O) + 10. This implies that despite aridity, significant evaporative enrichment is limited due to the short residence time of water and due to the minor contribution of runoff from the and middle and lower parts of the basin.;Hydrochemistry of the Indus River is dominated by Ca2+ > Mg2+ > (Na+ +K+) and HCO 3-- > (SO42-- +Cl--) > Si. Sediment weathering is the dominant source for major cations, silicate weathering is important only locally. Three end member compositions control the Sr-isotope systematics of the Indus River. These are: (a) weathering of old silicate (silicic) rocks with high 87Sr/86Sr ratios and represented by rivers draining the Precambrian high grade metamorphic rocks of the Nanga Parbat-Haramosh massif and the "Central Crystallines" of the Higher Himalayas; (b) young silicate (mafic) rocks with the lowest 87Sr/ 86Sr ratios of all the Indus tributaries and represented by rivers draining mafic-ultramafic units of the Cretaceous Kohistan-Ladakh arcs; and (c) weathering of sedimentary carbonates with intermediate 87 Sr/86Sr, represented by the lowland tributaries draining sedimentary carbonates and shales of the West Pakistan Fold Belt. (Abstract shortened by UMI.)... |
