Sammendrag
The Tibetan Plateau covers an area of about one fourth of Europe, has an average elevation over 4000 m
above sea level, and is the water sources for about 40% of world's population. In order to foresee future
changes in water quality, it is important to understand what pressures are governing the spatial variation in
water chemistry. In this paper the chemistry including major ions and trace elements in the headwaters of
four major Asian rivers (i.e. the Salween, Mekong, Yangtze River and Yarlung Tsangpo) in the Tibetan Plateau
was studied. The results showed that the content of dissolved salts in these Tibetan rivers was relatively high
compared to waters from other parts of the world. The chemical composition of the four rivers were rather
similar, with Ca2+ and HCO3
− being the dominating ions. The exception was the Yangtze River on the Plateau,
which was enriched in Na+, Cl−, SO42− and Li due to silicate weathering followed by strong evaporation
caused by a negative water balance, dissolution of evaporites in the catchment and some drainage from
saline lakes. The concentrations of heavy metals (Cu, Co, Cr, Ni, Cd, Pb, and Hg) and As, NH4
+ were generally
low in all the rivers. Anthropogenic impacts on the quality of the rivers were identified at a few locations in
the Mekong River and Yarlung Tsangpo basins. Generally, the main spatial variation in chemical
compositions of these under studied rivers was found to be governed mainly by difference in geological
variation and regional climatic-environment. Climate change is, therefore, one of main determining factors
on the water chemical characteristics of these headwaters of Asian major rivers in the Tibetan Plateau.
Vis fullstendig beskrivelse