An Introduction to Environmental Chemistry

water composition in the upper right (see also Table 6.1). The Colarado River in

the arid southwest of the USA is an interesting example. Construction of the

Hoover Dam on the Colorado created Lake Mead upstream of the dam, increas-

ing evaporation from the catchment. The concentration of dissolved solids

increased by 10–20% in outflowing water below the dam, while CaCO 3 precip-

itation occurred in Lake Mead. A more extreme example is seen in the Salton Sea

The Chemistry of Continental Waters 149

Pacific

Ocean

Atlantic

Ocean

Andes

N

0 1000

km

R. Amazon

R. Negro

Palaeozoic and older metamorphic rock

with highly weathered soils

Rocks in which evaporite minerals

(NaCl and CaSO 4 ) occur

Unshaded areas mainly Cenozoic

sedimentary rock

Fig. 5.4Simplified geological map of the Amazon Basin showing major river systems. After Stallard and
Edmond (1983), copyright (1983) American Geophysical Union modified by permission of American
Geophysical Union.