The Geochemistry of the Earth - Thanatia: The Destiny of the Earth's Mineral Resources - page 117

Table 5.9 The average concentrations of elements in filtered river
water. Concentration in ppb. Adapted from Li (1982)

Element Concentration Element Concentration

Li 3 Mo 0.6

Be 0.01 Ag 0.3

B 10 Cd 0.01

F 100 In

Na 6300 Sn 0.04

Mg 4100 Sb 0.07

Al 50 I 7

Si 6500 Cs 0.02

P 20 Ba 20

S 3700 La 0.05

Cl 7800 Ce 0.08

K 2300 Pr 0.007

Ca 15000 Nd 0.04

Sc 0.004 Sm 0.008

Ti 3 Eu 0.001

V 0.9 Gd 0.008

Cr 1 Tb 0.001

Mn 7 Ho 0.001

Fe 40 Er 0.004

Co 0.1 Tm 0.001

Ni 0.3 Y b 0.004

Cu 7 Lu 0.001

Zn 20 Hf

Ga 0.09 Ta

Ge 0.005 W 0.03

As 2 Re

Se 0.06 Au 0.002

Br 20 Hg 0.07

Rb 1 Tl

Sr 70 Pb 1

Y Bi

Zr Th 0.1

Nb U 0.04

Extensive compilations of groundwater composition in Maryland and New York
from different rock types were also recorded by White et al. (1963) as shown in
Table 5.10.

5.4.3 Ice caps, ice sheets and glaciers

Glaciers, ice sheets and ice caps are huge masses of frozen water, formed on land
by the compaction and re-crystallisation of snow. They are very important to the
stability of the environment and the alternation of landforms. Glaciers also exert
a direct influence on the hydrological cycle by slowing the passage of water. Like
groundwater they are considered to be key natural reservoirs of freshwater. They are
therefore extremely significant sources of water for human consumption, irrigation,
electric power and other industrial uses, especially during the summer, when ice
melt is highest and rainfall decreases.