INTRODUCTION

When referring to riverine material, many sedimentologists, geochemists, and even hydrobiologists consider global or continental averages. This tendency is now reinforced by the increasing use of present-day global river inputs to oceans to model past geochemical cycles (Berner et al., 1983; Wilkinson and Walker, 1989). Actually, global averages mask the extended chemical diversity of river water and particulates as well as the wide range of river transport rates.

The purpose of this chapter is (1) to assess the variability of river chemistry, (2) to review the main environmental factors that control these variations, and (3) to estimate the contributions to the global river loads from various geographic, geologic, and climatic environments. Because of the amount of information available, the focus is put on major elements, nutrients, and organic carbon. The anthropogenic influence is not considered here, [i.e., river data have been screened so that most polluted rivers have been discarded and only predamming data on total suspended solids (TSS) have been retained]. Extended compilations of river chemistry started in the 1960s (Durum et al., 1960; Livingstone, 1963; Turekian, 1969). More recent basic data have already been published or previously referenced (Meybeck, 1979, 1982, 1983, 1986, 1987, 1988; Kempe, 1982; SCOPE CARBON, 1982, 1983, 1985, 1987). In addition to these, some regional studies on river water chemistry in unpolluted or less polluted environments have been used: the Mackenzie river watershed (Reeder et al., 1972), Japan rivers in 1943 to 1957 (Kobayashi, 1960), Thailand rivers in 1956/1957 (Kobayashi, 1959), and the entire Amazon River basin (Stallard, 1980).

ENVIRONMENTAL FACTORS CONTROLLING CHEMISTRY OF WATER AND SUSPENDED MATTER

River water chemistry is controlled by many environmental factors, most of them known for a long time (Erikson, 1960; Gorham, 1961; Drever, 1982; Stallard and Edmond, 1981, 1983, 1987; Meybeck, 1984, 1986; Berner and Berner, 1987). They can be presented in three major groups: sources (lithosphere, atmosphere, biosphere), sinks (vegetation uptake, settling), and rate-controlling factors (temperature, water circulation). In addition, the river basin size plays a major part through the integration of diverse environments.

Lithology is a key factor for most major dissolved elements (Si, Ca, Mg, Na, Cl, S, C). Carefully selected, pristine monolithologic watersheds are characterized by distinctly different water quality compositions (Table 4.1A),

TABLE 4.1 Variability of Dissolved Major Elements in Pristine Stream Waters Draining Various Rock Types

 

Elec. cond.

pH

TZ+

SiO2

Ca2+

Mg2+

Na+

K+

Cl-

SO4-

HCO3-

A. Most common rock types

Granitea

35

6.6

166

150

39

31

88

8

0

31

128

Gneissa

35

6.6

207

130

60

57

80

10

0

56

135

Volcanic rocksa

50

7.2

435

200

154

161

105

14

0

10

425

Sandstonea

60

6.8

223

150

88

63

51

21

0

95

125

Shalea

770

150

404

240

105

20

20

143

580

Carbonate rocka

400

7.9

3,247

100

2,560

640

34

13

0

85

3,195

Evaporitic depositsb

1,700

8.0

18,000

125

3,060

1,440

13,500

90

13,500

2,340

2,160

Evaporitic depositsc

20,000

110

12,400

7,000

600

40

600

15,000

4,400

B. Influence of water-rock interaction on water chemistry

 

 

 

 

 

 

 

U.S. riversd    

 

 

2,800

232

1,600

700

430

70

300

650

1,800

U.S. groundwaterse    

 

 

4,914

282

2,500

950

1,400

64

450

700

3,700

Note: TZ+ is the sum of the cations µeq/l) SiO2 in µmole/l; ions in µeq/l.

a Averages from survey of 250 pristine streams in France (Meybeck, 1986) and from 75 sites worldwide, both corrected for oceanic Cylic salts (Meybeck, 1987).

b Mostly rock salt, 13 watersheds (Meybeck, 1987).

c Mostly gypsum and anhydrite, 6 French streams (Meybeck, 1986).

d Discharge-weighted average for the Mississippi, Columbia, and Colorado rivers; references in Meybeck (1979).

e Median distributution from Davis (1964), potable groundwaters.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement