430
range of 30 to 300 mg/I. Within this wide range, one
can distinguish several groups with similar characteristics:
- Low solute concentrations (TDS between 30 and
ca. 100 mg/I). This group comprises rivers largely
draining either tropical regions with thick soil covers
consisting of stable neo-minerals (e.g. Amazon,
Orinoco, Congo, Indonesian rivers) or crystalline
rocks in wet humid areas (e.g. Scandinavia, effect of
dilution) and rivers in subarctic regions (Fig. 9.8).
In most of these cases, the river water contains litde hydrogen carbonate and less TDS than the groundwater circulating in unweathered or only partly altered rocks, except
quartzitic sandstones (Fig. 9.6). The concentration of dissolved Si0 2 in these river waters, however, approaches the
average ofworld rivers (lI mg/I). The Siberian rivers Lena,
Ob, and Yenisei coming from subarctic areas with sparse
vegetation also have low TDS values, although carbonatebearing rocks are present in their drainage areas.
- Medium solute concentrations (ca.150 to 300
mg/I). Rivers originating in the Alps and Himalayas
(including the Yangtze River), as well as the Mississippi River belong to this category (Fig. 9.8). They
all display medium values for calcium and hydrogen
carbonate due to the presence of carbonate rocks in
their drainage areas.
- High solute concentrations (>300 mg/I) are only
found in a limited number of large river basins which
are markedly affected by the dissolution of rock salt
and/or gypsum (e.g. the Murray River in Australia
and the Rio Grande River in North America, Fig.
9.8).
Global Mean Values of Solute Concentrations
According to Livingstone (1963) and Meybeck
(1979, 1983, 1987) the average river water of the
world contains ab out 115 mg/l TDS (load-weighted
mean) and has a composition as shown in Fig. 9.8.
The most important constituent (by weight) is hydrogen carbonate HC0 3 - (about 58 mg/I) which, however, is derived to a large extent (-70%) from decaying plant material in the soil zone and is recycled into
the atmosphere. HC0 3 - is followed by Ca 2 + (about 14
mg/I), Si0 2 (about 11 mg/I), and SO/" (10 mg/I).
These four components generally make up more than
80% of the total dissolved river load.
Fig. 9.9. Water chemistry (total dissolved solids
TDS) in various morphological and lithological zones of river catchments. a,b Rivers Amazon and Orinoco, tropical wet climate. (After Drever 1982; Stallard 1985). dRiver Main, Germany, humid temperate
climate. Numbers refer to dissolved load in groundwater (in t/km 2 /a. (After Einseie and Hohberger
1978). c,e Downstream changing concentrations of
Chapter 9 Denudation and Mass Transport
Variations in Water Chemistry Along
River Courses
The mean concentrations of dissolved species common1y vary along the courses of large rivers which
drain regions of various lithologies. The reason for
this observation is the fact that their water chemistry
is affected not only by tributaries but to a large degree by groundwater originating from rocks of different chemical composition (Sect. 9.2.2)_
The water chemistry of the Amazon River, for example,
changes greatly along its course from the Andes to the Atlantic (Fig. 9.9a, band c). Water from the snow-covered
Andes, relatively rich in dissolved constituents, is diluted
by tributaries draining areas with deeply leached tropical
soils (e.g. Drever 1982; Stallard 1985). The major part
(86%) of the dissolved load entering the Atlantic Ocean is
supplied by 12% of the total drainage area of the river (the
Andes). The chemical denudation rates of the different
morphotectonic units of the Amazon and Orinoco drainage
basins vary by a factor of almost 100 and, if the evaporitic
sediments are inc1uded, even by a factor ofup to 1000 (Fig.
9.9b).
In the river Main, a major tributary of the river Rhine
in central Europe (temperate, humid climate), the
water chemistry also marked1y varies along its
course. Most of the total solute load (86%) is provided by groundwater from different rock types (Fig.
9.9d and e). Of these lithologic units, carbonate and
sulfate-bearing sedimentary rocks deliver approximately 90% of the dissolved load, whereas regions
with crystalline rocks and quartzitic sandstones
(comprising 22% of the total drainage area) yield
only 5%_ The average specific transport rate (or specific yield of TDS) of the entire drainage basin
amounts to about 100 t/km2/a, which corresponds to a
mean chemical denudation rate of 40 mmlka. In reality, the denudation rates vary from approximately 5
mmlka (Bunter sandstone ) to 80 mmlka (claystones
with gypsum).
chemical species. The river Amazon is influenced by
low-concentration tributaries from tropical soil regions; the river Main passes densely populated areas
of different soils and rock types. Even here, only a
small percentage of the dissolved river load (mainly
N0 3 - and some Na+, Cl- and partly SO/") comes from
anthropogenic sources (Udluft 1978)
range of 30 to 300 mg/I. Within this wide range, one
can distinguish several groups with similar characteristics:
- Low solute concentrations (TDS between 30 and
ca. 100 mg/I). This group comprises rivers largely
draining either tropical regions with thick soil covers
consisting of stable neo-minerals (e.g. Amazon,
Orinoco, Congo, Indonesian rivers) or crystalline
rocks in wet humid areas (e.g. Scandinavia, effect of
dilution) and rivers in subarctic regions (Fig. 9.8).
In most of these cases, the river water contains litde hydrogen carbonate and less TDS than the groundwater circulating in unweathered or only partly altered rocks, except
quartzitic sandstones (Fig. 9.6). The concentration of dissolved Si0 2 in these river waters, however, approaches the
average ofworld rivers (lI mg/I). The Siberian rivers Lena,
Ob, and Yenisei coming from subarctic areas with sparse
vegetation also have low TDS values, although carbonatebearing rocks are present in their drainage areas.
- Medium solute concentrations (ca.150 to 300
mg/I). Rivers originating in the Alps and Himalayas
(including the Yangtze River), as well as the Mississippi River belong to this category (Fig. 9.8). They
all display medium values for calcium and hydrogen
carbonate due to the presence of carbonate rocks in
their drainage areas.
- High solute concentrations (>300 mg/I) are only
found in a limited number of large river basins which
are markedly affected by the dissolution of rock salt
and/or gypsum (e.g. the Murray River in Australia
and the Rio Grande River in North America, Fig.
9.8).
Global Mean Values of Solute Concentrations
According to Livingstone (1963) and Meybeck
(1979, 1983, 1987) the average river water of the
world contains ab out 115 mg/l TDS (load-weighted
mean) and has a composition as shown in Fig. 9.8.
The most important constituent (by weight) is hydrogen carbonate HC0 3 - (about 58 mg/I) which, however, is derived to a large extent (-70%) from decaying plant material in the soil zone and is recycled into
the atmosphere. HC0 3 - is followed by Ca 2 + (about 14
mg/I), Si0 2 (about 11 mg/I), and SO/" (10 mg/I).
These four components generally make up more than
80% of the total dissolved river load.
Fig. 9.9. Water chemistry (total dissolved solids
TDS) in various morphological and lithological zones of river catchments. a,b Rivers Amazon and Orinoco, tropical wet climate. (After Drever 1982; Stallard 1985). dRiver Main, Germany, humid temperate
climate. Numbers refer to dissolved load in groundwater (in t/km 2 /a. (After Einseie and Hohberger
1978). c,e Downstream changing concentrations of
Chapter 9 Denudation and Mass Transport
Variations in Water Chemistry Along
River Courses
The mean concentrations of dissolved species common1y vary along the courses of large rivers which
drain regions of various lithologies. The reason for
this observation is the fact that their water chemistry
is affected not only by tributaries but to a large degree by groundwater originating from rocks of different chemical composition (Sect. 9.2.2)_
The water chemistry of the Amazon River, for example,
changes greatly along its course from the Andes to the Atlantic (Fig. 9.9a, band c). Water from the snow-covered
Andes, relatively rich in dissolved constituents, is diluted
by tributaries draining areas with deeply leached tropical
soils (e.g. Drever 1982; Stallard 1985). The major part
(86%) of the dissolved load entering the Atlantic Ocean is
supplied by 12% of the total drainage area of the river (the
Andes). The chemical denudation rates of the different
morphotectonic units of the Amazon and Orinoco drainage
basins vary by a factor of almost 100 and, if the evaporitic
sediments are inc1uded, even by a factor ofup to 1000 (Fig.
9.9b).
In the river Main, a major tributary of the river Rhine
in central Europe (temperate, humid climate), the
water chemistry also marked1y varies along its
course. Most of the total solute load (86%) is provided by groundwater from different rock types (Fig.
9.9d and e). Of these lithologic units, carbonate and
sulfate-bearing sedimentary rocks deliver approximately 90% of the dissolved load, whereas regions
with crystalline rocks and quartzitic sandstones
(comprising 22% of the total drainage area) yield
only 5%_ The average specific transport rate (or specific yield of TDS) of the entire drainage basin
amounts to about 100 t/km2/a, which corresponds to a
mean chemical denudation rate of 40 mmlka. In reality, the denudation rates vary from approximately 5
mmlka (Bunter sandstone ) to 80 mmlka (claystones
with gypsum).
chemical species. The river Amazon is influenced by
low-concentration tributaries from tropical soil regions; the river Main passes densely populated areas
of different soils and rock types. Even here, only a
small percentage of the dissolved river load (mainly
N0 3 - and some Na+, Cl- and partly SO/") comes from
anthropogenic sources (Udluft 1978)