The Earth As Transformed
by Human Action
Global and Regional Changes in the Biosphere
over the Past 300 Years
Edited by
B. L. TURNER II
Graduate School of Geography,
Clark University
WILLIAM C. CLARK
John F Kennedy School of Government,
Harvard University
ROBERTW. KATES
Alan Shawn Feinstein World Hunger Program,
Brown University
JOHN F. RICHARDS
Department of History,
Duke University
JESSICA T. MATHEWS
World Resources Inslitute
WILLIAM B. MEYER
Graduate Schoof of Geography
Clark University
With computer graphics by Montine Jordan
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24
Sulfur
RUDOLF B. HUSAR
JANJA DJUKIC HUSAR
Sulfur, along with carbon, nitrogen, phosphorus, and water,
is a key substance of life on earth. When sulfur arises from
combustion of fuels or mineral processing, it causes air and
water pollution. When it is deposited onto agricultural land, it
is called fertilizer or nutrient. It is not just a matter of
semantics, but of fact that sulfur compounds can be damaging
to one part of the ecosystem and beneficial to another.
This chapter summarizes the flow of sulfur through the
environment using a mass balance framework. In particular,
we wish to compare the human~induced sulfur flows to the
natural flows in air, land, and water.
Sulfur in the Four Spheres: Atmosphere, Hydrosphere,
Lithosphere, and Biosphere
Sulfur compounds on earth are distributed among four
major environmental compartments, or conceptual spheres:
atmosphere, hydrosphere, lithosphere, and biosphere. Although this compartmentalization of nature is rather arbitrary,
it serves to organize our existing knowledge on the distribution and flow of sulfur. A schematic representation of
the four environmental compartments and their interrelation~
ships is shown in Fig. 24.1. The circles represent the spheres
and the curved arrows" the flow pathways of sulfur. In the
diagram, circles and curved arrows are used instead of boxes
and straight~line connections to emphasize the close, dynamic,
inseparable, organic coupling among the environmental compartments; if one compartment or linkage changes, all other
compartments respond.
In this conceptual frame, every sphere has a two~way
linkage to every other sphere, including itself. The two-way
linkage signifies that matter may flow from one compartment
to another in both directions; the two-way transfer within a
given compartment indicates movement of the substance
from one physical location to another without changing the
sphere. Since matter cannot be created or destroyed, the
questions we seek to answer are the location and chemical
form of the substance at any given time_
The atmosphere is best envisioned as a transport-conveyer
compartment that moves substances from the atmospheric
sources to the receptors. Its storage capacity for sulfur is small
Figure 24.1 The four environmental spheres.
compared to the other spheres, but it has an immense capability for spatially redistributing sulfur, on the order of 1 ,000 km
from its emission source.
The biosphere is the thin shell of organic matter on the
earth surface. It occupies the least volume of all of the
spheres, but it is the heart, or the chemical pump, of the
natural sulfur flow throegh nature. Through chemical reduction, the sulfur compounds are volatilized by the biota, and
the sulfur cycle is maintained.
The lithosphere is the solid shell of inorganic material at
the surface of the earth. It is composed of soil particles and of
the underlying rocks to a 50-km depth. The soil layer is also
referred to as the pedosphere. Most of the sulfur interaction
is with the soil, which itself is a mixture of inorganic and
organic solid matter, air, water, and microorganisms. Within
the soil, biochemical reactions by microorganisms are responsible for most of the chemical changes to sulfur. For our
purposes, soil and rock are mainly storage compartments for
sulfur.
410
Transformations of the Global Environment
The hydrosphere may be envisioned as two compartments:
a conveyor (river system) that (1) collects the substances
within the watershed and (2) delivers them to the second
hydrologic compartment, the oceans.
Multimedia budgeting is not new. So far there have been
two general approaches: global steady-state budgets, and
small, "calibrated," watershed studies of multimedia sulfur
flow. Our objective is to bridge the spatial gap between these
two geographically extreme approaches. In the following, we
wish to maintain a closed-system approach that is characteristic of global budgets, i.e., treating all environmental compartments of nature. At the same time, we wish to retain
sufficient spatial and temporal resolution so that the budgeting
scheme includes the key processes and a dynamic structure.
A close analogy exists between our perception of sulfur
ft.ow through nature and the materials flow through a
chemical plant, say, a refinery: it is made of storage vessels,
reaction vessels, as well as conveyors, pipes, valves, pumps,
and a control mechanism that monitors and regulates the
ever-changing flow through the plant. This naive, engineering
analogy for the flow of matter through nature should not be
taken too seriously, beca\lse human beings will never be able
to, nor should they, control completely the flow of substances
as the chemical engineer controls the refinery. The fact is,
however, that human beings through manifold activities have
changed the natural circulation of many substances. In most
cases, the result of human intervention in nature's affairs has
been to increase the natural flows, most notably by the mining
and combustion of fossil fuels. In many ways, however,
human beings have also reduced the natural flows, e.g., by
virtually eliminating forest fires compared }O preindustrial
times.
The removal of carbon, sulfur, nitrogen, and crustal
material from the long-term reservoir (mining) is continued
for two purposes: (1) to "produce" energy from the fossil
fuels, and (2) to use the extracted minerals for the production
of disposable or "permanent" objects for human use. The
production of energy refers to the release of sulfur, by
combustion, and subsequent chemical and physical treatment. Hence, an overwhelming fraction of the humaninduced releases to the atmosphere occur in fossil~fuel
combustion and metal smelting.
The major elements released to the atmosphere during
fossil~fuel combustion - carbon, sulfur, and nitrogen - are
generally considered nature-friendly. Each of these elements
had had a sizable flow (circulation) rate through nature
well before the arrival of human beings on the global sce,ne.
Fossil-fuel combustion has enhanced significantly the flow
of carbon, sulfur, and nitrogen compared to the preindustrial
or natural flow rates. The possible environmental problems are caused not by their toxicity, but rather by the
sheer quantities involved. Finding out the tolerance range
can be aided substantially by accounting for the natural
and human-made flow of these compounds. Specifically, the
question we need to explore is: what is human-induced circu~
lation compared to the natural biogeochemical flow? Undoubtedly, the perturbed geochemical flow has caused changes
in the chemistry of atmosphere, land, water, and biota.
Whether the environmental and biological consequences of
the changing chemical balance are considered beneficial or
harmful is beyond our consideration here.
After these introductory remarks, one section reviews the
flows and changes resulting from natural and human sources;
the next examines the atmospheric segment of the flow in
more detail; and a third discusses the relevant hydrological
data.
Sulfur Flows and Pools - The Contemporary Picture
The Global Sulfur Cycle and Pools
The global sulfur cycle has been under investigation for
several decades. (Eriksson 1960; Freney, Ivanov, and Rodhe
1983; Friend 1973; Granat et al. 1976; Robinson and Robbins
1968; Ryaboshapko 1983.) A summary graph from Granat et
a1. 1976, shown in Fig. 24.2, illustrates the main component
of the global sulfur cycle between air, land, and the oceans.
The main preindustrial sources to the atmosphere were
volcanic emissions (3 Tg S/yr) and volatile biogenic sulfur
emissions from land (3 Tg S/yr) and from the oceans (34 Tg 51
yr), totaling 61 TgS/yr. (1 Tg ~ 1 teragram ~ lOl2 g .) Granat
et al. (1976) also estimated that the preindustrial sulfur runoff
through the world's rivers was 60Tg Slyr, mostly due to
weathering of rocks and soils. The estimated human contribution to the atmospheric emissions in the early 1970s was
65 TgS/yr.
The utIlity of such global views is that they show that the
global fluxes of sulfur induced by humans and those from
nature are of comparable magnitude. Human perturbation of
17~Seaair
Landair~2+16
A"'t"~P~g"'i'
~:~f;/3
/
Volatile sulfur
w".'" I"",d soil
34,\
19+16
Volatile sulfur
i I
I
40
fro~
Wet and dry
depottion
Gaseous
Figure 24.2 The global sulfur cycle in Tg S/yr. Small type denotes the
estimated natural/preindustrial contribution, and the bold figures
represent estimates for the anthropogenic contribution. Source:
Granat et al. 1976.
24. Sulfur
411
Table 24-1 Major sulfur reservoirs.
concentration occurs in effusive rocks (0,04% S), The amount
of sulfate sulfur varies from fractions of 1% in humic pelagic
formations to solid sulfate layers in evaporites,
In the pedosphere, the bulk of the sulfur Occurs in organic
compounds in soil and in living plants (1.210 4 Tg S), whereas
in the ocean, inorganic sulfate predominates, Carbonyl
sulfide appears to be the dominant form of sulfur in the
atmosphere (Freney et a1. 1983.)
Reservoir
Atmosphere
Troposphere
Sulfate in aerosols
Sulfur dioxide
Carbonyl sulfide
Other reduced sulfur gases
Total in troposphere
Stratosphere
TgS
0.7
0.5
2.3
0.8
4.3
0.5
4.8
Hydrosphere
Ocean water
1.3
X
10'
Lithosphere
Continental and subcontinental
Sedimentary
Granite
Basalt
, Oceanic
Sedimentary (layer J)
Tholeitic and olivine basalt (layer II)
Layer III
5.2 x lOY
7.8x109
8.8 X 10<.1
0.3
X
109
0.6 X lOy
1.6
X
109
24.3 X 109
Pedosphcre
Soil
Soil organic matter
Land plants
2.6
X
105
1.1 X 104
760
2.7
X
105
Source: Freney et al. 1983
the global sulfur cycle, however, is concentrated over the
industrialized parts of the world, which constitute a small
fraction ofthe earth's surface area. Hence, over those regions
the human-induced sulfur flow exceeds the natural flows by a
wide margin, A major purpose of this chapter is to illustrate
the spatial and temporal pattern of the human-induced sulfur
flow,
Table 24-1 summarizes the current information on distribution of sulfur between the various spheres, The bulk of
sulfur is contained in the lithosphere (24 x !09 TgS),
moderate amounts occur in the pedosphere, and only small
amounts (4,6TgS) are found in the atmosphere at anyone
time,
Within the lithosphere, most of the sulfur occurs in rocks of
the present continents and subcontinents (22 x 10 9 TgS), and
the major forms are metal sulfides and sulfates, The
maximum concentration of reduced sulfur is found in argillaceous rocks of platform areas (0.4% S), and the minimum
Natural Sulfur Mobilization
Natural sulfur mobilization processes involve rock and
soil weathering as enhanced by the water cycle, volcanic
emissions, the release of volatile sulfur by biota, and the
distribution of sea spray by the atmosphere.
Weathering of soils and rocks constitutes a major sulfur
source to rivers (Bischoff, Paterson, and MacKenzie 1982).
When atmospheric water is deposited onto the surface,
sulfide and sulfate minerals release the sulfate ion to the
hydrosphere, Based on the examination of the sulfur runoff
from the major rivers of the world, Husar and Husar (1985)
concluded that the global weathering rate should range
between 40 and 80 Tg S/yr. This estimate is consistent with
that of Granat et a1. (1976) - 60 Tg S/yr.
Gaseous, reduced sulfur compounds are formed by biological reduction of sulfates during decomposition processes.
Estimates of the oceanic and the continental biogenic sulfur
flow into the atmosphere vary from 3.3-30Tg S/yr (Bolin and
Charlson 1976; Varhelyi and Gravenhorst 1981) to 280Tg S/yr
(Eriksson 1963), Most recent data indicate the values of less
than 30 Tg S/yr, emitted mostly over the oceans. The geographic pattern of zones of high biological activity is depicted
in Fig. 24.3 (Ryaboshapko 1983). It includes both equatorial
and arctic coastal marine territories.
The estimates for global volcanic emissions to the atmosphere range between 1 TgS/yr (Kellogg et a1. 1972) and 10Tg
S/yr (Davey 1978). We tend to support estimates of Granat et
a1. (1976) of about 3 Tg S/yr.
The natural flow of sea-salt sulfur is an elusive quantity,
since most of the salt originates in deposits over the oceans.
According to Granat et a1. (1976), only about 4 Tg/yr of seasalt sulfur is deposited over land,
Human-induced Sulfur Emissions to the Atmo~phere
The human-induced sulfur mobilization that is emitted
to the atmosphere is responsible for much of the concern
related to sulfur, because it contributes to acid rain and other
effects. Atmospheric sulfur emissions are highly nonuniform
over the continents (Fig. 24.4), The Northern Hemisphere is
responsible for over 90% of the global sulfur emissions, as
depicted in the emission density maps of the continents.
Europe, due to its high emission rate and small size, has an
emission density of 3.3 g S/m 2 /yr, followed by North America
(0.8 gSlm2/yr) and Asia (0.7 g Slm'lyr). Within these continents, the emissions are concentrated over industrialized
subregions.
The spatial distribution of sulfur emissions in North
America is shown in more detail in Fig, 24,5, which illustrates
that the emission density over the Ohio River Valley exceeds
412
Transformations of the Global Environment
[J
II
II
!!Ii'
Zones of high
biological activity
Industrial regions
Zones of aeolian
weathering of sulfates
(J
Figure 24.3 Characteristic zones of the world. According to
Ryaboshapko 1983.
o
9 S/m 2 /yr
uj
Figure 24.4 Sulfur emission density of the continents. Source:
Authors' calculations.
0 <0.5
II OS2.0
II >2.0
24. Sulfur
413
gJm 2 Jyr
Ratio
[]
•
II
II
0,5 -1.0
1.0 -3.0
3.0-6.0
>6.0
Figure 24.5 Sulfur emission density for North America, 1977-78.
Source: Authors' calculations.
0
0-1.0
II
II
1.5-2.0
•
1.0 - 1.5
>2,0
Figure 24.7 Ratio of the river sulfur runoff density to total
atmospheric sulfur plus fertilizer sulfur deposition. Source: Authors'
calculations.
6gS/m 2/yr. The eastern U.S. average is about 3.4gS/m 2 /yr,
comparable to the emission density of Europe.
Multimedia Budget/or the Eastern United Stales
This section illustrates the multimedia flow of sulfur
over the eastern United States by examining the geographic
pattern of each budget component (Husar and Husar, 1985).
This will illustrate the major flow and budget components on
a spatial scale that is relevant to effects such as acid rain.
The sulfur dry deposition from the atmosphere has been
estimated from a regional air-pollution model. The average
S g/m'/yr
<S
•
()
0
II
II
II
1.0 - 2.0
2.0- 4.0
4.0-8.0
>8.0
1~
Figure 24.6 The sum of dry and wet human-made sulfur deposition
(g S/m 2 yr) for the eastern United States (total atmospheric sulfur
deposition) for 1978. Source: Authors' calculations.
dry deposition of the eastern United States has been
estimated to be 1.4 g S/m 2 Jyr. The wet deposition as monitored
by several precipitation chemistry networks and the resulting
wet deposition from anthropogenic sources was estimated to
be 0.7 g S/m 2 /yr.
The sum of the dry and wet human-induced sulfur deposition
from the atmosphere for the eastern United States is shown
in Fig. 24.6. In the Ohio River region, the total deposition
exceeds 4gS/m 2 /yr and the average in the eastern United
States is about 2.1 g S/m 2 /Yr.
The map of sulfur runoff density shows that over the upper
Ohio River region the sulfur runoff exceeds lOgS/m 2 /yr,
whereas over the coastal plains of South Carolina, Georgia,
and Alabama the runoff is less than 1 gS/m'/yr. Over the
eastern United States the river runoff averages 4.8 g S/m 2 /yr.
The ratio of river sulfur runoff to the sum of atmospheric
sulfur deposition and fertilizer use is shown in Fig. 24.7.
When the ratio is 1, the atmospheric and fertilizer input to the
region is equal to the sulfur output through the rivers, For the
southeastern plains, North and South Carolina, Alabama,
and Georgia, this ratio is <1, i.e., the river runoff over the
coastal plains is less than the atmospheric and fertilizer input.
On the other hand, for the industrialized Ohio River region,
this ratio is > 1, where the runoff exceeds the atmospheric'and
fertilizer use by a factor of 2. Thus, in the Ohio River region,
there are additional sources of river sulfur, beyond atmospheric deposition and fertilizer use, whereas in the southeastern plains, the land is a sink for atmospheric and fertilizer
sulfur.
This analysis clearly indicates that the multimedia budget
of sulfur needs to be treated on a spatial scale that is roughly
comparable to the spatial scale of the natural variations.
Nevertheless, it is useful to assemble a sulfur·f1ow diagram
that characterizes the average of the eastern United States
414
Transformations of the Global Environment
oa
~
VEGETATION
06
1.5
SOIL· ROCK
1.7
SURFACE WATERS
Figure 24.8 Multimedia sulfur flow diagram for the eastern United
States (g S/m2yr). Source: Author' calculations.
(Fig. 24.8). The units of flow rate are given in gS/m2/yr,
averaged over the area of the eastern United States (2.5 X
10 12 m2 ). The density of sulfur emissions to the atmosphere is
3.5 gS/m2/yr; fertilizer use is 0.2 gS/m 2/yr; and the average
mine runoff is estimated at 1.0gS/m 2/yr (by difference). The
atmospheric emission rate (3.5 g S/m 2 /yr) is distributed as
follows: lAgS/m 2/yr dry-deposited over land, 0.7gS/m2/yr
wet-deposited over land, and 1.4gS/m2/yr exported out of
the region. Terrestrial vegetation thus receives 2.1 gS/m 2 /yr
from the atmosphere, mostly through dry deposition. The
vegetation sulfur is partly transmitted to the soil (1.5 g SI
m'lyr), and a fraction (0.6gS/m2/yr) directly to the surface
waters. The soil compartment thus receives O.2gS/m 2/yr
from fertilizers, 1.5 gS/m 2 /yr transmitted through vegetation.
The soil release to the surface water is then estimated as
3.2gS/m2/yr, which includes 1.5 gS/m 2 /yr released from soilrocks by weathering. The total input to surface waters is
3.8gS/m 2/yr from the soil and vegetation (sewage) and
1.0gS/m 2 /yr from mine drainage, i.e., 4.8gS/m2/yr. The
latter is the measured sulfur runoff value.
The flow of sulfur through the environment of the eastern
United States is dominated by fuel-combustion emissions to
the atmosphere. Over the Great Lakes and over the Ohio
River valley, mine drainage and sewage input is comparable
to the atmospheric input. In the coastal plains of the southeastern United States, in which mine drainage and sewage are
insignificant, there is actually a loss of sulfur in the soilvegetation. The subregional differences in the multimedia
sulfur budget dictates that for future studies the spatial
resolution of such budgeting be reduced to 100-200 km or
less. The preceding constitutes a ITlass flow budget that is
consistent with the available data. For many linkages,
however, no data were assembled at this time.
Histories of Sulfur Mobilization by Human Action
The human-induced mobilization of sulfur falls into
three major categories: (1) mining and combustion of fossil
fuels, (2) mining and processing of sulfur-containing ores, and
(3) agricultural movement. The total fuel combustion,
smelting, and mined sulfur was es tirnated to be 148 Tg S/yr in
1984.
Fuel Combustion and Metal Smelting. Fossil-fuel production
is the most important category of hUIllan-made sources, and it
amounts to about l20TgS/yr (Fig. 24.9). Coal contains most
of the sulfur, followed by oil and natural gas. Smelting of
metals, including copper, zinc, and lead, is another significant
source of sulfur mobilization, aITlounting to about 13 Tg S/yr.
Historically, coal combustion contributed most of the the
sulfur mobilization. More recently, however, sulfur mined in
crude-oil products also became significant.
It is worth noting that the sharp rise of the sulfur
mobilization that began in the 1950s came to a halt by the
mid-1970s. The leveling of sulfur mobilization is caused
mainly by the reduced flow of oil products.
Sulfur Mining. Sulfur is mined either as elemental sulfur or
from sulfur-containing ores. Currently, the global minedsulfur production is estimated at 24 TgS/yr. The historical
trend of global sulfur mobilization due to mining is included
Mined
•
Coal, oil, gas
and metals
..
o
Mobilized
Fuels and metals
Emitted to atmosphere
Recycled
Coal, oil and
ga'
Emitted
1940
1960
1980
Figure 24.9 Sulfur flow from fuels and smelting. Data from United
Nations 1986; and U.S. Bureau of Mines Mineral Yearbooks
1933-1985.
1860
Figure 24.10 World industrial sulfur mobilization. Data from United
Nations 1986; and U.S. Bureau of Mines Mineral Yearbooks
1933-1985.
24. Sulfur
415
in Fig. 24.10 and shows a leveling-off during the decade
1975-1985.
Agriculture, Land Use, and Fires. Vegetation contains
sulfur, and agricultural activities mobilize sulfur through
the movement of crops. Similarly, transport of forest products contributes to the sulfur mobilization. Major changes in
land use also tend to influence the sulfur flow. Human beings
have also influenced (reduced) the occurrence of forest fires
and hence the natural biomass.
According to the U.S. Statistical Abstracts, the 1978
production of farm products in the United States was only
about 350 million tons. About one-third, or 100 million tons,
was exported to other countries. If we take the crop sulfur
content to be 0.3% by weight, 1 million tons of sulfur were
removed from the land by agricultural products. Much of this
removal occurred over the fertile midwestern farmland.
Following more detailed analysis, Beaton et al. (1974)
estimated that Americans are removing about 4 million tons
of sulfur per year by way of field or forage crops. Hence, this
sulfur flow by ground transportation of crops, from the
producers to the consumers, constitutes a significant soildepletion rate of these nutrients.
Regrettably, we are not in position to assemble the global
sulfur flow rates due to agriculture, land use, and fires.
Hence, they are omitted from the following discussions.
Atmospheric Emission Trends. A substantial fraction of the
sulfur that is mobilized by humans is emitted into the atmosphere as a waste product of fuel combustion and metal
smelting. This fraction is responsible for major environmental
effects, including acid rain, regional haze, and materials
damage to buildings and paints. For these reasons, much of
the impetus for the study of the sulfur cycle is driven by the
effects of sulfur as it passes through the atmosphere.
The trend of the total human-induced sulfur flow (Fig.
24.10) is used to estimate the atmospheric emissions. It is
assumed that all the mined sulfur is transformed to solid or
liquid chemicals and that it is not vaporized to the atmosphere. A fraction of sulfur contained in natural gas, in crude
oil, and in copper, zinc, and lead ores is extracted during the
refining process and is referred to here as recycled sulfur. In
1984, this fraction was about 30TgS. It is here assumed that
this fraction is not emitted to the atmosphere. Hence, the
recycled sulfur is mobilized from the geological reservoir by
mining, but it is not emitted to the atmosphere, being used
instead for agricultural and industrial purposes.
The fraction offuel and metal-ore sulfur that is not recycled
is assumed to be emitted to the atmosphere. In 1984, the
global human-induced sulfur emissions to the atmosphere
were estimated to be 90 Tg S, or 60% of the total mobilized
sulfur.
It is encouraging to observe that the global atmospheric
sulfur emissions have remained essentially constant for the
past decade. This constancy is evidently the consequence of
reduced oil consumption and increased recycling as part of
fuel and metal-refining processes.
Humall
illduced
Biogellic
emissiollS
Natural
weatherillg
1900
1920
1940
Figure 24.11 Global natural and human-induced sulfur mobilization.
Comparison of Natural and Human~lnduced Flows. The
global flow of sulfur induced by natural processes and human
action is displayed in Fig. 24.11. The natural mobilization is
dominated by weathering and by biogenic emissions. These
rates were assumed to be invariant over the past 150 years,
which may be a rather poor assumption. The human-induced
sulfur flow increased gradually until the 1950s, followed by a
sharp rise until the mid-1970s, and remaining roughly
constant since then. Hence, on the global scale, the current
sulfur flow from human actions exceeds the natural flow.
Over the industrialized regions of Europe and North America
the human-induced flow may be 5 to 10 times the natural
flow.
It is also worth considering a few estimates of sulfur flow
rates arising from simple "back-of-the-envelope" calculations.
Suppose that we pile the U.S. coal consumption over the
past century (amounting to 500 million t/yr) into a single
mountain. It would occupy 25 km 3 , j.e., a pyramid with a base
area of 6 X 6 km and 2 km high.
. ..
";""~Spread over the entire eastern half of the United Stat~~ a
layer of coal would be about 1 cm thick. From a geophysical
weathering perspective, this means that currently about
150 g S/m2/yr of crustal mineral material "goes up in smoke,"
considering coal consumption only in the eastern United
States. For comparison, the natural weathering of the earth's
surface minerals carried to the oceans in rivers is about
20g/m2/yr. Thus, humanity, as a geological redistributor of
the earth's crustal material, exceeds nature by an order of
magnitude over the eastern United States.
Over the past 100 years, the emission density average over
eastern North America was about 100-200gS/m'/l00yr.
Most of that sulfur returns to the ground somewhere over
eastern North America, resulting in an average sulfur flow of
100 g S/m'/100 yr. For comparison, the total sulfur content of
parent soils is 3-30 g S/m'.
It is also instructive to consider the sulfur flow from a
biological perspective: the U.S. average daily per capita
emission rate to the atmosphere is roughly 200 g sulfur
\
./
416
Transformations of the Global Environment
(400gS0 2). This amount is comparable in weight to the daily
per capita food consumption. The U.S. human~rnade sulfuremission rate is about 15 x 1012 g S/yr (15TgS/yr). Suppose
that we distribute these emissions uniformly over 8 x 1012 m2
of contiguous U.S. territory. We arrive at an average
emission density of 2gS/m 2 /yr, which is comparable to the
density of sulfur contained and removed yearly by agricultural
products, such as corn and wheat, from cultivated agricultural
land.
Water is continuously recycled near the earth's surface by
evaporation, condensation, and runoff. That is, it flows in
rivers from the lithosphere to the hydrosphere, and it returns
to rewash the land by way of the atmosphere. All watersoluble elements are certain to track the water cycle at least
partway from land to sea. In the biosphere, at least three
elements besides those of water fall in this mobile class carbon, nitrogen, and sulfur. Among airborne sulfur compounds are S02 and H 2S. It is interesting that when sulfur is
recycled, its valance changes: it is generally more reduced in
the biosphere than it is in the geosphere. Both the atmosphere
and the hydrosphere constitute an oxidizing environment,
whereas the biosphere tends to reduce these compounds. In
fact, it is the chemical reduction, or hydrogenation, that
makes sulfur volatile. In the absence of the biosphere, all
sulfur compounds ultimately would be washed to the oceans
and remain there.
It is fortunate that the sulfur transported with the water can
be monitored easily at two points in the cycle: (1) in the
precipitation of water as it reaches the earth's suface from the
atmosphere, and (2) in river runoffs as the surface waters
enter the ocean. The sulfur flow through river runoff was
discussed in this section; the sulfur in precipitation is treated
in the atmospheric section.
Historical Changes in Sulfur Flows: Atmosphere
The current global pattern of atmospheric sulfur can be
reconstructed from measurements of ambient concentrations
and precipitation chemistry, but historical data of atmospheric
sulfur compounds covering the past 100 years do not exist,
Nevertheless, the role of human activities in changing the
sulfur flow pattern can be estimated from spatial analysis of
the current chemical climate. It can be argued that measurements at remote locations in the Northern Hemisphere and
much of the data from the Southern Hemisphere represent
the preindustrial or natural sulfur flow. The excess flow rates
measured at industrial hot spots then represent the human~
induced flow. This section utilizes this approach to infer the
magnitude of human sulfur-flow enhancement through the
atmosphere.
The atmosphere disperses the sulfur over large geographic
areas, whereas the river system collects the sulfur over the
watersheds. The specific processes that are involved include
atmospheric dispersion with the winds, wet deposition
through precipitation, dry deposition through gaseous
absorption.
Atmospheric Transport
The atmosphere transports sulfur from the source to
the receptor. For sulfur compounds, this atmospheric redistri-
bution occurs over a SOO-I,OOO-km region surrounding each
source, which corresponds to an atmospheric residence time
of 2 to 4 days.
Wet and Dry Deposition
Sulfur is removed from the atmosphere by wet deposition (rain, snow, fog), following the path of the water cycle,
and by dry deposition (i.e., absorptio~, adsorption, and
settling to the earth surface).
It is our current thinking that on a regional scale, most of
the gaseous sulfur is absorbed or adsorbed by vegetation, and
only a minor fraction is taken up directly from the atmosphere
by soil and by continental surface waters.
The rate of wet deposition of sulfur can be obtained
directly from measurements. Motivated by increasing concern
about acid rain, several major rain-chemistry monitoring
networks have been made operational over Europe and
North America.
The continental-scale, wet-deposition patterns for North
America are shown in Fig. 24.12. The highest sulfate
deposition rate and concentration in precipitation occurs in
the region surrounding the eastern Great Lakes. The sulfate
wet deposition there exceeds 1 g S/m 2 /yr. For the region east
of the Mississippi River and south of the James Bay (defining
here eastern North America, ENA, area 5.8 X 10 12 m 2), the
sulfate wet deposition is about O.63gS/m 2 /yr. The lowest
sulfate deposition rate, about 0.lgS/m 2 /yr, is measured in
northwestern Canada and the southwestern United States,
Both of these regions have less than 0.5 m/yr of rainfall. The
weighted average sulfate concentration in precipitation ranges
between 15lleqvll. (in remote U.S. and Canadian regions)
and about 70 lleqv/L in the vicinity of the Great Lakes.
Hence, although the average regional deposition rate varies
tenfold over the continent, the average precipitation sulfate
concentration increases only fivefold from remote regions to
industrial regions.
It is also instructive to compare the measured wet~depo~
sition pattern and rates to the emission field of human-made
sulfur over the eastern United States (Fig. 24.5). The average
emission density over the eastern United States is 3.5 g SI
m2 /yr, whereas the average wet deposition over the same
region is 0.73 g S/m 2/yr, (i.e., about 20% of the known
human-emissions). If we further assume that the natural
sources contribute to wet deposition on the average 0.07 gSI
m 2 /yr, (Husar and Holloway 1982), the measured wet
deposition of sulfur amounts to less than 20% of the human~
made sulfur. The remaining 80% of the human~made sulfur is
then either dry-deposited as S02 or SO; or is exported from
the region by the prevailing winds. This leads one to conclude
that human-made sulfur deposition over the eastern United
States is 5 to 10 times that of the natural deposition.
Export to the Oceans
In spite of the uncertainties associated with the spatialtemporal coverage, the sampling and analytical procedures,
and the interpretation of the wet-deposition data, it is most
gratifying that such a continental-scale data base currently
exists for North America and Europe. Prudent use of such a
24. Sulfur
417
~eq/I
iO -25
0.10-0.25
0.25·0.50
0.50 - 1.00
>1.00
II
II
II
25-50
50 "75
>75
Figure 24.12 (a) Sulfur wet deposition (g S/m2/yr) and (b)
concentration (/-leq!I.) for 1977-1980 as monitored by the
precipitation chemistry networks.
Sulfur
Concentration
1970
mg S~
0
iii
II
<3.0
3.0·8.0
>8.0
Figure 24.13 Sulfur concentration in the world rivers around 1970.
data base undoubtedly will provide us with a much-improved
understanding of the flow of sulfur through the environment.
Historical Changes in Sulfur Flows: Hydrosphere
Rivers are the links between the atmosphere, the soil,
and the oceans. Atmospheric precipitation is the principal
source of water that makes up the lakes and rivers of the
earth's surface. The chemical content of river water reflects the
precipitation composition, physicaJ and chemical weathering
processes, industrial and residential waste water, and organisms' activity in the soils and rivers.
The chemical form of sulfur that occurs in surface waters is
predominantly in the form of sulfates (SO,). The sulfate ion
is chemically stable in most of the environments to which
natural waters are subjected.
418
Transformations of the Global Environment
Sulfur Runoff
1970
9 81m', yr
0
II
II
<1.2
1.2-2.0
,2.0
Figure 24.14 Sulfur runoff in the world rivers around 1970.
World River Runoff
Following the pioneering work of Livingstone (1963),
there is a reasonable understanding of mean composition of
major world rivers (Alekin and Brazhnikova 1968; Meybeck
1979).
As part of a continuing multimedia budgeting work, Husar
and Husar (1985) have recently reexamined the data on the
sulfur runoff in major rivers of the world (Figs. 24.13 and
24.14). Their primary goal was to examine the riverborne
flow of minerals over regions of the world that are weakly
influenced by people. In the Northern Hemisphere, such
regions should include the eastern Siberian rivers in Asia and
the arctic rivers in North America. They found that the major
rivers of the world carry about 130 10 12 gSlyr (105 TgSlyr in
the Northern Hemisphere and 25 Tg Slyr in the Southern
Hemisphere) into the oceans. By comparison, the global
anthropogenic sulfur emissions have been estimated to be
79 Tg Slyr, out of which 72 Tg Slyr are emitted in the
Northern Hemisphere, whereas only 7TgS/yr are emitted in
the Southern Hemisphere (Varhelyi 1985).
A density map of sulfur river runoffs for the world is given
in Fig. 24.14. It is evident that the sulfur river runoff is highest
in the industrially influenced regions of North America and
Europe, where it exceeds 1. 75 gS/m 2 /yr. The major rivers in
South America, Africa, and Australia show a sulfur runoff of
less than 1 g Slm 21Yr. Notably high sulfur runoffs are reported
for the island countries of Japan, Indonesia, New Guinea,
and New Zealand. Inspection of the chlorine runoff shows
that these high sulfur runoffs are not attributable to sea salt.
As a global average, the sulfur runoff is on the order of
1 g Slm 21Yr.
For our purposes, the most interesting results are those for
the arctic rivers of North America: the Yukon, McKenzie,
and Nelson rivers, which show a runoff of 1-1.75 gS/m 2 /yr.
In particular, the basins -of McKenzie and Nelson rivers are
within the Canadian Shield, which has a geologic structure
similar to that of the northeastern United States and
southeastern Canada. A puzzling question arises: what is the
source of high sulfur runoff in this region of North America?
Preliminary simulation modeling for atmospheric long-range
transport of human-made sulfur over North America suggests
that atmospheric deposition from human-made, North
American sources are unimportant for the Yukon, McKenzie,
and Nelson drainage basins.
A limited historical data set for river sulfur concentrations
is available for a few rivers in Europe and'North America, as
shown in Figs. 24.15, 24.16, and 24.17. The trend of sulfur
Sulfur concentration (mgtl)
35
•
+
30
o
25
•
Rhine
Seine
Oder and Vistula
..
.6. Elba
.
20
.
•••
"fl•••
0
15
.
10
!-~
--.--.
+__0 _ _- - /__-'>-
1840
1860
1880
1900
1920
1940
1960
1980
Figure 24.15 Trends in sulfur concentration in European rivers:
Rhine (II), Seine ( +), Oder and Vistula (0), and Elbe (6). Sources:
Meybeck 1979; Paces 1982; Steele 1980.
24. Sulfur
419
Sulfur concentration
(ma/I)
•
20
+
SI. Lawrence
•
15
10
.lL...c.•~._ _ _ .",~~
1840
1860
1880
action in Europe is perturbed more significantly then in
eastern North America, which is consistent with the observations (Fig. 24.4) that the current sulfur emission density for
Europe significantly exceeds that in eastern North America.
Mississippi
•
1900
+
1920
1940
1960
1980
Figure 24.16 Trend of sulfur concentration in North American
fivers: St Lawrence (+) and Mississippi (II). Source: Meybeck 1979.
concentration in European rivers (Fig. 24.15) shows about
a four-fold increase since the turn of the century. The sulfur
concentration in the Rhine, Seine, OcteT, Vistula, and Elbe
rivers ranged between Srng/l. and lOmg/l., 'before this
century. By the 1970s, the concentration range had increased
to 20-35 mgll.
In North America, the sparse data for the Mississippi and
St. Lawrence rivers show only slight increases in sulfur
concentration. Both of these rivers are somewhat removed
from the main industrial regions centered around the Ohio
River Valley. The map of sulfur concentration for these rivers
for the turn of this century is given in Fig. 24.17. It is evident
that, with the exception of the Rhine River, these early
concentration data are comparable to the values measured in
the rivers over the remote regions.
The historical river sulfur concentration data show an
increase in European rivers that is a factor of about 3
compared to a factor of 1.5 in the major North American
rivers. This would indicate that the sulfur flow due to human
Regional River Runoff
Budgets of sulfur, nitrogen, and other nutrients also
have been investigated for small experimental watersheds in
North America and Europe. The flow of ions has been
investigated through the forest canopy (Horntvedt et al.
1980), soil (Seip and Freedman 1980), small watersheds such
as Hubbard Brook, New Hampshire. (Likens et al. 1977),
southern Swedish lakes (Environment 1982), and small
streams in eastern Kentucky (Dyer and Curtis 1977) to assess
the relationship of atmospheric deposition and surface-water
concentration or effect of strip mining on first-order streams.
However, these studies are very few and cover only small
geographical areas. Thus such results cannot be easily
extrapolated to a regional scale.
For the United States, a spatially extensive and long-term
data base exists on the chemical composition of surface
waters. These data are available from the U.S. Geological
Survey (U.S.G.S) on magnetic tapes. In what follows we
present a small subset of this rich data base ... (Husar and
Husar 1985).
For the purposes of establishing a sulfur budget over regional scales, we have chosen 52 rivers in the eastern United
States with moderate watersheds ranging from 600 km 2 to
45,000 km 2 , These watersheds are sufficiently large to integrate
the small-scale runoff variability but sufficiently small to
yield the spatial runoff pattern for different parts of the
United States.
The 52 eastern U.S. rivers were selected because they have
o
mg 8/10
rJ
Del
Figure 24.17 Sulfur concentration of European and North American
rivers, 1846-1906.
<3.0
III
3.0-8.0
•
>8.0
420
Transformations of the Global Environment
Sulfur runoff (9 m 2/yr)
Southeastern Rivers Average (9 Rivers)
1.0
.8
,
A '"
~
A JlJ
A)\AI
.6
.4
/
f-2---1920
1930
'V
1940
1950
1960
1970
1980
Figure 24.20 Trend of average sulfur runoff in nine rivers of the
coastal plains in the eastern United States.
sulfur compounds to the concentration trends in rivers
through a physicochemical model. Nevertheless, it is comfort~
ing to observe the consistency of these trend data.
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Figure 24.18 Watersheds of the rivers in the Pennsylvania- West
Virginia mining district and over the coastal plains of the eastern
United States.
Pennsylvania Rivers Average
Monongahela, Youghlogheny, Mahoning
Sulfur runoff (g/m2/yr)
25
20
...
15
..
10
..
5
1920
1930
1940
1950
1960
1970
1980
Figure 24.19 Trend of sulfur runoff in the Monongahela,
Youghiogheny, and Mahoning rivers of the Pennsylvania- West
Virginia mining district.
reasonable long water data records for trend analysis. In
the following, we present the sulfur runoff trends for two
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coal-mining districts of Pennsylvania and West Virginia, and
another in the coastal plains of North Carolina, South
Carolina, and Georgia (Fig. 24.18).
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