Ecological Research Series
ANION MOBILITY IN SOILS: RELEVANCE TO
NUTRIENT TRANSPORT FROM TERRESTRIAL
TO AQUATIC ECOSYSTEMS
Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Corvallis, Oregon 97330
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RESEARCH REPORTING SERIES
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EPA-600/3-77-068
June 1977
ANION MOBILITY IN SOILS
Relevance to Nutrient Transport from Terrestrial to Aquatic Ecosystems
by
Dale W. Johnson and Dale W. Cole
College of Forest Resources
University of Washington
PR-CC6991995-J
Project Officer
Donald H. Lewis
Assessment and Criteria Development Division
Corvallis Environmental Research Laboratory
Corvallis, Oregon 97330
CORVALLIS ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CORVALLIS, OREGON 97330
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DISCLAIMER
This report has been reviewed by the Con/all is Environmental Laboratory,
U.S. Environmental Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the views and policies
of the U.S. Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation for use.
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FOREWORD
Effective regulatory and enforcement actions by the Environmental Protection
Agency would be virtually impossible without sound scientific data on pollu-
tants and their impact on environmental stability and human health. Respon-
sibility for building this data base has been assigned to EPA's Office of
Research and Development and its 15 major field installations, one of which
is the Corvallis Environmental Research Laboratory (CERL).
The primary mission of the Corvallis Laboratory is research on the effects of
environmental pollutants on terrestrial, freshwater, and marine ecosystems;
the behavior, effects and control of pollutants in lake systems; and the
development of predictive models on the movement of pollutants in the bio-
sphere.
This report describes the influence of soil anion adsorption properties on
the leaching of nutrients from soils and subsequent transport to streams.
This work was undertaken as a part of a research program at CERL to determine
the effects of acid rain on forest ecosystems.
A. F. Bartsch
Director, CERL
m
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ABSTRACT
Nutrient transport from terrestrial to aquatic ecosystems is strongly
mediated by soil chemical interactions. Ions depositied on or biologically
released within the soils can enter into a variety of exchange and precipita-
tion reactions prior to (or instead of) entering aquatic ecosystems. This
report reviews the current knowledge of soil anion adsorption reactions and
their effects on leaching, and suggests a simple model, based on anion produc-
tion and adsorption considerations, to predict and explain nutrient transport.
The relationship of this approach to that based on cation production and
adsorption is discussed.
This report was submitted in fulfillment of Contract No. PR-CC6991995-J
by Dr. Dale Johnson under the sponsorship of the U.S. Environmental Protection
Agency; work was completed as of March 31, 1977.
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CONTENTS
Foreword iii
Abstract iy
Figures vi
Tables vii
1. Introduction 1
2. Factors Affecting Anion Production and Mobility in Soils:
A Brief Literature Review 4
3. Summary and Conclusions 20
References 22
Appendix
A Brief Summary of Some Approaches Used in Modeling Cation
Exchange and Leaching in Soils 26
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FIGURES
Number Page
1 Conceptual scheme of ionic transport from terrestrial to
aquatic ecosystems using anion mobility as an index .... 3
2 Schematic diagram of events associated with carbonic acid
leaching in soils 5
3 Response of HCCU to changes in pH and C02 pressure (PC03) . 6
4 Schematic diagram of bicarbonate leaching following
harvesting or burning 8
5 Schematic diagram of transformation and leaching of urea
within the soil profile 9
6 Schematic representation of the effect of pH on surface
charge of sesquioxides 12
7 Comparison of sulfate adsorption isotherms for the Everett
and Bohannon soils 15
8 Adsorption isotherms for chloride, sulfide, nitrate and
phosphate on the Everett soil A-horizon 18
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TABLES
Number Page
1 Measured and Modeled Sulfate Flux and Soil Sulfate
Concentration After Acid Application 17
vn
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SECTION 1
INTRODUCTION
Nutrient transport from terrestrial to aquatic ecosystems is strongly
mediated by soil chemical interactions. Ions deposited on or biologically
released within the soil can enter into a variety of exchange and precip-
itation reactions prior to (or instead of) entering aquatic ecosystems. If
nutrient ions are precipitated or adsorbed to the soil, they cannot travel
out of the terrestrial ecosystem via solution phase, that is nutrients cannot
leach through the soil. Soil scientists have therefore had an intense inter-
est in soil adsorption reactions and their effects on leaching for many
decades. Historically, cation exchange reactions have been studied in great
depth by soil scientists because most soils have a greater cation exchange
capacity than an anion exchange capacity (Bear, 1955). Since cation exchange
is far better known and better defined than anion exchange, there are many
models available which describe cation exchange and cation movement through
the soil (Biggar, et al. 1966; Carlson and Buchannan, 1973; and Dutt and
Tanji, 1962, to name only a few examples). Bolt (1967) gives an excellent
review of cation exchange equations used in soil science and the theories
behind them, and Reiniger and Bolt (1972) give an excellent discussion of the
application of the theory of chromatography to cation exchange and leaching
in soils. A brief summary of some aspects of cation exchange modeling is
given in the Appendix, but no attempt will be made here to review the mass of
literature on the subject. The reader is referred to the above papers for
details.
While cation exchange models have proven useful in illuminating many
aspects of cation exchange processes and in certain practical applications
such as soil alkalinization and reclamation problems (Rible and Davis, 1955),
there are simplifying assumptions inherent in each of them which render them
inappropriate and perhaps useless for certain field applications. A major
assumption in many of these models is that the exchanger (e.g., the soil) is
unable to adsorb anions (Bolt, 1967), and it will be shown in this paper that
this assumption renders cation exchange models absolutely useless in predict-
ing soil leaching under many conditions.
It has been suggested that leaching in temperate forest soils is limited
by a lack of anions that are mobile in the soil (McColl and Cole, 1968;
Remezov, 1958). According to this concept, leaching cannot occur without an
anion or anions to maintain electrochemical neutrality in soil solution,
cation exchange reactions notwithstanding. According to the concept of
Mc_Coll and Cole (1968) and Cole, et al. (1975) nutrient leaching occurs when
H or other non-nutrient cations are introduced to the soil with an anion
that is mobile in the soil. If we adopt this view of leaching, we can couple
1
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anion mobility considerations with erosion considerations and produce a
simple conceptual picture of nutrient transport from terrestrial to aquatic
ecosystems as shown in Figure 1. Though cation budgets are not considered in
this picture, the total of cations must equal the total of anions, and one of
the many cation exchange models could easily be introduced if one desired to
consider individual cations. Paradoxically, it is in many ways easier to
employ anion production and adsorption considerations to predict and explain
nutrient transport than it is to consider cation production and adsorption,
even though there is a far greater wealth of information on the latter.
Also, in terms of pollution considerations, the nitrate and phosphate anions
are of more interest than the major cations.
Thus, it is the intent of this paper to discuss the factors affecting
anion mobility in soils, and to show how these factors in turn affect the
rates of nutrient leaching from soils. To do this, we must first review the
literature dealing with basic soil chemical reactions that are relevant to
the level of anions in soil solution. Soil anion adsorption is important in
this regard except in the case of bicarbonate. Thus, bicarbonate is discussed
separately, and following that the mechanisms of anion adsorption are reveiwed
and related to field applications.
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Inputs (Pollution, Fertilization)
Internal Release"
due to site disturbance>
(Clearcutting, Fire) .
V
Adsorbed
or
Precipitated
in soil
Leaching
Immobile onions
in soil .
Groundwater
.
.mobile onions in
solutions
AQUATIC
ECOSYSTEM
Figure 1. Conceptual scheme of ionic transport from terrestrial to aquatic ecosystems using anion
mobility as an index.
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SECTION 2
FACTORS AFFECTING ANION PRODUCTION AND MOBILITY IN SOILS: A BRIEF LITERATURE
REVIEW.
THE BICARBONATE ANION: A PRODUCT OF SOIL RESPIRATION
Factors Affecting the Concentration of Bicarbonate in Solution
Shilova (1959) and McColl and Cole (1968) showed that bicarbonate was
the major anion in soil solutions from the temperate forest sites they invest-
igated and they deduced that carbonic acid was the major soil leaching agent.
Cole, et al . (1975) described the carbonic acid leaching mechanism as follows.
Due to respiration and reduced C02 diffusivity in the soil, C02 pressure
builds up within the soil relative to the ambient atmosphere. An incoming
wetting front encounters this higher C02 pressure (and may increase it by
further reducing C02 diffusivity) and C02 dissolves to form carbonic acid
according to Henry's law:
C02 + H20 -»- H2C03
[H2C03*] = (Kh)(PC02) (1)
where Kh = Henry's law constant (= -1.46)
PCOo = C02 pressure in atmospheres
[H2C03*] = [H2C03] + [C02]aq (by convention)
Carbonic acid in turn dissociates to hydrogen and bicaronate ions (or to
carbonate at pH above 8.3):
H2C03* -» H+ + HC03
[H+] [HCO~]
* = K
[H2C03*] l
where K, = the first dissociation constant of carbonic acid.
Following this, hydrogen-cation exchange occurs and a bicarbonate salt
leaves the system. The scheme of events associated with this mechanism
is shown in Figure 2.
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Respiration CO
2
Hydrolyze hLO t-LCCL
23
Ionize This will occur at H HCOl
significant levels
only when the pH is
greater than 4.5
Displace H+ so formed can H+ -[cTay]
replace other cations
on the exchange sites +
K+ HCOg
Leach Bicarbonate functioning
as a mobile anion will
facilitate the transport
of cations in the soil K HCCC
Figure 2. Schematic diagram of events associated with carbonic acid leaching
in soils (from Cole, et al., 1975).
Following equation (1) and (2), it is easily seen that the. concentration
of bicarbonate is determined by C02 pressure (PC02) and pH ([H ]):
(K1)(Kh)(PCO?)
[HCQ-] = ! T L- (3)
3 [H+]
The response of bicarbonate to changes in pH and PC02 is shown in
Figure 3. Thus, we see that the rate of soil leaching by carbonic acid is
regulated by soil respiration, soil C02 diffusivity (which is also determined
by rainfall intensity), and final solution pH. C02 pressure may be thought
of as a potential for carbonic acid leaching, and the extent to which this
potential is realized is determined by solution pH.
Soil Properties in Relation to Solution Bicarbonate Levels
In rapidly respiring, finely porous soil, C02 pressure and carbonic acid
leaching potential will be high. Also, C02 can build up to high pressures
beneath impermeable ice or snow layers even though respiration is low (Mar-
karov, 1966).
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3.56
O)
5*
u
Figure 3. Response of HCO' to changes in pH and C02 pressure (PC02)
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Factors affecting pH are more complex. Soil solution pH can be affected
by percent base saturation, low base soils giving lower pH than high base
soils (Schofield, 1947). In cold-region podzols, however, organic acids are
typically present and they buffer solution pH at low levels (Strelkova,
1974); Ponomareva et al., 1968; Ponomareva, 1973).
The senior author investigated soil leaching processes in forests growing
under a variety of climatic conditions, and found that the importance of
carbonic acid leaching decreased as annual temperature decreased (Johnson,
1975). In the tropical soil, high soil respiration and low soil C02 diffusiv-
ity led to high soil C02 pressures which in turn led to intense carbonic acid
leaching. The temperate forest soil was also leached primarily by carbonic
acid, but at a less intense rate than the tropical soil due to lower soil C02
pressure. Organic acids were present in solutions from the subalpine and
northern soils, and they lowered solution pH to levels such that carbonic
acid played a minor or nonexistent role in leaching these soils (i.e., solu-
tion pH was so low that carbonic acid did not dissociate into H and HCOs).
Organic acids were found to be similarly important in solutions from cold-
region podzols in the Soviet Union as well (Ponomareva, et al, 1968; Ponomar-
eva, 1973).
Some Examples of Bicarbonate Leaching in Response to Site Manipulation
From the previous discussion, it is clear that any site manipulation
that affects soil C02 pressure or solution pH will affect solution bicarbonate
levels. In practice, solution pH is the more important of the two factors,
since a change of one pH unit causes a change of ten-fold in solution bicarb-
onate concentration.
Cole, et al. (1975) give an excellent review of the effects of urea
fertilization, harvesting and fire on bicarbonate leaching in a Douglas fir
forest soil. In terms of harvesting, the input of foliage and branches to
the forest floor compartment dramatically increases the nutrient content of
that compartment. This, coupled with an increase in surface temperature,
leads to a rapid acceleration in the decomposition rate (Gessel and Cole,
1965). This was because the more acid lower soil horizons donated hydrogen
ions to solution, reducing bicarbonate concentration and causing associated
cations to occupy exchange sites. These reactions are depicted in Figure 4.
Burning slash after clearcutting obviously alters the chemical nature of
the forest floor nutrient pool; it is, in essence, an instantaneous decomposi-
tion of the organic material as opposed to the slower, biological process.
Burning results in substantial volatilization of nitrogen and sulfur conver-
sion of non-volatilic minerals to oxides. The oxides soon convert to highly
soluble carbonates which remain in the ash layer; until they are leached.
With the onset of precipitation, carbonates (C03) dissolve a^nd consume hydro-
gen ions from exchange sites to form metal biocarbonates (K HCOa) (Figure 4).
With massive fluxes of these species, the soils buffering capacity is exceeded
and the result is significant increases in cation-bicarbonate concentrations
in solutions below the rooting zone. Even so, however, 70-90% of the cations
mobilized from the ash layer remained within the rooting zone. A loss of 10-
30% of the cation mineral reserve in the forest floor and foliage is worthy
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of consideration, but the loss by volatilization of 90% of the nitrogen in
those components is by far the most serious concern (Grier, 1975).
Oxidize
(Decomposition
or burning)
CO,
Hydrolyze
H20
H2C03
Ionize
anion will form in
that the surface pH ex-
ceeded pH 8 after burn-
ing, pH 7 after harvesting
H+ + HCO;
Displace
The H formed above can
replace cations from the
exchange sites
Leach
These anion-cation pairs
will leach through the soil
as long as the pH does not
decrease
Adsorbed As the soil solution en- HpCO,
counters more acid than
surface conditions H2C03
is again formed slowing
the leaching process
Figure 4. Schematic diagram of bicarbonate leaching following harvesting
or burning (from Cole, et al., 1975).
Urea fertilization has profound effects on the amount of cation transfer
in upper soil horizons as well. Urea is a highly soluble non-ionic polar
organic compound, and it is therefore readily leached if applied during rainy
periods. However, urea hydrolyzes to ammonia and carbon dioxide through an
enzymatic reaction involving urease. (Urease is commonly present in forest
soils). NHs then consumes hydrogen ions to form NF-L and C02 hydrolyzes to
form carbonic acid which in turn dissociates into H and HCOa, dependent upon
pH. Since carbonic acid is a weakly dissociated acid and there are two NH3
molecules produced for each C02, the net result is a sharp rise in solution
pH. In most cases HCOs remains the dominant carbonate form (pH remains below
8
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8.3), so that an ammonium Bicarbonate solution results. (This must result in
the initial transfer of NH^ to exchange sites in order to maintain mass
balance)^ As the ammonium bicarbonate solution my.es through the. soil pro-
file, NH4 displaces native cations such as K , Ca , MG , and H from the
exchange sites by mass action (Figure 5). Thus, urea fertilization makes +
many cation nutrients available for uptake in addition to NH^. Displaced H
combines with HCOs to form H2C03, so that bicarbonate concentrations as well
as ammonium concentrations decrease as solutions pass deeper into the soil.
The result is that NH^ is largely retained in the upper 15 cm of the soil.
Should the initial hydrolysis of urea be delayed or blocked, far greater
leaching losses of N would occur. In most cases the hydrolysis is rapid
enough so that little N loss occurs, however.
Solubilize
NH2CONH2
Leach
Urea freely leaches in
this un-ionized state
Hydrolyze
(ureolysis)
Ionize
Leach
Fixed
At the relatively high
pH values caused by this
reaction the HCCL is formed
The NHit interacts with
the exchange sites allow-
ing for slow leaching
NH4HC03
I
NH! HCO;
H?C03
Figure 5.
As the soil solution becomes
increasingly acid H2C03 is
formed, essentially stopping
the leaching process
Schematic diagram of transformation and leaching of urea within
the soil profile (Cole et al., 1975).
For reasons unknown, nitrification did not occur following urea fertili-
zation. This is fortunate in terms of N retention, in that NQ~3 is a relative-
ly mobile anion in the soil and would readily leach out.
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In soil where bicarbonate is normally absent, one would expect urea
fertilization to have a more dramatic effect on soil leaching than in soils
where bicarbonate is normally dominant. This author (Johnson, unpublished
data) tested the effect of urea fertilizer on bicarbonate leaching in a
subalpine ecosystem where bicarbonate is normally unimportant through most of
the soil, and it was found that annual leaching rates increased by a factor
of 7 in the upper 15 cm and by a factor of almost 2 in the 60 cm level. This
was a greater increase than that noted by Crane (1972) after similar urea
applications on a bicarbonate-dominated soil.
NITRATE, CHLORIDE, SULFIDE, AND PHOSPHATE LEACHING IN SOILS
Aside from bicarbonate and organic anions, sulfate, chloride, nitrate
and phosphate deserve careful consideration in terms of soil leaching.
Chloride is an important anion in soil solutions near coastal areas (Art, et
al., 1974; Johnson, 1975), and it is quite mobile in the soil. Like carbonic
acid production, the microbiological conversion of ammonium to nitrate, or
nitrification, produces both H and a mobile anion (NO^), thus allowing a
very effective leaching process. Likens, et al. (1969) showed clearly the
importance of nitrate to forest soil leaching following clearcutting in the
Hubbard Brook watershed, and Cole, et al (1976) show the importance of this
anion to leaching following wastewater application in western Washington.
Oxidation of sulfur in soils produces H and sulfate (S0£~) (Reuss,
1975), but field application of sulfuric acid to forest soils have led only
to small increases in leaching in western Washington (Johnson and Cole, 1976)
and in Norway (Abrahamsen, et al., 1975). In the Washington case, we showed
that sulfate adsorbed strongly to the soil and therefore leaching was greatly
restricted.
Phosphate (as well as the other anions discussed above) is commonly
applied in fertilizers. Fortunately phosphate adsorbs even more strongly to
soils than sulfate does, and in addition, it is immobilized by a variety of
precipitation reactions that are discussed later in this paper. Consequently,
changes of phosphate leaching through a soil profile are very much less than
those of sulfate, and changes of sulfate leaching are very much less than
those of nitrate due to soil adsorption properties.
With the exception of bicarbonate (which, as has been discussed, is
primarily regulated by C02 pressure and pH), soil anion adsorption caTi exert
a tremendous influence on the concentration of anions in soil solution and
consequently on the leaching processes within the soil. It is therefore
appropriate at this point to review some of the literature dealing with the
basic mechanisms of anion adsorption in soils. Following that, some examples
can be drawn from the literature as well as elsewhere to show the importance
of anion adsorption to the transport of nutrients through the soil.
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Adsorption Mechanisms
Anion adsorption is normally associated with oxides or hydrous oxides of
iron and aluminum, though kaolinite is known to be an absorber to a lesser
extent (Mekaru and Uehara, 1972; Gebhardt and Coleman, 1974; Alymore, et al,
1967; Kingston, et al., 1967; Chao, et al., 1964). Basically, there appear
to be two mechanisms of adsorption: 1) non-specific, in which anions are
held as counter-ions in the diffuse double layer next to a positively charged
colloidal surface, and 2) specific, in which anions enter into coordination
with metal oxide (i.e., they become bonded to two or more ions in the crystal
structure) and they displace another anion. The latter is sometimes called
ligand exchange (Mekaru and Uehara, 1972; Hingston, et al., 1967).
The difference between the two types of adsorption is as follows. Sites
for non-specific adsorption lie on the surfaces of colloids, and these sur-
faces can have a plus, minus, or zero charge depending on the concentration
of potential determining ions. For sesquioxides, the potential determining
ions are^ usually H and OH"; thus, surface charge is pH-dependent. At l_ow pH
(high H concentration) surfaces becorpe positively charged because of H
adsorption, whereas ^t high pH (low H concentration) become negatively
charged because of H dissociation (or OH~ adsorption), as shown in Figure 6
(Hingston, et al., 1967; Harward and Reisenauer, 1966; Yopps and Fuerstenau,
1964). The pH at which the surface has no charge is termed the zero point of
charge (ZPC). The ZPC of iron and aluminum oxides common in soils lies in
the vicinity of pH 9, thus, these surfaces have a net positive charge at most
normal soil pH's, and they provide sites for anion adsorption (Hingston, et
al., 1967; Yopps and Fuerstenau, 1964; Harward and Reisenauer, 1966). If pH
is lowered in a given soil, these surfaces become more positively charged and
anion adsorption increases, whereas if pH is raised, these surfaces become
less positively charged or negatively charged, and anion adsorption decreases.
All major anions are involved in non-specific adsorption, but not all
anions enter into specific adsorption reactions. Cl~ and H0~3 are termed
"indifferent" anions because they do not specifically adsorb and they can be
completely desorbed by eliminating the positive charge on colloidal surfaces
(e.g., by raising pH) (Hingston, et al., 1967; Mekaru and Uehara, 1972).
On the other hand, anions like sulfate and phosphate (also selenite,
silicate, and fluoride) enter into specific adsorption as well as non-specific
adsorption reactions. Hingston, et al. (1967) describe the nature of specific
adsorption in great detail, but only a few major points will be discussed
here. Phosphate always adsorbs more strongly than sulfate on a given soil,
and phosphate will displace adsorbed sulfate as well as nitrate and chloride
(Harward and Reisenauer, 1966). Donnan equilibrium equations apparently do
not apply, however, since sulfate will not displace phosphate, and in some
cases phosphate will not displace all adsorbed sulfate (Bornemisza and Llanos,
1967; Harward and Reisenauer, 1966). In general, the displacing or adsorbing
capacity of major anions are as follows: P0^~ > SOff > Cl~ = NO^. Recall
that the latter two are non-specifically adsorbed. Specific adsorption of
POiT or SOfT can result in increased negative charge (or less positive charge)
on colloids, and this is the primary means by which non-specifically adsorbed
anions are displaced by specifically adsorbed anions (Mekaru and Uehara,
11
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Low pH
Zero Point
of Charge
High pH
o
Sesquioxide
Surface
O
AIOH
H
At low pH, Sesquioxide
surfaces adsorb H+ from
solution and become
positively charged
O
Sesquioxide
Surface
O
AIOH
, ,
(aq)
At higher pH called the
Zero Point of Charge ,
adsorbed H+ dissociates
into solution, leaving the
surface with no net charge
O
Sesquioxide
Surface
O
AIOH
H(+aq)
At very high pH (>9); an
additional H+ dissociates,
leaving the surface
negatively charged
Figure 6. Schematic representation of the effect of pH on surface charge of sesquioxides
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1972; Hingston, et al., 1967). This increased negative charge naturally must
lead to an increase in cation exchange capacity as well (Mekaru and Uehara,
1972). Thus, in a soil that is subjected to heavy applications of sulfate or
phosphate, one would expect to see the release of whatever Cl" or NQl that
was non-specifically adsorbed to the soil (if any). As many examples will
show in the next section, however, little cation loss occurs with heavy
applications of sulfate and phosphate despite the possibility of this "anion
exchange" with chloride or nitrate, probably because of low initial levels of
adsorbed chloride and nitrate relative to the incoming sulfate or phosphate.
The increased cation exchange capacity with sulfate or phosphate adsorption
undoubtedly helps retain the applied cations also.
Phosphate undergoes immobilization reactions other than adsorption,
also. It readily precipitates with Al, Ca, Mg, and other common cations in
soil solution and can eventually form new minerals such as varsicite (AlPO^
2H20), fluorapatite (Ca10(P0lt)6(OH)2), and strengite (FePO^ 2H20), among
others (Lindsay and Moreno, 1960; Hsu and Jackson, 1960). There is evidence
that adsorbed or precipitated phosphate becomes "fixed" into mineral forms
and less easily desorbed with time and wetting and drying cycles (Lindsay and
Moreno, 1960; Sawhney and Hill, 1975). Thus, it seems safe to assume that
almost all soils (including calcareous) will strongly adsorb or otherwise
immobilize phosphate.
Of the major anions present in natural waters, only bicarbonate has been
left out of the discussion of anion adsorption. To the best of this author's
knowledge, no information is available as to the absorptivity of the bicarb-
onate anion. This is probably due to experimental difficulties in keeping
material balance for the bicarbonate anion, since it is in equilibrium with
atmospheric C02 in the soil, and it is so strongly affected by pH. For these
same reasons, however, it seems likely that soil C02 pressure and soil solu-
tion pH are far more important to the mobility of the bicarbonate anion than
soil adsorption is.
Soil Properties in Relation to Anion Adsorption
With the information summarized in the previous section, we can begin to
make some basic predictions as to the susceptibility of soils to leaching.
It is clear, for instance, that sesquioxide-rich soils like lateritic soils
will be more efficient anion adsorbers and thus allow less leaching than
sesquioxide-poor soils like those derived from granite. It is also clear
that for a given soil, applications of phosphate salts or acids will result
in less leaching than applications of sulfate salts or acids, and applications
of nitrate or chloride salts or acids will result in the most leaching. A
few specific examples of these relationships will now be given.
Early work by Chao, et al. (1962) in Oregon soils showed that of the 16
soils investigated, only two latosols, one reddish-brown lateritic soil, and
one andept adsorbed sulfate to any significant extent. Later the same authors
(Chao, et al., 1964) demonstrated good relationships between iron and aluminum
coatings and sulfate adsorption in soils from Oregon.
13
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Barrow, et al. (1969) found a strong correlation between amount of
rainfall and soil sulfate adsorption capacity. They hypothesized soils in
higher rainfall areas had higher aluminum and iron oxide contents, which in
turn gave them higher sulfate adsorption capacities. These authors also
noted that soils derived from silicaceous rocks such as granite and shale had
less sulfate adsorption capacity than those derived from basalt, as one would
expect by the generally lower aluminum content in the former.
Bornemisza and Llanos (1967) measured sulfate adsorption on a Latosol, a
volcanic soil, and an alluvial soil from Costa Rica, and they found sulfate
adsorption to be greatest in the Latosols, less in the volcanic soil, and
least in the alluvial soil, as one would expect from the relative sesquioxide
contents. The differences they reported were large, ranging from 50 to 90%
using the Latosol as a baseline.
This author (Johnson and Cole, 1976; Johnson, 1975; and unpublished
data) has measured sulfate, phosphate, nitrate, and chloride adsorption
isotherms for the Everett soil, a gravelly outwash from western Washington.
The interest here was in relating these isotherms to soil solution properties
in the field, and consequently the concentration values employed were much
lower than those reported in previous literature. As a result of this differ-
ence in scale, there are few points at which these isotherms can be compared
to those determined for other soils. In the case of nitrate, however, a
clear comparison can be made: no nitrate adsorption was observed for the
Everett soil, whereas Kinjo and Pratt (1971) measured significant nitrate
adsorption in Andepts and Oxisols from Central and South America. The authors
note that these soils are especially rich in amorphous iron and aluminum and
that little or no nitrate adsorption would be expected in most temperate
soils. Gebhardt and Coleman (1974) measured anion adsorption on some Andepts
from Hawaii, Mexico and Columbia for a solution concentration of 5 meq/1, so
that some comparisons between the Everett soil and the Andepts are possible.
The Everett soil retains 0.3 meq/lOOg of Cl~ and the Andept retains about 1
meq/lOOg of Cl~ at this solution level, and the values for sulfate are 0.8
and 2, respectively. Clearly, the Andept retains these anions better than
the gravelly Everett soil. A better comparison can be made between the
Everett soil and the Bohannon soil which is being used for part of EPA's acid
rainfall studies. The latter is a finer textured, older and more weathered
soil derived from sandstone, and consequently it probably has a higher sesqui-
oxide content than the Everett soil. The very fact that it is fine* textured
than the Everett may lend it greater adsorbing capacity, also, but it is
clear from the comparison in Figure 7 that it does indeed have a greater
adsorption capacity at a given solution level than the Everett does. Between
concentrations of 0 and 0.2 meq/1 the Everett appears to have a greater
capacity, but in all probability this is due to the extraction methods used
to get initial soil sulfate levels. Potassium phosphate was used to extract
the Everett soil, whereas potassium chloride was used to extract the Bohannon
soil, and the latter is a much weaker extractant than the former (Harward and
Reisenauer, 1966).
14
-------
:r 1.5
o
CO
O
O
D-
CD
CO
(D
0
v_
O
1.0
0.5
0
Bohannon
Soil
Everett Soil
i.o
2.0
3.0
[S0 ] in solution (meq/l)
Figure 7. Comparison of sulfate adsorption isotherms for tfte Everett and Bohannon soils
4.0
-------
Some Examples of Nitrate, Chloride, Sulfate and Phosphate Leaching in
Response to Site Manipulations
An example of the great importance of anion mobility is given by Mekaru
and Uehara (1972) in their excellent paper on anion adsorption in tropical
soils. They cite the results of Ayres and Hagihara (1953), who applied
potassium fertilizer to ferruginous tropical soils as salts of chloride,
sulfate, and phosphate. Naturally, potassium added as KC1 leached rapidly
away compared to potassium added as sulfate or phosphate. Since sulfate and
phosphate enter into specific adsorption reactions, addition of these salts
of potassium should result in not only retention of the anions, but also an
increase in cation exchange capacity which can in turn retain the added
potassium. Thus, as this example shows, the anion associated with cation
fertilizers is of the utmost importance and cannot be chosen at random.
Further examples of the importance of anion mobility to fertilizer
application come from the studies conducted by Overrein (1971) in Norway. He
describes the leaching of nitrogen applied in various forms to forest soils.
He found that the NH^ form was far le.ss mobile than the NOjj form of N, as one
would expect. He also found that NH4 leached farther into the soil when
ammonium chloride was applied than when urea was applied. Once again, the
mobility of the anion, Cl" in this case, strongly affects the mobility to
applied cations. Nitrogen applied as urea converts to ammonium bicarbonate,
and the concentration of bicarbonate is regulated by soil atmospheric C02 and
solution pH as previously discussed. Thus, though bicarbonate may be poorly
adsorbed to soil, it can escape to the atmosphere and is not conserved as
other anions are. As a result of this, urea is known to be retained strongly
within forest soils (Roberge and Knowles, 1966; Crane, 1972; Cole, et al.,
1975; Overrein, 1971).
The mobility of sulfate in soils is an important consideration in evalu-
ating the possible effect of pollution-caused acid rain on nutrient transport
from the soil. It cannot be assumed that inputs of sulfuric acid will result
in equivalent outputs of cation-sulfate solutions from the soil, as was
demonstrated in a simple experiment we performed on the gravelly Everett soil
(Johnson and Cole, 1976). To test the mobility of sulfate in the soil,
sulfuric acid was applied to the experimental plot at concentrations ranging
from 10 to 1000 stronger than that normally occurring in precipitation (John-
son and Cole, 1976). Results showed that significant increases in teaching
occurred in the forest floor and A horizon (12 cm deep in the soil), but no
increase was noted in the B horizon (50 cm deep). Soil analyses revealed
that all of the applied sulfate was retained within the soil profile.
Using the sulfate adsorption isotherm measured for the Everett soil
(Figure 7), it is possible to calculate the sulfate concentration at any
point in the soil profile given the value for the sulfate adsorbed to the
soil. Given the flux of water, it is then possible to calculate the leaching
of sulfate from any point in the profile to the next point in the profile.
Finally, for any given point in the profile, the pool of adsorbed sulfate can
be updated by adding the sulfate leaching in and subtracting the sulfate
leaching out, and new solution sulfate concentrations in solution can then be
calculated for the next leaching. Using this simple approach, a finite
16
-------
difference model was constructed for the Everett soil, and the sulfuric acid
applications described above were simulated (Johnson, 1975). The model also
incorporated the bicarbonate equilibrium equations described previously and a
cation exchange equation to account for hydrogen-cation exchange. Full
details and results are given in Johnson (1975). For the purposes of this
discussion, it is useful to compare the simulated and actual fluxes of sulfate
and the final value of soil adsorbed sulfate (Table 1). It is obvious that
the model overestimated the flux and underestimated the final soil adsorbed
sulfate in the A horizon, whereas it overestimated the soil adsorbed sulfate
in the B horizon. This result indicates that the assumption of complete
reversibility of soil sulfate adsorption is in error; the A horizon retained
more adsorbed sulfate in the B horizon than it would have if the adsorption
reaction were completely reversible. Thus, it appears that both adsorption
and desorption isotherms must be employed in efforts to predict the leaching
of sulfate (or phosphate) in a given soil.
TABLE 1. MEASURED AND MODELED SULFATE FLUX AND SOIL SULFATE CONCENTRATION
AFTER ACID APPLICATION (adapted from Johnson and Cole, 1976, and
Johnson, 1975)
Horizon Flux (equivalents/ha) Soil sulfate meq/lOOg)
A
B
Measured
15000
200
Modeled
32000
150
Measured
0.74
0.80
Modeled
0.30
1.10
Also, if other anions are introduced into the system, the interactions
between them must be determined and incorporated as well. The importance of
these interactions is implied in the results of sulfuric acid application to
forest soils in Norway. Abrahamsen, et al. (1975) noted a four-fold increase
in cation leaching as a result of acid application, yet the increase is not
balanced by increases in sulfate leaching (Teigen, et al., in press). Since
the leachates must maintain electrochemical neutrality, the increased cation
leaching must be balanced by increases in the level of an anion other than
sulfate, and this in turn suggests that some form of "anion exchange" is
taking place.
Some further examples from the Everett soil can illustrate the relative
mobilities of some major anions. Phosphate, sulfate, chloride, and nitrate
adsorption isotherms for the Everett soil are shown in Figure 8. No nitrate
adsorption occurred, and consequently the nitrate adsorption isotherm is a
horizontal line starting at 0 on the Y-axis (i.e., it is identical with the
X-axis line).
17
-------
oo
CJ>
O
O
O
CL
CD
JD
0
H2P04
246
Solution Phase (meq/l)
Figure 8. Adsorption isotherms for chloride, sulfate, nitrate and phosphate on the Everett soil A-horizon
-------
The relative adsorptivities of these anions as plotted here have also
been reflected in field results from the application of sulfuric acid and
wastewater to the Everett soil. In the case of sulfuric acid application,
the significant increase in leaching in the A horizon (Table 1) suggests that
the sulfate adsorption capacity of this horizon was being reached. On the
other hand, over 500 kg/ha of phosphate has been applied to the same soil
series in ongoing wastewater studies under the supervision of Dr. Dale Cole,
while less than a fraction of a percent of this amount has leached past the
10 cm soil depth (Cole, 1976). At the other extreme of the adsorptivity
scale, only about 30 kg/ha of nitrate has been applied in the same study,
while over 100 kg/ha has leached past the 200 cm depth in the soil, presumably
because of nitrification within the soil profile (Cole, et al., 1976). We
are now sampling the soils from the irrigation plots and we fully expect that
the final budgets will reflect the relative mobilities of these major anions
in the soil.
19
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SECTION 3
SUMMARY AND CONCLUSIONS
1. Anion production and leaching can be used effectively as an index of
total ionic leaching through soils.
2. An anion of major importance in many soil solutions is bicarbonate, and
the rate of bicarbonate leaching is regulated by soil C02 pressure and solu-
tion pH.
3. Anion adsorption is a very important feature of soils in terms of regu-
lating the leaching rates of anions other than bicarbonate. In general, the
order of affinities of major anions is P0^~ > S0£~ > Cl~ = NOs. The first
two anions can be adsorbed non-specifically and specifically whereas the
latter two can only be adsorbed non-specifically. Specific adsorption refers
to penetration of the anion into the coordination sphere of metal oxides, and
non-specific adsorption refers to anion retention in the diffuse double layer
next to oxide surfaces. Bicarbonate adsorption has not been well character-
ized, but it is exceptional in that it is regulated primarily by soil C02
pressure and solution pH.
4. The anion adsorption capacity of a soil is related to the content of
positively charged sesquioxides in the soil. Highly-weathered, iron and
aluminum-rich soils have higher adsorption capacities than younger iron and
aluminum-poor soils.
5. For a given soil: ^
a) Changes in pH will affect bicarbonate concentrations and anion
adsorptivity and therefore leaching rates. Such changes, affect non-
specific adsorption in that sesquioxide surfaces lose H and net positive
charge as pH increases. Bicarbonate concentration also increases as pH
increases. Consequently, increases in pH will mobilize non-specifically
adsorbed anions and bicarbonate and tend to increase leaching rates.
b) The addition of specifically adsorbed anions to a soil will result in
the mobilization of non-specifically adsorbed anions. This occurs
because the specific adsorption of anions increases the permanent nega-
tive charge of sesquioxide surfaces. The latter also results in increased
cation exchange capacity and greater cation retention power. Phosphate
is the most strongly adsorbed anion and will displace specifically
adsorbed sulfate as well as non-specifically adsorbed anions.
20
-------
In general, it is clear that the concept of anion mobility in soils is a
very useful tool for predicting the effects of site manipulations such
as fertilization, harvesting, burning, and wastewater application on
soil leaching rates. In considering terrestrial-to-aquatic nutrient
transport, it is critically important to consider the factors affecting
the addition, production and mobility of anions in the soil.
21
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REFERENCES
Abrahamsen, 6., R. Hornvedt, and G. Tveite. 1975. Impact of acid precipita-
tion on coniferous forest ecosystems. Research Report 2, Acid Precipitation-
Effects on Forests and Fish. Norwegian Forest Research Institute, As, Norway.
Alymore, L. A. G., M. Karin, and J. P. Ouirk. 1967. Adsorption and desorp-
tion of sulfate ions by soil constituents. Soil Sci. 103:10-15.
Art, N. W., F. H. Bormann, and G. M. Woodwell. 1974. Barrier Island forest
ecosystem: Role of meteorologic inputs. Science. 184:60-61.
Ayres, A. S. and H. H. Hagihara. 1953. Effect of the anion on the sorption
of potassium by some Humic and Hyrol Humic Latosols. Soil Sci. 75:1-17.
Barrow, N. J., K. Spencer, and W. M. McArthur. 1969. Effects of rainfall
and parent material on the ability of soils to adsorb sulfate. Soil Sci.
108:120-126.
Bear, F. E. 1955. Chemistry of the soil. 2nd Ed. Reinhold, New York. 515
P.
Biggar, J. W. and D. R. Nielsen. 1963. Miscible displacement. V. Exchange
processes. Soil Sci. Soc. Amer. Proc. 27:623-627.
Biggar, J. W., D. R. Nielsen, and K. K. Tanji. 1966. Comparison of computed
and experimentally measured ion concentrations in soil column effluents.
Trans., ASAE. 784-787.
Bolt, G. H. 1967. Cation exchange equations used in soil scienceA review.
Neth. J. Agric. Sci. 15:81-103.
Bornemisza, E. and R. Llanos. 1967. Sulfate movement, adsorption,"and
desorption in three Costa Rican soils. Soil Sci. Soc. Amer. Proc. 31:356-
360.
Bower, C. A., W. R. Gardner, and J. 0. Goertzen. 1957. Dynamics of cation
exchange in soil columns. Soil Sci. Soc. Amer. Proc. 21:20-24.
Carlson, R. M. and J. R. Buchanan. 1973. Calcium-magnesium-potassium
equilibria in some California soils. Soil Sci. Soc. Am. Proc. 37:851-855.
Chao, T. T., M. E. Harward, and S. C. Fang. 1962. Adsorption and desorption
phenomena of sulfate ions in soils. Soil. Sci. Soc. Amer. Proc. 26:234-237.
22
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Chao, T. T., M. E. Harward, and S. C. Fang. 1964. Iron or aluminum coatings
in relation to sulfate adsorption characteristics of soils. Soil Sci. Soc.
Amer. Proc. 28:632-635.
Cole, D. W. 1976. unpublished data.
Cole, D. W., W. J. B. Crane, and C. C. Grier. 1975. The effect of forest
management practices on water chemistry in a second-growth Douglas-fir eco-
system. Forest Soils and Land Management--Proc. of the Fourth North American
Forest Soils Conference, Quebec. B. Bernier and C. H. Winget (eds.). Les
Presses de 1'Universite Laval, Quebec. Pp. 195-208.
Cole, D. W., P. J. Riggan, D. W. Johnson, and D. W. Breuer. 1976. Nitrogen
nutrition and cycling in Douglas-fir ecosystems of the Pacific Northwest.
Presented at the Second ERDA Symposium on Mineral Cycling, Savannah River
Ecology Laboratory, University of Georgia, Savannah, GA, April 28-30, 1976.
Proceedings to by published.
Crane, W. J. B. 1972. Urea-nitrogen transformation, soil reactions, and
elemental movement via leaching and volatilization in a coniferous forest
ecosystem following fertilization. Ph.D. Thesis, Univ. of Washington, Seattle.
285 p.
De Vault, D. 1943. The theory of chromatography. J. Am. Chem. Sci. 65:534-
540.
Dutt, G. F. and K. K. Tanji. 1962. Predicting concentrations of solutes in
water percolated through a column of soil. J. Geophys. Res. 67:3437-3439.
Gebhardt, H. and N. T. Coleman. 1974. Am'on adsorption by allophanic trop-
ical soils. II. Sulfate adsorption. Soil Sci. Soc. Amer. Proc. 38:259-262.
Gessel, S. P. and D. W. Cole. 1965. Influence of removal of forest cover on
movement of water and associated elements through soil. J. Am. Water Works
Assoc. 1301-1310.
Grier, C. C. 1975. Wildfire effects on nutrient distribution and leaching
in a coniferous ecosystem. Can J. For. Res. 5:599-607.
Harward, M. E. and H. M. Reisenauer. 1966. Movement and reactions of inor-
ganic soil sulfur. Soil Sci. 101:326-335.
Heister, N. K. and T. Vermeulen. 1952. Saturation performance of ion ex-
change and adsorption columns. Chem. Eng. Prog. 48:505-516.
Hingston, F- J., R. J. Atkinson, A. M. Posner, and J. P. Quirk. 1967.
Specific adsorption of anions. Nature. 215:1459-1461.
Hsu, P. H. and M. L. Jackson. 1960. Inorganic phosphate transformations by
chemical weathering in soils as influenced by pH. Soil Sci. 90:16-24.
23
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Johnson, D. W. 1975. Processes of elemental transfer in some tropical,
temperate, alpine and northern forest soils: Factors influencing the avail-
ability and mobility of major leaching agents. Ph.D. Thesis, Univ. of Wash-
ington, Seattle, 169 p.
Johnson, D. W. and D. W. Cole. 1976. Sulfate mobility in an outwash soil in
western Washington. Proceedings of the First International Symposium on Acid
Precipitation and the Forest Ecosystem. USDA Forest Service General Technical
Report NE-23. Pp. 827-835.
Johnson, D. W., D. W. Cole, and S. P. Gessel. 1975. Processes of nutrient
transfer in a tropical rain forest. Biotropica. 7(3):208-215.
Kinjo, T. and P. F. Pratt. 1971. Nitrate adsorption: I. In some acid soils
of Mexico and South America. Soil Sci. Soc. Amer. Proc. 35:722-725.
Likens, G. E., F. H. Bormann, and N. M. Johnson. 1969. Nitrification:
Importance to nutrient losses from a cut-over forested ecosystem. Science.
163:1205-1206.
Lindsay, W. L. and E. C. Moreno. 1960. Phosphate phase equilibria in soils.
Soil Sci. Soc. Amer. Proc. 24:177-182.
Markarov, B. N. 1966. Air regime of a sod-podzolia soil. Soviet Soil Sci.
(1966):1289-1297.
McColl, J. G. and D. W. Cole. 1968. A mechanism of cation transport in a
forest soil. Northwest Sci. 42:134-140.
Mekaru, T. and G. Uehara. 1972. Anion adsorption in ferruginous tropical
soils. Soil Sci. Soc. Amer. Proc. 36:296-300.
Overrein, L. N. 1971. Isotope studies on nitrogen in forest soil. I.
Relative losses of nitrogen through leaching during a period of forty months.
Meddr. Norske Skogfors Ves. 29(114):261-280.
Ponomareva, V. V- 1973. (Acid-base properties of lysimetric water of pod-
zolic soils). Pochvovedenie 5:128-134. In Soils and Fert. 36:398.
Ponomareva, V. V., T. A. Rozhnova, and N. S. Sotnikova. 1968. Lysimetric
observations on the leaching of elements in podzolic soils. Trans., 9th Int.
Congr. Soil Sci. 1:155-164.
Reiniger, P. and G. H. Bolt. 1972. Theory of chromatography and its applica-
tion to cation exchange in soils. Neth. J. Agric. Sci. 20:301-313.
Remezov, N. P. 1958. Relation between biological accumulation and eluvial
processes under forest cover. Soviet Soil Sci. 1958:587-598.
24
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Reuss, J. D. 1975. Chemical and Biological Relationships Relevant to Ecol-
ogical Effects of Acid Rainfall. EPA 660/3-75-032. Ecological Research
Series, U.S. Environmental Protection Agency, Corvallis, Oregon. 46 p.
Rible, J. M. and L. E. Davis. 1955. Ion exchange in soil columns. Soil
Sci. 79:41-47.
Roberge, M. R. and R. Knowles. 1966. Ureolysis, immobilization, and nitrifi
cation in black spruce (Picea mariana Mill.) humus. Soil Sci. Soc. Amer.
Proc. 30:201-204.
Sawhney, B. L. and D. E. Hill. 1975. Phosphate sorption characteristics of
soils treated with domestic waste water. J. Environ. Qual. 4:342-346.
Schofield, R. K. 1947. A ratio law governing the equilibrium of cations in
solution. Proc. Eleventh Congr. Pure and App. Chem. 3:257.
Shilova, Y. I. 1959. Five-year observations of the qualitative composition
of lysimeter water in various types of virgin and cultivated podzolic soils.
Soviet Soil Sci. (1951):76-8.
Strelkova, A. A. 1974. (Processes in migration of substances with natural
water) jj^ Soil Investigations in the Karelia: Papers for the Tenth Inter-
national Congress of Soil Science (in Russian).
Teigen, 0., G. Abrahamsen, and 0. Haugbot. 1976. Experimentelle forgurins-
forsd5k0i skog. 2. LysimeterundersfSkelser. Norwegian Forest Research Insti-
tute, As, Norway (in press) (in Norwegian).
Yopps, J. A. and D. W. Fuerstenau. 1964. The zero point of change of alpha-
aluminum. J. Colloid Sci. 19:61-71.
25
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APPENDIX
A BRIEF SUMMARY OF SOME APPROACHES USED IN MODELING CATION EXCHANGE AND
LEACHING IN SOILS
In one of the earliest attempts at modeling cation transfer through
soils, Rible and Davis (1955) employed the chromatography theory of the De
Vault (1943). Devault's theory applies to the flow of a solution containing
an adsorbate through a column of absorbant, and it is based on material
balance in each differential section in the column (i.e., the change in
adsorbate content in each section is equal to inflow minus outflow from the
section). The basic equation derived by De Vault is (Rible and Davis, 1955):
x = v/[ct + Mf'(c)]
where x = depth in the column
v = volume of solution applied to the column
a = pore volume per unit length of column
m = amount of adsorbant per unit length of column
f(c) = adsorption isotherm of adsorbate to adsorbant
f'(c) = the first derivative of f(c) with respect to C.
The nature of the adsorption depends on the type of system being consid
ered and the assumptions being made. For cation exchange involving two
cations of the same valence, one could use a selectivity coefficient:
w (Mg)[Ca
where Q = the selectivity coefficient, parentheses denote exchangeable
phase, and brackets denote solution phase.
Rible and Davis used a modification of this to account for ions of different
valence also:
Q = (B2)
[B]}
(B,) ' [B2] '
where r, and r~ are the valence of B, and Bp, respectively.
For exchange between cations of equal valence, this equation is the same as
the one above. Any isotherm can be applied to the basic equation, but point-
by-point equilibrium between solution and adsorbed phase is inherently assumed
in this treatment.
26
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The chromatographic equations of Heister and Vermeulen (1952) allow for
a finite rate of cation exchange rather than assuming point-by-point equilib-
rium, and Bower, et al. (1957) found good agreement between model output and
experimental results from soil columns using this method.
Biggar and Nielson (1963) show that neither the De Vault nor Heister-
and-Vermuelen equations are adequate for describing cation exchange during
water flow through soils unless they account for miscible displacement, i.e.,
the effects of diffusion and variations in microscopic flow velocities on
mixing and dispersion within the wetting front. Biggar, et al. (1966) later
tested the finite plate method of modeling, which inherently introduces
mixing within each soil section. The method is similar in principle to the
chromatographic equations in that equilibrium is assumed and material balance
is kept by adding inflow and subracting outflow. The only difference is that
the modeled soil is divided into finite plates of a certain thickness, and
equilibrium solution is calculated for each plate, and this outflow from a
given plate is added to the plate below, where a new equilibrium is calcu-
lated, etc.
27
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
i. REPORT NO.
EPA-600/3-77-068
3. RECIPIENT'S ACCESSIOI*NO.
4. TITLE AND SUBTITLE
ANION MOBILITY IN SOILS: RELEVANCE TO NUTRIENT
TRANSPORT FROM TERRESTRIAL TO AQUATIC ECOSYSTEMS
5. REPORT DATE
June 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Dale W. Johnson and Dale W. Cole
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
College of Forest Resources
University of Washington
10. PROGRAM ELEMENT NO.
1AA602 (AP# 602A9)
11. CONTRACT/GRANT NO.
PR-CC6991995-J
12. SPONSORING AGENCY NAME AND ADDRESS
Con/all is Environmental Research Laboratory
Office of Research & Development
U.S. Environmental Protection Agency
200 S.W. 35th Street Corvallis, OR 97330
13. TYPE OF REPORT AND PERIOD COVERED
Final -- March 31. 1977
14. SPONSORING AGENCY CODE
EPA/600/02
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Nutrient transport from terrestrial to aquatic ecosystems is strongly mediated by
soil chemical interactions. Ions deposited on or biologically released within the
soil can enter into a variety of exchange and precipitation reactions prior to (or
instead of) entering aquatic ecosystems. This report reviews the current knowledge
of soil anion adsorption reactions and their effects on leaching, and suggests a
simple model, based on anion production and adsorption considerations, to predict
and explain nutrient transport. The relationship of this approach to that based on
cation production and adsorption is discussed.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATl Field/Group
Soil chemistry
Anion adsorption
Agriculture/
Agricultural
chemistry
02/A
13. DISTRIBUTION STATEMENT
Release unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. Np.OF PAGES
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
28
U.S. GOVERNMENT PRINTING OFFICE: 1977797-985/153 REGION 10
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