&EPA
United States
Environmental Protection
Agency
Environmental Research
Laboratory
Corvallis OR 97330
EPA-600/3-80-01 5
January 1980
Research and Development
Effects of Acid
Precipitation on Soil
Leachate Quality
Computer
Calculations
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3, Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6, Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
cies, and materials. Problems are assessed for their long- and short-term influ-
ences. Investigations include formation, transport, and pathway studies to deter-
mine the fate of pollutants and their effects. This work provides the technical basis
for setting standards to minimize undesirable changes in living organisms in the
aquatic, terrestrial, and atmospheric environments.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/3-80-015
January 1980
EFFECTS OF ACID PRECIPITATION ON SOIL LEACHATE QUALITY
Computer Calculations
by
Garrison Sposito
A. L. Page
Mark E. Frink
Repartment of Soil and Environmental Sciences
University of California
Riverside, California 92521
Contract Number B0836NAEX
Project Officer
Bruce Lighthart
Terrestrial 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
One of the principal reasons for the preparation of this report for the
Environmental Protection Agency was to supply scientifically valid information
which could be incorporated into the EPA S02-Particulate Matter criteria
document, presently in the final stages of preparation. A strict requirement
pertaining to that document is that any scientific information used there must
be published (or at least in press) by January 1, 1980. Because of this
demanding time constraint, it was necessary that the contractor prepare this
report in a shorter time than would ordinarily be attempted, and that it be
published by EPA without undergoing peer review. We feel that early publi-
cation of these results in order to stimulate the broadest scientific dis-
cussion prior to completion of the criteria document justified waiving our
normally more rigorous prepublication review requirements. Publication,
however, does not signifiy that the the contents necessarily reflect the views
and policies of EPA, nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
n
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FOREWORD
Effective regulatory and enforcement actions by the Environmental
Protection Agency would be virtually impossible without sound scientific data
on pollutants and their impact on environmental stability and human health.
Responsibility 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.
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 lakes and
streams; and the development of predictive models on the movement of pollu-
tants in the biosphere.
In the investigation reported here, a chemical thermodynamic model has
been used to predict the chemical species in solutions of soils, from three
northeastern states, affected by acid precipitation. This kind of information
is basic to the prediction of acid precipitation effects on soil fertility,
ecosystem productivity, and toxicity effects on aquatic species.
Thomas A. Murphy, Director
Corvallis Environmental Research Laboratory
m
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ABSTRACT
The multipurpose computer program GEOCHEM was employed to calculate the
equilibrium speciation in 23 examples of acid precipitation from New
Hampshire, New York, and Maine, and in the same number of mixtures of acid
precipitation with minerals characteristic of soils in the three states men-
tioned. Between 100 and 200 soluble inorganic and organic complexes were
taken into account in each speciation calculation. The calculations performed
on the acid precipitation samples showed that the metals (including heavy
metals) and the sulfate, chloride, and nitrate ligands would be almost en-
tirely in their free ionic forms, while the phosphate, carbonate, ammonia, and
organic ligands would be in their protonated forms. This result was indepen-
dent of the geographic location of the acid precipitation and the month of the
year in which the sample was collected.
The speciation calculations on the precipitation-soil mineral mixtures
showed that aluminum and iron levels in a soil solution affected by acid
precipitation would be significantly higher than in one whose chemistry is
dominated by carbonic acid. The higher levels found were caused by the lower
pH value of acid precipitation as well as by complexes formed with inorganic
and organic ligands. It was also shown that soil cation exchangers would
adsorb preferentially heavy metals, such as Cd and Pb, which are found in acid
precipitation.
This report was submitted in fulfillment of Contract No. B0836NAEX by the
University of California, Riverside, under the sponsorship of the U.S.
Environmental Protection Agency.
IV
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CONTENTS
Foreword iii
Abstract iv
Figures vi
Tables vi
Acknowledgements . viii
1. Introduction 1
2. Conclusions 2
3. Recommendations 3
4. The Computer Program GEOCHEM .... 4
Development of the program 4
General features of the program 4
Input data required by the program 8
5. Scenario for the Mixing of Acid Precipitation
with Surface Soils 8
Composition data and speciation for acid
precipitation 9
Interaction of acid precipitation with soil
minerals 24
6. Soil Response to Acid Precipitation 27
New Hampshire soils 27
New York and Maine soils 33
References 36
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FIGURES
Number Page
1 GEOCHEM computer program model 6
TABLES
Number Page
1 Code numbers and symbols for the metals and
ligands considered by GEOCHEM 10
2 Speciation in the mean annual precipitation at
Hubbard Brook 11
3 Speciation in the mean January precipitation at
Hubbard Brook 13
4 Speciation in the mean February precipitation at
Hubbard Brook 13
5 Speciation in the mean March precipitation at
Hubbard Brook 14
6 Speciation in the mean April precipitation at
Hubbard Brook 14
7 Speciation in the mean May precipitation at
Hubbard Brook 15
8 Speciation in the mean June precipitation at
Hubbard Brook 15
9 Speciation in the mean July precipitation at
Hubbard Brook 16
10 Speciation in the mean August precipitation at
Hubbard Brook 16
11 Speciation in the mean September precipitation at
Hubbard Brook 17
12 Speciation in the mean October precipitation at
Hubbard Brook 17
VI
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TABLES (cont'd)
Number Page
13 Speciation in the mean November precipitation at
Hubbard Brook "18
14 Speciation in the mean December precipitation at
Hubbard Brook 18
15 Speciation in the mean annual precipitation at
Mt. Moosilauke 19
16 Speciation in throughfall at Hubbard Brook (June
and October mean) 20
17 Speciation in throughfall at Mt. Moosilauke
(mean annual) 21
18 Speciation in precipitation at Ithaca, New York 22
19 Speciation in precipitation at Caribou, Maine 23
20 Total "baseline" soluble aluminum and iron in representative
soils from three precipitation study areas 25
21 Speciation in the mean annual precipitation/soil
mixture at Hubbard Brook . . . ' 28
22 Speciation in the mean January precipitation/soil
mixture at Hubbard Brook 29
23 Speciation in the mean July precipitation/soil
mixture at Hubbard Brook 30
24 Speciation in the mean annual precipitation/soil
mixture at Mt. Moosilauke 31
25 Speciation in the throughfalI/soil mixture at
Mt. Moosilauke 32
26 Speciation in the precipitation/soil mixture
at Ithaca, New York 34
27 Speciation in the precipitation/soil mixture
at Caribou, Maine 35
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ACKNOWLEDGEMENTS
The acquisition of experimental data on the chemical composition of acid
precipitation was made possible through the splendid assistance of Mr. Danny
Rambo, USEPA-Corvallis Environmental Research Laboratory. Gratitude is
expressed also to Dr. Christopher S. Cronan of the Department of Biological
Sciences at Dartmouth College for sending reprints and a preprint containing
data on the composition of acid precipitation, throughfall, and soil
percolate.
vm
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INTRODUCTION
Much evidence has accumulated during the past several years concerning
the phenomenon of acid precipitation in the northeastern United States. A
general consensus appears to be developing in regard to the importance of
obtaining a thorough understanding of the chemistry of the soil solution in
ecosystems affected by acid precipitation. It is appreciated now that pre-
dictions about soil fertility, ecosystem productivity, and toxicity effects on
aquatic species cannot be made unless information is available to permit a
detailed consideration of the chemical species which appear in soils receiving
meteoric waters containing excess strong inorganic acids.
One observation that has emerged in recent biogeochemical studies on acid
precipitation effects is that the replacement of a soil solution dominated by
carbonic and organic acids by one whose pH value is controlled by strong
inorganic acids, such as nitric and sulfuric acids, may produce increased
levels of soluble aluminum in the soil. This increase in aluminum solubility
is proposed to occur because of the enhanced dissolution of soil minerals.
The resultant high levels of aluminum in the soil solution are easily trans-
ferred to the channel system, if the pH value of the subsurface water remains
low, and thereby can disturb seriously the ecological balance among aquatic
species through toxicity.
In the present investigation, an attempt has been made to predict the
chemical species in a soil solution affected by acid precipitation. The
method is a calculation, based on chemical thermodynamic principles, performed
by the computer program GEOCHEM. GEOCHEM can compute the equilibrium specia-
tion in an aqueous solution where several hundred soluble complexes and solids
can form among as many as 36 metals and 66 inorganic and organic ligands. It
is, therefore, capable of accurate estimation of metal solubility charac-
teristics in a soil solution, despite the chemical heterogeneity expected in
this system.
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CONCLUSIONS
An application of the computer program GEOCHEM to the calculation of the
chemical species in acid precipitation collected in New Hampshire, New York,
and Maine has shown that the metals in precipitation are in their free ionic
forms, as are the ligands S04, Cl, and N03) while the ligands C03, P04, NH3,
and organic ligands are in their protonated forms. This result is based on
the consideration of about 140 possible complexes by the program and is in
agreement with the generally accepted view of acid precipitation as a solution
of salts mixed with sulfuric, hydrochloric, and nitric acids. The speciation
calculation produced virtually identical results regardless of the location of
collection of the acid precipitation or the time of year it was collected.
The interaction between acid precipitation and soil, simulated in specia-
tion calculations on a system comprising the precipitation, amorphous
Al(OH)3(s) and Fe(OH)3(s), and a cation exchange surface, was shown to produce
levels of Al and Fe in the soil solution which were orders of magnitude larger
than the levels predicted for a soil solution dominated by carbonic acid and
in equilibrium with amorphous Al and Fe hydrous oxides. These higher levels
were the result both of lower pH value in the acid precipitation and of the
presence of metal-complexing ligands. The cation exchanger in the soil was
found to adsorb preferentially the heavy metals in acid precipitation, such as
Cd and Pb. All of these effects occurred regardless of the geographical
location or month of collection of the acid precipitation data.
The calculations performed by GEOCHEM corroborated the recent suggestions
of ecologists and earth scientists, that percolation of acid precipitation
through the soil tends to dissolve the least stable soil minerals and raise
the levels of aluminum significantly in the subsurface runoff which ultimately
finds its way into the channel system of a watershed.
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RECOMMENDATIONS
Much more detailed chemical information about the interaction between
acid precipitation and northeastern U.S. soils could be obtained through
further simulation studies using GEOCHEM. In the present investigation, only
a portion of the aluminum-containing soil minerals was included and a very
simple set of soil solution organic ligands was employed. There is a need to
involve complex aluminosilicates which are known to exist in the soils of
interest, such as muscovite and vermiculite, in the simulations to obtain a
complete picture of the effect of acid precipitation on the dissolution of
aluminum-bearing soil minerals. There is also a need to consider a broad
range of organic acids which better represents the actual water-soluble
organic matter in the soil solution. These extensions are both possible with
the current level of development of GEOCHEM.
This study of the effect of acid precipitation on soils was made somewhat
more difficult than need be by the lack of available data on the complete
chemical composition and mineralogy of the pertinent surface soils. Every
effort should be made in the future to characterize the soils in the water-
sheds of interest with respect to their chemical properties just as completely
as the acid precipitation which infiltrates them has been characterized in the
past.
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THE COMPUTER PROGRAM GEOCHEM
DEVELOPMENT OF THE PROGRAM
GEOCHEM is a multipurpose computer program for calculating the equil-
ibrium speciation of the chemical elements in the soil solution (Mattigod and
Sposito, 1979; Sposito and Mattigod, 1979). The method of calculation em-
ployed in the program is based in chemical thermodynamics. For each component
of a soil solution, a mole balance equation is set up and thermodynamic equil-
ibrium constants corrected for ionic strength are incorporated into the vari-
ous terms of this equation according to the law of mass action. The solution
of the set of non-linear algebraic equations which results from mole balance
applied to all the components simultaneously ultimately provides the concen-
tration of each dissolved, solid, and adsorbed species in the soil system
under consideration. Some typical applications of GEOCHEM would include: (1)
prediction of the concentrations of inorganic and organic complexes of a metal
cation in a soil solution; (2) calculation of the concentration of a parti-
cular chemical form of a nutrient element in a solution bathing plant roots so
as to correlate that form with nutrient uptake; (3) prediction of the fate of
a pollutant metal added to a soil solution of known characteristics; and (4)
estimation of the effect of changing pH, ionic strength redox potential, water
content, or the concentration of some element on the solubility of a chosen
chemical element in a soil solution.
GEOCHEM is a modified version of the computer program REDEQL2, which was
developed at the California Institute of Technology by F. M. M. Morel, R. E.
McDuff, and J. J. Morgan. The detailed structure of REDEQL2 has been de-
scribed in several published articles (Morel and Morgan, 1972; Morel et al.,
1973; Morel and Yeasted, 1977) and in two reports (McDuff and Morel, 1973;
Ingle et aj., 1978). The methods of numerical analysis employed in the pro-
gram are discussed by Morel and Morgan (1972) and are compared with the
methods used in other computer programs by Leggett (1977). GEOCHEM differs
from REDEQL2 principally in containing more than twice as much thermodynamic
data; in utilizing thermodynamic data which have been selected critically
especially for soil systems; in containing a method for describing cation
exchange (Mattigod and Sposito, 1979),- and in employing a different subroutine
for correcting thermodynamic equilibrium constants for the effect of nonzero
ionic strength.
GENERAL FEATURES OF THE PROGRAM
GEOCHEM is written in IBM 370 FORTRAN IV and is compatible with the G
compiler, level 21.7. The program requires about 200K of core. For any soil
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solution data to be analyzed by the program, the chemical components are
identified as metals and unprotonated ligands instead of, for example, com-
plexes and solids containing metals and ligands. The principal variables
considered by the program are the free ionic concentrations of the metals and
ligands. Accordingly, the mole balance equation for a metal M is written in
the form:
M = [Mn+] + I a [Mn+f [H+]* [iT]? (1)
where MT is the total molar concentration of the metal CK „ is the condi-
tional stability or formation constant for the compound, M HyL ' H refers to
the proton, and L refers to a ligand. The conditional stability and formation
constant, K „, and the notation employed for a compound are discussed by
Sposito and Mattigod (1979). The point to be made here is that Eq. (1) and
the analogous expression for the total molar concentration of a ligand, LT,
are nonlinear algebraic equations in the free ionic concentrations. The
numerical analysis problem solved by GEOCHEM is to calculate the set of free
ionic concentrations that satisfies a given set of mole balance equations (one
equation for each metal and each ligand in the system being investigated),
subject to input values of the MT and L-.- along with the thermodynami c equili-
brium K _ which are stored in the program. During the computation, the ionic
strength is calculated using the current values of the concentrations of all
charged species that are possible and the CK . are computed in the usual way
with the values of the Kg and with single-ion activity coefficients (see,
e.g., Stumm and Morgan, 1970). Thus the computer calculation is done self-
consistently, with the total analytical concentrations and the thermodynamic
equilibrium constants corrected for ionic strength related through mole bal-
ance (see Figure 1).
GEOCHEM currently stores thermodynamic data for 36 metals and 66 ligands
which form more than 2,000 compounds. These metals and ligands are listed in
Table 1 along with their code numbers and code symbols. For a given metal-
ligand combination, up to six soluble complexes and up to three solids can be
considered by the program. In addition to the three solids per metal -ligand
combination, mixed solids containing more than one metal or ligand are in-
cluded in the program. Formation constants for up to 20 mixed solids may be
incorporated into GEOCHEM; at present there are 18 mixed solids, including
illite, muscovite, chlorite, vermiculite, and several montmorillomites.
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I INPUT I
"'
CONSTITUENT METALS AND LIGANDS
SET OF SOLIDS
MT,LT
Mrum+T
j-[M J
AT=[An-]
*
MOLE B
+ Zvc[CvcHyAva(
+ Zv [Cv HyAv (
9 C cl
f
ALANCES
aq)] + Zv1[Cv1H6Av2(s)] ^ 7
aq)] + Zv2[Cv1H6Av2
ELIMINATION OF SOLIDS
\
t
ELIMINATION OF COMPLEXES
CKs
x
| NEWTON- RAPHSON ALGORITHM 1
COh
•\
t
ICENTRATIONS OF FREE IONIC SPECIES, i
COMPLEXES, AND SOLIDS
YES-*
PRECIPITATION-
DISSOLUTION
OF SOLIDS
Figure 1.
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GEOCHEM can describe soil solution equilibria in which the partial pres-
sures of N2, 02> and C02 are permitted to vary. The variation in 02 pressure
is treated as an oxidation-reduction phenomenon through the inclusion of 24
redox equations in the program. These redox equations are discussed fully by
Sposito and Mattigod (1979).
There are several specific characteristics of GEOCHEM that should be kept
in mind as the results of this report are read. These characteristics are
most conveniently emphasized by the following list.
(1) The data bank of GEOCHEM consists of thermodynamic data at 25°C and
1 atmosphere. Therefore, all equilibrium calculations are performed at this
fixed temperature and pressure. It is possible for a user to run equilibrium
computations on GEOCHEM at temperatures and pressures other than 25°C and 1
atmosphere provided that a separate data bank is compiled by the user for the
temperature and pressure of interest.
(2) An accounting for metastable species and species that are not
favored kinetically can be incorporated into the computation by methods which
are described by Sposito and Mattigod (1979). It is not necessary to assume
complete thermodynamic equilibrium in order to do a calculation.
(3) The condition of electroneutrality is not imposed during a computa-
tion performed by GEOCHEM. The only constraint imposed is that of mole bal-
ance (i.e., mass conservation), as discussed above. The fact that charge
conservation is not considered by the program has the advantage that ana-
lytical data in which, for reasons of experimental error or omission, the
equivalents of metals do not equal the equivalents of ligands may still be
analyzed for speciation. On the other hand, there is no guarantee that the
weighted sum of positively-charged species will equal the weighted sum of
negatively-charged species according to the electroneutrality principle. This
condition may be useful when examining the speciation results for a complete
and accurate set of analytical data to see if the computer results are self-
consistent. If electrical neutrality is violated, the thermodynamic data that
were used may need revision or augmentation.
(4) Ionic strength corrections are made in the program through the use
of single-ion or single-molecule activity coefficients. The equation employed
to compute the activity coefficients (at 25°C) is:
1+aBV I
where A = 0.5116 dm3/2 mol-1/2, B = 0.3292 x 108 dm3/2 cm mol-1/2, Z is the
valence of the chemical species, and I is the true ionic strength in mol dm-3
(1 dm3 = 103 cm3). The values of the parameters a and B° in turn depend on
the value of I:
(a) If I < 0.5 mol dm-3, a = I/B and B° = 0.3AZ2. Thus Eq. (2) reduces
to the Davies equation.
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(b) If I > 0.5 mol dm-3, B° = 0.041 dm3 mol-1 and a = 4 x 10-8 cm, 5 x
10-8 cm, and 6 x TO-8 cm for monovalent, bivalent, and trivalent ions, respec-
tively. In this case, Eq. (2) becomes the Helgeson (1969) equation as modi-
fied by Truesdell and Jones (1973).
(c) For neutral species, at all values of I, B° = 0.1 dm3 mol-1 (see,
e.g., Helgeson, 1969). Since Z = 0 in this case, the first term in Eq. (2)
does not contribute to the calculation of T.
INPUT DATA REQUIRED BY THE PROGRAM
To some extent the data which must be input to GEOCHEM in order for the
program to do a speciation analysis depend on the type of problem to be con-
sidered. Some of the general requirements are as follows:
(1) Total molar concentrations of each metal and each ligand chosen from
Table 1.
(2) Either the pH value or the total net proton concentration in mol
dm-3. If the pH value is available, it should be used.
(3) If solids are to be considered, a choice must be made as to which
solid phases will be permitted to precipitate during the computation.
(4) If the soil solution is to be regarded as open with respect to C02,
the partial pressure of this gas must be imposed.
8
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SCENARIO FOR MIXING OF ACID PRECIPITATION
WITH SURFACE SOILS
COMPOSITION DATA AND SPECIATION FOR ACID PRECIPITATION
A diligent review of the available data on the chemical composition of
acid precipitation in the northeastern United States produced several sets of
total concentration values which could be employed in the present study.
These sets of data referred to three localities of current interest in acid
precipitation research: the area in or near the Hubbard Brook Experimental
Forest in New Hampshire, the area near Ithaca, New York, and the area near
Caribou, Maine. The composition data for New Hampshire were obtained from
four sources. Data on the major constituents of acid precipitation were taken
from tables compiled by Likens et al_. , (1977) and by Cronon (1979). In the
case of Cronan's data, it was necessary to compute Aly with the help of Eq.
(1) and the assumption that th_e only species to be jnciuded on the right-hand
side of the equation are Al3 , A10H2 , and A1(OH)2. These basic data were
augmented by the inclusion of organic acid and heavy metal components. The
added organic acid was citric acid, at a total concentration of 10-5'28M (1.1
x 10-6 kg dm-3) as suggested by Likens (1975). The added heavy metals were Cd
at 10-8>28M and Pb(II) at 10-7>19M, based on the data presented by Schlesinger
et aj. (1974). These additional data were included so as to obtain the most
complete overall chemical picture of the New Hampshire acid precipitation in
the present modeling effort. The composition data for New York were obtained
from Tables 1 and 2 in Likens (1972) and Table 2 in Likens (1975). In this
case, the organic acid component was taken to be acetic acid at three times
the molarity of the citric acid employed in the New Hampshire data. This
change was necessitated here and in certain cases reported in Section 6 by the
fact that convergence of the speciation calculation was improved when citric
acid was replaced. The composition data for Maine were obtained from maps
presented in Lodge et aj., (1968) and, for the trace metal components, Cd, Cu,
Fe, Mn, Ni, Pb, and Zn, from data provided by D. Rambo (personal communica-
tion, 1979). In all, 21 sets of composition data were generated for New
Hampshire acid precipitation, with one set each for New York and Maine. The
data gathered correspond to both different years and different months of the
year averaged over several seasons of data collection. It is expected that
the total concentration values obtained and analyzed will be representative of
the general chemical features of acid precipitation.
Table 2 lists the results of a speciation calculation for the mean annual
acid precipitation (1963-1974) at Hubbard Brook (Table 4 in Likens et a]_.,
1977). The second column in the table gives the negative common logarithm of
the total molar concentration of each component, the third column gives the
negative common logarithm of+the molar concentration of the free ionic species
of the component (e.g., Ca2 in the case of Ca and NOg in the case of N03),
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TABLE 1. CODE NUMBERS AND SYMBOLS FOR THE METALS AND LIGANDS CONSIDERED BY GEOCHEM
1. Ca2 + 8. Mm2*
2. Mg2* 9. Cu2+
3. Sr2* 10. Ba2*
4. K+ 11. Cd2+
5. Na+ 12. Zn2*
6. Fe3+ 13. Ni2+
7. Fe2 + 14. Hg2+
1. CO2." 13. S20§"
2. SOl' 14- CN"
3. Cl" 15. AC"
4. F" 16. ACAC"
5. Br" 17. CIT3"
6. I" 18. OX2"
7. NH§ 19. SAL2"
8. S2" 20. TART2"
9. POij" 21. EN°
10. P20f" 22. DIP0
11. P30fo 23. SUSAL3"
12. Si02(OH)2" 24. GLY"
*AC = acetate
ACAC = acetylactate
CIT = citrate
OX = oxalate
SAL = sal icylate
TART = tartrate
EN = enthylenediamine
DIP = dipyridyl
SUSAL = sulfosalicylate
GLY = glycine
GLU"' = glutamate
PIC = picolinate
NTA = nitrilotri acetate
15.
16.
17.
18.
19.
20.
21.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
Pb2+
Co2*
Co3+
Ag+
C^
A13+
Cs+
GLUT2"
PIC"
NTA3*
EDTA4"
DCTA4"
CYST2"
NOC3"
PHTH2"
ARG"
ORN"
LYS"
HIS"
EDTA = ethylenediaminetatraacetate
DCTA = 1 ,2-diaminocclohexane-tetracetate
CYST = cysteine
HOC = nocardamine (desferri-ferrioxamine)
PHTH = phthalate
AOG = arginine
ORN = orni thine
Metals
'22. Li+ 29. Ce3+
23. Be2+ 30. Au+
24. Sc3+ 31. Th4+
25. Ti02+ 32. U0i+
26. Sn2+ 33. Cu+
27. Sn4+ 34. CH3Hg+
28. La3+ 35. Rb+
50. H*
Ligands*
37. ASP" 49. SOS," 61. BES"
38. SER" so. SCN" 62. cio^
39. ALA" 51. NH2OH 63. CBER~
40. TYR2" 52. MoO|" 64. CHAM"
41. MET" 53. wo2" 65. FOR"
42. VAL" 54. AsO|" 90. ADS1
43. THR" 55. HVO|" 91. ADS2
44. PHE" 56. SeO§" 92. ADS3
45. ISO" 57. NOJ 93. ADS4
46. LEU" 58. DTPA5" 94. ADS5
47. PRO" 59. SeO|" 99. OH"
48. B(OH>4 60. MAL2"
LYS = lysine
HIS = histidine
DTPA = diethylenetriantinepentaacetate
ASP = aspartate
SER = serine
ALA = alanine
TYR = tyros ine
MET = methionine
VAL = valine
THR = threonine
PHE = phenyl alanine
ISO = isoleucine
LEU = leucine
PRO = proline
MAL = maleate
BES = benzyl sulfonate
CBER = Camp Berteau montmori 1 lonite
CHAM = Chambers bentonite
FOR = fornmate
ADS1-ADS5 = adsorption surfaces
10
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and the fourth column lists any species whose mole percentage of CT is ten or
greater. The actual mole percentages are given in parentheses.
TABLE 2. SPECIATION IN THE MEAN ANNUAL PRECIPITATION AT HUBBARD BROOK
Component
Ca
Mg
K
Na
Cd
Pb(II)
C03
S04
Cl
NH3
P04
CIT
N03
H
CT
5.37
5.69
5.75
5.28
8.28
7.19
7.00
4.52
4.84
4.91
7.07
5.28
4.64
Free Ion
5.37
5.69
5.75
5.28
8.28
7.20
15.40
4.52
4.84
9.77
18.26
8.28
4.64
4.13
Principal Species
Ca2"*" (99.3)
Mg2+ (99.6)
K+ (100.0)
Na+ (100.0)
Cd2+ (99.3)
Pb2+ (98.8)
H (100.0)
S0~4 (99.2)
Cl'^lOO.O)
NH^ (100.0)
H (100.0)
H (99.8)
N0"3(100.0)
H+ (100.0)
A glance at Table 2 shows that all of the metals are free ionic species,
as are N03, Cl, and S04, while C03, P04, NH3, and citrate are in their proto-
nated forms. This result is in complete agreement with the accepted charac-
terization of acid precipitation as a solution of sulfuric, hydrochloric, and
nitric acid. It should be mentioned that the speciation calculation performed
by GEOCHEM which led to Table 2 and the subsequent tables in this section took
into account the formation of 137 soluble inorganic and organic complexes.
Thus the resultant characterization of the acid precipitation data is based on
a calculation which is considerably more sophisticated than that indicated by
Likens (1975), which led to the same conclusion.
11
-------
In Tables 3 to 14 the speciation of acid precipitation at Hubbard Brook
by month of the year is given. The values of CT represent 12-year averages as
presented in Table 14 of Likens et al_. (1977).
An examination of each component listed in Tables 3 to 14 shows that
there are no changes in speciation i_n the acid precipitation throughout the
year. Thus, despite the seasonal trends in CT~values noted by Likens et al.
(1977), no trends appear in the species of the components. The largest
changes are seen in the trace metals such as Pb, which are expected to be the
most sensitive to any changes in pH and total ligand concentrations. However,
even these changes amount to only a few tenths of a percent (e.g., Pb2 is at
a high of 99.3% of PbT in February and is at a low of 98.4% of PbT in June and
July). ' '
Table 15 shows the results of a speciation calculation for acid precipi-
tation at Mt. Moosilauke (Cronan, 1979), which is about 13 km west of the
Hubbard Brook Experimental Forest. Although the total concentration data in
Table 15 are different from those in Table 2, the speciation of the components
which are common to both tables is not different. The speciation calculation
summarized in Table+ 15 took into account 102 inorganic complexes between the
seven metals plus H and the four ligands plus OH .
12
-------
TABLE 3. SPECIATION IN THE MEAN JANUARY PRECIPITATION AT HUBBARD BROOK
Component
Ca
Mg
K
Na
Cd
Pb
S04
Cl
NH3
P04
CIT
N03
H
TABLE 4. SPECIATION
Component
Ca
Mg
K
Na
Cd
Pb
S04
Cl
NH3
PO*
CIT
N03
H
CT
5.60
6.08
5.99
5.25
8.28
7.19
4.66
5.09
4.89
7.28
5.28
4.52
IN THE
CT
5.43
5.78
6.12
5.22
8.28
7.19
4.84
5.04
5.08
7.98
5.28
4.66
Free Ion
5.60
6.08
5.99
5.25
8.28
7.19
4.66
5.09
9.60
18.16
8.00
4.52
4.28
MEAN FEBRUARY
Free Ion
5.43
5.78
6.12
5.22
8.28
7.19
4.84
5.04
9.68
18.66
7.82
4.66
4.38
Principal Species
Ca2* (99.4)
Mg2* (99.7)
K+ (100.0)
Na+ (100.0)
Cd2"1" (99.5)
Pb2+ (99.0)
S04-2 (99.5)
Cl-1 (100.0)
NH< (100.0)
H (100.0)
H (99.7)
NOg-HlOO.O)
H+ (100.0)
PRECIPITATION AT HUB8ARD BROOK
Principal Species
Ca2+ (99.5)
Mg2"*" (99.8)
K+ (100.0)
Na+ (100.0)
Cd2* (99.6)
Pb2* (99.3)
S04-2 (99.5)
Cl-l(100.0)
NH+ (100.0)
H (100.0)
H (99.5)
NOa-^lOO.O)
H"1" (100.0)
13
-------
TABLE 5. SPECIATION IN THE MEAN MARCH PRECIPITATION AT HUBBARD BROOK
Component
Ca
Mg
K
Na
Cd
Pb
S04
CI
NH3
P04
CIT
N03
H
TABLE 6. SPECIATION
CT
5.30
5.78
5.99
5.28
8.28
7.19
4.58
5.03
4.93
7.50
5.28
4.50
IN THE
Free Ion
5.30
5.78
5.99
5.28
8.28
7.19
4.58
5.03
9.71
18.54
8.14
4.50
4.20
Principal Species
Ca2+ (99.4)
Mg2+ (99.6)
K+ (100.0)
Na""" (100.0)
Cd2+ (99.4)
Pb2"*" (98.9)
S04-2 (99.3)
CI-1 (100.0)
NH4 (100.0)
H (100.0)
H (99.7)
N03-1(100.0)
H+ (100.0)
MEAN APRIL PRECIPITATION AT HUBBARD BROOK
Component
Ca
Mg
K
Na
Cd
Pb
S04
Cl
NH3
P04
CIT
N03
H
CH-T
5.17
5.61
5.81
5.32
8.28
7.19
4.49
5.06
4.76
6.86
5.28
4.52
Free Ion
5.17
5.61
5.81
5.32
8.28
7.20
4.49
5.06
9.63
18.07
8.30
4.52
4.11
Principal Species
Ca2+ (99.3)
Mg2+ (99.6)
K+ (100.0)
Na4" (100.0)
Cd2"1" (99.4)
Pb2* (98.8)
S04-2 (99.2)
Cl-1 (100.0)
Nht (100.0)
H (100.0)
H (99.7)
NOa"1 (100.0)
H"1" (100.0)
14
-------
TABLE 7. SPECIATION IN THE MEAN MAY PRECIPITATION AT HUBBARD BROOK
Component
Ca
Mg
K
Na
Cd
Pb
S04
Cl
NH3
P04
CIT
N03
H
TABLE 8. SPECIATION
Component
Ca
Mg
K
Na
Cd
Pb
S04
Cl
NH3
P04
CIT
N03
H
CHT
5.20
5.69
5.59
5.32
8.28
7.19
4.39
4.93
4.78
6.86
5.28
4.52
IN THE
CH,
5.43
5.69
5.59
5.25
8.28
7.19
4.40
4.63
4.89
7.13
5.28
4.63
Free
5.20
5.69
5.59
5.32
8.28
7.20
4.39
4.93
9.73
18.22
8.44
4.52
4.03
MEAN JUNE
Free
5.43
5.69
5.59
5.25
8.28
7.20
4.40
4.63
9.77
18.35
8.31
4.63
4.11
Ion Principal Species
Ca2*
Mg2*
K*
Na*
Cd2*
Pb2*
S04-2
ci-1
H
H
H
NOa-1
H*
PRECIPITATION AT
(99.2)
(99.5)
(100.0)
(100.0)
(99.2)
(98.6)
(99.1)
(100.0)
(100.0)
(100.0)
(99.8)
(100.0)
(100.0)
HUBBARD BROOK
Ion Principal Species
Ca2*
Mg2*
K*
Na*
Cd2*
Pb2*
S04-2
Cl-1
NH*.
H
H
NO,-1
H*
(99.2)
(99.4)
(100.0)
(100.0)
(99.1)
(98.4)
(99.2)
(100.0)
(100.0)
(100.0)
(99.8)
(100.0)
(100.0)
15
-------
TABLE 9. SPECIATION IN THE MEAN JULY PRECIPITATION AT HUBBARD BROOK
Component
Ca
Mg
K
Na
Cd
Pb
S04
Cl
NH3
P04
CIT
N03
H
CH,
5.37
5.69
5.75
5.52
8,28
7.19
4.34
5.15
4.82
6.98
5.28
4.63
Free Ion
5.37
5.69
5.75
5.52
8.28
7.20
4.34
5.15
9.83
18.45
8.55
4.63
3.98
Principal Species
Ca2+ (99.1)
Mg2+ (99.4)
K+ (100.0)
Na+ (99.9)
Cd2* (99.2)
Pb2+ (98.4)
S04-2 (99.0)
Cl-:1 (100.0)
NH*. (100.0)
H (100.0)
H (99.9)
N03-l(100.0)
H+ (100.0)
TABLE 10. SPECIATION
IN THE
MEAN AUGUST
PRECIPITATION AT HUBBARD BROOK
Component
Ca
Mg
K
Na
Cd
Pb
S04
Cl
NH3
P04
CIT
N03
H
CHT
5.49
5.91
5.99
5.58
8.28
7.19
4.48
4:96
4.89
6.90
5.28
4.70
Free Ion
5.49
5.91
5.99
5.58
8.28
7.20
4.48
4.96
9.74
18.06
8.26
4.70
4.13
Principal Species
Ca2+ (99.3)
Mg2+ (99.5)
K+ (100.0)
Na+ (100.0)
Cd2* (99.3)
Pb2+ (98.7)
S04-2 (99.3)
Cl-1 (100.0)
NH^ (100.0)
H (100.0)
H (99.8)
N03-l(100.0)
H+ (100.0)
16
-------
TABLE 11. SPECIATION IN THE MEAN SEPTEMBER PRECIPITATION AT HUBBARD BROOK
Component
Ca
Mg
K
Na
Cd
Pb
S04
Cl
NH3
P04
CIT
N03
H
CHT
5.52
5.78
5.81
5.46
8.28
7.19
4.44
4.91
4.89
7.13
5.28
4.61
TABLE 12. SPECIATION IN THE
Free Ion
5.52
5.78
5.81
5.46
8.28
7.20
4.44
4.91
9.88
18.57
8.52
4.61
3.99
MEAN OCTOBER
Principal Species
Ca2*
Mg2*
K*
Na*
Cd2*
Pb2*
SO,-2
Cl-1
NH4
H
H
NO,-1
H+
(99.3)
(99.5)
(100.0)
(100.0)
(99.3)
(98.7)
(99.0)
(100.0)
(100.0)
(100.0)
(99.9)
(100.0)
(100.0)
PRECIPITATION AT HUBBARD BROOK
Component
Ca
Mg
K
Na
Cd
Pb
S04
Cl
NH3
P04
CIT
N03
H
5.20
5.48
5.48
5.00
8.28
7.19
4.57
4.55
4.89
6.86
5.28
4.56
5.20
5.48
5.48
5.00
8.28
7.19
4.57
4.55
9.75
18.06
8.29
4.56
4.11
Ca2*
Mg2*
K*
Na*
Cd2*
Pb2*
S04-2
Cl-1
NH4
H
H
(99.4)
(99.6)
(100.0)
(100.0)
(99.3)
(98.9)
(99.2)
(100.0)
(100.0)
(100.0)
(99.7)
N03-l(100.0)
H*
(100.0)
17
-------
TABLE 13. SPECIATION IN THE MEAN NOVEMBER PRECIPITATION AT HUBBARD BROOK
Component
Ca
Mg
K
Na
Cd
Pb
S04
Cl
NH3
P04
CIT
N03
H
CM,
5.46
5.54
5.64
5.13
8.28
7.19
4.64
4.52
5.05
7.28
5.28
4.60
Free Ion
5.46
5.54
5.64
5.13
8.28
7.19
4.64
4.52
9.82
18.32
8.14
4.60
4.19
Principal Species
Ca2* (99.5)
Mg2* (99.7)
K* (100.0)
Na* (100.0)
Cd2* (99.3)
Pb2* (99.0)
S04'-2 (99.3)
Cl-1 (100.0)
ml (loo.o)
H (100.0)
H (99.8)
N08-'(100.0)
H* (100.0)
TABLE 14. SPECIATION
IN 'THE
MEAN DECEMBER
PRECIPITATION AT HUBBARD BROOK
Component
Ca
Mg
K
Na
Cd
Pb
S04
Cl
NH3
P04
CIT
N03
H
CH,
5.65
5.91
5.89
5.41
8.28
7.19
4.78
5.07
5.21
7.28
5.28
4.66
Free Ion
5.65
5.91
5.89
5.41
8.28
7.19
4.78
5.07
9.83
17.99
7.85
4.66
4.37
Principal Species
Ca2* (99.5)
Mg2* (99.7)
K* (100.0)
Na* (100.0)
Cd2* (99.6)
Pb2* (98.2)
S04-2 (99.5)
Cl-1 (100.0)
NH*. (100.0)
H (100.0)
H (99.6)
N03-l(100.0)
H* (100.0)
18
-------
TABLE 15. SPECIATION IN THE MEAN ANNUAL PRECIPITATION AT MT. MOOSILAUKE
Component CH,-
Ca 5.35
Mg 5.82
K 5.52
Na 5.40
Fe(II) 6.30
Cd 8.28
Pb 7.19
Al 6.14
S04 4.43
Cl 5.15
NH3 4.89
N03 4.68
H
Free Ion
5.35
5.82
5.52
5.40
6.30
8.28
7.20
6.23
4.43
5.15
9.80
4.68
4.08
Principal Species
Ca2+ (99.4)
Mg2+ (99.5)
K+ (100.0)
Na"*" (100.0)
Fe2+ (99.5)
Cd2+ (99.3)
Pb2+ (98.7)
A13+ (80.9), OH (15.1)
S04-2 (99.0)
Cl-1 (100.0)
NHt (100.0)
NOa-HlOO.O)
H+ (100.0)
19
-------
Tables 16 and 17 give the results of two speciation calculations for
throughfall, one for Hubbard Brook (Likens e_t a]_. , 1977) and one for Mt.
Moosilauke (Cronan, 1979). For these calculations, the organic carbon con-
centrations were assumed to be divided equally between acetic and formic acids
on a molar basis. These two metal-complexing organic acids are common in
soil-plant systems and have been identified in soil leachates at Mt.
Moosilauke (Cronan et aj. , 1978; Cronan, 1979). They serve in the present
case as model organic ligands. The total number of inorganic and organic
complexes considered in the speciation calculations was 92.
TABLE 16. SPECIATION IN THROUGHFALL AT HUBBARD BROOK (JUNE-OCTOBER MEAN)
Component CHT
Ca 4.40
Mg 4.73
K 3.79
Na 5.22
S04 4.25
Cl 4.39
NH3 4.17
P04 5.80
AC 3.94
N03 4.97
FOR 3.94
H
Free Ion
4.41
4.73
3.79
5.22
4.25
4.39
8.16
15.20
4.15
4.97
3.96
5.00
Principal Species
Ca*+
Mg2+
K+
Na+
S04-2
Cl-1
NH4
H
AC-1
NOa-1
FOR-1
H+
(98.7)
(98.9)
(100.0)
(99.9)
(98.9)
(100.0)
(100.0)
(99.8)
(62.4), H (37.6)
(100.0)
(95.3)
(100.0)
20
-------
TABLE 17. SPECIATION IN THROUGHFALL AT MT. MOOSILAUKE (MEAN ANNUAL)
Component
Ca
Mg
K
Na
Fe(II)
Mn(II)
Al
S04
Cl
NH3
AC
N03
FOR
H
CHy
4.74
5.15
4.43
5.52
6.30
5.70
5.75
4.15
4.89
5.22
4.78
4.92
4.78
Free Ion
4.75
5.15
4.43
5.52
6.30
5.71
5.84
4.16
4.89
10.19
5.61
4.92
4.94
4.02
Principal Species
Ca'+
Mg2+
K+
Na+
Fe2+
Mn2+
A13+
S04-2
Cl-1
NH:
H
NOa-1
FOR-1
H+
(98.8)
(99.1)
(99.9)
(99.9)
(99.1)
(98.8)
(80.9), OH (12.0)
(98.5)
(100.0)
(100.0)
(85.2), AC"1 (14.8)
(100.0)
(68.6), H (31.4)
(100.0)
Once again, despite major increases in the total concentrations of all
components (except H ) in the throughfall relative to the corresponding pre-
cipitation, the data in Tables 16 and 17 show that there is very little dif-
ference in the speciation. The overall trend is toward a slight decrease in
the free ionic percentages for the metals in going from precipitation to
throughfall.
Tables 18 and 19 give the results of speciation calculations for acid
precipitation at Ithaca, New York and Caribou, Maine, respectively. The
calculations performed by GEOCHEM took into account 129 soluble complexes for
the New York data and 141 soluble complexes for the Maine data. Both precipi-
tation solutions were found to be supersaturated with respect to amorphous
Fe(OH)3(s). This result may be caused by the presence of colloidal Fe(OH)3(s)
or by disequilibrium with respect to the solid. Other than this special
characteristic, the data in Tables 18 and 19 show no significant differences
from the data in Table 2.
21
-------
TABLE 18. SPECIATION IN PRECIPITATION AT ITHACA, NEW YORK
Component CHT
Ca 4.77
Mg 5.18
K 5.81
Na 5.22
Fe(III) 6.14
Mn(II) 7.04
Al 5.73
C03 4.99
S04 4.37
Cl 4.54
NH3 4.62
P04 6.82
AC 4.25
N03 4.50
H
Free Ion
4.77
5.18
5.81
5.22
8.66
7.04
5.82
13.50
4.38
4.54
9.53
18.11
5.04
4.50
4.07
Principal Species
Ca*+
Mg2+
K+
' Na+
OH
Mn2+
A13+
H
S04-2
Cl-1
NHt
H
H
NOa-1
H+
(99.3)
(99.4)
(100.0)
(99.9)
(99.2)*
(99.3)
(80.9), OH (14.6)
(100.0)
(98.7)
(100.0)
(100.0)
(98.5)
(83.7), AC-1 (16.3)
(100.0)
(100.0)
Supersaturation with respect to amorphous Fe(OH)3(s).
22
-------
TABLE 19. SPECIATION IN PRECIPITATION AT CARIBOU, MAINE
Component CH-p
Ca 5.01
Mg 5.13
K 5.45
Na 5.00
Fe(III) 5.89
Mn(II) 6.79
Cu 6.66
Cd 7.75
Zn 5.97
Ni 6.77
Pb(II) 6.47
S04 4.44
Cl 5.13
N03 5.21
H
Free Ion
5.01
5.13
5.45
5.00
9.04
6.79
. 6.66
7.75
5.97
6.77
6.48
4.44
5.13
5.21
4.41
Principal Species
Ca2+
Mg2+
K+
Na+
OH
Mn2+
Cu2+
Cd2+
Zn2+
Ni2+
Pb2+
S04-2
Cl-1
N03-*
H+
(99.4)
(99.5)
(100.0)
(100.0)
(99.9)*
(99.4)
(99.2)
(99.3)
(99.2)
(99.4)
(98.7)
(99.3)
(100.0)
(100.0)
(100.0)
Supersaturation with respect to amorphous Fe(OH)3(s).
23
-------
INTERACTION OF ACID PRECIPITATION WITH SOIL MINERALS
According to Likens et al. (1977), rainwater impinging on the soils at
Hubbard Brook infiltrates directly and produces no significant overland flow.
Since vertical movement of the water tends to be impeded by the near-surface
occurrence of either bedrock or clayey layers, it may be concluded that inter-
flow is the principal mechanism of runoff at Hubbard Brook. This conclusion
is in agreement with the accepted picture of the runoff cycle in forested
areas (Ward, 1975).
Given that interflow is the principal means by which acid precipitation
is transported to the channel system in a watershed, it follows that the
chemical properties of the precipitation may .be altered by interaction with
the more soluble soil minerals. In particular, as has been proposed by Cronan
et al. (1978), Cronan (1979), Cronan and Schofield (1979), and Johnson (1979)
in recent papers, acid precipitation may interact with iron and aluminum
hydrous oxides to dissolve these minerals and release the metals they contain
into subsurface runoff. It was decided to check this hypothesis chemically
through a simulation using GEOCHEM.
For each of the three areas represented by the data in Tables 2 to 19,
soil surveys were consulted to identify the principal great groups (Likens
et al. , 1977; Soil Survey, Tompkins County, New York, 1965; Soil Survey,
Aroostook County, Maine, 1964). This accomplished, the chemical properties of
representative soil profiles in these great groups were obtained from soil
survey data presented in Appendix IV of Soil Taxonomy (Soil Survey Staff,
1975). Although the soils under consideration contain vermiculite, illite,
montmorillonite, muscovite, and other crystalline aluminosilicates (Johnson
et al., 1968), it is expected that amorphous aluminum and iron hydrous oxides,
which typically coat mineral surfaces, will be the most reactive with acid
precipitation (Johnson, 1979). Therefore, only these minerals were considered
in the simulation.
In order to establish a "baseline value" for Al and Fe in the soil solu-
tions prior to the intrusion of acid precipitation, the following calculation
was performed. Let W be the weight percent of Al(OH)3(s) or Fe(OH)3(s) in a
surface soil horizon and let M be the molecular weight of the hydroxide. Then
the molar concentration of the hydroxide iji toto in a water-saturated soil is
given by the equation:
CHy = W/MV (3)
where V is the volume of pore space per 100 g of soil. The parameter C,, is
the molar concentration of Al or Fe that would be found in the soil solution
if the soil were water-saturated and all of the hydroxide had dissolved. If
this total concentration is input to GEOCHEM, the program will predict how
much of it actually will form the solid hydroxide phase and how much will
remain in aqueous solution. The results of such a calculation for the three
acid precipitation study areas are given in Table 20.
24
-------
TABLE 20. TOTAL "BASELINE" SOLUBLE ALUMINUM AND IRON IN REPRESENTATIVE SOILS
FROM THE THREE PRECIPITATION STUDY AREAS
Area % Al % Fe V pH A1T<; Fe
(cmVlOO g) lb l
New Hampshire
New York
Maine
1.09
0.20
0.47
1.90
0.60
1.50
37
21
18
5.65
5.60
4.80
4.26
4.23
3.38
8.36
8.32
7.57
The second and third columns in Table 20 give the weight of amorphous Al
and Fe hydrous oxides per 100 g soil as obtained from soil survey data. The
fourth and fifth columns give the pore space volume and the soil pH value,
respectively, also obtained from soil survey data. The last two columns give
the negative common logarithm of the total molar concentration of Al and Fe in
the soil solution after the precipitation of Al(OH)3(am) and Fe(OH)3(am).
These latter figures were estimated by GEOCHEM in a speciatidn calculation
which included all known soluble hydrolytic species of Al and Fe, as well as
complexes of these metals with C03. The total concentration of C03 included
in each calculation was computed as that C03,. which is expected in a solution,
at the appropriate pH value given in Table 20, which is in equilibrium with
atmospheric C02 at a pressure of io-3'52 atm. No other ligands than C03 and
OH were considered. Thus the results in Table 20 refer to a soil solution
whose chemistry is dominated by carbonic acid.
With the "baseline" estimates in Table 20 in hand, a computer simulation
of the interaction between acid precipitation and amorphous Al and Fe hydrox-
ides in soil may be carried out quite easily. The simulation consists of a
speciation calculation on a system whose input total concentrations are those
of the acid precipitation under study plus the total concentrations of Al and
Fe corresponding to CH as calculated in Eq. (3). The program then can pre-
dict the total solubleyAl and Fe remaining in solution after Al(OH)3(am) and
Fe(OH)3(am) have precipitated in the system.
Because of the presence of trace metals, such as Pb and Cd, in the acid
precipitation, it was decided to include the possibility of cation adsorption
by clay minerals in the simulation. Adsorption often is observed to be an
effective mechanism for immobilizing trace metals. The degree to which this
mechanism may apply in the soils in this investigation was assessed by includ-
ing data on exchangeable cations in the simulation, following the procedures
outlined by Sposito and Mattigod (1979) for handling cation exchange phenomena
in GEOCHEM. The data on the distribution of exchangeable cations were taken
from soil surveys. The exchanger was assumed to be montmorillonite (as
modeled by Chambers bentonite).
25
-------
To simulate the effect of organic acids in the soil solution, acetic and
formic acids were included in all of the mixtures except for Maine at 10-4'54M
each in total concentration. This level was suggested by the leachate data of
Cronan et al. (1978).
26
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SOIL RESPONSE TO ACID PRECIPITATION
NEW HAMPSHIRE SOILS
The speciation of a mixture of acid precipitation and soil in New
Hampshire is illustrated in Tables 21 to 23. Table 21 gives the results of a
speciation calculation for the acid precipitation described in Table 2. The
principal effects on the soil are: (1) the solubilization of Al and Fe, and
(2) the adsorption of Cd and Pb. It may be noted that Al,. in Table 21 is more
than two orders of magnitude larger than the "baseline" value in Table 20 and
that Fey in Table 21 is about two orders of magnitude larger than the
"baseline" value. Hydrolytic species are in part responsible for this in-
crease in solubility, although the model organic acids, acetic and formic, and
the inorganic ligands, S04 and Cl did complex Al significantly.
An examination of Tables 22 to 24 reveals that the same trends seen in
Table 21 prevail. Therefore, the behavior of Al, Fe, Cd, and Pb does not
depend on time of year (Tables 22 and 23) or the (nearby) location of the acid
precipitation (Table 24). It may be noted that the predicted lack of dominant
organic complexation of Al and Fe (Table 24) did not preclude increased solu-
bility levels for these metals. The speciation calculations summarized in
Tables 21 to 24 took into account about 200 inorganic and organic complexes.
Table 25 illustrates the speciation in a mixture of throughfall and soil.
The trends shown in the table are identical with those in Tables 21 to 24,
with respect to Al and Fe solubilities.
27
-------
TABLE 21. SPECIATION IN THE MEAN ANNUAL PRECIPITATION/SOIL MIXTURE
AT HUBBARD BROOK
Component
Ca
Mg
K
Na
Fe(III)
Cd
Pb(II)
Al
C03
S04
Cl
NH3
P04
AC
N03
CHAM
FOR
CHT
1.49
2.39
5.75
5.28
6.83
8.28
7.19
1.83
4.91
4.52
4.84
4.91
7.07
4.35
4.64
1.14
4.54
Free Ion
1.49
2.39
5.75
5.28
9.45
9.69
19.69
1.95
13.33
5.87
4.97
9.78
18.58
5.22
4.70
1.14
5.05
Principal Species
Ca2+ (99.9)
Mg2+ (99.9)
K+ (100.0)
Na+ (100.0)
OH (100.0)
CHAM(s)(96.1)
CHAM(s)(100.0)
A13+ (75.9), OH (23.4)
H (98.4)
Al (67.4), Ca (25.6)
Cl-1 (74.8), Al (15.3)
NHt (100.0)
H (47.5), Ca (46.4)
H (61.7), Al (17.4),
AC l (13.5)
NOa-1 (86.6), Ca (13.1)
CHAM" HI oo.o)
Al (31.6), FOR"1 (30.
Ca (23.4), H (11.2)
4.13 H+ (100.0)
28
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TABLE 22. SPECIATION IN THE MEAN JANUARY PRECIPITATION/SOIL MIXTURE
AT HUBBARD BROOK
Component CHT
Ca 1 .49
Mg 2.39
K 5.99
Na 5.25
Fe(III) 7.01
Cd 8.28
Pb(II) 7.19
Al 2.26
C03 4.91
S04 4.66
Cl 5.09
NH3 4.89
P04 7.28
AC 4.54
CIT 5.28
N03 4.52
CHAM 1.14
FOR 4.54
Free Ion
1.49
2.39
5.99
5.25
9.91
9.70
19.70
2.41
13.03
5.76
5.17
9.61
18.50
5.26
26.51
4.58
1.14
4.93
Principal Species
Ca2+ (99.9)
Mg2+ (99.9)
K+ (100.0)
Na+ (100.0)
OH (100.0)
CHAM(s)(96.2)
CHAM(s)OOO.O)
A13+ (70.8), OH (29.5)
H (99.0)
Ca (45.7), Al (41.7)
Cl-1 (83.1), Ca (10.0)
NHj (100.0)
H (47.3), Ca (46.7)
H (61.8), Ac-1 (19.1),
AC-1 (13.5)
Al (100.0)
NOa-1 (86.6), Ca (13.1)
CHAM-^IOO.O)
FOR-1 (40.6), Ca (30.7),
Al (14.4), H (10.4)
4.28
H (100.0)
29
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TABLE 23. SPECIATION IN THE MEAN JULY PRECIPITATION/SOIL MIXTURE
AT HUBBARD BROOK
Component CH,
Ca 1 . 49
Mg 2.39
K 5.75
Na 5.52
Fe(III) 6.65
Cd 8.28
Pb(II) 7.19
Al 1.39
C03 4.91
S04 4.34
Cl 5.15
NH3 4.82
P04 6.98
AC 4.54
N03 4.63
CHAM 1.14
FOR 4.54
Free Ion
1.49
2.39
5.75
5.52
9.00
9.69
19.69
1.50
13.62
6.03
5.38
9.84
18.79
5.42
4.69
1.14
5.26
Principal Species
Ca2+ (100.0)
Mg2+ (1000.0)
K+ (100.0)
Na+ (100.0)
OH (100.0)
CHAM(s)(96.1)
CHAM(s)(100.0)
A13+ (77.6), OH (22.9)
H (97.1)
Al (85.3), Ca (11.5)
Cl-1 (58. )6, Al (33.7)
NHj (100.0)
H (48.3), Ca (45.6)
H (55.5), Al (31.2),
NOs-1 (86.6), Ca (13.1)
CHAM-1 (100.0)
Al (54.9), FOR-1 (19.
Ca (14.4)
H 3.98 H+ (100.0)
30
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TABLE 24. SPECIATION IN THE MEAN ANNUAL PRECIPITATION/SOIL MIXTURE
AT MT. MOOSILAUKE
Component CH-..
Ca 1.49
Mg 2.39
K 5.52
Na 5.40
Fe(III) 6.77
Fe(II) 6.30
Cd 8.28
Pb(II) 7.19
Al 1.67
C03 4.91
S04 4.43
Cl 5.15
NH3 4.89
AC 4.54
N03 4.68
CHAM 1.14
FOR 4.54
Free Ion
1.49
2.39
5.52
5.40
9.30
6.30
9.69
19.69
1.80
13.42
5.88
5.30
9.81
5.47
4.74
1.14
5.11
Principal Species
Ca2+ (99.9)
Mg2+ (100.0)
K+ (100.0)
Na+ (100.0)
OH . (100.0)
Fe2+ (100.0)
CHAM(s)(96.1)
CHAM(s)(100.0)
A13+ (74.1), OH (25.2)
H (98.0)
Al (74.0), Ca (20.4)
Cl-1 (70.4), Al (20.3)
NH^ (100.0)
H (60.3), Al (21.4),
AC-1 (11.8)
NOa-1 (86.6), Ca (13.1)
CHAM-HlOO.O)
Al (39.0), FOR-1 (27.
Ca (20.5), H (11.0)
H
4.08
H (100.0)
31
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TABLE 25. SPECIATION IN THE MEAN THROUGHFALL/SOIL MIXTURE AT Mt. MOOSILAUKE
Component CHT
Ca 1.49
Mg 2.39
K 4.43
Na 5.52
Fe(III) 6.69
Fe(II) 6.30
Mn 5.70
Al 1.48
C03 4.91
S04 4.15
Cl 4.89
NH3 5.22
AC 4.34
N03 4.92
CHAM 1.14
FOR 4.34
Free Ion
1.49
2.39
4.43
5.52
9.10
6.30
5.70
1.60
13.53
5.73
5.08
10.20
5.34
4.98
1.14
4.99
Principal Species
Ca2+ (99.9)
Mg2+ (99.9)
K+ (100.0)
Na* (100.0)
OH (100.0)
Fe2+ (100.0)
Mn2+ (100.0)
A13+ (75.9), OH (22.9)
H (97.5)
Al (81.4), Ca (14.5)
Cl-1 (63.9), Al (27.9)
H (100.0)
H (57.3), Al (27.4),
AC-1 (10.0)
NOa-1 (86.8), Ca (12.8)
CHAM-^IOO.O)
Al (48.8), FOR-1 (22.3
Ca (16.5), H (10.2)
4.02 H+ (100.0)
32
-------
NEW YORK AND MAINE SOILS
Tables 26 and 27 give the results of speciation calculations for mixtures
of acid precipitation and soil in the areas near Ithaca, New York, and
Caribou, Maine. These calculations involved the consideration of 139 and 191
soluble complexes, respectively. Both tables show significant increases in
the solubility of Al and Fe (see Table 20) and adsorption of trace metals by
clays (Table 27). The solubility increases for Al and Fe are about the same
as were found for the precipitation/soil mixtures in New Hampshire.
33
-------
TABLE 26. SPECIATION IN THE PRECIPITATION/SOIL MIXTURE AT ITHACA, NEW YORK
Component CHT
Ca 1.15
Mg 1 . 62
K 5.81
Na 5.22
Fe(III) 6.76
Mn(II) 7.04
Al 1.65
C03 4.99
S04 4.37
Cl 4.54
NH3 4.62
P04 6.82
AC 4.25
N03 4.50
CHAM 0.72
H
Free Ion
1.49
1.62
5.81
5.22
9.26
7.04
1.76
13.51
5.88
4.72
9.55
18.55
5.20
4.57
0.94
4.07
Principal Species
CHAM(s)(53.9), Ca2+ (46.1)
Mg2 +
K+
Na+
OH
Mn2+
A13+
H
Al
Cl-1
NH:
H
H
NO,-1
CHAM-
H+
(100.0)
(100.0)
(100.0)
(100.0)
(100.0)
(77.6), OH (22.9)
(97.9)
(69.1), Ca (17.5)
Mg (10.2)
(66.6), Al (20.6)
(100.0)
(37.4), Ca (35.9)
Mg (26.6)
(56.9), Al (21.6),
AC-1 (11.1)
(85.1), Ca (13.0)
1 (60.0), Ca(s) (40.0)
(100.0)
34
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TABLE 27. SPECIATION IN THE PRECIPITATION/SOIL MIXTURE AT CARIBOU, MAINE
Component
Ca
Mg
K
Na
Fe(III)
Mn(II)
Cu
Cd
Zn
Ni
Pb(II)
Al
C03
S04
Cl
N03
CHAM
H
CHT
0.47
1.25
5.45
5.00
7.15
6.79
6.66
7.75
5.97
6.77
6.47
2.58
5.00
4.44
5.13
5.21
0.10
Free Ion
1.50
1.60
5.45
5.00
10.29
6.79
11.40
10.10
8.00
6.77
20.10
2.79
12.86
5.53
5.22
5.28
0.93
4.41
Principal Species
CHAM(s)(90.7), Ca2+(99.
CHAM(s)(55.7), Mg2+(44.
K+ (100.0)
Na+ (100.0)
OH (100.0)
Mn2+ (99.9)
CHAM(s)(100.0)
CHAM(s)(99.6)
CHAM(s)(99.1)
Ni2+ (99.9)
CHAM(s)(100.0)
A13+ (61.7), OH (37.2)
H (99.0)
Ca (45.6), Mg (28.7)
Al (17.5)
Cl-1 (82.0), Ca (9.5)
NOa-1 (85.4), Ca (12.5)
Ca (77.4), CHAM-H14
H+ (100.0)
9)
3)
»
.7)
35
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REFERENCES
Cronan, C. S. 1979. Solution chemistry of a New Hampshire subalpine eco-
system: A biogeochemical analysis. Oikos (in press).
Cronan, C. S. , and C. L. Schofield. 1979. Aluminum leaching response to acid
precipitation: Effects on high-elevation watersheds in the northeast.
Science 204:304-306.
Cronan, C. S., W. A. Reiners, R. C. Reynolds, and G. E. Lang. 1978. Forest
floor leaching: Contributions from mineral, organic, and carbonic acids
in New Hampshire subalpine forests. Science 200:309-311.
Helgeson, H. C. 1969. Thermodynamics of hydrothermal systems at elevated
temperatures and pressures. Am. J. Sci. 267:729-804.
Ingle, S. E. , M. D. Schuldt, and D. W. Schults. 1978. A user's guide for
REDEQL - EPA. U.S. Environ. Prot. Agency Rpt. EPA-600/3-78-024.
Corvallis, Oregon. NTIS PB 280 149.
Johnson, N. M. 1979. Acid rain: Neutralization within the Hubbard Brook
ecosystem and regional implications. Science 204:497-499.
Johnson, N. M., G. E. Likens, F. H. Bormann, and R. S. Pierce. 1968. Rate of
chemical weathering of silicate minerals in New Hampshire. Geochim. et
Cosmochim. Acta 32:531-545.
Leggett, D. J. 1977. Machine computation of equilibrium concentrations --
some practical considerations. Talanta 24:535-542.
Likens, G. E. 1972. The chemistry of precipitation in the central Finger
Lakes region. Tech. Rpt. 50. Cornell Univ. Water Resources and Marine
Sciences Center, Ithaca, New York.
Likens, G. E. 1975. Acid precipitation: Our understanding of the pheno-
menon. Proc. Conf. on Emerging Environmental Problems (Reusselaerville,
New York), pp. 45-75.
Likens, G. E. , F. H. Bormann, R. S. Pierce, J. S. Eaton, and N. M. Johnson.
1977. Biogeochemistry of a forested ecosystem. Springer-Verlag, New
York.
Lodge, J. P., J. B. Pate, W. Basbergill, G. S. Swanson, K. C. Hill, E.
Lorange, and A. L. Lazrus. 1968. Chemistry of United States preci-
pitation. Final Rpt., National Center for Atmospheric Research, Boulder,
CO.
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McDuff, R. E. , and F. M. M. Morel. 1973.
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Pasadena.
Description and use of
Rpt. EQ-73-02. Calif.
the chemical
Inst. Tech.,
Mattigod, S. V., and G. Sposito. 1979. Chemical modeling of trace metal
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systems — Speciation, .sorption, solubility, and kinetics. ACS Symposium
Series No. 93. American Chem. Soc. , Washington, D.C.
Morel, F., and J. Morgan. 1972.
in aqueous chemical systems.
A numerical method for computing equilibria
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systems of New Hampshire. U.S.A. Envir. Pollution 6:39-47.
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38
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-80-015
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Effects of Acid Precipitation on Soil Leachate Quality:
Computer Calculations
5. REPORT DATE
January 1980 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Garrison Sposito, A. L. Page, and Mark E. Frink
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Soil and Environmental Sciences
University of California
Riverside, CA 92521
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO,
B0836NAEX
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Research Laboratory
U.S. Environmental Protection Agency
Corvallis, OR 97330
13. TYPE Of REPORTAND PERIODCOy
Final, ray-October 1979
ERED
14. SPONSORING AGENCY CODE
EPA/600/02
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The multipurpose computer program GEOCHEM was employed to calculate the equilibrium
speciation in twenty-three examples of acid precipitation from New Hampshire, New York,
and Maine, and in the same number of mixtures of acid precipitation with minerals charac-
teristic of soils in the three states mentioned. Between TOO and 200 soluble inorganic
and organic complexes were taken into account in each speciation calculation. The calcu-
lations performed on the acid precipitation samples showed that the metals (including
heavy metals) and the sulfate, chloride, and nitrate ligands would be almost entirely in
their free ionic forms, while the phosphate, carbonate, ammonia, and organic ligands
would be in their protonated forms. This result was independent of the geographic loca-
tion of the acid precipitation and the month of the year in which it was collected.
The speciation calculations on the precipitation-soil mineral mixtures showed that
aluminum and iron levels in a soil solution affected by acid precipitation would be sig-
nificantly higher than in one whose chemistry is dominated by carbonic acid. The higher
levels found were caused by the lower pH value of acid precipitation as well as by com-
plexes formed with inorganic and organic ligands. It was also shown that soil cation
exchangers would adsorb preferentially heavy metals, such as Cd and Pb, which are found
in acid precipitation.
This report was submitted in fulfillment of Contract No. B0836NAEX by the University
of California, Riverside, under the sponsorship of the U.S. Environmental Protection
Agency. This report covers the period April 27, 1979, to August 20, 1979, and work was
completed as of August 31, 1979.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Acidification, precipitation, soil chemistry
agricultural chemistry, agricultural
products
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
acid precipitation
acid rain
atmospheric deposition
02-A
02-D
8. DISTRIBUTION STATEMENT
Release to public
19. SECURITY CLASS (This Report}
21. NO. OF PAGES
48
20. SECURITY CLASS (Thispage}
unclassified
22. PRICE
EPA Perm 2220.1 (R»v. 4-77)
39
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