Open Journal of Soil Science, 2012, 2, 100-110
http://dx.doi.org/10.4236/ojss.2012.22015 Published Online June 2012 (http://www.SciRP.org/journal/ojss)
Formation and Changes of Humic Acid Properties during
Peat Humification Process within Ombrotrophic Bogs*
Oskars Purmalis, Maris Klavins
Department of Environmental Sciences, University of Latvia, Riga, Latvia.
Received March 12th, 2012; revised April 13th, 2012, accepted April 30th, 2012
ABSTRACT
Studies of the living organic matter humification process are essential for understanding the carbon biogeochemical
cycle. The aim of this study is to analyze relations between the properties of peat, peat humic acids and peat humifica-
tion degree. The analysis has been done on samples of humic substances extracted from peat profiles in two ombrotro-
phic bogs and relations between peat age, decomposition and humification degree, botanical composition and properties
of peat humic acids (elemental, functional composition) were studied. The found variability of peat properties is less
significant than differences in the properties of peat-forming living matter, thus revealing the dominant impact of humi-
fication process on the properties of peat. Correspondingly, composition of peat humic acids is little affected by differ-
ences in the composition of precursor living organic material.
Keywords: Peat; Humic Substances; Humic Acids; Humification
1. Introduction
In the carbon biogeochemical cycle, the transformation
of living organic matter into refractory part of organic
matter (humic substances, such as humic acids, fulvic
acids, and humin) or humification is of key importance.
Humification can be defined as the transformation of
numerous groups of substances (proteins, carbohydrates,
lipids etc.) and individual molecules present in living
organic matter into groups of substances with similar
properties (humic substances) [1]. Humification plays an
important role in the diagenesis of fossil carbon deposits
[2]. Humification is a sum of very complex processes in-
cluding degradation and synthetic reactions, but also con-
sidering the high variability of environmental conditions
under which living organic matter decays, slow pace of
humification reactions and large number of structural di-
fferences of the organic molecules composing living or-
ganic matter. It can be supposed that humification condi-
tions may have an impact on the structure and properties
of refractory intermediate transformation products of liv-
ing organic matter—humic substances. From this per-
spective, it is important to study humification processes
in a relatively homogeneous and stable environment, for
example, bogs to reduce the impact of natural environ-
mental variability.
Peat is a light brown to black organic material, which
is formed under waterlogged conditions from the partial
decomposition of mosses and other bryophytes, sedges,
grasses, shrubs, or trees [3]. The interest in peat proper-
ties is growing, as peat is a substance that supports and
influences bog and wetland ecosystems, while peat pro-
files can serve as “archives” indicating conditions in past
environments [4,5]. Significant amounts of organic car-
bon are stored in the form of peat. Therefore, peat re-
serves play a major role in the carbon biogeochemical
cycling, which is of key importance in the context of the
ongoing process of climate change [6,7]. Industrial and
agricultural uses of peat are growing [8,9], and signifi-
cant amounts of peat are mined industrially. Considering
this, there is an increasing interest into studies of peat
properties and their diagenesis. Humification in peat has
been taking place in very different conditions both geo-
graphically (from tropical regions to Arctic environment)
and temporally (historically peat development can last
for many thousands of years). During peat formation
even at one particular site, significant changes in vegeta-
tion, temperature, amount of precipitation and, corre-
spondingly, in the bog hydrological conditions and land
use in the basin of wetland [10-12] could have happened.
As a result, we can expect not only to understand changes
in the properties of peat humic substances but also to
identify molecular descriptors of organic matter diagene-
sis process. Notwithstanding the importance of this sub-
*The research was financially supported by ERAF, the project “Innova-
tion in Peat Studies for Development of New Applications”.
N
o: 210/0264/2DP2/2.1.1.1.0/10/APIA/VIAA/037

Formation and Changes of Humic Acid Properties during Peat Humification Process within Ombrotrophic Bogs 101
ject, relations between the properties of peat (especially
in full peat profiles) and those of peat humic substances
have been studied comparatively little, just in a few
studies [12-14].
The aim of this study is to analyze relations between
the properties of peat, peat humic acid and peat humifi-
cation degree.
2. Materials and Methods
2.1. Site Location
In-depth study of peat composition, humification degree
and peat humic acid properties was carried out in two
ombrotrophic bogs located in the central part of Latvia
(Figure 1). Full peat profiles were obtained and cut into
5-cm layers for analysis of peat properties and isolation
of humic acids. The analysis of botanical composition
was performed microscopically, using a Carl-Zeiss bino-
cular microscope, thereby determining the decomposition
degree [15].
2.2. Isolation of Peat Humic Acids
HAs were extracted and purified, using procedures re-
commended by the International Humic Substances So-
ciety (IHSS) [16].
2.3. Analysis of Peat and Humic Acid Properties
The 14C dating was done at the Institute of Geology of
the Tallinn Technical University (Estonia). Carbon, hy-
drogen, nitrogen and sulphur concentrations in the peat
and humic acid samples (elemental analysis of C, H, N, S)
were determined by combustion-gas chromatography te-
chnique, using an Elemental Analyzer Model EA-1108
(Carlo Erba Instruments). Ash content was measured
after heating 50 mg of each peat sample at 750˚C for 8 h.
Elemental composition was corrected considering the ash
content, and the oxygen amount was calculated as a di-
fference. Elemental analysis was used in order to cal-
culate the elemental ratios, degree of oxidation ω (1) [17]
and index of hydrogen deficiency
 (2).

H
2O 3NC



 (1)
(2C 2) H
2


 (2)
Atomic ratios were calculated from elemental analysis,
using the Equations (3), (4):
(Mc O%)
OC (MoC%)

 (3)
H
(McH%)
HC (MC%)

 (4)
where MX is the element molecular mass, and X% is
percentage of the element in the sample.
UV/Vis spectra were recorded on a Thermospectronic
Helios γ UV (Thermoelectron Co) spectrophotometer in a
1-cm quartz cuvette. The ratio E4/E6 [18], i.e. the ratio of
absorbance at 465 and 665 nm, was determined for 10
mg of humic acid solutions in 10 ml of 0.05 M NaOH.
2.4. Humification Degree (according to [19] and
Modified by [20])
1.00 g of peat sample was treated for 1(1/2) hrs with 25
ml of 8% NaOH in 25 ml plastic tube in a boiling water
bath (95˚C) and filtered. 12.5 ml of the filtrate were
Figure 1. Sampling sites: A—Dzelve bog; B—Eipurs bog.

Formation and Changes of Humic Acid Properties during Peat Humification Process within Ombrotrophic Bogs 102
diluted to 100 ml and absorption was measured at 540
nm. The peat humification degree was expressed as ab-
sorption at 540 nm.
2.5. Carboxylic Groups and Total Acidity
An automatic titrator TitroLine easy (Schott-Geräte GmbH)
was used for measuring carboxylic and phenolic acidity
of each HA. The known Ca-acetate method [16], based
on the formation of acetic acid, was used for determining
the total number of carboxylic groups. HAs (20 mg) were
weighed into a 100 ml Erlenmeyer flask, 10 ml of the 0.2
N calcium acetate solution were added and mixed under
N2 for 24 hours. Samples were potentiometrically titrated
to pH 9.0 with 0.1 M NaOH. To estimate the total acidity,
20 mg of humic acid, were dispersed in 10 ml 0.1 M
Ba(OH)2 solution, which was then shaken overnight un-
der N2 atmosphere, filtered and washed with water. The
filtrate, together with the washing solution, was poten-
tiometrically titrated with 0.1 M HCl down to pH 8.4
under N2 flow.
2.6. Hydrophobicity
Hydrophobicity of humic substances was characterized
by their distribution between water and polyethylene
(PEG) phases (PEG 20000, Fluka) [21] as distribution
coefficient KPEGW (analogous to octanol/water distribu-
tion coefficient—Kow). The 10% PEG-10% (NH4)2SO4-
HA-H2O systems were prepared by mixing 2 ml of 30%
PEG solution with 2 ml of ammonium sulphate solution
and 2 ml of HA (2 mg/ml in 0.05 M NaOH). The mix-
tures were shaken for 10 min. After complete phase sepa-
ration, 1 ml was taken from each phase and diluted by 10
times in 0.05 M NaHCO3. Then the absorbances at 465
nm were measured on a DR/2000 spectrophotometer
(Hach Co). The distribution coefficients were calculated
as follows: KPEGW = absorbance at 465 nm of the top
(PEG-rich) phase/absorbance at 465 nm of the bottom
phase.
2.7. Fluorescence Spectra
Fluorescence spectra were recorded, using Perkin Elmer
LS 55 fluorescence spectrometer, on aqueous solutions
of each sample at a concentration of 25 mg/L, adjusted to
pH 7 with 0.5 M HCl. Emission spectra were recorded
(scan speed 500 nm/min, with slit 10.0 nm over the
wavelength range of 380 to 650 nm) at a fixed excitation
wavelength of 350 nm. The ratio of fluorescence inten-
sity at 460 nm to intensity at 510 nm (I460/I510) was used,
as previously suggested by [22], as a humification indi-
cator.
2.8. Data Treatment
Statistical analyses were performed using SPSS 16 Soft-
ware. The correspondence of the obtained data to the
normal distribution was checked with the Kolmogorov-
Smirnov tests. In further analysis, non-parametric me-
thods were used. Relationships between different chara-
cteristics were assessed by Spearman’s rank correlation
coefficients. In all cases the significance level was p =
0.05.
3. Results and Discussion
3.1. Peat Composition and Their Changes
Peat humification process and development of peat hu-
mic acids were studied in the peat profiles from two he-
terogeneous ombrotrophic bogs in Latvia.
The results of the paleobotanical investigations (bota-
nical composition, pollen analysis) indicate both diffe-
rences and similarities in the development and peat pro-
perties of the studied bogs. Dzelve Bog has been formed
due to paludification of sandy ground as result of ground-
water level increase and wet conditions during the small
depression after the Ice Age. A raised bog cotton grass
peat layer covers the sandy bottom, overlaid by pine-
cotton grass peat. The upper part of peat section is repre-
sented by a 3.2 m thick Sphagnum fuscum peat layer with
a decomposition level 9% to 17% (Figure 2). The bota-
nical composition of most of the bog is relatively het-
erogeneous: Sphagnum fuscum (60% - 75%), Eriopho-
rum vaginatum (10% - 15%), Sphagnum rubellum (10% -
15%) and dwarf shrubs (10% - 15%).
The botanical composition of Eipurs Bog is comple-
tely different, although it is of a similar origin (Figure 3).
The lowest part of Eipurs Bog is formed by fen wood-
grass peat, Hypnum and sedge-Hypnum peat (Figure 3),
and these layers are covered by transition type wood peat.
The upper part is represented by a 3.45 m thick layer of
raised bog peat of different types and decomposition
degrees. For example, well decomposed (40% - 48%)
pine-cotton grass peat occurs at the depth interval of 1.18
- 1.39 m (Figure 3). Although these bogs are located
comparatively close to each other (distance 12 km), their
local conditions for peat formation have been different.
Basic peat properties were analyzed, using peat ele-
mental (C, H, N, O, S) composition. The elemental com-
position of the studied peat cores are summarized in
Figure 4, Table 1. The ash contents in the studied bogs
range between 0.30% ± 0.05% and 6.10% ± 0.05%, with
an average content of 1.8 ± 0.05. The C concentrations
range from 40 to 55%, H—from 5.4% to 6.7%, N—from
0.5% to 1.5%, S—from 0.2% to 1.7% and O—from 38%
to 49%. The elemental composition of peat in Eipurs Bog
is comparatively variable and reflects changes in the peat
decomposition degree and peat types. C concentration in
peat is increasing starting from the depth of 1 m up to the
level of 53% and then again decreasing. H concentrations

Formation and Changes of Humic Acid Properties during Peat Humification Process within Ombrotrophic Bogs 103
Figure 2. Peat stratigraphy in Eipurs bog.
Figure 3. Peat stratigraphy in Dzelve bog.
Figure 4. Elemental composition of peat in Eipurs bog.

Formation and Changes of Humic Acid Properties during Peat Humification Process within Ombrotrophic Bogs 104
Table 1. Peat decomposition degree and elemental composition of peat in Dzelve bog.
Depth, cm Decomposition, % C % H % N % S % O/C H/C N/C
5 12 44.77 5.91 0.73 0.89 0.80 1.58 0.014
105 14 45.68 5.78 0.53 0.88 0.77 1.52 0.010
160 12 46.05 5.81 0.55 0.88 0.76 1.51 0.010
205 10 45.53 5.60 0.47 0.81 0.78 1.47 0.009
240 9 44.84 5.47 0.45 0.88 0.81 1.46 0.009
305 13 47.42 5.75 0.76 0.87 0.72 1.45 0.014
320 12 45.73 5.55 0.62 1.22 0.77 1.45 0.012
325 24 44.73 5.44 0.60 0.64 0.82 1.46 0.012
335 30 52.10 5.20 1.51 0.73 0.58 1.20 0.025
340 38 52.70 5.20 1.70 0.77 0.56 1.18 0.028
350 >60 55.53 6.20 1.23 1.19 0.48 1.34 0.019
demonstrate a significantly higher variability. Changes in
N concentrations (increased in the upper and lower hori-
zons of the bog, and also demonstrating increased values
coinciding with the changes in the peat composition and
formation conditions) could be associated with changes
in the peat botanical composition and decomposition
degree. S concentrations are significantly lower just in a
few upper centimeters of the peat bog and comparatively
stable along the peat column. At the same time, the ele-
mental composition (Table 1) of Dzelve Bog is very
much different, and it largely reflects the peat column
composition: C content in the upper layers is much lower
(~45%) and comparatively uniform up to the depth of
3.25 m; then, it rapidly increases, reaching 55% for
highly decomposed peat.
The elemental ratio (Table 1, Figure 5) is much more
informative than the elemental composition of peat. N/C
ratio can be considered as a good indicator of the humi-
fication process at first due to specific microbial activity
in the anaerobic, acidic environment and enrichment of
the peat mass with nitrogen-containing compounds of ba-
cterial origin [7]. This ratio can be efficiently used as a
measure of peat degradation. The decreasing N/C ratios
indicate increasing peat decomposition (due to microbial
decay) and vice versa. H/C ratio is an index of molecular
complexity (and also of aromaticity), and it ranges from
1.6 to 1.2 [13]. It is relatively constant with depth; below
50 cm, it decreases. O/C ratio, for its part, is considered
as an indicator of carbohydrate and carboxylic group
contents and can be directly related to aromatization of
the peat-forming organic matter [13]. O/C ratio decreases
with depth; however, the values of this indicator are high
in the layers with higher decomposition degrees.
H/C and O/C values are rather fluctuating around the
average values common for peat and do not reflect high
variability of peat decomposition and high diversity
(Figure 2) of precursor living biota. N/C ratio in general
increases with the depth of the peat core, and this ratio is
high in the upper layer (possibly due to the presence of
proteinaceous materials of living organic matter). Sig-
nificant fluctuations follow with increasing depth (start-
ing from 250 cm). After that, the values of N/C ratio in-
crease again for more decomposed peat layers. This find-
ing demonstrates that the atomic ratio is only of a limited
value for study of the humification process due to the
significant impact of the original plant composition and
peat formation conditions.
The data of elemental analysis can also be used for
calculating the hydrogen deficiency  and oxidation de-
gree ω indexes [17]. However, in this case, these in-
dexes have only weak relations with the high variability
of peat properties in the peat core of Eipurs Bog, and the
peat hydrogen deficiency  and the degree of oxidation ω
can be considered as relatively homogeneous (Figure 6)
within studied peat profiles.
3.2. Peat Humification Character
Studying the transformation (humification) of living
organic material is of utmost importance for better under-
standing of carbon biogeochemical cycling. From this
perspective, studies of peat diagenesis within profiles and
identification of correlations among peat properties (age,
decomposition degree, botanical composition, elemental
and functional composition), peat humification and pro-
perties of humic acids isolated from peat are needed.
Such studies can help describe the process of humifi-
cation at a molecular level, supporting the development
of new knowledge of chemical and biochemical proce-
sses behind humification. Following this approach, in
this study, we selected two ombrotrophic bogs of a si-
milar age, located spatially close to each other (Figure 1),
but with very much differing peat column stratigraphy
(Figures 2, 3), bog profile botanical composition as well
as decomposition degree Thus, the selected study objects
are suitable for analyzing the relations between peat

Formation and Changes of Humic Acid Properties during Peat Humification Process within Ombrotrophic Bogs 105
Figure 5. Element ratio in peat from Eipurs bog.
Figure 6. Changes of the index of hydrogen deficiency  and
degree of oxidation ω in peat from Eipurs bog.
formation conditions and peat properties as well as for
identifying the humification indicators, best describing
the living organic material transformation process.
Absorption at 540 nm in the visible spectra of peat
alkaline extracts can be used as a simple indicator of hu-
mification process, as suggested and recently improved
by [20]. As it can be seen from Figure 7, this humifica-
tion index demonstrates expected differences when used
for describing Dzelve and Eipurs Bogs, and the changes
can be associated with both the peat decomposition de-
gree and the differences in peat composition. In order to
provide reliable quantitative information about the dia-
genesis of peat, we carried out further studies on the de-
pendence of parameters describing peat humification
(age and depth of the studied peat layer, decomposition,
HA/FA, D540, E4/E6 and I460/I510) on parameters describ-
ing peat composition (O/C, H/C, N/C) (Figure 8, Tables
Figure 7. Changes of humification index (adsorption of peat
extract at 540 nm) versus depth in peat from Dzelve and
Eipurs bogs.
Figure 8. Correlation between peat decomposition (%,
Eipurs and Dzelve bogs), elemental ratio of peat H/C and
D540.
2, 3). These relations slightly differ in the studied bogs.
In general, the found correlations allow to identify the
parameters most suitable for characterization of the pro-
cess of transformation of living organic matter into peat
organic matter.
As it can be seen from Figure 8, the parameter de-
scribing peat composition (atomic ratio H/C) is well cor-
related with the peat decomposition degree, thus indicat-
ing molecular mechanisms behind peat humification –
dehydrogenation (hydrogen removal from organic mole-
cules) during humification process.
The humification index describing basic changes in the
properties of peat is well correlated with the elemental
ratios in the peat cores, thus depicting changes in peat
organic materials during humification of living organic
matter. Other indicators of peat organic matter, generally
well describing peat transformation process, include HA/
FA, D540, E4/E6, whereas I460/I510 describes not so much
peat than humic matter properties (Tables 2, 3).
The UV-Vis absorption ratios were measured to pro-
vide information about the humification of peat samples.
The ratio E4/E6 is often used to describe the extent of

Formation and Changes of Humic Acid Properties during Peat Humification Process within Ombrotrophic Bogs 106
Table 2. Correlations between indicators describing decomposition of the precursor living materials (age and depth of the
studied peat layer, decomposition, HA/FA, D540, E4/E6 and I460/I510) and peat composition parameters (O/C, H/C, N/C) in
Eipurs bog.
O/C H/C N/C Age,
14C years E4/E6 I
460/I510 HA/FA D540
Decomposition, % 0.585 0.616 0.626 0.575 0.055 0.330 0.437 0.860
Depth, cm 0.517 0.588 0.624 0.858 0.175 0.393 0.201 0.794
O/C 0.667 0.487 0.292 0.051 0.568 0.474 0.543
H/C 0.582 0.476 0.008 0.555 0.543 0.592
N/C 0.636 0.242 0.387 0.578 0.667
Age, 14C years 0.313 0.250 0.323 0.741
E4/E6 0.239 0.260 0.664
I460/I510 0.843 0.857
HA/FA 0.776
Significance level p = 0.05.
Table 3. Correlations between indicators describing decomposition of the precursor living materials (age and depth of the
studied peat layer, decomposition, HA/FA, D540, E4/E6 and I460/I510) and peat composition parameters (O/C, H/C, N/C) in
Dzelve bog.
O/C H/C N/C Age,
14C years E4/E6 I
460/I510 HA/FA D540
Decomposition, % 0.587 0.689 0.469 0.871 0.525 0.466 0.458 0.792
Depth, cm 0.318 0.525 0.226 0.700 0.304 0.159 0.201 0.461
O/C 0.668 0.705 0.786 0.574 0.768 0.642 0.785
H/C 0.804 0.738 0.495 0.520 0.538 0.735
N/C 0.491 0.419 0.610 0.638 0.720
Age, 14C years 0.695 0.632 0.578 0.813
E4/E6 0.774 0.859 0.694
I460/I510 0.865 0.817
HA/FA 0.732
Significance level p = 0.05.
condensation of the aromatic C-containing structures:
low ratios reflect high degrees of condensation of aroma-
tics, while high ratios mean the presence of large quan-
tities of aliphatic structures and low amounts of con-
densed aromatics [23]. This ratio is also inversely related
to the degree of aromaticity, particle size, molecular
weight and acidity [24]. In the present study, the vari-
ability of the E4/E6 ratios in the peat profiles was ge-
nerally low (Tables 2, 3).
3.3. Elemental Composition and Functional
Characteristics of Peat Humic Acids
Studying the elemental composition of peat HAs ex-
tracted from a peat column can give information about
ongoing humification reactions during peat development.
Humification recently has been mostly studied with the
aim to analyze the composting and soil formation pro-
cesses. However, the humification process in peat is
much different from that in composts and soils, where
decomposition of organic matter is quite rapid in early
humification stages. In contrast to that, in waterlogged
environments, under the impact of anaerobic and acidic
conditions, the humification process in the saturated peat
layers is very much retarded. Therefore, in peat it is
possible to follow the humification process for very long
periods (thousands of years).
There were significant variations in the elemental
composition of HAs within peat profiles. Depending on
the bog and the intervals of changes, the elemental com-
positions of the studied peat HAs (Figure 9) were highly
variable: C was 42.74% - 59.49%; H was 3.98% - 5.41%,
N was 1.80% - 2.79%, S was 0.23% - 1.71% and ash was
0.34% - 1.46%. The O content, which was within the
range of 32.52% - 48.78%, was determined by mass ba-
lance. In general, whereas the concentrations of C and H
increased with depth, the concentrations of N decreased
with depth, and the concentration of S was very variable

Formation and Changes of Humic Acid Properties during Peat Humification Process within Ombrotrophic Bogs 107
Figure 9. Elemental composition of peat humic acids from Eipurs (a, c) and Dzelve (b, d) bog.
throughout the profile. The elemental composition of
HAs from peat in Latvia is of similar magnitude to those
for peat HAs from other regions of the world [12,13,
25-27].
Changes in the main atomic ratios (H/C, N/C and O/C)
within peat humic acid profiles are described in Figure
10, and the O/C vs. N/C atomic ratios indicate that the
decarboxylation processes were in line with the reduction
of N concentration relative to C content in HAs.
Changes of the H/C ratio in humic acids from Dzelve
Bog shows the importance of peat accumulation rate.
The bottom to middle bog layers show an increasing
H/C ratio. The upper layers of humic acids from Dzelve
Bog shows a relatively stable H/C ratio, a relatively high
amount of carbon and hydrogen, and a decreasing oxy-
gen percentage.
Changes of the H/C ratios in humic acids from Eipurs
Bog show differences between fen peat at the 3.5 - 4.62
m depth and other layers of bog, and these values are
lower for fen peat. Lower C, H percentage and H/C ratio
and higher O/C ratio are common for peat which is fully
or partly formed from wood (generally—pine). These
effects indicate the presence of lignin. At the same time,
wooden peat usually is better decomposed.
The relation between the H/C and O/C atomic ratios
(Figure 11) of HAs (van Krevelen graphs are frequently
applied for studies of HSs and the C biogeochemical cy-
cle) [29] reveals changes in the elemental composition of
humic acids, and thus is useful in identification of struc-
tural changes and the degree of maturity of HAs. Figure
11 can be considered as a graphical representation of the
humification process, indicating the degree of maturity
and the intensity of degradation processes, such as dehy-
drogenation (reduction of H/C ratio), decarboxylation
(reduction of O/C ratio) and demethylation occurring
during the genesis of humic acids. From the point of
view of chemistry, the elemental ratio of peat HAs dem-
onstrate changes in HA composition during peat diage-
nesis, considering it as a process in which more labile
structures (carbohydrates, amino acids, etc) are destroyed,
while thermodynamically more stable aromatic and pol-
yaromatic structures emerge. Comparatively, the studied
peat HAs are at the start of the transformation process of
living organic matter.
To provide reliable and quantitative information about
the diagenesis of HAs, we carried out further studies of
the dependence of the elemental composition of peat and
its humic acids on the peat age (depth and decomposition
degree) (Figure 12).
The trends of dependence between H/C values and the
depth of the peat samples were mostly negatively related,
demonstrating that dehydrogenation is amongst the do-
minant processes during ageing of peat HAs.
A study of correlations between the properties of hu-

Formation and Changes of Humic Acid Properties during Peat Humification Process within Ombrotrophic Bogs 108
Figure 10. Element ratios in peat humic acids from Eipurs (a, b) and Dzelve (c, d) bogs.
Figure 11. Van Krevelen (H/C vs. O/C atomic ratio) graph
of peat humic acids from Eipurs (♦) and Dzelve (▲) bogs,
bog plants (■) [28], coal HA (●) [28].
mic acids isolated from corresponding peat layers and
peat decomposition degree proves the concept about ma-
jor processes behind the humification and illustrates the
diagenesis of peat organic matter (Figure 13).
At first, the increased peat decomposition degree might
be associated with the dehydrogenation of peat humic
acids, probably leading towards the development of aro-
matic structures. Another evidently ongoing process is
the development of acidity—genesis of carboxylic groups
in peat humic substances during peat organic matter de-
Figure 12. Correlation between peat depth and H/C atomic
ratio of peat humic acids.
composition and humification.
4. Conclusion
A study of correlations between the properties of humic
acids isolated from corresponding peat layers and peat
decomposition degree proves the concept about major
processes behind the humification and illustrates the dia-
genesis of peat organic matter (Figure 13). At first, the
increased peat decomposition degree might be associated
with the dehydrogenation of peat humic acids, probably
leading towards the development of aromatic structures.

Formation and Changes of Humic Acid Properties during Peat Humification Process within Ombrotrophic Bogs 109
Figure 13. Correlation among the properties of humic acid and peat decomposition degree, and D540 of Eipurs bog.
Another evidently ongoing process is the development of
acidity—genesis of carboxylic groups in peat humic sub-
stances during peat organic matter decomposition and
humification.
REFERENCES
[1] O. Francioso, C. Ciavatta, D. Montecchio, V. Tugnoli, S.
Sanchez-Cortes and C. Gessa, “Quantitative Estimation of
Peat, Brown Coal and Lignite Humic Acids Using Chemi-
cal Parameters, 1H-NMR and DTA Analyses,” Biore-
source Technology, Vol. 88, No. 3, 2003, pp. 189-195.
doi:10.1016/S0960-8524(03)00004-X
[2] R. A. Houghton, “The Contemporary Carbon Cycle,” In:
K. K. Turekian and H. D. Holland, Eds., Treatise on
Geochemistry, Vol. 8, 2003, Elsevier, Dordrecht, pp. 473-
513. doi:10.1016/B0-08-043751-6/08168-8
[3] C. Cocozza, V. D’Orazio, T. M. Miano and W. Shotyk,
“Characterization of Solid and Aqueous Phases of a Peat
Bog Profile Using Molecular Fluorescence Spectroscopy,
ESR and FT-IR, and Comparison with Physical Proper-
ties,” Organic Geochemistry, Vol. 34, No. 1, 2003, pp.
49-60. doi:10.1016/S0146-6380(02)00208-5
[4] D. Yeloff and D. Mauquoy, “The Influence of Vegetation
Composition on Peat Humification: Implications for Pa-
leoclimatic Studies,” Boreas, Vol. 35, No. 4, 2006, pp.
662-673. doi:10.1111/j.1502-3885.2006.tb01172.x
[5] C. Zaccone, T. M. Miano and W. Shotyk, “Qualitative
Comparison between Raw Peat and Related Humic Acids
in an Ombrotrophic Bog Profile,” Organic Geochemistry,
Vol. 38, No. 1, 2007, pp. 151-160.
doi:10.1016/j.orggeochem.2006.06.023
[6] P. Falkowski, R. J. Scholes, E. Boyle, J. Canadell, D.
Canfield, J. Elser, N. Gruber, K. Hibbard, P. Hogberg, S.
Linder, F. T. Mackenzie, B. Moore, T. Pedersen, Y.
Rosenthal and K. H. Tan, “Humic Matter in Soil and the
Environment: Principles and Controversies,” Marcel
Dekker, New York, 2003.
[7] A. Borgmark, “Holocene Climate Variability and Peri-
odicities in South-Central Sweden, as Interpreted from
Peat Humification Analysis,” Holocene, Vol. 15, No. 3,
2005, pp. 387-395. doi:10.1191/0959683605hl816rp
[8] R. A. Ghaly, J. B. Pyke, A. E. Ghaly and V. I. Ugursal,
“Remediation of Diesel-Oil-Contaminated Soil Using
Peat, Energy Sources, A: Recovery, Utilization, and En-
vironmental Effects,” Chemosphere, Vol. 21, 1999, pp.
785-799.
[9] P. A. Brown, S. A. Gill and S. J. Allen, “Metal Removal
from Wastewater Using Peat,” Water Resources, Vol. 34,
2000, pp. 3907-3916.
[10] C. J. Caseldine, A. Baker, D. J. Charman and D. Hendon,
“A Comparative Study of Optical Properties of NaOH
Peat Extracts: Implications for Humification Studies,”
Holocene, Vol. 10, No. 5, 2000, pp. 649-658.
doi:10.1191/095968300672976760
[11] S. J. Chapman, C. D. Campbell, A. R. Fraser and G. Puri,
“FTIR Spectroscopy of Peat in and Bordering Scots Pine
Woodland: Relationship with Chemical and Biological

Formation and Changes of Humic Acid Properties during Peat Humification Process within Ombrotrophic Bogs 110
Properties,” Soil Biology and Biochemistry, Vol. 33, No.
9, 2001, pp. 1193-1200.
doi:10.1016/S0038-0717(01)00023-2
[12] C. Zaccone, C. Cocozza, A. K. Cheburkin, W. Shotyk and
T. M. Miano, “Enrichment and Depletion of Major and
Trace Elements, and Radionuclides in Ombrotrophic Raw
Peat and Corresponding Humic Acids,” Geoderma, Vol.
141, No. 3-4, 2007, pp. 235-246.
doi:10.1016/j.geoderma.2007.06.007
[13] H. Anderson and A. Hepburn, “Variation of Humic Sub-
stances within Peat Profile,” In: C. H. Fuchsman, Ed.,
Peat and Water, Academic Press, New York, 1986, pp.
177-194.
[14] C. Zaccone, C. Cocozza, A. K. Cheburkin, W. Shotyk and
T. M. Miano, “Distribution of As, Cr, Ni, Rb, Ti and Zr
between Peat and Its Humic Fraction along an Undis-
turbed Ombrotrophic Bog Profile (NW Switzerland),”
Applied Geochemistry, Vol. 23, No. 1, 2008, pp. 25-33.
doi:10.1016/j.apgeochem.2007.09.002
[15] I. I. Lishtvan and N. T. Korol, “Basic Properties of Peat
and Methods for Their Determination,” Nauka I Teknika,
Minsk, 1975 (in Russian).
[16] K. H. Tan, “Soil Sampling, Preparation, and Analysis,”
Second Edition, Taylor & Francis Group, New York,
2005.
[17] S. S. Fong and M. Mohamed, “Chemical Characterization
of Humic Substances Occurring in the Peats of Sarawak,
Malaysia,” Organic Geochemistry, Vol. 38, No. 6, 2007,
pp. 967-976. doi:10.1016/j.orggeochem.2006.12.010
[18] Y. Chen, N. Senesi and M. Schnitzer, “Information Pro-
vided on Humic Substances by E4/E6 Ratios,” Soil Sci-
ence Society of America Journal, Vol. 41, No. 2, 1977, pp.
352-358.
doi:10.2136/sssaj1977.03615995004100020037x
[19] J. J. Blackford and F. M. Chambers, “Determining the
Degree of Peat Decomposition for Peat-Based Paleocli-
matic Studies,” International Peat Journal, Vol. 5, 1993,
pp. 7-24.
[20] A. Borgmark, “The Colour of Climate: Changes in Peat
Decomposition as a Proxy for Climate Change—A Study
of Raised Bogs in South-central Sweden,” PhD Thesis,
Stockholm University, Stockholm, 2005.
[21] A. G. Zavarzina, V. V. Demin, T. I. Nifanteva, V. M.
Shkinev, T. V. Danilova and B. Y. Spivakov, “Extraction
of Humic Acids and Their Fractions in Poly(ethylene gly-
col)-Based Aqueous Biphasic Systems,” Analytica
Chimica Acta, Vol. 452, No. 1, 2002, pp. 95-103.
doi:10.1016/S0003-2670(01)01428-3
[22] D. M. B. P. Milori, L. M. Neto, C. Bayer, J. Mielniczuk
and V. S. Bagnato, “Humification Degree of Soil Humic
Acids Determined by Fluorescence Spectroscopy,” Soil
Science, Vol. 167, No. 1, 2002, pp. 739-749.
doi:10.1097/00010694-200211000-00004
[23] Y. Chin, G. R. Aiken and K. M. Danielsen, “Binding of
Pyrene to Aquatic and Commercial Humic Substances:
The Role of Molecular Weight and Aromaticity,” Envi-
ronmental Science and Technology, Vol. 31, No. 6, 1997,
pp. 1630-1635. doi:10.1021/es960404k
[24] C. S. Uyguner, C. Hellriegel, W. Otto and C. K. Larive,
“Characterization of Humic Substances: Implications for
Trihalomethane Formation,” Analytical and Bioanalytical
Chemistry, Vol. 378, No. 6, 2004, pp. 1579-1586.
doi:10.1007/s00216-003-2451-7
[25] T. Qiamg, S. Xiaoquan and N. Zheming, “Comparative
Characteristic Studies on Soil and Commercial Humic
Acids,” Fresenius Journal of Analytical Chemistry, Vol.
347, No. 8-9, 1993, pp. 330-336.
doi:10.1007/BF00323816
[26] T. Yamaguchi, H. Hayashi, Y. Yazawa, M. Uomori, F.
Yazaki and N. N. Bambalov, “Comparison of Basic
Characteristics of Humic Acids Extracted from Peats and
Other Sources,” International Peat Journal, Vol. 8, 1998,
pp. 87-94.
[27] E. Garnier-Sillam, S. Hariyento and Y. Bourezgui, “Hu-
mic Substances in Peats,” Analysis, Vol. 27, No. 5, 1999,
pp. 405-408. doi:10.1051/analusis:1999270405
[28] J. Šīre, M. Kļaviņš, O. Purmalis and V. Melecis, “Ex-
perimental Study of Peat Humification Indicators,” Pro-
ceedings of Latvian Academy of Sciences, B, Vol. 62, No.
1-2, 2008, pp. 18-27.
[29] D. W. Van Krevelen, “Graphical-Statistical Method for
the Study of Structure and Reaction Processes of Coal,”
Fuel, Vol. 29, 1950, pp. 269-228.