SHORT COMMUNICATION

Journal of Radioanalytical and Nuclear Chemistry, Vol. 247, No. 2 (2001) 419�424

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T. T. Efremova,1 S. P. Efremov,1 K. P. Koutsenogii,2 V. F. Peresedov3

1 Institute of Forest, Siberian Branch RAS, Krasnoyarsk 660036, Russia2 Institute of Chemical Kinetics and Combustion, Siberian Branch RAS, Novosibirsk 630090, Russia

3 Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Dubna, Moscow region 141980, Russia

(Received May 2, 2000)

In a eutrophic marsh, Fe, Mn, Ni, and Co are the elements of moderate biological capture and Cr is the element of weak biological capture. Over

the history of the peatbog formation migration of elements is determined by the oxidation-reduction zonality of the peatbog thickness, the quality

of humous barriers, and the carbonate equilibrium in the stagnant waters. No technogenic degradation of the marshes in the southern taiga of

Western Siberia has been detected.

Introduction

The marsh is a special type of the accumulating

systems of the biosphere in which superficial

accumulation of organic masses is superior to their

decay. A growing peatbog experiences continuous

changes determined not only by its bioclimatogenic

conditions but also by its geomorphological position,

i.e., the structure and material of the bedding rock,

regime and chemical composition of feeding waters, the

extent of microrelief development, etc. Thus, marshes,

the complex natural unities of interrelated and

interacting living and inert components should be

classified as bio-inert systems.

In the process of peat genesis alternating oxidation-

reduction conditions in the superficial soil horizons are

gradually replaced by the reduction (gley) conditions.

The establishment of a stable redox phase indicates a

transition of the peat soil to a qualitatively new state, an

organogenic soil-forming rock (peat), and subsequent

redistribution of elements over the deposit profile. The

formation of marsh causes a deep reconstruction of the

geochemical system following even relatively slight

changes the parameters of the medium.1 The stage of

diagenesis in the peat accumulation is the least studied

one. It is known that one of the most important functions

of marshes is their ability to accumulate pollutants

(marshes are powerful natural sorbents). The zone that

reflects a special role of some separate elements in the

technogenic epoch is the superficial layer of the deposit.

The objective of this investigation is to study the

peculiarities of the biogeochemical migration of Fe, Mn,

Cr, Ni, and Co in the peat genesis during Holocene and

reveal the existence of the technogenic areols of the

specified elemental composition in the marsh ecosystem

in the southern taiga of Western Siberia. According to

the classification of PERELMAN,2 Fe, Mn, Cr, Ni, Co

belong to the subgroup of sideriphylic metals of the iron

group.

Experimental

Samples for the chemical analysis of the peatbog

were taken within the bounds of a 0�50 cm soil layer

(peatgeneratrix) through the genetic horizons in deeper

deposit layers and the bedding of the marsh (loamy soil)

by boring an uninterrupted column. The sampling site is

an area deep in the heart of the peatbog massif. The

multielemental content of the peat was determined by

instrumental neutron activation analysis (INAA) in the

Laboratory of Neutron Physics of the Joint Institute for

Nuclear Research. The technique itself and the

methodological aspects of the analysis are described in

Reference 3. The INAA analytical possibilities and

detection limits in the determination of the elemental

content of vegetation are estimated in Reference 4.

The object of the present investigation is a deep-

seated (750�800 cm) eutrophic marsh located in the

northern part of the country between the Ob and Tom

rivers. This is a slightly rugged, wave-hilly plain with a

high level of swamping of up to 20�25%. The

investigated �Cranberry� marsh with the area over 1000

hectares is one of the largest sedgy-hypnum marshes in

the watershed. At present, the marsh is slightly drained

by means of a net of open channels. The current

vegetation cover consists of a number of different forest

formations. The investigations were performed in the

cedar forest with a green moss-grass underlayer.

The peat deposit is characterized by a low volumetric

mass, 0.09�0.23 g/cm3, and high porosity, 85�95%. The

ash content, 7�39%, is caused by strong iron

accumulation in the margin areas of the marsh.

The reaction of the medium over the profile of

the peat deposit is slightly acid, pH 5.8-6.6.

0236�5731/2001/USD 17.00 Akadémiai Kiadó, Budapest

© 2001 Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht

T. T. EFREMOVA et al.: BIOGEOCHEMICALMIGRATIONOFMETALSOFTHE IRONGROUP

The extent of peatbog decomposition versus the deposit

depth and the botanic content equals 26�45%. The

humidity of the soil peat forming horizon changes during

the warm season of the year from 330% to 600% (per

dry weight). The humidity of the peatbog inert thickness

outside the range of fluctuations of the level of soil-

subsoil waters is very stable and is on average 900%.

The soil-subsoil waters feeding the marsh are enriched

with dissolved organic substances of humus origin

(47�50 mg/l). The saturation of the surface water with

oxygen is low (1.7�3.3 mg/l) and the reaction of the

medium is slightly acid (pH 6.1). The waters are of the

hydrocarbonate calcium type as to their ionic

composition.

Results and discussion

A multielement analysis of the bedding gleyed loamy

soil (750�800 and 800�840 cm) shows (Table 1) it

being very poor in Ni, Fe, Cr, Co, and Mn (the

concentration clarks are 0.10, 0.19, 0.24, 0.35, and 0.56,

respectively). The distribution of Fe, Mn, Co, and Ni

over the peat does not contradict with the normal law

(Table 1). We proceed from the estimates of the

variation factor (Cν), normalized asymmetry (tAS), and

excess (tES). For symmetric series the values of (Cν) donot usually exceed 50% 5 and in the case of an �ideal�

normal distribution they are not higher than 33%.6

When tAS and tES are larger than 3, the deviation of an

empiric from normal series is considered as significant.7

A normal distribution is also characterized by the

coincidence of the absolute values of the arithmetical

mean, of the median and mode.5 A close to normal law

the distribution of the elements of the iron group over

the deposit profile allows their arithmetical means to be

considered as the peat background.

In the low-laid deposit of the investigated

�Cranberry� marsh the background elemental content is:

Fe (6657 ppm) > Mn (461) > Ni (2.4) = Co (2.2) > Cr

(1.5). The variations of Fe, Mn, Ni over the deposit

profile are significant (Cν>30%) and are moderate for

Co (Cν=22.7%).5 Chromium is just detected in separate

layers, mainly over upper 300 cm. It is mostly scattered

(clark of scattering � 59.2) in the thick of the deposit,

then go Ni (28.3), almost equally scattered Fe and Co

(7.1 and 8.6), and the least scattered Mn (1.8). Under the

normalization to the regional background distribution of

elements over mineral hydromorphous soils8 the extent

of the scattering of Co and Ni decreases, and of Mn

remains without change (Table 1).

The factors of biochemical absorption (the ratio of

mean element concentrations in peat moss and the

mineral bedding of the marsh) form the following

descending row: Mn (0.97) > Fe (0.72) > Ni (0.34) = Co

(0.34) > Cr (0.07). From here it follows that elements are

not accumulated but just captured in marsh ecosystems.2

Table 1. Distribution of chemical elements over the profile of a low-laid peatbog (in ppm)

Sideriphylic metals of iron group

Statistical and geochemical Fe Mn Cr Ni Co

parameters of distributions

Mean arithmetic 6657 461 4.52 2.42 2.20

Median 6500 450 1.52 2.30 2.10

Mode 7200 300 � 2.10 2.10

Average geometric 6373 432 � � 2.15

Standard deviation 2026 170.6 � 0.99 0.50

Error of arithmetic mean 442 37.2 � 0.22 0.11

Minimum 2400 180 0 0 1.5

Maximum 13000 960 6.5 4.6 3.7

Factor of asymmetry (AS) 1.36 0.98 � �0.13 1.20

Normalized AS 2.55 1.84 � �0.24 2.24

Factor of excess (ES) 4.87 2.58 � 1.17 2.73

Normalized ES 4.55 2.41 � 1.09 2.55

Factor of variation, % 30.4 36.9 � 41.0 22.7

Clarks of sedimental

clayee�rocks** 47200 850 90 68 19

Clark of concentration for

mineral bed of marsh 0.19 0.56 0.24 0.10 0.35

Factor of scattering in

peatbog deposit (FS) 7.10 1.80 59.2 28.3 8.60

FS normalized to regional

background � 1.8 69.7 16.1 4.00

** In accordance with TUREKIYAN and VEDEPOLE, 1961.2

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Table 2. Correlative matrix of multielemental analysis for powerful peatbog deposit of low-laid type over the

stratigraphic column

Element Fe Mn Co Ni

Na 0.43 � � �

Mg 0.80 0.42 � 0.70

Al 0.61 � � �

Cl � � � 0.49

Sc � � � �

Ca 0.86 0.66 0.71 0.67

V 0.64 � � 0.79

Mn 0.81 1.00 0.84 0.73

Fe 1.00 0.81 0.71 0.84

Co 0.71 0.84 1.00 0.53

Cu 0.88 0.91 0.85 0.78

Ni 0.84 0.73 0.53 1.00

As � 0.54 0.69 �

Br 0.88 0.85 0.80 0.82

Rb 0.85 0.66 0.76 0.64

Sr 0.85 0.63 0.59 0.86

Mo 0.44 0.56 0.55 0.61

In �0.61 �0.69 0.50 �0.63

Cs 0.85 0.73 0.67 0.57

Ba � � � 0.47

La 0.68 � � 0.44

Sm �0.50 � �0.68 �

Th 0.51 � � 0.45

U 0.88 0.59 0.55 0.82

The levels of capture are moderate for Mn, Ni, Co and

slight for Cr. Only the factor of the biological absorption

of Fe is beyond PERELMAN�s gradation system. This is

possibly due to of hydrogeochemical specialization of

low-laid peetbogs. The indicative geochemical amount

of Fe in marsh ecosystems is related to its high mobility

and polyvalency, abundance of organic matter in

different stages of transformation, high water supply,

alternating oxidative and reductive zones in the thick of

the peatbog.

All elements in the iron group are closely correlate

(Table 2). This is evidence of the fact that their

distribution over the deposit profile, reflecting the

biogeochemical history of the marsh massif in Holocene

has a similar trend. The variation limits of elements

within the interval of their background contents are

established using the error indexes of the arithmetical

mean. This smoothed the dynamics of the migration of

elements in the formation of the peatbog. Together with

the redox peculiarities of the peat soils9�11 the procedure

allows the peatbog thick to be divided into: Ioxi zone of

intense accumulation of elements in the oxidative

conditions of the upper layers in the main, IIoxi-red

depleted zone of the deposit in the alternating redox

conditions, IIIred1 zone with an almost background-like

content in the regime of stable anaerobiosis, and the

IVred2 enriched or depleted zone of the peatbog in the

expressed reductive conditions.

Fig. 1. Distributions of metals over the stratigraphic column of the

peat deposit

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T. T. EFREMOVA et al.: BIOGEOCHEMICALMIGRATIONOFMETALSOFTHE IRONGROUP

The above division of the deposit corresponds, to a

high degree, to the distribution of Fe, Co, and Mn during

the peatbog formation. Therefore, let us consider the

peculiarities of their biogeochemical migration on the

example of Fe (Fig. 1a) and then separetely for Ni

(Fig. 1b).

The zone of the intense accumulation is a least thick

surface layer of 10 cm. The maximal content of Fe, Mn,

and Cr accumulated over the history of the marsh massif

is concentrated in its surface layer. In the bedding

(0�4 cm) the concentrations of Cr and Mn are most

expressed and are 4.3 and 1.9 times higher than the

background. A 4�10 cm horizon is visibly enriched with

Fe (2 times) and to a less extent with Co 1.2 times. In

analogous conditions no visible accumulation of Ni was

observed. The zone depleted of elements from the iron

group is down to the depth 90�100 cm. It is typical for

all metals: the content of Fe, Co, and Ni is on average

80�82% of the background and of Mn it is 64%.

The zone in which the element content is close to its

background level is at the depth 100�450 cm for Co,

100�500 cm for Mn, and at 100�550 cm for Fe. At an

about equal depth (80�600 cm) there is observed an

increase of the content of Ni over the background with a

maximum at 200�250 cm (1.9 � times). However, the

behavior of the biogeochemical migration of the

elements of the Fe group has a similar trend within the

given zone.

A deeper zone of the peatbog at 450(550)�750 cm is

enriched with Fe, Co, and Mn, especially the layer at

600�650 cm with the content 1.5�1.7 times higher than

the background. However, the bottom layers are depleted

of Ni.

Thus, of all elements of the iron group the

biogeochemical migration of Ni during the formation of

the marsh is most original. A pronounced accumulation

of the element is absent in the zone of the oxidative

barrier near the surface, the bottom layers are notably

depleted of it. In the most part of the peatbog thick,

however, the content of Ni is higher than the

background.

Besides redox zonality, an important factor of the

redistribution of elements over the deposit profile is

humous compounds with a high mobilization and

accumulation of polyvalent metals. At the same time, a

determining role of the qualitative composition of humus

in this process is established. Thus, in the conditions of

upper 250 cm, for Fe, Co, Mn the role of organic

addends there play the humics and fulvoacids of the first

fraction hydrolyzed by 0.1 normal NaOH in the cold.

These are the mostly oxidized and hydrophylic

compounds enriched with carboxyl groups involved in

the heterogeneous system of peat humus substrates.12

The distribution of HA-1, FA-1, and FA-1a over the

deposit profile (Figs 2a, b, c) corresponds in general to

the direction of the biogeochemical migration of Fe. The

content of Ni in a 0�250 cm layer is closely related to

the distribution of humic acids in the deposit thick.

Fig. 2. The humic profile of the peat deposit: a � humic acids of the

first fraction; b � fulfoacids of the first fraction; c � fulvoacids of the

1-a fraction; d � sum of humic acids of different fractions

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T. T. EFREMOVA et al.: BIOGEOCHEMICALMIGRATIONOFMETALSOFTHE IRONGROUP

The first and third fractions (redox form) peptized by

0.02 NaOH under heating13 dominate in the content of

the peatbog. The first and third fractions are mainly

attracted by oxidative and redox conditions, respectively,

and the content of the last one increases with the depth

of the deposit. The interaction of humic acids with

polyvalent metals is determined, as is known, by the

ratio of the reacting components. The wider the

relationship is for the more mobile system. A Fe2O3concentration of 12�20 mg/g of carbon creates

favourable conditions for the beginning of mutual

coagulation in peatbog soils.14 After the stabilization of

the redox regime the group and fractional compositions

of humus retains the known invariability.13 This state of

the system of humus substances agrees with a relatively

constant distribution of Fe, Mn, and Co in the zone of

stable anaerobiosis.

Sharply reductive conditions of the medium in the

bottom layers of the deposit facilitate a transition of

elements of the iron group into a bivalent state. The

cations Fe2+, Mn2+, Co2+, Ni2+ are close in their

properties to Mn, Ca, and Sr whose differentiation in the

biosphere is closely related with the equilibrium of

carbon. In waters with a low content of CO2 bivalent

metal deposition is in the form of carbonates. In gley

marsh waters enriched with CO2 it is in the

hydrocarbonate form (HCO3�). So, it is carbonate

equilibrium that, most possibly, is the main factor of Fe,

Mn, and Co accumulation in the low-laid layers of the

deposit. In our opinion, the depletion of Ni in the bottom

strata is related with a low content of the element in the

mineral bedding of the marsh (scattering clark � 0.10).

The distribution of the elements of the Fe group over

the deposit profile based on the regularities of their

biospheric accumulation is also determined by the

migration in the adsorbed state of isomorphous

impurities or high-disperse mechanical suspensions over

the surface of colloidal micellas (mineral or organic).

It is proved that mineral associations on the surface

and in low-laid strata of the peat deposit are genetically

interrelated throughout all of the stages of the peatbog

genesis.1 Paragenic elemental associations, reflecting the

biogeochemical peculiarities of peatbog formation over

the entire history of the marsh are revealed on the basis

of the correlation factors (Table 2) calculated with the

use of NAA data, namely, Fe-Na-Mg-Al-Ca-V-Mn-Co-

Cu-Ni-Br-Rb-Sr-Mo-Cs-La-Th-U.

The existence of a strong correlation (r>0.80) of Fe

with Mg, Ca, Mn, Cu, Ni, Br, Rb, Cr, Cs, and U is

revealed.

Mn-Mg-Ca-Fe-Co-Cu-Ni-As-Br-Rb-Sr-Mo-Cs-U.

Most strongly, Mn correlates with Fe, Co, Cu, Br.

Co-Ca-Mn-Fe-Cu-Ni-As-Br-Rb-Sr-Mo-Cs-U. The

coupling of Co with Mn, Cu, Br has a maximum

statistical significance.

Ni-Mg-Cl-Ca-V-Mn-Fe-Co-Cu-Br-Rb-Sr-Mo-Cs-Ba-

La-Th-U. The existence of a significant coupling of Ni

with Fe, Br, Sr, and U is established as well.

The existence of negative associations of

Fe,Mn,Co,Ni with In and of Fe,Co with Sm is also

revealed.

Conclusions

In the conditions of an eutrophic marsh the metals

(Fe, Mn, Cr, Ni, Co) of the Fe group are considered to

be the elements of moderate or slight biological capture

of which it is not typical to have a biogenic

accumulation. Chromium and Ni are mostly scattered in

the deposit thick (scattering clark �59.2 and 28.3,

respectively). Almost equally there are scattered Fe and

Co (7.1 and 8.6) and least of all is Mn (1.8).

The biogeochemical migration of sideriphylic

elements in the process of peatbog formation is mostly

determined by physico-chemical processes: redox

zonality of the peatbog thick, state of the humus matter,

i.e., the quality of sorption humus barriers, and carbonate

equilibrium of marsh waters due to reduced forms of Fe,

Co, and Mn being able of isomorphous substitution of

bivalent metal atoms in carbonates.

In the history of the marsh, maximum accumulations

of Fe, Mn, Cr in a 0�4(10) cm layer are 2�4 times higher

than the peatbog background. They clearly outline the

zone of the oxidative barrier and reflect the iron

hydrochemical specialization of eutrophic marshes. The

concentrations of the elements within the zone of the

latest peat formation are significantly lower than their

clarks in sedimental rocks: by a factor of 70, 32, 14, and

3.6 for Co, Ni, Cr, and Fe, respectively. It is only Mn

that exceeds its clark value by 13%. Manganese,

however, has the third class of hazard. A maximal

allowed phytotoxic concentration of Mn is 1500 ppm in

the surface layer of the soil.15 It is significantly higher

than its actual value in the marsh. This reflects the

absence of real hazard of technogenic degradation of

marshes in southern taiga of Western Siberia at present.

*

The authors are grateful to their collaborators from the Institute of

Forest (SB RAS), the Institute of Chemical Kinetics and Combustion,

and the Institute for Nuclear Research for assistance in carrying out

the project and T. F. DROZDOVA for help in the preparation of the

English version of this manuscript.

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