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Base Cation Fluxes in Mountain Landscapesof Lake Baikal Southern Shore

Mikhail Y. Semenov

Limnological Institute of Siberian Branch of Russian

Academy of Sciences, Irkutsk, Russia and

Micro and Trace Analysis Centre, University of Antwerp, Belgium

Rene Van Grieken

Micro and Trace Analysis Centre, University of Antwerp, Belgium

Abstract: Assessing base cation [calcium (Ca2þ), magnesium (Mg2þ), potassium

(Kþ)] fluxes is necessary for determining ecosystem stability. This study was

conducted in the Osinovka River catchment located on the Khamar-Daban Ridge,

South Baikal, which is characterized by high precipitation (more than 1700 mm per

annum). The contributions of different ecosystem components such as atmospheric

deposition, soil exchange pool, minerals, vegetation, surface water, and groundwater

into the total base cations flux were evaluated, combining the strontium isotope

approach and budget study. Results show the leading role of atmosphere in

ecosystem supply with base cations. The atmosphere contributes 48% of total base

cations flux, and its contributions to plant-available nutrition pools of both organic

and mineral horizons are equal to 50%. This makes the vitality of vegetation, to a

great extent, dependent on the stability of atmospheric chemistry.

Keywords: Atmospheric deposition, base cations, soil exchange pool, strontium

isotopes, waters, weathering

INTRODUCTION

Evaluation of nutrient fluxes plays an important role in assessing the stability

of terrestrial ecosystems. This is especially important in the areas subjected to

Received 20 March 2006, Accepted 4 January 2007

Address correspondence to Mikhail Y. Semenov, Limnological Institute of

RAS/SB, 3, Ulan-Batorskaya St., 664033, Irkutsk, Russia. E-mail: smu@mail.ru

Communications in Soil Science and Plant Analysis, 38: 2635–2646, 2007

Copyright # Taylor & Francis Group, LLC

ISSN 0010-3624 print/1532-2416 online

DOI: 10.1080/00103620701662851

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anthropogenic loading. In connection with the problem of acidification,

which became particularly pressing in the 1970s first in Western Europe

and then in North America and southeastern Asia, scientists all over the

world carry out research on quantitative estimation of base cation

[calcium (Ca2þ), magnesium (Mg2þ), potassium (Kþ)] sources and release

rates. Early estimates were obtained mostly from budget studies. Later,

these data were used as a basis for biogeochemical modeling. Both of

these approaches have their own shortcomings. It is known that models

give the best results when the input data are close to those of which the

model was build on. Budget study data are quite precise and specific for

the target location but do not indicate the processes they have resulted

from. The isotopic approach, being properly applied, gives both the

processes and their quantitative characteristics. The history of budget

studies using strontium isotopes starts from works of W. C. Graustein and

J. R. Gosz (Graustein and Armstrong 1983; Gosz, Brookins, and Moore

1983). The method used in present study was described in the work of

Miller, Blum, and Friedland (1983). Later, particular attention to method-

ology of isotopic studies was paid by R. C. Capo, B. W. Stewart, and

O. A. Chadwick (Capo, Stewart, and Chadwick 1998; Stewart, Capo, and

Chadwick 1998).

In Russia, little attention was paid to the study of base cation (BC)

budgets because the acidification of natural environments was quite local.

The budget approach was usually used to study the geochemistry of wide-

spread elements such as silicon, aluminum, and iron or, in contrast, the geo-

chemistry of trace elements. Isotopic methods were used mostly in geology

for determining the age and genesis of rocks. Recently, the works on base

cation (BC) budgets in small catchments using a strontium isotope approach

have appeared (Semenov et al. 2005). The present study is devoted to

creating the first-order model of BC circulation in the ecosystem and

assessing, to some extent, the risk of acidification. The necessity of the

study is conditioned by the location and natural features of the study area

that are favorable for the development of acidification processes within the

whole ecosystem or at least in separate ecosystem components.

STUDY SITE DESCRIPTION

The study was conducted in the Osinovka River catchment of the Khamar-

Daban Ridge, located on the southeastern shore of Lake Baikal (Figure 1).

The river length is 23 km with the catchment area of 129 km2. The annual

average runoff rate is about 0.17 km3. Because of prevailing northwestern

air mass transfer, the spatial orientation of the ridge causes atmospheric pre-

cipitation on its windward slopes. Air masses go along the Angara River

Valley, passing through the Angara Gates. They reach Lake Baikal, become

saturated with water above the lake surface, and pass as a narrow front

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along the southern shore. The amount of precipitation, most of which

(85–90%) falls in summer, reaches 1700 mm . yr21 and more in mountains.

Up to a height of 1600–1900 m, depending on the exposition, mountain

slopes are covered with coniferous vegetation (Taiga). The predominant

species are Abies Sibirica, Pinus Sibirica, and Picea Sibirica. Above

1900 m height, the Taiga belt is substituted by highland bare area. In its

lower part (right above the forest belt), the bare area is represented by steep

rocks and rockslides. On the top, the bare area is a cold stony desert

covered with snow from October to June. The soils are almost absent; the veg-

etation is represented by lichens covering massive rocks and mosses in boggy

depressions. This is because of low temperatures and low precipitation

Figure 1. Study area: 1, river valleys; 2, mountain woodland; 3, highland bare area;

4, soil sampling sites; 5, water sampling sites.

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amounts. The bedrocks of the Khamar-Daban Ridge formed during the Ordo-

vician are mainly metamorphic: schist, gneisses and, to a lesser extent,

marbles (Kotov et al. 1997). Two soil types, Gelic Podzols (river terraces)

and Dystric Leptosols (mountain slopes), prevail over the other types (Tsibz-

hitov and Tsibzhitov 2000; Kuzmin 2002). The profile typical of Dystric

Leptosols in the study region consists of three horizons A, B, and C. The

surface Mollic A horizon is 2–8 cm thick, dark colored, rich in bases, and

of average bulk density about 0.70. The underlying yellowish red or

yellowish brown B horizon is 15–35 cm thick and extremely poor in bases

(Dystric); the average bulk density is 1.40. The B horizon is underlined by

the C horizon is composed of low-weathered coarse material. The important

features of these soils are high acidity (pHH2O, 5) in both organic and

mineral horizons.

MATERIALS AND METHODS

Most of the fieldwork was carried out within the period from July 1 to 25,

2005, when hydrological and hydrochemical parameters were close to

average for the season of ice-free water. Soil, surface water, and vegetation

(needles) were sampled at four sites located on mountain slopes along the

river (Figure 1). Soil and vegetation sampling sites were equally spaced

over the forested area and represented different parts of slopes—two of

them located in the middle parts of slopes and two in the upper ones. In

lower (flat) parts of slopes, soil and vegetation were not sampled because of

their small area and consequently small contribution to the river chemistry.

Moreover, there is always a possibility to sample highly weathered material

from an old terrace with 87Sr/86Sr ratios lower than that of riverine water.

Water was also sampled at two sites from under the ice at the end of

December when the groundwater was the only supply. These samples were

supposed to represent groundwater. All the sampling procedures were

performed according to international guidelines (UN/ECE 1994). The total

number of samples was 26.

For studying element cycling in small catchments, it is most convenient to

use strontium (Sr) isotopes as tracers. Because of physical and chemical prop-

erties of strontium, such as atomic and ionic radius, ionization energy, and

solubility of its compounds with inorganic anions, the migration of Sr is

similar to that of calcium; therefore, the concentrations of these elements

are always correlated (Faure 1986). There are four strontium isotopes: 84Sr,86Sr, 87Sr, and 88Sr. The ratio among 84Sr, 86Sr, and 88Sr is constant, but the

ratio between either of these three and the radiogenic 87Sr changes,

depending on the object history and the concentration of 87Rb, which is the

source of 87Sr. The use of the 87Sr and 86Sr isotopes ratio is the most con-

venient because of their similar occurrence. In the present study, the

mechanism of radial Sr flux forming was modeled by means of considering

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each ecosystem component as a two-component isotopic mixture and evaluat-

ing the contribution of component A to a mixture (Miller, Blum, and Friedland

1993; Capo, Stewart, and Chadwick 1998):

XA;% ¼ð87Sr=86Srmix �

87Sr=86SrBÞ

ð87Sr=86SrA �

87Sr=86SrB� 100;

where the subscripts A, B, and mix denote the value for the two sources and

the mixture.

The BC pool of every ecosystem component was considered as a

mixture of two sources. Litterfall BC were assumed to be a mixture of BC

extracted from the organic and mineral soil exchange pools. The organic

horizon exchange pool receives BC from litterfall and atmospheric depo-

sition. The exchangeable BC in the mineral horizons were assumed to be

derived from mineral weathering and BC transported by soil water perco-

lated from the organic horizons. Surface water was assumed to obtain its

BC from both the mineral horizon exchange pool and ground water. The87Sr/86Sr and BC/Sr ratios for each flux were assumed to be the same as

in the source reservoir except the vegetation uptake, for which vegetation

ratios were used. This is because nutrient uptake is mostly conditioned by

plant physiology rather than chemical peculiarities of nutrient source. It

was also assumed that the vegetation under study is mature and thus the

BC uptake by roots is equal to BC return with litterfall. The obtained

contributions were then transformed to Sr fluxes using the value of Sr depo-

sition as initial information. Atmospheric deposition of Sr was evaluated on

the basis of measured Sr concentration and precipitation volume. Strontium

flux values were multiplied by corresponding BC/Sr ratios to obtain BC

fluxes.

Chemical analyses as well as sampling procedures were performed

according to international guidelines (UN/ECE 1994). The exchangeable

cations were extracted from air-dried soil using 1 M ammonium acetate

solution. Dry vegetation samples were ashed, and the ash, as well as the

soil, was then dissolved in nitric acid. Cations in soil and vegetation

extracts and surface water samples were determined by flame spectropho-

tometry (Karl Zeiss, Jena AAS-30 spectrophotometer). The isotope compo-

sition of Sr was determined by thermal-ionization mass spectrometry

(Finnigan MAT 262 mass spectrometer) after acid dissolution and cation-

exchange column separation using AG-50WX 8 Hþ-type ion exchange

resins (200–400 mm) (BioRad Co.). For calibration, VNIIM-Sr standard

sample with 87Sr/86Sr ¼ 0.70802 was used. Reported uncertainties (+2s)

in the last one or two decimal places are a result of thrice-repeated measure-

ment of each sample (for single sample values) or from averaging-out data on

corresponding samples from all the sites (for averaged values).

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RESULTS AND DISCUSSION

The data presented in Table 1 (especially 87Sr/86Sr ratios) show very small

variation for corresponding ecosystem components (soil, water, deposition,

or vegetation). Both this fact and sampling site locations testify to strong

chemical homogeneity of the watershed and, consequently, to the represen-

tation of the sampling sites. The averaged data used for flux calculations are

given in Table 2. The pictorial model of BC fluxes is presented in Figure 2.

In the figure, arrows between the ecosystem components show flux directions;

on the right of arrows there are contributions (%) of components to a given

flux, and on the left are BC fluxes (keq . ha21 . yr21).

Judging by the figure, atmospheric deposition and vegetation contribute

55% and 45% of exchangeable bases to organic horizons, respectively. The

high contribution of atmospheric deposition to the plant-available nutrition

pool makes the vitality of vegetation, to a great extent, dependent on

stability of atmospheric chemistry. As it has already been mentioned, the

study site is situated on the way of predominant air mass transfer, bringing

the air from industrial pollution sources located along the Angara River

valley. Thus, the change in atmospheric composition in this location is quite

probable.

Seventy percent of exchangeable bases in mineral horizons are leached

from organic horizons and the other 30% come from weathering reactions.

The obtained rate of BC release due to weathering is 0.90 keq . ha21 . yr21.

This value is a little lower than that obtained for ancient river terraces of

the nearby Pereemnaya River catchment (Semenov et al. 2005) and very

close to modeled values using PROFILE model for the whole region

(Semenov, Bashkin, and Sverdrup 2001).

Chemical composition of surface waters depends mostly on the compo-

sition of water percolating from soil (85%) and, to a lesser extent, of

ground water (15%). The total value of BC flux from watershed is

2.42 keq . ha21 . yr21. This value is just 4% higher than that evaluated on

the basis of data on water discharge and nutrient concentrations given in

Table 2. Comparing the stock of exchangeable nutrients in soil the total flux

value can also give us an idea about the intensity of biogeochemical

turnover on the territory under study. The BC stock evaluated from concen-

trations presented in Table 2 and from the average depth and density of soil

horizons (0.05 m and 600 kg . m23 for organic horizons and 0.25 m and

1400 kg . m23 for mineral horizons) is about 190 keq . ha21. Thus, it takes

190/2.42 or 80 years to replace all the exchangeable cations in soil. Taking

into account the high percentage of atmosphere-originated cations in the

total soil exchange pool, the most probable explanation for such a long

residence time is their possible accumulation by means of incorporation

into soil organic matter.

Contributions of initial sources such as atmospheric deposition,

weathering, and ground water to the total flux are equal to 48, 37, and 15%

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Table 1. Chemical properties of ecosystem components

Site no. 87Sr/86Sr + 2sa Sr2þ Ca2þ Mg2þ KþBC (Ca2þ

þ

Mg2þþ Kþ)

Deposition (meq . l21)

Site 1 0.70968 + 5 0.025 56.02 8.94 7.89 72.85

Site 2 0.70979 + 6 0.021 49.45 12.35 10.24 72.04

Site 3 0.70984 + 9 0.019 40.01 13.66 12.37 66.04

Site 4 0.70991 + 3 0.020 37.21 14.37 13.57 65.15

Surface water (meq . l21)

Site 1 0.71357 + 8 0.095 79.89 49.66 34.26 163.81

Site 2 0.71389 + 7 0.099 85.74 51.63 36.47 173.84

Site 3 0.71402 + 5 0.097 90.07 53.02 38.37 181.46

Site 4 0.71414 + 5 0.101 92.64 55.28 40.87 188.79

Groundwater (meq . l21)

Site 1 0.71280 + 3 0.080 88.74 49.35 38.37 176.46

Site 2 0.71283 + 3 0.082 89.70 51.28 38.98 179.96

Vegetation (meq . kg21)

Site 1 0.71261 + 5 0.182 234.17 122.46 136.55 493.18

Site 2 0.71268 + 3 0.187 287.14 151.28 118.04 556.46

Site 3 0.71259 + 8 0.148 193.08 93.45 110.88 397.41

Site 4 0.71256 + 4 0.163 230.66 133.23 99.05 462.94

O horizon, exchangeable bases (meq . kg21)

Site 1 0.71090 + 7 0.092 183.25 26.44 18.66 228.35

Site 2 0.71116 + 11 0.121 214.64 25.14 25.72 265.50

Site 3 0.71132 + 5 0.086 168.06 21.05 17.30 206.41

(continued )

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Table 1. Continued

Site no. 87Sr/86Sr + 2sa Sr2þ Ca2þ Mg2þ KþBC (Ca2þ

þ

Mg2þþ Kþ)

Site 4 0.71128 + 9 0.101 191.42 29.78 23.34 244.54

B horizon, exchangeable bases (meq . kg21)

Site 1 0.71372 + 8 0.021 17.73 10.06 10.33 38.12

Site 2 0.71415 + 9 0.015 10.23 12.41 10.82 33.46

Site 3 0.71431 + 5 0.026 15.41 8.81 12.03 36.25

Site 4 0.71412 + 6 0.018 11.88 11.70 8.98 32.56

B horizon, minerals (meq . kg21)

Site 1 0.71795 + 7 1.927 791.33 958.82 1851.16 3601.31

Site 2 0.71821 + 7 1.850 914.35 1124.15 1900.03 3938.53

Site 3 0.71848 + 5 1.919 516.13 1030.88 1756.23 3303.24

Site 4 0.71863 + 6 1.944 613.57 891.77 1899.69 3405.03

aResulted from three repeated measurements of the corresponding sample.

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Table 2. Element fluxes from different sources and parameters used for calculations

Source 87Sr/86Sr + 2sa[Sr]

meq . l21[BC]

meq . l21[Sr]

meq . kg21[BC]

meq . kg21 BC/Sr

Sr flux

eq . ha21 . yr21BC flux

keq . ha21 . yr21

Atmospheric deposition 0.70981 + 19 0.021 69.02 3286.67 0.35 1.17

Surface water 0.71391 + 49 0.098 176.98 1805.92 1.34 2.42

Groundwater 0.71282 + 4 0.081 178.21 2200.12 0.17 0.37

Vegetation 0.71261 + 10 0.170 477.50 2808.82 0.34 0.96

O horizon, exchangeable

fraction

0.71117 + 38 0.100 236.20 2362.00 0.69 1.63

B horizon, exchangeable

fraction

0.71408 + 50 0.020 35.10 1755.00 1.17 2.05

B horizon, minerals 0.71832 + 60 1.910 3562.03 1864.94 0.48 0.90

Root uptake from O 0.71261 + 10 0.170 477.50 2808.82 0.17 0.48

Root uptake from B 0.71261 + 10 0.170 477.50 2808.82 0.17 0.48

aResulted from averaging data for all the sites.

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respectively. These data in the best way show the prevalence of nutrients from

outside the ecosystem, thus demonstrating the ecosystem’s dependence on

them.

Contributions of exchangeable cation pools of organic and mineral

horizons to vegetation make up to 50% or 0.48 keq . ha21 . yr21 each.

Because the weathering-originated BC constitutes 36% of the B horizon

exchange pool, they also constitute 36% of the B horizon contribution to veg-

etation. Thus, contribution of weathering source to vegetation is equal to

0.17 keq . ha21 . yr21 or 18% of the total uptake. Recycled cations from

both organic and mineral horizons constitute the remaining 82% of annual

uptake.

The approach used also allows predicting possible flux changes. As con-

tributions (%) of different ecosystem components have been calculated on the

basis of 87Sr/86Sr ratios, which stay unchangeable for thousands of years, and

atmospheric deposition has been used as input information, all the temporal

(natural or man-induced) variations come to the variation of Sr or BC depo-

sition value. Thus, any change in deposition will change proportionally

other flux values.

CONCLUSIONS

Atmospheric deposition is an important nutrition source on the territory

studied because of its climatic features. The contribution of atmospheric depo-

sition to the total flux is the highest among all the three initial nutrition sources

Figure 2. Pictorial model of base cation fluxes (represented by arrows), keq . ha21 . yr21

(on the left of arrows). The percentage contribution of each reservoir to a given flux is

on the right of arrows.

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in the ecosystem. It contributes more than half of exchangeable bases to

organic horizons and its flux is comparable to that of weathering. The high

contribution of atmospheric deposition to the plant-available nutrition pool

makes the vitality of vegetation, to a great extent, dependent on stability of

atmospheric chemistry. For the time being, there is a high probability

of cation accumulation in soil exchange pool. However, the acidification of

atmospheric deposition in this area is very probable because the study site

is situated on the way of predominant air mass transfer, bringing the air

from industrial pollution sources located along the Angara River Valley.

ACKNOWLEDGMENTS

The work of M. Semenov was supported via a grant from the Belgian Office

for Scientific, Technical, and Cultural Affairs. The study was also supported

by a grant from the Russian Federation President’s Fund and a Lavrentiev’s

grant from Siberian Branch of Russian Academy of Sciences.

REFERENCES

Capo, R.C., Stewart, B.W., and Chadwick, O.A. (1998) Strontium isotopes as tracers ofecosystem processes: Theory and methods. Geoderma, 82: 197–225.

Faure, G. (1986) Principles of Isotope Geology; John Wiley & Sons: New York.Gosz, J.R., Brookins, D.G., and Moore, D.I. (1983) Using strontium isotope ratios to

estimate inputs to ecosystems. Bioscience, 33: 23–30.Graustein, W.C. and Armstrong, R.L. (1983) The use of 87Sr/86Sr ratios to measure

atmospheric transport into forested watershed. Science, 219: 289–292.Kotov, A.B., Salnikova, E.B., Reznitsky, L.Z., Vasilyev, E.P., Kozakov, I.K.,

Yakovleva, S.Z., Kovach, V.P., and Berezhnaya, N.G. (1997) O vozraste metamor-fizma slyudyanskogo kristallicheskogo kompleksa (yugnoye pribaikalye): rezultatiU-Pb geohronologicheskih issledovanii granitoidov. Petrologiya, 5: 380–393(in Russian).

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Miller, E., Blum, J., and Friedland, A. (1993) Determination of soil exchangeablecation loss and weathering rates using Sr isotopes. Nature, 362: 438–441.

Semenov, M.Y., Bashkin, V.N., and Sverdrup, H. (2001) Critical loads of acidity forforest ecosystems of north Asia. Water, Air, and Soil Pollution, 130: 1193–1198.

Semenov, M.Yu., Sandimirova, G.P., Korovyakova, I.V., Troitskaya, E.S.,Khramtsova, T.I., and Donskaya, T.V. (2005) Comparative assessment of soilweathering rates in the northern slope of the Khamar-Daban Ridge. Geologiya iGeofizika, 46: 50–59.

Stewart, B.W., Capo, R.C., and Chadwick, O.A. (1998) Quantitative strontium isotopemodels for weathering, pedogenesis and biogeochemical cycling. Geoderma, 82:173–195.

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