ISSN 1028�334X, Doklady Earth Sciences, 2013, Vol. 451, Part 1, pp. 784–786. © Pleiades Publishing, Ltd., 2013.Original Russian Text © N.G. Granin, I.B. Mizandrontsev, A.I. Obzhirov, O.F. Vereshchagina, R.Yu. Gnatovskii, A.A. Zhdanov, 2013, published in Doklady Akademii Nauk, 2013,Vol. 451, No. 3, pp. 332–335.

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The discovery of methane hydrates in the bottomsediments of Lake Baikal [1], mud volcanoes, anddeep methane seeps [2–4] required solution of theproblem of estimation of the rates of its oxidation inthe lake water column for the background andincreased contents of the dissolved gas.

The analysis of the vertical profiles of distributionof the dissolved methane in normally aerated seas andLake Baikal in 2002–2004 has shown that its concen�trations and values of partial pressure in the main deeppart of the water column is usually lower than theirequilibrium values with the atmosphere. This is causedby aerobic methane oxidation in the water by methan�otrophs [5]. The quantitative estimation of the inten�sity of this process in situ is a topical task in descriptionof the formation of methane distribution and its par�ticipation in the carbon cycle and in gaseous exchangeof the water area with the atmosphere [6].

The potential rate of aerobic bacterial methane oxi�dation identified by the radioisotopic method is presentlyknown for the water column of the open Baikal [6]. Itcharacterizes the physiological activity of methanotrophs[7]. Generally, the oxidation rate decreases with thedepth and is 0.26–8.30 μl СН4 l–1 days–1 at an averagevalue of 0.5 μl СН4 l

–1 days–1 [8, 9]. The process inten�sity is less than 1.1 СН4 ⋅ l–1 days–1 for the majority ofdeep stations beyond the impact zones of gaseous seepsand mud volcanoes. According to the averaged profile of

the methane oxidation rate, its values in the main deeplake zone (>200 m) are 0.1–0.5 μl СН4 l–1 days–1 [10].The number of methanotrophs in the Baikal water col�umn is 10–100 to 1000 cell ml–1 based on single mea�surements [9].

The present work is aimed at quantitative estima�tion of the factual rate of oxidation of the dissolvedmethane in situ in a normally aerated fresh water res�ervoir with marine depths based on the age of its watermasses and vertical methane distribution. Knowledgeof the intensity of this process is necessary for balancecalculations and description of carbon cycle in Baikal,taking into account the sources and consumption ofmethane with the participation of specific microflora.

The study of the age of water masses of open Baikalin 1988–1997 has shown its increases with depth [11,12]. The age profiles for this period changed weakly.The vertical distribution of methane in the water col�umn of the pelagic zone was measured in 2002–2004[13]. It was established that the profiles of CH4 con�centrations in the main part of the water column(more than 200 m) also did not change significantlythrough time.

The present work uses the tritium–helium age ofthe waters [12] (Fig. 1) and averaged vertical profiles ofthe concentration of dissolved CH4 at the deep sta�tions in June 2003 (Fig. 2). The location of stationsand methane distribution in the water column on asection along the lake are given in [13].

The concentration of the dissolved methane inBaikal was determined using vacuum degassing by theIl’ichev Pacific Oceanological Institute, Far EastBranch, Russian Academy of Sciences. Gas chroma�tography analysis was carried out on a SRI 861C (SRI

Oxidation of Methane in the Water Column of Lake BaikalN. G. Granina, I. B. Mizandrontseva, A. I. Obzhirovb,

O. F. Vereshchaginab, R. Yu. Gnatovskiia, and A. A. Zhdanova

Presented by Academician M.A. Grachev October 24, 2012

Received October 24, 2012

Abstract—The rate of aerobic oxidation of methane was calculated based on average profiles of the tritium–helium age of the Baikal waters and concentrations of the dissolved methane in the water column. In the deeplake zone (>200 m), the intensity of oxidation vertically decreases and is (2–0.3) × 10–2 nl CH4 l–1 days–1 insouthern and central Baikal and (2.8–1.0) × 10–2 nl CH4 l–1 days–1 in northern Baikal. The effective coeffi�cient of the oxidation rate in the lake depressions is 3.6 × 10–4, 3.3 × 10–4, and 3.7 × 10–4 days–1, respectively.At current methane concentrations in the water column, about 80 t of methane is oxidized per year. Oxidationof the dissolved methane in the water column was estimated at a possible increase of its concentration.

DOI: 10.1134/S1028334X13070258

a Limnological Institute, Siberian Branch, Russian Academy of Sciences, ul. Ulan�Batorskaya 3, Irkutsk, 664033 Russiab Il’ichev Pacific Oceanological Institute, Far East Branch, Russian Academy of Sciences, ul. Baltiiskaya 43, Vladivostok, 690041 Russia

GEOGRAPHY

DOKLADY EARTH SCIENCES Vol. 451 Part 1 2013

OXIDATION OF METHANE IN THE WATER COLUMN OF LAKE BAIKAL 785

Instruments, United States) chromatograph with anaccuracy of ±5%.

The bacterial oxidation of methane dissolved in thewater performed by the labile methane monooxige�nase ferment system [5] is described by the Michaelis–Menten equation [7]. The Michaelis constant (KM) is5–10 μmole l–1 and 0.5 μmole CH4 l–1 in the lake andmarine water, respectively, which is three–four ordershigher than the background methane concentrationsin the deep Baikal zone. In this case, the formal kinet�ics of CH4 oxidation reduces to a process of the firstorder [13, 14].

The measurements of the tritium–helium age ofthe water masses and vertical methane distributionallowed imagination of the distribution of the CH4

concentration in the water column as kinetic curves inconcentration–time coordinates. Their semiloga�rithm anamorphoses are shown in Fig. 3. It followsfrom the description of the aerobic methane oxidationat low concentrations by the equation of the first orderreaction that the effective rate coefficient (specific

intensity of the reviewed process) is ,

where C is the СН4 concentration and t is the time (ageof the given water mass).

The value of α was calculated by selected couples ofages of the waters and concentrations at the horizonswith the depths z1 and z2 in the main part of the watercolumn with depths more than 200 m without thenear�bottom zone:

It was suggested that the initial concentration ofmethane С0 in the water mass of zero age is constant.Taking into account the CH4 content in the atmo�sphere registered by the global monitoring stations[15], the rates of its increase for the last two decadesgive a correction of only 3–4%.

α C 1– dCdt�����–=

α t z2( ) t z1( )–{ }1– C z2( )

C z1( )����������.ln–=

The calculated values of α for the deep part of thewater column of open Baikal beyond the zones ofdirect impact of gaseous seeps and mud volcanoesare (2.7–4.1) × 10–4, (1.9–3.8) × 10–4, and (2.9–4.4) ×10–4 days–1 for the southern, central, and northernlake depressions, respectively.

According to the linear regression equations for thedata in the lnC–t coordinates, the values of α are 3.6 ×10–4 (south Baikal), 3.3 × 10–4 (central Baikal), and3.7 × 10–4 (northern Baikal) days–1. The best descrip�tion of the decrease in the CH4 concentration with thedepth based on the one�dimensional diffusion modelwas achieved at α of 8.0 × 10–9 s–1 (6.9 × 10–4 days–1)[13]. The profile of the coefficient of vertical turbulentdiffusion was calculated after the К–ε model. Itshould be noted that value of α depends significantlyon the given profile of the turbulent diffusion coeffi�cient in the model experiments.

At the above�indicated values of α and the averageweighted values of concentration of the dissolved

200

40

400

600

800

1000

1200

1400

1600

2 6 8 10 12 14 16 18Age, year

Dep

th,

m

12

3

Fig. 1. Average profiles of the tritium–helium age of water[12] of open Baikal (southern (1), central (2), and north�ern (3) depressions).

200

200

400

600

800

1000

1200

1400

1600

40 60 80 100 120Concentration, nl CH4 ⋅ l−1

Dep

th,

m

12

3

Fig. 2. Average profiles of concentration of dissolved meth�ane in the water column of open Baikal (southern (1), cen�tral (2), and northern (3) depressions).

2.04

2.5

3.0

3.5

4.0

4.5

2 6 8 10 12 14 16 18Age, year

1

2

3

0

lnC100

200

400600

800900

800

800 900600

400

200200

400

1000

1200

1600

1000

Fig. 3. Dependence of concentration of dissolved methaneon the age of waters of the main water column for southern(1), central (2), and northern (3) Baikal. Lines of regres�sion: southern (dash), central (dotted), and northern(firm) depressions. Numbers near the points are the depthsof the horizon (m).

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GRANIN et al.

methane in the main part of the water column(>200 m) of 22 (southern and central Baikal) and 45(northern Baikal) nl СН4 l–1, the average rates ofmethane oxidation are 7.9 × 10–3, 7.3 × 10–3, and 17 ×10–3 nl СН4 l–1 days–1, respectively. Because the meth�ane content decreases with an increase in the depth,the rate of its oxidation also decreases vertically: from2.1 × 10–2 to 0.4 × 10–2 (southern Baikal), from 1.9 ×10–2 to 0.3 × 10–2 (central Baikal), and from 2.8 × 10–2 to1 × 10–2 (northern Baikal) nl СН4 l–1 days–1.

We suggest that the values of α in the upper mixedlayer (0–200 m) are similar to those in the deep zoneof corresponding lake depressions. Then, the annualconsumption of methane in the water column, whichis calculated based on the layer�by�layer water vol�umes, will be 18, 24, and 38 t in southern, central, andnorthern Baikal, respectively, at an average weightedmethane concentration of 31, 31, and 50 nl СН4 l–1,respectively. Thus, the quasi�stationary backgroundvertical distribution of methane in the lake waterrequires an annual gain of 80 t CH4 owing to function�ing external and internal sources. This estimationtakes no account of emission of gaseous methane intothe atmosphere by shallow seeps and also its localsource of dissolved gas and gaseous jets from the deepbottom sediments (mud volcanoes and seeps).

The elevated concentrations of dissolved methanewere observed in the deep part of the open lake in theimmediate vicinity of the gas vents [9, 10, 13]. It isassumed that the CH4 contents presently increase inthe water column. Supposing that the methane con�tent in the deep water of southern and central Baikalcurrently exceeds the background values of 2002–2004 by 10–30 times, its oxidation should be 420–1300 t CH4 year–1, which is comparable to the estima�tions of the methane flux from the deep bottom sedi�ments of 1400–2800 t year–1 [4].

ACKNOWLEDGMENTS

This work was supported by the Interdisciplinaryprojects of the Siberian Branch, Russian Academy ofSciences, and the Presidium of the Russian Academyof Sciences, project no. 23.9. The authors are thankfulto B.B. Namsaraev and O.P. Dagurova for consulta�tions.

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