Carbon Dioxide Evolution from Subarctic Peatlands in Eastern Canada

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Carbon Dioxide Evolution from Subarctic Peatlands in Eastern CanadaAuthor(s): T. R. MooreSource: Arctic and Alpine Research, Vol. 18, No. 2 (May, 1986), pp. 189-193Published by: INSTAAR, University of ColoradoStable URL: http://www.jstor.org/stable/1551128 .

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Arctic and Alpine Research, Vol. 18, No. 2, 1986, pp. 189-193

CARBON DIOXIDE EVOLUTION FROM SUBARCTIC PEATLANDS IN EASTERN CANADA

T. R. MOORE Department of Geography, McGill University

805 Sherbrooke St. W., Montreal, Quebec H3A 2K6 Canada

ABSTRACT

Measurements of carbon dioxide evolution were made by the alkali absorption method at five poor to very rich fen sites near Schefferville, subarctic Quebec. Daily evolution rates ranged from 1 to 10 g CO2*m-2, in the sequence poor to rich fen, with values dropping to <2 g CO2* m-2 * d- in early winter. There was a poor correlation between carbon dioxide evolution rates and temperature parameters, probably reflecting the seasonal change in metabolic activi- ties of many subarctic plants. Annual rates of evolution range from 300 to 660 g CO2 m-2, which is in the same sequence as estimated net primary production.

INTRODUCTION

Peatlands contain large amounts of organic carbon (up to 100 kg m-2, according to Schlesinger, 1977) and many of the major peatland areas occur in the boreal, subarctic, and arctic zones, where low temperatures and low rates of evapotranspiration readily lead to the build-up of slowly decomposing organic matter. Although generally regarded as sinks for atmospheric carbon dioxide, peatlands, like other ecosystems, evolve carbon dioxide back into the atmosphere through plant respiration and organic matter decomposition. Given the areal importance of peatlands, there is a need to know how much carbon dioxide is evolved back into the atmosphere. Moreover, there is current concern over the build-up of atmospheric carbon dioxide, and associated climatic changes, which may change the balance of carbon dioxide in ecosystems. Peatlands act as major global accumulators of organic carbon but this may change if peatland drainage and use for fuel increase (Bramryd, 1979, 1980, 1983) or if there are major climatic changes. The Alas- kan tundra, for example, may change from a sink to a source of atmospheric carbon dioxide (Billings et al., 1982, 1983).

Despite the large area covered by northern peatlands and their importance to the global carbon dioxide balance, there is a dearth of available data on carbon dioxide evolution rates. On the wet Alaskan tundra, values for carbon dioxide evolution range from 0.2 to 9.2 g CO2 m-2 d-1 (Bunnell et al., 1975; Peterson and Bill- ings, 1975; Billings et al., 1977), whereas values for lichen- heath, shrub and tussock tundra vary from 1.4 to 2.3 g CO2'm-2 d-1 (Poole and Miller, 1982). In Scandinavia, reported values range from 7 g CO2 m-2 'd- for a wet meadow (Skartveit et al., 1975) to 0.1 to 0.7 g CO2. m-2d-' for a subarctic mire (Svensson, 1980).

In this paper, I present results on carbon dioxide evolution from five peatland sites near Schefferville (55?43'N, 66?42'W) in subarctic Quebec. This area lies in the Low Subarctic Wetland Region of Zoltai and Pollett (1983) and the peatland sites examined range from poor to very rich fens, in the sense of Sj6rs (1950). The seasonal pattern of carbon dioxide evolution is presented, the relationship to temperature is analyzed and an estimate of annual evolution is made and compared to measurements of plant production.

?1986, Regents of the University of Colorado T. R. MOORE / 189



SITES AND METHODS

Each of the sites was within 25 km of the town of Schefferville, and a plot was selected within a fairly uni- form stand of vegetation, with minor microtopography. The plots were 15 x 15 m, except at site 5 where a 7.5 x 7.5 m plot was established. The plot was divided into 1 x 1 m quadrats, with a 0.5-m border between. The quadrats were used for measurements of carbon dioxide evolution, as well as primary production (Bartsch and Moore, 1985).

A variety of methods have been used for the measurement of carbon dioxide evolution, mainly being either absorption by alkali in a closed chamber, or by drawing a stream of air over the soil and determining the carbon dioxide concentration by infrared gas analysis. Although the latter method probably gives more reliable results (see Schlesinger, 1977, for review), it was not used here because of the difficulties of working in remote areas. The absorption method is robust and easy to use, but it suffers from several possible problems. The absorption of carbon dioxide by the alkali in the chamber can increase the rate of carbon dioxide diffusion from the soil, thereby over- estimating the true evolution rate. The alkali can be in- efficient in absorbing the carbon dioxide in the chamber, or can become saturated with carbon dioxide, thereby underestimating the evolution rate. The microclimate in the chamber can become warmer than outside the chamber, thereby causing an increase in the evolution rates.

Metal cylinders, approximately 20 cm diameter and 15 cm length, were closed at one end by placement and sealing a plastic sheet. These chambers were then painted white to reduce ambient temperature increases on sunny days. At each sampling date, four replicate quadrats were chosen within the 15 x 15 m plot and a 50-ml vial con- taining 10 ml of 1N.KOH placed in the quadrat, on the surface of the peat. The chamber was then placed over the vial and the edges of the chamber pushed down into the peat, until 2 to 5 cm were buried, to ensure an air- tight seal.

The vial was retrieved after 24 h and the alkali titrated with IN and 0.1N H2SO4 to the phenolphthalein and bromocresol green end points, respectively, to allow a cal- culation of the absorbed carbon dioxide, when the control sample value was subtracted (Bundy and Bremner, 1972). Measurements of evolution were made at approximately 2-wk intervals during the summers (June to August) of 1982 and 1983, and a further measurement was made in October 1982, just before the peatlands froze.

At each site, the thermal regime of the peat was mea- sured from thermistors placed at 5, 10, and 20 cm beneath either the peat surface or the water surface, which- ever was higher. A "weighted mean" temperature of the peat was obtained by taking the mean of the four read- ings at each sampling date. In addition, the daily mean screen temperature was recorded at the Schefferville Air- port 'A' meteorological station on the day of measure-

ment. Estimates of plant production at each site were made

by harvesting the aboveground sedge component and for the Sphagnum component by the cranked wire method, with conversion to areal values by using bulk density measurements (Clymo, 1970; Bartsch and Moore, 1985).

SITE 1 This site represents a poor fen, located in the central

portion of an elongated peatland (300 x 100 m). The vegetation is dominated by a sparse stand of Carex limosa and a mat of Sphagnum lindbergii, with a few small shrubs such as Chamaedaphne calycuta. The peat is very poorly consolidated, reaching down to about 2 m. Sea- sonal (June to September) surface peat water pH and conductivity average 5.1 and 1.4 /S cm-1, respectively, over the growing season.

SITE 2 This site represents a transitional fen, again in the

central section of an elongated peatland (500 x 100 m). Carex limosa is again the dominant sedge, in a somewhat denser stand than at site 1, with some Carex rostrata, Myrica gale, and Chamaedaphne calycuta. The peat is also very poorly consolidated, reaching down to about 1.5 m. Peat water pH and conductivity average 6.0 and 18 /S cm-', respectively.

SITE 3 This is also a transitional fen, but with a much denser

stand of sedges, mainly Carex rostrata and a thick carpet of Sphagnum russowii, again with Sphagnum angusti- folium and a few Chamaedaphne calycuta and Kalmia polifolia. The peat is much denser than at sites 1 and 2 and extends to 1.5 m. Peat water pH and conductivity average 5.8 and 19 AS cm-', respectively.

SITE 4 This site is a rich fen located in the lower section of

a larger peatland (1200 x 100 m), dominated by a dense stand of Carex chordorrhiza with a layer of Sphagnum riparium. The peat is partially consolidated, though a per- son walking is supported by the thick mat of roots. The average peat water pH and conductivity is 6.7 and 39 ,S cm-I, respectively, because of the occurrence of dolomite.

SITE 5 This is a very rich fen on a small (100 x 50 m) sloping

lower section of a large peatland. It is underlain by dolomite, giving high pH and conductivity values (7.0 and 201 /iS cm-~). There is a dense stand of Carex aquatilis with a moss layer dominated by Sphagnum warnstorfii. Drain- age is better than at the other sites and the water table lies at a depth of between 5 and 15 cm beneath the moss surface for much of the summer.

190 / ARCTIC AND ALPINE RESEARCH



RESULTS AND DISCUSSION

The seasonal variation in daily carbon dioxide evolution at the five sites over 1982/83 is presented in Figure 1. Establishment of statistically significant differences between sites or over the seasons is hindered by the high variability between the four replicates at each sampling date. The coefficients of variation (standard deviation as proportion of mean) averaged 0.29 to 0.38 for the five sites. This scale of spatial variability, even over small areas (225 m2), is common in many soil properties (Beckett and Webster, 1970) and Poole and Miller (1982) and Svensson (1980) noted a similar variability between replicates in their studies of carbon dioxide evolution from Alaskan tundra and Swedish mire sites, respectively. For clarity, individual standard deviations are not in- cluded on the diagrams, though average values are shown.

Rates of carbon dioxide evolution varied from 1 to 4 g CO2 m-2 d-1 at sites 1 and 2 to 3 to 10 g CO2 m-2 d-1 at sites 3, 4, and 5. There are considerable variations in evolution rate over the summer, though all sites show a decrease to less than 2 g CO2 m-2'd-1 in early October, when the air temperature had fallen to 2?C and the surface layers of the peat (5 to 20 cm depth) had fallen to 2 to 6?C. Particularly notable are the high rates of evolution observed during late May and early June, soon after snowmelt. The thermal data reveal that the top 20 cm of the peat can warm rapidly once the snow has melted, and temperatures of between 2 and 10?C are recorded by early June 1983. By midsummer, the surface layers of the peat have been heated to 12 to 20?C, though mean daily air temperatures can be warmer (Moore, unpub. ms.).

Previous studies of carbon dioxide evolution from soils have revealed the importance of temperature, especially when dealing with laboratory studies in which temperature and other factors can be carefully controlled (e.g., Peterson and Billings, 1975; Billings et al., 1977; Svensson, 1980). Comparison of peat and air temperatures and carbon dioxide evolution rates for the subarctic peatlands did not reveal many clear relationships (Table 1). The best correlations were obtained at sites 1, 2, and 3, whereas the most productive sites (4 and 5) showed no significant correlation (atp < 0.05 level). The relationships were most strongly developed for the temperature parameters closest to the surface, i.e., the temperature at 5 cm depth and the mean daily air temperature. Svensson (1980) was able to explain 787o of this variation of carbon dioxide evolution from his subarctic mire at Stordalen in terms of temperature at a depth of 2 to 3 cm, though only six sampling dates were used in his analysis.

In part, this poor correlation may be related to the small number of dates in which the air or peat temperature was low. The weak relationship may be related, how- ever, to other factors, such as the release of stored carbon dioxide from subsurface layers of peat as the peat thaws (Coyne and Kelley, 1974), the depletion of readily avail-

able photosynthate, the acclimation and reduced late summer growth of plants, the variation in nutrient supply or aeration and the exhaustion of readily decomposable substrates by mid-summer. Many of these phenomena have been recorded in Alaskan tundra, and therefore may apply to these subarctic peatlands (Billings et al., 1977; Kummerow and Russell, 1980; Poole and Miller, 1982). A further factor may be the production of methane by the decomposition of the peat, which becomes converted to carbon dioxide at the peat surface. Methane evolution from these subarctic peatlands is generally small, compared to that of carbon dioxide, when transparent chambers are used. The molar ratios of carbon dioxide to methane evolved from the surface layers of the peatlands during the summer range from about 4:1 at sites 3 and 4 to over 700:1 at the better drained site 5 (Moore and Knowles, unpub. ms.), with methane evolution rates between 10 and 50 mg CH4- m-2d-1.

Summation of the observed seasonal values provides an estimate, albeit approximate, of the annual carbon dioxide evolution of these subarctic peatlands (Table 2). Values range from 300 to 600 g C02 m2 yr-1 and reflect the increase in aboveground sedge and moss production at the sites, a trend which has been noted in Alaskan tundra vegetation types (Poole and Miller, 1982). These

TABLE 1 Statistical relationships between carbon dioxide

evolution rate and temperature parameters

Temperature Form of parametera relationshipb

T5 Rank Linear Polynomial

Tlo Rank Linear Polynomial

T20 Rank Linear Polynomial

TM Rank Linear Polynomial

TA Rank Linear Polynomial

Site

1 2 3

*c

*

*

*

*

*

4 5 *

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

aT, TIo, T20, TM, TA: temperatures at 5-, 10-, 20-cm depth, weighted mean of these depths, and mean daily air temperature, respectively.

bRank: Spearman's rank correlation coefficient; linear: Pearson's product moment correlation coefficient; polynomial: regression of y = c + aT+ bT2.

c* indicates significant relationship at p < 0.05 level.

T. R. MOORE / 191



10

O 4 E

0.

- 2

> 10--

Site 4 A Average Stand of the n

Sx~ / \ \Site 5 0

2 8

0 I J ,A I JUNE JULY AUG. SEPT. OCT. JUNE J

1982

FIGURE 1. The evolution of carbon dioxide from the five peatland sites during 1982 and 1983.

JULY AUG. SEPT.

1983

192 / ARCTIC AND ALPINE RESEARCH



values can be placed in a more general context, using the results collated by Schlesinger (1977): 136 to 771 g CO2 m-2 yr-1 in tundra, 2679 to 4954 g CO2 m-2 yr-1 in tem- perate and subtropical swamps and marshes, and 539 to 828 g CO2'm-2 yr-1 in boreal forests. When the large area of subarctic peatlands is taken into account, perhaps 3 x 105 km2 in Canada (Zoltai and Pollett, 1983), then these peatlands become major global sources of atmospheric carbon dioxide.

ACKNOWLEDGMENTS

The author gratefully acknowledges the field assistance of Kathy Bergquist, the logistic support of the McGill Subarctic Research Station, and the financial support of the Natural Sciences and Engineering Research Council of Canada.

TABLE 2 Estimated annual carbon dioxide evolution and net plant production at the five subarctic peatland sites

Estimated CO, evolution

Site (g CO, m-'2yrl)

1 2 3 4 5

300 350 570 590 660

Net plant production (gm-2 yr-l)a

Aboveground sedge

27 n.d.

90 233 164

Sphagnum

20 n.d. 100 25 89

aFrom Bartsch and Moore (1985) and subsequent measurements.

n.d. -not determined.

REFERENCES CITED

Bartsch, I. and Moore, T. R., 1985: A preliminary investigation of primary production and decomposition in four peatlands near Schefferville, subarctic Quebec. Canadian Journal of Botany, 63: 1241-1248.

Beckett, P. H. T. and Webster, R., 1970: Soil variability: A review. Soils and Fertilisers, 34: 1-15.

Billings, W. D., Luken, J. O., Mortenson, D. A., and Peterson, K. M., 1982: Arctic tundra: A source or sink for atmospheric carbon dioxide in a changing environment? Oecologia, 53: 7-11.

, 1983: Increasing atmospheric carbon dioxide: Possible effects on arctic tundra. Oecologia, 58: 286-289.

Billings, W. D., Peterson, K. M., Shaver, G. R., and Trent, A. W., 1977: Root growth, respiration and carbon dioxide evolution in an arctic tundra soil. Arctic and Alpine Research: 9: 129-137.

Bramryd, T., 1979: The conservation of peatlands as global carbon accumulators. Proceedings of the International Sym- posium on Classification of Peat and Peatlands, Hyytiala, Finland. Helsinki, Finland: International Peat Society, 297-305.

, 1980: The role of peatlands for the global carbon dioxide balance. Proceedings of the 6th International Peat Congress. Duluth, Minnesota: International Peat Society, 9-11.

, 1983: Human impact on the biogeochemical cycling of carbon between terrestrial ecosystems and the atmosphere. In Hallberg, R. (ed.), Environmental Biogeochemistry. Eco- logical Bulletin 35. Stockholm: Swedish Natural Science Re- search Council, 301-313.

Bundy, L. G. and Bremner, J. M., 1972: A simple titrimetric method for determination of inorganic carbon in soils. Soil Science Society of America Proceedings, 36: 273-275.

Bunnell, F. L., MacLean, Jr., S. F., and Brown, J., 1975: Barrow, Alaska, U.S.A. In Rosswall, T. and Heal, 0. W. (eds.), Structure and Function of Tundra Ecosystems. Eco- logical Bulletin 20. Stockholm: Swedish Natural Science Re- search Council, 73-124.

Clymo, R. S., 1970: The growth of Sphagnum: Methods of measurement. Journal of Ecology, 58: 13-49.

Coyne, P. I. and Kelley, J. J., 1974: Variations in carbon dioxide across an arctic snowpack during winter. Journal of Geo- physical Research, 79: 799-802.

Kummerow, J. and Russell, W., 1980: Seasonal root growth in the arctic tussock tundra. Oecologia, 47: 196-199.

Moore, T. R., unpub. ms.: The thermal regime of subarctic peatlands.

Moore, T. R. and Knowles, R., unpub. ms.: Methane and carbon dioxide evolution from subarctic peatlands.

Peterson, K. M. and Billings, W. D., 1975: Carbon dioxide flux from tundra soils and vegetation as related to temperature at Barrow, Alaska. American Midland Naturalist, 94: 88-98.

Poole, D. K. and Miller, P. C., 1982: Carbon dioxide flux from three arctic tundra types in north-central Alaska, U.S.A. Arc- tic and Alpine Research, 14: 27-32.

Schlesinger, W. H., 1977: Carbon balance in terrestrial detritus. Annual Review of Ecology and Systematics, 8: 51-81.

Sj6rs, H., 1950: On the relation between vegetation and elec- trolytes in north Swedish mire waters. Oikos, 2: 241-258.

Skartveit, A., Ryden, B. E., and Karenlampi, L., 1975: Cli- mate and hydrology of some Fennoscandian tundra ecosystems. In Wielgolaski, F. E. (ed.), Fennoscandian Tundra Eco- systems. Part 1. Plants and Micro-organisms. New York: Springer-Verlag, 41-56.

Svensson, B. H., 1980: Carbon dioxide and methane fluxes from the ombrotrophic parts of a subarctic mire. In Sonesson, M. (ed.), Ecology of a Subarctic Mire. Ecological Bulletin 30. Stockholm: Swedish Natural Science Research Council, 235-250.

Zoltai, S. and Pollett, F. C., 1983: Wetlands in Canada: Their classification, distribution and use. In Gore, A. J. P. (ed.), Mires: Swamp, Bog, Fen and Moor. Ecosystems of the World 4B. Amsterdam: Elsevier, 245-268.

Ms submitted June 1985

T. R. MOORE / 193



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Carbon Dioxide Evolution from Subarctic Peatlands in Eastern Canada