environments, yet the sensitivity of peatlands to climate change is of great
interest due to their potential ability to act as an atmospheric source
of greenhouse gases such as CO2 and CH4. The sequestration of carbon in
peatlands is dependent on the balance between photosynthesis, autotrophic
respiration and heterotrophic respiration. Each of which involve a number
of controlling environmental and climatological processes, making the peatland
carbon balance a complex area of study. Varying moisture conditions can
strongly influence soil temperature and the proportion of aerobic and anaerobic
respiration within peatlands. At water saturation the by-product of anaerobic
decomposition, CH4, is produced and can be emitted in large quantities,
while drier conditions promote aerobic respiration from plant and microbial
biomass. Meanwhile, plants counteract these atmospheric sources of carbon
by sequestering carbon dioxide and releasing it to the peat complex as litter.
Since most of the peatlands are located in the circumpolar north, a region
that is predicted to experience large changes in temperature and precipitation
in 2xCO2 scenarios (Cubasch et al. 2001), the effect of climate change on
the peatland carbon balance is of concern.
To investigate the response of northern peatlands to climate
change the Peatland Carbon Study (PCARS) was initiated in 1997 to measure
and model the influence of climate on the carbon balance of a peatland.
Since that time the PCARS investigators have collaborated to integrate Mer
Bleue into the Fluxnet-Canada Research Network as the Eastern Peatland site.
This has provided a number of benefits including financial support, expansion
of measurements, interaction among researchers and across disciplines and
rigorous testing and intercomparison of data collection and analyses.
There are four main activities at the Mer Bleue site: (1)
the development of an ecosystem model for peatlands that explicitly includes
aerobic and anaerobic decomposition processes; (2) the coupling of the ecosystem
model to the Canadian Land Surface Scheme (CLASS) which has been parameterized
to estimate the soil climate of peatlands; (3) the examination of the short-term
and long-term carbon accumulation rate of peat accumulation, and how the
rate varies with changes in past climate; and (4) through simulations derived
from the coupled ecosystem – climate model determine the sensitivity
of the peatland carbon pool to climate change and variability.
The principal PCARS research site is Mer Bleue, a 35 km2 ombrotrophic
bog located 10 km east of the city of Ottawa in the Ottawa River valley.
The central portion of the peatland started to form about 8400 years ago
accumulating Peat nearly 6 m deep. The porewater at Mer Bleue is highly
acidic, rich in dissolved organic carbonb and poor in nutrients. The surface
is slightly domed. Vegetation on the surface is composed of ericaceous shrubs
(dominantly Chamaedaphne calyculata, Kalmia angustifolia, and Ledum groenlandicum)
and grasses. The hummocks are covered by Sphagnum moss (dominantly Sphagnum
capillifolium and Sphagnum fuscum) while the hollows are covered by Smilacina
trifolia, Eriophorum vaginatum and Sphagnum magellannicum and Sphagnum angustifolium.
The instrument tower is located in the western end of the bog, about 250
m from the shore in a northwesterly direction. Instrumentation includes
a full suite of meteorological and flux measurements, including energy balance
and carbon dioxide. Tower measurements are supported by a number of on-going
field investigations on biomass quantification and decomposition, soil water
content, hydrology of the bog, and others. A more detailed description of
the instruments and measurements is provided on the FCRN
website and at Ameriflux.
The net ecosystem exchange of carbon dioxide (NEE) and its relationship
to light varies significantly between peatland types such as bogs, poor
fens and rich fens (Frolking et al. 1998). Consequently, the sensitivity
of annual peatland C budgets to climate variations is also expected to vary
between peatland types. In order to predict the potential consequences of
climate change on the large stores of C within northern peatlands, it is
critical to understand the biophysical factors, which control respiration,
photosynthesis, and aerobic and anaerobic oxidation of peat. By measuring
NEE in different peatland types within the same ecoclimatic region, differences
in ecosystem structure and function may be evaluated. Ultimately, measurements
such as these are critical for the further development and validation of
process-oriented C budget models such as the Peatland Carbon Simulator (PCARS)
(Frolking et al. 2002).
Using the eddy covariance technique, NEE and evaporation have
been continuously monitored since 1998 at the Mer Bleue peatland. Over this
period, this bog has been found to be a sink for CO2 of about 70 g C m-2
y-1 (Lafleur et al. 2001). However, remote-sensing imagery shows
marked variation in surface vegetation within the Mer Bleue bog and chamber
measurements of NEE vary with location.
The objectives of this study begun in 2004 are 1) to quantify
the spatial variation of daily and seasonal NEE within the Mer Bleue peatland
and between peatlands of different types and 2) to identify the processes
and the biophysical factors controlling these variations. The main tower
in the Mer Bleue bog is the permanent research site where NEE and water
vapour and energy fluxes are continuously measured using the eddy covariance
technique. Three additional sites have been established within the Mer Bleue
bog but outside of the current flux footprint. These include a cattail marsh,
a poor fen, and an ombrotrophic bog with a different composition of species
from that of the main tower’s flux footprint. All sites are outfitted
with a basic weather station and sensors monitoring microclimate conditions
while a mobile eddy covariance system is moved to one of the three satellite
sites every 1 to 1.5 months. Fluxes of methane and input/outputs of dissolved
organic and inorganic carbon are measured in co-operation with collaborating
researchers. At each site, peatland characteristics required for PCARS simulations
are also collected. This work will contribute to the development of the
PCARS model and its ability to assess the sensitivity of northern peatland
C budgets to climate and land-use change.
Wetlands have been a major focus of research at the Blue Lab. Dr. Peter
Lafleur has been involved in research at a number of wetlands in Canada
(apart from Mer Bleue), including sites at Kesagami River on James Bay,
BOREAS FEN site at Thompson, Manitoba, the Peace-Athabasca Delta in northern
Alberta, and Cape Race on Newfoundland. The focus of most of this research
has been the study of energy and water balances of these wetland ecosystems.
Information from many of these sites was used in the CLASS project for validation
of this land surface process model for wetlands. Here are some links to
other active investigators of the PCARS project:
Dr. Elyn Humphreys, Associate Professor, Carleton University
Dr. Tim Moore, Professor, McGill University
Dr. Nigel T. Roulet, Professor, McGill University
For a list of selected publications, please refer to: publication document
Cubasch, U and 40 others, 2001. Projections of future climate change. In:
Climate Change 2001: The Scientific Basis. Contribution
of Working Group I to the Third Assessment Report of the Intergovernmental
Panel on Climate Change. Cambridge
University Press, Cambridge, New York.
Frolking, S. et al., 2002. Modelling the seasonal to annual carbon balance
of Mer Bleue Bog, Ontario, Canada. Global Biogeochemical
Cycles, 16: 1029-1040.
Frolking, S. et al., 1998. Relationship between ecosystem productivity and
photosynthetically active radiation for
Global Biogeochemical Cycles, 12: 115-126.
Gorham, E., 1991. Northern peatlands: role in the carbon balance and probable
responses to climatic warming.
Lafleur, P.M., Roulet, N.T., and Admiral, S., 2001. The annual cycle of
CO2 exchange at a boreal bog peatland. J.
Turunen, J.E., T.K. Tolonen and A. Reinikainen, 2002. Estimating carbon
accumulation rates of undrained mires in
applications to boreal and subarctic regions. Holocene 12, 69-80.