1. science
2. ecology
3. pollution

Production and emission of CO2 in two
unproductive lakes in northern Sweden
Jan Åberg
Department of ecology and environmental science
SE-901 87 Umeå
Umeå 2009
Copyright © Jan Åberg. All rights reserved.
ISBN: 978-91-7264-878-4
Cover photos by Jan Åberg.
Printed by: VMC-KBC, Umeå, Sweden, 2009.
Till Susanne, Noomi och Miriam
Table of Contents
INTRODUCTION..................................................................1
The global carbon cycle ...............................................1
The role of lakes...........................................................2
Production of CO2 in lakes...........................................3
Emission of CO2 from lakes.........................................4
Aims and outline of the thesis.....................................5
METHODS............................................................................7
Hydrology, meteorology and water chemistry............7
Carbon measurements................................................8
Net CO2 production.....................................................8
Emission of CO2.........................................................10
Statistics (selected approaches)................................10
RESULTS AND DISCUSSION............................................13
Causes of CO2 variation in the surface water............13
Internal CO2 production............................................14
Fluxes of CO2 to the air..............................................15
Concluding remarks...................................................16
SVENSK SAMMANFATTNING ........................................19
Artikel I......................................................................20
Artikel II.....................................................................20
Artikel III....................................................................21
Artikel IV....................................................................22
Avslutningsvis............................................................22
ACKNOWLEDGMENTS....................................................23
REFERENCES....................................................................25
+ Four research papers, listed on the next page
List of Papers
PAPER I:
Anders Jonsson, Jan Åberg
and Mats Jansson (2007):
Variations in pCO2 during summer in the surface
water of an unproductive lake in northern Sweden
Tellus Series B-Chemical and Physical Meteorology,
59(5), 797-803, doi:10.1111/j.16000889.2007.00307.x.
PAPER II:
Jan Åberg, Mats Jansson, Jan Karlsson,
Klockar-Jenny Nääs and Anders Jonsson (2007):
Pelagic and benthic net production of dissolved
inorganic carbon in an unproductive subarctic lake
Freshwater Biology, 52(3), 549-560,
doi:10.1111/j.1365-2427.2007.01725.x.
PAPER III:
Anders Jonsson, Jan Åberg, Anders Lindroth
and Mats Jansson (2008):
Gas transfer rate and CO2 flux between an
unproductive lake and the atmosphere in northern
Sweden
Journal of Geophysical Research-Biogeosciences,
113(G4), doi:10.1029/2008JG000688.
PAPER IV:
Jan Åberg, Mats Jansson and Anders Jonsson:
The importance of water temperature and thermal
stratification dynamics for temporal variation of
surface water CO2 in a boreal lake
Manuscript submitted to the Journal of Geophysical
Research – Biogeosciences
Paper I and II is reprinted with permission from Blackwell Publishing Ltd.
Paper III is reprinted with permission from the American Geophysical Union.
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Introduction
Introduction
This doctoral thesis aims to bring further knowledge about production and emission of carbon dioxide (CO2) in lakes. This first chapter
begins by introducing the global carbon cycle and its importance
for the atmospheric CO2 concentration. Then, the role of lakes as CO2
sources, and the processes of in-lake CO2 production and emission,
are briefly reviewed. The last part of the introduction gives the
specific research aims of the thesis. In the chapters following, the
research methods and results are summarized and discussed, with
references to the four included research papers.
The global carbon cycle
The greenhouse effect caused by heat absorption in the atmosphere,
has regulated the climate on Earth for billions of years. Water vapor
(H2O) is the most important greenhouse gas, followed by carbon
dioxide (CO2), which has contributed to climate regulation during
most of the time of abundant life on Earth [Royer et al., 2007;
Retallack, 2009]. CO2 has also been widely noted due to the fact that
fossil fuel burning increases the air concentration of CO 2 and very
likely contributes to global warming [IPCC, 2007].
The major processes regulating the air concentration of CO2 are
related to carbon uptake in the planet's surface and carbon release
from the surface into the atmosphere. In the preindustrial times after
the last glaciation a global balance between carbon uptake and
release resulted in a stable store of ca 280 ppmv CO2 in the
atmosphere1. At present, the air CO2 concentration is more than 388
ppmv2, with a yearly release and removal of CO2 from the atmosphere
corresponding to approximately 218 Gtons and 215 Gtons of carbon,
respectively [Denman et al., 2007]. Fossil fuel burning and global
land-use change account for 8 Gtons of the release-flows, while
approximately 5 Gtons of the carbon uptake represents nature's
feedback response to the increasing air CO2 concentration. The
release flows are thus large enough to exceed the total uptake, and
significantly increase the air concentration of CO2.
1. The present atmospheric CO2 content is higher than in the last 420 000 years [Petit et al., 1999], but still low - or
much lower - than most time of the current Phanerozoic eon [Berner, 2006].
2. 388ppm in the global CO2 trend data from August 2009. Websource:
ftp://ftp.cmdl.noaa.gov/ccg/CO2/trends/CO2_mm_mlo.txt
Doctoral thesis 2009
1 (28)
Introduction
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
The continuously increasing levels of CO2 in the atmosphere have
been well known since the 1960's [Keeling, 1960], and have not been
much questioned, due to the fact that atmospheric CO2 is simple to
measure. On the other hand, the possibility of significant climatic
effects due to the CO2 increase have been strongly debated and are
still questioned, although most data now indicate that the increasing
atmospheric CO2 concentrations very likely contribute to increased
air temperatures on Earth [IPCC, 2007].
The global carbon cycle is expected to respond to global warming by
different feedback mechanisms, such as carbon storage release due to
permafrost melting or changes in global respiration and photosynthesis when global vegetation zones are moving. But, although
today’s knowledge clearly points out a great importance of the global
carbon cycle, its response to warming is not easy to predict. Many of
the processes transforming carbon within ecosystems are still poorly
understood, resulting in still large uncertainties of the terrestrial carbon budgets [Janssens et al., 2003; Canadell et al., 2007; Heimann
and Reichstein, 2008].
The role of lakes
Due to the particular warming of the northern hemisphere predicted
by IPCC [2007], carbon cycle studies in northern ecosystems are of
great interest. The specific importance of northern lakes is related to
the high abundance of lakes in the north [Downing et al., 2006].
Northern forests and undisturbed peatlands are generally regarded
as sinks of CO2 removing CO2 from the atmosphere [Janssens et al.,
2003]. Also lakes and streams were earlier regarded as sinks of CO2,
but was later shown to be net heterotrophic instead of autotrophic,
with a whole lake respiration of organic carbon that exceeds the CO2
uptake by the photosynthesis [del Giorgio et al., 1997]. The net
release of CO2 to the atmosphere from inland waters thus contrast the
general net uptake by the terrestrial biosphere [Heimann and
Reichstein, 2008].
Globally, inland waters are estimated to make a net contribution of
approximately 0.75 Gton carbon per year to the atmosphere [Cole et
al., 2007]. Of these, about 0.15 Gtons represents emissions of CO2
from lakes [Cole et al., 1994]. The lake estimate is however likely
underestimated, since only half of the global lake area was accounted
for in the calculation [Downing et al., 2006]. Furthermore, CO2
emissions from lakes have mostly been estimated with quite simple
models, in contrast to the still very few studies in which lake CO2
2 (28)
Doctoral thesis 2009
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Introduction
emissions have been directly measured [Anderson et al., 1999;
Eugster et al., 2003; Vesala et al., 2006; Paper III].
Taken together, the inland water carbon cycling is neither well known
nor well integrated in the calculations of terrestrial carbon budgets
[Cole et al., 2007]. Consequently many questions are raised related to
how aquatic processes affect the landscape net ecosystem exchange of
carbon. Better understanding of the inland water carbon cycling will
not only improve the terrestrial carbon budgets. It will also benefit
the management of inland waters, due to the great importance of
terrestrial carbon for aquatic ecosystem dynamics [eg. Jansson et al.,
2007].
Production of CO2 in lakes
The production of CO2 in lakes is mainly a result of organism
respiration of organic carbon either fixated by in-lake photosynthesis
(autochthonous organic carbon) or coming in to the lake from the
catchment (allochthonous organic carbon) [Cole et al., 1994; del
Giorgio et al., 1997]. With increased allochthonous input the total
community respiration can exceed the lake primary production,
turning lakes net heterotrophic [Cole et al., 1994]. Significant
importance of allochthonous organic carbon in aquatic food webs has
been shown especially in humic waters where poor light climate and
nutrient limitation favors microbial metabolism [Grey et al., 2001;
Kritzberg et al., 2004; Karlsson et al., 2009]. A large part of the CO2
production in unproductive lakes is therefore a result of bacterial
respiration of allochthonous organic carbon. The importance of this
process is stressed by low growth efficiencies (<10%) of bacteria in
unproductive lakes3. Production of CO2 is also related to photochemical mineralization of organic carbon, although the rapid light
attenuation in most natural waters means that this process is
generally not important for controlling the CO2 supersaturation
[Sobek et al., 2003].
Microbial respiration processes in both pelagic and benthic habitats
significantly contribute to the CO2 concentration of the lake water.
Generally the pelagic contribution of CO2 has been reported to be
larger [Pace and Prairie 2005], but with considerable variation and
with few data from unproductive lakes.
In sum, the net production of CO2 in lake water is a net result of the
balance between photosynthesis and respiration of organic carbon in
3. A growth efficiency of 10% mean that 90% of the total carbon consumption is used for respiration (CO2-production).
Doctoral thesis 2009
3 (28)
Introduction
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
the different lake habitats. External inflow of CO2 may, additionally,
increase the concentration [Jones et al., 2001; Huotari et al., 2009].
And furthermore, the in-lake CO2 balance is strongly influenced by
the abiotic processes which determine the transport of CO2 within the
water column and the exchange of CO2 across the lake surface
[Eugster et al., 2003; Huotari et al., 2009].
Emission of CO2 from lakes
The water column of net heterotrophic lakes become supersaturated
with respect to CO2, which results in a net flux of CO 2 from the lake
surface to the atmosphere [eg. Cole et al., 1994]. The mean emission
from boreal Swedish lakes is calculated to be 79 mg C/m 2/d
[Algesten et al., 2004].
Gas emissions from a water surface occur either by diffusion or the
release of gas bubbles (ebullition). Due to the high water solubility of
CO2 most of the CO2 emission can be expected to occur via diffusive
fluxes, while CH4, which is less soluble, to a greater extent is released
via ebullition [Casper et al., 2000; Huttunen et al., 2001; Poissant et
al., 2007].
The direction and magnitude of the diffusive flux of CO 2 and other
gases through the air-water interface are dependent on the
concentration gradient between the air and the surface water. The
magnitude of the flux depends also on the gas exchange coefficient, k,
determined by the particular properties of the micro boundary layer
between air and water [Liss and Slater, 1974; Cole and Caraco,
1998]. One widely used model for estimating CO2 emissions from
lakes was developed by Cole and Caraco [1998], who measured
different gas pathways and factors which characterized gaseous loss
of SF6 in Mirror Lake (Hubbard Brook, USA).
There are at least two main difficulties using models; to get accurate
predictions of k, and to get representative samples on temporal and
spatial scales. To solve the temporal problem, logger techniques can
be applied [Sellers et al., 1995; Carignan, 1998; Huotari et al.,
2009], but a reliable k is very difficult to obtain unless a lake-specific
model calibration/validation is conducted.
Another approach for measuring gas fluxes is to capture the flux in
chambers floating on the lake surface [St Louis et al., 2000;
Huttunen et al., 2003]. This method has the benefit of also capturing
4 (28)
Doctoral thesis 2009
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Introduction
gas bubbles. However by putting chambers on the surface, the gas
exchange coefficient will likely be altered in comparison to the
natural state. Duchemin et al. [1999] found that the boundary layer
method gave significantly lower fluxes than those obtained from
floating chambers, but that both methods gave values within the
same order of magnitude. A more recent study [Matthews et al.,
2003] showed that fluxes measured from floating chambers are likely
to be overestimates, at least in low wind environments.
Direct measurements using the eddy covariance (EC) technique
[Valentini, 2003], have been published from Williams lake
(Minnesota, USA, 37 ha) [Anderson et al., 1999]; Toolik Lake
(Alaska, USA, 150 ha) and Soppensee (Schweiz, 25 ha) [Eugster et
al., 2003] and Lake Valkea Kotinen (Finland. 4.1 ha) [Vesala et al.,
2006]. Williams Lake was monitored for about three weeks
distributed over three years, and Toolik Lake and Soppensee for
about three days in each lake. Lake Valkea-Kotinen was monitored
during one ice-free season.
The EC-technique is, in contrast to the boundary layer technique, a
direct measurement of turbulent scalar flows such as CO 2 emissions.
In principle, the vertical movement of the air is correlated with the
concentration of a scalar (e.g. CO2) that occurs across a virtual
surface at a certain distance above the lake surface [Baldocchi,
2003]. The resulting output is the flux in a specific area upwind of
the measuring sensors, often referred to as the ‘footprint’ or the
‘source area’.
Aims and outline of the thesis
Carbon turnover in lakes has mostly been studied in North America
and Northern Europe [Sobek et al., 2005]. This thesis follows this
tradition, but focuses on the less studied high latitude lakes. The
major aim of the thesis is to bring further knowledge about high
latitude lakes, with emphasis on analysis of whole lake carbon
turnover processes in one subalpine lake with short water retention
time, and one boreal lake with long water retention time and an area
large enough for EC-measurements in many wind directions. The
whole lake approach used in the four research papers aims to (1)
assess the relative importance of pelagic and benthic CO2 production
processes (2) to apply and confirm the EC-technique for
measurements of CO2 fluxes in the lake-atmosphere interface, and (3)
to analyze the causes of the CO2 variation in the surface water.
Doctoral thesis 2009
5 (28)
Introduction
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
The questions addressed in the thesis is generally related to where in
a lake CO2 is produced and how large the net lake ecosystem
exchange of CO2 is. In Paper I the variation of surface water CO2 in
the subarctic Lake Diktar-Erik is analyzed, while Paper II addresses
the pelagic and benthic net production of dissolved inorganic carbon
(DIC) in the same lake. Paper III presents the result of ECmeasurements of the exchange of CO2 between the boreal Lake
Merasjärvi and the atmosphere, while Paper IV analyzes the
relationship between the surface water CO2 concentrations and
variables related to hydrology, meteorology, water chemistry and the
vertical thermal stratification of the lake water, in Lake Merasjärvi.
6 (28)
Doctoral thesis 2009
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Methods
Methods
With focus on carbon turnover processes, two lakes in northern
Sweden (Figure 1) were intensively studied using both manual
sampling and automated methods. Paper I and II present results
based on data from the ice-free period in 2004 in the small subalpine Lake Diktar-Erik (8.8ha, 68°26'44"N, 18°36'18"E). Paper III
and IV presents results from the larger Lake Merasjärvi (380ha,
67°33'00"N, 21°58'30"E), with data from the ice-free period in 2005.
Some of the lake characteristics are compared in Table 1.
600 km
Figure 1. Lake Diktar-Erik is located in the sub-alpine zone of the northern
Scandes, while Lake Merasjärvi is located within the boreal forest zone of the north
Swedish archean plains.
Hydrology, meteorology and water chemistry
In order to supply detailed data about hydrological, meteorological
and chemical characteristics, logger systems were placed in the inlets
Doctoral thesis 2009
7 (28)
Methods
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
and outlets, and on the lakes. Campbell loggers, models CR10 or
CR10X, were used for all data storage except for vertical temperature
profiles which were logged with a set of Gemini TinyTag loggers at
different depths in the deepest part of the lake.
For methodological details about data logging see respective paper,
or Paper IV which includes a multivariate analysis of most of the
logged variables in Lake Merasjärvi.
Carbon measurements
Dissolved and particulate organic matter (DOC and POC) were
sampled manually in the inlets and outlets and at different depths
and locations in the lakes, and analyzed with standard methods (all
four papers). A more detailed analysis of the low molecular weight
compounds of the DOC was made in a study not included in the
thesis [Jonsson et al., 2007] but discussed in Paper I.
Inorganic carbon was analyzed both manually and with a logger
system. With manual sampling (used in all four papers) both the total
dissolved inorganic carbon concentration and the amount of
dissolved CO2 were analyzed with infrared gas analyzers (IRGAs).
The logger system only recorded dissolved CO2 in surface water (0.20.5m depth), but with 30 minute time-resolution (Paper I, III and
IV). The carbon source of the DIC produced in Lake Diktar-Erik was
analyzed with stable isotope analysis (Paper II).
Net CO2 production
In both lakes the net production of DIC was measured in the
sediments and in the pelagic waters (Paper II and III). The pelagic
net production of DIC was measured in incubation experiments as
the difference in DIC concentration between the start of the
experiment and after 48-72h. The incubations were made under in
situ light and temperature conditions at the sampling depths in the
lakes (Figure 2). Similarly, the benthic net production of DIC was
measured as the difference in DIC concentration between start of the
experiment and after 24 h incubation (in situ). Methodological
details for both approaches are described in Paper II.
8 (28)
Doctoral thesis 2009
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Methods
Figure 2. Preparation of an incubation tube for DIC-production measurements in
Lake Merasjärvi. Anders Jonsson. (photo: J Åberg).
Table 1. Characteristics of the two studied lakes and their catchments.
Lake
Diktar-Erik
Lake
Merasjärvi
Elevationa (m)
375- ca 500
306- ca 500
Lake area (ha)
8.8
380
Max depth (m)
16.5
17
Mean depht (m)
5
5
0.45
19.61
37, 28, 11
275, 162, 118
DOC (mg/l)
5.3 (3.3 to 6.6)
6.2 (5.8 to 6.7)
Secci depth (m)
4
3.2
Total N (µg/L)
200
113
6
6.6
Catchment area (km )
6.1
59
Bedrock in catchment
acidic
acidic
Major landcover in catchment
Bare bedrock (49%)
Boreal forest (51%)
Mean annual air temperaturec
-1°C
-1°C
3
Volume (Mm )
Water renewal times (days)
b
Total P (µg/L)
2
a) above sea level (m) (from lake to top of the catchment)
b) Three water retention times are given based on data from 2004 (Diktar-Erik) and in 2005 (Merasjärvi). The values
are given in the following order: annual mean, mean for the ice-free period, mean for a theoretical epilimnion volume
(0-5m depth) in July.
c) average for the years 1969-1990
Doctoral thesis 2009
9 (28)
Methods
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Emission of CO2
The diffusive fluxes of CO2 presented in Paper I and III were
calculated using a boundary layer model [Cole and Caraco, 1998],
where the k600 was recalculated to the actual temperature in the
surface water, using the Schmidt number at the measured water
temperature [Wanninkhof, 1992]. Air-borne flows of CO2 was
measured over Lake Merasjärvi using an EC-system (Figure 3). The
footprint area of the EC-system was estimated with Kljun’s webbased footprint calculator (http://footprint.kljun.net). The main
sensors of the system used in Lake Merasjärvi were a sonic
anemometer (Gill inc. model R3) and an open-path infrared gas
analyzer (IRGA, Licor inc., model LI-7500), which had fast responses
(20Hz sampling rates) in order to accurately record the turbulent
movement of CO2 in the air. The raw EC-data were processed in the
software Ecoflux 1.4 [Grelle and Lindroth, 1996], and thereafter
quality filtered (see paper III). The performance of the EC-system
was tested with a cross spectrum analysis and an energy balance
closure calculation, and by comparing the EC-fluxes with the carbon
budget of the lake. All three performance tests indicated that the
quality filtered data were of good quality. For details about the
processing and validation of the EC-data, see paper III.
Statistics (selected approaches)
Statistical methods found to be especially useful during the work with
Paper I-IV, are listed in brief below:
Sampling simulation (similar to the Monte-Carlo approach) was
performed in Paper I. In order to calculate confidence intervals for
averages based on differing number of samples, weighted standard
deviations were used (Paper II). In paper IV the variables were many
and dependent, which made the partial least squares regression
(PLS) a good choice for surface water CO2 modeling. The statistical
framework 'design of experiments' (DOE) was applied for making
multiple linear regression (MLR) meta-models of the Ecoflux
software during the preparations of Paper III. Fast fourier
transformation (FFT) was used both for scanning of frequencies in
time series (during the preparation of Paper IV) and for the cross
spectrum analysis in Paper III.
10 (28)
Doctoral thesis 2009
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Methods
Figure 3. The eddy covariance (EC) system in Lake Merasjärvi measured fluxes of
CO2 between the lake and the atmosphere. The system was composed of four parts;
a pole with sensors (left), a main raft (middle) and two solar panel rafts (right). The
pole and the main raft (3×3 m) were placed approximately 350 m from the nearest
shoreline. (photo: J. Åberg).
Doctoral thesis 2009
11 (28)
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Results and discussion
Results and discussion
This chapter summarizes the findings in Paper I-IV, with concluding remarks in the last section of the chapter.
Causes of CO2 variation in the surface water
In Lake Diktar-Erik the surface water concentration of CO2 showed a
large seasonal variation, with one especially large CO2 peak
connected to a summer rain-storm that caused extreme water
discharge. The high surface water CO2 concentrations were however
not likely caused by increased inflow of CO 2, since the relationship
between discharge and inlet water DIC was negative in Lake DiktarErik (Paper I). Increased concentrations of DOC and a higher
bioavailability of organic matter, on the other hand, were linked to
the CO2 increases (Paper I, [Jonsson et al., 2007]). The rate of DIC
production needed to explain the large CO2 increases during the
storm event was calculated to be 250 μg C/L/d, which was higher
than the measured maximum DIC production rate in Lake DiktarErik (157 μg C/L/d, cf. Paper II), but comparable to mineralization
rates in other similar systems [Graneli et al., 1996; Pace and Prairie,
2005]. The stratification depth in Lake Diktar-Erik probably also
influenced the CO2 of the surface water by controlling upwelling of
deep water CO2 and by regulation of the volume in which
mineralization of DOC occurred.
Also in Lake Merasjärvi the surface water concentration of CO2 varied
considerably (Figure 4), but not in connection to discharge and DOC,
due to the long water retention times. Instead the CO2 concentrations
increased with increasing temperatures in the water column, and
showed significant diurnal changes caused by diurnal variations in
the depth of the mixed layer (Paper IV). High surface water CO2
concentrations were also clearly linked to upwelling of CO2 rich
hypolimnetic water during periods with hypolimnion erosion.
Emissions of CO2 have earlier been related to mixed layer dynamics
by MacIntyre et al., [2001] and Eugster et al., [2003].
In summary, the levels of the surface water CO2 concentrations were
linked to mineralization of organic carbon in both Lake Diktar-Erik
and Lake Merasjärvi. In Lake Diktar-Erik, the large variation of
organic carbon was the driver of the CO2 variation, while the low
Doctoral thesis 2009
13 (28)
Results and discussion
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
variation of DOC in Lake Merasjärvi highlighted the effects of
temperature on respiration and the regulation of vertical transport
caused by dynamics in the vertical thermal stratification.
Internal CO2 production
In both lake Merasjärvi and Lake Diktar-Erik the benthic habitats
were net heterotrophic and showed little temporal variation in the
net DIC production (Paper II and III). The pelagic water had a more
variable net DIC production which clearly dominated over the
benthic net DIC production in both lakes. During the season, 69%
and 85% of benthic+pelagic DIC production occurred in the pelagic
water of Lake Merasjärvi and Lake Diktar-Erik, respectively. These
values agree well with the findings by den Heyer and Kalff, [1998],
but differ from the conditions in clear-water lakes where the benthic
habitat can be net autotrophic, while the pelagic water is still clearly
net heterotrophic [Ask et al., 2009].
The net DIC production in Lake Diktar-Erik decreased with depth
both in the pelagic water and in the sediments, and most of the net
DIC production occurred in the upper water column (Paper II). A
similar effect was seen in Lake Merasjärvi, where high temperatures
of large water volumes was correlated to high CO 2 concentrations
(Paper IV). Stable isotope data inferred that nearly 100% of the
accumulated DIC in the hypolimnion of Lake Diktar-Erik was of
allochthonous origin (Paper II). Similarly, 85% of accumulated DIC
Figure 4. Selected logger data for Lake Merasjärvi, showing the dynamics of the
surface water CO2 concentration in relation to the thermal stratification of the lake:
A) the surface water CO2 concentration expressed as the concentration in excess of
the atmospheric equilibrium (supersaturation). Black line = 24h (48pt) running
average. B) the vertical water temperature profile where the contours represents
water temperature (°C) in 0.5°C intervals.
14 (28)
Doctoral thesis 2009
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Results and discussion
was indicated to have an allochthonous organic carbon source in the
epilimnion. The pelagic DIC production, and most of the whole-lake
net production of DIC, were thus the result of respiration of
allochthonous organic carbon.
Fluxes of CO2 to the air
Lake Merasjärvi (380 ha) was the fifth lake in the world studied with
the EC-technique. The system used had an open-path design which
gave minimal flow distortions and required less processing of the
data in comparison to the traditional closed-path systems [e.g. Song
et al., 2005]. Best possible performance was indeed needed due to
the low sensor height required to capture lake-only footprints (cf.
Paper III).
Paper III showed that measurements using the EC-technique had
good quality and that the near 100% footprints were shorter than the
fetch in all cases. The impact from surrounding forest on the flux was
therefore expected to be minimal. The data from the EC-system were
additionally in line with the independently calculated energy balance
and an independent carbon budget, while the indirect estimates of
CO2 fluxes with the boundary layer technique were not (Paper III).
Consequently, the EC-measurements were considered to better than
the other measurement-methods reflect actual exchange of CO2
between lake water and the atmosphere in Lake Merasjärvi.
The summarized EC-flux of CO2 from Lake Merasjärvi during
summer 2005 was two times higher than the fluxes predicted with
models [Cole and Caraco, 1998; Wanninkhof, 1992]. By deriving the
gas transfer rate, k, from the EC-data (Paper III) this difference could
be related to underestimations made by the models during the most
common wind speeds over Lake Merasjärvi (Figure 5).
The correlation between the short-term EC-fluxes and the surface
water CO2 concentrations was found to be low (R2=0.146) (Paper IV),
which was to some extent counter-intuitive, considering the
importance of the CO2 concentrations in the flux-models [e.g. Cole
and Caraco, 1998]. On the other hand, the connection between flux
and concentration is expected to be both positive and negative on a
short-term time scale, since a high concentration promotes a high
flux, while high fluxes also tend to decrease the CO2 concentration.
Doctoral thesis 2009
15 (28)
Results and discussion
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Figure 5. At common wind speeds the gas transfer rates derived from EC-data
were found to be higher than predicted by models. The graph shows the normalized
(to 20°C) median gas transfer rate of CO2 (k600) as a function of the wind speed at
10 m height (U10). Data were structured into bin classes of 1 m/s. The black circle
represents the k600 at wind speed less than 1 m/s and was not accounted for in the
regression. Error bars represent the 95% confidence interval. Data are compared
with boundary layer estimates based on the models presented by Cole and Caraco
[1998] and Wanninkhof [1992].
Concluding remarks
In both Lake Diktar-Erik and Lake Merasjärvi, the surface water CO2
variations were mainly related to a pelagic respiration of allochthous
organic carbon, regulated by DOC input and whole lake water
temperatures. Both lakes thus contributed to reduce the effect of
carbon uptake by the land vegetation [cf. Cole et al., 2007].
Noticeably, the surface water CO2 concentration in Lake Merasjärvi
was related to the whole lake water temperature, at the same time as
the relationship between the surface water CO2 and the surface water
temperature still was weak [cf. Sobek et al., 2005]. This indicates that
predictions of surface water CO2 may benefit from including factors
related to the whole water column dynamics rather than only factors
in the surface water.
The concentration of CO2 in the surface was highly dependent on
diurnal and longer-term vertical water movements related to thermal
16 (28)
Doctoral thesis 2009
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Results and discussion
stratification dynamics and hypolimnion erosion. This in combination with changes in respiration rates, by temperature changes or
changing DOC levels, may contribute to large dynamics of the CO2
level in the surface of many lakes.
In lakes with large CO2 variations, accurate estimates of the average
CO2 concentration were shown to be dependent on a relatively
intense sampling (Table 2 in Paper I). Conditions of hydrological
stability or complete mixing of the water volume (especially in
autumn), on the other hand, can be expected to decrease the CO2
variation allowing less intensive sampling (cf. Figure 1 in Paper IV).
For CO2 flux calculations it must be pointed out that the short term
variation of the EC-flux was not clearly related to the CO 2
concentration (Paper IV). Also, the two CO2 flux models clearly
underestimated the gas transfer rate, k, at moderate wind speeds.
These circumstances indicate that accurate estimates of k may be
even more important for CO2 flux estimates than frequent sampling
of CO2.
In summary, the thesis bring more knowledge about carbon turnover
processes in high latitude lakes, with applications related to future
sampling and modeling of production and emission of CO2. The
results show that the pelagic habitat can be very important for the inlake CO2 production. They also point out a need for further studies
with direct (eddy covariance) measurements of emissions from lakes.
A strong indication of the results is that CO2 concentrations and CO2
emissions change fast due to changes of the organic carbon loading
and the temperature of the pelagic water.
Doctoral thesis 2009
17 (28)
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Svensk sammanfattning
Svensk sammanfattning
De flesta sjöar släpper ut koldioxid (CO2) till luften i så pass stor
mängd att även en liten tjärn bidrar med lika mycket CO 2 som en
genomsnittlig svensk medborgare. Bidraget från världens trehundra
miljoner sjöar är därför märkbart även i global skala. Än så länge
bidrar dock sjöarnas koldioxidutsläpp sannolikt inte till ökad global
uppvärmning. Detta kan förklaras med att sjöarnas kolomsättning
och koldioxidutsläpp har varit en del i ett relativt stabilt kolkretslopp
i tusentals år före den industriella revolutionen. Däremot saknas
ännu mycket kunskap om sjöarnas roll i det globala kretsloppet av
kol. Det finns exempelvis ännu många oklarheter kring hur sjöar
producerar och släpper ut CO2, och inte minst hur sjöarnas koldioxidutsläpp förändras som följd av global uppvärmning.
Sammantaget bidrar resultaten i denna avhandling till att ytterligare
belysa kolomsättningen i sjöar. Delar av de intressanta resultaten är
kopplade till användningen av en koldioxidlogger som med hög
tidsupplösning visade hur koldioxidhalterna i ytvattnet varierade
stort både på lång och kort sikt i både Diktar-Erik, 9 ha, och
Merasjärvi, 380 ha (artikel I respektive IV). Med hjälp av inkubationer av sjövatten och efterföljande analyser visas i artikel II och III att
större delen av koldioxiden producerades i vattenmassan och inte i
sedimenten. Vidare redovisas i artikel IV att koldioxidproduktionen
och ytvattnets halt av koldioxid ökade med ökad vattentemperatur,
och att detta samband komplicerades av att vattenmassans värmeskiktningar styrde vid vilka tidpunkter som koldioxiden uppträdde i
ytvattnet. Utsläppen av CO2 till atmosfären styrdes till stor del av
vindhastigheten, vilket var i linje med vad tidigare studier visat.
Däremot framkom att storleken på CO2-utsläppen i Merasjärvi var
ungefär dubbelt så höga som de utsläpp som beräknats med de två
vanligaste beräkningsmodellerna (Artikel III).
Med början på nästa sida sammanfattas de fyra artiklarna var för sig.
Doctoral thesis 2009
19 (28)
Svensk sammanfattning
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Artikel I
Variationer av koldioxid (Diktar-Erik)
I studien framkom att koldioxidhalten i ytvattnet kan variera relativt
mycket i en svensk fjällsjö. Artikeln diskuterar att koldioxidökningar
inte kan förklaras med ett ökat vattenburet inflöde av CO2, eller annat
oorganiskt kol, utan istället sannolikt beror på att främst bakterier
ökar förbränningen av färskt organiskt material.
Eftersom det underliggande kalla djupvattnet i sjön – hypolimnion –
var rikt på oorganiskt kol diskuterades också möjligheten att detta
förråd under vissa perioder kunde levera CO2 upp till ytan, och
koncentrera effekten av kolförbränningen i sjön. Vinden diskuterades
som en ytterligare viktig faktor som kan skapa både ökad
koldioxidemission från sjöytan och ökad uppvällning av koldioxidrikt
djupvatten. En viktig slutsats var att variationerna av CO2 i ytvattet
visserligen påverkades av inflödet av löst kol, men att de ökade
halterna av CO2 till största del måste härledas till interna transportprocesser och en mycket dynamisk intern koldioxidproduktion.
Tack vare den höga tidsupplösningen på data, analyserades också hur
provtagningsfrekvensen påverkar osäkerheten för mätningar av CO2 i
ytvattnet. På grund av den stora variationen av CO2 under sommaren
förbättras osäkerhetsmarginalen avsevärt vid provtagning varje
vecka, jämfört med provtagning varje månad.
Artikel II
Intern produktion av koldioxid (Diktar-Erik)
I Diktar-Erik skedde 85% av den totala koldioxidproduktionen i
vattenmassan, och 15% i sedimenten. Att en stor del av koldioxiden
producerades i vattenmassan kan tyckas förvånande, eftersom
sedimenten innehåller mycket mer organismer som bryter ned
organiskt material. Volymen sediment som bidrog till produktion av
koldioxid var dock så liten i förhållande till den volym vatten som
fanns i sjön att det slutliga resultatet ändå blev att vattenmassan
bidrog med mest koldioxid. I brunvattensjöar med stor sedimentyta i
förhållande till vattenmassa kan man däremot förvänta sig att
bidraget från sedimenten får en mer framträdande roll för utsläppen
av koldioxid (visas t.ex. i en studie av Åberg m.fl., [2004]).
20 (28)
Doctoral thesis 2009
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Svensk sammanfattning
I djupvattnet i Diktar-Erik bildades i stort sett all CO2 genom
förbränning av organiska ämnen med ett ursprung i vegetationen på
land. Även i den övre delen av vattenmassan kom merparten av koldioxiden, ca 85%, från sådana organiska ämnen. Ekosystemet i sjön
hade därmed en energitillförsel som till stor del var beroende av
produktionen av biomassa på land. Genom att ett sådant sjöekosystem till större delen 'importerar' den energi som går in i basen av
näringskedjan, betecknas det som 'netto-heterotroft', i motsats till
exemplelvis de generellt sett 'netto-autotrofa' skogsekosystemen som
både tillväxer i sin biomassa och 'exporterar' överskottet till sjöar och
vattendrag.
Artikel III
Koldioxidflödet mellan sjö och atmosfär (Merasjärvi)
Att mäta koldioxidutsläpp från sjöar är förknippat med vissa
svårigheter: Först och främst är det är praktiskt taget omöjligt att
fånga upp och mäta den gas som avgår från en normalstor sjö. Att
däremot fånga upp gas från små ytor i små kammare går bättre, men
med problemet att kamrarna riskerar att störa den naturliga
gasutbytesprocessen, samt att mätningar på en procentuellt sett
mycket liten yta av sjön inte nödvändigtsvis är representativa för hela
sjön. Indirekta beräkningsmodeller för gasflöden mellan vatten och
luft är också möjliga att använda, men dessa bygger på ett flertal
förenklingar och antaganden som begränsar noggrannheten.
Ett alternativ till både kammartekniker och beräkningsmodeller är
den så kallade eddy-covariance (EC)-tekniken, som med hög tidsupplösning mäter flödena av koldioxid i luften över en relativt stor yta på
sjön, utan att störa varken lokalklimat eller vind, samt med en
mindre grad av förenkling jämfört med en indirekt beräkningsmodell.
I artikeln redovisas resultat från EC-mätningar i sjön Merasjärvi,
några mil söder om Vittangi i Norrbotten. EC-mätningarnas resultat
jämförs med två vanliga indirekta beräkningsmodeller för gasflöden
mellan vatten och luft. Jämförelsen visade att beräkningsmodellerna
underskattade flödet av koldioxid till atmosfären med ungefär
hälften. Detta något kontroversiella påstående ansågs dock vara välgrundat, eftersom EC-mätningarna hade kvalitetsgranskats på flera
olika plan: dels kvalitetstestades alla data med ett urval av
publicerade testmetoder, dels undersöktes systemets förmåga att
mäta den virvelstorlek som förekom vid den specifika sjön. Vidare
Doctoral thesis 2009
21 (28)
Svensk sammanfattning
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
gjordes oberoende mätningar av sjöns kolbalans och energibalans i
förhållande till EC-mätningarnas resultat, samt därtill beräkningar
som visade att CO2-signalen som fångades av systemet inte kom från
skogen utan enbart från sjön.
Artikel IV
Betydelsen av vattentemperatur och termisk skiktning för
variationen av koldioxid i ytvattnet (Merasjärvi)
I Merasjärvi användes strömsnåla loggrar för att med hög tidsupplösning mäta en mängd olika variabler, i luften ovanför sjön, i
sjön, samt även i sjöns inlopp och utlopp. Även ytvattnets halt av
koldioxid mättes med hög tidsupplösning. Sammanlagt kunde 26
variabler sammanställas och ställas i relation till ytvattnets halt av
koldioxid. I själva analysen användes den statistiska metoden partial
least squares regression (PLS), som är speciellt anpassad för analyser
av många variabler.
Resultaten av PLS-analyserna visade att koldioxidhalterna i ytvattnet
var tydligast kopplade till vattentemperaturens variationer, samt till
djupvariationer i skiktningarna mellan varmt och kallt vatten.
Produktionen av koldioxid kunde därmed kopplas till att respirationen ökade med ökad temperatur, samt att värmeskiktningarnas
variationer både påverkade respirationen och reglerade tillgången på
CO2 i ytvattnet. Ett grunt epilimnion (det övre varma skiktet) hade i
enlighet med detta, totalt sett en lägre tillförsel av CO2 via
respiration, samtidigt som det genom att vara grunt förlorade mycket
CO2 genom emission till atmosfären och genom fotosyntes.
Avslutningsvis...
Likt pusselbitar som läggs till ett ganska stort och svårt pussel bidrar
resultaten i denna avhandling till att öka förståelsen om sjöars kolomsättning. Resultaten som presenteras indikerar t.ex. att sjöar som
Diktar-Erik och Merasjärvi snabbt kan öka CO2-produktionen vid
ökat inflöde av kol och vid ökad vattentemperatur. Trots det är det
ännu för tidigt att utifrån enbart detta arbete dra generella slutsatser
kring sjöars respons på t.ex. global uppvärmning. Resultatens kanske
främsta betydelse är istället att de ökar den totala kunskapsmassan
och lägger ytterligare grund för hur CO2-provtagning och CO2modellering – på bästa sätt – bör utföras i sjöar.
22 (28)
Doctoral thesis 2009
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Acknowledgments
Acknowledgments
First of all, I thank my wife and life companion, Susanne Åberg, for her support during my
thesis work. Her earthy common sense and every day presence have helped me to stay
balanced in a windy world. She also decided to move 720 km, to Vittangi, and live there
together with me and our newborn baby during the summer of 2005. This, definitely played
a crucial role for my commitment in Lake Merasjärvi, and for the results in Paper III and IV.
Also on my top-list of supporters are my two daughters Noomi and Miriam. Their love and
attitude to life is such a great inspiration. In the context of academic work I especially
acknowledge their extraordinary insights in the noble art of thinking outside the box.
Support of fundamental importance was also given by my two supervisors Mats Jansson
and Anders Jonsson. They have been very professional and helpful, during all these years.
They have also helped me much to understand the inside of the box. Without them this
thesis would not have been possible to write.
I also thank the following co-authors: Anders Lindroth for working with Paper III, and for
making the 'flux-course' in Lund in 2003 such a great experience; Klockar Jenny Nääs for
analysis of data, skillful fieldwork, and for philosophical conversations above the waters of
Diktar-Erik and Merasjärvi; Jan Karlsson for being a great colleague and for an important
contribution with the stable isotope analysis in Paper II.
Thomas Westin in Abisko is acknowledged for field assistance of fundamental importance,
and for skillful work with rafts and sampling equipment. I also thank Ingemar Bergström
for sharing knowledge about Lake Merasjärvi and for his help with essential practicalities in
the village of Merasjärvi.
Financial support was provided by the Swedish Research Council, The Kempe
Memorial Fund, Ebba and Sven Schwartz stiftelse, Stiftelsen Längmanska
Kulturfonden, The Lars Hierta Memorial Foundation and Umeå University.
Abisko Scientific Research Station contributed with parts of the meteorological data.
The work was also a collaboration within the Nordic Centre for Studies of Ecosystem
Carbon Exchange and its Interaction with the Climate System (NECC).
Finally, a list of important persons that I wish to thank:
My best friend and brother Andreas for his love, inspiring ideas and visits during fieldwork,
and for introducing me to DOE and MLR-modeling; Anita and Torgny for their visits
during field work and for day and night support in my life; my friend Anna who dropped by
in Abisko; and Urban who also visited me in Abisko; Sven-Erik och Ingegerd for visits
and great support; Anja, Christoffer and Andrea for their visits in Vittangi and
Merasjärvi; the staff at In Situ Instruments/Flux Systems in Ockelbo, with special
thanks to Micke for all help with software and hardware; the staff at Climate Impact
Research Centre and the Abisko Scientific Research Station, with special thanks to
Anne for being so hearty and kind; all people at EMG - past and present – with special
thanks to 1) my former room mates Åsa and Mårten, 2) my limnologist colleagues Anki,
Grete, Martin and Jenny, for help in many different ways, 3) teachers who improved my
teaching: Tom, Hans, Tord, Jonatan, Rich, Johan and Lena, 4) the administrative
staff, especially Kerstin K and Ingrid, and 5) my former 'kroken-neighbors' Matilda, Jan
P, Veronica, Annika H and Carola.
Och sedan till er andra: alla kära släktingar, vänner, grannar, kurskamrater, kollegor,
flyktiga bekantskaper och så vidare, som jag inte nämnt. Tack för att ni finns! Jag önskar er
all lycka! Kanske ses vi snart igen.
Doctoral thesis 2009
23 (28)
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
References
References
Åberg, J., A. K. Bergström, G. Algesten, K. Söderback, and M. Jansson (2004), A
comparison of the carbon balances of a natural lake (L. Örtrasket) and a
hydroelectric reservoir (L. Skinnmuddselet) in northern Sweden, Water
Research, 38(3), 531-538.
Algesten, G., S. Sobek, A. K. Bergström, A. Ågren, L. J. Tranvik, and M. Jansson
(2004), Role of lakes for organic carbon cycling in the boreal zone, Global
Change Biology, 10(1), 141-147.
Anderson, D. E., R. G. Striegl, D. I. Stannard, C. M. Michmerhuizen, T. A.
McConnaughey, and J. W. LaBaugh (1999), Estimating lake-atmosphere
CO2 exchange, Limnology and Oceanography, 44(4), 988-1001.
Ask, J., J. Karlsson, L. Persson, P. Ask, P. Byström, and M. Jansson (2009), Wholelake estimates of carbon flux through algae and bacteria in benthic and
pelagic habitats of clear-water lakes, Ecology, 90(7), 1923-1932.
Baldocchi, D. D. (2003), Assessing the eddy covariance technique for evaluating
carbon dioxide exchange rates of ecosystems: past, present and future,
Global Change Biology, 9(4), 479-492.
Berner, R. (2006), GEOCARBSULF: A combined model for Phanerozoic
atmospheric O2 and CO2, Geochimica Et Cosmochimica Acta, 70(23),
5653-5664, doi:10.1016/j.gca.2005.11.032.
Canadell, J. G., D. Pataki, R. Gifford, R. A. Houghton, Y. Lou, M. R. Raupach, P.
Smith, and W. Steffen (2007), Saturation of the terrestrial carbon sink, in
Terrestrial Ecosystems in a Changing World, edited by J. G. Canadell, D.
Pataki, and L. Pitelka, pp. 59-58, Springer-Verlag, Berlin Heidelberg.
Carignan, R. (1998), Automated determination of carbon dioxide, oxygen, and
nitrogen partial pressures in surface waters, Limnology and
Oceanography, 43(5), 969-975.
Casper, P., S. C. Maberly, G. H. Hall, and B. J. Finlay (2000), Fluxes of methane
and carbon dioxide from a small productive lake to the atmosphere,
Biogeochemistry, 49(1), 1-19, doi:10.1023/A:1006269900174.
Cole, J. J., and N. F. Caraco (1998), Atmospheric exchange of carbon dioxide in a
low-wind oligotrophic lake measured by the addition of SF6, Limnology
and Oceanography, 43(4), 647-656.
Cole, J. J., N. F. Caraco, G. W. Kling, and T. K. Kratz (1994), Carbon-Dioxide
Supersaturation in the Surface Waters of Lakes, Science, 265(5178), 15681570.
Cole, J. J. et al. (2007), Plumbing the global carbon cycle: Integrating inland waters
into the terrestrial carbon budget, Ecosystems, 10(1), 171-184,
doi:10.1007/s10021-006-9013-8.
Doctoral thesis 2009
25 (28)
References
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Denman, K. L. et al. (2007), Couplings Between Changes in the Climate System and
Biogeochemistry, edited by S. Solomon, D. Qin, M. Manning, Z. Chen, M.
Marquis, K. Averyt, M. Tignor, and H. Miller, Cambridge University Press,
Cambridge, United Kingdom and New York, NY, USA.
Downing, J. A. et al. (2006), The global abundance and size distribution of lakes,
ponds, and impoundments, Limnology and Oceanography, 51(5), 23882397.
Duchemin, E., M. Lucotte, and R. Canuel (1999), Comparison of static chamber and
thin boundary layer equation methods for measuring greenhouse gas
emissions from large water bodies, Environmental Science & Technology,
33(2), 350-357.
Eugster, W., G. Kling, T. Jonas, J. P. McFadden, A. Wuest, S. MacIntyre, and F. S.
Chapin (2003), CO2 exchange between air and water in an Arctic Alaskan
and midlatitude Swiss lake: Importance of convective mixing, Journal of
Geophysical Research-Atmospheres, 108(D12), 1-19.
del Giorgio, P. A., J. J. Cole, and A. Cimbleris (1997), Respiration rates in bacteria
exceed phytoplankton production in unproductive aquatic systems,
Nature, 385(6612), 148-151.
Graneli, W., M. Lindell, and L. Tranvik (1996), Photo-oxidative production of
dissolved inorganic carbon in lakes of different humic content, Limnology
and Oceanography, 41(4), 698-706.
Grelle, A., and A. Lindroth (1996), Eddy-correlation system for long-term
monitoring of fluxes of heat, water vapour and CO2, Global Change
Biology, 2(3), 297-307.
Grey, J., R. I. Jones, and D. Sleep (2001), Seasonal changes in the importance of
the source of organic matter to the diet of zooplankton in Loch Ness, as
indicated by stable isotope analysis, Limnology and Oceanography, 46(3),
505-513.
Heimann, M., and M. Reichstein (2008), Terrestrial ecosystem carbon dynamics
and climate feedbacks, Nature, 451(7176), 289-292,
doi:10.1038/nature06591.
den Heyer, C., and J. Kalff (1998), Organic matter mineralization rates in
sediments: A within- and among-lake study, Limnology and
Oceanography, 43(4), 695-705.
Huotari, J., A. Ojala, E. Peltomaa, J. Pumpanen, P. Hari, and T. Vesala (2009),
Temporal variations in surface water CO2 concentrations in a boreal humic
lake based on high-frequency measurements, Boreal Environment
Research, 14 (Suppl. A), 48-60.
Huttunen, J. T., J. Alm, A. Liikanen, S. Juutinen, T. Larmola, T. Hammar, J.
Silvola, and P. J. Martikainen (2003), Fluxes of methane, carbon dioxide
and nitrous oxide in boreal lakes and potential anthropogenic effects on the
aquatic greenhouse gas emissions, Chemosphere, 52(3), 609-621.
26 (28)
Doctoral thesis 2009
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
References
Huttunen, J. T., K. M. Lappalainen, E. Saarijarvi, T. Vaisanen, and P. J.
Martikainen (2001), A novel sediment gas sampler and a subsurface gas
collector used for measurement of the ebullition of methane and carbon
dioxide from a eutrophied lake, Science of the Total Environment, 266(13), 153-158.
IPCC (2007), Climate Change 2007 - The Physical Science Basis: Working Group
I Contribution to the Fourth Assessment Report of the IPCC, edited by S.
Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K. Averyt, M. Tignor,
and H. Miller, Cambridge University Press, Cambridge, United Kingdom
and New York, NY, USA.
Janssens, I. A. et al. (2003), Europe's terrestrial biosphere absorbs 7 to 12% of
European anthropogenic CO2 emissions, Science, 300(5625), 1538-1542.
Jansson, M., L. Persson, A. M. D. Roos, R. I. Jones, and L. J. Tranvik (2007),
Terrestrial carbon and intraspecific size-variation shape lake ecosystems,
Trends in Ecology & Evolution, 22(6), 316-322,
doi:10.1016/j.tree.2007.02.015.
Jones, R. I., J. Grey, C. Quarmby, and D. Sleep (2001), Sources and fluxes of
inorganic carbon in a deep, oligotrophic lake (Loch Ness, Scotland), Global
Biogeochemical Cycles, 15(4), 863-870.
Jonsson, A., L. Ström, and J. Åberg (2007), Composition and variations in the
occurrence of dissolved free simple organic compounds of an unproductive
lake ecosystem in northern Sweden, Biogeochemistry, 82(2), 153-163,
doi:10.1007/s10533-006-9060-4.
Karlsson, J., P. Byström, J. Ask, P. Ask, L. Persson, and M. Jansson (2009), Light
limitation of nutrient-poor lake ecosystems, Nature, 460(7254), 506-U80,
doi:10.1038/nature08179.
Keeling, C. D. (1960), The Concentration and Isotopic Abundances of Carbon
Dioxide in the Atmosphere, Tellus, 12, 200-203.
Kritzberg, E. S., J. J. Cole, P. M. L., W. Granéli, and D. Bade (2004),
Autochthonous versus allochthonous carbon sources to bacteria: Results
from whole lake 13C addition experiments., Limnology and Oceanography,
49, 588-596.
Liss, P. S., and P. G. Slater (1974), Flux of Gases across the Air-Sea Interface,
Nature, 247, 181-184.
MacIntyre, S., W. Eugster, and G. Kling (2001), The Critical Importance of
Buoyancy Flux for Gas flux Across the Air-water Interface, in Gas Transfer
at Water Surfaces, edited by M. A. Donelan, American Geophysical Union,
Washington, D.C., USA.
Matthews, C. J. D., V. L. St Louis, and R. H. Hesslein (2003), Comparison of three
techniques used to measure diffusive gas exchange from sheltered aquatic
surfaces, Environmental Science & Technology, 37(4), 772-780.
Doctoral thesis 2009
27 (28)
References
J. Åberg Production and emission of CO2 in
two unproductive lakes in northern Sweden
Pace, M. L., and Y. T. Prairie (2005), Respiration in lakes, in Respiration in
aquatic ecosystems, edited by P. A. del Giorgio and P. J. le B Williams, pp.
103-121, Oxford University Press, Oxford.
Petit, J. R. et al. (1999), Climate and atmospheric history of the past 420,000 years
from the Vostok ice core, Antarctica, Nature, 399(6735), 429-436.
Poissant, L., P. Constant, M. Pilote, J. Canário, N. O'Driscoll, J. Ridal, and D. Lean
(2007), The ebullition of hydrogen, carbon monoxide, methane, carbon
dioxide and total gaseous mercury from the Cornwall Area of Concern,
Science of The Total Environment, 381(1-3), 256-262,
doi:10.1016/j.scitotenv.2007.03.029.
Retallack, G. (2009), Greenhouse crises of the past 300 million years, Geological
Society of America Bulletin, 121(9-10), 1441-1455, doi:10.1130/B26341.1.
Royer, D., R. Berner, and J. Park (2007), Climate sensitivity constrained by CO2
concentrations over the past 420 million years, Nature, 446(7135), 530532, doi:10.1038/nature05699.
Sellers, P., R. H. Hesslein, and C. A. Kelly (1995), Continuous Measurement of CO2
for Estimation of Air-Water Fluxes in Lakes - an in-Situ Technique,
Limnology and Oceanography, 40(3), 575-581.
Sobek, S., G. Algesten, A. K. Bergström, M. Jansson, and L. J. Tranvik (2003), The
catchment and climate regulation of pCO2 in boreal lakes, Global Change
Biology, 9(4), 630-641.
Sobek, S., L. Tranvik, and J. J. Cole (2005), Temperature independence of carbon
dioxide supersaturation in global lakes, Global Biogeochemical Cycles,
19(2), doi:10.1029/2004GB002264.
Song, X., G. Yu, Y. Liu, X. Sun, C. Ren, and X. Wen (2005), Comparison of flux
measurement by open-path and close-path eddy covariance systems,
Science in China Series D-Earth Sciences, 48, 74-84,
doi:10.1360/05zd0007.
St Louis, V. L., C. A. Kelly, E. Duchemin, J. W. M. Rudd, and D. M. Rosenberg
(2000), Reservoir surfaces as sources of greenhouse gases to the
atmosphere: A global estimate, Bioscience, 50(9), 766-775.
Valentini, R. (2003), Fluxes of carbon, water and energy of European forests,
Springer, Berlin.
Wanninkhof, R. (1992), Relationship Between Wind-Speed and Gas-Exchange Over
the Ocean, Journal of Geophysical Research-Oceans, 97(C5), 7373-7382.
Vesala, T., J. Huotari, U. Rannik, T. Suni, S. Smolander, A. Sogachev, S.
Launiainen, and A. Ojala (2006), Eddy covariance measurements of carbon
exchange and latent and sensible heat fluxes over a boreal lake for a full
open-water period, Journal of Geophysical Research-Atmospheres,
111(D11).
28 (28)
Doctoral thesis 2009