Effect of temperature on methane and carbon dioxide fluxes from the sediment of a shallow peat lake in The Netherlands.
Author: Tom de Ruyter van Steveninck Student number: 10617094 Supervisor: Jolanda Verspagen
Commissioned by the University of Amsterdam Freshwater and Marine Ecology (FAME)
07-07-2017
Abstract
Carbon cycling in freshwater lakes experiences alterations due to climate change. Rising temperatures can affect the mineralization rate of organic carbon (OC) in lake sediments. Temperature induced changes can influence hydrological and chemical water properties and consequently carbon buffering of lakes. Changes in methane (CH4) and carbon dioxide
(CO2) emission rates can seriously alter the Global Warming Potential (GWP), and climate
feedbacks of freshwater ecosystems. This study aims on gaining insight on the impact of temperature on OC mineralization, by estimating total inorganic carbon fluxes, CH4, and CO2
emission rates. Field measurements were performed to support experimental observations for a shallow hypertrophic peat lake in the Netherlands. A sediment incubation experiment was conducted with temperatures ranging between 5 and 25°C. In situ gas fluxes in the sediment-water interface were measured with the use of a benthic chamber. Experimental CH4, and CO2 emissions were used to calculate total inorganic carbon fluxes, and were
compared to an in situ field assessment and preliminary findings. Gas emissions of CH4 and
CO2 showed exponential increase with temperature. CH4 showed a stronger correlation with
temperature than CO2, consequently altering emitted gas proportions. Experimental
inorganic carbon fluxes were substantially greater than field estimates and previous studies. Concludingly, this report emphasizes the importance of studying shallow peat lake
Introduction
Disturbances of natural systems by global warming and climate change pose a threat to a great deal of current ecosystems (Montoya & Raffaelli, 2010). Current estimates of future global warming scenarios still show great uncertainties, due to unpredictable human behavior and complex interactions and feedbacks within the climate system (IPCC, 2013). Increasing abundance of atmospheric CO2 will result in an increase in primary productivity of carbon limited aquatic systems (Geider et al. 2001, Verspagen et al. 2014). Additionally, rising temperature increases activity of a great variety of microbial organisms, whilst diminishing the capacity of water to hold oxygen. However, implications show great differences due to varying climate and ecosystem specific properties, underlining the relevance of enhancing the evaluation of ecosystem responses to an altering climate system.
Despite the small fraction surface area covered by inland waters, the role of freshwater systems in carbon cycling is of great importance for the global carbon system (Tranvik et al. 2009). Changes in carbon cycling within lakes can seriously alter the carbon buffering capacity, possibly changing lakes from carbon sinks to emitters. Organic carbon burial efficiency has been related to oxygen concentrations. However, only few experimental studies have been conducted on the effect of temperature on Organic Carbon (OC)
mineralization and burial efficiency (Zeikus & Winfrey 1976, Caspar et al., 2000, Gudazs et al. 2010). Decreased oxygen availability in the benthic layer increases the activity of
methanogenic microorganisms resulting in a rise in produced CH4(Tholen et al. 2007). On
the contrary, CO2 production is favored in more oxygen rich sediments.
Warmer waters are known for containing a reduced amount of dissolved oxygen, and are more likely to consist of stratified layers (Boehrer & Schultze, 2008). Consequently,
environmental factors related to warmer waters are simulating for methanogens (Huttunen et al. 2003).
When reaching the atmosphere, CH4 has an estimated Global Warming Potential (GWP) 25
times that of CO2 in a 100-year time scale (Howarth et al. 2011). Focusing on CH4 emissions
is therefore of great importance when estimating future global warming scenarios. Preliminary studies found that CH4 emissions from lakes account for 6-16% of the
non-anthropogenic emissions on a global basis (Bastviken et al.,2008). Direct effects of rising temperatures on sedimentary CO2:CH4 production ratios have been described in some
environments, emission patterns towards the atmosphere remain however unquantified for most lakes. Physical factors such as turbulence showed to impact the emission of CH4 from lakes, and have been previously studied (Laurion et al. 2010, Engle & Melack 2000,
Bartosiewicz et al. 2015). Mixed epilimnetic, and often more oxygenated, water bodies show to have greater CH4 emissions than stratified anoxic lakes (Milucka et al. 2015). Moreover,
Bastviken et al. (2008) point out the importance of CH4 oxidation when estimating lake
emissions. Increased retention time of dissolved gaseous CH4 augment the chances of
oxidation, implying that deeper lakes with anoxic hypolimnia emit less CH4. This can be
explained by the decreased exchange between deeper layers and water surface in stratified water bodies. Stratification increases effectivity of horizontal transport of CH4 in both
epilimnion and hypolimnion. Whereas vertical transport is reduced (Rudd & Hamilton 1978). The enhanced activity of methanotrophic bacteria in anoxic benthic layers, do not have to result in greater emission patterns. “This study indicates that future studies should also
focus on areas of lakes of low CH4 concentrations in combination with short CH4 residence
times where major routing of CH4 to the atmosphere occurs.” Bastviken et al. (2008).
Suggested is that shallow sediments are therefore greater emission contributors due to the shorter retention time and increased subjectivity to shear stress and turbulence. A focus solely on oxygen concentrations in water bodies is therefore not a complete CH4 emission
predictor.
In a study conducted by Zeikus & Winfrey (1976) sediment cores were examined for sedimentary CH4 productivity in relation to temperature, for samples taken from Lake
18m in a seasonally stratified lake. Methanogenic bacteria were found to be metabolically active between 4 and 45°C, with optimal temperatures between 35 and 42 °C.
Casper et al. (2000) surveyed a much smaller hypertrophic lake in northeast England (Priest Pot) for fluxes in CH4 and CO2. This lake showed high rates of CH4 oxidation after ebullition
from sediment. Moreover, a great deal of diffusive fluxes of CO2 was found to be recycled
within the system's primary production. Besides phytoplankton activity, lake stratification was found to strongly affect the lakes CH4 and CO2 emission patterns.
Another study conducted by Gudazs et al. (2010) studied 8 boreal lakes located in Sweden, with different trophic states and terrestrial Dissolved Organic Carbon (DOC) input. Some of the lakes were stratified, however sediments were overlain by oxygenated waters. Effects of temperatures were examined in a sediment core experiment with incubation temperature varying between 1 and 21 °C. Consequently, it was stated that increase in temperature decreases the carbon burial efficiency, and additionally will contribute to an elevation in greenhouse gas emissions from lake sediments.
Shallow lakes may be substantial carbon Greenhouse Gas contributors, because their low mixing depths allow little CH4 oxidation (Milucka et al. 2015). To investigate how temperature
affects CO2 and CH4 emissions from the sediment in a shallow lake, we measured CO2 and
CH4 gas fluxes from the sediments of a shallow hypertrophic peat lake. In the field, gas
fluxes were measured using a benthic chamber at ambient lake temperature. In the lab, gas fluxes were measured in sediment cores exposed to different temperatures in the range between 5 and 25 °C. The results of this study will give more insight into how gas fluxes from shallow lakes will respond to rising temperatures.
Materials and methods Description of sampling site.
All samples were taken from Lake Amstelveense Poel (AP), a small (0.48km2) and shallow
hypertrophic peat lake located southwest of Amsterdam in the province of North-Holland, The Netherlands. The lake is under supervision of the Rijnland district water control board. The current nutrient rich state is causing high algal densities from June to November. Vegetation around the lake is for two third made out of reed, nevertheless water plant abundance is marginal. During warmer seasonal periods high algal density diminishes light penetration. The sample site was situated in the Southwest corner of the AP (52.297259, 4.837264), at greater distance of urban areas, to minimize disturbance. Shallow water depth (1.0-1.5m) and minimal wind shelter improves turbulence and mixing of water body,
preventing long term stratification. Nutrient rich water input from the Nieuwe Meer, and the cultivated catchment stimulates high biological productivity, especially in the summer period. Field measurements were conducted between the 17th and the 18th of May 2017. Samples
incubation the day after. During sampling and field measurements the summer bloom did not set in yet, and Secchi depth was equal on all dates (0.70m).
Laboratory sediment incubation
To determine the influence of temperature on the benthic CH4 and
CO2 fluxes in the lake sediments, core samples were taken. Samples
were randomly taken at depth of 1.5 meter with the use of 0.5m cores with a diameter of 7.8cm (figure 1). Cores were stored with a minimum top water layer and lid on to minimize effect of disturbance by exchange with atmosphere. All 16 sediment samples were taken by filling the full core with sediment. Depth integrated water samples were taken from the lake into acid-rinsed water tanks. In the
laboratory only the top 20 cm was maintained in the core and the other 30cm was removed. The sediment was overlain with 15cm (716 cm3) of lake water filtered over a 50 µm mesh, allowing a 15 cm
(716 cm3) headspace. With the use of a Hydrolab multisensor probe,
data on salinity, oxygen saturation, chlorophyll-a fluorescence, pH and temperature were collected over the whole depth profile. The laboratory was customized to fit three temperature groups for the incubation experiment. The cores were placed in different water tanks with low light intensities during day and dark at night. A control core was incubated with unfiltered water to check for effect of large zooplankton or phytoplankton disturbance. Temperature groups were set on 5, 15 and 25 degrees Celsius. Temperature groups consisted of 5 cores, with an additional unfiltered core set at 25 °C. Plankton activity is greater at higher temperatures, thus disturbances due to presence of macro plankton will be greatest for 25 °C temperature
groups (Reigada et al.,2003). Appointing a control group was therefore thought to be best at 25 °C. However, significant effects of filtering cannot be proven due to small number
unfiltered core replicates (n=1). Consequently, it was chosen to include the core within the temperature analysis to increase statistical power. Before initiating the experiment and determining the zero values, cores were able to equilibrate to laboratorial atmospheric conditions overnight. Before initiation of the experiment measurements of pH and oxygen abundance were conducted with a Hach LDO field monitor, connected to a photosensitive and a potentiometric probe. This initial measurement was defined as starting point T0.
Sensors were held 10 cm above the sediment top layer and a slight stir was given to ensure the mixing of possibly formed gradients without disturbing the sediment.
Directly after the oxygen saturation and pH were determined, a customized lid was placed on the core, enabling opening and closure by two non-ferrous composition metal tubes and a displaceable non permeable rubber tube on top. The units of partial volume (ppm) of CO2
and CH4 were determined for the T0 with the use of a Innova 1312 photoacoustic gas
monitor, and closed air tight afterwards. All cores were kept overnight in the water bath according to the temperature groups. After 24 hours, measurements were repeated to determine the T24 values for partial volume unit (ppm) of CO2 and CH4 and the pH and
oxygen saturation.
After completing the first experiment, the cores were left in their designated basins with the lid placed off, again to equilibrate to equal atmospheric conditions. After 6 hours the
experiment was repeated for the same temperature groups.
Cores were re used a third time at different incubation temperatures. All previous 25 °C cores and two previously 5 °C cores were set on 20 °C. The 15 °C, and three of 5 °C cores of the first incubations were placed in a basin set on 10 degrees Celsius. Rubber lids were placed off for 3 days before starting measurements, providing longer environmental
equilibration. Methods of measurements were repeated and equal to the first and second experiment. Re using the cores with different temperatures in the third incubation showed however significant different effects on CH4 and CO2 fluxes. resulting unrealistic values and
are therefore excluded from the result section.
In situ field incubation
Vertical diffusive fluxes in CH4 and CO2 were measured with the use of a benthic chamber
and an Innova 1312 photoacoustic gas monitor at lake Amstelveen Poel. A benthic chamber (7.55dm2, 29.4dm3) filled with water was placed on the lake sediment to create a measurable
environment in the field. The chamber has a circular shape and is supported by a
surrounding surface to prevent sinking in sediment. Inside the chamber a pH and oxygen probe was installed, and a semipermeable tube enabled quantifiable gas exchange. This tube was connected to a non-permeable tube leading to water surface and was attached to the input of the gas analyzer. Before entering the gas analyzer, the tube was connected to a glass flask, to exclude the possibility of water entering the gas analyzer. A small
electromotor was incorporated to ensure mixture of the water body inside the chamber, but was malfunctioning at time of deployment and was therefore not used. Initial measurements were made on the 17th of May, defined as T0. Secchi depth was measured with a Secchi
disc as an indication of bloom density of the lake. Additionally, other water properties were measured with a Hydrolab multiprobe. The hoses connected to the Benthic chamber were left overnight in an anchored floating installation to ensure position. The following day the measurements were repeated, 26 hours after the start of incubation, and was defined as T24.
Measurements were collected for partial volume CH4 and CO2 of the gas phase, followed by
pH and oxygen saturation of the water in the chamber. Again the Hydrolab was used to determine natural water properties in undisturbed water. Depth integrated water samples from the first day followed an analyzation in the lab regarding the alkalinity with the use of a Titralab automatic titrator.
Calculations
After measuring the partial units of gases, values were converted to moles per liter using a series of equations (see appendix). Assumed was that solute gases within the aqueous phase were in equilibrium with the gases in the tubes. For the gas phases of CO2 and CH4
the ideal gas law was used. To determine the concentration of dissolved CH4 a calculation
had to be made based on the solubility of CH4, which is dependent on temperature and
salinity (see appendix). The dissolved CO2 is defined as the DIC, which was derived from
pH, pCO2 temperature, and salinity. Finally, the total produced CO2 and CH4 fluxes were
calculated per square meter.
Statistical analysis
All data was statistically analyzed with the use of programming language “R”. Benthic fluxes from all experiments were checked for normal distribution using the function shapiro.test. Non normality was found to be significant for several temperature groups, therefore a logarithmic transformation of all data was performed, resulting in normally distributed data. With a t test was proven that reusing the cores with different temperature set up in a third incubation influenced the fluxes of CH4 from the sediment. In further analysis the third
laboratorial incubation was excluded. Outliers were studied with the use of box and whisker plots, reporting outliers as extreme values situated outside of the whiskers. Within the second incubation one of the 5 °C cores resulted in a negative CO2 flux, and was therefore
removed from dataset.
Finally, the correlation of temperature with CO2 and CH4 fluxes was studied with the use of a
regression analysis. Focus of the regression analysis of CH4 and CO2 gas emissions was on
Results
Fluxes of CH4 in the 5, 15 and 25 °C sediment cores were all found to be positive during the
incubation period of 24 hours. The correlation between temperature and the CH4 flux
showed an exponential pattern. A logarithmic scale was used to express the pathway in a regression curve as is shown in figure 2. A significant correlation was found (r2 = 0.7294,
N=31, p=9.981e-10) 0 5 10 15 20 25 30 1 10 100 1000
CH4 flux
Temperature (°C)
Fl
u
x
(m
m
o
l/
m
2
/d
ay
)
figure 2. Benthic CH4 flux at increasing temperature. Note that the y- axis is logarithmic.
Fluxes of CO2 (gaseous CO2 + DIC) within the cores are described in figure 3. The
correlation of CO2 with temperature showed an exponential pattern. A significant correlation
was found r2 = 0.8857, N=31, p=3.42e-15). The correlation curve was found to be slightly
smaller (0.0098) in comparison to the CH4 flux.
0 5 10 15 20 25 30 100 1000 10000
CO2 flux
Temperature (°C)
Fl
u
x
(m
m
o
l/
m
2
/d
ay
)
figure 3. Benthic CO2 flux at increasing temperature. Note that the y- axis is logarithmic.
y = 10^(0.0613x + 0.3981) R² = 0.7294
Field measurements
Hydrolab data was used to make a depth profile of the lake on T0 for the field experiment
(figure 4). Water depth at specific site was 1.30m. From the profile can be derived that the mixing level of the lake is high, the absence of extreme gradients points out the lack of stratification in the water table. However, when reaching the sediment, temperature and pH experience a slight drop, whereas oxygen levels almost drop to anoxic levels.
Figure 4. depth profile of the Amstelveense Poel (17th May)
The deployment of the benthic chamber facilitated in situ measurements of CO2 and CH4
production, from which the total inorganic carbon flux was calculated (see appendix).
Derived data for the in situ carbon fluxes showed however to be unreliable. Negative change was found for the dissolved inorganic carbon within the chamber. Calculations were strongly influenced by a strong drop in pH of the water inside the chamber, for T0 and T24 respectively
8.28, 6.702, resulting in a negative DIC change. Due to malfunctioning of the electromotor, mixing within the water body of the benthic chamber was not optimal, possibly leading to instability in the measurements. Consequently, is the assumption of an equilibrium between gas and water exchange unjust. Results from the field incubation are shown in the appendix and suggestions for future research are given below.
Discussion
Increasing temperatures influence sedimentary CO2 and CH4 fluxes exponentially. Benthic
CH4 production in the laboratorial incubation showed the strongest correlation with
temperature. Therefore, it can be stated that with increasing temperatures it is likely that CH4
emission will increase more rapidly in comparison to that of CO2.
Gudazs et al (2010) point out an exponential correlation of temperature and OC
mineralization, which was defined as DIC released from the sediment. However, CO2 fluxes
found in this study were greater than the rates of Gudazs et al (2010) in boreal lakes. Moreover, the fluxes found for the sediment cores of Lake Amstelveense Poel, with a regression coefficient of 0.0515, are stronger correlated with temperature than cores sampled from boreal lakes, which showed a coefficient of 0.0362. Both studies focused on the implications of short term warming on sedimentary carbon fluxes and lake emissions.
Fluxes of CH4 showed to be a significant proportion of carbon released from the sediments. Caspar et al. (2000) measured a CH4 flux of 0.28 mmol/m2/day on the 18th of June in a stratified hypertrophic lake in North-England with a water temperature of 16.8C. The sediment core incubation in this study resulted in a mean CH4 flux of 38.8 mmol/m2/day for
the 15°C cores. The same sediment cores showed a mean CO2 flux of 430.9 mmol/m2/day.
Considering that the global warming potential of CH4 is 25 times greater than that of CO2,
warming due CH4 would be more than twice the effect of CO2, if all gases were to be emitted
from the water table. These findings emphasize the significance of CH4 productivity in the
sediment of Lake Amstelveense Poel.
Field study with the benthic chamber and hydrolab gained insight in the lakes chemical properties and effective inorganic carbon fluxes. As expected, the shallow position of the sediment allowed an oxygenated water layer covering the sediment due to great mixing. Temperature, oxygen and pH gradients within the lakes water table are little. However, when reaching the sediment, oxygen concentrations experience a significant drop.
DIC fluxes calculated form the benthic chamber data showed extremely low values (see appendix), that cannot be interpreted as realistic. Consequently, measured in situ inorganic carbon fluxes in the sediment-water interface of the benthic chamber showed little
resemblance with the laboratorial incubated sediments and previous studies. Directly
measuring DIC could improve the quality of measurements and avoid miscalculations (Åberg & Wallin 2014). Additionally, mixing within the chamber should be ensured for a reduction of formation of gradients within the microenvironment of the chamber. Moreover, will increasing the amount of replicate incubations in a transect over the lake area reduce the influence of stochastic differences between deployment locations. Differences in sediment pore
structures can influence the extent of ebullition from peat lakes (Ramirez et al. 2016). More open peat sediment structures show an erratic release pattern of CH4 ebullition, whereas
denser sediment structure lead to a steadier gas release.
The incubation in the lab showed to result in significant correlations of CH4 with temperature
and extensive CH4 fluxes from the sediment. However, extrapolating whole lake CH4 flux
estimations from sediment core incubation data will most likely not be accurate. Sediment structures in the experiment were situated more shallow (0.15 m) than under natural conditions in the lake (1.30 m). These differences in volume of overlaying water body will reduce the retention time of produced CH4, and consequently diminish the chances of
CH4 oxidation within the water body, possibly leading to an overestimation in the cores
(Michmerhuizen et al. 1996). Moreover, should estimations of methanotrophic processes such as CH4 oxidation be included in these predictions.
Effects of temperature on inorganic carbon liberation from sediment are important for freshwater carbon budgets (Rantala et al. 2016). However, when making predictions for future scenarios of carbon cycling in shallow lakes, more factors should be included. Whole lake biotic interactions with temperature can result in a significant control of CH4 and CO2
emissions (Audet et al. 2017). This emphasizes the need for more elaborate research on the lake-temperature interactions on the longer term. Besides complex lake interactions, climate change induced warming also results in more extreme weather events, simultaneously increasing the complication of temperature patterns (Meehl et al. 2000). Consequently, will complex climate patterns increase the complexity of carbon buffering in lakes (Kayranli et al. 2010).
Both Gudazs et al. (2010) and this study solely focus on short term warming, however long term warming of lakes might show different CO2 emission patterns than is expected from
core incubations. Long term whole lake implications of the experiment should be approached with great caution. Complexity in the carbon cycling system can result in different emission patterns than expected from solely short term CO2 fluxes. Therefore, it is important to
Conclusion
Warming of lake sediments will result in an exponential increase of CO2 and CH4 fluxes.
Sediment incubation experiments showed that CH4 fluxes are slightly stronger correlated
with temperature than gaseous CO2. This could cause a reinforced effect of freshwater lakes
on climate change, whereas CH4 is a more potent greenhouse gas than CO2. Consequently,
can warming of lakes sediments alter freshwater carbon cycling and create a positive feedback loop on global warming. Effect of increasing temperatures will affect sediments of shallow lakes the most. Moreover, are shallow lakes greater CH4 and CO2 emitters due to
increased sediment-atmosphere gas exchange caused by shorter retention time in water table. Sedimentary fluxes of CO2 are stronger correlated with temperature and more
extensive in Lake Amstelveense Poel than in boreal lakes. This emphasizes the role of shallow lakes in carbon cycling and gas emission in comparison to deeper lakes with reduced mixing. When estimating CO2 emissions based on DIC fluxes, it is of great
importance to simultaneously estimate lake productivity and thus DIC uptake from water column. Consequently, should whole lake carbon cycles be studied to estimate carbon balances, and predict whether lakes are a carbon source or sink.
This study underlines the importance of studying lake specific reactions to global warming, and emphasizes the importance of shallow sediments in carbon cycling. Understanding implications of altering climate on freshwater ecosystems is key when estimating global warming scenarios. Shallow lake interactions with long term effects of warming and extreme weather events should be studied more elaborately, due to its great contribution to CH4 and
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APPENDIX calculations
Solubility of both CH4 and CO2 are strongly dependent on temperature and salinity of water
(Weiss 1974, Yamamoto 1976). The Bunsen coefficient (�) is a widely accepted way of including this dependency in calculations on gases within the aqueous phase. Bunsen coefficient (�, volume CH4 /H20) is dependent on temperature and salinity (equation 1.).
A1,A2,A3,B1,B2 and B3 are methane specific constants determined by Yamamoto et al. (1976). The calculated Bunsen coefficient can be implemented in Henry’s law. The Henry solubility (Hcp, mol/ m3Pa) is determined by the Bunsen coefficient under standard pressure
and temperature (STP) (R=8.3 J/K/mol, T=273,15K) as is shown in the second equation. Ki is derived from the conversion of Hcp to mol/L/atm. Salinity of the water was 0.44ppt
resulting in the values for Ki shown in table 2. Pi (atm) is the partial pressure, partial units measured gas* air pressure. From this equation concentration gas in water is determined in mol/L.
Equation 2
Equation 3
Concentrations were multiplied by the volume of the chamber1 or core2 for
the aqueous phase, and volume of tubes + flask3 or gas in core4 for the gas phase. Absolute
produced quantities resulted in total moles carbon produced after summation, divided by surface area sediment5 gives the flux in mol/m2/day. An estimation of dissolved CH
4 was
made using the equations listed above (1-3).
DIC values were derived from the partial units of CO2 in the gas phase (equation series 4).
Assuming gas and water being in equilibrium, dissolved CO2, HCO3-, CO32- can be calculated
1 29.4L 2 0.716L 3 1.71L 4 0.716L
5 Benthic chamber: 0.0755m2, core: 4.78e-4m2
Equation 1 Table 2 T (°C) Ki (mol/L/atm) 5 0,002184 10 0,001913 15 0,001698 20 0,001526 25 0,001387
from K0, K1, and K2. Which are reaction specific constants for the dynamic equilibria CO2,
HCO3-, CO32- , dependent on salinity and temperature. Values for K0, K1, and K2 were derived
from Dickson & Riley 1979, Weiss 1974 and Millero et al. 2006. Values for H+ concentrations
were obtained from pH measurements.
Equation (series) 4.
For the amount of carbon in the gas phase, molar quantities were calculated for CO2 and
CH4 using the ideal gas law (equation 5). Where V is the amount of liters per mole, following
that V-1 is the amount of moles per liter. When multiplied by 10-6, a correction for ppm is
made, followed by a correction for volume of the gas phase (0.716L). P and R are constants (P= 1000N/m2 , R=8.3 J/K/mol), n is the quantity in moles, and T is absolute temperature in Kelvin.
Equation 5.
DIC (mmol/m2/day) -0.683
CO2 (mmo/m2/day) 0.546
CH4 (mmo/m2/day) 0.893
Total inorganic carbon flux (mmo/m2/day) 0.755
Table 1. Inorganic carbon fluxes in the benthic chamber (day=26 hour)
In table 1 values for the measured fluxes are given for the benthic chamber incubation in mmol/m2/day. Significance tests were not performed whilst the benthic chamber was only deployed once. All values were corrected for increased pressure at 1.3m depth. Change in DIC was negative, meaning that dissolved carbon was more concentrated at T0 than at T24.
In contrast, gaseous CO26 showed an increase during the incubation period. Nevertheless,
CH4 showed to be the greatest contributor to the total inorganic carbon flux during
deployment.
