Estimation of Carbon Dioxide emissions from forest soils based on CO2 concentrations

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MASTER THESIS

Masters in Applied Environmental Science

Estimation of Carbon Dioxide emissions from forest soils based on CO2 concentrations

Dennis Wilson

School of Business, Engineering and Science

Halmstad University

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Estimation of Carbon Dioxide emissions from forest soils based on CO2 con- centrations,

s u p e r v i s o r s: Siegfried Fleischer, Marie Mattsson l o c at i o n: Halmstad, September 2016

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"I can do all this through him who gives me strength"

— Philippians 4:13

Dedicated to my parents.

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A B S T R A C T

Forest soil is an important source of atmospheric CO2. Emission of CO2 from soil is the result of respiration of plant roots and soil organisms (Autotrophic and Heterotrophic respiration). This soil CO2 emission has a variation throughout the year with maximum emissions being in the summer. However, the seasonal variation affected by the external factors is not fully known.

The aim of this thesis is to analyze a relationship between concentration of CO2 in the soil-atmosphere and CO2 emissions to the above-ground atmosphere. When knowing the relationship between CO2 concentration in the soil-atmosphere and the emission of CO2 from the soil atmosphere, a function (equation) can be established.

Usually, the best fit is considered to establish the relationship. With the equations obtained, it is possible to calculate CO2 emissions using data from different projects, where only soil-atmosphere CO2 concentrations were determined. Using the relationships, emissions rates in different soil types and in forest transect have been analyzed for a large number of samples. The effect of nitrogen deposition on CO2 emissions and seasonal variation of CO2 emission has also been studied.

The sites chosen for this study were located in different parts of Southern Scandinavia and Germany. A closed chamber was used to measure CO2 emission from soil. Soil CO2 concentrations were measured at every station and the equations were established. Finally, these relationships were used for analyses and comparison of the sites. An equation (best fit) obtained was used to calculate the emission values of CO2. The soil texture had a great influence on the CO2 emissions from the soil besides the atmospheric pressure and temperature variations during the seasons.

It is concluded that, the soil texture has a great influence on the CO2 emission from the soil, besides the atmospheric pressure and temperature variations during the season. When knowing the equation showing CO2 concentration and emission for a special type of soil, it is possible to estimate emissions based on solely measured CO2 concentrations. Therefore, large scale sampling of CO2 concentrations could be done and this will facilitate the inventories carried out in e.g. global change studies.

Key Words : Soil Concentration, Soil CO2 production, Soil Respira- tion, seasonal variation.

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Earth provides enough to satisfy every man’s need, but not every man’s greed.

— M.K Gandhi (Schumacher 1973)

A C K N O W L E D G E M E N T S

I thank all who in one way or another contributed to the completion of this thesis. First, I give thanks to God for protection and ability to do work.

I am so grateful to the University scholarship scheme and the Fac- ulty of School of Business, Engineering and Science at the Halmstad University for making it possible for me to study here. I would like to thank my supervisor, Prof. - Siegfried Fleischer, for the patient guid- ance, encouragement, and advice he has provided throughout my time as his student. I have been extremely lucky to have a supervisor who cared so much about my work, and who responded to my questions and queries so promptly.

My sincere thanks also go to Marie Mattsson who helped me in along with my supervisor for her continuous support and sugges- tions given in my project.

I am also deeply thankful to my informants. Their names cannot be disclosed, but I want to acknowledge and appreciate their help and transparency during my research. Their information has helped me complete this thesis.

I also thank my family who encouraged me and prayed for me throughout the time of my research. This thesis is heartily dedicated to my mother who took the lead to heaven before the completion of this work.

May the Almighty God richly bless all of you.

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C O N T E N T S

1 introduction 1

1.1 Soil Carbon

1.2 Soil Respiration 2

1.3 Effect of Nitrogen-Deposition on the soil Carbon Diox- ide emissions 4

1.4 Purpose and issue 5

1.5 Limitations 6

2 m e t h o d o l o g y 7

2.1 Site Descriptions 7

2.2 Measurements 7

2.2.1 Closed Chamber measurements and Soil-atmosphere

sampling 7

2.3 Data Analysis 9

3 r e s u lt a n d d i s c u s s i o n 13

3.1 Relationship between the soil CO2 concentrations and

the emissions of CO2 13

3.2 Variation of Soil CO2 Concentrations in Transects 16 3.3 Comparison between Different Study Sites 18 3.4 Relationships between Concentrations of CO2 in Soil

Atmosphere and soil CO2 emissions of Different Forest

Soils 18

4 c o n c l u s i o n

23

b i b l i o g r a p h y 25

a a p p e n d i x 29

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L I S T O F F I G U R E S

Figure 1.1 3

Figure 1.2

Figure 2.1 Figure 3.1

13 Figure 3.2

Figure 3.3

Figure 3.4

Figure 3.5

Figure 3.6

Figure A.1

Figure A.2

The Carbon cycle - Soil Respiration (Jassal 2005).

N− Deposition pattern in Forest transects from the forest edge into the closed forest already during 1980s. This is a relative N-deposition measure of the percent in closed forest. (Fleis- cher - in prep).

CO2 Closed Chamber Experiment.

Soil CO2 emission is shown in relation with the Concentration of CO2 in Soil Atmosphere at South Scandinavian moraine soil (R²=0.849).

Stacked curves illustrate the calculated monthly averages of CO2 emissions and monthly soil concentrations represented in (g CO2 m⁻²hr⁻¹) and percent (%) respectively from (top) Nor-way spruce forest and (bottom) deciduous, mixed Forest in Scandinavia.

Clear-cut in Timrilt (150 samplings at different occasions over year and the variation is shown.) The point indicates the average values and the line is the median of measured values.

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I N T R O D U C T I O N

The atmospheric carbon dioxide concentrations have increased by about 40% to approximately 404 ppm (NOAA July-2016) from the pre-industrial concentration of 280 ppm (Solomon et al. 2007). CO2 uptake by the ocean causes a reduction in the pH and alters the chemical balance which together leads to ocean acidification and a weak- ened ocean carbon sink. Anthropogenic activities have resulted in the increased emission of various gases into the atmosphere leading to enhanced greenhouse effect during the past centuries which is expected to drive an additional rise in global temperature and climate change in the coming decades. Carbon dioxide is one of the principle gases involved in the greenhouse effect and is responsible for about 70% of climate forcing globally.

Human-induced activities such as deforestation, fossil fuel burning, and other industrial activities have resulted in the high emission of CO2 into the atmosphere. The exchange of CO2 with atmosphere, fossil fuels and soils are the most important anthropogenic source. The effects of global warming can be reduced by reducing the C (carbon) emissions and by sequestering the C stocks globally (Solomon et al., 2007). Concerned countries need to take a step in order to estimate and evaluate their flux and stock of C (Bell and Worral 2009).

Release of CO2 from soils has global significance as it occurs in ecosystems worldwide and its magnitude is such that it contributes significantly to the greenhouse effect. The greenhouse effect is a nat- ural property of our atmosphere in which greenhouse gases prevent the transfer of heat from the earth’s surface to outer space, thereby warming the atmosphere. Since the industrial revolution human activity (e.g., fossil fuel combustion and deforestation) has led to global increases in the concentrations of greenhouse gases (such as CO2) in our atmosphere. This rapid increase will likely lead to a cascade of environmental impacts such as global warming, sea level rise, alteration of precipitation patterns, and increased storm severity (IPCC 2007).

1.1 s o i l c a r b o n

Forest soils constitute an important carbon pool which commonly contain three times more carbon in the uppermost part of the soil than plant biomass and are a main terrestrial reservoir of organic carbon (OC) (Fischlin A et al. 2007). The C flux and stocks of the

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2 i n t r o d u c t i o n

forest ecosystem are influenced by forest management practices and land use.

Soil Carbon is either present in the form of organic carbon (1550 gigatons) or in inorganic form (950 gigatons) (Lal R., 2004). Soil inorganic carbon comprises of mineral forms of C, either from reaction of soil minerals with climatic CO2 or in the form of carbonate materials which is the major form in desert atmospheric conditions(Lal R., 2006). Soil Organic Matter (SOM) consists of soil−dwelling microbes such as bacteria and fungi, plant and animal tissues, decaying materials and the products of decomposition from the living organisms.

A major amount of organic carbon in plants is transferred to the soil as they shed their leaves. Organic matter is broken down by the de- composers (Ontl et al., 2012). It is a heterogeneous composition of thoroughly decomposed materials called humus mixed with materials that are fresh and are about to be decomposed such as the plant residues. SOM mixture is enriched in carbon. Organic carbon present in the organic matter is converted into CO2 and is released into the soil pores causing a high CO2 concentration in the soil atmosphere when comparing with the above ground atmosphere. This difference in concentration leads to the diffusion of CO2 to the atmosphere from the soil. Apart from decomposition, in the forest ecosystem, the root system performs cellular respiration, products of metabolization of carbohydrates by the plant body such as leaves are sent to the roots.

This CO2 release is estimated to be anywhere between 0−60% of soil’s emission (Jeffrey, 2009). Therefore, decomposition and root respiration are processes that produce CO2 in the soil, whereas CO2 emission is the movement of CO2 from soil to the atmosphere.

1.2 s o i l r e s p i r at i o n

Soil respiration (SR) is the total production of CO2 in the soil from roots and soil organisms (Raich, 1992).As the soil respiration increases and thus concentration increases, it forces a higher diffusion pressure and higher release of CO2 into the atmosphere from the forest ecosystem (Robert J et al. 2006). Soil respiration can greatly affect the atmospheric CO2 concentration. On an annual scale, soil respiration contributes roughly 75−100 x 10¹5 g C to the global carbon budget of net CO2 flux into the atmosphere (Boden et al., 2009, Schlesinger and Andrews 2000) which is nearly 80% of the total atmospheric CO2 transportation (Wang et al., 2002, Chris et al., 2005, Raich 1992), thus showing that agricultural and forest ecosystems have a dominating impact on the CO2 balance. The atmosphere−soil relationship and carbon flux are being calculated by knowing the net soil respiration.

Soil respiration can be separated into two fluxes − Autotrophic respiration (Ra) mainly contribute by the plant root and other root-linked organism, Heterotrophic respiration (Rh) is the result of the micro-

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1.2 soil respiration 3

bial activities in the saprophytic system. Gross heterotrophic respiration (GHR) represents the total release of CO2 in the saprophytic system, while net heterotrophic respiration (NHR) is the rest CO2 leaving the soil surface after a part of the CO2 respired has been re−consumed by autotrophic soil organism (a C−sink,(Fleischer and Bouse 2008). Important environmental variables which govern the soil respiration are− a) soil moisture (Davidson et al., 2000) b) soil temperature (Rustad et al., 2001) and c) plant photosynthesis (Hog- berg et al., 2001) and nutritional composition. Through the process of soil respiration, carbon is released from the organic matter degradation in the soil, representing the major component of the global carbon cycle (Bond−Lamberty B. 2010, Lal R., 2004). Apart from the climate change, a reduction of organic C content, fertility and pro- ductivity of the soil is also studied due to the soil CO2 emission. As plants grow, they take up CO2 from the atmosphere and store part of it. Carbon emission and sequestrations depend on the forest management practices and some of the methods adopted to reduce emissions and enhance sinks are achieved by avoiding the degradation of forests (De Wit 1999, Eriksson 2007).

Figure 1.1: The Carbon cycle - Soil Respiration (Jassal 2005)

Overall on an annual scale, soil CO2 emission is related to the air temperature, precipitation and net primary production (NPP) (Raich and Schlesinger 1992). In European forests, the CO2 uptake by photosynthesis to other forms of organic materials are stored as cell material. Soil respiration depicts a link between gross primary production (GPP) and soil CO2 emission (Janssens et al., 2001). On comparing few European forest sites, it was observed that large variation in SR occurred when the temperature and precipitation rates had less variation (Janssens et al., 2001). Whereas, in some Chinese forests both soil organic carbon content and root biomass had a correlation with CO2 flux (Wang et al., 2006). On the other hand, the mean CO2 emis-

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sion had a strong relation with soil C and N stock (Inclan et al., 2010).

The carbon stock and microbial activities in the soil are regulated by various site-particular components identified with atmosphere, soil properties, and management practices. Thick root systems and soil layers release CO2 in significant amounts and thus contribute to en- tire soil CO2 emission to a large extent (Borken and Beese 2005; Pe- ichl et al., 2010). Thus, different types of organic layers should also be taken into account when CO2 emission from the soil is considered.

All these conditions together result in a soil CO2 concentration, at any given sampling time forming the basis for determination of CO2 emission.

1.3 e f f e c t o f n i t r o g e n-deposition on the soil carbon d i o x i d e e m i s s i o n s

In forest soil, along with soil properties, soil moisture, and soil temperature one of the other greatest factor affecting the CO2 emission was N-deposition (Rastogi et.al., 2002). Even though nitrogen is the major element in the atmosphere; it cannot be used in its usual form (N2) except by nitrogen fixing organisms. Nitrogen can be used in its reactive forms of NO3⁻ and NH4⁺ as a result of deposition on land through various processes, as dry gas and wet deposition. At- mospheric nitrogen deposition has doubled from the 1950s and has been an important contributor as nitrogen source into the terrestrial ecosystem (Gundale 2013). Generally, about 10-20% of the nitrogen practiced to forests concentrate in wood; or a major portion often gets accumulated in the SOM. Figure 1.2 shows the relative N-deposition in a transect from the forest edge to the closed forests in Scandinavia (Grennfeldt, 1987) and central Europe (Bavaria) (Spangenberg and Kolling, 2004). The major proportion of deposition is through the wind especially in the form of ammonia gas. When the excess amount of deposition is at the edge it forms a filter and then spreads out. N- cycle has a strong connection with the global C cycle. To support this a demonstration was done by supplying nitrogen to soil which resulted in lowering of CO2 emissions initially which also effected the soil respiration. Later when nitrogen was supplied in surplus a grad- ual increase in CO2 emissions were obtained (Fleischer., 2012). The figure (Fig. 1.2) shows the Nitrogen deposition in percent of the deposition in the closed forest. N-Deposition pattern in forest transects shows a substantial decrease of nitrogen deposition from the forest edges to the interior of the forest sites. This is known as ’edge effect’ observed in most cases until a distance from 0 m to 50m from edge. Here, Bavaria has a higher N-deposition in absolute terms. Ac- cording to a study performed by Spangenberg and Kolling, it was concluded that increased dry deposition was the key reason for the edge effect (Spangenberg et. al 2004). N deposition has a strong effect

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1.4 purpose and issue 5

on the emission of greenhouse gasses. A high N deposition seems to decrease CO2 emissions initially but with a long-term deposition saturation is reached later on while emission of N2O increases and nitrate is leaching (Fleischer., 2003).

Figure 1.2: N− Deposition pattern in Forest transects from the forest edge into the closed forest already during 1980s. This is a relative N- deposition measure of the percent in closed forest. (Fleischer - in prep)

1.4 p u r p o s e a n d i s s u e

The main purpose of this study is to analyse the relationship between the concentration of CO2 in soil-atmosphere and CO2 emissions to the atmosphere. The focus with this approach was to show that

1. When knowing the relationship between CO2 concentration in soil-atmosphere and the emission values of CO2 from the soil atmosphere to the atmosphere, a best fit function (equation) can be established. Usually a best fit function is considered to establish the relationship.

2. With equations obtained, it is possible to calculate emission values using data from several previous projects conducted by Fleis- cher S. and Mattsson M., where only soil-atmosphere concentrations of CO2 has been determined. Using the relationships data emission rates in different soil types and in forest transects has been analysed for a large number of samples. The effect of nitrogen deposition on CO2 emission and seasonal variation of CO2 emissions has also been studied in more detail.

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Finally, the effect of seasonal variation and soil texture on soil respiration in different forest is discussed.

1.5 l i m i tat i o n s

Most of the sampled forest sites had the moraine type of soil and forest sites of different soil type were therefore not investigated. Also, there are certainly better ways to structure the existing data and more advanced models for statistical evaluation of the data could be used.

Furthermore, comparison of the calculated data (emission rates) with actual emission rates could not be made the due to practical limitations.

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2

M E T H O D O L O G Y

2.1 s i t e d e s c r i p t i o n s

In the present study, sampled sites are located in Scandinavia and Germany. The forests in Scandinavia are largely growing on moraine soils. The majority of the sites have Norway spruce tree species whereas some were beech, deciduous and pine trees. Some sites (forests) included sites which were previously used for agriculture. Most initial measurements were carried out within the study by Fleischer (2003) and thereafter as complimentary sampling within the field studies which are still going on. A description of the sites is given in Table 1.

2.2 m e a s u r e m e n t s

The field data in this study were taken from the various running projects which include published and unpublished measurements of soil CO2 concentrations and CO2 emissions from different forest soils (Fleischer) The data were used for description and analysis of the relationship between soil CO2 concentrations and CO2 emissions at each individual site. Measurements taken for this work were done along with the measurements taken for other projects from the early 1990s to 2016.

2.2.1 Closed Chamber measurements and Soil-atmosphere sampling The closed chamber methodology estimates the CO2 fluxes by an- alyzing the rates of CO2 accumulation in the chamber head-space over time (Fig.2.1). However, every change of the CO2 concentration from the ambient conditions feeds back on the CO2 fluxes by alter- ing the concentration gradients between the soil and the surrounding air. Thus, for assessing the CO2 flux, the rate of initial concentration change (the derivative at time zero) should be used when the alteration of the concentration gradients in soils has not changed.

This method is preferred to measurements of the mean rate of CO2 concentration change over the chamber closure period (Livingston and Hutchinson, 1995, Lamouroux, 2008). Measurement of CO2 concentration in the soil atmosphere was done by taking samples at a soil depth down to 10 cm as it is this layer that largely influences the exchange of gas with the atmosphere above the soil (Matts-son et.al.,2015). The depth has been chosen to avoid the influence of soil surface irregularities like that of a cracks as the latter significantly

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8 m e t h o d o l o g y

may alter the emission rates. Measurements at deeper layers are as- sumed to be less important for actual emissions rates.

The sampling of soil atmosphere is done using a stainless steel tube with an outside diameter of 6 mm along with a perpendicular hole on the side of a closed bottom end. A hand operated vacuum pump attached to a 12 ml Exetainer formed the basic apparatus. This was extended to a tube connected to a sampling needle through the polybutene septum which securely closed the Exetainer. The Exetainer with a tube and needle was linked to the steel tube which was in- serted in the soil similarly.

(a) CO2 Closed Chamber Instrument (b) Soil sampling - soil taken for sampling from a depth of 10 cm

(c) Sampling of CO2 from the chamber.

Figure 2.1: CO2 Closed Chamber Experiment

The vacuum pump transports the soil atmosphere into the exetainer. The emissions of greenhouse gas from the soil were measured in the laboratory from samples taken from circular chambers of stainless steel (φ 51 cm, 17 cm high). To prevent the stratification of the emitted gas into the chamber; the cover was rigged with a fan inside.

During the observation process, an aperture (φ 2 mm) with a 10 cm tube was attached in order to allow the compensation for air pressure oscillation without generating leakage. Similar to the procedure for soil atmosphere sampling, the samples were transferred into the 12ml exetainer through a polybutene septum from the closed chamber atmosphere. The samplings for soil emissions were started when

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2.3 data analysis 9

the cover was put on at time zero, and the samples were taken at intervals (5 minutes). It was observed that the CO2 concentration increase levelled off until equilibrium with the superficial soil CO2 concentration and from the slope at time zero, the rate of actual emission was calculated. A straight line is obtained initially at high emission rates throughout the experiment and the emission rate is revealed directly.

Therefore, the CO2 in soil atmosphere values were in the trend-line equation and CO2 emissions were calculated using this method from the plotted curves (Livingston and Hutchinson, 1995; Mattsson et al., 2015).

In Spruce and Deciduous forest sites, the closed chamber experiments were carried out at different stations to measure CO2 concentrations throughout the year in order to determine the seasonal variation.Variation of CO2 concentrations in soil transects into the closed forest was estimated by measuring at a distance of 2, 10, 20, 30, 40, 50 meters from the edge of the forest.

Emissions of CO2 from Ebbarp site a small forest within an agricultural area was determined by measuring the CO2 concentration in samples placed forest in a grid-like pattern. The measurements were then used to compute emissions and evaluate the variation of CO2 emission within the forested area.(Fig 3.5).

2.3 d ata a na ly s i s

Closed chambers were used to measure the CO2 emissions. Soil concentrations were measured at every station. CO2 emissions estimated for were estimated based on the relationship of average soil CO2 concentrations at the plot versus CO2 emissions, on condition that these certain relationships were specific for every plot. From the relationship, the mean of the emission rates from the actual measured data was also calculated for each plot. During the study period from July 1996 to October 2008, the atmospheric concentration has increased from 365 ppm to 389 ppm ( Pieter Tans, NOAA/ESRL) (Appendix).

When the concentration of CO2 in soil is equal to the atmospheric CO2 concentration no diffusion occurs. For this reason 0.036% was used as a mean value (atmospheric concentration) where the trend- line was forced through and for this value no emissions is expected to occur occur. Even if it was not forced through this point most of the plotted relationships actually passed through close to this value.

Confirming the accuracy of the relationships obtained.

A linear and non- linear (polynomial) regression method is used for the estimation of relationships between the soil CO2 concentrations and CO2 emissions. Later these relationships were used for analysis and comparison of emissions at the sites and circumstances. Different relationships were established for different sites that were studied.

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10 m e t h o d o l o g y

The relationship equation (y = 2.48x − 0.093) between the soil CO2 concentrations and the emission of CO2 (illustrated in Fig. 3.1) from the forest floor in southern Scandinavia. This equation was used in- order to calculated the monthly average of CO2 emissions for Norway Spruce and Deciduous forest & Mixed forest (Fig.3).

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2.3 data analysis 11

Table 2.1: Study Sites − Descriptions of region, corresponding characterises and magnitude

Site – (Refer- ences of Site Description)

Region, Country Characteristics Longitude, Latitude

Hjuleberg−

(Grip2006))

SW Sweden Intensive forestry, Norway spruce, former arable land

56^o58’N, 12^o43’E

Ebbarp− (T Nilsson et al.,(2016))

SW Sweden Farm has grown

agricultural land

55^o48⁰N, 14^o03’E

Skogaby−

(Jackson (1990))

SW Sweden Norway spruce 56^o32’N, 13^o11’E

Hainich−

(Mund (2004))

Thuringia, Ger- many

Old closed deciduous forest, beech, ash and others

51^o04’N, 10^o27’E

Wetstein−

(Anthoni et al.,(2004))

Thuringia, Ger- many

Norway spruce closed forest

50^o27’N, 11^o27’E

Biskopstorp−

(Lindblad (2007))

SW Sweden Norway Spruce

and Pine forest

58^o14’N, 14^o52’E

Sk ¨all ˙as−

(Sikstrom, (2005)

SW Sweden Norway spruce

site

56^o42’N, 13^o07’E

Timrilt−

(Belyazid et al.,(2006))

SW Sweden Norway Spruce

Forest, Clearcut area

56^o8’N, 13^o5’E Solling−

(Bredemeier et al.,(1995))

North Germany Norway spruce site; with a high percentage of forest cover

51^o42’N, 9^o33’E

Grillenburg−

(Prescher et al.,(2010))

Saxony, Germany Norway Spruce Forest

50^o57’N, 13^o30’E

Erzgebirge (Annaberg)

− (Fleischer et al.,(2013))

Saxony, Germany Norway Spruce

and Wind-

exposed forest edge, silt

50^o3’N, 12^o58’E

Fichtelgebirge

− (Spangen-

berg et

al.,(2004))

NE Bavaria, Ger- many

Norway Spruce, closed forest clear-cut, with spotted lingering surface water clay loam

50^o09’N, 11^o51’E

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3

R E S U LT A N D D I S C U S S I O N

3.1 r e l at i o n s h i p b e t w e e n t h e s o i l c o 2 c o n c e n t r at i o n s a n d t h e e m i s s i o n s o f c o 2

Figure 3.1 shows the relationship between the soil CO2 concentrations and the emission of CO2 from the forest floor in southern Scandi- navia which is grown on moraine soil type. These samplings are performed in one site (Norway spruce) and a trendline plotted against the observed values to obtain the linear relationship. The soil CO2 concentrations had a strong correlation to the CO2 emission. Here the emissions of CO2 and CO2 in soil atmosphere are measured in (g CO2 m⁻² hr⁻¹) and (%) respectively. The linear relation of the

Figure 3.1: Soil CO2 emission is shown in relation with the Concentration of CO2 in Soil Atmosphere at South Scandinavian moraine soil (R²=0.849)

trend-line (y = 2.480x − 0.093) included 63 samples with a R²= 0.849

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14 r e s u lt a n d d i s c u s s i o n

which shows how well the emission of CO2 cn be predicted from measurements of CO2 in soil atmosphere.

Average value of CO2 emissions and CO2 in soil atmosphere were taken for each month to plot the graph which shows the variations throughout the year of in Norway Spruce Forest (P

n = 1104) and Deciduous, Mixed Forest (P

n = 309)sites in Scandinavia in Fig. 3.2.

CO2 Emission and Soil CO2 concentration rates were estimated for each month at 21 locations. Both forest types demonstrate there is a relation between the two parameters (Soil CO2 concentration and CO2 Emissions) and the curves show that the emission rates and the soil concentration rates follow each other throughout the year. Based on the linear relation (y = 2.480x − 0.093) the emission rates for the seasonal variation for both Norway spruce and Deciduous, Mixed forest were estimated and the data is shown in Fig.3.2.

Figure 3.2: Stacked curves illustrate the calculated monthly averages of CO2 emissions and monthly soil concentrations represented in (g CO2 m⁻² hr⁻¹) and percent (%) respectively from (top) Norway spruce forest and (bottom) deciduous, mixed Forest in Scandi- navia.

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3.1 relationship between the soil co2 concentrations and the emissions of co2 15

On comparing the two forest types, during summer, CO2 emission rates for the forest sites showed a steep increase up to 0.43 g CO2 m⁻² hr⁻¹in Norway spruce site and 1 g CO2 m⁻²hr⁻¹in Deciduous and Mixed forest site. By contrast, the rates fell during winter to about 0.1 g CO2 m⁻² hr⁻¹ at both sites. During the summer period of May to July higher microbial activities and root respiration created an upward diffusion pressure resulting in larger CO2 emissions from the soils. Moreover, the key observation is that even when the trees in the both forest sites are growing on the same soil type (moraine), a higher emission of CO2 was noted in deciduous and mixed forest.

As this ecosystem had higher production of CO2 in the soil.

Further, higher production of CO2 was accounted in the months of June and July (during the summer) at both forests sites. This higher production of CO2 in the soil eventually resulted in higher emission of Co2 from the soil in the warmer periods of the year. Soil respiration is the product of two major biological processes; autotrophic respiration (growth and production of plant roots) and heterotrophic respiration via the microbial decomposition of carbohydrates from roots, litter, and other soil organic matter (Var-gas et al. 2011). Both of these two fluxes were greatly affected by higher temperatures. De- clined rates were observed during the winter season - from the month of December till mid of March. This is likely due to the fairly stable but low value of winter soil temperature and the thickness and dura- tion of snow cover (frost) (Elberling et al 2007).

Soil CO2 concentration showed a high values when measured from a soil depth of 10 - 50 cm. These values were higher from those measured using a syringe sampling done in early 2000 which hardly reaches up to 8 cm depth (Jassal et al., 2004; Drewitt et al., 2005). In the above mentioned study the calculations show that more than 75

% of the CO2 emissions originated from a depth more than 10 cm.

Due to this reason the soil sampling was done from a depth of 10 cm or above in this study too.

Research done in different forest types have noted that a small rain- fall event in a dry soil soil results in higher release of CO2 from the soil (Borken et al., 2003, Lee et al. 2004). The study carried out by (Lee et al. 2004) was done creating an artificial wetting in mixed forest. A sudden hike in the CO2 emission was observed when the water was sprayed and later the emission values returning back to its pre-wetting values after a time period of 1 hour. In another study by (Kim et al.,2008) the seasonally observed pattern, soil CO2 efflux varied strongly with soil temperature; increasing trends were evident during the early growing season, with sustained high rates from mid May through late October. Soil CO2 efflux was related exponentially to soil temperature (R² = 0.85), but not to soil water content. This seems to be the case also with this study. The relationships between

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the CO2 concentrations and emissions were generally strong despite sampling was carried out under varying water content (Fig. 3.6).

3.2 va r i at i o n o f s o i l c o 2 c o n c e n t r at i o n s i n t r a n s e c t s Concentrations were measured from the forest edge of the closed forest. Transects on the soil concentrations are shown in Appendix Fig A.5. Carbon dioxide emissions from the forest soils along the transect ranged between 0.093 to 0.209 g CO2 m⁻² hr⁻¹. These sampled soil concentration values were put in a relationship with one of the German site (Wetstein) where the relationship equation was (y = 6.3358x − 0.2127). Even thou these obtained values are not the actual values they give a rough estimate. The variation of concentrations in all sites showed small variations, Table 3.1. The lowest CO2 emissions were observed at Erzgebirge, while the largest emissions were observed in the forests from Solling (Table 3.1). The western part of the Solling site showed, however, a higher variation. It was prob- ably due to higher deposition of nitrogen as it was a wind exposed site. After the 2 occasions of clear-cut at Fichtelgebirge, the variation of CO2 concentrations in soil from Fichtelgebirge site was compared with Timrilt. Figure 3.3 shows the instability caused by storm felling at Timrilt site where the concentration in soil rates were high during the summer period.

Table 3.1: Calculated emission rates of CO2 from the Soil Average CO2 concentrations in four German Transects (Appendix Table. A.1, Fig. A.5). The concentrations were transformed to the emissions based on the relationship derived in the soils at Wetstein (y = 6.3358x − 0.2127) and should be considered with caution. n is the number of measured transects.

Meters/Site Solling (n=15)

Erzgebirge (n=13)

Fichtelgebirge (n=18)

Gillenburg (n=13)

2 0.158 0.118 0.120 0.096

10 0.178 0.109 0.192 0.129

20 0.203 0.106 0.126 0.138

30 0.151 0.100 0.130 0.149

40 0.205 0.093 0.139 0.144

50 0.209 0.105 0.125 0.167

Average 0.184 0.105 0.139 0.137

The table shows the calculated mean emission rates of CO2 transformed from the sampled CO2 concentrations in German Forest Sites shown in Fig Appendix A.5. The average emissions of the different forest sites does not differ much but still the highest emissions being at Solling forest site with 0.184 m⁻²hr⁻¹. As Solling being a Norway

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3.2 variation of soil co2 concentrations in transects 17

Figure 3.3: Clear-cut in Timrilt (150 samplings at different occasions over year and the variation is shown.) The point indicates the average values and the line is the median of measured values. See also Appendix Fig. A.5

Figure 3.4: Emission of CO2 from the Ebbarp Spruce Forest grown on former farmland. At each sampling occasion, 30 soil CO2 samples were taken in a grid pattern with the outer points situated 2m from the forest edge. The average of 5 sampling occasions, from 24July 2002 till 6 September 2004, is shown.

spruce site has high percent of forest cover which results in higher microbial activities in the soil and higher rates of soil respiration when compared with the other forest sites.

The emission of CO2 at the Spruce site Ebbarp is shown in Figure 3.4. The scale indicates the intensity of the emissions. The rates are much higher in the wind exposed forest edge. The pattern depicted with much higher CO2 emissions in SW wind exposed part of the forest (and in the corners) was the same during this period. Then a storm event felled the Norway spruce the part exposed in the wind direction, and this made further following up impossible.

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3.3 c o m pa r i s o n b e t w e e n d i f f e r e n t s t u d y s i t e s

A best fit regression method (linear and polynomial) was used to find the relationship between the mean emissions and soil CO2 concentration of the different forest sites is shown in Table 3.2. The mean emission were calculated from n number of samplings (replicates taken at each sites) which varied from 0.182 to 0.688 g CO2 m⁻²hr⁻¹.

The influence of the soil texture on CO2 emissions is clearly demon- strated when the Hainch and Wetstein sites are compared (Table 3.2).

Both these sampling sites are located in central Europe. Here Hainich, with its close clay soil, showed mean CO2 concentrations (0.449%) that were 3.5 times higher than measured in Wetstein (Sandy loam soil type) (0.119%), but the CO2 emissions at the Hainch site were less than half those at Wetstein.

The highest emissions were recorded for Biskopstrop, Sk ¨all ˙as and Wetstein forest site. They had emission rates of 0.618, 0.629 and 0.688 g CO2 m⁻² hr⁻¹ respectively which were the highest among the other forest sites. Meaning that these sites had a loose soil profile which causes the release of CO2 as soon as a low concentration of CO2 is produced in the soil. This was expected as these soils also have loose soil texture which results in the release of CO2 also when low concentration of CO2 is produced in the soil. It is also possible that the high emission rates in these soils are related to a higher microbial activity in these particular sites.

3.4 r e l at i o n s h i p s b e t w e e n c o n c e n t r at i o n s o f c o 2 i n s o i l at m o s p h e r e a n d s o i l c o 2 e m i s s i o n s o f d i f f e r e n t f o r- e s t s o i l s

The calculation of Emissions of CO2 as a result of Soil CO2 concentrations is charted and a graph has been created for each site (Appendix - Fig. A. 1,2). The soil material in the spruce forest is loosely packed resulting in a loose texture with low resistance to diffusion of gas resulting in the more direct release of CO2 after its production. Fig.3.5 shows the influence of upward force diffusion pressure from soil forcing to emit CO2 into the atmosphere.

In the early study of Hjuleberg, only 2 measurements of concentrations were done at each occasions while later on increased soil sampling (frequent sampling) has resulted in establishing stronger relationships. A strong relationship between the carbon dioxide concentration and soil texture is shown in Hainich forest site (R²= 0.989)

− as it has a tightly packed soil profile most of the year, high concentration of CO2 in the soil is needed even for the small emissions of CO2. Even-thou, Hainich site had a very loose soil texture it may be represented as a site which has high emissions despite of low soil CO2 concentrations of CO2.

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3.4 relationships between concentrations of co2 in soil atmosphere and soil co2 emissions of different forest soils 19

Table 3.2: Mean emissions calculated as a result of soil CO2 Concentration of different forest sites (n - number of samplings at each site Study Sites Mean Soil CO2 Con-

centration (%)

Mean Emission of CO2 -(g CO2 m⁻² hr⁻¹)

Hjuleberg, n=10 0.259 0.523

Ebbarp, n= 5 0.131 0.208

Skogaby, n= 12 0.128 0.224

Production forest, n= 15

0.214 0.243

Virgin Forest, n= 20 0.169 0.355

Hainich, n= 10 0.449 0.312

Wetstein, n= 11 0.119 0.688

Biskopstrop, n= 11 0.248 0.618

Sk ¨all ˙as, n= 8 0.176 0.629

Timrilt, n= 12 0.206 0.508

Norway Spruce For- est, n= 1104

0.118 0.182

Deciduous Forest, n=389

0.225 0.465

An exception from this situation was shown after a long drought period which caused the clay soil (red spots in Fig.3.6) in Hainch to develop cracks. These seemed to largely increase the soil surface exposed to the above soil atmosphere, and resulted in a drastical increase in CO2 emissions (Fig.3.6). In Wetstein and Sk ¨all ˙as (Norway Spruce), have a fairly strong relation; (R² = 0.876) and (R²= 0.959) respectively. These spruce forests with a loose soil texture have a large amount of coarse organic material and thus the higher emission of CO2 in relation to the CO2 concentration. Moreover, as soon as there is production of CO2 it is being released into the atmosphere. There- fore, smaller CO2 concentrations result in immediate emissions rates.

On comparing the relationships revealed at other sites , texture and CO2 production in the soil are major factors influencing the CO2 emission rates. Due to this reason these special conditions have been treated separately while plotting the relationship (Appendix Fig.A.1).

Sites Hjuleberg (R² = 0.814), Skogaby (R² = 0.952), Production and Virgin Forest (R² = 0.959 , R² = 0.965), Biskopstorp (R² = 0.954) and Timirilt (R² = 0.919) has nearly the same and strong correlations between the 2 parameters. The Biskopstorp, Virgin forest, Hjuleberg, Production forest and Norway spruce, as well as the clear cut Timrilt site, are on moraine soils which may explain the close relationships

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Figure 3.5: Relationships between Soil CO2 emissions and Concentrations of CO2 in Soil Atmosphere of twelve forest Soils. The strongest fit was plotted. Poly= Polynom.

they show. The Sk ¨all ˙as site is also on moraine but the long-term high nitrogen deposition, in addition to experimental N−fertilization, has created this loose soil comparable to the Wetstein spruce site with high atmospheric N−deposition.

Studies performed by Raich and Potter, (1995) show that under a semi-arid, temperate climate (grassland), CO2-emission rates were high during the summer and low during the snow covered winter period. The highest soil respiration rates were measured in managed grassland sites in Finland (peak values 0.10 - 0.22 g CO2 m⁻² s⁻¹).

The results from this study showed high values of CO2 emission rates during the summer in Deciduous and mixed forest (peak values 0.8 - 0.1 g CO2 m⁻²s⁻¹). Furthermore, soil respiration is enhanced by the process of fertilizing on grasslands. On an annual scale roughly 24- 57% increase was recorded in the total soil respiration in the first year after fertilizing under semi-arid temperate climate conditions (Inner Mon-golia; Peng et al., 2011).

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3.4 relationships between concentrations of co2 in soil atmosphere and soil co2 emissions of different forest soils 21

Figure 3.6: Forests with their Individual relationships between Soil Concen- tration of CO2 and Emission of CO2

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4

C O N C L U S I O N

Forest soils are an important source for atmospheric carbon dioxide.

Some of the factors that influence the CO2 emissions from the soil include texture and the effect of soil microbial activities. In addition, seasonal variation and atmospheric pressure also influence the release of CO2 from the forest soils. Moreover, the measured Soil CO2 concentration, and calculated CO2 emission had a strong correlation irrespective of forest sites. This opens for the possibility to estimate emissions based on CO2 concentrations and the chamber technique can be restricted to obtain the relationships. Then, large scale sampling of CO2 concentrations is performed and this will facilitate inter- ventions carried out in e.g. global change studies.

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A

A P P E N D I X

Figure A.1: Relationship between Emission of CO2 and Soil CO2 concentration in Pine and Deciduous Forest R² =0.954

Figure A.2: Erzgebirge - The red line indicates CO2 in soil atmosphere and the blue bar indicates the emissions measured at 5 m intervals in the transect

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30 _APPendix

Table A.1: Transects Of German Forest Sites Sampled CO2 Concentration Meters/Site Solling

(n=15)

Erzgebirge (n=13)

Fichtelgebirge (n=18)

Gillenberg (n=13)

2 0.158 0.118 0.120 0.096

10 0.178 0.109 0.192 0.129

20 0.203 0.106 0.126 0.138

30 0.151 0.100 0.130 0.149

40 0.205 0.093 0.139 0.144

50 0.209 0.105 0.125 0.167

Average 0.184 0.105 0.139 0.137

Figure A.3: Variation of Soil CO2 Concentrations in Transects of Forest Sites in Germany- n depicts the number of transects at each site which was taken at four different locations (at a distance of 2, 10, 20, 30, 40, 50 meters from the edge of the forest) respectively. In Fichtel- gebirge measurements were taken at 2 occasions after clear cut.

Each data point corresponds to a box. The lowest, second lowest, middle, second highest and highest box points represent the 10^th percentile, the median, 75^th percentile and the 90^th percentile respectively. Means are

represented by symbols.

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Appendix 31

Dennis Wilson

Masters in Applied Environmental Science Mob: +46726707769

Email: denwil15@student.hh.se deniz.92d@gmail.com