Carbon Emissions from

Western Siberian Inland Waters

Svetlana Serikova

Department of Ecology and Environmental Science

Umeå 2019

This work is protected by the Swedish Copyright Legislation (Act 1960:729) Dissertation for PhD ISBN: 978-91-7855-107-1 Cover design: Svetlana Serikova / Watercolor work: Julia Kropovinskaya Electronic version available at: http://umu.diva-portal.org/ Printed by: KBC Service Center Umeå, Sweden 2019

Маме и папе, которые посвятили 30 лет своей жизни

освоению русского севера…

To mom and dad who dedicated 30 years of their lives to the

Russian North…

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Table of Contents

List of chapters ................................................................................. 2 Author contributions ........................................................................................................3 Author abbreviations ........................................................................................................3

Abstract ............................................................................................. 4

Abbreviations .................................................................................... 5 Notes ................................................................................................................................. 5

Introduction ...................................................................................... 6 Aim .................................................................................................................................. 10

Materials and Methods .................................................................... 11 Study location and sites .................................................................................................. 11 Surface water pCO2 and pCH4 ........................................................................................ 13 C (CO2 + CH4) emissions ................................................................................................ 13 Water surface areas ........................................................................................................ 14

Results and Discussion .................................................................... 16 C (CO2) emissions from rivers ........................................................................................ 16 C (CO2 + CH4) emissions from lakes .............................................................................. 17 C (CO2 + CH4) emission from Western Siberian inland waters .................................... 18 The role of floodplain in net river C (CO2 + CH4) emission ......................................... 20

Conclusions and Outlook ................................................................. 21

Acknowledgements ......................................................................... 22

References ...................................................................................... 23

A Bad Case of the Arctic ..................................................................... 1

Арктическая болезнь ...................................................................... 3

Спасибо/Spasibo/Thanks ................................................................. 5

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List of chapters

The thesis is based on the following chapters:

Chapter I: High riverine CO2 emissions at the permafrost boundary of Western

Siberia.

Serikova, S., Pokrovsky, O.S., Ala-Aho, P., Kazantsev, V., Kirpotin, S.N.,

Kopysov, S.G., Krickov, I.V., Laudon, H., Manasypov, R.M., Shirokova,

L.S., Soulsby, C., Tetzlaff, D. and Karlsson, J. (2018).

Nature Geoscience, 11(11), 825–829. doi: 10.1038/s41561-018-0218-1

Chapter II: High carbon emissions from thermokarst lakes of Western Siberia.

Serikova, S., Pokrovsky, O.S., Laudon, H., Krickov, I.V., Lim, A.G.,

Manasypov, R.M., and Karlsson, J. (2019).

Nature Communications, 10(1), 1552. doi: 10.1038/s41467-019-09592-1

Chapter III: Carbon emission from Western Siberian Inland Waters.

Serikova, S., Pokrovsky, O.S., Vorobyev, S.N., Rocher-Ros, G., Denfeld,

B., and Karlsson, J.

In review.

Chapter IV: Carbon emission from the boreal floodplain of Ob’ River.

Serikova, S., Pokrovsky, O.S., Vorobyev, S.N., Krickov, I.V., Lim, A.G.,

Siewert, M.B., Vachon, D., and Karlsson, J.

Manuscript.

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Author contributions

Chapter I: J.K. and O.S.P. designed the study. S.N.K. organized sampling

campaigns and logistics. S.S., R.M.M., I.V.K. and V.K. contributed to sampling.

L.S.S. analysed DOC and DIC samples. S.G.K. complemented data with literature

material. S.S. analysed data, prepared figures and tables. C.S., D.T. and P.A.

helped with result interpretation. S.S. wrote the paper with contribution from

J.K., O.S.P. and H.L.

Chapter II: J.K., O.S.P. and S.S. designed the study. S.S., I.V.K., A.G.L.,

R.M.M. and O.S.P. contributed to sampling and chemical analyses. S.S. analyzed

data, prepared figures and tables. S.S. wrote the paper with contribution from

J.K. and O.S.P.

Chapter III: O.S.P. and J.K. conceived the study. S.N.V. collected the Ob’ main

channel pCO2 data. S.S. collected rivers and lakes C emission rates data as well

as analyzed all data. G.R.R. and B.D. assisted in data analysis. S.S. wrote the

manuscript with input from all co-authors.

Chapter IV: O.S.P., S.N.V. and J.K. conceived the study. S.S., I.V.K. and A.G.L.

collected the data. S.S. analyzed the data, prepared figures and tables. M.B.S.

assisted in drone imagery analysis. D.V. helped with results interpretation. S.S.

wrote the manuscript with the input from all co-authors.

Author abbreviations

A.G.L.: Artem Lim, B.D.: Blaize Denfeld, C.S.: Chris Soulsby, D.T.: Doerthe

Tetzlaff, D.V.: Dominic Vachon, G.R.R.: Gerard Rocher-Ros, H.L.: Hjalmar

Laudon, I.V.K.: Ivan Krickov, J.K.: Jan Karlsson, L.S.S.: Liudmila Shirokova,

M.B.S.: Matthias Siewert, O.S.P.: Oleg Pokrovsky, P.A.: Pertti Ala-Aho,

R.M.M.: Rinat Manasypov, S.G.K.: Sergey Kopysov, S.N.K.: Sergey Kirpotin,

S.N.V.: Sergey Vorobyev, S.S.: Svetlana Serikova, V.K.: Vladimir Kazantsev.

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Abstract

Inland waters (i.e. rivers, streams, lakes, ponds) emit carbon (C) into the

atmosphere. The magnitude of global inland water C emission has been estimated

to equal the global ocean C sink, thus making inland waters an important

component of the global C cycle. Yet, the data used in estimating the magnitude

of global inland water C emission lacks measurements of inland water C

emissions from permafrost-affected regions in general and from Russia in

particular, despite permafrost covering ~25% of the Northern Hemisphere and

~65% of Russia. This lack of data questions the accuracy of the current estimate

of global inland water C emission and its predictive power in assessing changes

in the global C cycle following permafrost thaw.

In this thesis, we conducted detailed measurements of river and lake C emissions

across ~1000 km permafrost gradient of Western Siberia (from permafrost-free

to continuous permafrost zone) and assessed the magnitude of the total C

emission from Western Siberian inland waters. We found that river and lake C

emissions varied across the permafrost gradient with river C emissions being

greatest in areas where permafrost is actively degrading, and lake C emissions

being greatest in areas where permafrost is still intact. We also found that river

and lake C emissions are likely driven by different factors with river C emissions

being mainly controlled by temperature and hydrological conditions, whereas

lake C emissions by sediment respiration and availability of recently thawed

organic C. Further, we estimated the total C emission from Western Siberian

inland waters to be greater than previously thought and exceeding the C export

from this region to the Arctic Ocean. Such finding implies that a major part of the

terrestrially-derived C is lost in Western Siberian inland waters, making this

region a hotspot for inland water C emission following permafrost thaw. We also

showed that apart from C emissions measurements across different inland water

types and across the landscape, estimates of inland water surface areas are

needed for accurate assessments of the total inland water C emission of any given

region. Particularly, water surface areas of streams and ponds as well as

inundated floodplains, especially in years of extreme flood events, are important

for quantifying the total inland water C emission. Overall, this thesis presents new

data related to C emissions from rivers and lakes in an area that undergoes rapid

permafrost thaw, and urges to account for all inland water types and their

respective water surface areas when attempting to achieve unbiased estimates of

the inland water contribution to the atmospheric C budget.

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Abbreviations

C Carbon

Catm Concentration of gas in water in equilibrium with

atmosphere

Cwater Concentration of gas in water

CH4 Methane

CO2 Carbon dioxide

F Flux of gas

GPP Gross primary production

IRGA Infrared gas analyzer

k Gas transfer velocity

Kh Henry’s coefficient

MAAT Mean annual air temperature

pCH4 Partial pressure of CH4

pCO2 Partial pressure of CO2

Notes

Emissions (plural) Flux of gas per unit water area per unit of time

Emission (singular) Flux of gas per unit of time (aggregated across all

water area)

Evasion (singular) Flux of gas per unit of time (aggregated across all

water area)

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Introduction

Carbon (C) is a major building block of life and is one of the most abundant

elements on Earth (Ciais et al., 2013; Cole et al., 2007). Due to its chemical

versatility, C can be found in organic and inorganic forms, and is present in the

terrestrial and aquatic environments as well as in the atmosphere (Cole et al.,

2007). Two C compounds, carbon dioxide (CO2) and methane (CH4), are

important components of the atmosphere and are potent greenhouse gases,

concentrations of which have been rising during the past decades and leading to

changes in Earth’s climate (Ciais et al., 2013; Pachauri & Meyer, 2015).

Estimating the sources of CO2 and CH4 emissions into the atmosphere is therefore

one of the major tasks for climate scientists that aim to constrain atmospheric C

budget and achieve accurate predictions of the Earth’s changing climate.

Inland waters (i.e. rivers, streams, lakes, ponds) are an important source of C

(CO2 + CH4) emissions into the atmosphere with recent global estimates (2.1 to

3.9 Pg C yr-1) corresponding to ~1/4 to 1/2 of global anthropogenic C emissions

(Ciais et al., 2013; Drake et al., 2017; Raymond et al., 2013). However, on the

regional scale the estimates of inland water C emissions vary considerably

(Borges et al., 2015; Richey et al., 2002; Stackpoole et al., 2017) and have large

uncertainties, much of which stem from a limited number of direct C emissions

measurements (Melack et al., 2004) across different inland water types. This is

especially true for high-latitude regions of the world that, despite being severely

affected by Earth’s warming climate (Grosse et al., 2016), lack geographically

diverse inland water C emissions data. The goal of this thesis is to quantify river

(Chapter I, IV) and lake (Chapter II) C emissions as well as estimate their

combined contribution to the atmospheric C budget (Chapter III) in one such

understudied high-latitude area – Western Siberia, Russia.

In inland water environments the flux of a nonreactive gas between water and the

atmosphere can be modelled as a Fickian diffusive process and is jointly

controlled by gas transfer velocity (k) and the partial pressure difference

(concentration gradient) of this gas across the air-water interface. This

relationship can be expressed by the following equation (Equation 1):

F = k × (Cwater - Catm) (1)

where F is a flux of a slightly soluble gas (g C m-2 d-1), k is the gas transfer velocity

(piston velocity, cm h-1) at the in-situ temperature, Cwater is the concentration of

the gas in the water (mol m-3) and Catm is the gas concentration of the water in

equilibrium with the atmosphere (Alin et al., 2011). Both Cwater and Catm are

calculated by applying corresponding solubility coefficients corrected for salinity

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and temperature (Henry’s coefficient, Kh, mol m-3 atm-1) to a measured partial

pressure of the gas X (pX, µatm) in water and atmosphere using Equation 2:

Cwater or atm = Kh × pXwater or atm (2)

Positive values of F represent flux from water into the atmosphere, while negative

values indicate the opposite direction of the flux from atmosphere to water (Alin

et al., 2011). In this thesis Equations 1-2 are used throughout all chapters to

calculate C emissions from Western Siberian inland waters.

Generally, inland waters (including permafrost-affected inland waters) are

saturated in CO2 and CH4 with respect to the atmosphere and thus have a positive

concentration gradient leading to C emissions from the water surface (Cole et al.,

1994). The saturation of inland waters in CO2 and CH4 is a result of respiration

(mineralization) of terrestrially-derived organic C in the water (Hotchkiss et al.,

2015) and sediments, as well as inputs of CO2 and CH4 from the surrounding soils

(Rasilo et al., 2017) and groundwater (Duvert et al., 2018) (Figure 1a). Some of

these processes, such as delivery of terrestrially-derived organic C to inland

waters followed by its respiration in the water column and sediments as well as

delivery of additional CO2 and CH4 from the surrounding soils, are predicted to

increase with warming and permafrost thaw (Vonk et al., 2015), thus leading to

greater inland water C emissions (Figure 1b).

Figure 1. Simplified diagram of CO2 and CH4 sources in permafrost-affected inland waters in (a) a

current state and in (b) a warmer climate when permafrost has thawed. (a) In a current state, CO2

8

is being produced by microbial respiration of terrestrially-derived organic matter (R) (Hotchkiss et

al., 2015; Jonsson et al., 2001) and delivered from the surrounding soils (Soil CO2) (Rasilo et al.,

2017), can be consumed by photosynthesis (gross primary production, GPP) (Hall et al., 2016) and

then returned back into the water column via respiration (Massicotte & Frenette, 2011). Also,

sunlight (UV) can produce additional CO2 by photochemical degradation of colored terrestrially-

derived organic matter (Lapierre & Del Giorgio, 2014) and concurrent respiration of its by-products.

All of these processes lead to C emissions from the water surface into the atmosphere. (b) Some of

these processes, such as delivery of terrestrially-derived organic matter and soil CO2 as well as

microbial respiration in the water column, are predicted to increase in a warmer climate and with

thawing permafrost (Vonk et al., 2015) (as indicated by wider arrows), leading to greater inland

water C emissions.

Conceptually, the effect of warming and permafrost thaw on inland water C

emissions can be visualized in a positive response, when any increase in the

export of terrestrially-derived C to inland waters will lead to its mineralization

and loss from the water surface into the atmosphere. At the same time, given that

this additional input of terrestrially-derived C will be respired (mineralized) and

evaded, the downstream C export from inland waters to coastal areas will remain

unaffected (Figure 2).

Figure 2. Conceptual representation of the expected effect of permafrost thaw on inland water C

fluxes. Warming and permafrost thawing increases export of terrestrially-derived C (black dashed

line) following mobilization of C stocks from thawing permafrost. An increasing fraction of the

exported terrestrially-derived C is mineralized and emitted from inland waters, leading to elevated

C emissions (red solid line), while leaving downstream C export to coastal areas (blue solid line)

unaffected.

Several studies have confirmed that terrestrially-derived organic C delivered from

thawing permafrost can be rapidly mineralized in inland waters and vented from

the water surface into the atmosphere (Abbott et al., 2014; Drake et al., 2015;

9

Mann et al., 2015; Vonk et al., 2013). However, no studies have attempted to

understand how permafrost thaw affects inland water C emissions from various

inland water types together (rivers, streams, lakes, ponds), and across different

permafrost zones (from permafrost-free to continuous permafrost zone) in any

high-latitude region where multiple permafrost zones are present. For example,

in the global database of water chemistry of rivers (GLORICH, Hartmann et al.,

2014) (Figure 3a) the data on partial pressure of CO2 (pCO2) in rivers and streams

of Western Siberia, despite covering all permafrost zones, is based on indirect

measurements and has no measurements of inland water C emissions. At the

same time, existing measurements of C emissions from inland waters of Western

Siberia (Golubyatnikov & Kazantsev, 2013; Repo et al., 2007; Sabrekov et al.,

2017; Terentieva et al., 2019) (Figure 3b) are rather scarce, covering only a

handful of lakes and ponds within certain permafrost zones of the region. Such

data gap between the global database and local studies highlights the fact that

current understanding of the impact of permafrost thaw on inland water C

emissions is rather fragmented, limiting our abilities to quantify contribution of

permafrost-affected inland waters to the atmospheric C budget and predict how

this contribution may change in a warmer future.

Figure 3. The location of sampling sites in Western Siberia with (a) indirect river or stream pCO2

measurements from the GLORICH database, (b) existing direct inland water C (CO2 or CH4)

emissions measurements and (c) direct in-situ pCO2 and C (CO2 + CH4) emissions measurements

presented in the respective chapters of this thesis.

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Aim

The main aim of this thesis is to provide quantitative estimates of river and lake

C emissions in Western Siberia, Russia (Figure 3c) – one of the least studied, but

largest northern terrestrial ecosystems in the world that currently undergoes

permafrost thaw. More specifically, the thesis focuses on:

• Chapter I: Quantifying river C (CO2) emissions across different

permafrost zones of Western Siberia.

• Chapter II: Estimating lake C (CO2 + CH4) emissions in permafrost-

affected regions of Western Siberia.

• Chapter III: Assessing the magnitude of total C emission from all

Western Siberian inland waters and their combined contribution to the

atmospheric C budget.

• Chapter IV: Quantifying floodplain C (CO2 + CH4) emissions in the

permafrost-free area of the Ob’ River basin and estimating the role of

floodplain in net river C evasion.

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Materials and Methods

Study location and sites

The research presented in this thesis was carried out in Western Siberia, Russia.

Western Siberia is a vast territory (~3.6 million km2) covered by peatlands (~0.6

million km2), containing large organic C stocks (~70 Pg C) (Sheng et al., 2004;

Smith, 2004) and underlain by permafrost (Figure 4a, b). Permafrost occupies

the greater part of Western Siberia stretching from the polar circle to the shores

of the Arctic Ocean over ~1000 km (Frey et al., 2007; Frey & McClelland, 2009)

and has been reported to undergo rapid thaw (Romanovsky et al., 2010). Western

Siberia harbors the Arctic’s largest watershed, the Ob’ River, which is the 2nd

largest freshwater contributor to the Arctic Ocean (Frappart et al., 2010), and is

one out of three Arctic rivers traversing through all permafrost zones (from

permafrost-free to continuous permafrost zone) (Brown et al., 2001). The study

region is also home to two other major Arctic rivers – Pur and Taz Rivers that,

contrary to the Ob’ River, lay entirely within the permafrost-affected part of

Western Siberia and drain only discontinuous and continuous permafrost zones.

Western Siberia has a moderate continental climate, with mean annual

temperature (MAAT) ranging from +2.8 °C (55°N) to -7.3 °C (69°N) and mean

annual precipitation ranging from 1035 mm yr−1 to 360 mm yr−1 accordingly

(data: https://rp5.ru/, station codes: 28698 and 23058, respectively). The

duration of the ice-cover period in the region varies latitudinally from five months

in the south to more than seven months in the north (Zakharova et al., 2009).

Western Siberia is characterized by a low and flat terrain (0 – 200 m a.s.l.)

(Karlsson et al., 2012) and is dominated by Pliocene sands and clays overlain by

a layer of peat (~1 – 3 m) (Pokrovsky et al., 2015). The thickness of seasonally

frozen soil varies from 1.7 – 2 m in the south (56°N) to less than 0.8 m in the

north (66°N) (Raudina et al., 2017).

The region is densely covered by rivers (Allen & Pavelsky, 2018) and lakes

(Verpoorter et al., 2014) (Figure 4c, d), with lakes being abundant even in the

most northern permafrost-affected area of the region (Polishchuk et al., 2017;

Polishchuk et al., 2018). The combination of extensive inland water coverage and

widespread permafrost makes this region relevant for understanding the impact

of permafrost thaw on inland water C emissions, as well as for assessing inland

water feedbacks to the climate system.

12

Figure 4. Map of Western Siberia with (a) location of the Ob’, Pur and Taz River basins, (b)

permafrost extent, (c) main river network and (d) lake abundance in the corresponding basins. Each

blue dot on panels (c, d) represents either a river segment (c) or an individual lake (d).

Chapter I focused on rivers along the permafrost gradient of Western Siberia

(from permafrost-free to continuous permafrost zone). We sampled 58 rivers and

streams spanning a wide range of watershed sizes from 2 to 150000 km2. These

rivers and streams had no systematic variation in watershed size, discharge or

13

such landscape characteristics as proportion of bogs or forests, etc., in the

respective catchments. We visited all sites during spring (10 − 25 June) and

summer (21 July – 19 August) 2015.

Chapter II studied lakes in the permafrost-affected part of Western Siberia. We

sampled 76 lakes formed as a result of permafrost thaw (thermokarst activity).

The size of the lakes varied from 0.0001 to 1.2 km2 in area. These lakes were

sampled three times over the open water season of 2016; after ice-off in spring

(20 May – 13 June), in summer (9 – 24 August) and before the development of

ice cover in autumn (26 September – 8 October).

Chapter III used the data from Chapters I and II together with new data on

pCO2 from the main channel of the Ob’ River. These data were collected on a boat

cruise from 54 to 66°N in summer 2016 (31 July – 11 August). Additional

literature data on lake C emissions from the permafrost-free zone of Western

Siberia (Sabrekov et al., 2017) were also included in this chapter.

Chapter IV studied the ~3 km2 floodplain in the boreal zone of the Ob’ River

basin. The floodplain was a wide and flat terrain (Vorobyev et al., 2015; Vorobyev

et al., 2019) represented by a mosaic of channels, lakes and ponds. We sampled

14 floodplain sites starting at the onset of flood event (5 – 15 May) and over the

entire open water season of 2018 (9 June – 19 October).

Surface water pCO2 and pCH4

Surface water pCO2 was measured in-situ (Chapter I – IV) with a hand-held

infrared gas analyzer (IRGA, GMT222 probe, Vaisala) of various detection range

enclosed within a waterproof and gas-permeable membrane. During the

sampling, the hand-held IRGA was placed directly into the water column of a

sampled river, stream, lake or pond, where it was allowed to equilibrate for

approximately 10 min (Figure 5a). The hand-held measurement indicator unit

(MI70, Vaisala) was connected to the IRGA, allowing readings of pCO2 in the

water column. Partial pressure of CH4 (pCH4) (Chapter I – IV) was determined

in the lab using headspace equilibration technique of gas extraction from the

sampled water (Pokrovsky et al., 2015).

C (CO2 + CH4) emissions

CO2 emissions from inland waters were estimated using floating chambers. For

the lakes and the floodplain (Chapter II and IV) we used multiple CO2 chambers

(from 2 to 6) per each sampling site. These CO2 chambers were small lightweight

plastic bins (~30-32 cm in diameter, ~300 g, 10 L) (Figure 5b), covered with

aluminium tape to minimize surface heating and equipped with non-dispersive

14

infrared CO2 loggers (SenseAir) (Bastviken et al., 2015). The CO2 accumulation

rate inside each chamber was recorded continuously at 300 sec interval and was

later computed by linear regression over first 30 min to 2 hours of chamber

deployment time. We estimated CO2 emissions by modifying Equation 1 and

using chamber-specific slopes to estimate k. We further calculated instantaneous

diffusive CH4 emissions for each of the chambers using chamber-specific k and

pCH4 measured in sampled water. The sum of CO2 and CH4 emissions constituted

C emissions from the respective sites. The site-specific C emissions were later

aggregated across seasons and multiplied by the duration of the open water

period to estimate annual C emissions for the respective sites.

Measurements of CO2 emissions from rivers and streams (Chapter I and IV)

were conducted using a floating chamber of similar properties (~30 cm in

diameter, ~300 g, 7 L) (Figure 5c). The river CO2 chamber was connected to an

IRGA and a pump (GM70, Vaisala) in a closed loop via CO2-impermeable tubing

with an intervening moisture trap. The pump was used to circulate air to the IRGA

during the measurement period, while the hand-held measurement indicator unit

(MI70, Vaisala) was used to record the measurements. Prior to chamber

deployment it was flushed with ambient air for ~30 sec, and later placed on the

water surface of a sampled river or a stream where it could drift freely with the

water current for ~5-10 min. The CO2 accumulation rate inside the chamber was

recorded continuously at 1-5 sec interval during ~5-10 min and the corresponding

CO2 and CH4 emissions were computed as above.

Water surface areas

We used global river (Allen & Pavelsky, 2018) and lake (Verpoorter et al., 2014)

databases to estimate river and lake water surface areas in the Ob’, Pur and Taz

Rivers basins (Chapter III). Because the databases did not cover water surface

areas of small streams and ponds, which are of importance in inland water C

emission (Holgerson & Raymond, 2016; Stanley et al., 2016), we estimated

stream and pond water surface areas using Pareto law (Allen & Pavelsky, 2018;

Messager et al., 2016; Muster et al., 2019). To estimate water surface area

dynamics of the floodplain (Chapter IV) we used drone imagery together with

image classification algorithm.

15

Figure 5. Examples of field equipment used during the sampling with (a) hand-held IRGA for in-situ

pCO2 measurements, (b) CO2 chambers for lakes and the floodplain, (c) CO2 chamber for rivers and

streams. Added are (d) motorboat for river and floodplain sampling, (e) rubber boat for lake

sampling (featuring all-terrain vehicle onshore).

16

Results and Discussion

C (CO2) emissions from rivers

In Chapter I we quantified river CO2 emissions across the permafrost gradient

of Western Siberia (from permafrost-free to continuous permafrost zone). We

found not only strong differences in annual CO2 emissions among rivers located

in different permafrost zones, but also a peak in annual river CO2 emissions

(Figure 6) instead of a linear increase with MAAT. Interestingly, this peak occurs

at -2 to -4°C MAAT, which coincides with the -2°C MAAT isotherm reported by

other studies (Frey, 2005; Frey et al., 2007; Frey & McClelland, 2009) marking

the border of permafrost appearance in this region. To assess the quantitative

importance of river CO2 emissions, we compared annual river CO2 emissions with

river C export across permafrost gradient of Western Siberia and observed high

emission/export ratios, particularly in the southern permafrost zones that are

most vulnerable to thaw.

Our results suggest that a range of climate-related factors control river CO2

emissions and emission/export ratios across Western Siberia. Higher MAAT

increases river CO2 emissions by promoting mineralization of terrestrially-

derived organic C in river water and by extending the ice-free period, and thus

the time window for atmospheric gas exchange. Higher MAAT also increases the

depth of active layers and likely enhances export of terrestrially-derived C.

Although we saw a trend in export of terrestrially-derived C across permafrost

zones of Western Siberia, the differences among the zones were not significant,

suggesting that impacts of climate on river CO2 emissions are mediated mainly

via temperature control of internal organic C processing, rather than the

magnitude of the terrestrial C supply. In addition to the strong role of MAAT, we

also suggest that high river CO2 emissions and emission/export ratios across the

region are a result of the long travel times of river water, which are governed by

the flat topography of the area that allows sufficient time for mineralization and

outgassing to occur. At the same time water travel times can also be influenced

by MAAT through changes in the duration of the ice-free period and the

magnitude of runoff. These results highlight a complex climate regulation of C

cycling in high-latitude rivers where changes not only in temperature, but also in

hydrological conditions control river CO2 emissions and emission/export ratios.

17

Figure 6. Conceptual representation of results from Chapter I in relation to the expected effect of

permafrost thaw on inland water C fluxes (inset). Warming increases export of terrestrially-derived

C (black dashed line) and an increasing fraction of the exported terrestrially-derived C is

mineralized and emitted from rivers, leading to elevated river C emissions (red solid line). The

downstream C export to coastal areas (blue solid line) is unaffected.

C (CO2 + CH4) emissions from lakes

In Chapter II we explored lake C emissions in permafrost-affected part of

Western Siberia (from isolated to continuous permafrost zone). We found strong

seasonality in lake C emissions as well as differences in annual lake C emissions

between permafrost zones of the region. Contrary to rivers, annual lake C

emissions did not peak at the border of permafrost appearance, but rather

showed a contrasting pattern, being higher in the northernmost permafrost zones

of Western Siberia and thus having a negative relationship with MAAT (Figure

7). Such finding is at odds with previous studies of boreal and arctic lakes and the

general understanding of the impact of warming on lake C cycling, where

warming-induced export of terrestrially-derived C and its mineralization in the

water column lead to increased C emissions (Vonk et al., 2015; Yvon-Durocher et

al., 2014). Further, contrary to what has been previously observed, we did not find

any dependence of lake C emissions on other factors (i.e. lake area, lake depth,

concentration of dissolved organic and inorganic C, etc.) that should affect C

emissions from lakes.

Our results suggest that lake C emissions in Western Siberia are controlled by a

complex interaction between climate and permafrost as well as area-specific

features of Western Siberian lakes. In Western Siberia lakes are typically shallow

(even lakes large in size), and owing to the overall flat terrain of the region, these

18

lakes have relatively small catchments. The combination of shallow depths and

small catchments implies that sediments play a larger role in lake C cycling,

compared to deeper lakes with larger catchments where lateral inputs of C and its

processing in the water column dominate. In Western Siberia, lake sediments are

composed of organic detritus from flooded peat bogs, and a major part of this

peat is mineralized over the course of lake development (Audry et al., 2011). This

suggests that the observed latitudinal pattern in annual lake C emissions with

higher C emissions in the cold areas is governed by a higher availability of organic

C for mineralization of recently thawed lake sediments in the northernmost

permafrost zones of the region. Interestingly, such finding also implies that a

northward shift of permafrost zones and their subsequent replacement with

permafrost-free regions will lead to a decrease in C emissions from Western

Siberian lakes. However, this assumption is likely unable to capture impacts of

new environmental conditions following permafrost thaw on lake C cycling,

prompting future work to test it.

Figure 7. Conceptual representation of results from Chapter II in relation to the expected effect of

permafrost thaw on inland water C fluxes (inset). Warming increases export of terrestrially-derived

C (black dashed line), leading to a decrease in lake C emissions (red solid line). The downstream C

export to coastal areas (blue solid line) is unaffected.

C (CO2 + CH4) emission from Western Siberian inland waters

Chapter III relies on the spatial patterns in river and lake C emissions found in

Chapters I – II, and integrates these findings across all inland water types

(rivers, streams, lakes, ponds) and across all permafrost zones of Western Siberia.

Here we ask what total contribution of all Western Siberian inland waters to the

19

atmospheric C budget would be. We found that although rivers C emissions are

greater than C emissions from lakes, lakes are generally more abundant across

the region, even in the most northern permafrost-rich zones of Western Siberia.

We also saw that the total C emission scaled to the land area (C yield) shows not

only high values across Western Siberia, but also strong differences among

different permafrost zones of the region.

These results imply the need to account for variability in both C emissions and

water surface areas of rivers and lakes across the landscape for accurate

assessment of inland water C emission and for projections of future conditions.

We estimated the total C emission from Western Siberian inland waters of 0.104

(± 0.013) Pg C yr-1, which is greater than previously thought (Lauerwald et al.,

2015; Raymond et al., 2013). Also, we found that the total C emission from

Western Siberian inland waters exceeds region’s C export (0.011 Pg C yr-1) to the

Arctic Ocean (Gordeev et al., 1996; Kaiser et al., 2017; Pokrovsky et al., 2015;

Tank et al., 2012), suggesting that a major part of the terrestrially-derived C is

lost in Western Siberian inland waters, which emphasizes the limitation of relying

on downstream C export as an indicator of change at high latitudes. Such finding

highlights that ignoring contribution of inland waters to the atmospheric C

budget may underestimate the impact of warming on high-latitude regions and

overlook their weakening capacity to act as terrestrial C sinks on the global scale.

Figure 8. Conceptual representation of results from Chapter III in relation to the expected effect of

permafrost thaw on inland water C fluxes (inset). Warming increases export of terrestrially-derived

C (black dashed line). Contrary to terrestrial C export, C emission (combined rivers and lakes C

emission scaled to the land area, red solid line) first increases with warming, and later on follows a

decreasing trend. The downstream C export to coastal areas (blue solid line) is unaffected.

20

The role of floodplain in net river C (CO2 + CH4) emission

Considering the importance of water surface areas for accurately assessing inland

water C emission (Chapter III), in Chapter IV we studied C emissions and

water area dynamics of the main channel and the floodplain in the boreal zone of

the Ob’ River. We found strong seasonality in both C emissions and water area

dynamics of the Ob’ main channel and the floodplain. We further estimated the

total annual C emission from the main channel and the floodplain of 940 (± 744)

t C yr-1 with the floodplain contribution of ~16% in net river C evasion. Given that

the studied site covered only ~15% of the entire flood terrace that is flooded once

in ~40-50 years (Vorobyev et al., 2019) and assuming the full width of flood

terrace (~20 km wide), we estimated that in years of extreme flood events the

floodplain contribution in net river C emission could increase to 76%.

These results suggest that in years of normal flood events (as the one covered in

this study) past assessments of river C evasion lacking the estimate of floodplain

C emission are not biased. However, it is not unlikely that floodplains can have

greater relative importance in net river C emission in other regions with more C-

rich floodplain soils and in more extreme flood years, when larger areas of land

become inundated. Thus, ignoring the floodplain C emission in such extreme

flooding conditions can lead to errors in riverine C budgets calculations and result

in underestimation of the total river C emission on the regional scale.

21

Conclusions and Outlook

This thesis has quantified river and lake C emissions as well as estimated their

combined contribution to the atmospheric C budget in Western Siberia, Russia.

We found that both rivers and lakes are sources of C emissions into the

atmosphere, the magnitude of which not only varies spatially across permafrost

gradient of this region, but is also controlled by different factors (i.e. temperature,

hydrology, topography, etc.). We also estimated the total C emission from

Western Siberian inland waters to be greater than previously thought and found

that it equals C consumption by the global rock weathering (0.1 Pg C yr-1) (Ciais

et al., 2013), which is a striking comparison suggesting that estimates of different

components of the global C cycle are likely underestimated. These findings

allowed us to conclude that Western Siberian inland waters play an important

role in the global C cycle, and ignoring their role may lead to biased predictions

of changes in the global C cycle following permafrost thaw.

One of the major outcomes of this thesis is not the questions it answers, but

rather the questions it raises for others to pursue. In this work we saw that

geographically diverse measurements of inland water C emissions and detailed

information on water surface areas of different inland water types are needed, as

these are critical for accurately assessing total inland water C emission of any

region. At the same time, the contrasting latitudinal patterns in river and lake C

emissions and in the total C emission suggest that a warmer future may decrease

C emission from Western Siberian inland waters, which is an interesting

hypothesis worth exploring. However, these contrasting latitudinal patterns

observed in our data may only be “transient”, when permafrost-affected inland

waters are responding to a warming climate, but once this period of “transition”

has passed, other factors will come at play and may counteract (or reinforce) the

observed trends. For example, our data suggest a possible role of gross primary

production (GPP) in rivers, lakes and the floodplain, which can result in a

decrease of inland water C emissions. Yet, the estimates of GPP from Western

Siberian inland waters are currently absent, encouraging future work to address

this knowledge gap. Also, such factors as quality of terrestrially-derived organic

C that enters inland waters of Western Siberia following permafrost thaw, its age

and lability are currently unknown, and will likely determine the magnitude of

future C emissions from inland waters of this region. Finally, the estimates of

terrestrial net ecosystem exchange from Western Siberia are absent, making it

harder to evaluate the strength of the terrestrial C sink (or its capacity to act as a

sink) in this region, as well as its link to the inland water C cycle. Once these

knowledge gaps are addressed, it will be possible to either verify or challenge

predictions made in this thesis, though that is yet to be seen in the future.

22

Acknowledgements

Thanks to Dagmar Egelkraut, Sylvain Monteux and Jan Karlsson for comments

and suggestions on this thesis summary. The thesis was supported by the Swedish

Research Council grant no. 325-2014-6898 awarded to Jan Karlsson. Arcum

Strategic Funding and Kempe Foundation grants awarded to Svetlana Serikova

are acknowledged.

23

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A Bad Case of the Arctic

Don’t bother looking for a complex vaccine;

don’t go searching through reference books…

This disease

has not been studied by medical science…

If a girl crouched in a tent

says with a melancholy air,

after a silence:

“I’ve got a bad case of the Arctic”,

there’s nothing a doctor can do.

A bad case of the Arctic

means

that the Arctic has taken your heart hostage;

that you have been summoned by the rough voice of the wind.

It means that

from now on

wherever your travels may take you,

on the threshold of any spring,

you will always be haunted by Arctic roads,

you will always dream snowy dreams…

What’s so special about it though,

this icy mess?

Warm rivers and high mountains

gave it a wide berth.

They short-changed it

2

like a poor cousin…

But who cares if they did?

If only you saw

the rough-hewn majesty of the ice,

if only you understood

the return

of the long-awaited sun,

if only you filled your lungs

with the tingling air

of these latitudes,

if only you ever tasted

the joy and grandeur

of earthly friendship,

then –

I give you my word –

you would say it along with me;

you would say it –

some of you in secret,

some at the top of your voice:

“I’ve got a bad case –

a really bad case of the Arctic!

There’s nothing a doctor can do!”

Robert Rozhdestvensky / Translation by Konstantin Andreev

Арктическая болезнь

Не трудись над хитрой вакциною,

в книги-справочники не лезь…

Существует здесь медициною

не изученная болезнь…

Если парень, сидя в палатке,

грустновато, не сгоряча,

говорит:

“Заболел я… Арктикой…” –

то к нему не зовут врача.

Заболел я Арктикой –

Это значит,

Арктика сердце взяла

и неласковым голосом ветра

человека к себе позвала!

Значит,

где б ты теперь ни странствовал,

на пороге любой весны,

будешь бредить полярными трассами,

будешь видеть снежные сны…

Ну, а что в ней, скажите, особого –

в этой путанице ледяной?

Реки теплые, горы высокие

обошли ее стороной.

Обошли, обделили, обидели…

4

Только это все – не беда!

Если б вы хоть однажды увидели

угловатую царственность льда,

если б вы хоть однажды поняли

долгожданного солнца приход,

если б легкие вы наполнили

звонким воздухом этих широт,

если б вы изведали счастье

и величие дружбы земной, –

вы,

конечно,

тогда ручаюсь я! –

повторили бы вместе со мной,

повторили одни украдкой,

а другие в голос крича:

– Заболел…

Заболел я Арктикой!

Не зовите ко мне врача.

Роберт Рождественский

Спасибо/Spasibo/Thanks

1540 days have passed since the day I became a PhD student, and finally, it is time

to print this book! Of course this book would not see light without so many people

that were a part of it and contributed to it coming true.

First of all I want to thank my big boss, Jan Karlsson, for taking me onboard this

wonderful PhD journey and for sharing his bright ideas I was so lucky to be a part

of. Thanks for your guidance and patience, even in moments when we could not

agree; I am particularly grateful for those, since in those moments I could grow

as a student and as a person. I learned a great deal from you Janne, which I will

never be able to repay. My thanks also go to my co-advisor, Oleg Pokrovsky,

whose passion and dedication during these 4 years were truly fascinating. Thanks

for inspiring me hundreds of times and giving me much necessary kick-in-the-

butt when it was and wasn’t needed. I really appreciated it, even if I did not seem

to from the beginning. Many thanks to my last co-advisor, Hjalmar Laudon, for

always being there when it was necessary, and for finding time to chat and to

encourage. I am grateful for all the support I got from you and for all the Xmas

cards I received. I truly hope they will never stop arriving.

This book would not be possible without the work of 3 fantastic guys: Ivan

Krickov, Rinat Manasypov and Artem Lim – the field crew. Thanks for fishing me

out multiple times from our lakes (I honestly did lose count how many times I fell

out of the boat), for all the help and assistance in the field, all the laughs and tears,

for all the beer- & filtering- nights and for being so genuinely awesome! I could

never wish for a better team. You guys will always have a special place in my heart.

My gratitude extends to David Bastviken and Vladimir Kazantsev for introducing

me to lake C emissions and Western Siberia. Without you, I doubt, I would ever

write a book like that! Tons of thanks go to Anders Jonsson, Erik Geibrink and

Karl Heuchel for all the technical support including the never-ending delivery of

SenseAir sensors (many of which have died a dignified death on the field

measuring CO2 emissions), and for all the sample analyses and calibration.

Thanks to you, the equipment was working as planned and I could always bring

data and lots of water back home.

Special thanks go to Pertti, the Post-Doc on the same projected I was a PhD

student of, for all the emails we exchanged discussing not only project-related

challenges and data, but also life. I was really lucky to have such a smart “isotope-

whisperer” and I did like the boxplots you made for me; they were mind-blowing!

6

Next, I would like to thank the ladies of EMG: Maria, Dagmar, Elin, fabulous

Helena, Isolde, Guo, Sofia, Sonia and Megan. Your sharp creative minds and the

courage you have in pulling these (at times) challenging research projects have

always fascinated me! I admire every single one of you and truly believe that the

future of science is female and beautiful in so many ways! Ladies, you rock.

My thanks also extend to the guys of EMG: Bror, Gerard, Dirk, Shun, Johan1,

Johan2, Johan3 (you guys decide who is who), Matthias and Sven. Thanks for all

the coffee- and/or beer- chats, pop- and movie- quizzes, for all the dancing and

all the pub evenings. It was a pleasure!

Also, special thanks go to Mohammed and Dominic for being terrific office-mates,

for all the discussions and ideas, and for never leaving the cookie-shelf empty.

Without it I could hardly survive these 4 years. Thanks a lot, guys, it was an honor

to discuss science with you.

I would like to thank the current and the past inhabitants of the EMG 4th floor:

Carolina, Blaize, Christian, Danny, Maja, Pär and Ryan. Thanks for all the

corridor and fika chats on any possible subject. Many thanks go to other EMG

folk: Joanna, Ingrid, Jolina, Reiner, Bent, Marcus, Judith, … (please insert your name if I

forgot to mention you) for all the help during these years.

Of course these 4 years would not be fun without the people I met in Umeå and

whom I am so happy to call my friends: Veronika & Sasha, Tobias & Linnea (and

little Hugo), Wiebke & Gui, Sylvain & Paula. You will always be welcome in my

home and I hope you know that! Sylvain, I think you are well aware that I could

write an entire paper on how grateful I am to have a friend like you (can even send

it to Nature), but I feel that I do not need to do that – you understand everything

way before I think of it.

Many thanks to Megan & Kostia, Adrian (for the famous Nature Geoscience cover

letter you helped me writing and which I recycled one more time for Nature

Communications; I am sure it was the cover letter that made these papers such a

success) & Åsa, Olga & Mikhail, to Alina, Lena, Matteo. You were there to talk, to

hang out, to go sight-seeing, to pick mushrooms, to BBQ, and to do all the fun

stuff. Thanks, guys.

Special thanks go to my family, Nelly & Denis, Jurchiks, Larisa Leonidovna and

Leonid Vladimirovich. You always supported me and encouraged me to go

forward, and I am grateful for that. Mom and dad, you are everything! Without

your love and patience nothing of this would be possible. Thank you for being

there 24/7 365/366 days a year. And last, but not least, thanks to my husband,

Eugene. You truly make me a better person.