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Dissertationes Forestales 215Linking water and carbon cycles: modeling latent heatexchange and dissolved organic carbonVille KasurinenDepartment of Forest SciencesFaculty of Agriculture and ForestryUniversity of HelsinkiAcademic dissertationTo be presented, with the permission of the Faculty Agriculture and Forestry of theUniversity of Helsinki, for public criticism in auditorium ls2, Latokartanonkaari 7, on 8th ofApril, 2016, at 12 o’clock noon.

2Title of dissertation: Linking water and carbon cycles: modeling latent heat exchange anddissolved organic carbonAuthor: Ville KasurinenDissertationes Forestales 215http://dx.doi.org/10.14214/df.215Thesis supervisors:University Lecturer, Frank Berninger, Ph.D., Department of Forest Sciences, University ofHelsinki.Professor, Knut Alfredsen, Ph.D., Department of Hydraulic and Environmental Engineering,Norwegian University of Science and Technology.University Lecturer, Anne Ojala, Ph.D., Department of Environmental Sciences, Universityof Helsinki.Professor, Jukka Pumpanen, Ph.D., Department of Environmental Sciences, University ofEastern Finland.Pre-examiners:Professor, Martin Heimann, Ph.D., Department of Physics, Division of Atmospheric Sciences, University of Helsinki.Leading researcher, Pirkko Kortelainen, Ph.D., Finnish Environment Institute .Opponent:Professor of Ecosystem Ecology, Peter A. Raymond, Ph.D., Yale School of Forestry & Environmental Studies.ISSN 1795-7389 (online)ISBN 978-951-651-520-8 (pdf)ISSN 2323-9220 (print)ISBN 978-951-651-521-5 (paperback)Printers:Unigrafia, Finland, Helsinki 2016Cover photo:www.jonohey.comPublishers:Finnish Society of Forest ScienceNatural Resources Institute FinlandFaculty of Agriculture and Forestry of the University of HelsinkiSchool of Forest Sciences at the University of Eastern FinlandEditorial Office:Finnish Society of Forest Science P.O. Box 18 FI-01301 Vantaa, Finlandhttp://www.metla.fi/dissertationes

3Kasurinen, V. 2016. Linking water and carbon cycles: modeling latent heat exchange and dissolved organic carbon. Dissertationes Forestales 215. 46 p. Available at http://dx.doi.org/10.14214/df.215Water and carbon cycles of the Earth are tightly linked to each other. One linkage of these cyclesis through the water use efficiency of photosynthetic production its interactions with drought, and itspossible changes. A second linkage between the water and carbon cycles: the transport of terrestrialcarbon as dissolved organic carbon (DOC) to aquatic ecosystems has received much less attention andis, therefore, the subject of this thesis.The thesis shows that latent heat exchange in boreal and arctic biomes differs, under similar climaticconditions, between different land cover types in the boreal and arctic climatic zones. Furthermore, wefound that there are large differences in the way ecosystems are exchanging water in the winter and thesummer. Winter time surface resistances were much higher and the transition between the winter andsummer phenological stages was slow.Similarly, stream water DOC concentrations show high temporal and spatial variability between different catchments in boreal landscapes and globally between big river systems. The model, developedhere and applied to a boreal catchment simulates stream water DOC concentrations as a function ofcatchment water storage, soil temperature and runoff. The model is parsimonious, i.e. all parameterscould be estimated statistically and it its performed better than previous models for the 18 partiallynested sub-catchments of the Kryckland research area.Finally, the contribution of terrestrial DOC promoting heterotrophic food webs in coastal waters wasquantified after receiving a radiation dose corresponding UV-radiation absorbed by Earth’s surface ina month. Irradiation removed approximately half from the initial terrestrial chromophoric dissolvedorganic matter (tCDOM) suggesting that sun-light induced photochemistry is a significant sink of tCDOM in coastal waters. Tropical rainforest covered large basins of Amazon and Congo Rivers contributed the highest production of biologically labile photoproducts (BLPs) and the highest tCDOMfluxes of investigated rivers, which might be linked to large water fluxes and carbon sequestration intheir basins.A strong relationship between photobleaching of tCDOM and bacterial production based on bioavailable labile photoproducts (BLPs) was found and used to estimate BLP production globally. Extrapolation of production revealed that the majority of tDOC will be mineralized to CO2 either directlyor through bacterial respiration in coastal waters. In these research articles, I have investigated biogeochemical cycles of water and carbon focusing to latent heat exchange and DOC dynamics in landscapes,as well as, in coastal waters, describing their variability across space and time.Keywords: Latent heat, evapotranspiration, DOC, hydrology, photochemistry

4AcknowledgementsWhen I graduated from high school in spring 1999, I was lacking study motivation and decided towork and earn money instead. For a young man, it can take ages to see things more clearly. In this case,it took until the autumn 1999 before I found the motivation again. I continued my studies and signedin to Open University web courses for environmental sciences. When I studied at the Open University,I never dreamed the possibility to become a researcher, but continued to wonder how to get in to theUniversity. During the following years I managed to practice writing in entrance exams four or fivetimes, start a family and work more that I actually had time beside my studies. When I finally receiveda decision letter from the department of bio- and environmental sciences in the summer 2006 only onething was certain: I will never become a researcher. I would have never believed a prediction claimingthat I will deference my doctoral thesis ten years later.I started my doctoral studies in April 2012 and changed the topic from limnology to forest scienceswithout any idea what I am doing. It took some time to get in to a new scientific field and link that tomy previous interests. These past four years in my life has been the most challenging in many ways,but one thing turned out to be very clear already in the early phase of this trip. I just love the work I amdoing.I can never start to describe how grateful I am for all the support I have received from my wife, mysupervisors and colleagues during the process. Without all this support, I would have never succeeded.I have been privileged and had the opportunity to experience the supportive and creative atmosphere,which is supported by my all colleagues in Finland, Sweden, Norway and all over the world throughpeople that have co-authored my studies included in this doctoral thesis. It is a pleasure to work withpeople that are passionate about science and are ready to share their knowledge for the greater good.Although, it is not possible to thank everyone personally in this short space, there are some individualswhose impact should be highlighted.Firstly, I want to thank my wife Jolin for all the unconditional support she has given me during the upsand downs of this process. I also want to thank my daughters Jorunn and Tora for their patience withme when my brain has been overloaded and codes have been crashing. I want to thank Barbro Slottefor providing all needed help and being super nanny for our children during the time I have worked andstudied.Secondly, I want to thank Frank Berninger for the continuous support and positive but critical thinkingin science and in life general. Knut Alfredsen was the key person regarding the arrangements duringmy stay in Trondheim and created the basics for hydrological modeling utilized in my studies. AnneOjala encouraged me to apply for Ph.D positions from Sweden and Finland and strongly influencedmy decision to continue research. Anne together with Jukka Pumpanen provided several inspiringdiscussions during these four years and I am looking forward to develop new research ideas in the future.I thank Finnish Center of Excellence and Nordic Center of Excellence (CRAICC) for the receivedfunding. Markku Kulmala, Jaana Bc̈k, Timo Vesala, Michael Boy and Knut Alfredsen arranged togetherthe required financial support for my doctoral studies.Thirdly, I want to thank my ex-colleagues at Helsinki Deaconess Institute for the support during myadmistrative career. Ilkka Holopainen, Eija Tuukkanen, Kiikka Sandberg and Timo Mutalahti neverstopped to believe in me. Although the environment was turbulent, I managed to stand on my owntwo feet and continue the work I believed in. Finnish Environment Institute provided the first practicalinsights to the research field. Matti Verta, Jaakko Mannio, Jukka Mehtonen, Timo Seppälä, Päivi Munneand Taina Nysten encouraged me to continue the work I was good at. The impact of these kind wordsshould not be underestimated.The decisions I made during the autumn 1999 led finally to my doctoral defense, although it took 17years, nearly half of my life to see the outcome. This has been a extremely interesting trip, but mostlikely it is just a start for another journey. Finally, I want to dedicate my public defense and dissertationto my father, Reijo Kasurinen, who never got a chance to witness this moment in my life as he sadlypassed away on the 9th of May 2013.

5LIST OF ORIGINAL ARTICLESThis thesis consists of an introductory review, followed by four research articles. In theintroductory part, these papers are cited according to their roman numerals. The articles Iand IV are reprinted with the kind permission of the publishers, while articles II-III are theauthors version of the manuscripts send to the series.I Kasurinen V., Alfredsen K., Kolari P., Mammarella I., Alekseychik P., Rinne J., VesalaT., Bernier P., Boike J., Langer M., Belelli Marchesini L., van Huissteden K., DolmanH., Sachs T., Ohta T., Varlagin A., Rocha A., Arain A., Oechel W., Lund M., GrelleA., Lindroth A., Black A., Aurela M., Laurila T., Lohila A. and Berninger F. (2014).Latent heat exchange in the boreal and arctic biomes, Global Change Biology, 40II Alekseychik P., Lindroth A., Mammarella I., Lund M., Rinne J., Kasurinen V., Nilson M.B., Peichl M., Lohila A., Aurela, M., Laurila, T., Shurpali, N., Tuittila, E.-S.,Martikainen, P., Vesala T. (2015). Energy partitioning and evapotranspiration in eightFennoscandian peatlands. 1-12. ManuscriptIII Kasurinen V., Alfredsen K., Ojala A., Pumpanen J., Weyhenmeyer G.A., Futter M.N.,Laudon H. and Berninger F. (2015). Modeling Dissolved Organic Carbon Transport inBoreal Catchments. 1-13. ManuscriptIV Kasurinen V., Aarnos H. and Vähätalo, A. (2015). Biologically labile photoproductsfrom riverine non-labile dissolved organic carbon in the coastal waters. BiogeosciencesDiscussions. 12, 15Author’s contribution:In paper (I) the co-authors provided the data. V. Kasurinen wrote the analytical codeand carried out the data analysis. V. Kasurinen took the lead in the writing. All authorscontributed to the writing process. In paper (II) V. Kasurinen participated to the writingprocess of the research. The article will also be included in the doctoral thesis ofPavel Alekseychik. In paper (III) V. Kasurinen wrote the analysis code, developedand parameterized the model. V. Kasurinen wrote the paper with contributions of allco-authors. In paper (IV) V. Kasurinen was responsible for the laboratory work undersupervision of Hanna Aarnos and contributed to the writing process under supervisionof Anssi Vähätalo.

TABLE OF CONTENTS1INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.1Energy exchange, latent heat and water cycle . . . . . . . . . . . . .1.2Dissolved organic carbon and photochemistry . . . . . . . . . . . . .1.3Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.4Aim of the study . . . . . . . . . . . . . . . . . . . . . . . . . . . .2MATERIAL AND METHODS . . . . . . . . . . . . . . . . . . . . . . . . .2.1Data sources and management . . . . . . . . . . . . . . . . . . . . .2.1.1Eddy covariance data (I, II) . . . . . . . . . . . . . . . . .2.1.2Stream water dissolved organic carbon data (III) . . . . . .2.1.3Terrestrial chromophoric dissolved organic carbon samples (IV) . . . . . . . . . . . . . . . . . . . . . . . . . . .2.2Analytical methods . . . . . . . . . . . . . . . . . . . . . . . . . . .2.2.1Modeling latent heat (I) . . . . . . . . . . . . . . . . . . .2.2.2Comparison of Fennoscandic peatlands (II) . . . . . . . .2.2.3Modeling stream water dissolved organic carbon concentrations (III) . . . . . . . . . . . . . . . . . . . . . . . . .2.2.4Modeling production of biologically labile photoproductsbased on chromophoric terrestrial dissolved organic matter (IV) . . . . . . . . . . . . . . . . . . . . . . . . . . . .3RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.1Latent heat exchange in boreal and arctic biomes (I) . . . . . . . . .3.1.1Phenological parameters . . . . . . . . . . . . . . . . . .3.1.2Adaptation to increasing air temperature . . . . . . . . . .3.1.3Surface resistance . . . . . . . . . . . . . . . . . . . . . .3.1.4Modeling ecosystem scale latent heat exchange . . . . . .3.1.5Latent heat exchange in peatlands (II) . . . . . . . . . . .3.2Simulating regional hydrology and stream water DOC concentrationsin boreal catchments (III) . . . . . . . . . . . . . . . . . . . . . . . .3.3Production of biologically labile photoproducts based on chromophoricterrestrial dissolved organic carbon (IV) . . . . . . . . . . . . . . . .3.3.1Bacterial response . . . . . . . . . . . . . . . . . . . . . .3.3.2Global estimate for BLPs . . . . . . . . . . . . . . . . . .4DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4.1Linking water and carbon cycles . . . . . . . . . . . . . . . . . . . .4.2Latent heat exchange (I, II) . . . . . . . . . . . . . . . . . . . . . . .4.3Modeling DOC transport (III) . . . . . . . . . . . . . . . . . . . . .4.4Photochemical transformation of terrestrial chromophoric dissolvedorganic matter and production of BLPs (IV) . . . . . . . . . . . . . .5CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28282829303334

71INTRODUCTIONLatent heat exchange (energy used for evapotranspiration) between atmosphere and land surface is one of the ubiquitous biogeochemical processes in which living plants are involved(Collatz et al. 1991; Leuning et al. 1995). In surface energy exchange incoming shortwavesolar radiation is converted to latent heat or sensible heat (Kiehl and Trenberth 1997). Latentheat exchange of vegetation is a trade off, where water will be released through a stomataof a plant at the same time when carbon dioxide (CO2 ) is taken in (Baldocchi et al. 1988).CO2 is used in photosynthesis and stored to chemical energy, which will be then available forthe plant and later also heterotrophic organisms (Farquhar and Sharkey 1982; Farquhar et al.1989).Latent heat exchange (λ E) and carbon cycle are directly linked in biogeochemical processes when organic tissue of a plant senescene (Schlesinger and Melack 1981; Aufdenkampe2011). After the death of a plant, formerly living tissues will be converted to soil organic matter (SOM) trough degradation (Kalbitz et al. 2000; Neff and Asner 2001). SOM constitutesthe largest storage of organic carbon that is greater than the atmospheric carbon storage andthe carbon storage in living biomass combined (Batjes 1996; Thurner et al. 2014). Therefore,SOM has a significant role in global biogeochemical carbon cycle (Schlesinger and Andrews2000; Jobbágy and Jackson 2000).SOM is linked to water cycle trough precipitation, snow and discharge (Cole et al. 2007;Tranvik et al. 2009). The water content of soil is regulating the degradation of SOM togetherwith soil temperature (Schlesinger and Andrews 2000; Worrall and Burt 2004). In this continuum, the water content of soil is the source of water for plants and water that cannot beretained in soil, generates discharge (Bergström 1992; Bergström 1995). Limited water availability can limit photosynthetical efficiency and latent heat exchange (Lagergren and Lindroth2002; Bernier et al. 2006; Wharton et al. 2009; Duursma et al. 2008) leading to decreasingcarbon uptake (Clark et al. 2005; Barr et al. 2007). The fraction of SOM, which gets dissolved to water and is transported to rivers, lakes and other water bodies is called dissolvedorganic carbon. This transport of DOC provides a tight linkage between the water and carboncycle (Battin et al. 2009; Aufdenkampe 2011; Müller et al. 2013), including responses ofDOC exports due to changes in evapotranspiration.Increasing atmospheric CO2 concentration might be linked to the water use efficiencyof plants (Frank et al. 2015) and the water cycle in land surface (Keenan et al. 2013). Onthe other had, increasing mean temperature in boreal biomes are suggested to have an effectto the behavior of the soil organic matter storage (Schlesinger and Andrews 2000) and couldincrease SOM turnover rates to DOC. Most of the climate scenarios have predicted increasingprecipitation for the boreal and arctic region, which would lead to increased transportation ofDOC to rivers and ocean (Aufdenkampe 2011; Mann et al. 2012).Although these biogeochemical processes are suggested to be sensitive to a changing climate (Sheffield et al. 2012; Jasechko et al. 2013), we do not understand well how phenologyof the vegetation in the boreal and arctic biomes affect the water balance and its intra-annualvariation (Jung et al. 2010; Jasechko et al. 2013).1.1Energy exchange, latent heat and water cycleIncoming solar radiation absorbed by the Earth and its atmosphere will be balanced troughthe release of outgoing long-wave radiation (Figure 1) (Kiehl and Trenberth 1997). Troughthose processes that reflect, absorb or convert incoming solar energy to water vapor and sensible heat or store the radiation energy into living tissues of plants is called energy exchange

URFACE&168&W&m & &324&W&m,2&&Figure 1.Annual and Global Mean Energy Balance of the Earth modified from IPCC2007. Note that terms are not balanced and figure does not show all terms given in theoriginal.(Sellers et al. 1997). Approximately half of the incoming extraterrestrial radiation is absorbedby the surface of the earth and about half of the absorbed energy is converted to latent heattrough evaporation and transpiration of plants, which are together defined as evapotranspiration (Figure 1) (Kiehl and Trenberth 1997).Latent heat exchange of the earth surface is the energy used for evapotranspiration, whichdescribes the amount of water evaporated by plants and the soil. The role evapotranspiration is significant in the global water cycle (Figure 2). It will return a part of the precipitation back to atmosphere through plants, which utilize only 1% of the taken water for theformation of products of photosynthesis and release 99% trough the transpiration back toatmosphere.Although transpiration of vegetation dominates the terrestrial ecosystem water fluxes removing up to half of the annual precipitation, it is poorly constrained in earth system models(ESM) (Jasechko et al. 2013). However, global climate predictions seems to be sensitive tochanges in latent heat exchange (Sellers et al. 20