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  • Valve, Heikki (2012)
    Tässä tutkielmassa tarkastellaan Cantorin joukkoa ja sen soveltamista muutamiin matemaattisiin tarkoituksiin. Cantorin joukon määrittelyssä otetaan huomioon sen monet topologiset ominaisuudet. Tarkoituksena on muotoilla Cantorin joukkoon liittyvät matemaattiset erikoisuudet mahdollisimman ymmärrettävällä tavalla matematiikkaa vain vähän opiskelleelle. Cantorin joukko on hämmentänyt matemaatikkoja sen ensimmäisestä esiintymisestä lähtien. Joukko muodostetaan vaiheittain poistamalla yksikkövälistä [0, 1] avoimia kolmanneksia. Prosessin ensimmäisessä vaiheessa välistä [0, 1] poistetaan väli (1/3, 2/3). Seuraavassa vaiheessa kahdesta välistä [0, 1/3] ja [2/3, 1] poistetaan jälleen niiden keskimmäiset kolmannekset eli välit (1/9, 2/9) ja (7/9, 8/9). Kun tätä prosessia jatketaan loputtamasti, välistä [0, 1] lopulta jäljelle jäävät pisteet muodostavat Cantorin joukon. Cantorin joukkoon kuuluvat ainakin kaikkien poistettujen välien päätepisteet. Yhtenä joukon erikoisuutena on kuitenkin se, että siihen kuuluu vielä ylinumeroituvasti ääretön määrä pisteitä, jotka eivät ole poistettujen välien päätepisteitä. Tämän seurauksena myös Cantorin joukko on siis ylinumeroituvasti ääretön. Topologiset ominaisuudet ovat Cantorin joukolla myös erikoisia. Voidaan osoittaa, että joukolla ei ole sisäpisteitä eli pisteitä, joilla olisi jokin Cantorin joukkoon kuuluva ympäristö. Lisäksi voidaan osoittaa, että jokainen Cantorin joukon piste on kasautumispiste eli piste, jonka jokaisessa ympäristössä on jokin toinen Cantorin joukon piste. Pirunporrasfunktionakin tunnetun Cantorin funktion lähtö- ja maalijoukko on yksikköväli [0, 1] eli gamma : [0, 1] -> [0, 1]. Funktion määrittely aloitetaan kuitenkin usein Cantorin joukon avulla. Nimen pirunporrasfunktio on saanut portaikkoa muistuttavasta kuvaajastaan. Vaikka gamma muistuttaa portaikkoa ja ensisilmäyksellä vaikuttaa katkonaiselta, niin se on kuitenkin jatkuva ja jopa tasaisesti jatkuva. Viimeisenä asiana tässä tutkielmassa esitetään lyhyesti Cantorin joukkoon liittyvä Lebesguen käyrä. Lebesguen käyrää sanotaan avaruuden täyttäväksi käyräksi, koska se kulkee jokaisen maalijoukkonsa, tässä tapauksessa yksikköneliön [0; 1] x [0; 1], pisteen kautta.
  • Tschamurov, Viveka (2013)
    A model is been built where two countries compete for a multinational enterprise’s (MNE’s) foreign direct investment (FDI) provided that its arrival will increase the host country’s social welfare. Both potential host countries have unionised labour markets where monopoly labour unions determine the level of the wage setting to be either decentralised, intermediate level, or centralised. The governments may influence the unions’ decision by setting a lump-sum tax on them. Both countries have two sectors, a non-sheltered and sheltered sector. The MNE will enter in the non-sheltered sector and is assumed to be more productive than the incumbent firms there. Product market competition between the MNE and domestic incumbent firms is ruled out to isolate the effect of product market competition from the effect of pure wage compression. The game evolves in five stages: (1) the governments set taxes, (2) the monopoly unions choose the level of the wage setting, (3) the MNE chooses its investment location, (4) the monopoly unions set wages, and (5) the firms set output. The purpose of the model is to learn whether the degree of centralisation of wage setting can be used as a strategic choice to attract foreign direct investment. The main results of the paper are the following. It was found that the MNE’s (incumbent unions’) most preferred choice is always centralised (decentralised) wage setting. It was shown that the governments’ most preferred choice is either decentralised or centralised wage setting – depending on the relative sizes of the two sectors. If the social welfare in country 1 is the highest under decentralised wage setting, then the optimal policy of government 1 is to set zero income taxes. If the social welfare in country 2 is the highest under centralised wage setting, then the optimal policy of government 2 is to set positive taxes slightly over that required to make the domestic incumbent labour unions prefer centralised wage setting. Given this, the MNE will always invest in country 2. The exact expressions for the stage-contingent lump-sum taxes were derived. To my best knowledge, this is a novel contribution that cannot be found elsewhere.
  • D'Ulivo, Lucia (Helsingin yliopisto, 2010)
    This doctoral thesis describes the development of a miniaturized capillary electrochromatography (CEC) technique suitable for the study of interactions between various nanodomains of biological importance. The particular focus of the study was low-density lipoprotein (LDL) particles and their interaction with components of the extracellular matrix (ECM). LDL transports cholesterol to the tissues through the blood circulation, but when the LDL level becomes too high the particles begin to permeate and accumulate in the arteries. Through binding sites on apolipoprotein B-100 (apoB-100), LDL interacts with components of the ECM, such as proteoglycans (PGs) and collagen, in what is considered the key mechanism in the retention of lipoproteins and onset of atherosclerosis. Hydrolytic enzymes and oxidizing agents in the ECM may later successively degrade the LDL surface. Metabolic diseases such as diabetes may provoke damage of the ECM structure through the non-enzymatic reaction of glucose with collagen. In this work, fused silica capillaries of 50 micrometer i.d. were successfully coated with LDL and collagen, and steroids and apoB-100 peptide fragments were introduced as model compounds for interaction studies. The LDL coating was modified with copper sulphate or hydrolytic enzymes, and the interactions of steroids with the native and oxidized lipoproteins were studied. Lipids were also removed from the LDL particle coating leaving behind an apoB-100 surface for further studies. The development of collagen and collagen decorin coatings was helpful in the elucidation of the interactions of apoB-100 peptide fragments with the primary ECM component, collagen. Furthermore, the collagen I coating provided a good platform for glycation studies and for clarification of LDL interactions with native and modified collagen. All methods developed are inexpensive, requiring just small amounts of biomaterial. Moreover, the experimental conditions in CEC are easily modified, and the analyses can be carried out in a reasonable time frame. Other techniques were employed to support and complement the CEC studies. Scanning electron microscopy and atomic force microscopy provided crucial visual information about the native and modified coatings. Asymmetrical flow field-flow fractionation enabled size measurements of the modified lipoproteins. Finally, the CEC results were exploited to develop new sensor chips for a continuous flow quartz crystal microbalance technique, which provided complementary information about LDL ECM interactions. This thesis demonstrates the potential of CEC as a valuable and flexible technique for surface interaction studies. Further, CEC can serve as a novel microreactor for the in situ modification of LDL and collagen coatings. The coatings developed in this study provide useful platforms for a diversity of future investigations on biological nanodomains.
  • Owusu, Henry (2000)
    That the financial system is an important source of instability and the propagation mechanism for cyclical fluctuations has come to the fore in the face of the Asian financial crisis. Many economist have argued that, the unregulated operation of the financial markets can lead to excessive fluctuations even in the absense of shocks impinging on the rest of the economy. The study analyses the effects of financial market integration in developing market economies. The basic model is a dynamic open-economy model with two inputs; tradable and non-tradable inputs being used in production and a credit-constraint as to the amount of credit firms' can borrow. We first show that economies at an intermediate level of financial development are more vulnerable to instability than either advanced or least developed economies. In these economies, temporary shocks may have large and long lasting effects. However, there is a limit to which such economies may cycle. This suggests that countries going through financial restructuring may become unstable in the short run. In addition, combining capital market imperfections and unequal access to investment opportunities for individuals can lead to permanent fluctuations in income and investment. Thus governments should aim at reducing inequality of access to credit which may be necessary for macroeconomic stability. Aside the above, other factors such as increases in interest rates, increased uncertainty,and assest market effects on balance sheets may impinge on the stability of small economies. These calls for countercyclical policies targeted at specific problems to be implemented in order to put the economy on a sound footing, for example, during recessions.
  • Eriksson, Einar (1994)
    Capnocytophaga cynodegmi löytyi 9:stä eläimestä (26%) ja C.canimorsus 5:sta (14%) 35 kissan otoksestamme. Rapid-paneelit olivat nopeat ja helppokäyttöiset. Testisarjojen antamat tulokset on esitetty taulukoissa 2A - 4B. C. cynodegmikantojen "mikrokoodeja" ei löytynyt valmistajan käsikirjasta. C. canimorsus antoi satunnaisesti saman mikrokoodin kuin Gardenella vaginalis, mutta bakteerit ovat helposti erotettavissa toisistaan, koska G. vaginalis on aina katalaasinegatiivinen. Sakkaroositestinsä ansiosta Rapid NH kykeni erottamaan C. cynodegmin ja C. canimorsuksen toisistaan, mihin Rapid NF+ ei kunnolla pystynyt. Rapid NF+ erotti kuitenkin eläinperäiset Capnocytophagat muista testitietokantaan kuuluvista bakteereista. Mikäli valmistaja lisäisi kyseiset mikrokoodit luetteloihinsa, eläinperäisten Capnocytophagojen identifioiminen olisi nykyistä huomattavasti nopeampaa (4 h verrattuna 5-7 päivään). Bakteeri pystyttäisiin löytämään useammin kuin ennen, sillä usein verilevyt hävitetään 3 vrk:n inkubaation jälkeen, vaikka Capnocytophagat kasvavat silmin näkyviksi pesäkkeiksi CO2-atmosfäärissäkin vasta n. 5 vrk:ssa. Harvinaisia bakteereita ei laboratorioissa monesti osata lainkaan epäillä. Mikäli DF-2-bakteerien nimi tulisi "automaattisesti" kaupallisen testisarjan tiedostosta, niiden tunnistus osuisi oikeaan nykyistä selvästi useammin.
  • Liljeroos, Lassi (Helsingin yliopisto, 2013)
    Paramyxoviridae constitute a family of pleomorphic, enveloped viruses including several human pathogens. Understanding of the structure and assembly of paramyxoviruses has been hindered by the lack of whole-virion three-dimensional structures. In this work, measles and human respiratory syncytial viruses were studied with three-dimensional electron microscopy and biochemical analysis of recombinant proteins. The analysis revealed significant differences in the structure and assembly of the two viruses. The differences were most notable in the way the matrix protein, the main factor driving budding from host cell, was organized inside the virions. In measles virions, the matrix was found to cover the genome-containing ribonucleocapsid, whereas in human respiratory syncytial virus the matrix was lining the inner surface of the membrane vesicle. These differences have implications on models of how each ribonucleoprotein complex assembles and how the viruses bud from the host cell. The early control of measles ribonucleoprotein assembly was subsequently investigated to further reveal the details of the precise manner in which the intricate molecular ballet of viral assembly is orchestrated inside the host cell. The results presented in this thesis expand the understanding of enveloped virus structure and assembly, which is important in rational approaches to fight the pathogenic members in the group.
  • Stenvall, Maija (Helsingin yliopisto, 2011)
    The thesis explores the discourse of two global news agencies, the Associated Press (AP) and Reuters, which together with the French AFP are generally regarded as the world s leading news distributors. A glance at the guidelines given by AP and Reuters to their journalists shows that these two news agencies make a lot of effort to strive for objectivity the well-known journalistic ideal, which, however, is an almost indefinable concept. In journalism textbooks definitions of objectivity often contain various components: detachment, nonpartisanship, facticity, balance, etc. AP and Reuters, too, in their guidelines, present several other ideals besides objectivity , viz., reliability, accuracy, balance, freedom from bias, precise sourcing, reporting the truth, and so on. Other central concepts connected to objectivity are neutrality and impartiality. However, objectivity is, undoubtedly, the term that is most often mentioned when the ethics of journalism is discussed, acting as a kind of umbrella term for several related journalistic ideals. It can even encompass the other concept that is relevant for this study, that of factuality. These two intertwined concepts are extremely complex; paradoxically, it is easier to show evidence of the lack of objectivity or factuality than of their existence. I argue that when journalists conform to the deep-rooted conventions of objective news reporting, facts may be blurred, and the language becomes vague and ambiguous. As global distributors of news, AP and Reuters have had an influential role in creating and reinforcing conventions of (at least English-language) news writing. These conventions can be seen to work at various levels of news reporting: the ideological (e.g., defining what is regarded as newsworthy, or who is responsible), structural (e.g., the well-known inverted pyramid model), and stylistic (e.g., presupposing that in hard news reports, the journalist s voice should be backgrounded). On the basis of my case studies, I have found four central conventions to be worthy of closer examination: the conventional structure of news reports, the importance of newsworthiness, the tactics of impersonalisation which tends to blur news actors responsibility, and the routines of presenting emotions. My linguistic analyses draw mainly on M.A.K. Halliday s Systemic Functional Grammar, on notions of transitivity, ergativity, nominalisation and grammatical metaphor. The Appraisal framework, too, has provided useful tools for my analyses. The thesis includes six case studies dealing with the following topics: metaphors in political reporting, terrorism discourse, terrorism fears, emotions more generally, unnamed sources as rhetorical constructs, and responsibility in the convention of attribution.
  • Rainio, Johanna (Helsingin yliopisto, 2009)
    Growing human populations and increasing exploitation of natural resources threaten nature all over the world. Tropical countries are especially vulnerable to human impact because of the high number of species, most of these endemic and still unknown. Madagascar is one of the centers of high biodiversity and renowned for its unique species. However, during the last centuries many endemic species have gone extinct and more are endangered. Because of high natural values, Madagascar is one of the global conservation priorities. The establishment of Ranomafana National Park (RNP) was intended to preserve the unique nature of Madagascar. Containing several endemic and threatened species, Ranomafana has been selected as one of UNESCO’s World Natural Heritage sites. However, due to strong human pressures the region immediately surroundings the protected area has severely degraded. Aims of this thesis were to inventory carabid fauna in RNP and evaluate their use as indicators of the environmental change. Carabid beetles were collected from protected area (secondary and primary forests) and from its degraded surrounding area. Collecting was mostly conducted by hand during years 2000-2005. Species compositions between the protected area and its surroundings were compared, and species habitat preferences and seasonal variations were studied. In total, 4498 individuals representing 127 carabid species (of which 38 are new species) were collected. Species compositions within and outside of the protected area were markedly different. Most of the species preferred forest as their primary habitat and were mainly collected from trees and bushes. Their value as indicators is based on their different habitat requirements and sensitivity to environmental variables. Some of the species were found only in the protected forest, some occupied also the degraded forests and some preferred open areas. Carabid fauna is very species rich in Ranomafana and there are still many species to be found. Most of the species are arboreal and probably cannot survive in the deforested areas outside the park. This is very likely also the case for other species. Establishment and continued protection of RNP is probably the only way to conserve this globally important area. However, new occupations and land use methods are urgently needed by the local people for improving their own lives while maintaining the forest intact.
  • Kolari, Pasi (2010)
    The forest vegetation takes up atmospheric carbon dioxide (CO2) in photosynthesis. Part of the fixed carbon is released back into the atmosphere during plant respiration but a substantial part is stored as plant biomass, especially in the stems of trees. Carbon also accumulates in the soil as litter and via the roots. CO2 is released into the atmosphere from these carbon stocks in the decomposition of dead biomass. Carbon balance of a forest stand is the difference between the CO2 uptake and CO2 efflux. This study quantifies and analyses the dynamics of carbon balance and component CO2 fluxes in four Southern Finnish Scots pine stands that covered the typical economic rotation time of 80 years. The study was based on direct flux measurements with chambers and eddy covariance (EC), and modelling of component CO2 fluxes. The net CO2 exchange of the stand was partitioned into component fluxes: photosynthesis of trees and ground vegetation, respiration of tree foliage and stems, and CO2 efflux from the soil. The relationships between the component fluxes and the environmental factors (light, temperature, atmospheric CO2, air humidity and soil moisture) were studied with mathematical modelling. The annual CO2 balance varied from a source of about 400 g C/m2 at a recently clearcut site to net CO2 uptake of 200 300 g C/m2 in a middle-aged (40-year-old) and a mature (75-year-old) stand. A 12-year-old sapling site was at the turning point from source to a sink of CO2. In the middle-aged stand, photosynthetic production was dominated by trees. Under closed pine canopies, ground vegetation accounted for 10 20% of stand photosynthesis whereas at the open sites the proportion and also the absolute photosynthesis of ground vegetation was much higher. The aboveground respiration was dominated by tree foliage which accounted for one third of the ecosystem respiration. Rate of wood respiration was in the order of 10% of total ecosystem respiration. CO2 efflux from the soil dominated the ecosystem respiratory fluxes in all phases of stand development. Instantaneous and delayed responses to the environmental driving factors could predict well within-year variability in photosynthetic production: In the short term and during the growing season photosynthesis follows primarily light while the seasonal variation is more strongly connected to temperature. The temperature relationship of the annual cycle of photosynthesis was found to be almost equal in the southern boreal zone and at the timberline in the northern boreal zone. The respiratory fluxes showed instantaneous and seasonal temperature relationships but they could also be connected to photosynthesis at an annual timescale.
  • Mikkola, Reija (2013)
    Carbon capture and storage may become an inevitable means in mitigating climate change. However, it is a new technology involving a great deal of uncertainties. It is of utmost importance to understand on one hand, the risks caused by the technology and on the other, what is holding it back. This way unforeseen setbacks and environmental or other damage could be avoided. This thesis is a part of a wider research project on the risk governance of carbon dioxide capture and storage (RICCS). The present study gives additional insights to CCS risk analysis by diving into the stories that the media tells about the risks. I analyze the media coverage on the risks of CCS in the most wide spread newspapers of Norway and Finland with the aim of identifying what kind of risk framings are portrayed by the media; how strong is the presence of uncertainties and what kind of uncertainties are brought up. The media is seen as a mirror of public perception, but also one of the players influencing it. The possible effects that the analyzed articles could have on public perception of risks are discussed. The theoretical framework consists of theories of systemic risks, narrative policy analysis and framing of environmental risks in the media. I describe the nature of systemic risks. Then I move on to framing, more specifically how environmental risks are framed in the media and how it can effect public perception. After this I explain how narrative analysis can be used as a tool for identifying framings. Then I describe Klinke and Renn’s Prometheus theory that I will use for analyzing the level of uncertainty in the framing of the articles and for discussing the implications of my findings. The results show that the risks caused by CCS are mainly the lock-in in fossil fuels, it’s possible negative effect on developing renewable energy and environmental and health risks in general. The risks towards successful CCS seem to be mainly connected to funding, which connects to emissions’ prices, the climate agreement and viability of investments. The differences between the two countries are quite related to the situation in which each country is in terms of CCS development. Norway is very active and pushing CCS forward. Consequently, the Norwegian articles are generally not very critical of the technology itself, but discuss what is holding it back. Generally, the Finnish articles bring out more aspects on the issue, both positive and negative, leaving quite an ambiguous image to the reader. The implications of my findings for future policy practices are quite extensive and therefore not very useful, since most policy recommendations seem more or less relevant. What is interesting though, is that based on my findings I could identify the turning points in which public perception is most relevant. These are: What kind of energy production is supported? Is CCS an acceptable mitigation means? Is the risk of leakage taken as severe? These issues represent turning points for the future of CCS technology and deliberative processes can be crucial when discussing them.
  • Huotari, Jussi (Helsingin yliopisto, 2011)
    Lakes serve as sites for terrestrially fixed carbon to be remineralized and transferred back to the atmosphere. Their role in regional carbon cycling is especially important in the Boreal Zone, where lakes can cover up to 20% of the land area. Boreal lakes are often characterized by the presence of a brown water colour, which implies high levels of dissolved organic carbon from the surrounding terrestrial ecosystem, but the load of inorganic carbon from the catchment is largely unknown. Organic carbon is transformed to methane (CH4) and carbon dioxide (CO2) in biological processes that result in lake water gas concentrations that increase above atmospheric equilibrium, thus making boreal lakes as sources of these important greenhouse gases. However, flux estimates are often based on sporadic sampling and modelling and actual flux measurements are scarce. Thus, the detailed temporal flux dynamics of greenhouse gases are still largely unknown. ----- One aim here was to reveal the natural dynamics of CH4 and CO2 concentrations and fluxes in a small boreal lake. The other aim was to test the applicability of a measuring technique for CO2 flux, i.e. the eddy covariance (EC) technique, and a computational method for estimation of primary production and community respiration, both commonly used in terrestrial research, in this lake. Continuous surface water CO2 concentration measurements, also needed in free-water applications to estimate primary production and community respiration, were used over two open water periods in a study of CO2 concentration dynamics. Traditional methods were also used to measure gas concentration and fluxes. The study lake, Valkea-Kotinen, is a small, humic, headwater lake within an old-growth forest catchment with no local anthropogenic disturbance and thus possible changes in gas dynamics reflect the natural variability in lake ecosystems. CH4 accumulated under the ice and in the hypolimnion during summer stratification. The surface water CH4 concentration was always above atmospheric equilibrium and thus the lake was a continuous source of CH4 to the atmosphere. However, the annual CH4 fluxes were small, i.e. 0.11 mol m-2 yr-1, and the timing of fluxes differed from that of other published estimates. The highest fluxes are usually measured in spring after ice melt but in Lake Valkea-Kotinen CH4 was effectively oxidised in spring and highest effluxes occurred in autumn after summer stratification period. CO2 also accumulated under the ice and the hypolimnetic CO2 concentration increased steadily during stratification period. The surface water CO2 concentration was highest in spring and in autumn, whereas during the stable stratification it was sometimes under atmospheric equilibrium. It showed diel, daily and seasonal variation; the diel cycle was clearly driven by light and thus reflected the metabolism of the lacustrine ecosystem. However, the diel cycle was sometimes blurred by injection of hypolimnetic water rich in CO2 and the surface water CO2 concentration was thus controlled by stratification dynamics. The highest CO2 fluxes were measured in spring, autumn and during those hypolimnetic injections causing bursts of CO2 comparable with the spring and autumn fluxes. The annual fluxes averaged 77 (±11 SD) g C m-2 yr-1. In estimating the importance of the lake in recycling terrestrial carbon, the flux was normalized to the catchment area and this normalized flux was compared with net ecosystem production estimates of -50 to 200 g C m-2 yr-1 from unmanaged forests in corresponding temperature and precipitation regimes in the literature. Within this range the flux of Lake Valkea-Kotinen yielded from the increase in source of the surrounding forest by 20% to decrease in sink by 5%. The free water approach gave primary production and community respiration estimates of 5- and 16-fold, respectively, compared with traditional bottle incubations during a 5-day testing period in autumn. The results are in parallel with findings in the literature. Both methods adopted from the terrestrial community also proved useful in lake studies. A large percentage of the EC data was rejected, due to the unfulfilled prerequisites of the method. However, the amount of data accepted remained large compared with what would be feasible with traditional methods. Use of the EC method revealed underestimation of the widely used gas exchange model and suggests simultaneous measurements of actual turbulence at the water surface with comparison of the different gas flux methods to revise the parameterization of the gas transfer velocity used in the models.
  • Strakova, Petra (Finnish Society of Forest Science, Finnish Forest Research Institute, Faculty of Agriculture and Forestry of the University of Helsinki, School of Forest Sciences of the University of Eastern Finland, 2010)
    Pristine peatlands are carbon (C) accumulating wetland ecosystems sustained by a high water level (WL) and consequent anoxia that slows down decomposition. Persistent WL drawdown as a response to climate and/or land-use change directly affects decomposition: increased oxygenation stimulates decomposition of the old C (peat) sequestered under prior anoxic conditions. Responses of the new C (plant litter) in terms of quality, production and decomposability, and the consequences for the whole C cycle of peatlands are not fully understood. WL drawdown induces changes in plant community resulting in shift in dominance from Sphagnum and graminoids to shrubs and trees. There is increasing evidence that the indirect effects of WL drawdown via the changes in plant communities will have more impact on the ecosystem C cycling than any direct effects. The aim of this study is to disentangle the direct and indirect effects of WL drawdown on the new C by measuring the relative importance of 1) environmental parameters (WL depth, temperature, soil chemistry) and 2) plant community composition on litter production, microbial activity, litter decomposition rates and, consequently, on the C accumulation. This information is crucial for modelling C cycle under changing climate and/or land-use. The effects of WL drawdown were tested in a large-scale experiment with manipulated WL at two time scales and three nutrient regimes. Furthermore, the effect of climate on litter decomposability was tested along a north-south gradient. Additionally, a novel method for estimating litter chemical quality and decomposability was explored by combining Near infrared spectroscopy with multivariate modelling. WL drawdown had direct effects on litter quality, microbial community composition and activity and litter decomposition rates. However, the direct effects of WL drawdown were overruled by the indirect effects via changes in litter type composition and production. Short-term (years) responses to WL drawdown were small. In long-term (decades), dramatically increased litter inputs resulted in large accumulation of organic matter in spite of increased decomposition rates. Further, the quality of the accumulated matter greatly changed from that accumulated in pristine conditions. The response of a peatland ecosystem to persistent WL drawdown was more pronounced at sites with more nutrients. The study demonstrates that the shift in vegetation composition as a response to climate and/or land-use change is the main factor affecting peatland ecosystem C cycle and thus dynamic vegetation is a necessity in any models applied for estimating responses of C fluxes to changes in the environment. The time scale for vegetation changes caused by hydrological changes needs to extend to decades. This study provides grouping of litter types (plant species and part) into functional types based on their chemical quality and/or decomposability that the models could utilize. Further, the results clearly show a drop in soil temperature as a response to WL drawdown when an initially open peatland converts into a forest ecosystem, which has not yet been considered in the existing models.
  • Zhang, Huizhong (Helsingin yliopisto, 2014)
    Lakes play an important role in both global and regional carbon cycling, especially, the role of lakes is pronounced in the boreal zone, where lakes cover up to 20% of the land area. Allochthonous carbon is discharged mainly from terrestrial processes, but also through anthropogenic eutrophication. The role of allochthonous carbon load in lacustrine ecosystems is important, which can have far-reaching effects on lacustrine biogeochemistry in general and especially on carbon cycling. Part of dissolved organic carbon is transformed to carbon dioxide (CO2) and methane (CH4) in biological processes that result in carbon gas concentrations in water that increase above atmospheric equilibrium, thus making boreal lakes serve as sources of the important greenhouse gases. Lake Vesijärvi is renowned for its clear-water, but it has suffered eutrophication for a long history. The severely affected Enonslkä lake basin is the most eutrophic part since it surrounded mainly by urban area (28%) and forests (31%). To improve the water quality, large scale aeration in the autumn 2009 was started with the Mixox-oxygenerators. Aeration is used to weaken thermal stratification and recharge oxygen by increasing vertical flow circulation within the water columns. This leads to most chemical cocnetrations become more homogenous with depth and concentrations of reduced forms decrease in the hypolimnion. The aeration units were operated on campaign basis in summer 2013. One aim here was to investigate carbon gas concentrations and fluxes from the urban boreal lake basin, and examine the impacts of artificial aeration on greenhouse gases during the open water period in 2013. Besides CO2 and CH4 concentrations and fluxes, I measured also the water temperature and dissolved oxygen concentration of the water columns for monitoring the efficiency of artificial aeration. All gas samples were analyzed at the Lammi Biological Station of University of Helsinki with gas chromatography using the head space technique. As background data I used the information on temperature and oxygen profiles collected from the measuring platform on Lake Vesijärvi, and a reference study on CO2 and CH4 concentrations and fluxes dating back to 2005 when there was no aeration going on. In 2013, the studied lake basin was a source of CO2 to the atmosphere during the open water period, although the lake basin showed uptake of CO2 from the atmosphere for short times. The lake acted as a steady source of CH4 to the atmosphere throughout the measuring period. The mean CO2 flux was 34.1 mmol m-2 d-1, which was over 2.5 times higher than in the reference year 2005 when there was no the aeration yet. During the campaigns, the CO2 fluxes were higher from aerated than non-aerated water column and from the longer aerations as well. Therefore, aeration mixed stratified water columns and thus enhanced release of gases such as CO2 from surface water to the atmosphere. The mean CH4 flux was 0.2 mmol m-2 d-1. The CH4 fluxes from the Enonselkä basin were slightly decreased in 2013. These decreased CH4 fluxes in Enonselkä basin can be attributed to the limited CH4 production and high rate of CH4 oxidation in the oxygenated hypolimnion and surface of sediment. The daily CH4 fluxes fluxes during the long time aerated operations decreased. The significance of aeration to carbon cycling processes dpended on the residual CH4 concentrations in the water column.