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In Germany, basic data on the biology, ecology and distribution of rare mosquito species are insufficiently recorded leading to knowledge gaps, for example regarding their vector potential. The introduction of new mosquito species and of the pathogens they transmit has increased the risk of diseases previously uncommon in Germany. These circumstances have led to increased efforts within the past 10 years to better understand the spatio-temporal occurrence and underlying habitat binding of mosquito species and to predict their future distribution, particularly with regard to the changing climatic conditions and changing landscape. A reliable morphological and genetic identification was lacking for several native mosquito species, which forms the basis for any robust monitoring within mosquito surveillance programs or insect conservation projects.
The aim of this thesis was to gain detailed knowledge on the current spatial and temporal occurrence, the habitat binding, and morphological and genetic features with regard to species identification for the non-native species Aedes albopictus (Skuse, 1895), the native species of the Aedes Annulipes Group, and the native and rare species Aedes refiki Medschid, 1928, Culex martinii Medschid, 1930 and Culiseta ochroptera (Peus, 1935).
The thesis compares the suitability of the local climate for the persistence of the species Aedes albopictus sporadically observed in Jena (Thuringia) from 2015 to 2018 with two populations in southern Germany. The focus was on the analysis of extreme winter temperatures and the duration below selected temperature thresholds. In addition to critical temperature conditions, aquatic habitat conditions were of importance. The results of this study suggest that the population could become established in the long term.
Through the monitoring conducted for this thesis, the very rare mosquito species Aedes refiki, Culex martinii in Thuringia and Culiseta ochroptera were rediscovered at several sites in northern and eastern Germany. It was possible to add new information on habitat binding, distribution and abundance for the considered mosquito species. The survival of these rare native mosquito species depends on the preservation of a few remaining habitats. In addition, it can be assumed that these species will become even rarer with future climate change in Germany and, therefore, should be considered endangered. In contrast, other mosquito species could benefit from an increase in average temperatures or precipitation in individual cases.
Due to the contribution to species identification, difficulties in the morphological and genetic identification of selected mosquito species native to Germany could be dispelled. Three forms each were assigned to the known morphological variants of Aedes refiki and Culiseta ochroptera and their peculiarities were described, as well as a new character for species identification was highlighted in the case of Culiseta ochroptera. Generated CO1 mtDNA sequences provide the first DNA-barcodes of Aedes refiki and Culex martinii for Germany.
In five native mosquito species of the Aedes Annulipes Group, twenty types of aberrant tarsal claws were illustrated and described in their morphology. Morphological peculiarities and an asymmetrical occurrence of the aberrant claw types were observed and possible causes for their development were discussed. Together with the development of a basic blueprint of mosquito tarsal claws, the results opened another field of research for the taxonomy, developmental biology and aquatic ecology of arthropods.
Peatlands are the most space-efficient terrestrial carbon sink on earth, storing more carbon than all other vegetation types in the world combined. The amount of carbon input into peatlands is determined by the primary production and decomposition of plants. The fragile relationship between these two processes is massively disturbed by intensive land use and the associated drainage of large peatland areas, releasing as much carbon dioxide annually as global air travel. Aiming for the substantial reduction of greenhouse gas emissions, rewetting measures have been initiated worldwide to protect and sustainably manage peatlands by restoring the waterlogged conditions required for peat formation. However, the increase in droughts across Europe adds another threat for peatlands by lowering water tables and affecting plant productivity, litter decomposition and phenology, which can reduce their potential for carbon storage.
Fens are minerotrophic peatlands that make up over a third of the peatland area in Europe. The growth and turnover of root biomass is particularly important for the formation and degradation of peat in fens; thus, a special focus should lie on root dynamics research. However, despite their pivotal role for peat formation, we still lack knowledge about root responses to environmental changes caused by rewetting or drought in fens. This thesis aims to advance our knowledge about root processes as well as their abiotic drivers in drained and rewetted fen peatlands of NE Germany, and how they may be affected by an extreme drought. For this purpose, destructive (i.e. in-growth cores, litter bags, soil coring) along with non-destructive measurements (i.e. minirhizotrons, NDVI) were used in situ in forested (alder forests) and graminoid-dominated (sedges and grasses) plant communities representative of the prevailing fen peatlands of Central Europe.
In this thesis, I investigate the environmental drivers of root growth (Chapters I-III), the annual production and decomposition (Chapter II), phenology and temporal dynamics of root growth (Chapters I and III), and the response of root biomass distribution and their functional traits to environmental changes linked to rewetting (Chapter IV). To understand the fundamental differences in productivity of plant communities on mineral and organic soils, above-and belowground phenology and their environmental drivers were compared among different temperate ecosystems (i.e. a beech forest, a forested peatland and two graminoid-dominated fen peatlands) in Central Europe (Chapter I). The study provides evidence that generalizations of aboveground to belowground production are not likely to reflect seasonal dynamics in temperate fen peatlands. Furthermore, the study shows that fine root production can be up to 10 times higher for peatland plant communities than for a beech forest on mineral soil, highlighting the importance of roots for contributing substantially to the formation of organic soils. By comparing annual productivity and decomposition between drained and rewetted fens, it is shown that rewetted fens maintained their productivity under the drought conditions experienced in Central Europe in the year 2018, leading to a higher carbon storage potential despite similar decomposition rates (Chapter II). A deeper understanding on the drivers of this high productivity in the rewetted sites is provided by the analysis of temporal dynamics of root growth and their potential abiotic drivers (Chapter III). Here, the important role of root phenology in the maintenance of productivity of rewetted fens under drought conditions is revealed, since higher root productivity in response to rewetting was driven by an extension of the growing season rather than through a higher growth rate (Chapter III). This thesis shows that rewetting can be beneficial for plant production under drought conditions, which is central to the maintenance of the carbon sink function of peatlands (Chapters II and III). Rewetting maintained high water tables, favouring a plant community adapted to water saturation and also to fluctuating environmental conditions, and thus a community able to cope with periodic water table drawdowns that might increase in the future. Contrarily, drainage caused water tables to constantly drop below rooting depth of plants that might be adapted to drier conditions, but not drought. To gain a deeper understanding of the changes that roots undergo with rewetting and their potential effects on soil carbon storage, a fourth study focuses on the changes in biomass distribution and functional traits of roots along the soil profile (Chapter IV). Together with root age determination the study indicates higher rates of carbon turnover in shallow soil layers and higher belowground carbon investments with rewetting compared to drainage in a forested peatland.
This thesis demonstrates that generalizations of phenological events from plant communities of mineral to organic soils, even though they face the same macroclimatic conditions, are misleading, as they are not subject of the same environmental controls (Chapter I). Rewetting of forest and graminoid-dominated fen peatlands supports their function as carbon sink by enhancing renewed carbon sequestration in form of root biomass (Chapters II-IV). Knowledge about root phenology is crucial to understand plant productivity of peatlands, one of the main drivers of organic matter accumulation (Chapter III). Even though roots are pivotal for mediating the input of carbon into the soil, their dynamics remain one of the least understood aspects of plant function. This thesis contributes to fill this knowledge gap by shedding light on root processes that contribute to the formation of peat and the complexity of the underlying abiotic drivers in rewetted and drained fens in face of a warmer and drier climate.
Over thousands of years, peatlands around the world have accumulated carbon (C) stocks of global importance. Drainage for agriculture, forestry and peat extraction has transformed many peatlands from long-term sinks into strong sources of carbon dioxide (CO2). Peat extraction is worldwide responsible for about ten percent of drained peatlands and is mainly carried out in northern countries and Eastern Europe. In Belarus, 0.3 Mha of peatlands are drained for peat extraction, which is twelve percent of the country's peatland area. From 2006 to 2013, 21,333 ha of this area have been rewetted to protect these peatlands from fire and further degradation, reduce their greenhouse gas (GHG) emissions, turn them back into C sinks and promote biodiversity. A further 260,000 ha are no longer used for peat extraction and their rewetting would be a great benefit for nature conservation and climate protection.
Rewetting of abandoned peat extraction areas usually leads to inundation of large areas where not adapted plants die and new species establish, depending on water level and nutrient conditions. Beavers, of which there are many in Belarus, also play an important role in the rewetting of peatlands. They dam up ditches in drained and rewetted peatlands, thus contributing to water level increases and vegetation changes. The aim of this PhD thesis was to investigate the impact of inundation on vegetation and GHG emissions in formerly extracted fens in Belarus, to determine the role of water level in this process, and to study whether such fens develop back into C sinks with an almost neutral GHG balance within one or two decades after rewetting (Papers II and III). Also the potential of beaver activities for peatland restoration was assessed (Paper III).
Two very different fens, rewetted after peat extraction, were chosen as study areas. The first one, Giel'cykaŭ Kašyl, is a former flood mire and was rewetted with water from the Jasiel'da River in 1985. During the study period 2010–2012 this site was a shallow lake (~ 1 m deep) dominated by very productive, tall reed. Shallower areas along the edges had a partly floating vegetation cover of cattail (Typha latifolia, T. angustifolia) and sedges (Carex elata, C. vesicaria). The second fen, Barcianicha, is fed by groundwater. Rewetting from 1995 onwards resulted in water levels at or slightly above surface and a lower nutrient availability compared to Giel'cykaŭ Kašyl'. This was reflected in the establishment of mesotrophic communities of Eriophorum angustifolium and Carex rostrata. Phragmites australis stands, which were also dominant here, were shorter and less productive than in Giel'cykaŭ Kašyl'. The southern area of Barcianicha was not used for peat extraction and has not been rewetted. Until 2009 vegetation of this part was characterized by forbs (Urtica dioica) and wet meadows (Agrostis stolonifera). From autumn 2009, a beaver dam in the main drainage ditch caused flooding of these areas and led to diverging vegetation development depending on water levels.
Within the framework of this doctoral thesis annual fluxes of CO2, methane (CH4) and nitrous oxide (N2O) and the development of water levels and vegetation were monitored for two years at nine sites and evaluated (Papers II and III). Three of the sites, respectively, were located (a) in Giel’cykaŭ Kašyl’, flooded in 1985, (b) in the central area of Barcianicha, which was rewetted in 1995, and (c) in the southern part of Barcianicha, which was flooded by beavers end of 2009. GHG measurements were carried out with manual chambers from August 2010 to September 2012. Annual net CO2 exchange rates (NEE) were modeled based on light response curves of gross primary production (GPP) and on temperature response curves of ecosystem respiration (Reco), which were determined every third to fourth week by alternating measurements with transparent (cooled) and opaque chambers (both with fan) along the daily amplitude of photosynthetically active radiation (PAR) and temperature. Annual CH4 emissions were calculated mainly based on the temperature response of CH4 fluxes over the course of the year, based on biweekly (in summer) to monthly (in winter) repeated single measurements with opaque chambers (without fan). This was done, although all longer rewetted sites were dominated by aerenchymatic plants whose gas transport during the vegetation period may change over the course of the day and can be influenced by shading. This might apply to the six longer rewetted sites, two of which were dominated by Phragmites australis, and the others by Typha latifolia, Carex elata, Carex rostrata or Eriophorum angustifolium. For these six sites therefore studies on the daily course of CH4 release and the influence of chamber shade were conducted, covering 8–24 hours and lasting at least from sunrise to afternoon. Also the extent to which flux rates were affected by a lack of chamber headspace mixing by fans was investigated in the mentioned studies (Papers I and II).
The daytime course of CH4 emissions showed a pronounced dynamic for Phragmites australis in both fens, with minimum release during the night and maximum during the day (Paper I). The other sites in contrast did not show a significant diurnal CH4 flux dynamic (Paper II). Lack of headspace mixing by fans as compared to chambers with fan resulted in a slight underestimation of CH4 emissions at very high chambers (220 and 250 cm), as used for Phragmites australis in Giel'cykaŭ Kašyl', while there was no difference at lower chambers (≤185 cm), as used for the other sites. Opaque chambers resulted for sites dominated by Typha latifolia and Carex elata in significantly (1.2 times and 1.1 times, respectively) lower CH4 fluxes compared to transparent chambers. For the other sites, opaque chambers did not significantly reduce CH4 emissions. This result was unexpected, especially for Phragmites australis, as PAR out of all parameters tested had the strongest influence on CH4 emissions from both reed sites, and clouds directly led to reduction of their emissions. Presumably the gas flow in the reed shoots located within opaque chambers was maintained by shoots outside the chamber that were connected to the enclosed shoots by rhizomes (Paper I). The investigations showed that single measurements between 9 a.m. and 6 p.m. with opaque chambers without fan, as performed for the determination of annual CH4 fluxes, resulted for Carex rostrata and Eriophorum angustifolium in estimates similar to the daily mean, but for Phragmites australis in estimates that were rather above the daily mean. Annual CH4 fluxes from Phragmites australis could therefore be slightly overestimated. CH4 fluxes from Typha latifolia and Carex elata during the vegetation period were corrected by a factor of 1.2, although darkness inside of opaque chambers matters only at day, not at night. Daily and annual CH4 fluxes from these sites have been therefore most likely slightly overestimated, too.
Water saturation and the establishment of adapted vegetation were the most important conditions for the restoration of C sinks (gaseous CO2 and CH4 fluxes) in the investigated peatlands. The only site with falling water levels in summer and thus temporarily aerated peat was the beaver flooded forbs (Urtica dioica) site at Barcianicha. This site was a very strong CO2 emitter and the only significant N2O source of the entire study (Paper III). All other sites were permanently wet, had much lower CO2 emissions or were even net C sinks (Papers II and III). Establishment of adapted vegetation depended on inundation depth and time since rewetting. For example, within one year the meadow site in Barcianicha shallowly flooded by beaver was colonized by Carex rostrata and other adapted helophytes and developed into a CO2 sink, while the deeper flooded site at the same meadow initially attracted only Chara and some individuals of Alisma plantago aquatica and remained a moderate CO2 source. However, the results of the longer rewetted sites show, that also deeply (~ 1 m) flooded fen areas can become densely populated with mire plants in the course of 25 years and develop into net C sinks. Highest annual C uptake in both fens was achieved by the reed sites. Eriophorum angustifolium and Carex rostrata in mesotrophic Barcianicha were smaller C sinks. Typha latifolia and Carex elata in the eutrophic Giel'cykaŭ Kašyl', on the other hand, released CO2, presumably because the high and fluctuating water levels imposed stress to the plants, and because the large supply of nutrients and dead plant material allowed for strong heterotrophic respiration (Paper II). The simultaneously high CH4 emissions made Typha latifolia and Carex elata major sources of GHG. CH4 emissions from Phragmites australis in Giel'cykaŭ Kašyl' were even higher, but due to extremely high CO2 uptake the site was only a small net GHG source. CH4 emissions in Barcianicha were much lower and comparable to undisturbed sedge fens. The difference between Giel'cykaŭ Kašyl' and Barcianicha was mainly due to the different nutrient supply and the related productivity of the plants. Important conclusions are that stable inundation is an appropriate measure for restoration of the C sink of formerly extracted fens, but nutrient input with water needs to be stopped or reduced in order to decrease CH4 production. If this is not possible, establishment of Phragmites australis and other strong C sinks could help to compensate for the climate impact of high CH4 emissions from eutrophic sites.
The effect of the beaver dam on the development of the southern part of Barcianicha depended not only on the initial situation but mainly on the water level. Under optimal conditions, it led to the rapid establishment of adapted mire plants, the restoration of a C sink and a significant reduction of GHG emissions. However, this situation in the shallowly flooded meadow was achieved by chance. In comparison to planned rewetting measures, which aim to raise the water level evenly over the entire peatland, beavers dam ditches in order to improve their immediate habitat, thus influencing water levels only up to a certain distance, but rarely over the entire peatland. Nevertheless, beaver activity is of high value both for mire conservation projects, where existing dams are supplemented by beaver dams, and for abandoned, drained peatlands, like former peat extraction areas in Belarus, many of which at least partially have been rewetted by beavers.
The genus Sphagnum (L.) belongs to the Bryophyte plant division and includes 150 to 400 species. As all mosses Sphagnum has no roots and can hardly regulate its water uptake. As long as enough water is available Sphagnum can grow nearly unlimited while the lower, older parts die off and may accumulate as peat. Single Sphagnum species are able to build up an acrotelm as a hydrological self-regulating mechanism of a bog, a type of intact peatland (mire) only fed by precipitation. Because Sphagnum dominates nearly half of the peatlands in the world, it is one of the globally most important peat formers.
Sphagnum biomass is an important raw material for many valuable products, but in a much larger scale Sphagnum is used in its fossil state – as Sphagnum peat. With a consumption of c. 40 million m³ per year globally, Sphagnum peat is the predominant raw material for horticultural growing media. To get Sphagnum biomass it is currently collected from wild populations, to get Sphagnum peat it is extracted from bogs.
By far, more peatlands (including bogs) are subjects to drainage for agri- and silvicultural use since centuries, which harms their ecosystem services, including their typical biodiversity, carbon storage capacity, water regulation function and palaeo-environmental archive. In Europe, c. 25 % of all peatlands are used for agriculture, in Germany more than 80 %. Globally drained peatlands cover 0.4 % of land surface but produce 5 % of all anthropogenic greenhouse gas emissions.
Sphagnum farming aims to cultivate Sphagnum biomass on rewetted degraded bogs as a new agricultural crop. Sphagnum farming is paludiculture and contributes to the protection of bogs and their peat by conserving the peat body through rewetting and by offering a climate-friendly alternative to fossil peat in horticulture. Next to climate change mitigation, Sphagnum farming has benefits for nutrient retention and biodiversity conservation.
This thesis contributes to the development of Sphagnum farming by studying the conditions under which Sphagnum may reach maximal growth. Under (semi)controlled glasshouse conditions, we tested the effects of different water regimes and fertilisation levels on the productivity of various Sphagnum species. On a 1260 m² large irrigated field on cut-over bog in Lower Saxony (Germany) we studied length increase, biomass productivity and tissue nutrient content of Sphagnum over a period of 10 years. Finally, we reviewed all scientific literature and practical experiences with respect to Sphagnum farming worldwide as a first step towards a science-based implementation manual.
The main conclusions of our studies are:
1. It is possible to cultivate Sphagnum on rewetted cut-over bog and on rewetted former bog grassland.
2. The rapid establishment of a closed, highly productive Sphagnum lawn requires the deployment of a loose, >1(–5) cm thick Sphagnum layer (80–100 m³ of Sphagnum founder material per hectare) at the start of the growing season (when long frost periods are no longer probable) and adequate water supply.
3. Water table management must be very precise until a dense, well-growing Sphagnum lawn has established. For highest yields the water table should rise with Sphagnum growth and be kept a few centimetres below the Sphagnum capitula. Water supply via open irrigation ditches seems to function better than via subsurface irrigation pipes.
4. Fertilisation does not increase Sphagnum productivity on sites with high atmospheric nitrogen deposition and irrigation with phosphate-rich surface water from the agricultural surroundings. To avoid growth reduction a balanced stoichiometry is important.
5. From all studied species, Sphagnum fallax has the highest productivity. Its fast decomposition and low water holding capacity, however, may make this species less suitable for use in horticultural substrates.
6. Vascular plant cover on Sphagnum production fields can be kept low (<50 % cover) by regular mowing. Higher covers retard Sphagnum growth and reduce its quality for growing media.
7. Pathogenic fungi occurred far more in the glasshouse than in the field and have to be controlled for highest Sphagnum yields. We found Sphagnum vitality and growth rate to be stimulated by high water levels, where Sphagnum is less vulnerable to fungal or algal infection despite high nutrient loads.
8. The rate of Sphagnum biomass accumulation may remain constant over at least 4–5 years after establishing a Sphagnum production field with sufficient water supply. At dry conditions Sphagnum biomass accumulation is lower as a result of lower biomass productivity and higher decomposition rates.
Das Gezeter des Seggenrohrsängers, die Alarmrufe der Uferschnepfe, das Gemecker der Bekassine, das Geschnarre des Wachtelkönigs und die Pfiffe des Tüpfelsumpfhuhns - kaum ein anderer Lebensraum weist so viele exklusive Vogelarten auf wie die Flusstalmoore. Dieser Moortyp dominiert die Grundmoränenlandschaft des südlichen Ostseeraumes. Jedoch wurde auch kein anderer Lebensraum vom Menschen so gründlich in seiner ökologischen Funktionstüchtigkeit gestört. Insbesondere die grossflächigen und tief gehenden Entwässerungen des 20. Jahrhunderts führten zum Verstummen zahlreicher Vogelarten. So ist etwa der Seggenrohrsänger heute vom globalen Aussterben bedroht. In Nordostdeutschland wurden in den letzten 15 Jahren grosse Anstrengungen unternommen, die Ökosystemleistungen der Flusstalmoore neu zu beleben. Dazu wurden über 20 000 Hektar Moorfläche wiedervernässt. Wie reagiert die Vogelwelt auf diese neuen Veränderungen? Bestehen Chancen für eine Wiederansiedlung verschollener Vogelarten? Wie können die Wiedervernässungsmassnahmen gestaltet werden, um gefährdete Vogelarten zu begünstigen? Lässt sich das Leitbild des Artenschutzes mit den Leitbildern des Moor- und Klimaschutzes und zukünftigen Bewirtschaftungsformen vereinen? Diesen Fragen ist der Autor in einer umfassenden Studie von Vogelwelt, Vegetation und Hydrologie am Beispiel des Peene- und Trebeltals in Mecklenburg-Vorpommern nachgegangen und stellt seine Ergebnisse hier vor.
Late Quaternary evolution and carbon cycling of tropical peatlands in equatorial Southeast Asia
(2014)
Peatlands are an important component in the global carbon cycle as they act as both long-term sinks for carbon dioxide and significant sources for methane. Over the Holocene period (the past 11,700 years) continuous CO2 uptake by peat accumulation exceeded methane emissions in northern peatlands and resulted in a net-radiative cooling effect on the global climate.Although 11% of the global peatland area is located in the tropics, the role of tropical peatlands in the global carbon cycle and in influencing the Earth’s radiative budget has not been resolved. Climate-carbon cycle models have thus far not included tropical peatlands because reliable data on their past rates of carbon uptake and release are not available. In this thesis this problem has been approached by reconstructing peatland expansion and rates of carbon storage and release over the Late Quaternary (Latest Pleistocene and Holocene) for the largest tropical peatland area, which is located in equatorial SoutheastAsia (i.e. Sumatra, Borneo, Peninsular Malaysia). Peat accumulation in the tropics remains an enigmatic phenomenon, because the constantly high temperatures of 26-27°C should theoretically drive rapid soil carbon turnover and thus not enable the accumulation of peat. Therefore this thesis also explores the mechanisms that cause peat formation in the SoutheastAsian tropics as well as the drivers behind changing rates of carbon accumulation. Carbon dynamics were analyzed at the regional scale (103–105 km2) of SoutheastAsia over millennial timescales (paper, I, II) and at the local scale (101–102 m2) of a peatland site on annual to centennial timescales (paper III, IV). Paper I presents the first systematic classification of the nearly 160,000 km2 SoutheastAsian lowland peatlands (below 70 m a.s.l.) into geographic peatland types. The peatlands were divided into 1) coastal peatlands of PeninsularMalaysia, Sumatra, and Borneo (~130,000 km2) and into inland peatlands (~30,000 km2) of 2) Central Kalimantan (southern Borneo), 3) the Kutai basin (eastern Borneo), and 4) the Upper Kapuas basin (western Borneo). Coastal peatlands formed by primary mire formation directly on freshly exposed marine or mangrove soils with the lowering of the sea level during the Late Holocene. In contrast, inland peatlands formed via paludification on either terrestrial sand soils (Central Kalimantan) or by both paludification and terrestrialization (Kutai basin, Upper Kapuas basin). The sequence of peatland initiation was established by applying the common cumulative basal date frequency approach (paper I). This method revealed clear differences in the timing of peatland initiation: 1) the Upper Kapuas peatlands are the oldest postglacial peat formations and date from 20,000-13,000 cal BP (calendar years before present), 2) inland Central Kalimantan peatlands date from 14,500-9000 cal BP, 3) the Kutai peatlands date from 8300-4900 cal BP, and 4) and the coastal peatlands date from 7700-200 cal BP. Coastal peatlands have a Holocene average carbon accumulation rate of 77 g C m-2 yr-1, being recognized as the globally most effective terrestrial ecosystems in terms of long-term carbon sequestration. Except for the Kutai peatlands, the Holocene average carbon accumulation rates of inland peatlands are significantly lower (20-30 g C m-2 yr-1) and very similar to the average long-term rates of northern peatlands. Fluctuations in past rates of carbon accumulation of SoutheastAsian peatlands could for the first time be linked to paleoclimatic changes, primarily variations in moisture availability (paper I, II). Hydroclimatic influences on carbon accumulation rates were related to shifts in the mean position of the Intertropical Convergence Zone, changes in the intensity of theAustral-Asian monsoon system, and variations in the frequency of the El Niño- Southern Oscillation. In contrast, peatland initiation and expansion was driven by sea-level change (paper I, II). The deglacial rise in sea-level is identified as the primary driver for inland peatland formation in Borneo, because the rising sea-level 1) lowered the hydrological gradients in the SoutheastAsian island archipelago inducing rising ground and surface water levels on these islands, and 2) led to higher atmospheric moisture availability due to the associated expansion of marine water masses on the shelf floor. Paper II shows that inland peatland initiation and expansion was most extensive during deglacial meltwater pulses, when the rate of sea-level rise exceeded 10 mm yr-1. Only when the rate of sea-level rise had slowed down to a threshold of 2.4 mm yr-1 by ~7000 cal BP could peat accumulation along the coasts keep up with the sea-level rise and coastal peatlands could form. Hydro-isostatic adjustment of the Sunda Shelf led to a sea-level lowering by ca. 5 m over the past 4500 years. Falling sea levels exposed extensive marine areas that were rapidly colonized by peat swamp forests.Anewly 140 developed method for the reconstruction of past peatland area based on transfer functions (paper II) reveals that 70%of the peatlands of Sumatra and Kalimantan only formed during the past 4000 years.Moreover, this new transfer function approach shows that the common basal dates approach overestimated the extent of peatlands in the past. This method, in general, leads to higher rates of reconstructed cumulative peat carbon uptake for the past. By combining reconstructed peatland areas and mean rates of carbon accumulation over millennial timescales from each peatland type the carbon uptake of all peatlands from Sumatra and Kalimantan could be quantified for the past 15,000 years (paper II). Carbon uptake remained below 1 Teragram (Tg) C yr-1 from 15,000-5000 cal BP because the total area of peatlands was less than 30,000 km2. Rapid peatland expansion driven by the lowering of sea-level over the past 5000 years increased carbon uptake on Sumatra and Kalimantan to over 7 Tg C yr-1 and resulted in an exponential growth of the regional peat-carbon reservoir to a size of over 20 Pg C. SoutheastAsian peatlands therefore had no significant role in the Late Pleistocene and Early Holocene global carbon cycle. However, because of their rapid expansion after 5000 cal BP by over 100,000 km2 the peatlands of SoutheastAsia became a globally important carbon sink during the Late Holocene and likely caused an atmospheric CO2 drawdown of 1-2 ppm (paper II). This previously unrecognized biospheric carbon sink partly compensated for contemporaneous terrestrial carbon losses associated with the desertification of Northern Africa. The mechanisms that enable high rates of carbon accumulation of coastal peatlands were explored in a peat core study presented in paper III. Here the use of a new coring technique for the tropics and the application of noninvasive geophysical measurements were employed to derive a high-resolution record of carbon accumulation rates. This study provides the first description of peatland pools for SoutheastAsia, which form as tip-up pools from falling trees such as Shorea albida. Based on a pollen and macrofossil record a fossil tip-up pool could be identified in the core and an associated carbon accumulation rate of 100 to over 900 g C m-2 yr-1 determined. Thus tip-up pools function as local hot spots for carbon accumulation, fundamentally different from northern hemisphere peatland pools, which act as net-carbon sources. From a time-series of aerial photographs the rate of tree fall and thus pool formation was determined at 0.4 tree ha-1 yr-1 (paper III).Asimulation model indicates that up to 60%of the peat deposited in peat domes of Borneo is derived from filled up fossil pools – changing the paradigm that Southeast Asian peatlands mainly form from belowground biomass and providing an explanation for the rapid carbon accumulation of these ecosystems. The climate impact of peatlands is, however, not only related to their capacity to rapidly store carbon, because peatlands also release the strong greenhouse gas methane – a by-product of anaerobic decomposition.Ametaanalysis of methane emission data from SoutheastAsian peatlands (paper IV) shows that their average annual methane release of 3 g CH4 m-2 yr-1 is lower than the average annual release of ~9 g CH4 m-2 yr-1 from northern peatlands, although the higher tropical soil temperatures should lead to significantly higher emissions. The limited degree of anaerobic decay is explained by the recalcitrance of the deposited biomass, which contains high amounts of lignin and tannin, providing another explanation for rapid carbon accumulation. Low anaerobic decomposition together with high rates of carbon accumulation imply that limits to vertical peat bog growth in SoutheastAsia are not set by cumulative anaerobic decay as in northern raised bogs. Instead peat bog growth is limited by aerobic decomposition related to water-table lowering as shown by a derived linear relationship between the amount of released CO2 from aerobic peat decomposition and the mean annual depth of the peatland water-table (paper IV). The climatic effect of Southeast Asian peatlands was determined by the global warming potential (GWP) method, which compares carbon uptake with methane emissions in terms of CO2-equivalents. The low methane emissions and high carbon accumulation rates of coastal peatlands result in a net annual uptake of 1340 kg CO2- equiv. ha-1 yr-1 over a 100 year GWP time-horizon. Under natural conditions coastal Southeast peatlands exert a significant net cooling effect on the global climate in contrast to northern peatlands, which have a warming effect or act climatic neutral on this time frame. It can be concluded that the tropical peatlands of SoutheastAsia are the strongest carbon sinks among all peatlands globally with a notable influence on the Earth’s radiative budget. However, today an estimated 90,000 km2 of peatlands in SoutheastAsia is drained for agriculture (e.g. oil palm plantations) and deforestation. These drained peatlands release annually over 140 Tg C yr-1 from aerobic peat 141 decomposition. Drainage also facilitates the regular spread of peat fires in this region, which on average release around 75 Tg C yr-1. Ongoing total carbon losses (~220 Tg C yr-1) exceed the natural carbon uptake by a factor of 25 and demonstrate that the entire SoutheastAsian peatland region has recently switched from a globally important carbon sink to a globally significant source of atmospheric CO2 (paper II, IV).
Carbon dioxide (CO2) is one of the most important factors of the Earth’s carbon cycle. Peatlands are well-known to be a long term sink for atmospheric carbon dioxide. Under changing environmental conditions, the carbon balance and hence the CO2 fluxes can be significantly changed, and peatlands may even become a significant atmospheric carbon source. To be able to predict the changes in climatic conditions and their effects on ecosystems, it is important to understand the contemporary CO2 exchange of the ecosystems. Many studies on peatland CO2 fluxes have been conducted in the boreal zone of North America and Scandinavia. Still little scientific evidence is available from peatland ecosystems of boreal Russia. This dissertation presents the detailed investigation of CO2 dynamics and the relevant processes and environmental factors from the boreal peatland site Ust-Pojeg (61°56'N, 50°13'E) in Komi Republic, northwest Russia. On the small spatial scale (microform), the investigated peatland was characterised by high variability in vegetation composition and coverage as well as in water table level which resulted in large variability in CO2 fluxes not only between the microform types but also within one microform type. The cumulative flux over the investigation period for the different microforms ranged from strong CO2 sources to CO2 sinks. An area-weighted estimate for the entire peatland showed that it was a CO2 source for the investigation period, which was characterised by average conditions in terms of precipitation and temperature. The CO2 fluxes were measured at different scales: by the closed chamber method at the microform scale and by the eddy covariance technique at the ecosystem scale. Three different upscaling methods were used to compare the fluxes. Irrespective of the upscaling methods, the discrepancies between the estimates based on the upscaled chamber measurements and estimates based on measurements by the eddy covariance technique were high. The high spatial heterogeneity of the vegetation and the water table level and thus of the CO2 fluxes were recognised as reasons for high potential errors when upscaling CO2 fluxes from the microform to the ecosystem level. Large discrepancies were also observed in comparison between measured CO2 fluxes and CO2 estimates based on the mechanistic ecosystem model LPJ-GUESS. Insufficient model forcing may have led to errors in the timing of the onset and the end of the growing season, and the modelled vegetation did not always reproduce the observed vegetation. These two factors may have led to the discrepancies in the model-measurement comparison. Although the closed chamber technique is widely used for measurements of CO2 fluxes between ecosystems and the atmosphere, the errors which might occur during the measurement itself or which are associated with the used measurement devices as well as the flux calculation from chamber-based CO2 concentration data are still under discussion. The study showed that the CO2 fluxes measured by the closed chamber method can be overestimated during low-turbulence nighttime conditions and can be seriously biased by inappropriate application of linear regression for the flux calculation. The methodological studies were conducted at the boreal peatland Salmisuo in eastern Finland (62°46'N, 30°58'E). The methods developed in this dissertation could contribute significantly to improved CO2 flux estimates. VI