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Summary
Raised bogs are raised above the regional ground water level and only fed by rain. To be able to be ‘high yet wet’, they have developed intricate self-regulation mechanisms. The most important of these mechanisms in Sphagnum raised bogs is the acrotelm. This upper layer of peat and vegetation shows a distinct gradient from large pores at the top to small ones at the bottom. When the water table drops, water can only flow through small pores and run-off is effectively reduced. Still, the acrotelm has high storativity, which restricts water table fluctuations to this layer. The acrotelm presents a compromise between small pore space to minimise run-off and large pore space to maximise storativity.
These two ‘tasks’ of the acrotelm can also be split in horizontal space. The dry hummocks on the surface of a raised bog have much lower transmissivity and storativity than the wet hollows. These two surface elements can be organised in strikingly regular patterns of elongated strings of hummocks and so-called flarks of hollows arranged perpendicular to the slope. The origin of regular string-flark patterns was studied in chapter 2.
In a simple, heuristic, spatially explicit simulation model, each cell in a square grid is randomly declared either a hummock or a hollow. The grid is on a slope and water is allowed to flow from each cell to its four neighbouring cells until water tables stabilise. Then, every cells changes state based on its water table: if the water table is low, the cell will more likely be a hummock, if it is high a hollow. If the parameter settings are right, this procedure will result in regular striping patters. Chapter 2 was the first study to search the parameter space for settings that result in patterning. Systematic analysis showed that the parameter space in which patterns develop is sharply delineated, indicating positive feedback mechanisms. Once a pattern develops, water tables in the model diverge: the flarks become wetter and the strings become drier. The hummock and hollow cells have combined into higher order units, the strings and flarks, that emerge as more effective in regulating water flow.
Applying the same model for the first time to the dome shape of a raised bog (capther 3), pattern formation appeared to occur on three organisational levels. On the lowest nanotope level, we find strings and flarks, again combined in a string-flark complex, but this complex occurs alongside an all hummock rand and a wet, featureless central plateau. These three mire sites constitute the second, microtope level. On the third, mesotope level we can distinguish different types of bog domes that are defined by different combinations of mire sites. Classical literature on peatland classification used the same approach to classify bog domes, but also other and larger peatland areas. Our modelling shows that the mire sites actually exist as functional units in a self-organising bog and that they are not mere human classification constructs.
To test our ideas on self-regulation and -organisation as well as the modelling results, we studied a patterned raised bog in Tierra del Fuego in terms of its plant cover, its water and its peat (chapter 4). The studied bog is almost completely covered by Sphagnum magellanicum. In northern peatlands the different niches from high and dry hummock to low and wet hollow are filled by different species of Sphagnum, each with their specific growth form. In the studied bog, all niches from dry to wet are occupied by Spagnum magellanicum, showing a wide range in growth form. Yet, we found it has only limited genetic diversity that is not linked to these niches and growth forms.
Detailed measurements were made along a 498 m long transect crossing the bog, including water table measurements (every metre), vegetation relevés (2 × 2 m), hydraulic conductivity just below the water table (n = 246) and hydraulic conductivity in 11 depth profiles to a depth of 2 m (n = 291); the degree of humification of the corresponding peat was assessed in conjunction with the hydraulic conductivity measurements (n = 537). Sphagnum magellanicum moss samples were collected every 2 m along this transect and genotyped (n = 242). In addition, along short, 26 m long transects crossing strings and flarks water table and hydraulic conductivity just below the water table were measured every metre. Sphagnum growth forms were assessed and the vegetation of the entire bog was mapped in 10 × 10 m relevés (n = 3322). The simulation model was applied to a generalised form of the bog.
There was an almost perfect match between plant cover and water tables. As expected, hydraulic conductivity just below the water table was about 7 times lower in the dry than in the wet measurement spots. These observations are valid on the low level of the nanotope: hummocks and hollows or dry and wet spots in general. Other observations only made sense on higher organisational levels like the microtope. For example, the hydraulic conductivity profiles of the string-flark complex show a gentler gradient than those of the plateau and the rand. The peat in the string-flark complex originates on this level of organisation and combines characteristic of both its dry and wet constituents. On the mesotope level, the simulation model produced a good match with the patterns on the actual dome. We analysed the abundant data on different organisational levels ranging from small single plants to the large mire system of fens and domes of which the studied dome is part. We looked for commonalities and discrepancies to help us better understand how the close link between plants, water and peat functions in reality.
The results of all measurements were integrated with information from literature and discussed in the framework of a self-regulating and -organising raised bog. The field measurements considerably sharpened existing theoretical considerations. We identified nineteen hydrological feedback mechanisms. We found that the various mechanisms overlap both in space and time, which means there is redundancy in the self-regulation capacity of the system. Raised bogs, when in a natural state, are among the most resilient ecosystems known; resilience that is provided by feedbacks and back-up systems to these feedbacks.
We used our ideas and insights on self-regulation in Sphagnum raised bogs to look for similar patterns and responses in tropical domed peat swamps (chapter 5). We know that in Sphagnum raised bogs the tasks of the acrotelm can be split in horizontal space. When we looked at undisturbed tropical peat swamps with this new search image, we recognised how hummocks of root material and litter and particularly buttress roots regulate run-off and storage of water. We could identify several additional hydrological feedback loops that mirror the mechanisms found in Sphagnum raised bogs.
This thesis considerably advances our understanding of raised bogs as self-organising systems. The patterns and processes they display on multiple levels can be seen as a form of ecosystem diversity that exists independent of species and genetic diversity.
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.
High resolution palaeo-ecological analysis of an Arctic ice-wedge polygon mire (Kytalyk, NE Siberia)
(2020)
Ice-wedge polygon mires are typical features of the Artic and therefore especially affected by climate change. They show, caused by soil-ice action, an amazing regular polygonal structure in meter dimension of higher and lower elevated dry and wet parts, and to this microtopography adapted vegetation. Polygon mires play, analogous to other mires, an important role in carbon sequestration, water balance, wildlife habitat and archive value with local to global significance. By storing enormous amounts of the global soil carbon polygon mires are crucial for our climate. Despite this relevance by covering large areas, polygon mires are comparatively poorly scientifically investigated and understood. It is still difficult to make forecasts on how polygon mires will develop under a changing climate in the Arctic, especially because internal factors and self-organisation complicate the understanding of their functioning. Therefore the investigation of modern and past polygon mires is necessary. This dissertation presents high resolution palaeo-ecological studies of a Northeast Siberian model polygon: ice-wedge polygon Lhc11 located in the Indigirka Lowlands at the scientific station Kytalyk. During field work in July 2011 the study site, covering an area of 26 × 21 m was divided into 546 plots, in which vegetation composition and microtopographical elevation characteristics were assessed and surface samples were collected. For palaeoecological analysis a 105.5 cm long peat section was excavated from the same site. Cluster analysis revealed five plant communities, which are clearly separated with respect to ground surface height, frost surface height and coverages of open water and vegetation, confirming the pattern already identified in other studies of Arctic ice-wedge polygons. The correct recognition of these patterns is crucial in palaeoecological studies in order to reconstruct landscape elements and their dynamics. This recognition requires insight in the short-distance relationships between surface elevation/wetness, vegetation and pollen deposition. The applied pollen-vegetation reference study shows that in general modern pollen deposition in polygon Lhc11 corresponds well with actual vegetation, allowing accurate reconstruction of local site conditions from fossil palynomorph sequences, including the reconstruction of the dynamics of closely spaced microtopographical elements. We conducted an evaluation of common palaeo proxies to compare their wetness reconstruction potential. The analysed proxies macrofossils, pollen, testate amoebae, geochemistry and sediment properties show similar wetness trends. Macrofossils provided the most detailed wetness reconstruction, spanning several wetness classes from very dry to wet, because they could be identified to genus or species level. However, as the proxies sometimes show contradictory results, a multi-proxy approach is preferable over a single proxy interpretation as it allows the reconstruction of environmental development in a broader palaeoecological context. For a better understanding of polygon dynamics and former greenhouse gas fluxes, more detailed and better quantified palaeo-microtopographical information is required. Therefore we developed a new transfer approach for modelling past Ground Surface Heights (GSH) in polygon mires from plant fossils. Based on the composition of modern vegetation we constructed two sets of potential fossil types (plant macrofossils and pollen), an extensive and a more restricted one. We applied Canonical Correspondence Analysis to model the relationships between potential fossil types and measured GSH. Both models show a strong relationship between modelled and measured GSH values and a high accuracy in prediction. Finally, we used the models to predict GSH values for Holocene peat samples. We found a fair correspondence with expert-based multi-proxy reconstruction of wetness conditions, even though only a minor part of the encountered fossils were represented in the GSH models, illustrating the robustness of the approach. The method can thus be used to reconstruct palaeoenvironmental conditions in a more objective way and can serve as a template for further palaeoecological studies. The 4000 years lasting history of the Lhc11 polygon site started with the establishment of a low-centre polygon in a drained thermokarst lake basin. Polygon Lhc11 formed part of a low-centre polygon for about 2000 years, experiencing enormous environmental influences discernible by incidence of silt, charred detritus, change of fossils composition and strongly declined peat accumulation rates and finally developed into a mature and degradation stage, into a low-high-centre polygon, currently characterized by high elevation differences. In the context of less studied but large-scale polygon mire occurrence, the high-resolution analysed ice-wedge polygon Lhc11 delivers insights into state and dynamics of a representative Siberian polygon site, in terms of modern and past vegetation and elevation characteristics. Furthermore the present study provides facilities for palaeoecological polygon studies including a new quantitative elevation modelling approach and provides valuable datasets for future research, e.g. greenhouse gas emissions and therefore contributes to a better understanding of these climate relevant ecosystems.
Der rundblättrige Sonnentau (Drosera rotundifolia L.) ist typisch für nährstoffarme Hochmoore und nimmt eine besondere Rolle im Moor-Ökosystem ein. Die Pflanzenart gilt in vielen europäischen Ländern als gefährdet bzw. stark gefährdet. Ihre Gefährdung lässt sich auf drei Ursachen zurückführen:
1) Seit Jahrzehnten führt die Bewirtschaftung der europäischen Moore und die damit einhergehende Entwässerung und Düngung zu einem deutlichen Rückgang der von Drosera-Arten bevorzugten oligotrophen, nassen und sauren Standorte.
2) Bereits im Mittelalter waren Drosera-Arten als Heilpflanzen bekannt und wurden hauptsächlich zur Behandlung von Atemwegserkrankungen (Asthma, Bronchitis, Keuchhusten etc.) eingesetzt.
3) Obwohl seit den 1920er Jahren bereits immer wieder Kultivierungsversuche mit Drosera-Arten durchgeführt wurden, konnte bisher keine Methode für den großflächigen Anbau von Sonnentau realisiert werden, um die von der Pharmaindustrie benötigten Mengen des Drosera-Rohstoffs zu produzieren. Daher werden bis heute europäische und nicht europäische Drosera-Arten immer noch in großen Mengen in natürlichen Mooren gesammelt.
Die zunehmende Zerstörung der natürlichen Moore und die Sammlung für arzneiliche Zwecke stellen zusammen eine ernsthafte Bedrohung für den Erhalt von D. rotundifolia dar. Die Torfmooskultivierungsflächen in Deutschland sind in vieler Hinsicht vergleichbar mit intakten Hochmooren. Das nährstoffarme Milieu der kultivierten Torfmoose dient als Lebensraum für heimische Drosera-Arten, wie Drosera rotundifolia L. und Drosera intermedia Hayne. Daher bieten diese Kulturflächen eine neue Alternative für den Anbau von Drosera-Arten.
In vier Studien wurde die Eignung von Torfmoosrasen für den Drosera-Anbau untersucht, mit Schwerpunkt auf den Anbau von Drosera rotundifolia auf Torfmoos- kultivierungsflächen. In der ersten Studie wurde das Wissen über die Morphologie, Verbreitung, Ökologie, Reproduktion, Nutzung, den Schutz und den Anbau von D. rotundifolia erstmals zusammenfassend diskutiert, um eine wissenschaftliche Grundlage für einen erfolgreichen Anbau auf Torfmoosrasen zu schaffen. Basierend auf diesen Kenntnissen konzentriert sich die zweite Studie auf die Keimfähigkeit von D. rotundifolia und die Überlebensrate von jungen Drosera-Pflanzen auf Torfmoosrasen unter natürlichen, naturnahen und künstlichen Bedingungen. Die dritte Studie fokussiert auf den Gehalt pharmakologisch wirksamer Inhaltsstoffe angebauter und „wild wachsender“ D. rotundifolia- sowie D. intermedia-Pflanzen auf Torfmooskultivierungsflächen. Die vierte Studie untersucht die Biomasseproduktivität und den Ertrag, d. h. den Biomasseanteil der geerntet wird, von beiden o. g. Drosera-Arten auf Torfmooskultivierungsflächen.
Die generierten Daten und Erkenntnisse der vier Studien wurden in vier wissenschaftlichen Artikeln zusammengefasst, wovon zwei bereits veröffentlicht und zwei eingereicht sind.
Die wichtigsten Ergebnisse dieser Studien sind die Folgenden:
I) Drosera rotundifolia ist sehr stark mit Sphagnum-dominierten Pflanzengemeinschaften verbunden, welche durch Entwässerung europaweit zurückgegangen bzw. verschwunden sind. Dadurch ist D. rotundifolia in den meisten europäischen Ländern eine seltene und geschützte Pflanzenart geworden.
II) Verschiedene Drosera-Arten, u. a. D. rotundifolia, D. intermedia, D. anglica und D. madagascariensis, werden immer noch von Pharmaunternehmen verwendet. Die Pflanzen werden in der freien Natur gesammelt, weil deren Anbau zeitaufwendig und (noch) nicht effizient ist. Daher ist die Entwicklung von Anbaumethoden erforderlich.
III) Die selbstentwickelte „Torf-Gefäß-Methode“ ergab sich als die meist geeignete Drosera-Anbau-Methode durch das spezielle Mikroklima des Sphagnum- Rasens, das konkurrenzarme Milieu und den permanent nassen Sphagnum- Torf in den Pflanzgefäßen.
IV) In den Feldversuchen wurden bei der Aussaat sehr niedrige Keimungsraten < 1 % registriert. Deshalb sind für den Anbau mit Aussaat große Mengen an Samen erforderlich.
V) Die Entfernung von Gefäßpflanzen zeigte im ersten Jahr eine positive Korrelation mit der Anzahl der Drosera-Keimlinge und führte im zweiten Jahr zu einer höheren Anzahl überlebender Drosera-Pflanzen.
VI) Auf Torfmooskultivierungsflächen wachsende Drosera-rotundifolia-Pflanzen wiesen eine 7- bis 8-mal höhere Konzentration von 7-Methyljuglon auf als D. madagascariensis, die hauptsächlich für ‘Droserae herba’ verwendet wird.
VII) Für Drosera rotundifolia gab es bezüglich der Tageszeit keine signifikanten Unterschiede in den Konzentrationen bioaktiver Inhaltsstoffe. Dies bedeutet, sie kann ganztägig zwischen 7 und 16 Uhr gesammelt werden. Die höchsten Konzentrationen bioaktiver Inhaltsstoffe wurden für D. rotundifolia und D. intermedia bei 13 bis 24 Monate alten blühenden Pflanzen festgestellt
VIII) Im Vergleich zu natürlichen Mooren Mittel- und Nordeuropas, zeigte D. rotundifolia auf den Torfmooskultivierungsflächen eine 3-34 Mal höhere Biomasseproduktivität (275 kg ha-1 a-1) und einen 2-21 Mal höheren Ertrag (214 kg ha-1 a-1).
IX) Der höchste Ertrag von D. rotundifolia und D. intermedia wurde im Juli und August dokumentiert. In diesen Monaten erreichen die Pflanzen ihr höchstes Gewicht. Auf Torfmooskultivierungsflächen erreichte D. rotundifolia einen viermal höheren Ertrag als D. intermedia. Deshalb ist D. rotundifolia für den Anbau zu bevorzugen.
X) Für eine langfristige nachhaltige Produktion von Drosera wird die Ernte von mindestens 12 Monate alten Pflanzen empfohlen.
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.
Drainage has commonly been a pre-requisite for the productive use of peatlands. The biased focus on agriculture, forestry and peat extraction has long ignored the destructive effects of drainage and the successive degradation of ecosystem functions of wet peatlands. Accelerated by the climate crisis, the finite nature of drainage-based peatland use is increasingly recognised. Consequently, productive land use options for wet or rewetted peatlands (paludiculture) are required as sustainable alternatives. A wide range of paludiculture plants and options of biomass utilisation are identified as suitable and promising. Despite the growing interest, experiences with and research on the economic viability of paludiculture are still rare.
This thesis addresses the lack of knowledge on paludiculture in terms of practical feasibility, costs and benefits at the farm level, market prospects and framework conditions. I selected the two currently most advanced paludicultural practices in Europe: a) Harvesting natural reed beds as a traditional ‘low-input’ paludiculture, i. e. the utilisation of existing ‘wild’ vegetation stands; b) ‘Sphagnum farming’ as a novel ‘high-input’ paludiculture including stand establishment and water management required for the active transformation from drainage-based peatland use to paludiculture. In both cases, I investigate three different biomass utilisation avenues. This thesis adds to the fields of problem-driven sustainability and land-use science. Procedures and costs of paludiculture were studied in transdisciplinary research projects in close cooperation with practitioners. Due to the novelty of the topic, I put special emphasis on the triangulation of methods and data sources: pilot trials, field measurements, semi-structured expert interviews, structured questionnaires, secondary data from trade statistics and literature. To account for uncertainty related to costs and revenues, I conduct stochastic scenario analysis (Monte Carlo simulation) for the extended contribution margin accounting of harvesting reeds and sensitivity analysis for the investment appraisal of Sphagnum farming.
Paludiculture on fens: harvesting reeds
Paper I investigates harvesting procedures for reed-dominated (Phragmites australis) vegetation stands. In many European countries special-purpose tracked machinery is applied for large-scale conservation management and the commercial harvest of thatching reed. Stochastic scenario analysis reveals a wide range of possible economic outcomes (ca. € -1000 to € 1500 ha-1 a-1) and identifies material use of reed superior to its use as a source of energy. Winter harvest of high-quality thatching reed in bundles is the most profitable option. Winter harvest of bales for direct combustion is suitable for low-quality stands and has a limited risk of loss. In the case of summer harvest, revenues for green chaff for biogas production cannot cover harvesting costs but non-market income via subsidies and agri-environmental payments may ensure profitability. While biomass for energy generation is limited to a local market, thatching reed is traded as an international commodity. The market situation for thatching reed is investigated for Europe (Paper II) and Germany (Paper III). The major reed consuming countries in Western Europe (Netherlands, Germany, UK, Denmark) rely on imports of up to 85 % of the national consumption, with reed being imported from Eastern and Southern Europe and since 2005 also from China. The total market volume for reed for thatching in Northern Germany is estimated with 3 ± 0.8 million bundles of reed with a monetary value at sales prices of € 11.6 ± 2.8 million. Most of the thatchers (70 %) did not promote reed of regional origin to their customers due to insufficient availability in the first place and a lack in quality as second reason. The cultivation of reed in paludiculture may improve quantity and quality of domestic thatching reed. An area of 6000 ± 1600 ha with an average yield of 500 bundles per hectare would allow covering the current total demand of 3 million bundles of the German thatching reed market (Paper III).
Paludiculture on bogs: Sphagnum farming
Sphagnum farming provides an alternative to peatland degradation in two ways: Firstly, Sphagnum mosses can be cultivated as new agricultural crops on rewetted peatlands. Secondly, the produced Sphagnum biomass is a high-quality raw material suitable to replace peat in horticultural growing media (Paper V). Pilot trials have demonstrated the practical feasibility of establishing Sphagnum cultures on former bog grassland, cut-over bogs and mats floating on acidic waters bodies; Paper IV compares for the three types of production sites the specific procedures, costs and area potential in Germany. Water-based Sphagnum farming is not recommended for large-scale implementation due to highest establishment costs, major cultivation risks and limited area potential. For soil-based Sphagnum farming, the most important cost positions were Sphagnum shoots to set up pilots, investment for water management and regular weed management. Bog grassland has the highest area potential, i. e. 90,000 ha in NW Germany. Paper V assesses the profitability of Sphagnum farming on former bog grassland based on extrapolating five years of field experience data (establishment ņ management ņ harvest) to a total cultivation time of twenty years. Cultivating Sphagnum biomass as founder material for Sphagnum farming or restoration was profitable even in pessimistic scenarios with high costs, high bulk density and low yields. Selling Sphagnum for orchid production was economically viable in the case of medium to high yields with a low bulk density. Cost-covering prices for Sphagnum biomass substituting peat seem achievable if end consumers pay a surcharge of 10 % on the peat-free cultivated horticultural end-product. An area of 35,000 ha of Sphagnum farming suffices to meet the annual demand of the German growing media industry for slightly decomposed Sphagnum peat.
Framework conditions affecting feasibility of paludiculture
The relation of revenues from selling biomass to its production costs is an important piece of the paludiculture feasibility puzzle. Further aspects effecting the economic viability and competitiveness of paludiculture encompass the market demand, the availability of mature technology, legal restrictions, the eligibility for agricultural subsidies, a remuneration of external benefits and the opportunity costs of present farming activities (Paper I, V). Legal and policy regulations are of major importance for land use decisions on peatlands – both for keeping up drainage and for shifting to paludiculture.
Conclusion and Outlook
This thesis provides a first assessment of the costs and profitability of large-scale harvesting of reeds and Sphagnum farming based on real-life data. The paludicultural practices investigated may be a solution for a minor share of the more than 1 million ha of peatlands drained for agriculture in Germany. Future research should also address other biomass utilisation options and other crops. Large-scale pilots are required to improve technical maturity of procedures and machinery, gather reliable data to replace assumptions on costs and revenues and study long-term effects on economics and ecosystem services. The micro-economic perspective needs to be complemented by the societal perspective quantifying and monetising external effects of peatland restoration, paludiculture and drainage-based peatland use. There is a high need for intensified research, large-scale implementation and accelerated adaption of the policy and legal framework to develop paludiculture as an economically viable option for degraded peatlands.