Multiscale studies of the peatland-atmosphere interactions in northern Eurasia

North Eurasia (NE) is recognized as a region of high importance for the global climate change. Large and systematic shifts in temperature and precipitation, predicted for NE, are expected to cause irreversible disturbances in the ecosystem-atmosphere interactions. The region is dominated by natural boreal and arctic ecosystems, which are experiencing increasing levels of anthropogenic influence through environmental pollution (mainly agriculture- and mining-related) and land use change. However, despite the general consensus on the importance of environmental changes in NE, many aspects of the problem remain poorly understood. Due to the great extent of NE, many crucial areas remain inaccessible or lack the required infrastructure, thereby relevant surface-atmosphere exchange measurement data remains scarce. This thesis examines the surface budgets of carbon dioxide and energy of subarctic peatlands, which count among the most important ecosystems in NE owing to their large carbon storage and areal coverage, and their high sensitivity to climate and land use changes. Peatlands are also heterogeneous ecosystems, with large diversity found both internally and between the ecosystem subtypes. Peatland heterogeneity is notable on several characteristic scales, including the single plant, microsite, microtopography element and ecosystem type. Different scales of variation are covered with specific measurement techniques, i.e. plant-scale gas exchange, chamber and eddy-covariance (EC) technique. The latter is in the focus of this work. Aerodynamic roughness length (z0) and photosynthesis rate measured by EC were compared with the plant- and microsite-scale measurements of leaf area index (LAI) and photosynthesis rate. High correspondence between the estimates on different scales was found, indicating that the transition between the upscaled plant and ecosystem-scale estimates is possible, and thus adding credibility to both. In the fen Siikaneva-1, LAI showed a strong linear relationship with z0, while the EC-derived photosynthesis rate closely followed the upscaled plant chamber estimate. Ecosystem-scale EC measurements made in 2015 at a typical raised bog in West Siberian middle taiga (Mukhrino Field Station) revealed a high cumulative May-August net ecosystem exchange (NEE) of 202 gC m-2 and a mean Bowen ratio (ratio of sensible to latent heat flux) of 0.28, which was lower than expected. Inter-site differences in terms of energy balance were investigated for a selection of eight Fennoscandian peatland sites with different mire types and management histories. The site mean Bowen ratio ranged from 0.28 to 1.35, evapotranspiration (ET) from 1.2 to 2.8 mm/day, and the decoupling parameter (Ω, indicating the relative strength of radiation and surface conductance controls on evapotranspiration) from 0.11 to 0.48. Generally, the energy balance and ecosystem features were found to be tightly linked, corroborating the predictability of peatland energy balances across a wide spectrum of ecosystems. Finally, on a yet larger scale, the current measurement station network of the entire NE is discussed. Measurement gaps are identified based on ecosystem type and climate representation by the existing field stations, with the focus on peatlands. Tentative developments for the NE measurement network are proposed.It is established that Siberia is a region very sparsely covered by ecosystem and climate change monitoring sites, especially when state of the art techniques are concerned (e.g. EC).N/

Eddies in motion : visualizing boundary-layer turbulence above an open boreal peatland using UAS thermal videos

High-resolution thermal infrared (TIR) imaging is opening up new vistas in biosphere-atmosphere heat exchange studies. The rapidly developing unmanned aerial systems (UASs) and specially designed cameras offer opportunities for TIR survey with increasingly high resolution, reduced geometric and radiometric noise, and prolonged flight times. A state-of-the-art science platform is assembled using a Matrice 210 V2 drone equipped with a Zenmuse XT2 thermal camera and deployed over a pristine boreal peatland with the aim of testing its performance in a heterogeneous sedgefen ecosystem. The study utilizes the capability of the UAS platform to hover for prolonged times (about 20 min) at a height of 500ma.g.l. while recording high frame rate (30 Hz) TIR videos of an area of ca. 430 x 340 m. A methodology is developed to derive thermal signatures of near-ground coherent turbulent structures impinging on the land surface, surface temperature spectra, and heat fluxes from the retrieved videos. The size, orientation, and movement of the coherent structures are computed from the surface temperature maps, and their dependency on atmospheric conditions is examined. A range of spectral and wavelet-based approaches are used to infer the properties of the dominant turbulent scene structures. A ground-based eddy-covariance system and an in situ meteorological setup are used for reference.Peer reviewe

Multi-year methane ebullition measurements from water and bare peat surfaces of a patterned boreal bog

We measured methane ebullition from a patterned boreal bog situated in the Siikaneva wetland complex in southern Finland. Measurements were conducted on water (W) and bare peat surfaces (BP) in three growing seasons (2014-2016) using floating gas traps. The volume of the trapped gas was measured weekly, and methane and carbon dioxide (CO2) concentrations of bubbles were analysed from fresh bubble samples that were collected separately. We applied a mixed-effect model to quantify the effect of the environmental controlling factors on the ebullition. Ebullition was higher from W than from BP, and more bubbles were released from open water (OW) than from the water's edge (EW). On average, ebullition rate was the highest in the wettest year ( 2016) and ranged between 0 and 253 mg m(-2) d(-1) with a median of 2 mg m(-2) d(-1), 0 and 147 mg m(-2) d(-1) with a median of 3 mg m(-2) d(-1), and 0 and 186 mg m(-2) d(-1) with a median of 28 mg m(-2) d(-1) in 2014, 2015, and 2016, respectively. Ebullition increased together with increasing peat temperature, weekly air temperature sum and atmospheric pressure, and decreasing water table (WT). Methane concentration in the bubbles released from W was 15-20 times higher than the CO2 concentration, and from BP it was 10 times higher. The proportion of ebullition fluxes upscaled to ecosystem level for the peak season was 2 %-8 % and 2 %- 5 % of the total flux measured with eddy covariance technique and with chambers and gas traps, respectively. Thus, the contribution of methane ebullition from wet non-vegetated surfaces of the bog to the total ecosystem-scale methane emission appeared to be small.Peer reviewe

Varying Vegetation Composition, Respiration and Photosynthesis Decrease Temporal Variability of the CO2 Sink in a Boreal Bog

We quantified the role of spatially varying vegetation composition in seasonal and interannual changes in a boreal bog’s CO2 uptake. We divided the spatially heterogeneous site into six microform classes based on plant species composition and measured their net ecosystem exchange (NEE) using chamber method over the growing seasons in 2012–2014. A nonlinear mixed-effects model was applied to assess how the contributions of microforms with different vegetation change temporally, and to upscale NEE to the ecosystem level to be compared with eddy covariance (EC) measurements. Both ecosystem respiration (R) and gross photosynthesis (PG) were the largest in high hummocks, 894–964 (R) and 969–1132 (PG) g CO2 m−2 growing season−1, and decreased toward the wetter microforms. NEE had a different spatial pattern than R and PG; the highest cumulative seasonal CO2 sink was found in lawns in all years (165–353 g CO2 m−2). Microforms with similar wetness but distinct vegetation had different NEE, highlighting the importance of vegetation composition in regulating CO2 sink. Chamber-based ecosystem-level NEE was smaller and varied less interannually than the EC-derived estimate, indicating a need for further research on the error sources of both methods. Lawns contributed more to ecosystem-level NEE (55–78%) than their areal cover within the site (21.5%). In spring and autumn, lawns had the highest NEE, whereas in midsummer differences among microforms were small. The contributions of all microforms to the ecosystem-level NEE varied seasonally and interannually, suggesting that spatially heterogeneous vegetation composition could make bog CO2 uptake temporally more stable.Peer reviewe

Net ecosystem exchange and energy fluxes measured with the eddy covariance technique in a western Siberian bog

Very few studies of ecosystem-atmosphere exchange involving eddy covariance data have been conducted in Siberia, with none in the western Siberian middle taiga. This work provides the first estimates of carbon dioxide (CO2) and energy budgets in a typical bog of the western Siberian middle taiga based on May-August measurements in 2015. The footprint of measured fluxes consisted of a homogeneous mixture of tree-covered ridges and hollows with the vegetation represented by typical sedges and shrubs. Generally, the surface exchange rates resembled those of pinecovered bogs elsewhere. The surface energy balance closure approached 100 %. Net CO2 uptake was comparatively high, summing up to CO2 gCm(-2) for the four measurement months, while the Bowen ratio was seasonally stable at 28 %. The ecosystem turned into a net CO2 source during several front passage events in June and July. The periods of heavy rain helped keep the water table at a sustainably high level, preventing a usual drawdown in summer. However, because of the cloudy and rainy weather, the observed fluxes might rather represent the special weather conditions of 2015 than their typical magnitudes.Peer reviewe

Species-specific temporal variation in photosynthesis as a moderator of peatland carbon sequestration

In boreal bogs plant species are low in number, but they differ greatly in their growth forms and photosynthetic properties. We assessed how ecosystem carbon (C) sink dynamics were affected by seasonal variations in the photosynthetic rate and leaf area of different species. Photosynthetic properties (light response parameters), leaf area development and areal cover (abundance) of the species were used to quantify species-specific net and gross photosynthesis rates (P-N and P-G, respectively), which were summed to express ecosystem-level P-N and P-G. The ecosystem-level P-G was compared with a gross primary production (GPP) estimate derived from eddy covariance (EC) measurements. Species areal cover, rather than differences in photosynthetic properties, determined the species with the highest P-G of both vascular plants and Sphagna. Species-specific contributions to the ecosystem P-G varied over the growing season, which, in turn, determined the seasonal variation in ecosystem P-G. The upscaled growing season P-G estimate, 230 gCm (-2), agreed well with the GPP estimated by the EC (243 gCm (-2)). Sphagna were superior to vascular plants in ecosystemlevel P-G throughout the growing season but had a lower P-N. P-N results indicated that areal cover of the species, together with their differences in photosynthetic parameters, shape the ecosystem-level C balance. Species with low areal cover but high photosynthetic efficiency appear to be potentially important for the ecosystem C sink. Results imply that func-tional diversity, i. e., the presence of plant groups with different seasonal timing and efficiency of photosynthesis, may increase the stability of C sinks of boreal bogs.Peer reviewe

El desarrollo de cascos en los reinos cristianos de la península ibérica entre 1150 y 1230 d.C.: evidencias de un único estilo regional

The knightly helmets used in the Christian kingdoms of the Iberian Peninsula in the 12th and early 13th centuries presented a range of designs that reflect both the local military fashion trends and the cultural influences from France in the northeast and Muslim-held regions in the south. Despite the near-complete absence of an archaeological record for helmets, these designs are amply represented in visual arts. This study analyses 56 artworks depicting helmets with developed facial protection executed within the historical territories of Aragon, Navarra, Castile and Leon. The proposed typology outlines three possibly endemic Iberian helmet types, as well as three further types common in the art of other European regions. The temporal and geographical distributions of sources are discussed. It is concluded that the earliest depictions of both the masked and enclosed helmets in Europe are found in Navarre, although generally, the Iberian depictions of helmets with developed facial protection are contemporary with those in the rest of Europe.Los cascos de caballería utilizados en los reinos cristianos de la península ibérica en el siglo XII y principios del XIII presentaban una variedad de diseños que reflejan tanto las tendencias de la moda militar local como las influencias culturales de Francia en el noreste y las regiones controladas por musulmanes en el sur. A pesar de la ausencia casi total de registros arqueológicos, estos diseños están ampliamente representados en las artes visuales. Este estudio analiza 56 obras de arte que representan cascos con protección facial usados en los territorios históricos de Aragón, Navarra, Castilla y León. Una tipología propuesta describe tres tipos de casco endémicos ibéricos, así como tres tipos comunes en el arte de otras regiones europeas. Se discuten las distribuciones temporales y geográficas de las fuentes. Se concluye que las primeras representaciones de cascos con facial y completamente cerrados en Europa se encuentran en Navarra y que, en general, las representaciones ibéricas de cascos con protección facial desarrollada son anteriores a las del resto de Europa

Boreal bog plant communities along a water table gradient differ in their standing biomass but not their biomass production

Question: Peatlands are globally important for carbon storage due to the imbalance between plant biomass production and decomposition. Distribution of both live standing biomass (BM, dry mass g/m(2)) and biomass production (BMP, dry mass gm(-2) growing season(-1)) are known to be dependent on the water table (WT). However, the relations of BM and BMP to WT variation are poorly known. Here we investigated, how the above- and below-ground BM and BMP of three different plant functional types (PFTs), dwarf shrubs, sedges and Sphagnum mosses, relate to natural WT variation within an ombrotrophic boreal bog. In addition, we estimated ecosystem-level BMP and compared that with ecosystem net primary production (NPP) derived from eddy covariance (EC) measurements. Location: Siikaneva bog, Ruovesi, Finland. Methods: We quantified above- and below-ground BM and BMP of PFTs along the WT gradient, divided into six plant community types. Plant community scale BM and BMP were up-scaled to the ecosystem level. NPP was derived from EC measurements using a literature-based ratio of heterotrophic respiration to total ecosystem respiration. Results: BM varied from 211 to 979 g/m(2) among the plant community types, decreasing gradually from dry to wet community types. In contrast, BMP was similar between plant community types (162-216 g/m(2)), except on nearly vegetation-free bare peat surfaces where it was low (38 g/m(2)). Vascular plant BM turnover rate (BMP:BM, per year) varied from 0.14 to 0.30 among the plant community types, being highest in sedge-dominated hollows. On average 56% of the vascular BM was produced below ground. Mosses, when present, produced on average 31% of the total BM, ranging from 16% to 53% depending on community type. EC-derived NPP was higher than measured BMP due to underestimation of certain components. Conclusions: We found that the diversity of PFTs decreases the spatial variability in productivity of a boreal bog ecosystem. The observed even distribution of BMP resulted from different WT optima and BMP:BM of dwarf shrubs, sedges and Sphagnum species. These differences in biomass turnover rate and species responses to environmental conditions may provide a resilience mechanism for bog ecosystems in changing conditions.Peer reviewe

On measurements of aerosol particles and greenhouse gases in Siberia and future research needs

The role of the world's boreal forest for our understanding of the climate system is indisputable. Due to the large area covered, the forest's biophysical (e.g. surface energy balance, albedo) and biogeochemical (e.g. bidirectional exchange of greenhouse gases or aerosol precursors) processes are known to affect today's climate, and will need to be accounted for in studies of climate feedbacks in response to anthropogenic warming. However, observations that are needed to develop and evaluate terrestrial and climate models are still relatively scarce, especially for the Siberian part of the boreal forest. Here, we present a short overview of aerosol and greenhouse gas measurements over Siberia, aiming to also survey a large fraction of the existing literature in Russian. We aim to highlight areas of least data coverage and argue that, due to the importance of Siberia in the global climate system, a coordinated research program is needed to address some of the open research questions: The Pan Siberian Experiment

Temporal Variation of Ecosystem Scale Methane Emission From a Boreal Fen in Relation to Temperature, Water Table Position, and Carbon Dioxide Fluxes

We have analyzed decade-long methane flux data set from a boreal fen, Siikaneva, together with data on environmental parameters and carbon dioxide exchange. The methane flux showed seasonal cycle but no systematic diel cycle. The highest fluxes were observed in July-August with average value of 73 nmol m(-2) s(-1). Wintertime fluxes were small but positive, with January-March average of 6.7 nmol m(-2) s(-1). Daily average methane emission correlated best with peat temperatures at 20-35 cm depths. The second highest correlation was with gross primary production (GPP). The best correspondence between emission algorithm and measured fluxes was found for a variable-slope generalized linear model (r(2) = 0.89) with peat temperature at 35 cm depth and GPP as explanatory variables, slopes varying between years. The homogeneity of slope approach indicated that seasonal variation explained 79% of the sum of squares variation of daily average methane emission, the interannual variation in explanatory factors 7.0%, functional change 5.3%, and random variation 9.1%. Significant correlation between interannual variability of growing season methane emission and that of GPP indicates that on interannual time scales GPP controls methane emission variability, crucially for development of process-based methane emission models. Annual methane emission ranged from 6.0 to 14 gC m(-2) and was 2.7 +/- 0.4% of annual GPP. Over 10-year period methane emission was 18% of net ecosystem exchange as carbon. The weak relation of methane emission to water table position indicates that space-to-time analogy, used to extrapolate spatial chamber data in time, may not be applicable in seasonal time scales.Peer reviewe