Jutta Holst

Lund University

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Anders Lindroth

Lund University

Helmut Mayer

University of Freiburg

Janne Rinne

Natural Resources Institute Finland

Meelis Mölder

Lund University

Patrik Vestin

Lund University

Matthias Peichl

Swedish University of Agricultural Sciences

Michal Heliasz

Lund University

Ivan Mammarella

University of Helsinki

Tuomas Laurila

Finnish Meteorological Institute

Per Weslien

University of Gothenburg

Cooperative Institutions

Lund University

University of Helsinki

Finnish Meteorological Institute

Google (United States)

Karlsruhe Institute of Technology

University of Freiburg

ETH Zurich

University of Copenhagen

University of Nebraska–Lincoln

Mediterranean Center for Environmental Studies

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Investigations on the exchange of phosphorus in teeth using radio-active phosphorus as indicator.

G. HEVESY Jutta Holst Anders Krogh

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Field-scale CH4 emission at a subarctic mire with heterogeneous permafrost thaw status

Biogeosciences (2021)

Patryk Łakomiec Jutta Holst Thomas Friborg P. M. Crill Niklas Rakos

Abstract. The Arctic is exposed to even faster temperature changes than most other areas on Earth. Constantly increasing temperature will lead to thawing permafrost and changes in the methane (CH4) emissions from wetlands. One of the places exposed to those changes is the Abisko–Stordalen Mire in northern Sweden, where climate and vegetation studies have been conducted since the 1970s. In our study, we analyzed field-scale methane emissions measured by the eddy covariance method at Abisko–Stordalen Mire for 3 years (2014–2016). The site is a subarctic mire mosaic of palsas, thawing palsas, fully thawed fens, and open water bodies. A bimodal wind pattern prevalent at the site provides an ideal opportunity to measure mire patches with different permafrost status with one flux measurement system. The flux footprint for westerly winds was dominated by elevated palsa plateaus, while the footprint was almost equally distributed between palsas and thawing bog-like areas for easterly winds. As these patches are exposed to the same climatic and weather conditions, we analyzed the differences in the responses of their methane emission for environmental parameters. The methane fluxes followed a similar annual cycle over the 3 study years, with a gentle rise during spring and a decrease during autumn, without emission bursts at either end of the ice-free season. The peak emission during the ice-free season differed significantly for the two mire areas with different permafrost status: the palsa mire emitted 19 mg-C m−2 d−1 and the thawing wet sector 40 mg-C m−2 d−1. Factors controlling the methane emission were analyzed using generalized linear models. The main driver for methane fluxes was peat temperature for both wind sectors. Soil water content above the water table emerged as an explanatory variable for the 3 years for western sectors and the year 2016 in the eastern sector. The water table level showed a significant correlation with methane emission for the year 2016 as well. Gross primary production, however, did not show a significant correlation with methane emissions. Annual methane emissions were estimated based on four different gap-filing methods. The different methods generally resulted in very similar annual emissions. The mean annual emission based on all models was 3.1 ± 0.3 g-C m−2 a−1 for the western sector and 5.5 ± 0.5 g-C m−2 a−1 for the eastern sector. The average annual emissions, derived from these data and a footprint climatology, were 2.7 ± 0.5 and 8.2 ± 1.5 g-C m−2 a−1 for the palsa and thawing surfaces, respectively. Winter fluxes were relatively high, contributing 27 %–45 % to the annual emissions.

Mire

Subarctic climate

10.5194/bg-18-5811-2021

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Intercomparison of eight state-of-the-art eddy covariance methane gas

Olli Peltola A. Hensen Carole Helfter Luca Belelli Marchesini Ivan Mammarella

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Evaluating the performance of commonly used gas analysers for methane eddy covariance flux measurements: the InGOS inter-comparison field experiment

Biogeosciences (2014)

Olli Peltola A. Hensen Carole Helfter Luca Belelli Marchesini Fred C. Bosveld

Abstract. The performance of eight fast-response methane (CH4) gas analysers suitable for eddy covariance flux measurements were tested at a grassland site near the Cabauw tall tower (Netherlands) during June 2012. The instruments were positioned close to each other in order to minimise the effect of varying turbulent conditions. The moderate CH4 fluxes observed at the location, of the order of 25 nmol m−2 s−1, provided a suitable signal for testing the instruments' performance. Generally, all analysers tested were able to quantify the concentration fluctuations at the frequency range relevant for turbulent exchange and were able to deliver high-quality data. The tested cavity ringdown spectrometer (CRDS) instruments from Picarro, models G2311-f and G1301-f, were superior to other CH4 analysers with respect to instrumental noise. As an open-path instrument susceptible to the effects of rain, the LI-COR LI-7700 achieved lower data coverage and also required larger density corrections; however, the system is especially useful for remote sites that are restricted in power availability. In this study the open-path LI-7700 results were compromised due to a data acquisition problem in our data-logging setup. Some of the older closed-path analysers tested do not measure H2O concentrations alongside CH4 (i.e. FMA1 and DLT-100 by Los Gatos Research) and this complicates data processing since the required corrections for dilution and spectroscopic interactions have to be based on external information. To overcome this issue, we used H2O mole fractions measured by other gas analysers, adjusted them with different methods and then applied them to correct the CH4 fluxes. Following this procedure we estimated a bias of the order of 0.1 g (CH4) m−2 (8% of the measured mean flux) in the processed and corrected CH4 fluxes on a monthly scale due to missing H2O concentration measurements. Finally, cumulative CH4 fluxes over 14 days from three closed-path gas analysers, G2311-f (Picarro Inc.), FGGA (Los Gatos Research) and FMA2 (Los Gatos Research), which were measuring H2O concentrations in addition to CH4, agreed within 3% (355–367 mg (CH4) m−2) and were not clearly different from each other, whereas the other instruments derived total fluxes which showed small but distinct differences (±10%, 330–399 mg (CH4) m−2).

10.5194/bg-11-3163-2014

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Modification of Human-Biometeorologically Significant Radiant Flux Densities by Shading as Local Method to Mitigate Heat Stress in Summer within Urban Street Canyons

Advances in Meteorology (2013)

Hyunjung Lee Jutta Holst Helmut Mayer

Increasing heat will be a significant problem for Central European cities in the future. Shading devices are discussed as a method to mitigate heat stress on citizens. To analyze the physical processes, which are characteristic of shading in terms of urban human-biometeorology, experimental investigations on the thermal effects of shading by a building and shading by tree canopies were conducted in Freiburg (Southwest Germany) during typical Central European summer weather. Urban human-biometeorology stands for the variables air temperatureTa, mean radiant temperatureTmrt, and physiologically equivalent temperature PET, that is the human-biometeorological concept to assess the thermal environment which was applied. The measuring setup consists of specific human-biometeorological stations, which enable the direct or indirect determination ofTa,Tmrt, and PET. With respect to both shading devices, theTareduction did not exceed 2°C, while PET as a measure for human heat stress was lowered by two thermal sensation steps according to the ASHRAE scale. AsTmrthas the role of a key variable for outdoor thermal comfort during Central European summer weather, all radiant flux densities relevant to the determination ofTmrtwere directly measured and analyzed in detail. The results show the crucial significance of the horizontal radiant flux densities forTmrtand consequently PET.

10.1155/2013/312572

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Effect of the 2018 European drought on methane and carbon dioxide exchange of northern mire ecosystems

Philosophical Transactions of the Royal Society B Biological Sciences (2020)

Janne Rinne Juha‐Pekka Tuovinen Leif Klemedtsson Mika Aurela Jutta Holst

We analysed the effect of the 2018 European drought on greenhouse gas (GHG) exchange of five North European mire ecosystems. The low precipitation and high summer temperatures in Fennoscandia led to a lowered water table in the majority of these mires. This lowered both carbon dioxide (CO2) uptake and methane (CH4) emission during 2018, turning three out of the five mires from CO2 sinks to sources. The calculated radiative forcing showed that the drought-induced changes in GHG fluxes first resulted in a cooling effect lasting 15-50 years, due to the lowered CH4 emission, which was followed by warming due to the lower CO2 uptake. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.

Mire

10.1098/rstb.2019.0517

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Dependence of mean radiant temperature within urban structures on three-dimensional radiation flux densities

29th Conf. on Agricultural and Forest Meteorology/19th Symp. on Boundary Layers and Turbulence/Ninth Symp. on the Urban Environment (1-6 August 2010) (2010)

Helmut Mayer Jutta Holst

Radiant flux

Mean radiant temperature

Thermal Radiation

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Modelling Daily Gross Primary Productivity with Sentinel-2 Data in the Nordic Region–Comparison with Data from MODIS

Remote Sensing (2021)

Zhanzhang Cai Sofia Junttila Jutta Holst Hongxiao Jin Jonas Ardö

The high-resolution Sentinel-2 data potentially enable the estimation of gross primary productivity (GPP) at finer spatial resolution by better capturing the spatial variation in a heterogeneous landscapes. This study investigates the potential of 10 m resolution reflectance from the Sentinel-2 Multispectral Instrument to improve the accuracy of GPP estimation across Nordic vegetation types, compared with the 250 m and 500 m resolution reflectance from the Moderate Resolution Imaging Spectroradiometer (MODIS). We applied linear regression models with inputs of two-band enhanced vegetation index (EVI2) derived from Sentinel-2 and MODIS reflectance, respectively, together with various environmental drivers to estimate daily GPP at eight Nordic eddy covariance (EC) flux tower sites. Compared with the GPP from EC measurements, the accuracies of modelled GPP were generally high (R2 = 0.84 for Sentinel-2; R2 = 0.83 for MODIS), and the differences between Sentinel-2 and MODIS were minimal. This demonstrates the general consistency in GPP estimates based on the two satellite sensor systems at the Nordic regional scale. On the other hand, the model accuracy did not improve by using the higher spatial-resolution Sentinel-2 data. More analyses of different model formulations, more tests of remotely sensed indices and biophysical parameters, and analyses across a wider range of geographical locations and times will be required to achieve improved GPP estimations from Sentinel-2 satellite data.

Moderate-resolution imaging spectroradiometer

Enhanced vegetation index

10.3390/rs13030469

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Volatile Organic Compound fluxes in a subarctic peatland and lake

Roger Seco Thomas Holst Andreas Westergaard‐Nielsen Tao Li Tihomir Simin

Arctic climate is warming twice as much as the global average, due to a number of climate system feedbacks, including albedo change due to retreating snow cover and sea ice, and the forest cover expansion across the open tundra. Northern ecosystems are known to emit trace gases (e.g., methane and volatile organic compounds, VOCs) to the atmosphere, from sources as diverse as soils, vegetation and lakes. These trace gas fluxes are likely to show a trend towards greater emissions with climate warming.Here we report ecosystem-level VOC fluxes from Stordalen Mire, a subarctic peatland complex with a high fraction of open pond and lake surfaces, underlain by discontinuous permafrost and located in the Subarctic Sweden (68&#186;20' N, 19&#186;03' E).In 2018, we deployed two online mass spectrometers (PTR-TOF-MS) to measure rapid fluctuations in VOC mixing ratios and to quantify ecosystem-level fluxes with the eddy covariance technique. One of the instruments obtained a growing-season-long dataset of biogenic emissions from palsa mire vegetation dominated by mosses (e.g., Sphagnum spp.), graminoids (such as Eriophorum spp. and Carex spp.), dwarf shrubs (e.g. Empetrum spp. and Betula nana) surrounding the ICOS Sweden Abisko-Stordalen long-term measurement station. The second instrument measured VOC fluxes during two contrasting periods (the peak and the end of the growing season) from a subarctic lake and its adjacent fen, permafrost-free, minerotrophic wetland with vegetation dominated by tall graminoids, mainly Carex rostrata and Eriophorum angustifolium.At both sites, isoprene was the dominant VOC emitted by vegetation, showing clear diurnal patterns along the season and especially during the peak of the growing season in July. At the ICOS Sweden station, isoprene fluxes exceeded 2 nmol m-2 s-1 on several days in July, with a July monthly average midday emission of 1 nmol m-2 s-1. The fen site showed average midday emissions of 2 nmol m-2 s-1 during the peak growing season. Other VOCs emitted by vegetation at both sites in July were, with decreasing magnitude, methanol, acetone, acetaldehyde and monoterpenes. In contrast, acetaldehyde and acetone were not emitted but mostly deposited to the fen at the end of the season. In contrast to the wetland, the lake was a sink for acetaldehyde and acetone during all measurement periods.Thermal imaging and spectral analysis of vegetation will be used to assess relationships between VOC fluxes, vegetation surface temperatures and phenology under varying environmental conditions.

Subarctic climate

Mire

Sphagnum

10.5194/egusphere-egu2020-9007

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Citations (1)

Human thermal comfort in summer within an urban street canyon in Central Europe

Meteorologische Zeitschrift (2008)

Helmut Mayer Jutta Holst Paul Dostal Florian Imbery Dirk Schindler

Regional climate models predict an intensification of extreme heat waves in Central Europe. Against this background, the significance of human-biometeorologically orientated urban planning strategies is increasing by which the impairment of thermal comfort for people in cities in the future can be minimised. Such strategies require quantitative information on factors determining human thermal comfort within different urban quarters. With respect to these problems, the joint research project KLIMES funded by the German Federal Ministry of Education and Research was initiated. Its methodical approaches and objectives are presented in this article. One part of KLIMES are experimental investigations on human thermal comfort within different urban street canyons, whose variable arrangement generally characterises urban quarters. The investigations are conducted in Freiburg (SW Germany). The experimental design and the concept to analyse the measured data related to the objectives of KLIMES are exemplarily explained based on investigations in the Rieselfeld quarter on a typical summer day in 2007. The internationally well-known physiologically equivalent temperature PET is used as thermal index to quantify the perception of the thermal conditions by a collective of people within cities. During typical summer weather in Central Europe, PET is strongly influenced by the radiation heat, which is parameterised by the mean radiant temperature T mrt. Therefore, the short- and long-wave radiation flux densities from the three-dimensional surroundings of a standardised standing person representing mean properties of a collective of people in cities are analysed in detail. For the specific conditions at the stationary site Rieselfeld (NW-SE oriented urban street canyon, H/W = 0.49, SVF = 0.51, SW oriented sidewalk), the contribution of the total long-wave radiation flux density absorbed by a standing person to T mrt increased during the day from about 70% in the morning to about 90% in the evening before sunset.

Street Canyon

10.1127/0941-2948/2008/0285

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Citations (210)