| 1. |
- Franz, D, et al.
(författare)
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Towards long-term standardised carbon and greenhouse gas observations for monitoring Europe´s terrestrial ecosystems: a review
- 2018
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Ingår i: International Agrophysics. - : Walter de Gruyter GmbH. - 0236-8722 .- 2300-8725. ; 32, s. 439-455
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Tidskriftsartikel (refereegranskat)abstract
- Research infrastructures play a key role in launching a new generation of integrated long-term, geographically distributed observation programmes designed to monitor climate change, better understand its impacts on global ecosystems, and evaluate possible mitigation and adaptation strategies. The pan-European Integrated Carbon Observation System combines carbon and greenhouse gas (GHG; CO2, CH4, N2O, H2O) observations within the atmosphere, terrestrial ecosystems and oceans. High-precision measurements are obtained using standardised methodologies, are centrally processed and openly available in a traceable and verifiable fashion in combination with detailed metadata. The Integrated Carbon Observation System ecosystem station network aims to sample climate and land-cover variability across Europe. In addition to GHG flux measurements, a large set of complementary data (including management practices, vegetation and soil characteristics) is collected to support the interpretation, spatial upscaling and modelling of observed ecosystem carbon and GHG dynamics. The applied sampling design was developed and formulated in protocols by the scientific community, representing a trade-off between an ideal dataset and practical feasibility. The use of open-access, high-quality and multi-level data products by different user communities is crucial for the Integrated Carbon Observation System in order to achieve its scientific potential and societal value.
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| 2. |
- Luyssaert, S., et al.
(författare)
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CO2 balance of boreal, temperate, and tropical forests derived from a global database
- 2007
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 13:12, s. 2509-2537
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Forskningsöversikt (refereegranskat)abstract
- Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this carbon over both short and long timescales. Relevant data to address these uncertainties are being collected at many sites around the world, but syntheses of these data are still sparse. To facilitate future synthesis activities, we have assembled a comprehensive global database for forest ecosystems, which includes carbon budget variables (fluxes and stocks), ecosystem traits (e.g. leaf area index, age), as well as ancillary site information such as management regime, climate, and soil characteristics. This publicly available database can be used to quantify global, regional or biome-specific carbon budgets; to re-examine established relationships; to test emerging hypotheses about ecosystem functioning [e.g. a constant net ecosystem production (NEP) to gross primary production (GPP) ratio]; and as benchmarks for model evaluations. In this paper, we present the first analysis of this database. We discuss the climatic influences on GPP, net primary production (NPP) and NEP and present the CO2 balances for boreal, temperate, and tropical forest biomes based on micrometeorological, ecophysiological, and biometric flux and inventory estimates. Globally, GPP of forests benefited from higher temperatures and precipitation whereas NPP saturated above either a threshold of 1500 mm precipitation or a mean annual temperature of 10 degrees C. The global pattern in NEP was insensitive to climate and is hypothesized to be mainly determined by nonclimatic conditions such as successional stage, management, site history, and site disturbance. In all biomes, closing the CO2 balance required the introduction of substantial biome-specific closure terms. Nonclosure was taken as an indication that respiratory processes, advection, and non-CO2 carbon fluxes are not presently being adequately accounted for.
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| 3. |
- Poyatos, R., et al.
(författare)
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Global transpiration data from sap flow measurements: the SAPFLUXNET database
- 2021
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Ingår i: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 13:6, s. 2607-2649
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Tidskriftsartikel (refereegranskat)abstract
- Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land-atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The "sapfluxnetr" R package - designed to access, visualize, and process SAPFLUXNET data - is available from CRAN.
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| 4. |
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| 5. |
- Cea, B., et al.
(författare)
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Development and Evaluation of an Innovative Method Based on Dilution to Sample Solid and Condensable Fractions of Particles Emitted by Residential Wood Combustion
- 2021
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Ingår i: Energy & Fuels. - : American Chemical Society. - 0887-0624 .- 1520-5029. ; 35:23, s. 19705-
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Tidskriftsartikel (refereegranskat)abstract
- An innovative and simple method based on dilution, named as the dilution chamber (DC), allowing the measurement of solid and condensable fractions of particulate matter emitted by residential wood combustion appliances has been developed, and its performances have been evaluated. The DC method was then tested by five European institutes (Ineris, ISSI/ENEA, DTI, and RISE) on advanced residential wood log/pellet stoves, under nominal output and low output combustion conditions and using different fuel types. The aim of the study was to evaluate the capability of the DC method to collect the condensable fraction. The DC method was compared with another manual method used to collect the solid and condensable fractions at the same time, the dilution tunnel (DT), on four sampling platforms. A third method, a combining heated filter and impinger filled in with isopropanol collection (SPC-IPA), was also used by Ineris only for comparison with the DC method. PM measurements based on the DC method globally showed a linear correlation with PM measurements based on DT (R2 ranged between 0.81 and 0.99, p < 0.05) specifically for the residential wood stoves under low output conditions when the condensable fraction contributes the most. An analysis and quantification of PAHs related to the total mass of PM of samples taken by the DC method and performed by ENEA/ISSI showed that it produces a condensation effect of semivolatile species comparable or even greater than the DT method. PM emission factors calculated from PM measurements based on the DC method were (i) about 2- to 20-fold higher for the residential wood stoves (EF ranged between 201 to 2420 g GJ-1) compared to those obtained for the residential pellet stoves (EF ranged between 108 to 556 g GJ-1) and (ii) of the same magnitude of PM emission factors from the literature or the EMEP/EEA air pollutant emission inventory guidebook.
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| 6. |
- Hillberg, Emil, et al.
(författare)
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Flexibility to support the future power systems
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Power system flexibility relates to the ability of the power system to manage changes. Solutions providing advances in flexibility are of utmost importance for the future power system. Development and deployment of innovative technologies, communication and monitoring possibilities, as well as increased interaction and information exchange, are enablers to provide holistic flexibility solutions. Furthermore, development of new methods for market design and analysis, as well as methods and procedures related to system planning and operation, will be required to utilise available flexibility to provide most value to society. However, flexibility is not a unified term and is lacking a commonly accepted definition. The flexibility term is used as an umbrella covering various needs and aspects in the power system. This situation makes it highly complex to discuss flexibility in the power system and craves for differentiation to enhance clarity. In this report, the solution has been to differentiate the flexibility term on needs, and to categorise flexibility needs in four categories: Flexibility for Power, Flexibility for Energy, Flexibility for Transfer Capacity, and Flexibility for Voltage. Here, flexibility needs are considered from over-all system perspectives (stability, frequency and energy supply) and from more local perspectives (transfer capacities, voltage and power quality). With flexibility support considered for both operation and planning of the power system, it is required in a timescale from fractions of a second (e.g. stability and frequency support) to minutes and hours (e.g. thermal loadings and generation dispatch) to months and years (e.g. planning for seasonal adequacy and planning of new investments). The categorisation presented in this report supports an increased understanding of the flexibility needs, to be able to identify and select the most suitable flexibility solutions.
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| 7. |
- Wingate, L., et al.
(författare)
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Interpreting canopy development and physiology using a European phenology camera network at flux sites
- 2015
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4189. ; 12:20, s. 5995-6015
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Tidskriftsartikel (refereegranskat)abstract
- Plant phenological development is orchestrated through subtle changes in photoperiod, temperature, soil moisture and nutrient availability. Presently, the exact timing of plant development stages and their response to climate and management practices are crudely represented in land surface models. As visual observations of phenology are laborious, there is a need to supplement long-term observations with automated techniques such as those provided by digital repeat photography at high temporal and spatial resolution. We present the first synthesis from a growing observational network of digital cameras installed on towers across Europe above deciduous and evergreen forests, grasslands and croplands, where vegetation and atmosphere CO2 fluxes are measured continuously. Using colour indices from digital images and using piecewise regression analysis of time series, we explored whether key changes in canopy phenology could be detected automatically across different land use types in the network. The piecewise regression approach could capture the start and end of the growing season, in addition to identifying striking changes in colour signals caused by flowering and management practices such as mowing. Exploring the dates of green-up and senescence of deciduous forests extracted by the piecewise regression approach against dates estimated from visual observations, we found that these phenological events could be detected adequately (RMSE < 8 and 11 days for leaf out and leaf fall, respectively). We also investigated whether the seasonal patterns of red, green and blue colour fractions derived from digital images could be modelled mechanistically using the PROSAIL model parameterised with information of seasonal changes in canopy leaf area and leaf chlorophyll and carotenoid concentrations. From a model sensitivity analysis we found that variations in colour fractions, and in particular the late spring 'green hump' observed repeatedly in deciduous broadleaf canopies across the network, are essentially dominated by changes in the respective pigment concentrations. Using the model we were able to explain why this spring maximum in green signal is often observed out of phase with the maximum period of canopy photosynthesis in ecosystems across Europe. Coupling such quasi-continuous digital records of canopy colours with co-located CO2 flux measurements will improve our understanding of how changes in growing season length are likely to shape the capacity of European ecosystems to sequester CO2 in the future.
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| 8. |
- Yi, Chuixiang, et al.
(författare)
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Climate control of terrestrial carbon exchange across biomes and continents
- 2010
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 5:3
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2 exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid-and high-latitudes, (2) a strong function of dryness at mid-and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45 degrees N). The sensitivity of NEE to mean annual temperature breaks down at similar to 16 degrees C (a threshold value of mean annual temperature), above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence.
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| 9. |
- Knauer, Jürgen, et al.
(författare)
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Towards physiologically meaningful water-use efficiency estimates from eddy covariance data
- 2018
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 24:2, s. 694-710
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Tidskriftsartikel (refereegranskat)abstract
- Intrinsic water-use efficiency (iWUE) characterizes the physiological control on the simultaneous exchange of water and carbon dioxide in terrestrial ecosystems. Knowledge of iWUE is commonly gained from leaf-level gas exchange measurements, which are inevitably restricted in their spatial and temporal coverage. Flux measurements based on the eddy covariance (EC) technique can overcome these limitations, as they provide continuous and long-term records of carbon and water fluxes at the ecosystem scale. However, vegetation gas exchange parameters derived from EC data are subject to scale-dependent and method-specific uncertainties that compromise their ecophysiological interpretation as well as their comparability among ecosystems and across spatial scales. Here, we use estimates of canopy conductance and gross primary productivity (GPP) derived from EC data to calculate a measure of iWUE (G1, “stomatal slope”) at the ecosystem level at six sites comprising tropical, Mediterranean, temperate, and boreal forests. We assess the following six mechanisms potentially causing discrepancies between leaf and ecosystem-level estimates of G1: (i) non-transpirational water fluxes; (ii) aerodynamic conductance; (iii) meteorological deviations between measurement height and canopy surface; (iv) energy balance non-closure; (v) uncertainties in net ecosystem exchange partitioning; and (vi) physiological within-canopy gradients. Our results demonstrate that an unclosed energy balance caused the largest uncertainties, in particular if it was associated with erroneous latent heat flux estimates. The effect of aerodynamic conductance on G1 was sufficiently captured with a simple representation. G1 was found to be less sensitive to meteorological deviations between canopy surface and measurement height and, given that data are appropriately filtered, to non-transpirational water fluxes. Uncertainties in the derived GPP and physiological within-canopy gradients and their implications for parameter estimates at leaf and ecosystem level are discussed. Our results highlight the importance of adequately considering the sources of uncertainty outlined here when EC-derived water-use efficiency is interpreted in an ecophysiological context.
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| 10. |
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