The effect of rainfall amount and timing on annual transpiration in a grazed savanna grassland

The role of precipitation (P) variability with respect to evapotranspiration (ET) and its two components, transpiration (T) and evaporation (E), from savannas continues to draw significant research interest given its relevance to a number of ecohydrological applications. Our study reports on 6 years of measured ET and estimated T and E from a grazed savanna grassland at Welgegund, South Africa. Annual P varied significantly with respect to amount (508 to 672 mm yr(-1)), with dry years characterized by infrequent early-season rainfall. T was determined using annual water-use efficiency and gross primary production estimates derived from eddy-covariance measurements of latent heat flux and net ecosystem CO2 exchange rates. The computed annual T for the 4 wet years with frequent early wet-season rainfall was nearly constant, 326 +/- 19 mm yr(-1) (T/ET=0.51), but was lower and more variable between the 2 dry years (255 and 154 mm yr(-1), respectively). Annual T and T/ET were linearly related to the early wet-season storm frequency. The constancy of annual T during wet years is explained by the moderate water stress of C4 grasses as well as trees' ability to use water from deeper layers. During extreme drought, grasses respond to water availability with a dieback-regrowth pattern, reducing leaf area and transpiration and, thus, increasing the proportion of transpiration contributed by trees. The works suggest that the early-season P distribution explains the interannual variability in T, which should be considered when managing grazing and fodder production in these grasslands.Peer reviewe

The uncertain climate footprint of wetlands under human pressure

Significant climate risks are associated with a positive carbon–temperature feedback in northern latitude carbon-rich ecosystems,making an accurate analysis of human impacts on the net greenhouse gas balance of wetlands a priority. Here, we provide a coherent assessment of the climate footprint of a network of wetland sites based on simultaneous and quasi-continuous ecosystem observations of CO2 and CH4 fluxes. Experimental areas are located both in natural and in managed wetlands and cover a wide range of climatic regions, ecosystem types, and management practices. Based on direct observations we predict that sustained CH4 emissions in natural ecosystems are in the long term (i.e., several centuries) typically offset by CO2 uptake, although with large spatiotemporal variability. Using a space-for-time analogy across ecological and climatic gradients, we represent the chronosequence from natural to managed conditions to quantify the “cost” of CH4 emissions for the benefit of net carbon sequestration. With a sustained pulse– response radiative forcing model, we found a significant increase in atmospheric forcing due to land management, in particular for wetland converted to cropland. Our results quantify the role of human activities on the climate footprint of northern wetlands and call for development of active mitigation strategies for managed wetlands and new guidelines of the Intergovernmental Panel on Climate Change (IPCC) accounting for both sustained CH4 emissions and cumulative CO2 exchange

The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data

The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.Peer reviewe

Climate control of terrestrial carbon exchange across biomes and continents

Peer reviewe

Inköp i Virtual Design and Construction : En fallstudie

Construction firms currently spend more than half of revenue on purchase of materials and services. This makes effective management of suppliers an important part of corporate strategy. Also, since firms become more specialized, more services have to be purchased; the consequence is an increased dependence of suppliers. This suggests that construction companies need to aim towards long-term open collaboration with suppliers. However, currently, purchasing is performed in a short-term and competitive manner. The current fixation on price obstructs a reduction of total costs of the entire supply chain. Price is just the tip of the iceberg and under the surface there are hidden costs for management of: operations, supplies, inventory, capital and supplier relationship as well as cost of administration, R&D, support and maintenance which all have to be considered in order to reduce the total cost of ownership. Also, alongside this, virtual construction technologies are introduced to improve the product. This creates opportunity for integration of new information in BIM-models to support the purchasing process. Only using BIM limits users to the product, which creates the risk of organizational and process costs being left behind. Virtual Design and Construction, VDC, is a more holistic approach that also takes into account the organization which designs and builds and the process followed by the organization to design and build the product. In this study VDC is explored as a possible aid in the construction company’s purchasing activities.The study is based on existing theory in the fields of purchasing, construction process and Virtual Design and Construction and a case study of the purchasing process at Veidekke Entreprenad AB. In the case study the purchasing process is mapped during tendering, production preparation and production through interviews. To make sure the entire process was covered respondents were selected to cover different roles in the construction company. From covered purchasing theory a specification for purchasing was created for comparison with the studied purchasing process.In the case study, a manual and experience-based purchasing process was identified where relationships with suppliers was primary transactional. Purchasing activities are primarily based on paper-based documentation and streamlining tools to facilitate the purchasing process is missing. Supplier selection is primarily based on past experience and available information about past suppliers are stored in old project archives which requires that a person looking for information have to know where to look. Selection of final supplier is based on price or estimated total cost. In the process, similar activities are carried out but a standardized approach to procurement is missing and the only measurement performed regarding purchasing was reduction of purchasing price from tendering estimates. However, the case study also showed a purchasing process in transition and henceforth project buyers will be responsible for all project purchases. Based on theory and the case study three areas are presented, where VDC can support the purchasing process:• Implementation of location-based scheduling (LBS) enables project management in aspects of time as well as in space. LBS creates an opportunity to improve delivery schedules and visualization of the production in time and space. These delivery schedules can be the basis for procurement of materials and delivery based on production needs. Visualisation of production can be used to prioritize purchasing work and to support material and service supplier selection. During negotiation visualization can be used as a tool to ensure that criteria for negotiation improve production flow.• At the centre of VDC lies continuous measurement to enable control and predictions of the process. Objectives are established in three levels: Project outcome objectives which are measurable at the end of the project; Project process objectives which influence project outcome are measured regularly; Project controllable factors used by leaders to support daily decisions. This framework can also be used for measuring purchasing- and supplier performance to support supplier selection and continuous improvement. • Integrated Concurrent Engineering (ICE) can be used to make sure that purchasing flexibility is not compromised. Through the usage of cross-functional teams of buyers, planning managers and production managers and an ICE procedure it is possible to explore alternative products and solutions. It is also possible to maintain flexibility in negotiation with suppliers to develop the most favorable technical- and financial solution. The method also opens up for the early involvement of suppliers in order to secure production flow. To achieve full effect, a procedure in which the construction company can affect project design is needed.The results show room for improvement in several areas. To facilitate the development of Veidekke’s future work in the field of VDC, a development model which covers all sub-disciplines of VDC is presented, exemplified using the purchasing process. The model is based on the three maturity levels of VDC implementation. The purpose is to provide support to the implementation and integration of the purchasing routines in the VDC process within the company.Validerat; 20130226 (global_studentproject_submitter

Two contrasting years of continuous N₂O and CO₂ fluxes on a shallow-peated drained agricultural boreal peatland

Abstract Drained agricultural boreal peatlands comprise a large source of nitrous oxide (N₂O) and carbon dioxide (CO₂) but a small sink or source of methane (CH₄). N₂O fluxes have high spatial and temporal variability and are often measured with the chamber technique. Therefore, continuous measurements of N₂O fluxes are needed to better understand how N₂O emissions are triggered and to reduce the uncertainty of annual N₂O budget estimations. Here we present a two-year-long time series of continuous measurements of CO₂ and N₂O fluxes of a shallow-peated drained agricultural boreal peatland cultivated for grass silage. The fluxes were measured with the area-averaging eddy covariance technique. Several NO peak events were observed throughout all seasons. The peaks were associated with meteorological or management events, such as soil thawing or freezing, precipitation, fertilization and glyphosate application. The annual N₂O budget was 4.74 ±0.47 and 6.08 ±0.49 kg NO-N ha⁻¹ y⁻¹ in 2020 and 2021, respectively. The annual CO₂ budget, comprising the sum of net ecosystem exchange and biomass export, was 3.70 ±0.22 and 5.54 ±0.33 t CO₂-C ha⁻¹ y⁻¹ in 2020 and 2021, respectively. The N₂O budget during the first, warmer winter was 106% higher than during the second, meteorologically more typical winter, due to the higher frequency of soil freezing–thawing cycles. The average annual NO budget was 36%–50% lower than the IPCC Emission Factor (EF) while the CO₂ budget was in accordance with the IPCC EF. CO₂ emissions dominated the total CO₂-eq emissions of our site but N₂O also had a significant contribution of 12%. Our results also suggest that glyphosate application enhanced N₂O emissions in the last quarter of 2021. However, the full rotation should be measured to confirm whether there is a need to re-evaluate the N₂O IPCC EF for ‘grassland drained boreal’ land-use class

Spatially varying peatland initiation, Holocene development, carbon accumulation patterns and radiative forcing within a subarctic fen

Abstract High latitude peatlands act as globally important carbon (C) sinks and are in constant interaction with the atmosphere. Their C storage formed during the Holocene. In the course of time, the aggregate effect of the C fluxes on radiative forcing (RF) typically changes from warming to cooling, but the timing of this shift varies among different peatlands. Here we investigated Holocene peatland development, including vegetation history, vertical peat growth and the lateral expansion of a patterned subarctic fen in northern Finland by means of multiple sampling points. We modelled the Holocene RF by combining knowledge on past vegetation communities based on plant macrofossil stratigraphies and present in situ C flux measurements. The peatland initiated at ca. 9500 calibrated years Before Present (cal yr BP), and its lateral expansion was greatest between ca. 9000 and 7000 cal yr BP. After the early expansion, vertical peat growth proceeded very differently in different parts of the peatland, regulated by internal and external factors. The pronounced surface microtopography, with high strings and wet flarks, started to form only after ca. 1000 cal yr BP. C accumulation within the peatland recorded a high degree of spatial variability throughout its history, including the recent past. We applied two flux scenarios with different interpretation of the initial peatland development phases to estimate the RF induced by C fluxes of the fen. After ca. 4000 cal yr BP, at the latest, the peatland RF has been negative (cooling), mainly driven by C uptake and biomass production, while methane emissions had a lesser role in the total RF. Interestingly, these scenarios suggest that the greatest cooling effect took place around ca. 1000 cal yr BP, after which the surface microtopography established. The study demonstrated that despite the high spatial heterogeneity and idiosyncratic behaviour of the peatland, the RF of the studied fen followed the general development pattern of more southern peatlands. Holocene climate variations and warm phases did not seem to induce any distinctive and consistent peatland-scale patterns in C accumulation, whereas our data suggests that the changes in vegetation related to autogenic succession were reflected in the C accumulation patterns and RF more clearly

DO₃SE modelling of soil moisture to determine ozone flux to forest trees

The DO₃SE (Deposition of O₃ for Stomatal Exchange) model is an established tool for estimating ozone(O₃) deposition, stomatal flux and impacts to a variety of vegetation types across Europe. It has been embedded within the EMEP (European Monitoring and Evaluation Programme) photochemical model to provide a policy tool capable of relating the flux-based risk of vegetation damage to O₃ precursor emission scenarios for use in policy formulation. A key limitation of regional flux-based risk assessments has been the assumption that soil water deficits are not limiting O₃ flux due to the unavailability of evaluated methods for modelling soil water deficits and their influence on stomatal conductance (gsto), and subsequent O₃ flux. This paper describes the development and evaluation of a method to estimate soil moisture status and its influence on gsto for a variety of forest tree species. This DO₃SE soil moisture module uses the Penman-Monteith energy balance method to drive water cycling through the soil-plantatmosphere system and empirical data describing gsto relationships with pre-dawn leaf water status to estimate the biological control of transpiration. We trial four different methods to estimate this biological control of the transpiration stream, which vary from simple methods that relate soil water content or potential directly to gsto, to more complex methods that incorporate hydraulic resistance and plant capacitance that control water flow through the plant system. These methods are evaluated against field data describing a variety of soil water variables, gsto and transpiration data for Norway spruce (Picea abies), Scots pine (Pinus sylvestris), birch (Betula pendula), aspen (Populus tremuloides), beech (Fagus sylvatica) and holm oak (Quercus ilex) collected from ten sites across Europe and North America. Modelled estimates of these variables show consistency with observed data when applying the simple empirical methods, with the timing and magnitude of soil drying events being captured well across all sites and reductions in transpiration with the onset of drought being predicted with reasonable accuracy. The more complex methods, which incorporate hydraulic resistance and plant capacitance, perform less well, with predicted drying cycles consistently underestimating the rate and magnitude of water loss from the soil. A sensitivity analysis showed that model performance was strongly dependent upon the local parameterisation of key model drivers such as the maximum gsto, soil texture, root depth and leaf area index. The results suggest that the simple modelling methods that relate gsto directly to soil water content and potential provide adequate estimates of soil moisture and influence on gsto such that they are suitable to be used to assess the potential risk posed by O₃ to forest trees across Europe