Energy balance closure of two bog surfaces in central Sweden

Typical bogs in the boreal forest zone can be characterised by hummock and hollow micro-topography and sparsely vegetated surfaces. Their energy balance has been studied much less than for other types of surface, i.e. fields and forests. Micrometeorological measurements were carried out in central Sweden at two bogs in different summer seasons. From the measured profiles of wind speed, air temperature and humidity, the turbulent sensible and latent heat fluxes were calculated according to the Monin-Obukhov similarity theory. The daytime sensible and latent heat fluxes were typically of similar size, with the latent heat fluxes still being slightly higher. Independent measurements of turbulent, radiative and ground heat fluxes allowed to consider the surface energy balance closure. During fair weather conditions, the net radiation exceeded the sum of turbulent and ground heat fluxes by up to 200 W m-2 when measurements with ground heat flux plates were used in the analysis. It is difficult to attribute this discrepancy to errors in turbulent fluxes, because the fetch was long enough (400 m or more). Also, the size and shape of the two bogs and the positions of the tower were different, but the discrepancies in the energy budget were very similar. It is, however, known that measurements with heat flux plates in the peat are problematic. The ground heat flux measured with plates was very low and was considered to be the most unreliable component of the surface energy balance. An alternative method from the literature, which used temperature measurements in the peat and at the surface but did not require any information on the soil thermal properties near the surface, was used for alternative ground-heat-flux calculations. The use of this method improved the closure of the surface energy balance, but an about 100 W m-2 large discrepancy still remained unexplained. A further improvement is expected when lateral heat exchange in the hummocks could be taken into account

Dynamics of biogenic gas bubbles in peat and their effects on peatland biogeochemistry

This is the peer reviewed version of the following article: Strack, M., Kellner, E. and Waddington, J.M. 2005. The dynamics of biogenic gas bubbles in peat and their effects on peatland biogeochemistry. Global Biogeochemical Cycles, 19, GB1003, doi: 10.1029/2004GB002330, which has been published in final form at https://doi.org/10.1029/2004GB002330. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.Production and emission of peat gas has attracted great interest because substantial amounts of methane (CH4) are emitted to the atmosphere from peat soils. Many studies indicate supersaturation of CH4 in peat water, implying a high potential for gas bubble formation. However, observations of bubbles in peat are often only qualitatively described, and in most cases the presence of entrapped gas has been largely ignored in peatland studies. On the basis of a review of literature, a conceptual model of entrapped gas dynamics was developed and investigated using field and laboratory measurements at a poor fen in central Quebec. We investigated variations in production and volume of gas and the effect of this gas on trace gas emissions, peat buoyancy, and pore water chemistry during 2002 and 2003. Measurements made with moisture probes and subsurface gas collectors revealed that gas volume varied throughout the growing season in relation to hydrostatic and barometric pressure. Shifts in entrapped gas volume were also coincident with changes in dissolved pore water CH4. The presence of these bubbles has important biogeochemical effects, including the development of localized CH4 diffusion gradients, alteration of local flow paths affecting substrate delivery, peat buoyancy, and the potential episodic release of CH4 via ebullition events. These interactions must be included in peatland models to describe accurately the hydrology and greenhouse gas emissions from these ecosystems and to make predictions about their response to environmental change.This research was supported by Premier’s Research Excellence Award, a NSERC Discovery Grant, and a Canadian Foundation for Climate and Atmospheric Sciences grant to J. M. W. and a NSERC Julie Payette Scholarship and NSERC Canada Graduate Scholarship to M. S

Towards a Realistic Energy Model for Wireless Sensor Networks

Energy consumption is one of the most critical protocol properties in a wireless sensor network. Therefore, a precise energy model is required for the evaluation of protocols. In addition to evaluation, an energy model can also be used for on-line energy accounting. After processing user queries, nodes aware of the energy model can send an energy bill towards the network\u27s sink. This allows the user to adjust future queries to be more energy efficient. The contribution of this paper is twofold: First, a theoretical energy model based on simple finite automata is presented. This model can be used for on-line accounting, simulation and generation of a-priori knowledge. Second, the proposed theoretical model is backed up by practical measurements using a new measurement device called SNMD that also offers management functions for sensor-net testbeds. Therewith, output of the theoretical model can be compared to and justified by real-world measurements

Statistical properties of hybrid estimators proposed for GEDI – NASA’s Global Ecosystem Dynamics Investigation

NASA’s Global Ecosystem Dynamics Investigation (GEDI) mission will collect waveform lidar data at a dense sample of ∼25 m footprints along ground tracks paralleling the orbit of the International Space Station (ISS). GEDI’s primary science deliverable will be a 1 km grid of estimated mean aboveground biomass density (Mg ha ^−1 ), covering the latitudes overflown by ISS (51.6 °S to 51.6 °N). One option for using the sample of waveforms contained within an individual grid cell to produce an estimate for that cell is hybrid inference, which explicitly incorporates both sampling design and model parameter covariance into estimates of variance around the population mean. We explored statistical properties of hybrid estimators applied in the context of GEDI, using simulations calibrated with lidar and field data from six diverse sites across the United States. We found hybrid estimators of mean biomass to be unbiased and the corresponding estimators of variance appeared to be asymptotically unbiased, with under-estimation of variance by approximately 20% when data from only two clusters (footprint tracks) were available. In our study areas, sampling error contributed more to overall estimates of variance than variability due to the model, and it was the design-based component of the variance that was the source of the variance estimator bias at small sample sizes. These results highlight the importance of maximizing GEDI’s sample size in making precise biomass estimates. Given a set of assumptions discussed here, hybrid inference provides a viable framework for estimating biomass at the scale of a 1 km grid cell while formally accounting for both variability due to the model and sampling error

Joint ICES/EUROMARINE: Workshop on common conceptual mapping methodologies (WKCCMM; Outputs from 2021 meeting)

The Joint ICES/EUROMARINE Workshop on Common Conceptual Mapping Methodologies (WKCCMM) aimed to advance approaches to support inter- and transdisciplinary science via qualitative conceptual models to inform Integrated Ecosystem Assessment (IEA) throughout Eu-ropean seas and beyond. The workshop focused on developing a common understanding of conceptual mapping meth-odologies, their key uses and limitations, and processes for effective conceptual modelling with stakeholders for a variety of applications (e.g. developing food-webs, socio-ecological modelling, scoping exercises, rapid/initial management action and/or impact evaluations). Discussion in-volved presentation and discussion of a range of conceptual modelling approaches and contexts through the examination of case studies. These case studies gave rise to a suite of recommenda-tions, including the development of a workflow for IEA, and more generic guidelines and best practice advice for the use of conceptual modelling approaches with stakeholders. Although stakeholders were not able to be included in this workshop, they were very much at the heart of discussions, with the challenges and good practices of stakeholder inclusion addressed. WKCCMM also investigated how the methodologies can be best used to contribute to IEA, and may otherwise be applied throughout the ICES community, including identifying opportunities for cross-collaboration and knowledge transfer within the network.info:eu-repo/semantics/publishedVersio

Aboveground biomass density models for NASA's Global Ecosystem Dynamics Investigation (GEDI) lidar mission

NASA's Global Ecosystem Dynamics Investigation (GEDI) is collecting spaceborne full waveform lidar data with a primary science goal of producing accurate estimates of forest aboveground biomass density (AGBD). This paper presents the development of the models used to create GEDI's footprint-level (similar to 25 m) AGBD (GEDI04_A) product, including a description of the datasets used and the procedure for final model selection. The data used to fit our models are from a compilation of globally distributed spatially and temporally coincident field and airborne lidar datasets, whereby we simulated GEDI-like waveforms from airborne lidar to build a calibration database. We used this database to expand the geographic extent of past waveform lidar studies, and divided the globe into four broad strata by Plant Functional Type (PFT) and six geographic regions. GEDI's waveform-to-biomass models take the form of parametric Ordinary Least Squares (OLS) models with simulated Relative Height (RH) metrics as predictor variables. From an exhaustive set of candidate models, we selected the best input predictor variables, and data transformations for each geographic stratum in the GEDI domain to produce a set of comprehensive predictive footprint-level models. We found that model selection frequently favored combinations of RH metrics at the 98th, 90th, 50th, and 10th height above ground-level percentiles (RH98, RH90, RH50, and RH10, respectively), but that inclusion of lower RH metrics (e.g. RH10) did not markedly improve model performance. Second, forced inclusion of RH98 in all models was important and did not degrade model performance, and the best performing models were parsimonious, typically having only 1-3 predictors. Third, stratification by geographic domain (PFT, geographic region) improved model performance in comparison to global models without stratification. Fourth, for the vast majority of strata, the best performing models were fit using square root transformation of field AGBD and/or height metrics. There was considerable variability in model performance across geographic strata, and areas with sparse training data and/or high AGBD values had the poorest performance. These models are used to produce global predictions of AGBD, but will be improved in the future as more and better training data become available

En fattigmyrs ytenergiutbyte och hydrologi

Mires surface energy and water budgets govern the conditions for climatic, hydrological, ecological and carbon balance processes. The components of the water and surface energy budgets were quantified over two growing seasons for an open boreal mire. The measurements of fluxes were complemented with data on the spatial variation of water content and temperature in different micro-relief elements (hummocks and hollows). Since measurements on mires are scarce, special investigations of aerodynamic properties were done as well as a calibration of TDR function for peat. The partitioning of available energy at the surface depended mainly on air temperature and relative humidity. There was a trend of falling Bowen ratio both during the day and during the season from May (monthly value 0.9) to September (0.6). The bulk surface resistance (rs) to evapotranspiration was considerable and varied little (mean rs = 160 s m-1). The cause of its relatively large value could be found in a great aerodynamic resistance within the canopy layer, and the peat wetness variation influenced little. In the scale of the whole mire, the water storage were similar over the central, open areas. On a smaller scale, the presence of a pronounced micro-topography caused a variation of the surface wetness. This was also reflected in the spatial variation of soil temperatures. The heat storage in hummock was largely influenced by lateral heat fluxes. There were considerable effects of peat elasticity and approximately 40 % of the changes in water storage was caused by swelling/shrinking of the whole peat mound. This effect should be incorporated in future models of mire-water dynamics

Årstidsbunden kvävebelastning och denitrifikation i dammar

A simple model was developed in order to investigate nitrogen retention by denitrification in pnds under the influence of different pond dimensions. Model input data, concerning water flow rate and nitrification concentration in the water, were taken from the runoff records from two small basins on arable land in southern Sweden. A water voume balance and a nitrate-nitrogen balace were determine in discrete time increments. The denitrification was assumed to take place only in the bottom sediments, depending on the nitrate concentration of the pond water. Four different calculations of denitrification was preformed, representing two diffrent sediment types with two seasonsl variations respectively, in addition, the calculations were preformed in three different ways, in three versions. In version I the nitrate concentration was assumed to be homogeneous in the whole of the pond, while in version II and III, the pond was assumed to be homogeneous in the whole of the pond, while in version II and III, the ond was divided into eight sections, in order to get more diversified concetrations in the pnd. In version III, a bottom outlet was added with the intention of getting a smoother outflow. Calculations with the version II and III were mainly performed with the purpose to compare them and combinations of them with each other, both in large single ponds and in pond systems/series with ponds of different sizes. The difference between the nitrate concentration at the inlet and the outlet depended in the current flow rate. At low flow periods, there was a conciderable difference between inlet- and outlet concentrations, while during high flow cnditions this difference decreased and, at times, was negligible. The yearly amount of denitrified nitrogen increased with increasing nitrogen input, corresponding to a high average nitrate concentration in the pond. At the same time, the relative reduction of transported nitrogen decreased, due to the connection between nitrogen transport and water flow. At high flow situations, the time during which the water was exposed to the sediment was reduced, leadeing to small reduction in nitrate concentrations in the pond. When compareing ponds with the same depth, a good agreement was found between the early relative rdeuction of the nitrogen transport and the average water retention time. The amount of denitrified nitrogen increased with increasing pond size. It was also found that the pond area has greater inpact than the pond depth. In comparisons btween version II and III, the total differences in the amout of denitrified nitrogen between different pond system were small. The denitrification was lower in the first pond with bottom outlet. As its water vlume decreased faster during low flow periods than in the pond without bottom outlet, its nitrate supply for denitrication also decreased faster. However, the smoother outflow from the pond with bottom outlet gave better conditions for denitrification to the subsequent ponds. The good agreement between average water retention time and relative reduction seems to be a reasonable starting point in using this type of model for pond dimensioning. However, special care must be taken when wirking with areas where the runoff pattern and nitrate concentrations differ considerably from those used as imput data. Comparing simulations were made, in which real measurements in a pond in southern Sweden were compared with calculated nitrogen retentions. The measured retention wasthen about 50 % higher than estimated. As the model calculations only deal with denitrification, it is also very likely that the total retention in sunderestimated. The denitrification itself is propably underestimated as well, as diffusion of nitrate into the sediment should increase in situations with high water flow. The strong dependence between flow rates and relative reduction of the nitrate transport seems, however, to agree with some published measurements

The stress-dependent dynamics of Saccharomyces cerevisiae tRNA and rRNA modification profiles

RNAs are key players in the cell, and to fulfil their functions, they are enzymatically modified. These modifications have been found to be dynamic and dependent on internal and external factors, such as stress. In this study we used nucleic acid isotope labeling coupled mass spectrometry (NAIL-MS) to address the question of which mechanisms allow the dynamic adaptation of RNA modifications during stress in the model organism S. cerevisiae. We found that both tRNA and rRNA transcription is stalled in yeast exposed to stressors such as H2O2, NaAsO2 or methyl methanesulfonate (MMS). From the absence of new transcripts, we concluded that most RNA modification profile changes observed to date are linked to changes happening on the pre-existing RNAs. We confirmed these changes, and we followed the fate of the pre-existing tRNAs and rRNAs during stress recovery. For MMS, we found previously described damage products in tRNA, and in addition, we found evidence for direct base methylation damage of 2′O-ribose methylated nucleosides in rRNA. While we found no evidence for increased RNA degradation after MMS exposure, we observed rapid loss of all methylation damages in all studied RNAs. With NAIL-MS we further established the modification speed in new tRNA and 18S and 25S rRNA from unstressed S. cerevisiae. During stress exposure, the placement of modifications was delayed overall. Only the tRNA modifications 1-methyladenosine and pseudouridine were incorporated as fast in stressed cells as in control cells. Similarly, 2′-O-methyladenosine in both 18S and 25S rRNA was unaffected by the stressor, but all other rRNA modifications were incorporated after a delay. In summary, we present mechanistic insights into stress-dependent RNA modification profiling in S. cerevisiae tRNA and rRNA