Partitioning autotrophic and heterotrophic respiration in an ombrotrophic bog

Northern peatlands are globally significant carbon stores, but the sink strength varies from year to year due to changes in environmental conditions. Ecosystem respiration (ER) is composed of both autotrophic respiration (AR) that consists of respiration by plant parts, and heterotrophic respiration (HR) that consists of respiration by microbial bacteria in the soil, fungi, etc. Manual measurements only crudely partition AR and HR, which may lead to erroneous estimates if a change favours one form of respiration over another and may influence our interpretation in the magnitude of respiration. HR has also been thought to be more linked to vegetation dynamics, particularly in wetter, sedge-dominated ecosystems like fens. It is unknown whether such plant-soil-root interactions influence HR in peatlands dominated by woody shrubs whose water table is located further below the surface. The objectives of this study were to 1) determine the contributions of AR and HR at Mer Bleue, an ombrotrophic bog, 2) explore how environmental conditions influence ER and its components, 3) determine how different methodological approaches (e.g. directly measured respiration using automatic chambers vs. extrapolated calculations) can influence our interpretation in the magnitude of respiration, and 4) compare the respiration dynamics with those found in the literature for other peatland types. Our results revealed differences in AR and HR contributions to ER compared to other peatland types reported in the literature. The AR/HR ratio was 3.0 and AR contributions to ER were similar to 75% at our study bog, which is generally higher than AR contributions from fens, but also decreased substantially during extended drier periods. HR contributions increased with rising temperature and water table depth. Directly measured ER was smaller than when ER was estimated using night-time relationships with temperature. The magnitude of ER changed depending on the plant biomass, which we believe to be a result of vegetation dynamics influencing HR. The results of this study improved our understanding of peatland carbon cycling as well as the conceptualization of HR

GigaRad – a multi-purpose high-resolution ground-based radar system

Recently DLR has developed and constructed a new experimental radar instrument for various applications like radar signature collection, SAR/ISAR imaging, motion detection, tracking, etc., where high performance and high flexibility have been the key drivers for system design. Consequently a multi-purpose and multi-channel radar called GigaRad is operated in X band and allows an overall bandwidth of up to 6 GHz, resulting in a theoretical range resolution of up to 2.5 cm. Hence, primary obligation is a detailed analysis of various possible error sources, being of no or less relevance for low-resolution systems. A high degree of digital technology enables advanced signal processing and error correction to be applied. The paper outlines technical main features of the radar, the basic error correction strategy and illustrates some first imaging results

Soil moisture controls the partitioning of carbon stocks across a managed boreal forest landscape

Boreal forests sequester and store vast carbon (C) pools that may be subject to significant feedback effects induced by climatic warming. The boreal landscape consists of a mosaic of forests and peatlands with wide variation in total C stocks, making it important to understand the factors controlling C pool sizes in different ecosystems. We therefore quantified the total C stocks in the organic layer, mineral soil, and tree biomass in 430 plots across a 68 km2 boreal catchment. The organic layer held the largest C pool, accounting for 39% of the total C storage; tree and mineral C pools accounted for 38% and 23%, respectively. The size of the soil C pool was positively related to modelled soil moisture conditions, especially in the organic soil layer (R2 = 0.50). Conversely, the tree C pool exhibited a unimodal relationship: storage was highest under intermediate wetness conditions. The magnitude and variation in the total soil C stocks observed in this work were comparable to those found at the national level in Sweden, suggesting that C accumulation in boreal landscapes is more sensitive to local variation resulting primarily from differences in soil moisture conditions than to regional differences in climate, nitrogen deposition, and parent material

The effects of the recent economic crisis on social protection and labour market arrangements across socio-economic groups

The Great Recession did not only affect European countries to a varying extent, its impact on national labour markets and on specific socio-economic groups in those markets also varied greatly. Institutional arrangements such as employment protection, unemployment insurance benefits and minimum income support, working time flexibility and wage setting played a crucial role in determining to what extent the economic crisis led to higher unemployment, wage cuts or income losses and rising poverty. As the crisis gained momentum, the action of automatic stabilisation mechanisms built into the national tax-benefit and social protection systems was accompanied by heterogeneous sets of discretionary policy measures. While these factors can explain cross-country variation in labour market developments, they also lead to an unequal distribution of economic risks associated with the crisis across socio-economic groups. The present paper aims to investigate and assess to what extent the financial and economic crisis that hit the global economy in 2008-2009 impacted these labour market developments and to what extent different socio-economic groups were affected

Parameter interactions and sensitivity analysis for modelling carbon heat and water fluxes in a natural peatland, using CoupModel v5

In contrast to previous peatland carbon dioxide (CO2) model sensitivity analyses, which usually focussed on only one or a few processes, this study investigates interactions between various biotic and abiotic processes and their parameters by comparing CoupModel v5 results with multiple observation variables. Many interactions were found not only within but also between various process categories simulating plant growth, decomposition, radiation interception, soil temperature, aerodynamic resistance, transpiration, soil hydrology and snow. Each measurement variable was sensitive to up to 10 (out of 54) parameters, from up to 7 different process categories. The constrained parameter ranges varied, depending on the variable and performance index chosen as criteria, and on other calibrated parameters (equifinalities). Therefore, transferring parameter ranges between models needs to be done with caution, especially if such ranges were achieved by only considering a few processes. The identified interactions and constrained parameters will be of great interest to use for comparisons with model results and data from similar ecosystems. All of the available measurement variables (net ecosystem exchange, leaf area index, sensible and latent heat fluxes, net radiation, soil temperatures, water table depth and snow depth) improved the model constraint. If hydraulic properties or water content were measured, further parameters could be constrained, resolving several equifinalities and reducing model uncertainty. The presented results highlight the importance of considering biotic and abiotic processes together and can help modellers and experimentalists to design and calibrate models as well as to direct experimental set-ups in peatland ecosystems towards modelling needs

Limitations and Challenges of MODIS-Derived Phenological Metrics Across Different Landscapes in Pan-Arctic Regions

Recent efforts have been made to monitor the seasonal metrics of plant canopy variations globally from space, using optical remote sensing. However, phenological estimations based on vegetation indices (VIs) in high-latitude regions such as the pan-Arctic remain challenging and are rarely validated. Nevertheless, pan-Arctic ecosystems are vulnerable and also crucial in the context of climate change. We reported the limitations and challenges of using MODerate-resolution Imaging Spectroradiometer (MODIS) measurements, a widely exploited set of satellite measurements, to estimate phenological transition dates in pan-Arctic regions. Four indices including normalized vegetation difference index (NDVI), enhanced vegetation index (EVI), phenology index (PI), plant phenological index (PPI) and a MODIS Land Cover Dynamics Product MCD12Q2, were evaluated and compared against eddy covariance (EC) estimates at 11 flux sites of 102 site-years during the period from 2000 to 2014. All the indices were influenced by snow cover and soil moisture during the transition dates. While relationships existed between VI-based and EC-estimated phenological transition dates, the R-2 values were generally low (0.01-0.68). Among the VIs, PPI-estimated metrics showed an inter-annual pattern that was mostly closely related to the EC-based estimations. Thus, further studies are needed to develop region-specific indices to provide more reliable estimates of phenological transition dates.Peer reviewe

Broadband Polarizer Miter Bend for High Power Radar Applications

Polarizer miter bends are used to alter the polarization in overmoded waveguides. For future space debris observation with broadband high power W-band radar sensors these are important transmission line components. A polarizer miter bend uses a grooved mirror as phase grid for polarization. The present paper addresses a suitable design of such a phase grid for broadband high power radar applications within the frequency range from 90GHz to 100GHz. An appropriate parameter combination is found by a parametric study. For reduction of the required amount of calculation a plane wave approximation and unit cell simulations are used. With a suitable parameter combination a cross polarization of Xpol B −26 dB can be achieved within the considered frequency range. This corresponds to a suitable value for radar applications

Isotopic Branchpoints : Linkages and Efficiencies in Carbon and Water Budgets

Forests pass water and carbon through while converting portions to streamflow, soil organic matter, wood production, and other ecosystem services. The efficiencies of these transfers are but poorly quantified. New theory and new instruments have made it possible to use stable isotope composition to provide this quantification of efficiencies wherever there is a measurable difference between the branches of a branchpoint. We present a linked conceptual model that relies on isotopes of hydrogen, carbon, and oxygen to describe these branchpoints along the pathway from precipitation to soil and biomass carbon sequestration and illustrate how it can be tested and generalized. Plain Language Summary The way a forest works can be described in terms of carbon and water budgets, which describe the ways that carbon and water flow through the forest. The paths of such flows are frequently branched and the branches are often different in their stable isotope composition. This means that stable isotopes can be used to describe the branching events. We present isotopic methods of quantifying several such events, then link them in a chain that begins with the evaporation of water and ends with biomass production.Non peer reviewe

Inverse Synthetic Aperture Radar Imaging of Space Targets Using Wideband Pseudo-Noise Signals with Low Peak-to-Average Power Ratio

With the number of new satellites increasing dramatically, comprehensive space surveillance is becoming increasingly important. Therefore, high-resolution inverse synthetic aperture radar (ISAR) imaging of satellites can provide an in-situ assessment of the satellites. This paper demonstrates that pseudo-noise signals can also be used for satellite imaging, in addition to classical linear frequency-modulated chirp signals. Pseudo-noise transmission signals offer the advantage of very low cross-correlation values. This, for instance, enables the possibility of a system with multiple channels transmitting instantaneously. Furthermore, it can significantly reduce signal interference with other systems operating in the same frequency spectrum, which is of particular interest for high-bandwidth, high-power systems such as satellite imaging radars. A new routine has been introduced to generate a wideband pseudo-noise signal with a peak-to-average power ratio (PAPR) similar to that of a chirp signal. This is essential for applications where the transmit signal power budget is sharply limited by the high-power amplifier. The paper presents both theoretical descriptions and analysis of the generated pseudo-noise signal as well as the results of an imaging measurement of a real space target using the introduced pseudo-noise signals