Altered energy flow pathways in a lake ecosystem following manipulation of fish community structure

We used carbon and nitrogen stable isotope analyses to assess the relative contributions from pelagic and littoral energy sources to higher trophic levels in a lake ecosystem before and after a major food web perturbation. The food web structure of the lake was altered when the population sizes of the most abundant fish species (small perch, roach and bream) were reduced during an attempt to improve water quality by biomanipulation. Fish removal was followed by dense year classes of young fish, which subsequently increased the utilisation of pelagic resources. This was reflected as a decrease in relative energy contribution from littoral sources and also led to more distinct pelagic and littoral food chains after fish removal. Community metrics calculated from stable isotope data indicated increased trophic diversity and occupied niche area, and reduced trophic redundancy in the food web. However, only minor changes were observed in fish trophic positions, although roach and pike occupied slightly lower trophic positions after fish removal. Despite the Jyväsjärvi ecosystem becoming more dependent on pelagic energy after fish removals, the littoral energy contribution was still substantial, particularly to certain fish species. Hence, our results support recent arguments for the importance of benthic production in lake ecosystems. More generally, our results illustrate how large-scale perturbations of food web structure can alter energy flow patterns through an entire ecosystem.     

A climatology of infrasound detections in northern Norway at the experimental ARCI array

The study of infrasound is experiencing a renaissance in recent years since it was chosen as a verification technique for the Comprehensive Nuclear-Test-Ban Treaty. Currently, 60 infrasound arrays are being installed to monitor the atmosphere for nuclear tests as part of the International Monitoring System (IMS). The number of non-IMS arrays also increases worldwide. The experimental ARCES infrasound array (ARCI) is an example of such an initiative. The detectability of infrasound differs for each array and is a function of the array location and configuration, the state of the atmosphere, and the presence of natural and anthropogenic sources. In this study, a year of infrasound data is analyzed as recorded by ARCI. Contributions of the atmosphere and the sources are evaluated in both a low- (0.1–1.0 Hz) and high-frequency (1.0–7.0 Hz) pass-band. The enormous number of detections in the low-frequency band is explained in terms of the stratospheric wind and ocean wave activity and compared with the detection of microseism. Understanding the detectability in the low-frequency band is of utmost importance for successfully applying infrasound as a verification technique since small-sized nuclear test will show up in this frequency range.     

Matching INSPIRE Quality of Service Requirements with Hybrid Clouds

A lot of effort has been invested in Spatial Data Infrastructures (SDIs) during the last decade regarding interoperable standards for services and data. But still the scalability and performance of SDI services is reported to be crucial especially if they are accessed concurrently by a high number of users. Furthermore, laws and provisions such as the INSPIRE directive specify challenging requirements regarding the performance, availability and scalability of SDI services. This article presents a Hybrid Cloud architecture for matching INSPIRE‐related Quality of Service (QoS) requirements, without investing in rarely used hardware in advance, by occupying external third‐party resources on a pay‐as‐you‐go basis. The presented Hybrid Cloud is a composition of a local IT‐infrastructure (Private Cloud) and the computational resources of third‐party vendors (Public Cloud). The local infrastructure is laid out to handle the average main load of a service and in lasting peak times additional resources of external providers are allocated and integrated on demand into the local infrastructure to provide sufficient service quality automatically. A proof‐of‐concept implementation of the proposed Hybrid Cloud approach is evaluated and benchmarked with respect to INSPIRE‐related QoS requirements.     

Advanced constitutive modelling of shotcrete: Model formulation and calibration

Shotcrete is one of the main support elements for tunnels constructed according to the principles of the New Austrian Tunnelling Method (NATM). In this paper, a sophisticated constitutive model for the complex mechanical and time-dependent behaviour of shotcrete is presented, which is formulated within the framework of elasto-plasticity. Two independent yield surfaces govern the material behaviour in compression and tension under multi-axial loading conditions, which is further controlled by non-linear plastic strain hardening and softening rules following uniaxial stress–strain curves. The main novelty of the model is the introduction of normalised hardening and softening parameters which enable a more realistic simulation of the shotcrete loading history. In addition, cracking of the shotcrete is treated within the smeared crack concept by applying a fracture energy approach as a regularisation technique, which eliminates the dependency of the results on the size of the elements in a finite element mesh. Furthermore, the model takes into account the gradual change of the main material properties of the shotcrete due to cement hydration during the first 28 days after spraying. Other important time effects such as creep, shrinkage and hydration temperature induced deformations at early ages are considered in the current model formulation. This paper aims to describe in detail the developed structure of the constitutive model and model calibration.     

Dust deposition in the Aral Sea: implications for changes in atmospheric circulation in central Asia during the past 2000 years

We investigated mineral aerosol (dust) deposition in the Aral Sea with intention to understand the variability of dust in central Asia and its implications for atmospheric circulation change in the late Holocene. Using an 11.12-m sediment core of the lake, we calculated bulk sediment fluxes at high time-resolution and analyzed grain-size distributions of detrital sediments. A refined age-depth model was established by combined methods of radiocarbon dating and archeological evidence. Besides, a principal component analysis (PCA) of grain-size fractions and elements (Fe, Ti, K, Ca, Sr) was used to assess the potential processes controlling detrital inputs. The results suggest that two processes are mainly relevant for the clastic input as the medium silt fractions and Ti, Fe and K are positively correlated with Component 1 (C1), and the fine size fractions (<6 μm) are positively correlated with Component 2 (C2). Taking the results of the PCA, geological backgrounds, clastic input processes into account, we propose that the medium silt fractions and, in particular, the grain-size fraction ratio (6–32 μm/2–6 μm), can serve as indicators of the variability of airborne dust in the Aral Sea region. On the contrary, the fine size fractions appear to be contributed mainly by the sheetwash processes. The bulk sediment deposition fluxes were extremely high during the Little Ice Age (LIA; AD 1400–1780), which may be related to the increased dust deposition. As indicated by the variations of grain-size ratio and Ti, the history of dust deposition in central Asia can be divided into five distinct periods, with a remarkably low deposition during AD 1–350, a moderately high value from AD 350–720, a return to relatively low level between AD 720 and AD 1400 (including the Medieval Warm Period (MWP, AD 755–1070)), an exceptionally high deposition from AD 1400 to 1940s and an abnormally low value since 1940s. The temporal variations in the dust deposition are consistent with the changes in the Siberian High (SH) and mean atmospheric temperature of the northern hemisphere during the past 2000 years, with low/high annual temperature anomalies corresponding to high/low dust supplies in the Aral Sea sediments, respectively. The variations in the fine size fraction also show a broadly similarity to a lacustrine δ¹⁸O record in Turkey (Jones et al., 2006), implying that there was less moisture entering western central Asia from the Mediterranean during the LIA than during the MWP.     

Electron microprobe study of detrital amphiboles from Famennian synorogenic clastic sediments of the Saxothuringian belt (Erbendorf Paleozoic,NE-Bavaria,Germany): Consequences for provenance and geotectonic development

Abstract

Detrital amphiboles from the Famennian, Saxothuringian greywackes of the “Erbendorf Paleozoic” in Bavaria were analysed with an electron microprobe. The results were compared with recalculated literature data of amphiboles from potential source rocks to obtain more detailed information about the provenance of the oldest preserved synorogenic sediments in the Saxothuringian belt.

All of the detrital amphiboles show very similar, homogeneous chemical compositions. All of them are Ca-amphiboles (with (Ca+Na)_B ≥: 1.34; Naf_B < 0.67; (Na+K)_A < 0.50 and Ti < 0.50), mostly inagnesio-hornblende and tschermakitic hornblende. The comparison with amphiboles from rocks of potential provenance areas reveals that the Randamphibolit-Series of the Miinchberg Massif – or an equivalent, already eroded unit – can be regarded as source rock of the detrital amphiboles.

The presented data are the first evidence, that the Randamphibolit of the Miinchberg Massif was exhumed as early as in the Famennian, shortly after its metamorphism. It can be concluded that before Famennian time the complete Saxothuringian oceanic crust and large parts of the Saxothuringian continental crust had been subducted at the active margin. This implies that the collision of the Saxothuringian plate with the Tepla-Barrandian microplate, leading to the accretion of the Saxothuringian plate, happened 15–20 Ma earlier than previous authors had supposed. Accordingly, the collisional stage must have been reached not later than in the middle Devonian (approx. 380 Ma).     

Dark Carbon Fixation in the Columbia River’s Estuarine Turbidity Maxima: Molecular Characterization of Red-Type cbbL Genes and Measurement of DIC Uptake Rates in Response to Added Electron Donors

Dark CO₂ fixation has been shown to rival the importance of oxygenic photosynthesis in the global carbon cycle, especially in stratified environments, such as salt wedge estuaries. We investigated this process in the Columbia River estuary using a variety of techniques including functional gene cloning of cbbL (the large subunit of form I RuBisCO), quantitative real-time PCR (qPCR) estimations of cbbL abundance, and analyses of stimulated ¹⁴C-bicarbonate assimilation. A diversity of red-type cbbL genes were retrieved from clone libraries, with 28 unique operational taxonomic units determined from 60 sequences. The majority of the sequences formed two clusters that were distinct from the major clusters typically found in soil environments, revealing the presence of a unique community of autotrophic or facultatively autotrophic/mixotrophic microorganisms in the Columbia River estuary. qPCR estimates indicated that roughly 0.03–0.15 % of the microbial population harbored the cbbL gene, with greater numbers of total bacteria and cbbL gene copies found in the estuarine turbidity maxima (ETM) compared to non-ETM events. In vitro incubations with radiolabeled bicarbonate indicated maximum stimulation by thiosulfate and also suggested that a diversity of other potential electron donors may stimulate CO₂ fixation, including nitrite, ammonium, and Mn(II). Taken together, these results highlight the diversity of the microbial metabolic strategies employed and emphasize the importance of dark CO₂ fixation in the dynamic waters of the Columbia River estuary despite the abundance of organic material.     

Fault zone signatures from ambient vibration measurements: a case study in the region of Visp (Valais, Switzerland)

Investigations of tectonic features, such as faults, are important challenges for geologists and engineers. Although direct investigational methods, such as boreholes and trenches, have the potential to provide accurate data, these direct methods are usually expensive and time consuming, and give only punctual insights into subsurface structures. Geophysical methods, for example electric surveys and ground penetrating radar, are less expensive and faster to implement. However, these geophysical methods may be difficult or sometimes even impossible to apply in regions with rough topography or regions which are highly urbanized. In this study, we propose an easy-to-use and affordable method to detect fault zones based on ambient vibration observations. We apply this method in the region between Visp and Unterstalden (canton Valais, Switzerland) on a small fault branch, which has no explicit surface expression, and which is linked to a major fault zone, the Simplon Fault Zone. The assumption is that the fault of interest is surrounded by damage zone consisting of fractured rock, and that this results in lateral changes of both seismic velocity and attenuation. The objective was, first, to identify such lateral changes in the observed seismic wave-field, and second, to map any anomalies and combine them with the available geological information. In this way, we were able to follow the fault trace even without a clear surface expression of the fault. Our observations showed the existence of a signature in the power spectra of the seismic noise that may correspond to a damage zone. Such signature is observed along the trace of the expected fault.