Chironomids as quantitative indicators of mean July air temperature: validation by comparison with century-long meteorological records from northern Sweden

This study evaluates the potential of using chironomid assemblages to estimate past temperature changes by comparing chironomid-inferred temperatures to meteorological data for the last 87 years. This comparison is made using high-resolution (i.e., sub-decadally resolved) short cores of four lakes along a gradient of altitude (Lake Njulla, 999 m a.s.l., Lake 850, 850 m a.s.l., Lake Alanen Laanijavri, 365 m a.s.l. and Lake Vuoskkujavri, 348 m a.s.l.), vegetation (pine forest to alpine tundra vegetation) and temperature (mean July temperature of 12.4 to 8.1°C). Patterns of chironomid-inferred changes in mean July air temperature were highly comparable to changes in the meteorological data. Moreover, instrumental data were almost always within the specific errors of the quantitative estimates using chironomids. These results indicate that chironomids can be used as a powerful tool to reconstruct temperatures and that chironomids are sensitive enough to record temperature changes of low magnitude such as those recorded during the Holocene. Although this relationship between temperature and chironomid community is strong for the last 87 years, we cannot assume that other environmental factors such as organic matter, changes of lake water depth or oxygen availability were not more significant over longer temporal scales of the Holocene, or longer.     

Tropospheric water vapour soundings by lidar at high Arctic latitudes

Ground-based lidars can provide continuous observations of tropospheric humidity profiles using the Raman scattering of light by water vapour and nitrogen molecules. We will present specific humidity profiles obtained at the high Arctic location Ny-Ålesund (Spitsbergen, 79°N). Under nighttime conditions the observations cover a range from about 500 m altitude up to the upper troposphere. Daylight limits the observations to the lower troposphere, depending on atmospheric transmission and the water vapour content. In a case study on 29 January, simultaneous observations of humidity and aerosol extinction show distinct differences in the various altitudes during the advection of aerosol-rich air masses. In the boundary layer, the aerosol is less affected by the humidity. In the free troposphere, the lidar ratio was observed to be up to 60 sr with some evidence for the uptake of water vapour by the aerosol particles. In another case study from 28 February 2002, the influence of the mean wind direction and the orography on the water vapour concentration near the ground and in the free troposphere will be discussed. During wintertime, a humidity inversion up to about 1.5 km altitude with dry air near the ground has frequently been found with wind from the southeast. Such local effects and small-scale structures observed by stationary lidar mostly cannot be resolved by other sounding methods like passive satellite soundings.     

Balloon Intercomparison Campaigns: Results of remote sensing measurements of HCl

All of the techniques used to measure stratospheric HCl during the two BIC campaigns involved high resolution infrared spectroscopy. The balloon-borne instruments included five different spectrometers, three operating in the solar absorption mode and two in emission (at distinctly different wavelengths). Ground-based and aircraft correlative measurements were made close to the balloon locations, again by near-infrared spectroscopy.Within this set of results, comparisons between different techniques (absorption vs emission) viewing the same airmass (i.e., on the same gondola) were possible, as were comparisons between the same technique used on different gondolas spaced closely in time and location. The final results yield a mean profile of concentration of HC1 between 18 and 40 km altitude; an envelope of ±15% centered on this profile encompasses all of the results within one standard deviation of their individual mean values. The absolute accuracy of the final profile is estimated to be no worse than 10%. It is concluded also that the measurement techniques for HCl have reached a level of performance where a precision of 10% to 15% can be confidently expected.     

Differential geodetic stereo SAR with TerraSAR-X by exploiting small multi-directional radar reflectors

In this paper, we report on the direct positioning of small multi-directional radar reflectors, so-called octahedrons, with the synthetic aperture radar (SAR) satellite TerraSAR-X. Its highest resolution imaging mode termed staring spotlight enables the use of such octahedron reflectors with a dimension of only half a meter, but still providing backscatter equivalent to 1–2 cm observation error. Four octahedrons were deployed at Wettzell geodetic observatory, and observed by TerraSAR-X with 12 acquisitions in three different geometries. By applying our least squares stereo SAR algorithm already tested with common trihedral corner reflectors (CRs), and introducing a novel differential extension using one octahedron as reference point, the coordinates of the remaining octahedrons were directly retrieved in the International Terrestrial Reference Frame (ITRF). Contrary to our standard processing, the differential approach does not require external corrections for the atmospheric path delays and the geodynamic displacements, rendering it particularly useful for joint geodetic networks employing SAR and GNSS. In this paper, we present and discuss both methods based on results when applying them to the aforementioned Wettzell data set of the octahedrons. The comparison with the independently determined reference coordinates confirms the positioning accuracy with 2–5 cm for the standard approach, and 2–3 cm for the differential processing. Moreover, we present statistical uncertainty estimates of the observations and the positioning solutions, which are additionally provided by our parameter estimation algorithms. The results also include our 1.5 m CR available at Wettzell, and the outcomes clearly demonstrate the advantage of the multi-directional octahedrons over conventional CRs for global positioning applications with SAR.     

Testing Nano-Powder and Fused-Glass Mineral Reference Materials for In Situ Rb-Sr Dating of Glauconite,Phlogopite, Biotite and Feldspar via LA-ICP-MS/MS

Reference materials (RMs) with well-characterised composition are necessary for reliable quantification and quality control of isotopic analyses of geological samples. For in situ Rb-Sr analysis of silicate minerals via laser ablation inductively coupled plasma tandem mass spectrometry (LA-ICP-MS/MS) with a collision/reaction cell, there is a general lack of mineral-specific and matrix-matched RMs, which limits wider application of this new laser-based dating technique to certain minerals. In this work, pressed nano-powder pellets (NP) of four RMs, GL-O (glauconite), Mica-Mg (phlogopite), Mica-Fe (biotite) and FK-N (K-feldspar), were analysed and tested for in situ Rb-Sr dating, complemented by isotope dilution (ID) MC-ICP-MS Rb-Sr analyses of GL-O and Mica-Mg. In addition, we attempted to develop alternative flux-free and fused ‘mineral glasses’ from the above RMs for in situ Rb-Sr dating applications. Overall, the results of this study showed that among the above RMs only two NP (Mica-Mg-NP and GL-O-NP) were suitable and robust for in situ dating applications. These two nano-powder reference materials, Mica-Mg-NP and GL-O-NP, were thus used as primary RMs to normalise and determine Rb-Sr ages for three natural minerals: MDC phlogopite and GL-O glauconite grains, and also Mica-Fe-NP (biotite). Our in situ analyses of the above RMs yielded Rb-Sr ages that are in good agreement (within 8%) of published ages, which suggests that both Mica-Mg-NP and GL-O-NP are suitable RMs for in situ Rb-Sr dating of phlogopite, glauconite and biotite. However, using secondary RMs is recommended to monitor the quality of the obtained ages.     

Copper- and iron-induced injuries in roots and rhizomes of reed (Phragmites australis)

About 1 mg/g dw Cu²⁺ and 8 mg/g dw Fe²⁺ were found in roots of reed plants when fed with heavy metal concentrations of 100 μM Cu²⁺ and 10 mM Fe²⁺ under hypoxia. Roots seemed to act as a kind of filter since the amounts in rhizomes were only 0.06 mg Cu²⁺/g dw and 2 mg Fe²⁺/g dw. Increased contents of both ions reduced posthypoxic respiration capacity by 40–50% and also the sum of adenylates (ATP, ADP, AMP) by the same order of magnitude, although energy charge values remained above 0.85 in Cu²⁺ and 0.79 in Fe²⁺ treatments. Energy metabolism of rhizomes was not affected. Copper and iron contents of roots as well as of rhizomes were high enough to induce oxidative stress when roots were fed with 40 μM Cu²⁺ and 1 mM Fe²⁺, respectively.From our results we conclude that increased, but environmentally attainable, amounts of copper and reduced iron ions disturb root energy metabolism, and therefore root functioning and development. Latent injuries, based on oxidative stress, may be harmful for roots and rhizomes under long term exposure.     

Modeling ground water flow in alluvial mountainous catchments on a watershed scale

In large mountainous catchments, shallow unconfined alluvial aquifers play an important role in conveying subsurface runoff to the foreland. Their relatively small extent poses a serious problem for ground water flow models on the river basin scale. River basin scale models describing the entire water cycle are necessary in integrated water resources management and to study the impact of global climate change on ground water resources. Integrated regional-scale models must use a coarse, fixed discretization to keep computational demands low and to facilitate model coupling. This can lead to discrepancies between model discretization and the geometrical properties of natural systems. Here, an approach to overcome this discrepancy is discussed using the example of the German-Austrian Upper Danube catchment, where a coarse ground water flow model was developed using MODFLOW. The method developed uses a modified concept from a hydrological catchment drainage analysis in order to adapt the aquifer geometry such that it respects the numerical requirements of the chosen discretization, that is, the width and the thickness of cells as well as gradients and connectivity of the catchment. In order to show the efficiency of the developed method, it was tested and compared to a finely discretized ground water model of the Ammer subcatchment. The results of the analysis prove the applicability of the new approach and contribute to the idea of using physically based ground water models in large catchments.     

Influence of root characteristics and soil variables on the uprooting mechanics of Avena sativa and Medicago sativa seedlings

The success of seedlings and rejuvenated woody debris growing on river bedforms depends on the resistance to uprooting by flow provided by their simple root architecture. Avena sativa and Medicago sativa seedlings were used in flume experiments as prototypes for juvenile riparian plants. Very little is known about the magnitude of root anchoring forces and the role of secondary roots of such simple root systems. We performed 1550 vertical uprooting experiments on Avena sativa and Medicago sativa seedlings grown in quartz sand. Seedlings were pulled up by direct traction using a wheel driven by a computer‐controlled motor and the force was recorded. Roots were scanned and architectural parameters (root length and number of roots) determined. Uprooting force and work (the integral of the applied force times the distance over which it is applied) were then related to root architecture and soil variables. Resistance to uprooting increased with decreasing sediment size and sediment moisture content. The initial response of the root–soil system to uprooting showed linear elastic behaviour with modulus increasing with plant age. While the maximum uprooting force was found to increase linearly with total root length and be mainly dependent on the length of the main root, uprooting work followed a power law and has to be related to the whole root system. Thus, for the young plants we considered, secondary roots are responsible for the ability to withstand environmental disturbances in terms of duration rather than magnitude. This distinction between primary and secondary roots can be of crucial importance for seedlings of riparian species germinating on river bars and islands where inundation is a main cause of mortality. Beyond clarifying the biomechanical role of soil and root variables, the uprooting statistics obtained are useful in interpreting and designing ecomorphodynamic flume experiments. Copyright © 2014 John Wiley & Sons, Ltd.