Estimating flow and transport parameters in the unsaturated zone with pore water stable isotopes

The first author was funded by the DFG Research Group: From Catchments as Organised Systems to Models based on Functional Units (FOR 1598). The second author was funded by the DFG project Coupled soil-plant water dynamics – Environmental drivers and species effects (contract numbers: GE 1090/10-1 and WE 4598/2-1). The isotope data in the precipitation for Roodt were provided by FNR/CORE/SOWAT, project of the Luxembourg Institute of Science and Technology – LIST. Sampling of the isotope profiles was made possible by the support of the CAOS Team and Begona Lorente Sistiaga, Benjamin Gralher, Andre Böker, Marvin Reich and Andrea Popp. Special thanks to Britta Kattenstroth and Jean Francois Iffly for their technical support in the field and Barbara Herbstritt for her support in the laboratory. For Roodt, soil texture and hydraulic parameter information were provided by Conrad Jackisch and Christoph Messer (KIT, Karlsruhe, Germany) and hydraulic conductivity data were provided by Christophe Hissler and Jérôme Juilleret (LIST). Pore water isotope and soil moisture data for Hartheim were provided by Steffen Holzkämper and Paul Königer. Temperature and precipitation data for Hartheim were provided by the Chair of Meteorology and Climatology, University of Freiburg.Peer reviewedPublisher PD

Das hydrologische Extremjahr 2011: Dokumentation, Einordnung, Ursachen und Zusammenhänge

Beteiligte Personen und Organisationen: Kohn, Irene; Albert-Ludwigs-Universität Freiburg und Bundesanstalt für Gewässerkund

Herstellung und Charakterisierung von plasmonischen Nanomaterialien

Im Rahmen dieser Arbeit wurden bottom-up Herstellungsverfahren für plasmonische Sensoren entwickelt. Sie wurden durch eine Kombination von kolloidaler Lithographie und chemischer Goldabscheidung präpariert. Als Kolloide kamen Hydrogelkugeln zum Einsatz, deren Volumen durch externe Stimuli verändert werden kann. Diese weichen Mikrosphären bilden durch Selbstorganisation zweidimensionale nicht-dichtest-gepackte Gitter. Ihre Gitterkonstante und der Kolloid-Durchmesser konnten hier erstmalig unabhängig voneinander kontrolliert werden. Die Hydrogelkugeln dienten sowohl als Maske für die Erzeugung eines periodischen Lochmusters in einem Goldfilm als auch als Matrix für die Abscheidung von Gold in den Löchern.Die optischen Eigenschaften von Goldnanostrukturen werden durch Oberflächenplasmonenresonanz bestimmt, die durch die Morphologie der Goldnanostruktur beeinflusst wird und empfindlich auf Veränderungen im Brechungsindex reagiert. Daher werden Goldnanostrukturen als Sensoren eingesetzt. Im Rahmen dieser Arbeit wurden zwei Sensoren mit gesteigerter Empfindlichkeit auf Basis von periodischen Lochmustern in Goldfilmen realisiert. Der erste Sensor bestand aus einer koaxialen Goldstruktur, die durch Modifizierung der Hydrogelkugeln mit Goldnanopartikeln und thermische Behandlung erzeugt wurden. Sie wiesen im Vergleich zu einer Lochstruktur ohne Goldnanopartikel eine doppelt so hohe Empfindlichkeit auf. Im zweiten Sensor wurden die Hydrogelkugeln in den Löchern des Goldfilmes belassen und mit einer Goldschicht bedeckt. Die im Lochfilm eingebetteten Gold/Hydrogelkugeln steigerten die Sensitivität des Sensors um mehr als eine Größenordnung

Occurrence and formation of indole-3-acetamide in Arabidopsis thaliana

An HPLC/GC–MS/MS technique (high-pressure liquid chromatography in combination with gas chromatography–tandem mass spectrometry) has been worked out to analyze indole-3-acetamide (IAM) with very high sensitivity, using isotopically labelled IAM as an internal standard. Using this technique, the occurrence of IAM in sterile-grown Arabidopsis thaliana (L.) Heynh. was demonstrated unequivocally. In comparison, plants grown under non-sterile conditions in soil in a greenhouse showed approximately 50% higher average levels of IAM, but the differences were not statistically significant. Thus, microbial contributions to the IAM extracted from the tissue are likely to be minor. Levels of IAM in sterile-grown seedlings were highest in imbibed seeds and then sharply declined during the first 24 h of germination and further during early seedling development to remain below 20–30 pmol g–1 fresh weight throughout the rosette stage. The decline in indole-3-aetic acid (IAA) levels during germination was paralleled by a similar decline in IAM levels. Recombinant nitrilase isoforms 1, 2 and 3, known to synthesize IAA from indole-3-acetonitrile, were shown to produce significant amounts of IAM in vitro as a second end product of the reaction besides IAA. NIT2 was earlier shown to be highly expressed in developing and in mature A. thaliana embryos, and NIT3 is the dominantly active gene in the hypocotyl and the cotyledons of young, germinating seedlings. Collectively, these data suggest that the elevated levels of IAM in seeds and germinating seedlings result from nitrilase action on indole-3-acetonitrile, a metabolite produced in the plants presumably from glucobrassicin turnover

Soil moisture: variable in space but redundant in time

Soil moisture at the catchment scale exhibits a huge spatial variability. This suggests that even a large amount of observation points would not be able to capture soil moisture variability. We present a measure to capture the spatial dissimilarity and its change over time. Statistical dispersion among observation points is related to their distance to describe spatial patterns. We analyzed the temporal evolution and emergence of these patterns and used the mean shift clustering algorithm to identify and analyze clusters. We found that soil moisture observations from the 19.4 km2 Colpach catchment in Luxembourg cluster in two fundamentally different states. On the one hand, we found rainfall-driven data clusters, usually characterized by strong relationships between dispersion and distance. Their spatial extent roughly matches the average hillslope length in the study area of about 500 m. On the other hand, we found clusters covering the vegetation period. In drying and then dry soil conditions there is no particular spatial dependence in soil moisture patterns, and the values are highly similar beyond hillslope scale. By combining uncertainty propagation with information theory, we were able to calculate the information content of spatial similarity with respect to measurement uncertainty (when are patterns different outside of uncertainty margins?). We were able to prove that the spatial information contained in soil moisture observations is highly redundant (differences in spatial patterns over time are within the error margins). Thus, they can be compressed (all cluster members can be substituted by one representative member) to only a fragment of the original data volume without significant information loss. Our most interesting finding is that even a few soil moisture time series bear a considerable amount of information about dynamic changes in soil moisture. We argue that distributed soil moisture sampling reflects an organized catchment state, where soil moisture variability is not random. Thus, only a small amount of observation points is necessary to capture soil moisture dynamics

Neutrinos as a diagnostic of cosmic ray Galactic/extra-galactic transition

Motivated by a recent change in viewing the onset of the extra-galactic component in the cosmic ray spectrum, we have fitted the observed data down to $10^{8.6}$ GeV and have obtained the corresponding power emissivity. This transition energy is well below the threshold for resonant $p\gamma$ absorption on the cosmic microwave background, and thus source evolution is an essential ingredient in the fitting procedure. Two-parameter fits in the spectral and redshift evolution indices show that a standard Fermi $E_i^{-2}$ source spectrum is excluded at larger than 95% confidence level (CL). Armed with the primordial emissivity, we follow Waxman and Bahcall to derive the associated neutrino flux on the basis of optically thin sources. For $pp$ interactions as the generating mechanism, the neutrino flux exceeds the AMANDA-B10 90%CL upper limits. In the case of $p\gamma$ dominance, the flux is marginally consistent with AMANDA-B10 data. In the new scenario the source neutrino flux dominates over the cosmogenic flux at all energies. Thus, should data from AMANDA-II prove consistent with the model, we show that IceCube can measure the characteristic power law of the neutrino spectrum, and thus provide a window on the source dynamics.Comment: To be published in Phys. Rev.

Tree-, stand- and site-specific controls on landscape-scale patterns of transpiration

Transpiration is a key process in the hydrological cycle, and a sound understanding and quantification of transpiration and its spatial variability is essential for management decisions as well as for improving the parameterisation and evaluation of hydrological and soil–vegetation–atmosphere transfer models. For individual trees, transpiration is commonly estimated by measuring sap flow. Besides evaporative demand and water availability, tree-specific characteristics such as species, size or social status control sap flow amounts of individual trees. Within forest stands, properties such as species composition, basal area or stand density additionally affect sap flow, for example via competition mechanisms. Finally, sap flow patterns might also be influenced by landscape-scale characteristics such as geology and soils, slope position or aspect because they affect water and energy availability; however, little is known about the dynamic interplay of these controls. We studied the relative importance of various tree-, stand- and site-specific characteristics with multiple linear regression models to explain the variability of sap velocity measurements in 61 beech and oak trees, located at 24 sites across a 290 km2 catchment in Luxembourg. For each of 132 consecutive days of the growing season of 2014 we modelled the daily sap velocity and derived sap flow patterns of these 61 trees, and we determined the importance of the different controls. Results indicate that a combination of mainly tree- and site-specific factors controls sap velocity patterns in the landscape, namely tree species, tree diameter, geology and aspect. For sap flow we included only the stand- and site-specific predictors in the models to ensure variable independence. Of those, geology and aspect were most important. Compared to these predictors, spatial variability of atmospheric demand and soil moisture explains only a small fraction of the variability in the daily datasets. However, the temporal dynamics of the explanatory power of the tree-specific characteristics, especially species, are correlated to the temporal dynamics of potential evaporation. We conclude that transpiration estimates on the landscape scale would benefit from not only consideration of hydro-meteorological drivers, but also tree, stand and site characteristics in order to improve the spatial and temporal representation of transpiration for hydrological and soil–vegetation–atmosphere transfer models