Modellierung des turbulenten Austausches zwischen der Prandtl-Schicht und der Waldatmosphäre

Für die quantitative Beschreibung der Depositions- und Emissionsraten atmosphäri- scher Spurengase in Waldökosystemen mit Hilfe von Profilmessungen ist es notwendig, die turbulenten Austauscheigenschaften in der atmosphärischen Grenzschicht ober- und innerhalb der Waldbestände zu modellieren. Zu diesem Zweck werden im allge- meinen lokale Turbulenzschließungsansätze verwendet- Messungen zeigen jedoch, daß bei der Durchströmung von Waldbeständen im stamm- raum neben den von der Umströmung der Pflanzenelemente herrührenden Wirbeln auch Wirbel von der Größenordnung des Bestandes auftreten, somit also nichtloka- le Turbulenzeffekte. Solche Effekte können mit lokalen Turbulenzschließungansätzen nicht erfaßt werden. Nach den Messungen ergibt sich ein Größenspektrum von in einer Höhe gleichzeitig wirkenden Wirbeln, welches als Ursache für die häufig zu beobach- tenden Flüsse gegen den lokalen vertikalen Eigenschaftsgradienten (counter -gradient -Flüsse) angesehen wird. Um diese Flüsse richtig simulieren zu können, wurde ein eindimensionales Grenz- schichtmodell aufgebaut und an einen Fichtenbestand im Solling -Gebirge südwestlich von Hannover angepaßt, in dem ein nichtlokaler Austauschansatz verwendet wird. Da- bei handelt es sich um eine nach Inclan et al. für Waldbestände modifizierte Schließung nach der transilienten Turbulenztheorie von Stull (Stull 1994 , Inclan et al. 1996). Anhand der Modellrechnungen zeigte sich, daß dieses Turbulenzschließungsverfahren prinzipiell in der Lage zu sein scheint, den turbulenten Austausch in und über einem Waldbestand im Solling qualitativ richtig widerzugeben. Trotz einiger Probleme bei der realistischen Widergabe der gemessenen Profile der Windgeschwindigkeit im Kronen- raum stimmen die modellierten Impulsflüsse direkt über dem Bestand bei instationärer Rechnung sehr gut mit den Daten von Eddy -Kovarianzmessungen überein. Wie ein Vergleich mit den Modellergebnissen eines bei gleicher Modellphysik mit lokaler Tur- bulenzschließung (K -Schließung) arbeitenden Modells an einem Beispieltag gezeigt hat, wurde der Impulsfluß über dem Bestand vom K -Schließungsmodell betragsmäßig überschätzt, während die vom transilienten Modell berechneten Werte besser mit den Messungen übereinstimmten. Die fühlbaren Wärmeflüsse werden von beiden Model- len in den instationären Rechnungen gut widergegeben. Bei den latenten Wärmeflüssen! werden die Werte vom instationären transilienten Modell jedoch meist unterschätzt, während das K- Schließungsmodell eher zu einer Überschätzung neigt. Bei den berechneten Profilen der turbulenten Eigenschaftsflüsse von Impuls, fühlbarer und latenter Wärme hat sich gezeigt, daß das Modell auf der Basis der lokalen Turbu- lenzschließung erwartungsgemäß prinzipiell keine Flüsse gegen den lokalen Gradien- ten innerhalb des Bestandes modellieren kann. Beim transilienten Schließungsansatz ist dies sehr wohl möglich. Insbesondere beim vertikalen Transport von Impuls ergibt sich eine prinzipielle Übereinstimmung mit einem negativen turbulenten Diffusionsko- effizienten im Stammraum als Analogon zu den Flüssen gegen den lokalen Gradienten. Die mit dem transilienten Modell durchgeführten stationären Rechnungen haben prin- zipiell schlechtere Ergebnisse geliefert, als die instationären Rechnungen. So werden die berechneten turbulenten Flüsse über dem Bestand für alle betrachteten Größen betragsmäßig zu allen Tageszeiten deutlich unterschätzt. Eine Erweiterung des Modells auch auf andere atmosphärische Prozesse, z.B. CO2 -Flüsse wird zeigen, inwieweit sich die Modellergebnisse bei der Verwendung des transilienten Schließungsansatzes gegenüber dem K -Schließungsansatz verbessem

Historical Patterns of Anthropogenic Impacts on Freshwaters in the Berlin-Brandenburg Region

Since humans are preferentially settling in flood plains they often influence freshwater systems intensely. The first signs of anthropogenic impacts on surface waters in the Berlin-Brandenburg region are approximately 3000 years old. Considering the multiple and intense human uses of surface waters in this region, we analysed when, how and to which extent regional rivers and streams became impacted by dams, water mills and fish weirs resulting in changes in morphology, hydrology and ecological functioning. We hypothesise that the development and growth of cities in this region necessitated (1) efficient navigability of rivers linking them, (2) efficient use of hydropower resources for mills, and (3) significant pollution of surface waters especially with the beginning of industrial development. We analyse these hypotheses by means of three regional examples and delineate the effects of human uses on selected surface water bodies. Understanding the effects of these historic modifications of surface water supports the identification of options for a sustainable use of surface waters that are currently still subjected to multiple uses but face a significant decrease in discharge due to climate change

Integral Flow Modelling Approach for Surface Water-Groundwater Interactions along a Rippled Streambed

Exchange processes of surface and groundwater are important for the management of water quantity and quality as well as for the ecological functioning. In contrast to most numerical simulations using coupled models to investigate these processes, we present a novel integral formulation for the sediment-water-interface. The computational fluid dynamics (CFD) model OpenFOAM was used to solve an extended version of the three-dimensional Navier–Stokes equations which is also applicable in non-Darcy-flow layers. Simulations were conducted to determine the influence of ripple morphologies and surface hydraulics on the flow processes within the hyporheic zone for a sandy and for a gravel sediment. In- and outflowing exchange fluxes along a ripple were determined for each case. The results indicate that larger grain size diameters, as well as ripple distances, increased hyporheic exchange fluxes significantly. For higher ripple dimensions, no clear relationship to hyporheic exchange was found. Larger ripple lengths decreased the hyporheic exchange fluxes due to less turbulence between the ripples. For all cases with sand, non-Darcy-flow was observed at an upper layer of the ripple, whereas for gravel non-Darcy-flow was recognized nearly down to the bottom boundary. Moreover, the sediment grain sizes influenced also the surface water flow significantly.Deutsche ForschungsgemeinschaftPeer Reviewe

Developing a reliable strategy to infer the effective soil hydraulic properties from field evaporation experiments for agro-hydrological models

The Richards equation has been widely used for simulating soil water movement. However, the take-up of agro-hydrological models using the basic theory of soil water flow for optimizing irrigation, fertilizer and pesticide practices is still low. This is partly due to the difficulties in obtaining accurate values for soil hydraulic properties at a field scale. Here, we use an inverse technique to deduce the effective soil hydraulic properties, based on measuring the changes in the distribution of soil water with depth in a fallow field over a long period, subject to natural rainfall and evaporation using a robust micro Genetic Algorithm. A new optimized function was constructed from the soil water contents at different depths, and the soil water at field capacity. The deduced soil water retention curve was approximately parallel but higher than that derived from published pedo-tranfer functions for a given soil pressure head. The water contents calculated from the deduced soil hydraulic properties were in good agreement with the measured values. The reliability of the deduced soil hydraulic properties was tested in reproducing data measured from an independent experiment on the same soil cropped with leek. The calculation of root water uptake took account for both soil water potential and root density distribution. Results show that the predictions of soil water contents at various depths agree fairly well with the measurements, indicating that the inverse analysis is an effective and reliable approach to estimate soil hydraulic properties, and thus permits the simulation of soil water dynamics in both cropped and fallow soils in the field accurately

LPMLE3 : a novel 1-D approach to study water flow in streambeds using heat as a tracer

We introduce LPMLE3, a new 1-D approach to quantify vertical water flow components at streambeds using temperature data collected in different depths. LPMLE3 solves the partial differential equation for coupled water flow and heat transport in the frequency domain. Unlike other 1-D approaches it does not assume a semi-infinite halfspace with the location of the lower boundary condition approaching infinity. Instead, it uses local upper and lower boundary conditions. As such, the streambed can be divided into finite subdomains bound at the top and bottom by a temperature-time series. Information from a third temperature sensor within each subdomain is then used for parameter estimation. LPMLE3 applies a low order local polynomial to separate periodic and transient parts (including the noise contributions) of a temperature-time series and calculates the frequency response of each subdomain to a known temperature input at the streambed top. A maximum-likelihood estimator is used to estimate the vertical component of water flow, thermal diffusivity, and their uncertainties for each streambed subdomain and provides information regarding model quality. We tested the method on synthetic temperature data generated with the numerical model STRIVE and demonstrate how the vertical flow component can be quantified for field data collected in a Belgian stream. We show that by using the results in additional analyses, nonvertical flow components could be identified and by making certain assumptions they could be quantified for each subdomain. LPMLE3 performed well on both simulated and field data and can be considered a valuable addition to the existing 1-D methods

A redundant transcription factor network steers spatiotemporal Arabidopsis triterpene synthesis

25 Pág.Plant specialized metabolites modulate developmental and ecological functions and comprise many therapeutic and other high-value compounds. However, the mechanisms determining their cell-specific expression remain unknown. Here we describe the transcriptional regulatory network that underlies cell-specific biosynthesis of triterpenes in Arabidopsis thaliana root tips. Expression of thalianol and marneral biosynthesis pathway genes depends on the phytohormone jasmonate and is limited to outer tissues. We show that this is promoted by the activity of redundant bHLH-type transcription factors from two distinct clades and coactivated by homeodomain factors. Conversely, the DOF-type transcription factor DAG1 and other regulators prevent expression of the triterpene pathway genes in inner tissues. We thus show how precise expression of triterpene biosynthesis genes is determined by a robust network of transactivators, coactivators and counteracting repressors.This Article was written in loving memory of A. Van Moerkercke (1979–2021). The authors thank A. Bleys for critically reading the manuscript; D. Gasperini for kindly sharing the ProMYCs:NLS-VENUS reporter lines, and P. Vittorioso for the dag1 mutant, ProDAG1:GUS and DAG1 over-expressing lines; J. R. Wendrich and T. Eekhout for assistance in the launching and analysis of the scRNAseq experiment; and S. Desmet and G. Goeminne from the VIB Metabolomics Core – Ghent for the thalianol profiling. This work was supported by the European Community’s Seventh Framework Program (FP7/2007–2013) under grant agreement 613692-TriForC and H2020 Program under grant agreement 760331-Newcotiana to A.G.; the Special Research Fund from Ghent University to A.G. and A.R. (project BOF18/GOA/013), and M.M. (project BOF20/GOA/012); the Flemish Government (AI Research program) to Y.S.; the Research Foundation Flanders with research project grants to A.G. (G004515N and G008417N) and a postdoctoral fellowship to P.F.-C.; a Swiss National Science Foundation postdoctoral fellowship (P300PA_177831) to M.C.; and a China Scholarship Council PhD scholarship to Y.B. A.O. acknowledges funding support from the John Innes Foundation and the BBSRC Institute Strategic Program Grant ‘Molecules from Nature – Products and Pathways’ (BBS/E/J/000PR9790).Peer reviewe

A specialized metabolic network selectively modulates Arabidopsis root microbiota

Plant specialized metabolites have ecological functions, yet the presence of numerous uncharacterized biosynthetic genes in plant genomes suggests that many molecules remain unknown. We discovered a triterpene biosynthetic network in the roots of the small mustard plant Arabidopsis thaliana. Collectively, we have elucidated and reconstituted three divergent pathways for the biosynthesis of root triterpenes, namely thalianin (seven steps), thalianyl medium-chain fatty acid esters (three steps), and arabidin (five steps). A. thaliana mutants disrupted in the biosynthesis of these compounds have altered root microbiota. In vitro bioassays with purified compounds reveal selective growth modulation activities of pathway metabolites toward root microbiota members and their biochemical transformation and utilization by bacteria, supporting a role for this biosynthetic network in shaping an Arabidopsis-specific root microbial community

Delineation of metabolic gene clusters in plant genomes by chromatin signatures

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