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Datum: Dienstag, 28.09.2021
9:30 - 11:00Block 2.1: Hydrogeologie, Hydrologie und Wasserisotope
Virtueller Veranstaltungsort: Block 2.1 - Meeting Link
Chair der Sitzung: Christoph Schüth, TU Darmstadt
Chair der Sitzung: Florian Einsiedl, TUM
Chair der Sitzung: Diana Burghardt, TU Dresden
9:30 - 10:00
Session Keynote

Oxygen is all around...

Johannes A.C. Barth1, Robert van Geldern2

1GeoZentrum Nordbayern, Deutschland; 2Friedrich-Alexander-Universität Erlangen-Nürnberg

Oxygen is the most abundant element within the earth system. At the earth´s surface and in its molecular form as O2 it is also one of the most important RedOx agents in both gaseous and dissolved forms. For such reactions, tracing of oxygen can identify fundamental processes including photosynthesis, respiration and exchange between the atmosphere and water. Moreover, as part of the water molecule oxygen can serve as a tracer of origin, mixing and movement of H2O. However, water can also release O2 via its splitting by for instance photosynthesis. Such processes also offer relationships to carbon cycling on various scales. While tracing of water with oxygen stable isotope ratios finds applications in a wide spectrum of fields including hydro(geo)logy, plant sciences and medicine, isotope tracing of gaseous and dissolved O2 is much less common. Future challenges and opportunities lie in combinations of water and molecular oxygen cycles via their stable isotope ratios to outline and constrain sources and sinks of this important element.

10:00 - 10:15

Impact of the 2018-2020 drought in Central Germany on the nitrogen cycling in a meso-scale catchment: Insights from hydrochemical and stable isotope investigations

Christin Mueller, Ronald Krieg, Ralf Merz, Kay Knoeller

Helmholtz Centre for Environmental Research UFZ, Deutschland

Recent investigations of the nitrate pollution in groundwater and surface water bodies in Germany confirm the well-known fact that the threshold value for nitrate concentrations (50 mg L-1) is exceeded in 18% of all sampling sites belonging to the nitrate monitoring network (German Federal Environmental Agency). Besides the input of excess nitrogen into the aquatic system by human activities, climate change related hydrological variability (extreme precipitation events or longer summer droughts) may also have an effect on nitrate loads in ground- and surface water.

Especially in the last years (2018-2020), a severe drought was observed in central Germany. In order to find out the potential impact of that drought on the catchment scale nitrogen cycling, we investigated the ground- and surface water compartments of the Holtemme watershed, a meso-scale river catchment in the Harz Mountains, Central Germany. The analysis of nitrate concentrations and corresponding isotopic signatures for groundwater and surface water samples were conducted during the entire dry period and were continued until discharge conditions went back to the long term mean in early 2021. The survey revealed decreasing nitrate concentrations for both compartments during drought conditions and a significant increase in the post-drought phase. Isotopic investigations allowed us to differentiate between distinct nitrate sources and microbial turnover processes. The time series analysis of δ15N-NO3 showed regular oscillations within the year, which illustrates a periodic fertilizer application. Corresponding δ18O-NO3 signatures show higher, seasonal-independent variations that can be explained by the normal isotopic variability of the ambient water that provides two thirds of the oxygen that is incorporated into the nitrate molecule during nitrification. However, flow paths for nitrate mobilization into the surface water seem to be unaffected by the drought because contributions of each nitrate source decreased equally during dry conditions. Nitrate concentrations increased after the dry period independently of recent nitrate supply. This implies that the soil system acts as a storage compartment, from which nitrate is easily released after the drought.

Our study confirms that hydrological variability is a highly important driver for nitrate mobilization at the catchment scale. Therefore, we suggest that the impact of changing hydrological conditions needs to be taken into consideration for management practices and policy actions.

10:15 - 10:30

Spatiotemporal analysis of Central European young water fractions

Michael Stockinger, Christine Stumpp

Universität für Bodenkultur, Wien, Österreich

The travel time of precipitation entering a catchment and leaving it as streamflow varies according to the flow paths precipitation takes. Fast precipitation travel times through catchments are especially interesting as they pose a high risk to river water quality. However, investigating influences on travel times is challenging due to complex water flow through heterogeneous landscapes. In this study, we investigated the fraction of streamflow younger than three months (Fyw) of nine major catchments in Central Europe and compared it to catchment characteristics and a teleconnection pattern that influences European large-scale weather: the North Atlantic Oscillation index (NAO). Adjacent catchments had similar long-term average and time-variable Fyw. These patterns were explained using catchment characteristics in a multiple regression analysis with prior collinearity removal, with grassland and 20-40% tree cover density explaining 84% of Fyw variability. Besides this spatial analysis, the annual changes in Fyw resembled each other in most catchments, leading to the hypothesis that a common, annually changing influence controls it. While total water storage in the catchments had no relationship to the time-variable Fyw, the NAO of the previous year was negatively correlated with this year’s Fyw (R² = 0.68). Three hypotheses are discussed as to how this inter-annual correlation could have happened, but no distinct explanation could be found. We recommend additional studies into this relationship as well as multiple regression with prior collinearity removal for future studies of the complex interplay of spatiotemporal variables on Fyw.

10:30 - 10:45

Stable water isotope analysis and improved lumped-parameter modeling for characterizing unsaturated subsurface flow

Anne Imig, Fatemeh Shajari, Florian Konrad, Florian Einsiedl, Arno Rein

Chair of Hydrogeology, Faculty of Civil, Geo and Environmental Engineering, Technical University of Munich, Germany

The characterization of water flow in the unsaturated zone is an important task, e.g., for evaluating water resources and stresses imposed by climate change and for protecting groundwater resources. In a 3-year field study, we have measured stable water isotopes (δ2H and δ18O) in precipitation and the outflow of two vegetated lysimeters situated in Wielenbach, Germany. The lysimeters contained soil cores of different textures, i.e. sandy gravel (Ly1) and clayey sandy silt (Ly2). Maize has been cultivated on top of the lysimeters, and four different herbicides have been applied to the maize plantation.

Lumped-parameter modeling was applied for interpreting stable water isotope observations in lysimeter outflow and for determining the mean transit time of water in the subsurface and the dispersion coefficient. Usually, lumped-parameter model (LPM) approaches consider steady-state flow, which is due to their model structure that implements analytical solutions (with constant coefficients) for simulating stable water isotope transport. In this work, we have extended this approach by subdividing the simulation time into hydrologically relevant sub-periods. Flow and transport parameters vary between these sub-periods, so that temporally varying flow is mimicked (keeping constant coefficients in each sub-period). Furthermore, preferential flow paths were considered and implemented in the model. For validation, numerical modeling of unsaturated flow and stable water isotope transport was carried out using HYDRUS-1D.

Application of the extended LPM approach could significantly improve the simulation of stable water isotopes observed in lysimeter outflow, by considering seasonal changes of flow and transport parameters. In general, LPM results corresponded well to numerical modeling results. Observations were more difficult to describe for Ly2, where the seasonal fluctuation of stable water isotopes seems not fully met by numerical modeling. The consideration of a constant δ18O upshift could improve simulations, i.e. representing, in a simplified assumption, the influence of immobile (isotopically enriched) water as an additional component that contributes to the isotopic signature of lysimeter outflow water. Both the LPM and numerical approach are hence considered to be well suited for decision support. As an advantage of the LPM approach, less input data and fitting parameters (with associated uncertainties) are required, making it a powerful tool for groundwater management methodologies.

10:45 - 11:00

Identifizierung von Oberflächenwasser-Grundwasser-Interaktionen anhand von charakteristischen Isotopensignalen

Michael Engel1,2, Simon Mischel1, Sabrina Quanz1, Dirk Radny1, Francesco Comiti2, Lars Düster1, Axel Schmidt1

1Bundesanstalt für Gewässerkunde, Deutschland; 2Freie Universität Bozen-Bolzano, Italien

Die Verwendung stabiler Wasserisotope kann entscheidend zum Prozessverständnis von Oberflächenwasser-Grundwasser-Interaktionen an Flüssen beitragen. Flusswasser weist im Gegensatz zu Grundwasser eine höhere Variabilität in der Isotopenzusammensetzung auf, die durch Abflussereignisse wie Schneeschmelze oder Hochwasser nach Starkregenereignissen gesteuert wird. Die kontrastierende Isotopenzusammensetzung von Flusswasser und Grundwasser kann verwendet werden, um ein Mischungsmodell aus den Eingangsgrößen Flusswasser und Grundwasser vor sowie während des Ereignisses aufzustellen. Hierzu liefert der folgende Beitrag zwei Beispiele mit sehr unterschiedlich großen Einzugsgebieten aus der wissenschaftlichen Praxis.

An der Ahr, einem 53 km langen Gebirgsfluss mit einem Einzugsgebiet von 629 km² (in Südtirol, Italien) wurden monatliche Wasserproben von Flusswasser und Grundwasser von 2016 bis 2018 genommen und auf stabile Wasserisotope (δ18O und δ2H) analysiert. Die durch Schneeschmelzereignisse ausgelöste, isotopisch leichtere Flusswassersignatur (z.B. δ2H: -88,2 bis -101 ‰) konnte als ein charakteristisches Isotopensignal verwendet werden, um ein Mischungsmodell von Flusswasser und Grundwasser aufzustellen. Die Analyse zeigt, dass das Ereigniswasser ca. 41 Tage ± 10 bis zum Brunnen benötigt. Dies entspricht einer Fließgeschwindigkeit von ungefähr 0,2 bis 0,3 m d-1. Der maximale Anteil an Flusswasser im Grundwasser konnte auf ca. 4% ± 1, 15% ± 2, 19% ± 4 and 51% ± 4 für die Ereignisse im Juni 2016, Mai 2017 sowie Mai und Juli 2018 geschätzt werden.

Im deutschen Teil der Mosel, einem 232 km langen Abschnitt des zweitlängsten Nebenflusses des Rheins, werden am Schleusenstandort Lehmen seit Sommer 2020 monatliche Wasserproben von der Mosel im Ober- und Unterpegel der Stauhaltung sowie Grundwasser von 4 Grundwassermessstellen genommen. Die Analyse auf stabile Wasserisotope zeigt, dass hier das Oberflächenwasser isotopisch etwas leichter ist (δ2H: -62,3 ‰) als das Grundwasser (δ2H: -51,3 ‰). Erste Ergebnisse deuten einen monatlichen Versatz der Flusswasser-Isotopensignatur im Grundwasser an. Eine Schleusenwartung im September 2020 führte zu einer Absenkung des Flusswasserspiegels um 1,5 m und damit zu einem veränderten hydraulischen Gradienten zwischen Fluss- und Grundwasser. Es konnten während dieser Zeit nur geringfügige Veränderungen in der Isotopenzusammensetzung des Grundwassers nachgewiesen werden.

Beide Beispiele bestätigen den Nutzen stabiler Wasserisotope bei grundlagenorientierten, wie auch angewandten hydrologischen Fragestellungen, um komplexe Vorgänge bei der Oberflächenwasser-Grundwasser-Interaktion zu verstehen.

11:00 - 11:15Poster Kurzvorträge - Themenblock 2: Hydrogeologie, Hydrologie und Wasserisotope
Virtueller Veranstaltungsort: Poster Kurzvorträge - Meeting Link
11:00 - 11:04

Stable water isotopes as natural tracers in a hydrogeological study of riverbank filtration in N’Djamena, Chad

Maike Gröschke, Lilli Witt, Paul Königer, Sara Vassolo

Federal Institute for Geosciences and Natural Resources (BGR), Groundwater Resources - Quality and Dynamics

To assess the potential of riverbank filtration along the Chari River in the Lake Chad basin, a hydrogeological test site at a large water supply well located in close proximity to the river was established in N’Djamena, Chad. At the site, the aquifer is composed of Quaternary sediments with a total thickness of about 50-55 m and consist of alternating layers of sand and clay or silt. There are two high permeable layers at depths between ̴ 23-27 m and ̴ 45-50 m separated by a fine sand/silt layer. To date, the site consists of five deep and five shallow observation wells located around the supply well, and a shallow and a deep observation well on the opposite riverbank in Cameroon. Since 2019, samples from the Chari River, the supply well, and the observations wells on the Chadian side were collected every two weeks for hydrochemistry and water stable isotopes - with some interruptions - whereas groundwater levels were recorded with automatic data loggers.

The water level data shows that aquifer discharge conditions prevail throughout the year and that the hydraulic head in the shallow aquifer is always higher than in the deeper one. The largely fluctuating stable isotope compositions from the river can be traced in the shallow aquifer, which allow for an estimation of groundwater flow velocities ( ̴ 0.9 m/d), while the isotopic compositions in the deep observations wells remain constant throughout the year. The isotopic composition of the water supply well lies between that of the shallow and the deep observation wells without any seasonal variations. It is still unclear whether different flow paths and travel times towards the well in the shallow aquifer dampen the isotopic signal, or if a significant groundwater flow component in the fine sand/silt separating the medium sand layers contributes to the water budget of the supply well.

11:04 - 11:08

Isotopen-hydrobiogeochemische Untersuchungen an anoxischen Grundwässern off- und on-shore der norddeutschen Küste

Michael Ernst Böttcher1,2,3, Anna-Kathrina Jenner1,3, Cátia M.E. von Ahn1,2, Iris Schmiedinger1, Andreas Roskam4

1Leibniz Institute of Baltic Sea Research (IOW), Deutschland; 2University of Greifswald, Deutschland; 3University of Rostock, Deutschland; 4NLWKN Aurich, Deutschland

Die Leybucht liegt im Einzugsgebiet der Osterems und wird durch die vorgelagerten ostfriesischen Inseln vor der offenen Nordsee geschützt. Seit dem Mittelalter steht die Leybucht unter dem Einfluss von Verlandungserscheinungen (NLÖ, 2001). Im Jahre 2017 wurde im Küstenvorfeld in größtenteils fein- und mittelsandigen Sedimenten eine Bohrung (R144) abgeteuft, die für die Grundwasserbeobachtung in 57 bis 61 m unter Geländekante verfiltert wurde. In der vorliegenden Studie wurden das Grundwasser dieser Bohrung sowie zwei on-shore Grundwässer (Leybuchtsiel 1 und 2) in den Jahre 2019 und 2020 beprobt und hydrochemisch auf Haupt- und Spurenelemente analysiert. Diese Messungen wurden ergänzt um die Vermessung der stabilen Wasserisotope (2H, 18O), der C-Isotopenzusammensetzung des DIC sowie der S- und O--Isotopenzusammensetzung des gelösten SO4. Die Daten wurden darüber hinaus einer physikochemischen Analyse mit PHREEQ-C unterzogen.

Die Untersuchungsergebnisse zeigen, dass alle Wässer anoxisch sind und sich durch hohe gelöste Eisengehalte auszeichnen. Die drei Grundwässer unterscheiden sich hinsichtlich ihrer Wasserisotopen-Signatur, liegen aber auf der für Cuxhaven etablierten lokalen meteorischen Wasserlinie und ähneln Süßwasser-beeinflussten Porenwässer, die in tiefen Sanden im Rückseitenwatt der Insel Spiekeroog gefunden wurden (Böttcher et al., 2014). Die Bohrungen R144 und Leybuchtsiel 1 verzeichnen den Einfluss von Nordseewasser. Die Isotopenzusammensetzung des DIC und Sulfats verweist auf die Mineralisierung von gelöstem organischen Kohlenstoff hin unter Verwendung der Elektronenakzeptoren z.B., Sauerstoff, Nitrat, und Sulfat, z.T. hat bereits Methanogenese stattgefunden. Die gelösten Eisengehalte können der dissimilatorisch-mikrobiellen Reduktion von Eisenoxiden und/oder der mikrobiell-katalysierten Zersetzung von Eisensulfiden stammen (z.B., Zhang et al., 2012). Ein Austritt dieser Wässer in der Nordsee hätte eine Erhöhung des Entgasungpotenzials für CO2 zur Folge.


Böttcher M.E., Lipka M., Winde V., Dellwig O., Böttcher E.O., Böttcher T.M.C., Schmiedinger I.(2014) Multi-isotope composition of freshwater sources for the southern North and Baltic Sea. Proc. 23rd SWIM conference, Husum, 46-49.

NLÖ (2001) Beweissicherung Küstenschutz Leybucht. Morphologisch-sedimentologische Untersuchungen. Forschungsstelle Küste. Abschlußbericht.

Zhang Y.-C., Slomp, C.P., Broers H.P., Passier H.F., Böttcher, M.E., Omoregie E.O., Lloyd J.R., Polya D.A. & van Cappellen P. (2012) Isotopic and microbiological signatures of pyrite-driven denitrification linked to pyrite oxidation in a sandy aquifer. Chem. Geol., 300-301, 123-132.

11:08 - 11:12

Measuring high-resolution geochemical depth-profiles in hyporheic stream sediments with focus on aerobic and anaerobic methane oxidation

Tamara Michaelis, Anja Wunderlich, Florian Einsiedl

Technische Universität München, Lehrstuhl Hydrogeologie, Deutschland

A large part of carbon and nutrient cycling in rivers and streams takes place in the hyporheic zone, a hotspot of biogeochemical activity in the river bed where surface- and groundwater meet. Typically, redox zones with different dominant electron acceptors form sequentially, sorted by the energy yield of the respective redox reactions. This zonation is subject to the influence of multiple parameters such as sediment composition, river temperature, surface- and groundwater interaction, water and sediment chemical composition and others. In anaerobic sediments, methane production takes place as last step in this so-called redox ladder making many rivers net carbon emitters. Understanding sources and sinks of methane, the second most important greenhouse gas in the world, is crucial in times of climate change, but due to high spatial and temporal heterogeneity of redox processes in hyporheic sediments the relationship between methanogenesis and microbial methane oxidation is not yet fully understood.

To help filling this knowledge gap, our research group is measuring high-resolution depth-depending geochemical profiles at different locations across a stream bed. A sediment peeper is used to obtain pore water samples with a 1 cm depth-resolution. Concentration gradients of dissolved oxygen, nitrate, nitrite, sulfate, ammonia and methane show depth and width of the different redox zones. To explain the dominant methane production pathway and to interpret concentration gradients, stable carbon isotopes in methane (δ13C-CH4) are measured. The δ13C-CH4 in the methanogenic zone can be used to distinguish between aceticlastic and hydrogenotrophic methanogenesis. An isotopic enrichment in δ13C values of methane towards the sediment surface may indicate microbial degradation while measurements of dissolved oxygen can be used to separate aerobic from anaerobic methane oxidation. In the absence of oxygen, other electron acceptors may become relevant for microbial methane oxidation, for example nitrate, nitrite or sulfate. In addition, the performance of a simple 1D diffusion model will be compared with the results of a 1D diffusion-reaction model in their ability to capture the measured methane concentration gradients. This will be used as a supporting evidence of the findings from concentration and isotope measurements.

In a poster, we want to present geochemical profiles in combination with modeled concentration gradients and carbon stable isotope measurements in methane for different locations across the stream. The different sampling sites are compared in terms of sediment composition and location in the stream bed.

11:12 - 11:15

Karstic springs as strong emitters of CO2

Kern Lee1,2, Robert van Geldern1, Johannes Barth1

1Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), Deutschland; 2Alberta Environment and Parks, Edmonton, Canada

Inland aquatic systems play an important role in the global carbon cycle. They not only transport terrestrial carbon to the oceans but also emit carbon in the form of carbon dioxide to the atmosphere. Among inland water types rivers are significant sources of CO2 to the atmosphere, and karstic watersheds are particularly important in this respect due to their large availability of inorganic carbon.

In this context, few studies have quantified CO2 fluxes from temperate source springs and headwaters in karstic basins yet. Our study addressed this information gap by investigating CO2 outgassing from streams and groundwater-fed springs in a karstic terrain in central Germany, known as the Franconian Alb. We used DIC concentration and stable isotope (δ13CDIC) data to separate biological and geological factors that might be responsible for temporal and spatial variations and gradients in CO2 losses. This study examined characteristics of dissolved inorganic carbon (DIC) and excess partial pressures of CO2 (epCO2) in the source springs and headwaters of four watersheds in a Central European karstic region, via dissolved inorganic carbon concentration and stable carbon isotope measurements.

Our results showed the most 13C-depleted δ13CDIC values at the source springs, which become rapidly enriched downstream due to CO2 degassing. Concurrently, epCO2 values, while consistently in excess of atmospheric concentrations at the spring sources, show decreases of up to 92% within only 50 m downstream. In conjunction with the large observed flux estimates of up to 88 g C m–2 day–1, these findings suggest that karstic springs can act as focussed major CO2 sources to the atmosphere. Because headwater streams constitute the bulk of the surface area of most watersheds, they may provide a disproportionately large contribution to CO2 effluxes in carbonate-dominated basins, in which source springs play a particularly important role.


Lee, van Geldern and Barth (2021), Extreme gradients in CO2 losses downstream of karstic springs. Science of the Total Environment, 778, 146099,

11:15 - 11:30Pause
11:30 - 12:15Block 2.2: Hydrogeologie, Hydrologie und Wasserisotope
Virtueller Veranstaltungsort: Block 2.2 - Meeting Link
Chair der Sitzung: Christoph Schüth, TU Darmstadt
Chair der Sitzung: Florian Einsiedl, TUM
Chair der Sitzung: Diana Burghardt, TU Dresden
11:30 - 11:45

Neue Einblicke in die Infiltrationsbedingungen des Oberjura Thermalwassers in der südlichen Bayerischen Molasse mit Hilfe der 14CDOC Methode

Theis Winter, Florian Einsiedl

Technische Universität München, Deutschland

Der Oberjura Thermalwasser Aquifer im Süddeutschen Molassebecken ist der Hauptexplorationshorizont für die geothermische Energiegewinnung in Bayern. Der karbonatische Oberjura Aquifer zeigt sowohl klein- als auch großräumig starke Heterogenitäten hinsichtlich seines strukturgeologischen Aufbaus auf. So sind im Oberjura Aquifer Karsterscheinungen und tiefreichende Störungssysteme zu finden. Die neusten Literaturarbeiten unterscheiden, anhand von statistischen Clusteranalysen, zwischen drei unterschiedliche Wassertypen hinsichtlich der hydrochemischen und isotopengeochemischen Beschaffenheit im zentralen Teil des Süddeutschen Molassebeckens in Bayern und lassen ein alpennahes Infiltrationsgebiet im Süden des Süddeutschen Molassebeckens vermuten.

Anhand hydrochemischer und isotopengeochemischer Parameter untersuchen wir die Infiltrationsbedingungen des Oberjura Thermalwassers und grenzen den zeitlichen Rahmen der Infiltration mithilfe Piston Flow Grundwasseralter ein.

Prinzipiell ist das Oberjura Thermalwasser in diesem Gebiet vom Na-HCO3-Cl Grundwassertyp, zeigt aber an den südlichen Standorten Ca2+ und Mg2+ Gehalte unter den zu erwartenden Gehalten. Die Werte der stabilen Wasserisotope liegen zwischen -10,6 und -11,7 ‰ für δ18O und -85,0 bis-86,0 ‰ für δ2H und deuten auf eine Infiltration insbesondere während kaltzeitlicher Bedingungen hin.

Die Kombination aus den Ergebnissen der Hydrochemie, stabilen Wasserisotopen und den Piston Flow Grundwasseraltern aus den 14CDOC und 14CDIC Altersbestimmungen in Verbindungen mit 81Kr-Altern aus der Literatur bestätigen die Ergebnisse der stabilen Wasserisotope und geben nun Hinweise darauf, dass sich das Thermalwasser des Oberjura im Süden aus mindestens zwei Grundwasserkomponenten zusammensetzt. Auf Grund der ermittelten Piston Flow Alter der untersuchten Grundwässer ist eine Infiltration nur über „Bypass“-Strukturen, die in der überlagernden Molasse zu finden sind, zu erklären.

11:45 - 12:00

Supporting the interpretation of δ¹⁵N values of dissolved NH₄⁺ and NO₃⁻ in the water column of a seasonal stratified lake using Numerical modeling and PCR gene amplification

Gisela Alejandra Pena Sanchez1, Florian Einsiedl1, Clara Duffner2,4, Stephanie Schulz2,4, Bernhard Mayer3, Anja Wunderlich1

1Technical University of Munich; 2TUM School of Life Sciences; 3University of Calgary; 4Helmholtz Centre Munich

Occurring simultaneously with denitrification in anaerobic environments, other pathways like anaerobic oxidation of ammonium (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) may play an important role for the removal of fixed nitrogen (N) to gaseous N₂ from freshwater ecosystems. Recent studies that were conducted in freshwater ecosystems showed that the relevance of anammox, denitrification and DNRA, significantly changes depending on site conditions, and thus significance of anammox in freshwater is still largely unknown.

Here we investigate the pathways and relevance of nitrogen losses at the seasonal stratified lake Fohnsee during the development of the vertical redox stratification. Our approach combines concentration profiles and corresponding stable isotope compositions of NO₃⁻ and NH₄⁺, with qPCR of the hydrazine synthase gene (hzsB), nitrite reductase (nirK and nirS) genes, and numerical modeling of δ¹⁵N-NH₄⁺ values during the stratification period.

Increasing stable isotope values of nitrate (δ¹⁵N and δ¹⁸O) together with the identification of two specific marker genes for denitrification (nirK and nirS) indicate that denitrification is occurring in the anoxic water column of Fohnsee. However, stable isotope values of δ¹⁵N of ammonium and water chemistry results were ambiguous about the occurrence of anaerobic ammonium oxidation within the water column. Modeling results and qPCR analysis using hzsB marker gene for anammox showed that the observed stable isotope shift in δ¹⁵N of ammonium may be the result of mixing processes between ammonium remaining from nitrification in the oxic water column with strongly enriched δ¹⁵N values of 25‰, and ammonium that is formed by degradation of organic carbon during methanogenesis in the lake sediments with δ¹⁵N values of around 11‰.

We concluded that in a highly dynamic ecosystem such as seasonal stratified lakes, anammox bacteria only overcome limiting conditions occasionally, and may be active at most at low rates and on a temporal scale, thus, denitrification is suggested to be the principal path of nitrogen loss at the seasonal stratified lake Fohnsee. Finally, this study highlights the importance of solid understanding of the various transformations and isotope effects within a natural ecosystem for the successful interpretation of isotopic data.

12:00 - 12:15

Investigation of chloroform degradation mechanisms using multi-dimensional isotope fractionation analysis: Hydrodechlorination over Pd and Rh vs reductive dechlorination with Fe0

Berhane Abrha Asfaw1,2, Kaori Sakaguchi-Söder2, Christoph Schüth1

1Hydrogeology, Institute IAG, TU Darmstadt; 2Material Flow Management and Resource Economics, Institute IWAR, TU Darmstadt

Multi-dimensional isotope fractionation analysis is a useful tool to investigate degradation mechanisms of organic substances. In this study, we investigated the chlorine, carbon and hydrogen isotope fractionation patterns of chloroform during catalytic hydrodechlorination using two commercial catalysts palladium-on-alumina (Pd/Al2O3) and rhodium-on-alumina (Rh/Al2O3). The fractionation patterns of catalytic reaction were further compared to the pattern of reductive dechlorination of chloroform with zero valent iron (Fe0).

100 ml of deionized water in a reactor was saturated with hydrogen, which serves as an electron donor. The initial concentrations of chloroform and catalysts were designed to be 100 mg/l and 0.04 g/l, respectively. At specified time intervals, 1 ml of the water phase was taken from the reactor and placed in a 2 ml vial. Chlorine isotope analysis was implemented by GC-qMS (Agilent Technologies) coupled to a purge and trap sampler (PTA 3000, IMT GmbH) using the water phase from each 2 ml vial. For the carbon and hydrogen isotope analyses, a certain volume of the headspace in the 2 ml vial was injected into GC-C/Py-IRMS (Thermo Fisher Scientific).

The dual isotope slopes (ΛC-Cl = Δδ13C/Δδ37Cl) during the catalytic dechlorination of chloroform over Pd and Rh were determined to be 2.3 ± 0.12 and 2.1 ± 0.14, respectively. These values are significantly lower than the reported ΛC-Cl value of 8 ± 2 (Torrentó et al., 2017) and 8 ± 1 (Rodríguez-Fernández et al., 2018) for the reductive dechlorination of chloroform with ZVI. Our results indicate that the degradation mechanism of chloroform over Pd and Rh differs from the mechanisms with ZVI.

We further investigated the apparent kinetic isotope effects (AKIE) of carbon and chlorine isotopes. Whereas no significant difference was observed in AKIEC between degradation with catalysts and ZVI, AKIECl with Pd and Rh (1.037 and 1.032, respectively) are much higher than the theoretical limit for C-Cl bond cleavage (KIECl = 1.013) by Elsner et al., 2005. The large AKIECl with Pd and Rh suggest non-concerted, step-wise reaction, i.e. no intramolecular competition among the three chlorine atoms exists during the degradation process of chloroform, unlike concerted reaction that is known to take place during reductive dechlorination of chloroform with ZVI.

In summary, our study showed that 1) dual isotope slope and AKIE are useful tools to investigate degradation mechanisms and 2) chloroform degradation mechanism over Pd and Rh is assumed to be none-concerted, step-wise reaction based on the AKIE of Cl.

Key words: chloroform hydrodechlorination, Multi-dimensional CSIA, Palladium, Rhodium, Fe0

12:15 - 13:00Block 3: Paläoklima, Sedimentologie, Boden
Virtueller Veranstaltungsort: Block 3 - Meeting Link
Chair der Sitzung: Matthias Hinderer, TU Darmstadt
Chair der Sitzung: Michael Zech, TU Dresden
Chair der Sitzung: Christine Stumpp, BOKU
12:15 - 12:30

Carbon isotope excursions in a Paleocene to early Eocene lignite bearing succession at the southern edge of the proto-North Sea (Schöningen, Germany)

Olaf K. Lenz1,2, Mara Montag2, Volker Wilde1, Katharina Methner3,5, Walter Riegel1, Andreas Mulch3,4

1Senckenberg Forschungsinstitut und Naturmuseum Frankfurt, Deutschland; 2Technische Universität Darmstadt, Institut Für Angewandte Geowissenschaften, Deutschland; 3Senckenberg Biodiversity and Climate Research Centre (SBiK-F), Frankfurt am Main, Deutschland; 4Goethe Universität Frankfurt, Institut für Geowissenschaften, Frankfurt am Main, Deutschland; 5Stanford University, Department of Earth System Science, Department of Geological Sciences, USA

Long-term effects of present global warming on ecosystems on timescales beyond those covered by the human record of the last few centuries are still a matter of speculation. Since long-term greenhouse periods and short-term warming events occurred repeatedly in the history of the earth, they may be the subject for detailed studies on the reaction of ecosystems to global warming on different timescales. The Early Eocene Climatic Optimum (EECO) and its superposed short-term warming events such as the Paleocene-Eocene Thermal Maximum (PETM) represent the last greenhouse period before today which is especially suited for comparisons to the presently developing greenhouse since fauna and flora had reached an evolutionary state already similar to today.

The sedimentary succession of the former Helmstedt Lignite Mining District in northern Germany covers the entire Paleogene greenhouse phase and its gentle demise between the upper Paleocene and the early middle Eocene almost continuously in an estuarine situation at the southern edge of the proto-North Sea. Due to the interaction between changes in sea level, salt withdrawal in the subsurface and climate-related changes in runoff from the hinterland the area was subject to frequent changes between marginal marine and terrestrial conditions, repeatedly leading to peat formation. This offers the rare opportunity to study Paleocene–Eocene near-coastal ecosystems and to trace the effects of long- and short-term climate perturbations on the diversity and composition of the plant communities across 10 million years during the Paleogene greenhouse.

Here, we present high-resolution carbon isotope data of bulk organic matter (δ13CTOC) from a 98 m thick sequence from the lower part of the succession (Schöningen Formation). We observed six negative carbon isotope excursions (CIEs) reflecting massive short-term carbon cycle perturbations, which can be related to the PETM, probably to the Eocene Thermal Maximum 2 and to the EECO. Palynological analysis proved that shifts in δ13CTOC valuesare correlated with changes in the peat forming wetland vegetation. Furthermore, the PETM-related CIE shows a distinct rebound to higher δ13CTOC valuesshortly after the onsetof the CIE, which is here recognized as a common feature of terrestrial and marginal marine PETM-records worldwide and may be related to changes in the vegetation.

12:30 - 12:45

18O analyses of bulk lipids as novel paleoclimate tool in loess research – a pilot study

Jakob Labahn1, Philip Hirschmann1, Lucas Bittner1, Diana Burghardt2, Bruno Glaser3, Slobodan Markovic4, Michael Zech1

1Physische Geographie mit SP Paläoumweltforschung, Technische Universität Dresden, Deutschland; 2Institut für Grundwasserwirtschaft, Technische Universität Dresden; 3Bodenbiogeochemie, Martin-Luther-Universität Halle-Wittenberg; 4Universität Novi Sad, Serbien

The analysis of the stable oxygen isotopes 18O and 16O has revolutionized paleoclimate research since the middle of the last century. Particularly, 18O of ice cores from Greenland and Antarctica is used as paleotemperature proxy and 18O of deep-sea sediments is used as proxy for global ice volume. Important terrestrial archives to which 18O as paleoclimate proxy is successfully applied are for instance speleothems, lake sediments or tree rings. By contrast, 18O applications to loess-paleosol sequences (LPSs) are scarce, despite for instance a compound-specific 18O analytical tool for sugar biomarkers was developed and presented already years ago (Zech et al., 2014. Geochimica et Cosmochimica Acta 126, 614-623).

Here we present a first continuous 18O record (n=50) for the LPS Crvenka in Serbia, SE Europe, spanning the last glacial-interglacial cycle. From a methodological point of view, we took advantage of a recently proposed paleoclimate/-hydrological tool/proxy based on bulk 18O analyses of plant-derived lipids. The 18­­­Olipid values range between -10.2 ‰ and +23.0 ‰ and are systematically more positive in the interglacial and interstadial (paleo-)soils compared to the loess layers. In our conference contribution, we compare our 18­­­Olipid record from the LPS Crvenka with the marine oxygen-isotope stages as well as with the Greenland 18­­­Oice core records revealing the famous Dansgaard-Oeschger events (stadials and interstadials). Concerning the interpretation of our LPS 18­­­Olipid record, we will discuss several influencing factors, such as temperature-control on 18O, relative humidity-dependent evaporative leaf water enrichment, post-sedimentary effects and pool-effects.


Zech, M., Mayr, C., Tuthorn, M., Leiber-Sauheitl, K. and Glaser, B., 2014. Oxygen isotope ratios (18O/16O) of hemicellulose-derived sugar biomarkers in plants, soils and sediments as paleoclimate proxy I: Insight from a climate chamber experiment. Geochimica et Cosmochimica Acta 126, 614-623.

12:45 - 13:00

Plant and fungal contributions to soil organic matter fractions assessed by 13C and 15N isotope natural abundances

Saskia Klink1, Adrienne Keller2, Andreas Wild1, Vera Baumert4, Matthias Gube5, Eva Lehndorff3, Nele Meyer3, Carsten Mueller6, Richard Phillips2, Johanna Pausch1

1Department of Agroecology, Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Germany; 2Department of Biology, Indiana University Bloomington, IN, USA; 3Department Soil Ecology, Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Germany; 4Chair of Soil Science, School of Life Sciences, Technical University of Munich, Freising, Germany; 5Soil Science of Temperate Ecosystems, Büsgen-Institute, Georg-August University Göttingen, Germany; 6Department of Geosciences and Natural Resource Management, University of Copenhagen, Denmark

Soil organic matter (SOM) consists of a multitude of organic compounds forming a continuum of decay, from fresh detritus to highly processed organic matter stabilized on mineral surfaces. To date, we still lack crucial knowledge about the contribution of plant and microbial residues to SOM fractions and we know almost nothing about the contribution of distinct fungal functional guilds such as arbuscular (AM), ectomycorrhizal (ECM), and saprotrophic (SAP) fungi to SOM fractions.

Aiming to address this knowledge gap, we investigated sources of particulate and mineral associated organic matter (POM and MAOM) around trees with distinct mycorrhizal types, Liriodendron tulipifera (AM association) and Quercus alba (ECM association), in a temperate deciduous forest in Indiana, USA. In ECM-associated systems, we expect ECM fungi to be the main contributors to SOM, while in AM-associated systems, SAP fungi will mainly contribute to SOM due to the facilitation by AM fungi.

To assess various sources of SOM fractions, we combined stable isotope natural abundance analyses with measurements of microbial residues using amino sugars. Specifically, the 13C and 15N signatures of large-, medium- and small-sized POM and MAOM fractions were analyzed and compared to that of leaves and roots of the two dominant tree species as well as to tissues of mycorrhizal and saprotrophic fungi. The sources of C and N to SOM fractions were calculated by a Bayesian inference isotope mixing model.

Our data revealed a shift from relatively 13C- and 15N-depleted POM, which is close to the isotopic composition of plant material, to 13C- and 15N-enriched MAOM. Mixing model calculations suggests a higher contribution of plant (~ 76 %) than fungal inputs to POM for both tree systems, with a higher contribution of saprotrophic (SAP) fungi than ectomycorrhizal (ECM) fungi (~ 17 % and ~ 5 %, respectively). In contrast, the model for MAOM fractions suggests a dominance of fungal residues relative to plant C, with SAP fungi contributing more than ECM fungi in most SOM fractions, even under the ECM tree. As expected, AM fungal residues contribute only little to SOM fractions. Microbial necromass - measured as amino sugars - confirmed the important role of ECM and SAP fungal residues for SOC storage in both, POM and MAOM fractions.

Overall, our results highlight the importance of distinct fungal functional guilds for soil C storage and call for future studies on the role of mycorrhizal types for soil C storage in a changing world.

13:00 - 14:00Mittagspause
13:30 - 14:00Posterausstellung
Virtueller Veranstaltungsort: Posterausstellung
14:00 - 14:45Vortrag Isotopenpreis
Virtueller Veranstaltungsort: Isotopenpreis - Meeting Link
14:45 - 15:30Block 4.1: Ökosysteme
Virtueller Veranstaltungsort: Block 4.1 - Meeting Link
Chair der Sitzung: Gerhard Gebauer, Universität Bayreuth
14:45 - 15:00

Orchid Cremastra appendiculata on the path to self-supply with changing fungal companion

Franziska Zahn1, Yung-I Lee2, Gerhard Gebauer1

1BayCEER – Laboratory of Isotope Biogeochemistry, University of Bayreuth, Bayreuth, Germany; 2Biology Department, National Museum of Natural Science, Taichung, Taiwan

Covering one achlorophyllous, leafless and three chlorophyllous, leafy species the orchid genus Cremastra from East Asia allows inference on the evolutionary development from autotrophy to mycoheterotrophy of plant lineages mycorrhizal with saprotrophic fungi (Ogura-Tsujita et al. 2021). Particularly, the chlorophyllous, terrestrial orchid Cremastra appendiculata is unique with respect to its fungal mycorrhiza partners. Rather specialized wood/litter-decaying saprotrophic fungi are known to induce seed germination in the initially mycoheterotrophic protocorm stage (Yagame et al. 2013), while adult individuals either exploit wood-decaying Psathyrellaceae being partially mycoheterotrophic (Suetsugu et al. 2021) or form mycorrhiza with fungi of the ubiquitous saprotrophic rhizoctonia group.

We examined how a change in fungal community and subterranean morphology accompanies a nutrition mode alteration during the life cycle of Cremastra appendiculata.

Trophic strategies were revealed by comparing different development stages of Cremastra appendiculata to surrounding autotrophic reference plants based on multi-element natural abundance stable isotope analyses (δ13C, δ15N, δ2H, δ18O) and total N concentrations. Here we present the first stable isotope patterns of tiny protocorms related to non-rhizoctonia saprotrophic fungal partners and 18O and 2H natural abundance isotopic signatures of fully mycoheterotrophic terrestrial orchid specimens associated with saprotrophic fungi. Mycorrhizal fungi in Cremastra appendiculata protocorms, rhizomes and roots of seedling, and roots of adult were determined using next generation DNA sequencing.

We identified saprotrophic non-rhizoctonia Psathyrellaceae as dominant mycorrhizal fungi in protocorm and seedling rhizomes, while roots of seedlings and mature Cremastra appendiculata were mainly colonizes with rhizoctonia fungi. Mature Cremastra appendiculata did not differ in isotopic signature from autotrophic reference plants suggesting a fully autotrophic nutrition mode. Characteristic of orchid specimens entirely relying on fungal nutrition, Cremastra appendiculata protocorms were enriched in 15N, 13C and 2H compared to reference plants. Seedlings with very early green leaves showed a dispersive, intermediate isotopic signature, underpinning their transitional nutrition mode and the differences in fungal community depending on their subterranean morphology.

In conclusion, chlorophyllous terrestrial orchid Cremastra appendiculata is a key species being able to feature both extremes on the continuous transition from autotrophy to mycoheterotrophy with changing fungal companion during its ontogenetic development. Our results on Cremastra appendiculata together with knowledge from recent literature (e.g. Suetsugu and Matsubayashi (2021)) suggest a high within-species variability in nutrition and fungal association depending on development stage and subterranean morphology of Cremastra appendiculata.

Ogura-Tsujita Y, Yukawa T, Kinoshita A. 2021. Evolutionary histories and mycorrhizal associations of mycoheterotrophic plants dependent on saprotrophic fungi. Journal of Plant Research 134: 19–41.

Suetsugu K, Haraguchi TF, Tayasu I. 2021. Novel mycorrhizal cheating in a green orchid: Cremastra appendiculata depends on carbon from deadwood through fungal associations. New Phytologist.

Suetsugu K, Matsubayashi J. 2021. Subterranean morphology modulates the degree of mycoheterotrophy in a green orchid Calypso bulbosa exploiting wood‐decaying fungi . Functional Ecology: 1–11.

Yagame T, Funabiki E, Nagasawa E, Fukiharu T, Iwase K. 2013. Identification and symbiotic ability of Psathyrellaceae fungi isolated from a photosynthetic orchid, Cremastra appendiculata (Orchidaceae). American Journal of Botany 100: 1823–1830.

15:00 - 15:15

Unravelling shoot:root drought responses in VOC emissions through 13C-pyruvate labelling

Erik Daber, Philipp Nolte, Jürgen Kreuzwieser, Mirjam Meischner, Christiane Werner

Chair of Ecosystem Physiology, Albert-Ludwigs-University of Freiburg, Germany

Plant shoots and roots reveal highly diverse and specialized metabolic adaptations to ensure plant survival above- and belowground while being faced by a multitude of external stressors. Plants hereby produce a plethora of biogenic volatile organic compounds (BVOCs) to communicate with their environment, e.g. to attract pollinators, repel herbivores or directly reduce effects of external stressors such as drought. Root and leaf metabolism are intertwined, with roots delivering minerals, nutrients and water, as well as carbohydrates to the leaves while receiving a multitude of metabolites from the leaves, including precursors for BVOC biosynthesis. Especially under drought stress, balanced resource allocation between leaves and roots is compromised. Even though many studies have focused on the complex dynamics of organ specific metabolome adaptations and changes in resource allocation under drought, little is known about metabolomic adjustments of BVOC biosynthesis of leaves relative to roots.

In our controlled climate chamber experiment, we aimed to unravel these dynamics by measuring compound-specific 13C-incorporation in BVOCs after position-specific ([1-13C]/[2-13C]-pyruvate) labelling of leaves and roots of potted, two-year old Fagus sylvatica and Picea abies saplings before and during drought stress, using flow-through chambers. BVOC emissions were measured online by PTR-TOF-MS in combination with GC-C-IRMS for further compound validation and 13C incorporation into specific monoterpenes. To quantify [1-13C]- and [2-13C]-pyruvate allocation into decarboxylation processes during primary and secondary metabolism, we used 13CO2 laser spectroscopy. Drought stress was determined by controlling soil moisture and measuring of plant physiological traits, such as leaf transpiration, assimilation rate and leaf water potential.

With this approach, we aim to identify active metabolic pathways responsible for BVOC biosynthesis in leaves and roots and how regulatory patterns changed due to drought. Considering our preliminary results, net CO2 assimilation, transpiration and respiration declined under drought. Overall BVOC composition and drought response, however, varied between organs in both species. Leaf emissions showed higher BVOC diversity even under drought. Monoterpene composition in leaves and roots of Fagus sylvatica differed and overall emissions were higher in roots. Contribution of de-novo synthesis of BVOCs in leaves was elevated due to storage depletion under drought in both species. Our results indicate major changes in BVOC emission pattern in leaves and roots under drought stress, providing first insights to elucidate drought-induced trade-offs in resource allocation into BVOCs above- and belowground.

15:15 - 15:30

Field 15N pool dilution approach to determine gross nitrification rate

C. Florian Stange, Axel Lamparter, Julia Jaquemotte

BGR, Deutschland

Nitrification is the microbial oxidation of ammonium (NH4+) to nitrate (NO3) and is one of the most important processes of the terrestrial nitrogen cycle. Nitrification is known to promote nitrogen leaching from soils as the less mobile cation ammonium (NH4+) is oxidized by nitrifiers to the mobile anion nitrate (NO3). Additionally, nitrification promotes NO and N2O formation, directly as a by-product of nitrate formation and indirectly as a source of substrate for denitrification.

In numerous studies gross nitrification rates are determined using 15N pool dilution technique in laboratories, but only few field experiments with undisturbed soil structure were done. An appropriate in situ sprinkler method with a low irrigation rate and very even 15N-nitrate application was developed 2018 for sandy soils. The first test with a tracer solution confirmed that high amounts of the soil water can replaced from the top soil by applying a low irrigation rate by a special sprinkling device, and therefore all assumptions of the 15N-pool dilution technique can be fulfilled in the field by this method. Subsequently, the method was used to measure the small scale field heterogeneity (dm to m) and variability between field of gross nitrification at eight 3m*3m plots at sites with sandy soils (Fuhrberger Feld, northern Germany) in spring 2021. The results of the first application of the new method and der measurements in the Fuhrberger Feld will be shown. Different approaches to calculate the nitrification rates between two sampling dates t0 and t1 will be presented, and the heterogeneity of the nitrification rate will be discussed.

15:30 - 15:45Poster Kurzvorträge - Themenblock 3: Paläoklima, Sedimentologie, Boden
Virtueller Veranstaltungsort: Poster Kurzvorträge - Meeting Link
15:30 - 15:33

Ein ~15 ka δ2Hn-alkane-Record vom Bichlersee, Oberbayern

Maximilian Prochnow1, Marcel Bliedtner1, Paul Strobel1, Michael Zech2, Roland Zech1

1Physical Geography, Institute of Geography, Friedrich Schiller University Jena, Jena, Germany; 2Heisenberg Chair of Physical Geography, Institute of Geography, Technische Universität Dresden, Dresden, Germany

Die Alpen sind eine Schlüsselregion, um vergangene Veränderungen des Klimas und der atmosphärischen Zirkulation in Europa zu rekonstruieren. Biomarker- und komponentenspezifische Stabilisotopenanalysen in Seesedimenten bieten dabei großes Potenzial, sind aber bisher im Alpenraum kaum angewendet worden. Wir präsentieren neueste Ergebnisse vom Bichlersee, Oberbayern, die vor allem das Spätglazial hochaufgelöst (50 Proben) abdecken. Die Blattwachsmuster (n-Alkane) zeigen durchweg einen dominanten Eintrag langkettiger Homologe (C27 bis C33), also ein terrestrisches Signal (im Vergleich zu kürzerkettigen, aquatischen Homologen von Algen und Makrophyten). Die markante Abnahme der mittleren Kettenlänge von >30 auf <30 am Ende der Jüngeren Dryas hängt vermutlich mit der Wiederbewaldung zu Beginn des Holozäns zusammen. Die 2H-Isotopie der dominanten C29- und C31-Kettenlängen ändert sich sehr konsistent und nahezu stetig im Verlauf des Spätglazials von –180 auf –210‰, um dann im Holozän wieder auf positivere Werte anzusteigen. Auch wenn wir dies im Moment insbesondere auf eine Änderung der Niederschlagsisotopie zurückführen, können wir den Einfluss sich verändernder Vegetation – z. B. durch mehr Gräser während des Spätglazials – und evapotranspirativer Anreicherung nicht quantifizieren. Dazu sind für die folgenden Arbeiten komponentenspezifische 18O-Analysen an Zuckern geplant.

15:33 - 15:36

Last millennium hydroclimate variability from Lake Höglwörth, Bavaria, Germany

Sudip Acharya1, Marcel Bliedtner1, Paul Strobel1, Josefin Sperling1, Thomas Kasper1, Michael Zech2, Roland Zech1

1Physical Geography, Institute of Geography, Friedrich Schiller University, Jena, Germany; 2Heisenberg Chair of Physical Geography, Institute of Geography, Technische Universität Dresden, Dresden, Germany

During the past decades, unusual rapid warming and significant changes in the precipitation seasonality and pattern have been recorded in almost the entire European Alps. To put these recent changes and climate projections into an adequate context, reconstructions of paleoenvironmental and –climate dynamics on a regional and local scale are prerequisite. Moreover, paleoenvironmental studies help to identify drivers and forcings of past (hydro)climate variability. In this study we present a high resolution continuous environmental and hydroclimatic record from a small forealpine lake “Lake Höglwörth” (Bavaria, Germany), covering the past millennium based on n-alkanes and their compound-specific isotopic composition (δ2H). The relatively high abundance of C27 to C33 indicates input from higher terrestrial plants, but also abundance of C23 and C25 document the presence of aquatic plants, particularly from AD 1100 to 1300, between AD 1550 and 1750, as well as since 1850. C29 and C31 reveal very similar isotopic (δ2H) signal and down-core trends. They are relatively enriched (~ -202.1 ‰ for C31) between AD 1100 and 1450 with maximum enrichment (~ -180 ‰ for C31) between AD 1200 and 1300. Rather depleted values (~ -210 ‰ for C31) are found from AD 1450 to 1650, however, an enrichment is obvious after 1650. Due to the primarily origin of the C29 and C31 in terrestrial vegetation, we assume that δ2H of these n-alkanesmainly reflects past changes in the isotopic composition of precipitation. However, effects related to changing vegetation and evapotranspirative enrichment cannot be ruled out. However, C23 is variably enriched compared to C29 and C31, and we suggest that this reflects the evaporative enrichment of the lake water and might thus enable to calculate relative humidity. We are now aiming to (i) increase the temporal resolution (continuous ~ decadal), (ii) compare our results to other regional records, and (iii) establish high-resolution d18O records from sugar biomarkers in order to more robustly disentangle the various factors influencing the isotopic composition of the leaf waxes.

15:36 - 15:39

Ca isotope partitioning upon experimental precipitation of carbonated hydroxy-apatite (CHAP)

Nikolaus Gussone1, Michael Ernst Böttcher2, Anika C. Conrad2, Iris Schmiedinger2, Jens Fiebig3, Markus Peltz4, Georg Grathoff4, Burkhard C. Schmidt5

1Institut für Mineralogie, Westfälische Wilhelms Universität Münster; 2Leibniz Institute of Baltic Sea Research and University of Greifswald, Deutschland; 3Institute of Geosciences, Goethe-University of Frankfurt, Germany, and Senckenberg Biodiversity and Climate Research Center, Frankfurt (Main), Germany; 4Economic Geology, University of Greifswald, Germany; 5Department of Experimental and Applied Mineralogy, Georg-August-University of Göttingen, Germany

Carbonated hydroxy-apatite (CHAP) was experimentally synthesized in batch-type set-ups by mixing of calcium (Ca)- and phosphate-bearing aqueous solutions and the transformation of calcite powder in aqueous solution between 11° and 65°C (Gussone et al., 2020). Compositional changes of the experimental solution and solid phase products were followed by elemental analysis, Raman spectroscopy, scanning-electron microscopy, and powder XRD. In the mixing experiments, crystallization of CHAP took place following the precipitation of metastable brushite as precursor that was then transformed into CHAP. In the transformation experiments using synthetic calcite as a precursor phase it was found that the reaction at pH values between 7.5 and 7.9 occurs via the direct replacement of calcium carbonate by CHAP.

Calcium isotope fractionation led to an enrichment of the light isotope in the solid CHAP compared to the aqueous solution by about -0.5 to -1.1 ‰, independent from the experimental approach, and the magnitude was essentially independent of temperature. The metastable brushite formed prior to transformation to CHAP showed a reduced fractionation compared to the CHAP. The observed Ca isotope fractionation into the CHAP lattice resembles that of natural phosphorites and lies within the range of the view existing theoretical and experimental studies.

Reference: Gussone N., Böttcher M.E., Conrad A.C., Fiebig J., Pelz M., Grathoff G., Schmidt B.C. (2020) Calcium isotope fractionation upon experimental apatite formation. Chem. Geol., 551, 119737

The study was supported by German Science Foundation (DFG) to M.E.B and J.F. within the EXCALIBOR project (BO1548/8 and FI 948/7), and to N.G. (GU1035/10), and by Leibniz IOW.

15:39 - 15:42

Stable isotopic and trace elemental fingerprints in carbonate precipitated by modern hard-water creeks of the temperate climate zone

Michael Ernst Böttcher1,2, Vera Winde1,3, Jens Bünning1, Olaf Dellwig1, Katrin Müller1, Ulrich Struck4, Maria-Theresia Schafmeister5, Peter Escher1,6

1Leibniz Institute of Baltic Sea Research, FRG; 2Marine Geochemistry, University of Greifswald, FRG; 3Present address: Hydroisotop, Schweitenkirchen, FRG; 4Naturhistorisches Museum, Berlin, FRG; 5Applied Geology, University of Greifswald, FRG; 6Ecoandmore, Freiburg, FRG

Processes in the dissolved carbonate system of surface waters may contribute and are sensitive to variations of boundary conditions associated with climate change. Carbon dioxide super- and calcium carbonate -saturated ground waters that emerge from springs lose dissolved carbon dioxide to the atmosphere; this process leads to the development of CaCO3 supersaturation of the aqueous solution. When exceeding a critical value, solid carbonates precipitate, thereby linking the past marine with the present terrestrial carbon cycles. The associated distribution of trace elements and stable isotopes leads to proxy formations. The magnitude of trace element and isotope fractionations is linked to non-equilibrium processes, impacted by the initial solution composition, hydrodynamics, and possible biological activity in the stream beds.

Two examples of recent sinter formation from streams in the temperate climate zone were investigated: Site R is positioned in a cliff zone of Rügen Island, southern Baltic Sea and Site W near Westerhof in the south-western Harz foreland. Two phases of surface water development can be differentiated: An induction period starting at the spring, where only degassing of carbon dioxide takes place, and a second stage where calcite formation from the highly supersaturated solution is continuously driven by further degassing. The liberation of CO2 is associated with an enrichment of the heavy carbon isotope in the remaining dissolved inorganic carbon. By following the isotope and trace element composition of aqueous solutions and recent calcite precipitates along the flow path, distribution coefficient (Li, Na, Mg, Sr, Ba, SO4, 13C, 18O) are derived. The empirical quantitative observations at Site W can be compared with observations dating back to the late 60s of the last century. Those at Site R are compared to results from laboratory experiments using the natural water as starting solution. Furthermore, the distribution coefficients are compared to calibrated experimental studies to estimate calcite precipitation rates. Trace-element based rate estimates for Site W are higher than published direct measurements, which is likely due to hydrodynamic boundary conditions impacting the in-situ growth experiments. Idiomorphic BaSO4 was observed in recent carbonate sinter at Site W for the first time, which is in agreement with slight supersaturations modeled for the stream water.

At the bottom of the cliff (Site R), the carbonate stream water is finally entering the Baltic Sea where mixing with brackish surface waters occur. The excess in dissolved CO2 compared to the atmosphere is enhancing the degassing capacity in the mixed coastal waters.

15:42 - 15:45

Identification of paleosols of a Namibian sediment core (WW203303) using pedogenic features, trace fossils and stable isotope compositions

Feiyu Wang1, Paul Koeniger2, Matthias Hinderer1

1TU Darmstadt, Deutschland; 2Federal Institute for Geosciences and Natural Resources, Geozentrum Hannover

Stable carbon and oxygen isotopes of carbonates from paleosols can be used as proxies to reconstruct paleoclimate and paleoenvironment conditions (Cerling & Quade, 1993). Paleosols are identified from the Namibian sediment core WW203302 (Houben et al., 2020) using stable isotopes, pedogenic features and a conceptual model generated by Hasiotis et al. (2012). Pedogenic features such as nodules, mottling and peds are clear indexes for paleosol in sediment. However, these features appear only sporadically in this 400 m long sediment core, trace fossils are used as index to distinguish paleosols from sediment.

Bioturbation patterns generally created by trace fossils occur nearly in the entire sediment core. Density, abundance, and depth of bioturbation follow the degree of soil development (Hasiotis et al. 2012). Pedogenesis, bioturbation and sedimentology are criteria to classify paleosols in sediment sections, from which nodules were selected, into compound, composite, and cumulative fractions (Kraus, 1999). Stable carbon and oxygen isotopes of bulk samples from different types of paleosols are compared to that of nodules to examine whether bulk samples from this sediment core can be used for paleoclimate interpretations.

The δ13C values of all types of bulk samples show basically the same trend as nodule samples (r2=0.88), bulk samples from well-developed paleosols, compound and composite paleosols show a better correlation to corresponding nodule samples than cumulative paleosols and phreatic layers for δ18O values (r2=0.64). Covering sands of nodule samples are more negative than corresponding nodules for δ18O, but either more negative or positive than nodules for δ13C, regardless of soil types. Furthermore, dolomites as a component of nodule samples, are generally more enriched in δ18O and mostly depleted in δ13C, regardless of soil type.

Cerling, T. E., & Quade, J. (1993). Stable Carbon and Oxygen Isotopes in Soil Carbonates. 217–231.

Hasiotis, S. T., & Platt, B. F. (2012). Exploring the sedimentary, pedogenic, and hydrologic factors that control the occurrence and role of bioturbation in soil formation and horizonation in continental deposits: An integrative approach. The Sedimentary Record, 10(3), 4–9

Houben, G. J., Kaufhold, S., Miller, R. M. G., Lohe, C., Hinderer, M., Noll, M., Hornung, J., Joseph, R., Gerdes, A., Sitnikova, M., & Quinger, M. (2020). Stacked megafans of the kalahari basin as archives of paleogeography, river capture, and cenozoic paleoclimate of Southwestern Africa. In Journal of Sedimentary Research (Vol. 90, Issue 9)

Kraus, M. J. (1999). Paleosols in clastic sedimentary rocks: Their geologic applications. Earth Science Reviews, 47(1–2), 41–70.

15:45 - 16:00Pause
16:00 - 17:30Block 4.2: Ökosysteme
Virtueller Veranstaltungsort: Block 4.2 - Meeting Link
Chair der Sitzung: Gerhard Gebauer, Universität Bayreuth
16:00 - 16:30
Session Keynote

Carbon isotope ratio as a measure of photosynthetic water-use efficiency: reconciling a biophysical discrepancy

John Marshall

SLU, Swedish University of Agricultural Sciences

In most plants, d13C of their tissues provides an estimate of the carbon:water exchange, or water-use efficiency, of photosynthesis. This is important because photosynthesis and transpiration represent an important evolutionary trade-off for plants, but also because they link two major parts of the ecosystem carbon and water cycles. The discovery that this trade-off could be quantified with d13C led to a burst of research in fields as diverse as plant breeding, ecosystem ecology, and global climate change. However, there was always some concern that the predicted isotopic composition did not exactly match biophysical theory, which was essentially a Rayleigh distillation model with a strong enzymatic fractionation. The discrepancy favoured overestimates and was approximately as large as the isotope effects under study, leading to some scepticism about the isotopic technique. I will review proposed explanations for the discrepancy, ending with the recent convergence on mesophyll conductance. Mesophyll conductance can now be measured with high precision in the field, offering a mechanistic adjustment leading to water-use efficiency estimates with high precision and accuracy. Eliminating this discrepancy returns d13C to a position of credibility as a measure of the linkage between carbon and water fluxes of plant leaves and canopies.

16:30 - 16:45

Impact of nutrient and water availability on grassland functioning - achieving a process based understanding across scales

Maren Dubbert1, Angelika Kübert2, Youri Rothfuss3, Christiane Werner2

1Zalf, Deutschland; 2Uni Freiburg, Deutschland; 3FZ Jülich, Deutschland

Two important threats to the sustainable functioning of seminatural grasslands in temperate zones are (1) nutrient loading due to agricultural fertilization and pollution, and (2) the increase of extreme drought events due to climate change. These threats may cause substantial shifts in species diversity and abundance and considerably affect the carbon and water balance of ecosystems. The synergistic effects between those two threats, however, can be complex and are poorly understood. Here, we experimentally investigated the effects of nitrogen addition and extreme drought (separately and in combination) on a seminatural temperate grassland, located in Freiburg (South Germany). To study the grassland response, we combined eddy-covariance techniques, open gas exchange systems from the leaf to the plot scale with biomass and beiodiversity assessments. Open gas exchange chambers were connected to an infrared gas analyzer and water isotope spectrometer, which allowed the partitioning of net ecosystem exchange and evapotranspiration. Vegetation parameters were described by species richness, species abundance, and leaf area index. Our results suggest that grassland communities, strongly weakened in their stress response by nitrogen loading, can substantially lose their carbon sink function during drought. While nitrogen addition caused a significant loss in forb species (−25%), precipitation reduction promoted a strong dominance of grass species at season start. Consequently, the grass-dominated and species-poor community suffered from a strong above-ground dieback during the dry summer months, likely caused by lower water use efficiency and weaker drought adaptations of the species community. Over the growing season (April-September), the carbon sequestration of the studied grassland was reduced by more than 60% as a consequence of nitrogen addition. Nitrogen addition in combination with precipitation reduction decreased carbon sequestration by 73%. Eutrophication can severely threaten the resilient functioning of grasslands, in particular when drought periods will increase as predicted by future climate scenarios. Our findings emphasize the importance of preserving high diversity of grasslands to strengthen their resistance against extreme events such as droughts.

16:45 - 17:00

Application of 2-dimensional stable isotope measurements of methane to constrain sources and sinks in a seasonally stratified freshwater lake

Teresa Einzmann1, Moritz Schroll1, Jan F. Kleint1,2, Thomas Klintzsch1,3, Frank Keppler1,4, Markus Greule1

1Institute of Earth Sciences, Heidelberg University, Heidelberg, Germany; 2MARUM – Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Bremen, Germany; 3Institute for Plant Nutrition, Justus Liebig University, Giessen, Germany; 4Heidelberg Center for the Environment (HCE), Heidelberg University, Heidelberg, Germany

Supersaturation of methane (CH4) in the oxic surface water layer of lakes has been suggested to play an important role in releasing CH4 to the atmosphere and emissions are predicted to increase with future climate change. Microbial CH4 oxidation in limnic systems as a counteracting sink has the potential to efficiently diminish CH4 effluxes. In this study, sources and sinks of CH4 were investigated in a seasonally stratified, eutrophic lake in southwestern Germany during summer using carbon and hydrogen stable isotope measurements.

In the lake water body, aerobic CH4 oxidation at the oxic-anoxic interface increased in intensity with rising CH4 concentrations over summer. This was accompanied by a strong increase in stable carbon and hydrogen isotope values of the CH4 pool. Incubation experiments with 13C-labeled CH4 revealed CH4 oxidation rates varying between 49-106 nM/d. In the lake sediment, anaerobically produced CH4 was reduced in its concentration through microbial anaerobic CH4 oxidation in sulfate-methane transition zones possible due to high sulfate concentrations in the lake (~2 mmol/l). The decrease in upward migrating sedimentary CH4 was partly accompanied by increasing stable carbon and hydrogen isotope values.

Sources of CH4 were characterized using a novel isotope indicator Δ(2,13) recently introduced by Tsunogai et al. (2020), which is based on dual isotope characterization of CH4 and corrects for isotopic fractionation effects caused by CH4 oxidation. Surface water CH4 showed different Δ(2,13) values if compared with CH4 from the hypolimnion and sediment and was furthermore distinguishable from littoral Δ(2,13) values. In order to investigate the occurrence of oxic CH4 production in the surface water layer, an incubation experiment was performed with 13C-labeled methylphosphonate, a known precursor substrate for aerobic CH4 formation, which showed a strong increase in the stable carbon isotopic composition of CH4 over time. In conclusion, our results strongly indicate internal oxic CH4 production by aerobic organisms as a possible source of excess CH4 in the surface water layer of the lake.


Tsunogai, U. et al. 2020. Dual stable isotope characterization of excess methane in oxic waters of a mesotrophic lake. Limnol. Oceanogr. 65: 2937–2952.

17:00 - 17:15

Belowground C allocation of tropical rainforests in response to drought: an ecosystem 13CO2 labeling approach

lingling shi1, Pratiksha Acharya1, Xujuan Bai1, Niklas Schmuecker1, Nemiah Ladd2, Christiane Werner2, Laura.K Meredith3,4, Michaela Dippold1

1Biogeochemistry of Agroecosystems, Department of Crop Science, Faculty of Agriculture, Georg August University of Göttingen; 2Ecosystem Physiology, University of Freiburg, Freiburg, Germany; 3School of Natural Resources and the Environment, University of Arizona, Tucson, United States of America; 4Biosphere 2, University of Arizona, Tucson, United States of America

Drought affects carbon (C) sources and sinks in forest ecosystems, with potential consequences for belowground C allocation, a vital process of the terrestrial C cycle. However, the extreme drought impacts on the ecosystem are poorly understood, particularly in the tropical rainforests. Within the framework of our large-scale ecosystem manipulation experiment on "Rain Forest Water, Atmosphere, and Life Dynamics" (WALD) at the Biosphere 2 in Arizona, we conducted a whole ecosystem stable isotope labeling with atmospheric 13CO2 to gain in-depth insights into tree belowground C allocations and the C partitioning at the soil–microbe-root interface under ambient conditions and drought stress. In particular, we hypothesized that key drought-adaptation strategies would include i) increased C allocation into subsoil layers that drought down slower than topsoil and ii) increased C investment into rhizodeposits and mycorrhizal fungi. Our data on tree C allocation highlight that drought stress increased the proportion of recently assimilated C translocated into the roots in both the top- and sub-soil with no correlation of C allocation with soil water content or root biomass. In response to drought, the rhizodeposition, and thus allocation of assimilated C into rhizospheres soil, was reduced in topsoil but increased in subsoil. However, we found pronounced plot-specific differences in belowground C allocation, especially between plots with only understory plants vs those with tall trees, suggesting species-specific drought response strategies. However, generally our observations underline that trees attempt to invest assimilated C into the deeper soil layers’ roots and rhizosphere to access subsoil resources. The C investment into deeper soil layers and the absence of any correlation with root biomass suggest that drought adaptation strategies are based on rhizomicrobial mechanisms rather than on C investment into root growth. The upcoming results of 13C incorporation into phospholipid fatty acids will provide further insights into microbial C utilization in the rhizosphere and complete our picture of belowground drought adaptation strategies. In summary, quantification of tree C belowground allocation patterns at the plant-microbe-soil interface will enable us to disentangle belowground drought response strategies of tropical rainforests.

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