TY - JOUR A1 - van Rees, Charles B. A1 - Waylen, Kerry A. A1 - Schmidt-Kloiber, Astrid A1 - Thackeray, Stephen J. A1 - Kalinkat, Gregor A1 - Martens, Koen A1 - Domisch, Sami A1 - Lillebo, Ana A1 - Hermoso, Virgilio A1 - Grossart, Hans-Peter A1 - Schinegger, Rafaela A1 - Decleer, Kris A1 - Adriaens, Tim A1 - Denys, Luc A1 - Jaric, Ivan A1 - Janse, Jan H. A1 - Monaghan, Michael T. A1 - De Wever, Aaike A1 - Geijzendorffer, Ilse A1 - Adamescu, Mihai C. A1 - Jähnig, Sonja C. T1 - Safeguarding freshwater life beyond 2020 BT - recommendations for the new global biodiversity framework from the European experience JF - Conservation letters N2 - Plans are currently being drafted for the next decade of action on biodiversity-both the post-2020 Global Biodiversity Framework of the Convention on Biological Diversity (CBD) and Biodiversity Strategy of the European Union (EU). Freshwater biodiversity is disproportionately threatened and underprioritized relative to the marine and terrestrial biota, despite supporting a richness of species and ecosystems with their own intrinsic value and providing multiple essential ecosystem services. Future policies and strategies must have a greater focus on the unique ecology of freshwater life and its multiple threats, and now is a critical time to reflect on how this may be achieved. We identify priority topics including environmental flows, water quality, invasive species, integrated water resources management, strategic conservation planning, and emerging technologies for freshwater ecosystem monitoring. We synthesize these topics with decades of first-hand experience and recent literature into 14 special recommendations for global freshwater biodiversity conservation based on the successes and setbacks of European policy, management, and research. Applying and following these recommendations will inform and enhance the ability of global and European post-2020 biodiversity agreements to halt and reverse the rapid global decline of freshwater biodiversity. KW - climate change KW - conservation KW - ecosystem services KW - rivers KW - sustainable KW - development goals KW - water resources KW - wetlands Y1 - 2020 U6 - https://doi.org/10.1111/conl.12771 SN - 1755-263X VL - 14 IS - 1 PB - Wiley CY - Hoboken ER - TY - THES A1 - Repasch, Marisa T1 - Fluvial sediment routing and the carbon cycle BT - insights from the Rio Bermejo, Argentina BT - Einblicke aus dem Rio Bermejo, Argentinien N2 - By regulating the concentration of carbon in our atmosphere, the global carbon cycle drives changes in our planet’s climate and habitability. Earth surface processes play a central, yet insufficiently constrained role in regulating fluxes of carbon between terrestrial reservoirs and the atmosphere. River systems drive global biogeochemical cycles by redistributing significant masses of carbon across the landscape. During fluvial transit, the balance between carbon oxidation and preservation determines whether this mass redistribution is a net atmospheric CO2 source or sink. Existing models for fluvial carbon transport fail to integrate the effects of sediment routing processes, resulting in large uncertainties in fluvial carbon fluxes to the oceans. In this Ph.D. dissertation, I address this knowledge gap through three studies that focus on the timescale and routing pathways of fluvial mass transfer and show their effect on the composition and fluxes of organic carbon exported by rivers. The hypotheses posed in these three studies were tested in an analog lowland alluvial river system – the Rio Bermejo in Argentina. The Rio Bermejo annually exports more than 100 Mt of sediment and organic matter from the central Andes, and transports this material nearly 1300 km downstream across the lowland basin without influence from tributaries, allowing me to isolate the effects of geomorphic processes on fluvial organic carbon cycling. These studies focus primarily on the geochemical composition of suspended sediment collected from river depth profiles along the length of the Rio Bermejo. In Chapter 3, I aimed to determine the mean fluvial sediment transit time for the Rio Bermejo and evaluate the geomorphic processes that regulate the rate of downstream sediment transfer. I developed a framework to use meteoric cosmogenic 10Be (10Bem) as a chronometer to track the duration of sediment transit from the mountain front downstream along the ~1300 km channel of the Rio Bermejo. I measured 10Bem concentrations in suspended sediment sampled from depth profiles, and found a 230% increase along the fluvial transit pathway. I applied a simple model for the time-dependent accumulation of 10Bem on the floodplain to estimate a mean sediment transit time of 8.5±2.2 kyr. Furthermore, I show that sediment transit velocity is influenced by lateral migration rate and channel morphodynamics. This approach to measuring sediment transit time is much more precise than other methods previously used and shows promise for future applications. In Chapter 4, I aimed to quantify the effects of hydrodynamic sorting on the composition and quantity of particulate organic carbon (POC) export transported by lowland rivers. I first used scanning electron miscroscopy (SEM) coupled with nanoscale secondary ion mass spectrometry (NanoSIMS) analyses to show that the Bermejo transports two principal types of POC: 1) mineral-bound organic carbon associated with <4 µm, platy grains, and 2) coarse discrete organic particles. Using n-alkane stable isotope data and particle shape analysis, I showed that these two carbon pools are vertically sorted in the water column, due to differences in particle settling velocity. This vertical sorting may drive modern POC to be transported efficiently from source-to-sink, driving efficient CO2 drawdown. Simultaneously, vertical sorting may drive degraded, mineral-bound POC to be deposited overbank and stored on the floodplain for centuries to millennia, resulting in enhanced POC remineralization. In the Rio Bermejo, selective deposition of coarse material causes the proportion of mineral-bound POC to increase with distance downstream, but the majority of exported POC is composed of discrete organic particles, suggesting that the river is a net carbon sink. In summary, this study shows that selective deposition and hydraulic sorting control the composition and fate of fluvial POC during fluvial transit. In Chapter 5, I characterized and quantified POC transformation and oxidation during fluvial transit. I analyzed the radiocarbon content and stable carbon isotopic composition of Rio Bermejo suspended sediment and found that POC ages during fluvial transit, but is also degraded and oxidized during transient floodplain storage. Using these data, I developed a conceptual model for fluvial POC cycling that allows the estimation of POC oxidation relative to POC export, and ultimately reveals whether a river is a net source or sink of CO2 to the atmosphere. Through this study, I found that the Rio Bermejo annually exports more POC than is oxidized during transit, largely due to high rates of lateral migration that cause erosion of floodplain vegetation and soil into the river. These results imply that human engineering of rivers could alter the fluvial carbon balance, by reducing lateral POC inputs and increasing the mean sediment transit time. Together, these three studies quantitatively link geomorphic processes to rates of POC transport and degradation across sub-annual to millennial time scales and nanoscale to 103 km spatial scales, laying the groundwork for a global-scale fluvial organic carbon cycling model. N2 - Der globale Kohlenstoffkreislauf bestimmt das Klima und die Bewohnbarkeit unseres Planeten durch die Regulierung der Kohlenstoffkonzentration in unserer Atmosphäre. Erdoberflächenprozesse spielen eine zentrale, aber nicht ausreichend verstandene Rolle in der Regulierung der Kohlenstoffflüsse zwischen terrestrischen Reservoiren und der Atmosphäre. Flusssysteme steuern globale biogeochemische Kreisläufe, indem sie große Mengen Kohlenstoff in der Landschaft umverteilen. Dabei bestimmt das Gleichgewicht zwischen Kohlenstoffoxidation und -konservierung, ob der Flusstransport in einer atmosphärischen Netto CO2-Quelle oder -Senke resultiert. Die Auswirkungen von Sedimentverlagerungsprozessen werden in bestehenden Modellen für den Kohlenstofftransport in Flüssen jedoch nicht berücksichtigt, was zu großen Unsicherheiten in der Bestimmung von Kohlenstoffflüssen von Quellen zu Senken führt. In dieser Dissertation adressiere ich diese Wissenslücke mithilfe von drei Studien, die verschiedene Komponenten des Stofftransfers von Quelle zu Senke und seine Auswirkungen auf die Zusammensetzung und den Transfer des organischen Kohlenstoffs im Fluss herausgreifen. Die in diesen drei Studien aufgestellten Hypothesen wurden in einem analogen alluvialen Tieflandflusssystem - dem Rio Bermejo in Argentinien - getestet. Der Rio Bermejo exportiert jährlich mehr als 100 Mt Sedimente und organisches Material aus den Zentralanden und transportiert dieses fast 1300 km flussabwärts ohne Einfluss von Nebenflüssen durch das Tieflandbecken. Dies erlaubt die Isolierung der Auswirkungen geomorphologischer Prozesse auf den organischen Kohlenstoffkreislauf im Fluss. Die Studien basieren auf geochemischen Daten eines Satzes Sedimentproben der Suspensionsfracht, die entlang des Rio Bermejo aus Flusstiefenprofilen entnommen wurden. In Kapitel 3 habe ich mir das Ziel gesetzt die mittlere Flusssedimenttransitzeit des Rio Bermejo sowie die geomorphologischen Prozesse, die die Geschwindigkeit des Sedimenttransfers flussabwärts regulieren, zu bestimmen. Dazu habe ich ein Framework entwickelt, wie meteorisches kosmogenes 10Be (10Bem) als Chronometer verwendet werden kann, das die Dauer des Sedimenttransits von der Bergfront stromabwärts entlang des ~ 1300 km langen Kanals des Rio Bermejo misst. Ich habe 10Bem -Konzentrationen an den Tiefenprofilen der Suspensionsfracht gemessen und dabei einen Anstieg von 230% entlang des Flusstransfers festgestellt. Für die zeitabhängige Akkumulation von 10Bem auf der Überflutungsebene habe ich ein einfaches Modell angewendet und dadurch eine mittlere Sedimenttransitzeit von ~ 8,5 ± 2,2 kyr abgeschätzt. Meine Daten haben zusätzlich gezeigt, dass Unterschiede in der lateralen Migrationsrate und der Kanalmorphodynamik Unterschiede in der Sedimenttransitgeschwindigkeit verursachen. Dieser Ansatz zur Messung der Sedimenttransitzeit ist viel präziser als andere bisher verwendete Methoden und hat ein großes Potential für zukünftige Anwendungen. Kapitel 4 habe ich darauf ausgerichtet die Auswirkungen der vorübergehenden Speicherung in Überflutungsebenen, der Verfeinerung der Korngrößen flussabwärts und der organomineralischen Assoziationen auf die Zusammensetzung und Menge des Exports von fluvialem partikulärem organischem Kohlenstoff (POC) zu quantifizieren. Daten stabiler n Alkan-Isotope zeigten eine vertikale Sortierung organischer Stoffe in der Flusswassersäule, durch die 13C -angereichertes, mineralassoziiertes POC am oberen Ende der Wassersäule konzentriert wurde. Mithilfe von Rasterelektronenmikroskopie (SEM) und nanoskalige Sekundärionen-Massenspektrometrie (NanoSIMS) -Analysen habe ich gezeigt, dass Organomineralassoziationen größtenteils in feinen, plattigen Mineralkörnern mit niedrigen Absetzgeschwindigkeiten gefunden werden, welche zum Aufsteigen des mineralgebundenen POC in der Wassersäule führen. Organomineralassoziationen und 13C -Anreicherung sind typisch für den Abbau von organischem Kohlenstoff im Boden, was darauf hindeutet, dass mineralgebundener POC größtenteils aus der Erosion verwitterter Auenböden stammt. Ich habe gezeigt, dass> 70% des suspendierten POC-Exports in Zusammenhang mit feinem Sediment seht. Dieser POC ist wahrscheinlich aufgrund des Abbaus während der vorübergehenden Lagerung in den Überflutungsebenen stärker an 13C angereichert. Da mineralgebundenes POC und diskrete organische Partikel in der Wassersäule in unterschiedlichen Tiefen transportiert werden, weisen sie wahrscheinlich unterschiedliche Flusslaufzeiten und damit unterschiedliche Oxidationswahrscheinlichkeiten während des Flusstransfers auf. Zusammenfassend zeigt diese Studie, dass hydrodynamische Sortiereffekte die Zusammensetzung und das Schicksal des fluvialen POC während des Transits von Quelle zu Senke steuern. In Kapitel 5 habe ich die POC-Transformation und -Oxidation während des Flussdurchgangs charakterisiert und quantifiziert. Dazu habe ich den Radiokohlenstoffgehalt und die stabile Kohlenstoffisotopenzusammensetzung der Suspensionsfracht des Rio Bermejo analysiert. Die Daten zeigten sowohl eine Alterung des POC während des Flusstransits und als auch den Abbau von POC während der vorübergehenden Ablagerung in Überflutungsebenen. Unter Verwendung dieser Daten entwickelte ich ein konzeptionelles Modell für den Fluss-POC-Kreislauf, das die Abschätzung der POC-Oxidation im Verhältnis zum POC-Export ermöglicht und zeigt, ob ein Fluss eine Nettoquelle oder -senke für CO2 in der Atmosphäre darstellt. Durch diese Studie fand ich heraus, dass der Rio Bermejo jährlich mehr POC exportiert, als während des Transits oxidiert wird, was hauptsächlich auf die hohen seitlichen Migrationsraten zurückzuführen ist, die zur Erosion der Auenvegetation und der Auenböden in den Fluss führen. Diese Ergebnisse deuten darauf hin, dass die menschliche Gestaltung von Flüssen die Kohlenstoffbilanz im Fluss verändern könnte, indem die seitlichen POC-Einträge reduziert und die mittlere Sedimenttransitzeit erhöht werden. Zusammengenommen verknüpfen diese drei Studien geomorphologische Prozesse quantitativ mit den Raten des POC-Transports und der POC-Degradation über sub-jährliche bis tausendjährige Zeitskalen und Nano bis 103 km räumlichen Skalen und bilden die Grundlage für ein Modell des globalen, fluvialen, organischen Kohlenstoffkreislaufs. T2 - Flusssedimenttransfer und Kohlenstoffkreislauf KW - biogeoscience KW - geomorphology KW - rivers KW - Biogeowissenschaften KW - Geomorphologie KW - Flüsse Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-493978 ER - TY - JOUR A1 - Menges, Johanna A1 - Hovius, Niels A1 - Andermann, Christoff A1 - Lupker, Maarten A1 - Haghipour, Negar A1 - Märki, Lena A1 - Sachse, Dirk T1 - Variations in organic carbon sourcing along a trans-Himalayan river determined by a Bayesian mixing approach JF - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society N2 - Rivers transfer particulate organic carbon (POC) from eroding mountains into geological sinks. Organic carbon source composition and selective mobilization have been shown to affect the type and quantity of POC export, but their combined effects across complex mountain ranges remain underexplored. Here, we examine the variation in organic carbon sourcing and transport in the trans-Himalayan Kali Gandaki River catchment, along strong gradients in precipitation, rock type and vegetation. Combining bulk stable nitrogen, and stable and radioactive organic carbon isotopic composition of bedrock, litter, soil and river sediment samples with a Bayesian end-member mixing approach, we differentiate POC sources along the river and quantify their export. Our analysis shows that POC export from the Tibetan segment of the catchment, where carbon bearing shales are partially covered by aged and modern soils, is dominated by petrogenic POC. Based on our data we re-assess the presence of aged biospheric OC in this part of the catchment, and its contribution to the river load. In the High Himalayan segment, we observed low inputs of petrogenic and biospheric POC, likely due to very low organic carbon concentrations in the metamorphic bedrock, combined with erosion dominated by deep-seated landslides. Our findings show that along the Kali Gandaki River, the sourcing of sediment and organic carbon are decoupled, due to differences in rock organic carbon content, soil and above ground carbon stocks, and geomorphic process activity. While the fast eroding High Himalayas are the principal source of river sediment, the Tibetan headwaters, where erosion rates are lower, are the principal source of organic carbon. To robustly estimate organic carbon export from the Himalayas, the mountain range should be divided into tectono-physiographic zones with distinct organic carbon yields due to differences in substrate and erosion processes and rates. KW - particulate organic carbon KW - Himalaya KW - rivers KW - carbon cycle KW - stable KW - isotopes KW - erosion KW - end-member mixing Y1 - 2020 U6 - https://doi.org/10.1016/j.gca.2020.07.003 SN - 0016-7037 VL - 286 SP - 159 EP - 176 PB - Elsevier CY - New York [u.a.] ER - TY - THES A1 - Menges, Johanna T1 - Organic Carbon Storage, Transfer and Transformation in the Himalaya BT - insights from the Kali Gandaki Valley in Central Nepal N2 - The transfer of particulate organic carbon from continents to the ocean is an important component of the global carbon cycle. Transfer to and burial of photosynthetically fixed biospheric organic carbon in marine sediments can effectively sequester atmospheric carbon dioxide over geological timescales. The exhumation and erosion of fossil organic carbon contained in sedimentary rocks, i.e. petrogenic carbon, can result in remineralization, releasing carbon to the atmosphere. In contrast, eroded petrogenic organic carbon that gets transferred back to the ocean and reburied does not affect atmospheric carbon content. Mountain ranges play a key role in this transfer since they can source vast amounts of sediment including particulate organic carbon. Globally, the export of both, biospheric and petrogenic organic carbon has been linked to sediment export. Additionally, short transfer times from mountains to the ocean and high sediment concentrations have been shown to increase the likelihood of organic carbon burial. While the importance of mountain ranges in the organic carbon cycle is now widely recognized, the processes acting within mountain ranges to influence the storage, cycling and mobilization of organic carbon, as well as carbon fluxes from mountain ranges remain poorly constrained. In this thesis, I employ different methods to assess the nature and fate of particulate organic carbon in mountain belts, ranging from the molecular to regional landscape scale. These studies are located along the Trans-Himalayan Kali Gandaki River in Central Nepal. This river traverses all major geological and climatic zones of the Himalaya, from the dry northern Tibetan plateau to the high-relief, monsoon dominated steep High Himalaya and the lower relief and abundant vegetation of the Lesser Himalayan region. First, I document how biospheric organic matter has accumulated during the Holocene in the headwaters of the Kali Gandaki River valley, by combining compound specific isotope measurements with different dating methods and grain size data, and investigate the stability of this organic carbon reservoir on millennial timescales. I show, that around 1.6 ka an eco-geomorphic tipping point occurred leading to a destabilization of the landscape resulting in today’s high erosion rates and the excavation of the aged organic carbon reservoir. This study highlights the climatic and geomorphic controls on biospheric organic carbon storage and release from mountain ranges. Second, I systematically investigate the spatial variation of particulate organic carbon fluxes across the Himalaya along the Kali Gandaki River, using bulk stable and radioactive isotopes combined with a new Bayesian modeling approach. The detailed dataset allows the distinction of aged and modern biospheric organic carbon as well as petrogenic organic carbon across the Himalayan mountain range and the investigation of the role of climatic and geomorphic factors in their riverine export. The data suggest a decoupling of the particulate organic carbon from the sediment yield along the Kali Gandaki River, partially driven by climatic and geomorphic processes. In contrast to the suspended sediment, a large part of the particulate organic carbon exported by the river originates from the Tibetan part of the catchment and is dominated by petrogenic organic carbon derived from Jurassic shales with only minor contributions of modern and aged biospheric organic carbon. These findings emphasize the importance of organic carbon source distribution and erosion mechanisms in determining the organic carbon export from mountain ranges. In a third step, I explore the potential of ultra-high resolution mass spectrometry for particulate organic carbon transport studies. I have generated a novel and unprecedented high-resolution molecular dataset, which contains up to 103 molecular formulas of the lipid fraction of particulate organic matter for modern and aged biospheric carbon, petrogenic organic carbon and river sediments. First, I test if this dataset can be used to better resolve different organic carbon sources and to identify new geochemical tracers. Using multivariate statistics, I identify up to 10² characteristic molecular formulas for the major organic carbon sources in the upper part of the Kali Gandaki catchment, and trace their transfer from the surrounding landscape into the river sediment. Second, I test the potential of the molecular dataset to trace molecular transformations along source-to-sink pathways. I identify changes in molecular metrics derived from the dataset, which are characteristic of transformation processes during incorporation of litter into soil, the aging of soil material, and the mobilization of the organic carbon into the river. These two studies demonstrate that high-resolution molecular datasets open a promising analytical window on particulate organic carbon and can provide novel insights into the composition, sourcing and transformation of riverine particulate organic carbon. Collectively, these studies advance our understanding of the processes contributing to the storage and mobilization of organic carbon in the Central Himalaya, the mountain belt that dominates global erosional fluxes. They do so by identifying the major sources of particulate organic carbon to the Trans-Himalayan Kali Gandaki River, by elucidating their sensitivity to climate and geomorphic processes, and by identifying some of the transformations of this material on the molecular scale. As a result, the thesis demonstrates that the amount and composition of organic carbon routed from mountain belts is a function of the dynamic interactions of geologic, biologic, geomorphic and climatic processes within the mountain belt. This understanding will ultimately help in answering whether the build-up and erosion of mountain ranges over geological time represents a net carbon source or sink to the atmosphere. Beyond this, the thesis contributes to our technical ability to characterize organic matter and attribute it to sources by scoping the potential of high-end molecular analysis. KW - organic carbon cycle KW - biomarker KW - isotopes KW - Himalaya KW - rivers Y1 - 2020 ER -