ALBERT

Description: With increasing resolution of numerical weather prediction (NWP) models, classical subgrid‐scale processes become increasingly resolved on the model grid. In particular, turbulence in the planetary boundary layer (PBL) is vertically already partially resolved in contemporary models. For classical local PBL schemes, resulting up‐gradient heat transports cannot be treated correctly. Thus, nonlocal turbulence schemes have been developed in the past. As the horizontal grid sizes of NWP models become smaller than a few kilometers, the large turbulence eddies in the PBL will also start to become partially resolved in the horizontal direction. A very flexible way to formulate nonlocal turbulent exchange is the transilient matrix method, which is used here to develop a new turbulence parameterization. The resulting NLT3D scheme applies transilient mixing matrices to subgrid‐scale transports in all three dimensions. We compare results of WRF real‐case simulations including our scheme, a classical local turbulence scheme (MYNN), and an existing nonlocal one‐dimensional scheme (ACM2) with observations from field campaigns over homogeneous terrain (CASES‐99) and complex terrain (CAPTEX). Over homogeneous terrain, all three schemes similarly well capture the observed surface fluxes and radiosonde profiles, whereas over complex terrain more differences become obvious. During a tracer release experiment (CAPTEX) over the Appalachian mountain region, the mixing and vertical extent of the PBL turn out to be decisive to reproduce the observed advection speed of the tracer‐marked air mass. Deeper mixing not only accelerates surface winds but also enables tracer to travel faster at higher altitudes and then mix back to the ground. As results from a version of NLT3D with only standard horizontal Smagorinsky diffusion (NLT1D) demonstrate, simulating three‐dimensional turbulence can be beneficial already at horizontal grid sizes of a few kilometers.

Description: Decreasing grid sizes in numerical weather prediction models demand the inclusion of nonlocal effects and horizontal turbulence in turbulence parameterizations. This is the motivation for the development of the nonlocal three‐dimensional turbulence (NLT3D) scheme. Vertical nonlocal mixing accelerates the horizontal transport of near‐surface tracers by fast advection at higher altitudes (see figure), and horizontal turbulence enhances tracer dispersion. As validated by observations, both effects are beneficial to the forecast quality already at grid sizes of a few kilometers.

Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

Description: The 2011/2012 summer drought in Southeastern South America (SESA) was a short but devastating event. What would this event have looked like under pre‐industrial conditions, or in a +2 degC world? We find that climate change causes the region to be at a higher risk of drought. However, we found no large‐scale changes in the half‐month water budgets. We show that the climate change induced positive precipitation trend in the region outweighs the increased temperatures and potential evapotranspiration during the 2011/2012 drought. image

Description: Aerosol can affect clouds in various ways. Beside the microphysical impact of aerosol particles on cloud formation, the interference of aerosol with atmospheric radiation leads to changes in local heating, surface fluxes and thus mesoscale circulations, all of which may also modify clouds. Rather little is known about these so‐called semi‐direct effects in realistic settings – a reason why this study investigates the impact of absorbing aerosol particles on cloud and radiation fields over Germany. Using advanced high‐resolution simulations with grid spacings of 312 and 625 m, numerical experiments with different aerosol optical properties are contrasted using purely scattering aerosol as a control case and realistic absorbing aerosol as a perturbation. The combined effect of surface dimming and atmospheric heating induces positive temperature and negative moisture anomalies between 800 and 900 hPa, impacting low‐level cloud formation. Decreased relative humidity as well as increased atmospheric stability below clouds lead to a reduction of low‐level cloud cover, liquid water path and precipitation. It is further found that direct and semi‐direct effects of absorbing aerosol forcing have similar magnitudes and contribute equally to a reduction of net radiation at the top of the atmosphere.

Description: Atmospheric aerosol particles can absorb solar radiation, altering the thermal structure of the atmosphere and surface fluxes. Using advanced high‐resolution simulations over Germany with grid spacings of 312 and 625 m, we find that boundary‐layer absorbing aerosol reduces low‐level cloud cover, liquid water path and precipitation. Direct and semi‐direct effects have similar magnitudes and contribute equally to a positive absorbing aerosol forcing.

Description: German Ministry for Education and Research EU Horizon 2020 project CONSTRAIN

Description: https://cera-www.dkrz.de/WDCC/ui/cerasearch/entry?acronym=DKRZ_LTA_1174_ds00001

Description: Using a household and plot‐level survey conducted in Ethiopia, this study analyses the difference in farmers' adoption of sustainable land management (SLM) practices between their rainfed and irrigated plots. The paper also investigates the varying influence of different types of irrigation water management systems and associated irrigation technologies on the adoption of SLM practices in irrigated plots. After controlling for heterogeneity among different irrigation water management systems and technologies, we found that access to irrigation play major role in enhancing farmers' motivation to adopt more SLM practices. Furthermore, the combined effect of irrigation water management system and irrigation technology on type and number of SLM practices adopted is quite varied and very significant. The evidence highlights that farmers adopt more SLM practices in their plots with pump irrigation compared with those plots where gravity irrigation is applied because pump irrigation systems enhance complementarities with SLM practices. Finally, the findings underscore that the type of irrigation water management and the irrigation technology applied play an important role in restoring degraded lands and maintaining soil fertility, even when farmers' adoption of irrigation was not explicitly triggered by concerns for soil health.

Description: Center for Development Research (ZEF), University of Bonn

Description: CGIAR Research Program on Water, Land, and Ecosystems

Description: Deutscher Akademischer Austauschdienst (DAAD) http://dx.doi.org/10.13039/501100001655

Description: Dr. Hermann Eiselen Doctoral Program of the Foundation Fiat

Description: Federal Ministry for Economic Cooperation and Development (BMZ) of Germany, The Water‐Energy‐Food Nexus: Global, Basin and Local Case Studies of Resource Use Efficiency Under Growing Natural Resource Scarcity

Description: Classification of atmospheric circulation patterns (CP) is a common tool for downscaling rainfall, but it is rarely used for West Africa. In this study, a two‐step classification procedure is proposed for this region, which is applied from 1989 to 2010 for the Sudan‐Sahel zone (Central Burkina Faso) with a focus on heavy rainfall. The approach is based on a classification of large‐scale atmospheric CPs (e.g., Saharan Heat Low) of the West African Monsoon using a fuzzy rule‐based method to describe the seasonal rainfall variability. The wettest CPs are further classified using meso‐scale monsoon patterns to better describe the daily rainfall variability during the monsoon period. A comprehensive predictor screening for the seasonal classification indicates that the best performing predictor variables (e.g., surface pressure, meridional moisture fluxes) are closely related to the main processes of the West African Monsoon. In the second classification step, the stream function at 700 hPa for identifying troughs and ridges of tropical waves shows the highest performance, providing an added value to the overall performance of the classification. Thus, the new approach can better distinguish between dry and wet CPs during the rainy season. Moreover, CPs are identified that are of high relevance for daily heavy rainfall in the study area. The two wettest CPs caused roughly half of the extremes on about 6.5% of days. Both wettest patterns are characterized by an intensified Saharan Heat Low and a cyclonic rotation near the study area, indicating a tropical wave trough. Since the classification can be used to condition other statistical approaches used in climate sciences and other disciplines, the presented classification approach opens many different applications for the West African Monsoon region.

Description: A two‐step classification of daily atmospheric circulation patterns is used to describe seasonal and daily rainfall variability in West Africa. The approach clearly distinguishes between dry and wet patterns if sea level pressure and stream function at 700 hPa are used. The two wettest patterns trigger about half of heavy rainfall events in Central Burkina Faso. They are characterized by an intensified Saharan Heat Low and a cyclonic rotation indicating a tropical wave trough near the study area.

Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347

Description: Accurate and reliable precipitation data with high spatial and temporal resolution are essential in studying climate variability, water resources management, and hydrological forecasting. A range of global precipitation data are available to this end, but how well these capture actual precipitation remains unknown, particularly for mountain regions where ground stations are sparse. We examined the performance of three global high‐resolution precipitation products for capturing precipitation over Central Asia, a hotspot of climate change, where reliable precipitation data are particularly scarce. Specifically, we evaluated MSWEP, CHIRPS, and GSMAP against independent gauging stations for the period 1985–2015. Our results show that MSWEP and CHIRPS outperformed GSMAP for wetter periods (i.e., winter and spring) and wetter locations (150–600 mm·year−1), lowlands, and mid‐altitudes (0–3,000 m), and regions dominated by winter and spring precipitation. MSWEP performed best in representing temporal precipitation dynamics and CHIRPS excelled in capturing the volume and distribution of precipitation. All precipitation products poorly estimated precipitation at higher elevations (〉3,000 m), in drier areas (〈150 mm), and in regions characterized by summer precipitation. All products accurately detected dry spells, but their performance decreased for wet spells with increasing precipitation intensity. In sum, we find that CHIRPS and MSWEP provide the most reliable high‐resolution precipitation estimates for Central Asia. However, the high spatial and temporal heterogeneity of the performance call for a careful selection of a suitable product for local applications considering the prevailing precipitation dynamics, climatic, and topographic conditions.

Description: We present the first quantitative evaluation of global high‐resolution (below 12 km) precipitation products against independent ground observations over Central Asia. Our results show that MSWEP was best at representing temporal precipitation dynamics, and CHIRPS was most prominent in representing the volume and distribution of precipitation. This is especially the case of wet seasons, altitudes below 3,000 m, and regions dominated by spring and winter precipitation. Our analysis provides key insights on the precipitation products' suitability for local hydrological applications.

Description: Leibniz‐Institut für Agrarentwicklung in Transformationsökonomien

Description: Volkswagen Foundation http://dx.doi.org/10.13039/501100001663

Description: We review the widely used concepts of “buoyancy” and “convective available potential energy” (CAPE) in relation to deep convection in tropical cyclones and discuss their limitations. A fact easily forgotten in applying these concepts is that the buoyancy force of an air parcel, as often defined, is non‐unique because it depends on the arbitrary definition of a reference density field. However, when calculating CAPE, the buoyancy of a lifted air parcel is related to the specific reference density field along a vertical column passing through that parcel. Both concepts can be generalized for a vortical flow and to slantwise ascent of a lifted air parcel in such a flow. In all cases, the air parcel is assumed to have infinitely small dimensions. In this article, we explore the consequences of generalizing buoyancy and CAPE for buoyant regions of finite size that perturb the pressure field in their immediate environment. Quantitative calculations of effective buoyancy, defined as the sum of the conventional buoyancy and the static vertical perturbation pressure gradient force induced by it, are shown for buoyant regions of finite width. For a judicious choice of reference density, the effective buoyancy per unit mass is essentially a unique force, independent of the reference density, but its distribution depends on the horizontal scale of the buoyant region. A corresponding concept of “effective CAPE” is introduced and its relevance to deep convection in tropical cyclones is discussed. The study is conceived as a first step to understanding the decreasing ability of inner‐core deep convection in tropical cyclones to ventilate the mass of air converging in the frictional boundary layer as the vortex matures and decays.

Description: The buoyancy force of an infinitesimally small air parcel is non‐unique, depending on the arbitrary definition of a reference density field. When calculating the “convective available potential energy” (CAPE), the buoyancy of a lifted air parcel is related to the reference density field along a vertical column passing through that parcel. We generalize buoyancy and CAPE for buoyant regions of finite size that perturb the pressure field in their immediate environment and discuss the relevance to deep convection in tropical cyclones.

Description: The Madden–Julian oscillation (MJO) is the dominant component of tropical intraseasonal variability, with wide‐reaching impacts even on extratropical weather and climate patterns. However, predicting the MJO is challenging. One reason is the suboptimal state estimates obtained with standard data assimilation (DA) approaches. These are typically based on filtering methods with Gaussian approximations and do not take into account physical properties that are important specifically for the MJO. In this article, a constrained ensemble DA method is applied to study the impact of different physical constraints on the state estimation and prediction of the MJO. The quadratic programming ensemble (QPEns) algorithm utilized extends the standard stochastic ensemble Kalman filter (EnKF) with specifiable constraints on the updates of all ensemble members. This allows us to recover physically more consistent states and to respect possible associated non‐Gaussian statistics. The study is based on identical twin experiments with an adopted nonlinear model for tropical intraseasonal variability. This so‐called skeleton model succeeds in reproducing the main large‐scale features of the MJO and closely related tropical waves, while keeping adequate simplicity for fast experiments on intraseasonal time‐scales. Conservation laws and other crucial physical properties from the model are examined as constraints in the QPEns. Our results demonstrate an overall improvement in the filtering and forecast skill when the model's total energy is conserved in the initial conditions. The degree of benefit is found to be dependent on the observational setup and the strength of the model's nonlinear dynamics. It is also shown that, even in cases where the statistical error in some waves remains comparable with the stochastic EnKF during the DA stage, their prediction is improved remarkably when using the initial state resulting from the QPEns.

Description: Unsatisfactory predictions of the MJO are partly due to DA methods that do not respect non‐Gaussian PDFs and the physical properties of the tropical atmosphere. Therefore the QPEns, an algorithm extending a stochastic EnKF with state constraints, is tested here on a simplified model for the MJO and associated tropical waves. Our series of identical twin experiments shows, in particular, that a constraint on the truth's nonlinear total energy improves forecasts statistically and can, in certain situations, even prevent filter divergence. image

Description: Deutsche Forschungsgemeinschaft : Heisenberg Award (DFG JA1077/4‐1); Transregional Collaborative Research Center SFB / TRR 165 “Waves to Weather” http://dx.doi.org/10.13039/501100001659

Description: Office of Naval Research (ONR) http://dx.doi.org/10.13039/100000006

Description: Sewage disposal onto agricultural land may result in the high accumulation of organic wastes, which questions the applicability of typical elemental analysis used for the soil components. To monitor the contamination status of agricultural soils at a former sedimentation basin, after the long‐term cessation of wastewater irrigation, 110 locations (15–20 cm depth) and 4 boreholes (up to 100 cm depth) were sampled to determine pH, loss on ignition, and concentration of Ni, Cu, Pb, Zn, and Cr. Additionally, the applicability of portable X‐ray fluorescence (pXRF) for the soil samples highly influenced by the organic wastes was evaluated. The study revealed the presence of a relatively homogenous sewage waste layer (depth of 20 cm), characterized by slightly acidic to neutral pH (6.3–7.5), high organic matter (OM) accumulation (up to 49%), and elevated concentration (mg kg −1) ranges between: Pb (5–321), Cu (31–2828), Ni (10–193), Cr (14–966), and Zn (76–6639). The pXRF analysis revealed metal concentration increase in mineral samples (up to 50%). The regression models and correction factors demonstrated high correlation and significance of pXRF measurement with response to increasing OM content, with the lowest r 2 = 0.86 obtained for Ni. Correlation of pXRF and AES measurement illustrated element‐dependent response for soils high in organics. Zn, Cu, and Cr pXRF analysis led to a slight underestimation in lower values, but overall good correlations (0.87; 0.89; and 0.88 respectively). Pb and Ni pXRF measurement revealed higher deviation from the reference in both lower and higher concentrations (0.74 and 0.70, respectively).

Description: German Federation of Industrial Research Associations http://dx.doi.org/10.13039/501100002723

Description: Federal Ministry for Economic Affairs and Energy http://dx.doi.org/10.13039/501100006360

Description: 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.

Description: 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.