TY - GEN A1 - Kumar, Rohini A1 - Hesse, Fabienne A1 - Rao, P. Srinivasa A1 - Musolff, Andreas A1 - Jawitz, James A1 - Sarrazin, Francois A1 - Samaniego, Luis A1 - Fleckenstein, Jan H. A1 - Rakovec, Oldrich A1 - Thober, S. A1 - Attinger, Sabine T1 - Strong hydroclimatic controls on vulnerability to subsurface nitrate contamination across Europe T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Subsurface contamination due to excessive nutrient surpluses is a persistent and widespread problem in agricultural areas across Europe. The vulnerability of a particular location to pollution from reactive solutes, such as nitrate, is determined by the interplay between hydrologic transport and biogeochemical transformations. Current studies on the controls of subsurface vulnerability do not consider the transient behaviour of transport dynamics in the root zone. Here, using state-of-the-art hydrologic simulations driven by observed hydroclimatic forcing, we demonstrate the strong spatiotemporal heterogeneity of hydrologic transport dynamics and reveal that these dynamics are primarily controlled by the hydroclimatic gradient of the aridity index across Europe. Contrasting the space-time dynamics of transport times with reactive timescales of denitrification in soil indicate that similar to 75% of the cultivated areas across Europe are potentially vulnerable to nitrate leaching for at least onethird of the year. We find that neglecting the transient nature of transport and reaction timescale results in a great underestimation of the extent of vulnerable regions by almost 50%. Therefore, future vulnerability and risk assessment studies must account for the transient behaviour of transport and biogeochemical transformation processes. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1352 KW - travel time distributions KW - groundwater vulnerability KW - flux tracking KW - transit-time KW - water age KW - nitrogen KW - model KW - dynamics KW - pollution KW - patterns Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-549875 SN - 1866-8372 IS - 1 ER - TY - JOUR A1 - Kumar, Rohini A1 - Hesse, Fabienne A1 - Rao, P. Srinivasa A1 - Musolff, Andreas A1 - Jawitz, James A1 - Sarrazin, Francois A1 - Samaniego, Luis A1 - Fleckenstein, Jan H. A1 - Rakovec, Oldrich A1 - Thober, S. A1 - Attinger, Sabine T1 - Strong hydroclimatic controls on vulnerability to subsurface nitrate contamination across Europe JF - Nature Communications N2 - Subsurface contamination due to excessive nutrient surpluses is a persistent and widespread problem in agricultural areas across Europe. The vulnerability of a particular location to pollution from reactive solutes, such as nitrate, is determined by the interplay between hydrologic transport and biogeochemical transformations. Current studies on the controls of subsurface vulnerability do not consider the transient behaviour of transport dynamics in the root zone. Here, using state-of-the-art hydrologic simulations driven by observed hydroclimatic forcing, we demonstrate the strong spatiotemporal heterogeneity of hydrologic transport dynamics and reveal that these dynamics are primarily controlled by the hydroclimatic gradient of the aridity index across Europe. Contrasting the space-time dynamics of transport times with reactive timescales of denitrification in soil indicate that similar to 75% of the cultivated areas across Europe are potentially vulnerable to nitrate leaching for at least onethird of the year. We find that neglecting the transient nature of transport and reaction timescale results in a great underestimation of the extent of vulnerable regions by almost 50%. Therefore, future vulnerability and risk assessment studies must account for the transient behaviour of transport and biogeochemical transformation processes. KW - travel time distributions KW - groundwater vulnerability KW - flux tracking KW - transit-time KW - water age KW - nitrogen KW - model KW - dynamics KW - pollution KW - patterns Y1 - 2020 U6 - https://doi.org/10.1038/s41467-020-19955-8 SN - 2041-1723 VL - 11 IS - 1 SP - 1 EP - 10 PB - Nature Publishing Group UK CY - London ER - TY - GEN A1 - Jing, Miao A1 - Kumar, Rohini A1 - Heße, Falk A1 - Thober, Stephan A1 - Rakovec, Oldrich A1 - Samaniego, Luis A1 - Attinger, Sabine T1 - Assessing the response of groundwater quantity and travel time distribution to 1.5, 2, and 3 °C global warming in a mesoscale central German basin T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Groundwater is the biggest single source of high-quality freshwater worldwide, which is also continuously threatened by the changing climate. In this paper, we investigate the response of the regional groundwater system to climate change under three global warming levels (1.5, 2, and 3 ∘C) in a central German basin (Nägelstedt). This investigation is conducted by deploying an integrated modeling workflow that consists of a mesoscale hydrologic model (mHM) and a fully distributed groundwater model, OpenGeoSys (OGS). mHM is forced with climate simulations of five general circulation models under three representative concentration pathways. The diffuse recharges estimated by mHM are used as boundary forcings to the OGS groundwater model to compute changes in groundwater levels and travel time distributions. Simulation results indicate that groundwater recharges and levels are expected to increase slightly under future climate scenarios. Meanwhile, the mean travel time is expected to decrease compared to the historical average. However, the ensemble simulations do not all agree on the sign of relative change. Changes in mean travel time exhibit a larger variability than those in groundwater levels. The ensemble simulations do not show a systematic relationship between the projected change (in both groundwater levels and travel times) and the warming level, but they indicate an increased variability in projected changes with adjusting the enhanced warming level from 1.5 to 3 ∘C. Correspondingly, it is highly recommended to restrain the trend of global warming. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1402 KW - climate change impacts KW - hydrological models KW - coupled surface KW - water fluxes KW - catchment KW - recharge KW - dynamics KW - aquifer KW - flow KW - parameterization Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-509343 SN - 1866-8372 IS - 3 ER - TY - JOUR A1 - Jing, Miao A1 - Kumar, Rohini A1 - Heße, Falk A1 - Thober, Stephan A1 - Rakovec, Oldrich A1 - Samaniego, Luis A1 - Attinger, Sabine T1 - Assessing the response of groundwater quantity and travel time distribution to 1.5, 2, and 3 °C global warming in a mesoscale central German basin JF - Hydrology and Earth System Sciences N2 - Groundwater is the biggest single source of high-quality freshwater worldwide, which is also continuously threatened by the changing climate. In this paper, we investigate the response of the regional groundwater system to climate change under three global warming levels (1.5, 2, and 3 ∘C) in a central German basin (Nägelstedt). This investigation is conducted by deploying an integrated modeling workflow that consists of a mesoscale hydrologic model (mHM) and a fully distributed groundwater model, OpenGeoSys (OGS). mHM is forced with climate simulations of five general circulation models under three representative concentration pathways. The diffuse recharges estimated by mHM are used as boundary forcings to the OGS groundwater model to compute changes in groundwater levels and travel time distributions. Simulation results indicate that groundwater recharges and levels are expected to increase slightly under future climate scenarios. Meanwhile, the mean travel time is expected to decrease compared to the historical average. However, the ensemble simulations do not all agree on the sign of relative change. Changes in mean travel time exhibit a larger variability than those in groundwater levels. The ensemble simulations do not show a systematic relationship between the projected change (in both groundwater levels and travel times) and the warming level, but they indicate an increased variability in projected changes with adjusting the enhanced warming level from 1.5 to 3 ∘C. Correspondingly, it is highly recommended to restrain the trend of global warming. KW - climate change impacts KW - hydrological models KW - coupled surface KW - water fluxes KW - catchment KW - recharge KW - dynamics KW - aquifer KW - flow KW - parameterization Y1 - 2020 U6 - https://doi.org/10.5194/hess-24-1511-2020 SN - 1607-7938 SN - 1027-5606 VL - 24 IS - 3 SP - 1511 EP - 1526 PB - Copernicus Publ. CY - Göttingen ER - TY - JOUR A1 - Scherler, Dirk A1 - Schwanghart, Wolfgang T1 - Drainage divide networks BT - Part 2: Response to perturbations JF - Earth surface dynamics N2 - Drainage divides are organized into tree-like networks that may record information about drainage divide mobility. However, views diverge about how to best assess divide mobility. Here, we apply a new approach of automatically extracting and ordering drainage divide networks from digital elevation models to results from landscape evolution model experiments. We compared landscapes perturbed by strike-slip faulting and spatiotemporal variations in erodibility to a reference model to assess which topographic metrics (hillslope relief, flow distance, and chi) are diagnostic of divide mobility. Results show that divide segments that are a minimum distance of similar to 5 km from river confluences strive to attain constant values of hillslope relief and flow distance to the nearest stream. Disruptions of such patterns can be related to mobile divides that are lower than stable divides, closer to streams, and often asymmetric in shape. In general, we observe that drainage divides high up in the network, i.e., at great distances from river confluences, are more susceptible to disruptions than divides closer to these confluences and are thus more likely to record disturbance for a longer time period. We found that across-divide differences in hillslope relief proved more useful for assessing divide migration than other tested metrics. However, even stable drainage divide networks exhibit across-divide differences in any of the studied topographic metrics. Finally, we propose a new metric to quantify the connectivity of divide junctions. KW - dynamics KW - landscape evolution KW - low-relief KW - patterns KW - river KW - scale KW - tectonics Y1 - 2020 U6 - https://doi.org/10.5194/esurf-8-261-2020 SN - 2196-6311 SN - 2196-632X VL - 8 IS - 2 SP - 261 EP - 274 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Anders, Janet A1 - Sait, Connor R. J. A1 - Horsley, Simon A. R. T1 - Quantum Brownian motion for magnets JF - New journal of physics : the open-access journal for physics N2 - Spin precession in magnetic materials is commonly modelled with the classical phenomenological Landau-Lifshitz-Gilbert (LLG) equation. Based on a quantized three-dimensional spin + environment Hamiltonian, we here derive a spin operator equation of motion that describes precession and includes a general form of damping that consistently accounts for memory, coloured noise and quantum statistics. The LLG equation is recovered as its classical, Ohmic approximation. We further introduce resonant Lorentzian system-reservoir couplings that allow a systematic comparison of dynamics between Ohmic and non-Ohmic regimes. Finally, we simulate the full non-Markovian dynamics of a spin in the semi-classical limit. At low temperatures, our numerical results demonstrate a characteristic reduction and flattening of the steady state spin alignment with an external field, caused by the quantum statistics of the environment. The results provide a powerful framework to explore general three-dimensional dissipation in quantum thermodynamics. KW - open quantum systems KW - coloured and quantum noise KW - memory effects KW - spin KW - dynamics KW - LLG equation KW - magnetisation KW - quantum thermodynamics Y1 - 2022 U6 - https://doi.org/10.1088/1367-2630/ac4ef2 SN - 1367-2630 VL - 24 IS - 3 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Jay, Raphael M. A1 - Vaz da Cruz, Vinicius A1 - Eckert, Sebastian A1 - Fondell, Mattis A1 - Mitzner, Rolf A1 - Föhlisch, Alexander T1 - Probing solute-solvent interactions of transition metal complexes using L-edge absorption spectroscopy JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - In order to tailor solution-phase chemical reactions involving transition metal complexes, it is critical to understand how their valence electronic charge distributions are affected by the solution environment. Here, solute-solvent interactions of a solvatochromic mixed-ligand iron complex were investigated using X-ray absorption spectroscopy at the transition metal L-2,L-3-edge. Due to the selectivity of the corresponding core excitations to the iron 3d orbitals, the method grants direct access to the valence electronic structure around the iron center and its response to interactions with the solvent environment. A linear increase of the total L-2,L-3-edge absorption cross section as a function of the solvent Lewis acidity is revealed. The effect is caused by relative changes in different metal-ligand-bonding channels, which preserve local charge densities while increasing the density of unoccupied states around the iron center. These conclusions are corroborated by a combination of molecular dynamics and spectrum simulations based on time-dependent density functional theory. The simulations reproduce the spectral trends observed in the X-ray but also optical absorption experiments. Our results underscore the importance of solute-solvent interactions when aiming for an accurate description of the valence electronic structure of solvated transition metal complexes and demonstrate how L-2,L-3-edge absorption spectroscopy can aid in understanding the impact of the solution environment on intramolecular covalency and the electronic charge distribution. KW - basis-sets KW - charge-transfer KW - density KW - dynamics KW - electron localization KW - iron KW - solvation KW - spin-crossover KW - tranfer excited-state KW - x-ray-absorption Y1 - 2020 U6 - https://doi.org/10.1021/acs.jpcb.0c00638 SN - 1520-6106 SN - 1520-5207 VL - 124 IS - 27 SP - 5636 EP - 5645 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Marschall, Raphael A1 - Skorov, Yuri A1 - Zakharov, Vladimir A1 - Rezac, Ladislav A1 - Gerig, Selina-Barbara A1 - Christou, Chariton A1 - Dadzie, S. Kokou A1 - Migliorini, Alessandra A1 - Rinaldi, Giovanna A1 - Agarwal, Jessica A1 - Vincent, Jean-Baptiste A1 - Kappel, David T1 - Cometary comae-surface links the physics of gas and dust from the surface to a spacecraft JF - Space science reviews N2 - A comet is a highly dynamic object, undergoing a permanent state of change. These changes have to be carefully classified and considered according to their intrinsic temporal and spatial scales. The Rosetta mission has, through its contiguous in-situ and remote sensing coverage of comet 67P/Churyumov-Gerasimenko (hereafter 67P) over the time span of August 2014 to September 2016, monitored the emergence, culmination, and winding down of the gas and dust comae. This provided an unprecedented data set and has spurred a large effort to connect in-situ and remote sensing measurements to the surface. In this review, we address our current understanding of cometary activity and the challenges involved when linking comae data to the surface. We give the current state of research by describing what we know about the physical processes involved from the surface to a few tens of kilometres above it with respect to the gas and dust emission from cometary nuclei. Further, we describe how complex multidimensional cometary gas and dust models have developed from the Halley encounter of 1986 to today. This includes the study of inhomogeneous outgassing and determination of the gas and dust production rates. Additionally, the different approaches used and results obtained to link coma data to the surface will be discussed. We discuss forward and inversion models and we describe the limitations of the respective approaches. The current literature suggests that there does not seem to be a single uniform process behind cometary activity. Rather, activity seems to be the consequence of a variety of erosion processes, including the sublimation of both water ice and more volatile material, but possibly also more exotic processes such as fracture and cliff erosion under thermal and mechanical stress, sub-surface heat storage, and a complex interplay of these processes. Seasons and the nucleus shape are key factors for the distribution and temporal evolution of activity and imply that the heliocentric evolution of activity can be highly individual for every comet, and generalisations can be misleading. KW - comets KW - coma KW - gas KW - dust KW - dynamics KW - modelling KW - inversion Y1 - 2020 U6 - https://doi.org/10.1007/s11214-020-00744-0 SN - 0038-6308 SN - 1572-9672 VL - 216 IS - 8 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - van Velzen, Ellen T1 - Predator coexistence through emergent fitness equalization JF - Ecology : a publication of the Ecological Society of America N2 - The competitive exclusion principle is one of the oldest ideas in ecology and states that without additional self-limitation two predators cannot coexist on a single prey. The search for mechanisms allowing coexistence despite this has identified niche differentiation between predators as crucial: without this, coexistence requires the predators to have exactly the same R* values, which is considered impossible. However, this reasoning misses a critical point: predators' R* values are not static properties, but affected by defensive traits of their prey, which in turn can adapt in response to changes in predator densities. Here I show that this feedback between defense and predator dynamics enables stable predator coexistence without ecological niche differentiation. Instead, the mechanism driving coexistence is that prey adaptation causes defense to converge to the value where both predators have equal R* values ("fitness equalization"). This result is highly general, independent of specific model details, and applies to both rapid defense evolution and inducible defenses. It demonstrates the importance of considering long-standing ecological questions from an eco-evolutionary viewpoint, and showcases how the effects of adaptation can cascade through communities, driving diversity on higher trophic levels. These insights offer an important new perspective on coexistence theory. KW - coexistence KW - competition KW - competitive exclusion KW - defense KW - eco-evolutionary feedbacks KW - emergent facilitation KW - predator KW - prey KW - dynamics Y1 - 2020 U6 - https://doi.org/10.1002/ecy.2995 SN - 0012-9658 SN - 1939-9170 VL - 101 IS - 5 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Omelʹchenko, Oleh E. T1 - Nonstationary coherence-incoherence patterns in nonlocally coupled heterogeneous phase oscillators JF - Chaos : an interdisciplinary journal of nonlinear science N2 - We consider a large ring of nonlocally coupled phase oscillators and show that apart from stationary chimera states, this system also supports nonstationary coherence-incoherence patterns (CIPs). For identical oscillators, these CIPs behave as breathing chimera states and are found in a relatively small parameter region only. It turns out that the stability region of these states enlarges dramatically if a certain amount of spatially uniform heterogeneity (e.g., Lorentzian distribution of natural frequencies) is introduced in the system. In this case, nonstationary CIPs can be studied as stable quasiperiodic solutions of a corresponding mean-field equation, formally describing the infinite system limit. Carrying out direct numerical simulations of the mean-field equation, we find different types of nonstationary CIPs with pulsing and/or alternating chimera-like behavior. Moreover, we reveal a complex bifurcation scenario underlying the transformation of these CIPs into each other. These theoretical predictions are confirmed by numerical simulations of the original coupled oscillator system. KW - chimera states KW - synchronization KW - networks KW - Kuramoto KW - populations KW - dynamics KW - bumps KW - model Y1 - 2020 U6 - https://doi.org/10.1063/1.5145259 SN - 1054-1500 SN - 1089-7682 VL - 30 IS - 4 PB - American Institute of Physics CY - Melville ER -