julilili42/papers huggingface dataset:
Nano-antennas with decoupled transparent leads for optoelectronic studies
2024-03-08

Abstract Performing electrical measurements on single plasmonic nanostructures presents a challenging task due to the limitations in contacting the structure without disturbing its optical properties. In this work, we show two ways to overcome this problem by fabricating bow-tie nano-antennas with indium tin oxide leads. Indium tin oxide is transparent in the visible range and electrically conducting, but non-conducting at optical frequencies. The structures are prepared by electron beam lithography. Further definition, such as introducing small gaps, is achieved by focused helium ion beam milling. Dark-field reflection spectroscopy characterization of the dimer antennas shows typical unperturbed plasmonic spectra with multiple resonance peaks from mode hybridization.
On the value of slug tracer injections and the naturally occurring radon for observing hyporheic exchange
2024-03-08

The exchange of stream water and groundwater (hyporheic exchange) plays an important role in hydrological and biogeochemical processes in rivers. Hyporheic flow comprises a distribution of subsurface flow paths characterized by distinct transit times and flow path lengths. Much of the previous research relied on the interpretation of slug tracer experiments that only capture a portion of the overall hyporheic exchange, given their relatively short (minutes to hours) duration. Therefore, there is a need to go beyond the characterization of shorter flow paths in hyporheic research to understand flow paths of the entire transit time distribution. We hypothesize that environmental tracers provide complementary information into longer hyporheic flow paths. Here we derive and compare commonly used transport metrics for hyporheic exchange derived from radon and slug tracer injections and aim to identify combinations of model parameters that predict the concentrations of both tracers along experimental stream reaches. For this purpose, we measured the environmental tracer radon (222Rn), that increases with time along hyporheic flow paths, at several stream sections along Oak Creek, Oregon (USA). We conducted slug tracer (sodium chloride) injections at the same stream sections. We employed a transient storage model that includes radon specific processes such as radioactive decay to ensure comparability in the information acquired on hyporheic exchange from radon and the typically applied slug tracer experiments. We calibrated final stream discharge and hyporheic exchange metrics through a global identifiability analysis and subsequently calculated relevant transport metrics using the refined parameters. Results with the field data will be obtained soon. Hence, this study will contribute to a more holistic understanding of hyporheic flow paths and related processes, such as the biogeochemical turnover processes in rivers.
Trace organic compounds in wastewater-loaded lowland River Erpe &#8211; Key findings from 12 years of research
2024-03-08

Increasing concentrations of trace organic compounds (TrOCs) in water bodies worldwide are of great concern. In addition to a general load reduction and a better understanding of the ecotoxicological effects of TrOC cocktails, it is important to better understand the pathways and fate of this large group of compounds in the environment. The lowland River Erpe (Berlin/Brandenburg, Germany), which receives treated wastewater from an urban wastewater treatment plant, is an excellent site for such research, as TrOC concentrations are exceptionally high compared to other German rivers, allowing reliable process studies without much analytical effort such as prior enrichment steps of water samples. In addition, the river system offers a variety of reaches that differ in hydrology and streambed morphology, allowing for different types of investigations. Over the past 12 years, more than 100 researchers have been involved in several large and numerous smaller studies on the River Erpe. Topics have included the role of hyporheic zones in the self-purification capacity of streams with respect to TrOCs, seasonal changes, interactions between easily degradable organic matter and TrOC attenuation, the importance of identifying flow paths for understanding biogeochemical processes, the effects of management actions such as macrophyte removal on the fate of TrOCs, the effects of losing conditions on TrOC input to aquifers and bank filtration systems, the effects of discharge of treated effluent from a large new industrial site on river water composition, and the identification of microbial key players associated with TrOC removal, and much more. Ongoing research includes topics such as bioremediation, the effects of migrating bedforms on the fate of TrOCs, and the effects of droughts on water quality at bathing sites in the receiving River Spree. Research highlights and future directions are presented.
Leptochelins A-C, Cytotoxic Metallophores Produced by Geographically Dispersed Leptothoe Strains of Marine Cyanobacteria
2024-03-08

Metals are important co-factors in the metabolic processes of cyanobacteria including photosynthesis, cellular respiration, DNA replication, and the biosynthesis of primary and secondary metabolites. In adaptation to the marine environment, cyanobacteria use metallophores to acquire trace metals when necessary as well as reduce potential toxicity from excessive metal concentrations. Leptochelins A-C were identified as structurally novel metallophores from three geographically dispersed cyanobacteria of the genus Leptothoe. The leptochelins are halogenated linear NRPS-PKS hybrid products with multiple heterocycles that have potential for hexadentate and tetradentate coordination with metal ions. The genomes of the three leptochelin producers were sequenced, and retrobiosynthetic analysis revealed one candidate biosynthetic gene cluster (BGC) consistent with the structure of leptochelin. The putative BGC is highly homologous in all three Leptothoe strains, and all possess genetic signatures associated with metallophores. Post-column infusion of metals using an LC-MS metabolomics workflow performed with leptochelin A and B revealed promiscuous binding of iron, copper, cobalt, and zinc, but with greatest preference for copper. Iron depletion and copper toxicity experiments support the hypothesis that leptochelin metallophores may play a key ecological role in iron acquisition and in copper detoxification. In addition, the leptochelins possess significant cytotoxicity against several cancer cell lines.
High resolution subglacial topography from airborne swath radar beneath the Northeast Greenland Ice Stream (NEGIS)
2024-03-08

Here we present an extensive swath radar dataset collected in the onset region of the Northeast Greenland Ice Stream, surrounding the East Greenland Ice Core Project site (EGRIP). We produce a new digital elevation model (DEM) of the subglacial topography at a resolution of 25 m, covering a study area of 40 km by 60 km. The data was collected using the AWI airborne ultra-wideband radar system, in profiles mainly perpendicular to the ice flow direction with a spacing of 2 km so that the swaths overlapped.The high-resolution subglacial topography DEM shows subglacial landforms beneath an active ice stream, located approximately 600 km into the interior of the ice sheet. These landforms indicate spatially variable bed conditions which are partly reflected in the surface velocity field. Some features appear to be crag and tail formations up to 4 km in length, with steep stoss-side slopes and tapering lee-side tails which are oriented in the direction of ice flow. Megascale glacial lineations up to 7 km in length are evident, but appear restricted to the inner ice stream within the modern shear margins, where the ice flow velocity increases from approximately 11 m/a to 58 m/a. Meltwater channels curve around a high point in the topography, which are on the scale of tunnel valleys formed from subglacial meltwater incision. Seismic data located in a channel at the eastern shear margin indicates soft sedimentation inflow. In summary, differences in landform morphology can be seen within and outside of the ice stream shear margins, indicating that NEGIS ice flow may have been transitory in this region.This survey provides a new insight into the active subglacial environment of a Greenlandic ice stream, matching in quality surveys from ice-free land surface or marine areas. Further analysis will contribute to the understanding of how glacially sculpted landscapes are formed, as well as the effects of small-scale topography on the dynamics and the surface of the overlying ice sheet, in particular ice streams. Moreover, the dataset emphasises the usage of swath radar mapping of bedforms and thus a more widespread application of this method in all radar surveys.
Spatial and temporal changes in surface mass balance derived from airborne radio sounding for the plateau area in Dronning Maud Land
2024-03-08

Contrary to the rest of the Antarctic ice sheet, East Antarctica currently gains mass due to an increase in snow accumulation over the last decades. How or if this increase is linked to anthropogenic warming is not yet clear and requires better understanding of the surface mass balance history over the last centuries, and also the dependency of snow accumulation with the local surface slopes across different spatial scales.Here, we present a novel airborne dataset using the multichannel ultra-wideband radar system from the Alfred Wegener Institute in Germany with a decadal vertical resolution for the plateau area in Dronning Maud Land. We assess the spatial and temporal variability of surface mass balance and snow accumulation for the past centuries for an area of ~200,000 km2. With this contribution, we aim to (1) show the potential to use ultra-wideband radar systems to reconstruct the recent surface mass balance and accumulation rates in low-accumulation regions, (2) present information on large spatial scales, and (3) discuss potential overlap of interests and/or data in this and/or other areas on the plateau of East Antarctica.
A stochastic model of catchment baseflow dynamics
2024-03-08

Groundwater discharge profoundly influences river flow, especially during dry spells, potentially exacerbating drought conditions, an issue compounded by escalating climate change-induced hydrological extremes. Amidst this, understanding aquifer systems' efficacy in mitigating (sub-)seasonal fluctuations and their ecological impacts gains significance even in moderate climates.This work introduces a stochastic modeling approach for groundwater-fed baseflow, as an alternative to the traditional hydraulic theory by accounting for spatial heterogeneity of subsurface storage properties and associated uncertainties. Leveraging on readily available rainfall-generated recharge and river discharge series, stochastic tools determine baseflow characteristics. The model&amp;#8217;s foundation lies on representing groundwater recharge and subsurface storage as stochastic variables.With the subsurface storage represented as multiple linear reservoirs with stochastic storage parameters, the proposed model reveals the baseflow dynamics and the interplay between heterogeneous reservoir timescales and recharge variability, elucidating temporal variance of baseflow at the catchment scale. Furthermore, the study investigates equivalent parameters for an upscaled unique reservoir to model catchment behavior. Utilizing established stochastic analysis tools in subsurface hydrology, this research advances our understanding of heterogeneous hydrological catchments. In addition, the investigation analyzes the temporal statistical moments of baseline discharge dependent on input recharge and sub-catchments' response times. This detailed analysis unveils the system's attenuation effect as a metric for catchment resilience during prolonged droughts, significantly influenced by underlying hydrogeological properties. As a practical consequence, quantifying the dependency of the attenuation factor on both temporal and hydrogeological variability can help in identifying particularly sensitive watersheds, crucial for tailored adaptation strategies.
Microbial iron(III) reduction of iron-organic carbon phases across a permafrost thaw gradient and its impact on methane emissions
2024-03-08

Wetlands account for roughly 20-30% of global methane (CH4) emissions, in part due to (permanently) anoxic conditions that promote methanogenesis. Low-lying permafrost peatlands are expected to be an increasing source of CH4 due to permafrost thaw in the future, due to waterlogging, anoxia and organic carbon (OC) mobilization. These processes can force an increase of the extent of wetlands and higher total CH4 emissions. Net release of CH4 depends on the availability of more energetically favorable electron acceptors in soil, such as ferric iron (Fe(III)). Fe(III) may be present as Fe(III) oxyhydroxides or Fe(III)-OC phases in peatlands. Since Fe(III)-reducing microbes and methanogens compete for the same substrates (e.g., small organic molecules such as acetate), CH4 production is often suppressed as long as there is bioavailable Fe(III) present. However, the dissolution of Fe(III)-OC phases during Fe(III) reduction would release the previously bound OC and make it more bioavailable to fermenting microorganisms. This would produce more substrates for methanogens and could therefore increase CH4 production. It is currently unknown to what extent microbial reduction of Fe(III)-OC phases and the coupled OC release effects CH4 emissions across permafrost thaw.In this study, we therefore aim to elucidate the extent of reduction of Fe(III)-OC phases upon permafrost thaw and the corresponding effect on CH4 emissions across three distinct thaw stages: (i) recently collapsed palsa hills, (ii) partly thawed bog and (iii) fully thawed fen habitats. We simulated permafrost thaw by a series of incubation experiments with soils from each thaw stage from a permafrost peatland (Stordalen Mire, Abisko, Sweden). Soils were incubated under anoxic, flooded conditions for 30 days, after which synthesized 57Fe-labelled Fe(III)-OC coprecipitates were added as representative Fe-OC phases. Over the course of the incubations (42 days), we followed Fe speciation and 57Fe fractions in the dissolved and solid phases using geochemical and synchrotron-based spectroscopy techniques in addition to quantification of greenhouse gas production. Results show that added coprecipitates were completely reduced (within 1 day) in palsa and bog soils, leading to increases in dissolved Fe2+, OC concentrations and CO2 emissions. CH4 production was not detected in palsa soils over the course of the incubation and CH4 suppression in bog soils due to Fe(III) reduction was only short-term. In contrast, added coprecipitates in fen soils were only reduced by 10% after 42 days, likely due to low dissolved OC concentrations. However, this led to a significantly higher inhibition of methanogenesis than in the palsa and bog soils. We also studied the microbial community by 16S rRNA amplicon (gene) sequencing and quantified mcrA gene copy numbers to assess the potential activity of methanogens. Overall, these results help to understand the influence of Fe-OC coprecipitates on methane emissions in thawing permafrost peatlands.
Synergistic relationships between the age of soil organic matter, Fe speciation, and aggregate stability
2024-03-08

Understanding the formation and stability of soil aggregates is crucial for sustaining soil functions. This study investigates the impact of organic matter (OM), pedogenic Fe (oxyhydr)oxides, and aggregate size on aggregate stability in an arable soil. Samples were collected from the Ap and Bt horizons of a Luvisol after 14 years of bare fallow, and results were compared with a control field under permanent cropping. In the Ap horizon, bare fallow led to a 26% reduction in the median diameter of the 53-250 &amp;#181;m size fraction, indicating decreased stability of larger microaggregates. Simultaneously, the mass of the 20-53 &amp;#181;m size fraction increased by 65%, suggesting reduced stability, particularly of larger soil microaggregates, due to the absence of fresh OM input. The 14carbon (14C) fraction of modern C (F14C) under bare fallow ranged from 0.50 to 0.90, lower than the cropped site (F14C between 0.75 and 1.01). This difference was most pronounced in the smallest size fraction, indicating the presence of older C. Higher stability and reduced C turnover in
Preconditioned biosphere flux extremes in terrestrial carbon cycle models and reanalyses in the recent past, present, and future
2024-03-08

The increasing frequency and severity of climate extremes pose a multifaceted threat to health, economic stability, and both natural and human-made environments. Potential overlap and accumulation of extremes as compound extremes poses further challenges. Ongoing climate change intensifies these challenges, underscoring the importance of a better understanding of the causes and drivers for compound events. Earth system model projections suggest that more frequent climatic compound extremes affect terrestrial biosphere fluxes, potentially reducing the land&amp;#8217;s CO2 storage potential. However, whether models are able to represent such interactions like the priming of the biosphere towards extremes accurately remains to be shown.Here, we focus on the role of concurrent precipitation and temperature as drivers of biosphere flux extremes and investigate their change in frequency and intensity based on their occurrence in historical simulations, reanalyses, and future projections. We use thresholds to define concurrent extremes and Monte Carlo randomization to constrain uncertainties. Further, we examine the association of climatic compound events with anomalies in biosphere carbon fluxes to ascertain their mutual relation, aiming to establish how these climatic compound events contribute to preconditioning extremes in the biosphere. Given this assessment of the occurrence change of climatic compound events and their connection to extremes in biosphere carbon fluxes, we infer how climatic compound events may precondition the biosphere for extremes. Lagged overlaps show significant seasonality and spatial heterogeneity in preconditioning. Comparing reanalyses and historical simulations in a model of the terrestrial carbon cycle and a comprehensive Earth System Model, we examine how well primed biosphere extremes agree in different data sources. Leveraging these findings, we evaluate if model projections show signs of stronger climatic priming of the biosphere in the next century.
Geotectonic Influences on the Lake Elementeita Ecosystem (Central Kenya Rift): Insights from Field and Space-Based Observations
2024-03-08

In the backdrop of the global freshwater crisis exacerbated by human activities and climate change, our study addresses the need to understand the forces shaping lacustrine ecosystems in Eastern Africa, particularly within the East African Rift System (EARS). The Lake Elmenteita basin in the Central Kenya Rift represents the intricate interplay between intense geotectonic forces and escalating human activities. This study aims to unravel the complex interactions shaping this critical ecosystem, with a particular emphasis on the geotectonic aspects that underpin the lake's environmental dynamics. Lake Elmenteita is ecologically vital, supporting a diverse habitat including numerous bird species and serving as a primary food source for up to half a million flamingos.Our research employs a multidisciplinary approach, integrating tectonic geomorphology, geological remote sensing, geochemistry, soil science, and micropaleontology. This approach is designed to differentiate the lake's natural geological influences from anthropogenic impacts.Field investigations have demonstrated that tectonic activity controls mobilization of soils and sediments, primarily through processes of uplift and exhumation. Additionally, fault zones are correlated with hydrothermal activity influencing element mobilization and distribution. This is particularly evident through fault-controlled thermal springs along the lake shore and within its catchment, notably in areas like the Kinangop Plateau. Here, intensive agriculture amidst complex faulting has heightened vulnerability to soil erosion. The geological diversity, marked by erodable trachytic tuffs and more resistant basaltic sources, dictates distinct erosion patterns, further compounded by deforestation. This deforestation is visible in Landsat time series data from 1984 to 2023, and particularly severe in the basaltic regions of the Aberdare Range, and trachytic regions of the Kingangop plateau indicating a correlation with increased agricultural activity.Remote sensing analysis, using multispectral (Aster, Landsat, Sentinel) and topographic&amp;#160; (TanDEM-X, Copernicus DEM) data, has been instrumental in mapping the lake's geological diversity and intricate fault network. The analysis highlights active fault zones, such as those along the NW sector of the Sattima fault and the Gilgil segment of the Kijabe fault. These faults are crucial in shaping the drainage patterns of the Kinangop plateau and influencing the hydrology of the lake.The preliminary findings of this study place a spotlight on the dominant role of geotectonic processes in the environmental makeup of Lake Elmenteita, while also acknowledging the significant, albeit secondary, impact of human activities. By closely examining these combined forces, the research aims to contribute substantially to the understanding and management of this sensitive ecosystem. This insight is vital not only for Lake Elmenteita but also for other lacustrine systems within rift environments.
Sediment-laden basal ice units near the onset of a fast-flowing glacier in East Antarctica
2024-03-08

Understanding the material properties and physical conditions of basal ice is crucial for a comprehensive understanding of Antarctic ice-sheet dynamics. Yet, direct data are sparse and difficult to acquire, necessitating geophysical data for analysis. We employed high-resolution ultra-wideband radar to map high-backscatter zones near the glacier bed within East Antarctica's Jutulstraumen drainage basin. In addition, we used radar forward modelling to constrain their material composition. Our results reveal along-flow oriented sediment-laden basal ice units connected to the basal substrate, extending to several hundred meters thick. Three-dimensional thermomechanical modelling suggests these units initially form via basal freeze-on of subglacial water originating upstream. We suggest that basal freeze-on and the entrainment and transport of subglacial material play a significant role in an accurate representation of the material, physical, and rheological properties of the Antarctic ice sheet's basal ice, ultimately enhancing the accuracy and reliability of ice-sheet modelling.