bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal ecosystem vulnerability to climatic anomalies in the Mediterranean
Authors: Vogel Johannes
Published: March 2021

The ecosystems of the Mediterranean Basin are particularly prone to climate change and related alterations in climatic anomalies. The seasonal timing of climatic anomalies is crucial for the assessment of the corresponding ecosystem impacts; however, the incorporation of seasonality is neglected in many studies. We quantify ecosystem vulnerability by investigating deviations of the climatic drivers temperature and soil moisture during phases of low ecosystem productivity for each month of the year over the period 1999 – 2019. The fraction of absorbed photosynthetically active radiation (FAPAR) is used as a proxy for ecosystem productivity. Air temperature is obtained from the reanalysis data set ERA5 Land and soil moisture and FAPAR satellite products are retrieved from ESA CCI and Copernicus Global Land Service, respectively. Our results show that Mediterranean ecosystems are vulnerable to three soil moisture regimes during the course of the year. A phase of vulnerability to hot and dry conditions during late spring to midsummer is followed by a period of vulnerability to cold and dry conditions in autumn. The third phase is characterized by cold and wet conditions coinciding with low ecosystem productivity in winter and early spring. These phases illustrate well the shift between a soil moisture-limited regime in summer and an energy-limited regime in winter in the Mediterranean Basin. Notably, the vulnerability to hot and dry conditions during the course of the year is prolonged by several months in the Eastern Mediterranean compared to the Western Mediterranean. Our approach facilitates a better understanding of ecosystem vulnerability at certain stages during the year and is easily transferable to other study areas and ecoclimatological variables.
Impact of different tree species and soil texture on physicochemical properties, carbon and macronutrient content of post-fire forest soils
Authors: Woś Bartłomiej , Józefowska Agnieszka , Likus-Cieślik Justyna , Chodak Marcin , Pietrzykowski Marcin
Published: March 2021

The objective of this study was to compare the impact of Scots pine (Pinus sylvestris L.), European larch (Larix decidua Mill.) and common birch (Betula pendula Roth) on the properties of regenerated soils in a reforested post-fire site in southern Poland (Central European conditions). The samples of O horizons (litter) and uppermost mineral soil (0-5 cm) were taken under pure stands of investigated tree species, aged from 26 to 27 years old and growing on sandy and loamy soils. In the litter samples, the pH, carbon and macronutrient (N, Ca, Mg and K) content were determined. The mineral soil samples were measured for texture, pH, soil organic carbon (SOC), total nitrogen (Nt), exchangeable acidity (Hh), basic exchangeable cations (Ca2+, K+, Mg2+, Na+) and cation exchangeable capacity (CEC). The obtained results indicated that the effect of tree species on soil properties was evident. The litter layers under birch had a higher pH and a lower C:N ratio, and they contained more N, P, Ca, and Mg than the litter layers under pine and larch. In the mineral soil, birch brought about a higher accumulation of SOC and CEC than the studied coniferous species. Higher SOC accumulation in mineral soil under birch was related to higher acidity under the species compared with the conifers. Soil texture in the studied range - from sands to loams - had only a limited effect on the properties of the studied post-fire soils. Thus, our results indicate that the tree species used for the reforestation of post-fire sites are crucial to the properties of regenerating soils and restoring the ecological functions of soils. Among the studied tree species, the common birch has the most pronounced effect on soil properties, and this is especially significant because the species has appeared by spontaneous succession.

The study was financed by The National Science Centre, Poland, Grant No. 2018/31/D/ST10/02137.
Palaeoglaciation in the low latitude, low elevation tropical Andes, northern Peru
Authors: Lee Ethan , Ross Neil , Henderson Andrew , Russell Andrew , Jamieson Stewart , Fabel Derek
Published: March 2021

Palaeo-glaciological studies of former ice thickness and extent within the tropical Andes have tended to focus on locations where glaciers are currently present, or in high elevation locations where evidence exists of recently deglaciated cirques. Few studies have focussed on low elevation regions due to the presumption that glaciers could not have existed at such low altitudes within the tropics. A latitudinal ‘data gap’ exists between Ecuador and more central and southern Peru where evidence for former glaciation is abundant. To fill this gap we present rare evidence of past glaciation from the Las Huaringas region, northern Peru, located in a relatively low elevation massif (<3900 m).

Within Las Huaringas a large valley glacier existed, extending N-S ~12 km down valley to ~2900 m in elevation while glacial cirques existed exhibiting an E-W orientation on the western facing hillslope of the massif with pronounced moraine complexes and bedrock erosion. We used high-resolution remotely sensed imagery, a 30 m ALOS DEM, and preliminary field observations to identify and map an abundance of geomorphic evidence of glaciation. These include moraines at different stages of preservation and predominance, eroded bedrock surfaces, cirque landforms and overdeepened valleys to develop the first glacial geomorphological map of the region. We performed morphometric analysis (e.g. width, length, altitude, azimuth) of the mapped glacial landforms and cirques along with hypsometric analysis of the main valley of Laguna Shimbe, yielding a hypsometric maxima of 3250 m. Using the geomorphological map, we determine the former extent and thickness of palaeoglaciers in the area and use delineated glacial outlines of their furthest extent to reconstruct Equilibrium Line Altitudes (ELAs) of these ice masses using a combination of ELA estimation techniques.

Ongoing research aims to determine whether the palaeoglacial evidence is consistent with formation by valley glaciers or an icecap and whether the timing of the local Last Glacial Maximum (LGM) was synchronous with the global timing. A set of hypotheses for the timing and drivers of the reconstructed extent of former glaciers in the area will be presented. Our analysis confirms the presence of former glaciers in a low elevation and low latitude region of the tropical Andes. Our ongoing work aims to unveil the timing of the glacial events and the drivers of the glacial and climate history seen within this important region.
Paleomagnetic study in lava and volcanoclastic materials of the Late-Carboniferous-Permian Cadí basin (Central-Eastern Pyrenees)
Authors: Simon-Muzas Ana , Casas-Sainz Antonio M , Soto Ruth , Beamud Elisabet , Oliva-Urcia Belén , Pueyo Emilio L , Gisbert Josep
Published: March 2021

This work presents preliminary paleomagnetic results from the Cadí basin, one of the Pyrenean Late-Carboniferous-Permian basins.

These basins are the consequence of a complex tectonic evolution. At the outset, they were controlled by an extensional or transtensional regime during the progressive dismantling of the Variscan chain that gradually changed to a strike-slip fault regime. Afterwards, during Pyrenean compression (Late Cretaceous to Cenozoic) most of these basins were inverted and transported southwards as a part of the basement units. All of them are characterized by a similar subsidence pattern interpreted as graben or half-graben continental troughs. In a close relationship with its genesis, during Late-Carboniferous-Permian times, several magmatic events took place. Because of that, fluvio-lacustrine sediments present lateral changes to volcanic and volcanoclastic deposits and materials are sometimes cut by intrusions.

The studied zone, the Cadí basin, is located at the eastern Pyrenees, south of the Axial Zone, and shows a high variability of Late-Carboniferous-Permian volcanic products in E-W continuous outcrops that reach several hundred meters of thickness with a good preservation and exposition. The Late Carboniferous-Permian evolution of the Cadí basin was strongly controlled by tectonics and volcanism. In order to characterize this stage and its volcanic rocks, we applied in a previous work the anisotropy of magnetic susceptibility (AMS) technique to determine the primary magnetic fabric of lava flows and volcanoclastic materials. A dominant WNW-ESE direction of the magnetic lineation was recognized related to the paleoflow direction. Paramagnetic minerals and magnetite were recognized as the main carriers of the AMS.

In this work we present the paleomagnetic results from 15 sites (about 150 specimens) in volcanic, volcanoclastic and intrusive materials sampled along four N-S cross sections. The obtained results indicate that the carrier of the magnetization are both magnetite and haematite. The thermal demagnetization of samples shows a paleomagnetic component with unblocking temperatures from 480ºC with reversed polarity and very low inclination after bedding correction. In some sites a normal polarity component is also recognized. These results seem to be coherent with a magnetization coetaneous with the emission and deposition of these materials during Permian times. In cases where the samples record a normal component is important to take into account the complex structural situation of these outcrops.
Modelling landslide-flood interactions: an example from Colorado
Authors: Panici Diego , Bennett Georgie
Published: March 2021

Landslides and debris flows represent natural phenomenon with high geomorphic impact and of significant cascading hazards to human lives and built environment. Intense rainfall events are key triggers of landslides and, as a result, landslides end up interacting with river channels during floods. Large masses of sediment can overwhelm the sediment transport capacity of a river channel and result in the formation of a dam. Nevertheless, this build-up process is not always evident in the aftermath of the event: when a dam burst occurs, a surge of mixed solid and fluid material is produced resulting in significant erosion in the downstream channel. Eventually, the blockage is removed, leaving the process of dam build-up and bursting undocumented. Due to the abrupt nature of this phenomenon, field observations are difficult to obtain.

In this study, we carried out a preliminary analysis by using a computational model to replicate the formation of a channel blockage downstream of a series of landslides during an event that occurred in the North St Vrain Creek in Colorado, USA, during the Great Colorado Storm in September 2013 (estimated to be a 1 in 1000 years event). In this case, there is limited documented evidence of a blockage, but a dam and its busting were hypothesised by analysing very large erosional patterns in a downstream reach that could not be explained by typical erosive processes (e.g. stream power). We employed the free source code r.avaflow, which is a two-phase model. This code can simulate complex chain phenomena, rapid routing mass flows, and entrainment-deposition processes. Topography of the area was obtained by using high resolution LiDAR DEM before and after the flood event in 2013 and was used as basal topography for simulations, as well as to estimate the amount of sediment released by the landslides. The flood flow employed for the simulation was based on estimated rainfall-runoff and kept constant, since the total simulation time was small compared to the actual flood curve duration. We also tested a limited range of parameters to account for the inherent uncertainties in the variables used.

The model was able to represent the erosion from the landslides and on the river channel, but also displayed the formation of a dam downstream of the landslides across all simulations. Although the topographic change and volume of mobilised sediments were affected by the variation of the model parameters, the formation of the channel blockage was always observed. This modelling will provide the basis for further modelling on landslide-channel interactions and will explain those phenomena that have only been postulated but not directly observed.
Biblical Tel Burna: contribution of POSL and PXRF to the discussion on sedimentary and site formation processes in archaeological contexts of the southern Levant
Authors: Janovský Martin , Horák Jan , Ackermann Oren , Tavger Aharon , Cassuto Deborah , Šmejda Ladislav , Hejcman Michal , Anker Yaakov , Shai Itzhaq
Published: March 2021

An ancient tell is a multi-period archaeological site, where anthropogenic, and natural sedimentation processes took place. Although a tell is primarily an anthropogenic type of geomorphological feature, it is affected by natural processes as well. This contribution discusses how these processes can be determined within the context of archaeological research and how it is possible to differentiate and interpret past-human activities and natural processes. Tel Burna, a site intensively occupied from the Early Bronze to Iron Ages (3rd millennium BCE – 6th century BCE) located in the southern Levant, was chosen for this study of the studying sedimentary processes and chemical compositions of sediments. The sedimentary processes were studied in the course of an archaeological excavation using POSL (portable optically stimulated luminescence), granulometry and PXRF (portable X-ray fluorescence). Focusing on the area along the fortification walls, data was collected from strata around the casemate fortifications dating from the Late Bronze Age to the Late Iron Age.

The gradual increase of OSL values obtained inside the casemate wall, indicate accumulation of sediment during a long period of time. Whereas similar values along the entire profile outside the casemate wall indicate sediment accumulation in one-time event. This might be related to defensive preparations, allegedly in response to advances made by Sennacherib’s army in 701 BCE. Results from the PXRF demonstrated a correlation between the Cu, P, K, Zn, Mn content and human activities. Ca content decreased as sampling descended from the tell's surface, suggesting its origin in post-abandonment aeolian processes.  The results demonstrate that the use of POSL and PXRF can be useful for determining sedimentary processes at ancient tells. The presented abstract is adapted from the article published in Quaternary International in 2020.

Acknowledgements:

The research is supported by project “Geochemical insight into non-destructive archaeological research” (LTC19016) of subprogram INTER‐COST (LTC19) of program INTEREXCELLENCE by Ministry of Education, Youth and Sport of the Czech Republic.
A comparison of emerging contaminant fingerprinting techniques to assess the impact of human wastewater on karst groundwater quality
Authors: Vucinic Luka , O'Connell David , Dubber Donata , Behan Patrice , Crowley Quentin , Coxon Catherine , Gill Laurence
Published: March 2021

Lowland karst aquifers in Ireland are extremely complex to understand and are considered to be highly vulnerable to pollution (e.g. low-lying karst catchments exhibit a lot of surface water – groundwater interactions which makes them very susceptible to direct contamination). These aquifers are impacted by multiple contamination sources on land (in particular, rural sources from agriculture and on-site domestic wastewater effluent) which makes their protection and management challenging. Human wastewater effluent is identified as significant threat to groundwater quality in such lowland Irish karst environments, since approximately one-third of the population in Ireland is relying on decentralized wastewater treatment systems for the treatment of domestic wastewater. However, it is difficult to distinguish between human wastewater effluent and agricultural pollution impacts on karst aquifers using only traditional water quality parameters or any single environmental tracing method. Hence, the impact of microbial and chemical contaminants of human wastewater origin on groundwater quality must be assessed using a multiple-tracer approach, ideally targeting source-specific tracers. This paper presents an overview of the results obtained during the research conducted throughout the last several years at nine karst catchments in Ireland using a range of methodologies in order to determine and quantify domestic wastewater pollution impacts on karst springs. Microbial pollution was assessed using flow cytometric fingerprinting and faecal indicator bacteria, while chemical pollution impact assessment included the analysis of fluorescent whitening compounds (FWCs; well-known indicators of human contamination since their origin is mostly from laundry detergents), specific anion ratio signatures (Cl/Br), quantification and identification of microplastic particles using Fourier-transform infrared spectroscopy (FTIR), and faecal sterol and stanol profiles and ratios. A thorough analysis of the results obtained using a multiple-tracer approach has been conducted and methodologies have been evaluated in terms of applicability and sensitivity in a range of different karst catchments. The ability of these methodologies and techniques to determine and quantify human faecal pollution impacts on karst springs will be discussed. The results show a significant correlation between microplastic particle counts and detected FWCs signals at different springs, which helps to understand the contribution of household-derived contaminants to this environmental problem. Moreover, our results indicate that faecal sterols and stanols can be useful faecal source tracking method in karst aquifer systems despite the fact that concentrations of sterols and stanols of interest were usually low which makes the interpretation of results challenging.
Finding of artisanal uses of elemental mercury in the city of Murcia in medieval times
Authors: Esbrí José María , Mansilla-Plaza Luis , Sanchez-Gonzalez María Jesús , Higueras Pablo
Published: March 2021

Mercury (Hg) was used in gilding techniques since ancient times. This metal gilding technique consisted of applying an amalgam of Au and Hg to the surface of a metallic object and then removing the Hg to achieve adhesion of the Au to the support. The traditional preparation of amalgam was a mixture of Au with Hg (in a ratio of 1/8). After this preparation, the mixture usually was ground in a mortar, heated, and then cooled by pouring it into water. The paste was applied to the areas to be browned and then the piece was subjected to mild temperatures so that the Hg evaporated, leaving a thin layer of Au on the surface of the object.

The origin of this work is the discovery of an evident quantity of liquid Hg on a site under construction, near the old wall of the city of Murcia, at a level identified as from medieval times. To elucidate the origin of this Hg, a sampling of medieval materials has been carried out throughout the site, including both the area with liquid Hg, the entire area what appears to be the work room and the adjacent rooms. The sampling has been carried out using an Ejkelkamp sampler at various depths. These soil samples were analysed by Energy Dispersion X-Ray Fluorescence using a PanAlytical device. Total Hg and Hg speciation data were obtained by Atomic Absorption Spectrometry using a Lumex equipment. In addition to this, a gaseous mercury monitoring has been carried out using a portable atomic absorption equipment to search Hg sources and gaseous Hg dispersion in the atmosphere of the studied site. Results of the survey has shown an evident and intense soil Hg pollution in a small area of 2x2 m. This affected area was located near the outer wall of the medieval building and was very restricted, which suggests that it was a storage place for liquid Hg for later use in other areas. The degassing of these recently uncovered materials produced a significant dispersion of the Hg gas throughout the enclosure. In addition to this, samples of medieval materials have shown very high concentrations of Hg in the vicinity of the contaminated area, and high concentrations in the rest of the enclosure. Speciation analysis have shown that the Hg in this part of the enclosure is in the form of metacinnabar and Hg bound to humic acids, which suggests the presence of an atmosphere with extremely high concentration of gaseous Hg in medieval times that was later deposited in the soil, being fixed to its organic phase. Multielemental analysis has shown additional high concentrations of Pb, Cu and Sn, suggesting that the artisanal works in the enclosure involved these elements too. While waiting for more specific archaeology works that can corroborate it, the origin of this Hg in the area could be the storage for the realization of gilding work on metals with this element.

This work was funded by the company “Obras y Proyectos Soyma”.
Impact of ENSO on stratospheric ozone
Authors: Benito-Barca Samuel , Calvo Natalia , Abalos Marta
Published: March 2021

El Niño‐Southern Oscillation (ENSO) is the main source of interannual variability in the global climate. Previous studies have shown ENSO has impacts on stratospheric ozone concentrations through changes in stratospheric circulation. The aim of this study is to extend these analysis by examining the anomalies in residual circulation and mixing associated with different El Niño flavors (Eastern Pacific (EP) and Central Pacific (CP)) and La Niña in boreal winter. For this purpose, we use four 60-year ensemble members of the Whole Atmospheric Community Climate Model version 4, reanalysis and satellite data.

Significant ozone anomalies are identified in both tropics and extratropics. In the northern high-latitudes (70-90N), significant positive ozone anomalies appear in the middle stratosphere in early winter during both CP and EP El Niño, which propagates downward during winter to the lower stratosphere only during EP-El Niño events. Anomalies during La Niña events are opposite to EP-El Niño. The analysis of the different terms in the continuity equation for zonal-mean ozone concentration reveals that Arctic ozone changes during ENSO events  are mainly driven by advection due to residual circulation, although contributions of mixing and chemistry are not negligible, especially in upper stratosphere.

The ENSO impact on total ozone column (TOC) is also investigated. During EP-El Niño, a significant reduction of TOC appears in the tropics and an increase in the middle latitudes. During La Niña the response is the opposite. The TOC response to CP El Niño events is not as robust. In the Northern Hemisphere polar region the TOC anomalies are not significant, probably due to its large variability associated with sudden stratospheric warmings in this region.
Effects of litter cover on partitioning of natural rainfall for plantation Pinus tabulaeformis forest in the Loess Plateau of China
Authors: Cui Yongsheng , Pan Chengzhong , Zhang Geng , Sun Zhanwei , Wang Fuxing
Published: March 2021

      Litter accumulates yearly since vegetations were widely planted for reforestation, and it plays an important role in hydrologic cycling. There is little information on the effects of litter on re-allocation of rainfall processes. Eight runoff plots were established in the Pinus tabulaeformis stand with four litter (needle-leaf) masses (0, 0.6, 1.2, 1.8 kg/m2), and the surface runoff (R), evaporation (E), infiltration and soil moisture dynamics were measured throughout the mainly rainy season from August 4 to September 28 in the Loess Plateau. The results showed that, soil evaporation mainly occurred in daytime for bare soil, and decreased with increasing litter masses, and litter cover is prone to hinder the heat and water exchange between soil and atmosphere, especially for the soil layer 0~5 cm. Litter cover greatly decreased surface runoff, and it may hinder infiltration at the beginning of rainy season, but increasing soil water storage (SWS) with deeper infiltration depth for the long run, especially for the litter masses 1.2 and 1.8 kg/m2. With the litter covered, the ratio of R to precipitation (P) was less than 10%, no matter it was heavy rain or light rain. However, the proportion of R was amplified when the rainfall was intense for the bare soil. And the ratio of E to P was always below 10% for all treatments, except for light rainfall. With the increased litter masses, the proportion of R and E all decreased, and the SWS/P has well nonlinear positive relationship with litter masses, and it was proved that more than a half of rainfall was stored even for bare soil. This study may helpful to better understanding the effects of litter on hydrological response, and promotes practical measurements to the management of precipitation in a forest stand view.
Polar Lows - Moist Baroclinic Cyclones Developing in Four Different Vertical Wind Shear Environments
Authors: Stoll Patrick , Spengler Thomas , Graversen Rune Grand
Published: March 2021

Polar lows are intense mesoscale cyclones that develop in polar marine air masses. Motivated by the large variety of their proposed intensification mechanisms, cloud structure, and ambient sub-synoptic environment, we use self-organising maps to classify polar lows.

We identify five different polar-low configurations which are characterised by the vertical wind shear vector, the change of the horizontal-wind vector with height, relative to the propagation direction. Four categories feature a strong shear with different orientations of the shear vector, whereas the fifth category contains conditions with weak shear. This confirms the relevance of a previously identified categorisation into forward and reverse-shear polar lows. We expand the categorisation with right and left-shear polar lows that propagate towards colder and warmer environments, respectively.

For the strong-shear categories, the shear vector organises the moist-baroclinic dynamics of the systems. This is apparent in the low-pressure anomaly tilting with height against the shear vector, and the main updrafts occurring along the warm front located in the forward-left direction relative to the shear vector. These main updrafts contribute to the intensification through latent-heat release and are typically associated with comma-shaped clouds.

Polar low situations with a weak shear, that often feature spirali-form clouds, occur mainly at decaying stages of the development. We thus find no evidence for hurricane-like intensification of polar lows and propose instead that spirali-form clouds are associated with a warm seclusion process.
Oceanic Primary production decline halved in eddy-resolving simulations of global warming
Authors: Couespel Damien , Lévy Marina , Bopp Laurent
Published: March 2021

The decline in ocean primary production is one of the most alarming consequences of anthropogenic climate change. This decline could indeed lead to a decrease in marine biomass and fish catch, as highlighted by recent policy-relevant reports. Because of computational constraints, current Earth System Models used to project ocean primary production under global warming scenarios have to parameterize flows occurring below the resolution of their computational grid (typically 1°). To overcome these computational constraints, we use an ocean biogeochemical model in an idealized configuration representing a mid-latitude double-gyre circulation, and perform global warming simulations under increasing horizontal resolution  (from 1° to 1/27°) and under a large range of parameter values for the eddy parameterization employed in the coarse resolution configuration. In line with projections from Earth System Models, all our simulations project a marked decline in net primary production in response to the global warming forcing. Whereas this decline is only weakly sensitive to the eddy parameters in the eddy-parametrized coarse resolution, the simulated decline in primary production is halved at the finest eddy-resolving resolution (-12% at 1/27° vs -26 at 1°). This difference stems from the high sensitivity of the subsurface nutrient transport to model resolution. Our results call for improved representation of the role of eddies on nutrient transport below the seasonal mixed-layer to better constrain the future evolution of marine biomass and fish catch potential for decision-making.
Dry deposition fluxes of NH4+-N and NO3--N at a rural site of Indo-Gangetic Plain, India.
Authors: Naseem Moh , Kulshrestha Umesh
Published: March 2021

The world’s acute reactive nitrogen (Nr) deposition is chronically eroding the biospheric integrity and undermining earth system’s resilience to be in an accommodatable state. The present study comprehensively attempts to decipher the dry depositions of atmospheric inorganic Nr along with other major ions through dustfall fluxes. Authentic atmospheric dust samples were collected by incorporating a surrogate-surface approach at an agriculturally intensive rural site in Indo-Gangetic plain of India over a year-long temporal scale from October 2017-September 2018. The mean (±Standard Error) dry deposition fluxes of NH4+-N and NO3--N during the whole study period were observed as 0.41±0.09 kg ha-1 yr-1 and 6.51±1.58 kg ha-1 yr-1, respectively. The total percent ionic contribution to the dustfall flux was observed 2.95% and the descending order of their percent contribution in total ionic fluxes were observed as SO42- (31.46%) > Cl- (15.74%) > K+ (15.04%) > Ca2+ (13.97%) > Na+ (10.23 %) > NO3- (7.06%) > Mg2+ (4.43%) > F-(1.62%) > NH4+ (0.44%). The relative dominance of NO3--N over NH4+-N fluxes was maintained in all seasons during the whole monitoring period which could be attributed to the competitive exclusion of NH4+-N from acid-base neutralization reactions by other strong base cations in dustfall. Size-distribution and morphological analysis of dust particles from Scanning Electron Microscope images signified the anthropogenic involvement in shaping the dominant mode of particle-size distribution in dust fall fluxes which culminated into the dominance of fine-mode fraction over course-mode in dustfall.
Improvement of the simulation of high and low flows in the LSM based hydrological modeling chain SASER applied to the Ebro river basin
Authors: Cenobio-Cruz Omar , Barella-Ortiz Anaïs , Quintana-Seguí Pere , Garrote Luis
Published: March 2021

The SASER (Safran-Surfex-Eaudysee-Rapid) hydrological modeling chain is a physically-based and distributed hydrological model that has been implemented over two domains: Iberia and the Pyrenees. Currently, it is used for drought studies (HUMID project) and water resources analysis (PIRAGUA project).

In this modeling chain, SAFRAN provides the meteorological forcing, SURFEX is the LSM that performs the water and energy balances and Eaudyssée-RAPID simulates daily streamflow. SAFRAN and SURFEX are run at a spatial resolution of 5 km for the Iberian implementation and 2.5 km for the Pyrenean one. Daily streamflow is calculated by the RAPID river routing scheme at a spatial resolution of 1 km in both cases. SAFRAN analyzes daily observed precipitation, which is then interpolated to the hourly scale. For precipitation, relative humidity is currently used to hourly distribute the daily precipitation.

SASER is able to simulate adequate streamflow on the Ebro basin (KGE>0.5 on 62% of near-natural gauging stations when the LSM is run at 2.5 km of spatial resolution). However, due to the lack of a hydrogeological model, low flows are often poorly reproduced by this scheme. Furthermore, peak flows could also be improved.

This work aims at improving high and lows by correcting the distribution of hourly precipitation and adding linear reservoirs to improve low flows.

The increase of the spatial resolution from 5 to 2.5 km has caused a relevant improvement of peak flows. However, most of the peak flows are still underestimated. One way of improving simulated streamflow is improving the hourly distribution of the precipitation, as SAFRAN distributes precipitation through the day with unrealistic low hourly intensities. This will impact runoff generation and, thus, peak flow. We have used two ERA-Interim driven RCM simulations from the CORDEX project to improve the hourly distribution of precipitation. As a result, we now produce more realistic temporal patterns of hourly precipitation.

The current SASER implementation is not able to sustain low flows. A physical-based solution (hydrogeological model) would be desirable, but as it is difficult to implement we chose to introduce a linear reservoir, following the steps of Artinyan et al (2008) and Getinara et al. (2014). The reservoir is able to improve low flows in most near-natural subbasins. The challenge now is how to set its parameters in non-natural basins.
Biogeochemical zonation reveals three zones of nitrogen turnover in the Ems estuary
Authors: Schulz Gesa , Sanders Tina , Dähnke Kirstin
Published: March 2021

Estuaries are nutrient filters for coastal waters and can act as nitrate sink or source depending on predominant microbial processes, environmental conditions and geomorphological characteristics. Such environmental factors can change along the estuary itself. This study aims to identify different zones of nitrogen turnover in the Ems estuary and to determine the main processes.

Water column properties, dissolved inorganic nitrogen and dual stable isotopes of nitrate were measured along the Ems estuary during two research cruises in August 2014 and June 2020. Based on mixing calculations and stable isotope changes, we found that the estuary in both years is clearly divided into three zones that vary in the predominant nitrate turnover pathways. This was confirmed by principle component analysis.

The zonation mainly corresponded to changes in the geomorphology of the estuary, but a spatial shift of the zones occurred between 2014 and 2020. In both years, the most upstream zone acted as a clear nitrate sink. A strong fractionation (~30 ‰) of nitrate stable isotopes points towards removal by water column denitrification in this hyperturbid estuarine section.  In the middle reach of the estuary, nitrification gained in importance, turning this section into a net nitrate source during both sampling campaigns. In contrast to the biogeochemical active inner zones, mixing dominates nitrate distribution in the outermost section of the estuary.

Overall, the Ems estuary acted as a nitrate sink in both years. However, the zonation showed that relative stable zones of nitrification and denitrification existed along the estuary, which can change – and possibly move – when biogeochemical properties vary. 
Cold Fronts Transport Features of North China Pollutant over the Yangtze River Delta, China
Authors: Liu Duanyang , Gu Peishu , Qian Junlong
Published: March 2021

An air pollution process in Jiangsu Province, China on December 22–23, 2016 is discussed by analyzing various data set, including the meteorological observation data, the reanalysis data from National Centers for Environmental Prediction (NCEP), the Air Quality Index (AQI), the PM2.5 and PM10 concentrations data, and the airflow backward trajectory model of National Oceanic and Atmospheric Administration (NOAA). The results show that the air pollution episode was under the background of a medium cold front from the west of the Hetao area, and caused by regional transport of pollutants from North China. The primary pollutant was PM2.5 and PM10. The PM2.5 and PM10 concentrations increase significantly 4–6 h after the cold front passing and reached the peak in 13–24 h. The obvious lag phenomena of the rising period and the peak-moment of PM2.5 and PM10 concentrations were found at the Suzhou, Huai'an, Taizhou and Xuzhou stations, and the maximum of 3h-allobaric, the maximum and average values of the wind speed near the ground were larger one by one at the four stations respectively in the northwestern Jiangsu, north-central Jiangsu, along with the Yangtze river Jiangsu, and southeastern Jiangsu. The period of middle –heave level pollution in Suzhou was 7–9 h later than in Huai'an and Taizhou, and was 24 h later than in Xuzhou, because of the lower PM2.5 and PM10 concentrations at early December 21, the delay of pollutants from upstream, and the larger wind speed from the boundary layer to the surface in southeastern Jiangsu. WRF-Chem model can well reveal the pollutant transport process. The high-value zone has a close relationship with the position of cold front. At 1200 LST on December 22, the cold front reached Xuzhou accompanied by high PM2.5 concentration. At 1400 LST on December 22, the cold front advanced to Huai'an. The high PM2.5 concentration zone moved south alongside the cold front and covered Xuzhou and Huai'an. Suzhou, far away from the upstream, was less vulnerable to pollutant transport. The high-value did not fell until the northwest wind shifted to the north wind. The backward trajectory analysis of air pollution also indicated that regional transport of pollutants from North China led to the middle –heave level pollution weather.
Grain scale investigation of shear reactivation by fluid pressurization
Authors: Nguyen Hien Nho Gia , Scholtès Luc , Guglielmi Yves , Donzé Frédéric Victor , Ouraga Zady , Souley Mountaka
Published: March 2021

Fluid pressurization of critically stressed sheared zones can trigger slip mechanisms at the origin of many geological rupture processes such as earthquakes and landslides. It is now well assumed that the reduction of effective stress induced by fluid pressurization can lead to the reactivation of shear zones. However, the micromechanisms that govern this reactivation remain poorly understood. By using discrete element modeling, we simulate pore-pressure-step creep test experiments on a sheared granular layer at a sub-critical stress state in order to investigate the micromechanical processes at stake during fluid induced reactivation. The simulated responses are consistent with both laboratory and in situ experiments, confirming the scale independent nature of fluid induced slip. The progressive increase of pore pressure promotes slow steady slip at sub-critical stress states and fast accelerated dynamic slip once the critical strength is overcome. The analyses of both global and local quantities show that these two emergent slip behaviors correlate to characteristic deformation modes: diffuse deformation for slow slip and highly localized deformation for fast slip. Our results suggest that, besides the control of the fabric of shear zones on their emergent slip behavior, failure is associated to grain rotations resulting from unlocking of interparticle contacts mostly located within the shear band, which, as a consequence, acts as a roller bearing for the surrounding bulk.
Leveraging coherent wave field analysis and deep learning in fiber-optic seismology
Authors: Schwarz Benjamin , Sager Korbinian , Jousset Philippe , Currenti Gilda , Krawczyk Charlotte , Tsai Victor
Published: March 2021

Fiber-optic cables form an integral part of modern telecommunications infrastructure and are ubiquitous in particular in regions where dedicated seismic instrumentation is traditionally sparse or lacking entirely. Fiber-optic seismology promises to enable affordable and time-extended observations of earth and environmental processes at an unprecedented temporal and spatial resolution. The method’s unique potential for combined large-N and large-T observations implies intriguing opportunities but also significant challenges in terms of data storage, data handling and computation.

Our goal is to enable real-time data enhancement, rapid signal detection and wave field characterization without the need for time-demanding user interaction. We therefore combine coherent wave field analysis, an optics-inspired processing framework developed in controlled-source seismology, with state-of-the-art deep convolutional neural network (CNN) architectures commonly used in visual perception. While conventional deep learning strategies have to rely on manually labeled or purely synthetic training datasets, coherent wave field analysis labels field data based on physical principles and enables large-scale and purely data-driven training of the CNN models. The shear amount of data already recorded in various settings makes artificial data generation by numerical modeling superfluous – a task that is often constrained by incomplete knowledge of the embedding medium and an insufficient description of processes at or close to the surface, which are challenging to capture in integrated simulations.

Applications to extensive field datasets acquired with dark-fiber infrastructure at a geothermal field in SW Iceland and in a town at the flank of Mt Etna, Italy, reveal that the suggested framework generalizes well across different observational scales and environments, and sheds new light on the origin of a broad range of physically distinct wave fields that can be sensed with fiber-optic technology. Owing to the real-time applicability with affordable computing infrastructure, our analysis lends itself well to rapid on-the-fly data enhancement, wave field separation and compression strategies, thereby promising to have a positive impact on the full processing chain currently in use in fiber-optic seismology.
Impact of transpiration rates on foliar silicon concentrations across a range of angiosperm species exposed to water stress.
Authors: Guzman Thomas , Burlett Regis , Delvigne Camille , Parise Camille , Dubois Sabrina , Martin-Gomez Paula , Opfergelt Sophie , Wingate Lisa
Published: March 2021

It is widely observed that silicon availability (Si) can enhance plant growth and increase the tolerance of plants to a range of biotic and abiotic stresses, although the specific mechanisms underlying these positive effects are not always understood. Silicon is acquired by plants both actively via transporters located in roots and/or passively as plants transport water during transpiration. The relative importance of each of these mechanisms depends strongly on the plant species and the level of stress experienced by the plant. Currently there is a lively debate in the literature regarding the relationship between plant Si accumulation and transpiration rates. Rates of transpiration can affect the amount of Si moving through a plant and in turn the concentration of available Si in soils can make the plant less vulnerable to the effects of drought stress. In order to better understand these relationships between plant water fluxes and Si accumulation in leaves, nine angiosperm tree species (from five families including both deciduous and evergreen species) were grown in a greenhouse and exposed to contrasting watering treatments. For each species, three trees were well watered throughout the growing season whilst three others were exposed to water stress. Whole plant transpiration fluxes were monitored continuously with balances, and pre-dawn leaf water potentials were measured regularly during the experiment. In addition the foliar Si concentrations of each plant were measured by ICP-AES after alkaline fusion both at the beginning and the middle of the growing season. In this presentation, we show our first results examining the relationship between leaf Si concentrations and plant water fluxes in contrasting species. We tested the hypothesis that drought stress significantly decreased the foliar Si concentration in all of the species measured and that foliar Si concentrations were correlated with the cumulative transpiration rates of plants and thus expected to increase significantly over the growing season. 
Ecosystem scale evidence for the contribution of vanadium-based nitrogenase to biological nitrogen fixation. 
Authors: Bellenger Jean-Philippe , Darnajoux Romain , Magain Nicolas , Renaudin Marie , Lutzoni Francois , Zhang Xinning
Published: March 2021

Nitrogen is the primary limiting nutrient in high latitude ecosystems. Biological nitrogen fixation (BNF) by microorganisms associated with cryptogamic covers, such as cyanolichens and bryophytes, is an important source of new reactive nitrogen in pristine, high-latitude ecosystems. BNF is catalyzed by the enzyme nitrogenase, for which three isoforms have been described; the canonical molybdenum (Mo) nitrogenase which requires Mo in its active site and two alternative nitrogenases, the vanadium and iron-only nitrogenases. The low availability of Mo on land has been shown to limit BNF in many ecosystems from the tropical forest to the arctic tundra. Alternative nitrogenases have been suggested as viable alternatives to cope with Mo limitation of BNF, however, field data supporting this long-standing hypothesis have been lacking.

Here, we elucidated the contribution of the vanadium nitrogenase to BNF by cyanolichens across a 600 km latitudinal transect in eastern Canadian boreal forests. We report a widespread activity of the vanadium nitrogenase which contributed between 15 to 50% of total BNF rates on all sites. Vanadium nitrogenase contribution to BNF was more robust in the northern part of the transect. Vanadium nitrogenase contribution to BNF also changed during the growing season, with a three-fold increase between the early (May) and late (September) growing season. By including the contribution of the vanadium nitrogenase to BNF, estimates of new N input by cyanolichens increase by up to 30%, a significant change in these low N input ecosystems. Finally, we found that Mo availability was the primary driver for the contribution of the vanadium nitrogenase to BNF with a Mo threshold of ~ 250 ng.glichen-1 for the onset of vanadium based BNF.

This study on N2-fixing cyanolichens provides extensive field evidence, at an ecosystem scale, that vanadium-based nitrogenase greatly contributes to BNF when Mo availability is limited. The results showcase the resilience of BNF to micronutrient limitation and reveal a strong link between the biogeochemical cycle of macro- and micronutrients in terrestrial ecosystems. Given widespread findings of Mo limitation of BNF in terrestrial ecosystems, additional consideration of vanadium-based BNF is required in experimental and modeling studies of terrestrial biogeochemistry.
Anisotropic diffusivities' effects in rotating magnetoconvection and geodynamo problems
Authors: Filippi Enrico , Brestenský Jozef
Published: March 2021

There are many examples which show how the anisotropic diffusive coefficients crucially influence geophysical and astrophysical flows and in particular flows in the Earth’s outer core. Thus, many models concerning rotating magnetoconvection with anisotropy in the viscosity, thermal and magnetic diffusivities have been developed.  

Different models correspond to different cases of anisotropic diffusivities. For example, we consider several anisotropic models: one with anisotropy in all diffusivities and other models with various combinations of anisotropic and isotropic diffusivities.  

Firstly, all kind of anisotropies are reminded and described. Then, a thorough comparison of these anisotropies, especially of the physical differences among them is done. All physical systems with the above mentioned anisotropies are prone to the occurrence of convection and other instabilities. We show how different types of anisotropy cause a different convection and a different balance among the main forces in the Earth’s Outer Core (Magnetic, Archimedean, Coriolis).  

As usually, to study instabilities in such systems, we use analysis in term of normal modes and search for preferred modes. In all our models, only marginal modes with zero growth rate have so far been studied. Now, we present the bravest modes, i.e. the ones with maximum growth rate. The comparison of the modes dependent on basic input parameters - Prandtl numbers, anisotropic parameter, Ekman and Elsasser numbers - is made mainly for values corresponding to the Earth’s outer core. In all our models the anisotropic diffusive coefficients are represented as diagonal tensors with two equal components different from the third one giving the chance to define simply the anisotropic parameter.  

We stress how magnetoconvection problems with the anisotropy included, became more and more important among the geodynamo problems in the last years; indeed, the origin of flows necessary for dynamo action, as studied in magnetoconvection with resulting instabilities, is important, as well as the problem of the origin of magnetic fields.  