bluuebunny/crossref_metadata_2025 huggingface dataset:
Intracellular energy storage mediating soil microbial resource stress
Authors: Ding Yang , Komainda Martin , Mason-Jones Kyle , Dippold Michaela , Banfield Callum C.
Published: March 2022

A diverse range of soil microorganisms accumulate energy to secure their future needs under resource fluctuation or deficiency. Microbial intracellular storage can substantially mediate the stress of resource variability across time, thereby supporting growth and reproduction. Microbial storage is well known in industrial applications and under pure culture conditions, yet few studies address its importance in the soil. To evaluate how widespread microbial energy storage is in soil, we quantified the contents of two intracellular storage compounds, polyhydroxybutyrate (PHB) and triacylglycerides (TAGs), from seven permanent grasslands in Germany differing in field management (grazing/mowing and fertilizing) and soil types. In winter 2021, soil was collected from two depths, 5-10 cm called topsoil, and >30 cm called subsoil, to capture different soil carbon inputs from grass roots. The storage compound contents were determined by gas chromatography–mass spectrometry (GC-MS). We hypothesized that the carbon input controls the storage compound levels. From topsoil to subsoil, as root carbon inputs (estimated from the fresh root weight) drop with depth, microbial storage levels follow suit. Dissolved organic carbon (DOC) was measured to qualify carbon availability to microorganisms, and microbial biomass carbon (MBC) was to assess microbial biomass. The root weight in the topsoil was 20-50 times higher than in the subsoil, while MBC and DOC contents were 3-4 and 1.5-2.5 times higher, respectively. Storage levels and MBC decreased with depth, and showed a positive correlation with DOC. This experiment allowed us to quantify intracellular storage occurrence in soils and to understand how its distribution related to root carbon input. These results point out that microbial intracellular carbon storage might accumulate according to the available carbon level (root carbon inputs) for microorganisms. Thus, this carbon plays a pivotal role for microbial ecology of soils as it prepares the microbial cells to survive throughout the winter when less carbon is provided by plants.
Accelerometer calibration for thermospheric neutral density estimation with GRACE data by dynamic Precise Orbit Determination (POD) with tailored parametrization
Authors: Wöske Florian , Rievers Benny
Published: March 2022

The neutral mass density of the upper atmosphere (thermosphere) can be determined by orbit and accelerometer data from Low Earth Orbit (LEO) satellites. Especially the accelerometers of geodetic satellites, measuring the non-gravitational accelerations acting on the satellites, are a very useful observation for precise density determination also on very short time scales.

Nevertheless, the accelerometers of geodetic satellites are affected by bias and drift. Therefore a calibration of the data is indispensable. A time dependent bias and scale factor are to be determined. Usually calibration parameters are estimated by dynamic Precise Orbit Determination (POD) or Gravity Gield Recovery (GFR), together with all other parameters of interest. In both cases, the estimated accelerometer calibration parameters are not the major interest. With the used parametrizations and weighting of the observations, good gravitational field and orbit solutions, do not necessarily give good or physical accelerometer calibration solutions. This is unsatisfying, especially for the anticipated use in density determination and the direct comparison to modeled non-gravitational accelerations.

In this contribution we use dynamic POD and investigate different parametrization strategies tailored for an accurate and physical accelerometer calibration for thermospheric density determination. For example we investigate the effect of constraining the accelerometer calibration parameters in that way, that a continuous calibration over all arcs is achieved, where normally each arc is treated locally separated from all other arcs, leading to jumps in the calibration. The scale factor, which is highly correlated to the estimated bias, is concurrently estimated but over a longer batch of arcs. We compare different bias parametrizations, arc lengths, as well as different observation data and weighting strategies.

Finally we show some preliminary density estimation results with our approach and the influence of the accelerometer calibration.
Residual sediment transport in a stratified estuarine channel
Authors: Niesten Iris , Hoitink Ton , Huismans Ymkje
Published: March 2022

After major storm surge protection works in the Rhine-Meuse Delta, referred to as the Delta Works (Vellinga et al., 2014), the New Waterway has become the only remaining open channel connecting the estuary to the North Sea. Like in many harbour areas, continuous deepening of this channel for navigation purposes has led to strong stratification and often salt wedge conditions, which likely has a strong impact on the marine sediment import. The sediment balance for various fractions is highly uncertain (Cox et al., 2021). Based on field measurements and sediment transport modelling, we aim to unravel the mechanisms controlling residual sediment fluxes in highly stratified estuarine channels, by focusing on the New Waterway.

A measurement campaign was set up consisting of two 13-hour surveys, one during spring tide and one during neap tide. A measurement frame was equipped with a LISST-100x, a Seapoint turbidity meter and a CTD probe. Suspended sediment samples are collected every hour at three depths, next to water temperature, salinity and turbidity. The flow was monitored continuously based on a vessel-mounted ADCP transects across and along the channel .

The ADCP-measurements show a clear distinction in flow magnitude and direction between the upper fresh water layer and lower saline layer, confirming the high degree of stratification especially during neap tide. After low water slack, most suspended sediment is found in the lower half of the water column. Suspended sediment concentrations (SSCs) increase during the flood acceleration phase, suggesting local resuspension during this phase of the tide. When reaching high water slack, SSCs decrease with flow velocity. At high water slack, the ADCP-backscatter profiles indicate settling of the suspended sediment on top of the pycnocline. During the ebb phase, SSCs increase again, and the water column is better mixed compared to the flood phase. Preliminary results of the grain size analysis indicate coarsening of the suspended sediment at the end of the flood acceleration and ebb acceleration phases. Ongoing analysis of these data and numerical modelling of SSC will provide more insight in the suspended sediment transport processes under various degrees of stratification.

 

Cox, J. R., Huismans, Y., Knaake, S. M., Leuven, J. R. F. W., Vellinga, N. E., van der Vegt, M., et al. (2021). Anthropogenic effects on the contemporary sediment budget of the lower Rhine-Meuse Delta channel network. Earth's Future, 9, e2020EF001869. https://doi.org/10.1029/2020EF001869

Vellinga, N. E., A. J. F. Hoitink, M. van der Vegt, W. Zhang, en P. Hoekstra. ‘Human Impacts on Tides Overwhelm the Effect of Sea Level Rise on Extreme Water Levels in the Rhine–Meuse Delta’. Coastal Engineering 90 (1 augustus 2014): 40–50. https://doi.org/10.1016/j.coastaleng.2014.04.005.
Identifying the underlying mechanisms of present and future inter-annual variability of oceanic carbon uptake using a machine learning approach with CMIP6 simulations.
Authors: Couespel Damien , Tjiputra Jerry , Johannsen Klaus
Published: March 2022

The ocean plays an instrumental role in regulating the Earth’s climate through the buffering of the anthropogenic-induced excess carbon. Our capacity to predict long-term future oceanic carbon uptake depends on highly sophisticated numerical Earth system models, whose simulations of future climate have a wide inter-model dispersion. Inter-model spread in projections arises from three distinct sources: 1) internal variability of the climate system, 2) model uncertainty, and 3) scenario uncertainty. The spread related to (1) and (2) is even greater when predicting changes at regional scales. In order to elucidate the main origins of present and future internal variability and model uncertainty in oceanic carbon uptake, it is important to identify the uncertainty and sensitivity of the major underlying mechanisms in different ocean regions and across models. A limitation of this approach is the high costof computational and manpower required to systematically assess all mechanisms and identify processes that are important in a consistent way, especially across a large ensemble of model sets. Machine learning methods can be applied to simultaneously estimate the sensitivity of variable sets and explore them automatically across the ensemble of models. Here, we use the Kernel non-linear regression approach to reconstruct the inter-annual carbon uptake variability using monthly outputs of surface temperature, salinity, nutrient, dissolved inorganic carbon,alkalinity, atmospheric CO2 concentration, surface wind speed, and sea-ice cover. The exercise was performed on preindustrial, historical, and future scenario simulation outputs. The algorithm was optimized with a subset of ‘training’ data and evaluated with ‘test’ data. We applied bootstrapping method to delineate the main drivers for the projected inter-annual sea-air carbon fluxes variability in different ocean domains.
Convective aggregation in idealized stochastic models
Authors: Biagioli Giovanni , Tompkins Adrian Mark
Published: March 2022

Numerical simulations of radiative-convective equilibrium in high-resolution cloud-resolving models (CRMs) revealed the tendency of atmospheric convection to self-aggregate on periods of several weeks when the domain is sufficiently large. Nevertheless, even though CRM simulations manage to identify some of the physical mechanisms driving convective clustering, the occurrence of organization seems to be dependent on the model setup, physics and parameterizations. Robust findings from simpler, idealized models, which may reproduce some of the features of the full-physics systems, are thus beneficial to better understand the differences existing between CRMs.

To this end, we have developed a simplified two dimensional stochastic model able to predict the evolution of column total water relative humidity (CRH) in the tropical free troposphere. The model prognostic equation includes a convective moistening term, diffusive lateral transport and subsidence drying, similar to model of Craig and Mack (2013), but one novelty of the new model is that, instead of the convective moistening term as a smooth deterministic function of the background humidity, we treat convection as a point process and account for stochastic variability in the convective moistening process. Therefore the model allows experiments to use domain sizes and grid resolutions similar to those used for the idealized CRM experiments.

It is found that, depending on the chosen parameter settings, the simple model can reproduce equilibrium states of strong convective aggregation and also randomly distributed states, analogous to the CRM results. A sensitivity of the occurrence of self-organization to the initial conditions, i.e., a modest hysteresis, is also found, which also agrees with the full physics CRMs. Large ensembles of numerical experiments were performed for different values of the subsidence timescale, the moisture diffusion coefficient and the parameter that determines convective sensitivity to background humidity, as well as for a range of domain sizes and horizontal grid spacings. Using dimensional arguments, combined with empirical fits from numerical data, we define a dimensionless parameter whose value indicates whether a clustered state is likely to emerge for a given set of parameter values and experimental configurations. This quantity contains dependencies on all the model processes, while also explicitly including the domain size and resolution in an attempt to explain these latter sensitivities observed in the full-physics CRM experiments.
Exploring the resilience and resistance of soil against hydraulic and osmotic stress in unsaturated column experiments
Authors: Guhra Tom , Van Overloop Léon , Ritschel Thomas , Totsche Kai Uwe
Published: March 2022

Sudden or extreme changes in the hydraulic and chemical conditions severely alter water flow and chemical interactions in soil. In response, this may cause an internal erosion of pore space as soil constituents are disaggregated, released and transported, which ultimately even shapes soil horizons. The resilience and resistance of soils against hydraulic and osmotic stress determines their susceptibility to internal erosion. However, the impact of single stress events cannot be observed in field experiments due to a multitude of parallel processes and boundary conditions that change simultaneously. In contrast, unsaturated column experiments using undisturbed soil monoliths offer close-to-natural packing conditions while at the same time providing full control over the boundary conditions.

To investigate how susceptible soils are for internal erosion and thus to the release of (in-)organic soil constituents, unsaturated column experiments were performed with undisturbed topsoil monoliths of a Luvisol and a Regosol formed on loess. Hydraulic and osmotic stress events were simulated by irrigation sequences with two drainage events (desiccation; hydraulic stress), two flow interrupts (ponding; hydraulic stress), and two tracer applications (osmotic stress).

After each stress event, an increase in particle concentration was measured in the effluent, most pronounced when the ionic strength of the influent decreases after the tracer breakthrough. Likewise, the release of soil organic matter (OM) responds predominantly to osmotic stress events and OM fluorescence points to the release of plant derived and microbial processed OM. Moreover, the application of X-ray µ-CT imaging on soil monoliths revealed the alteration of soil structure during the experiment. Especially, the position of secondary carbonates and macropores were identified as useful reference points to reveal structural changes such as pore refilling and soil compaction. In this way, we were able to show how the evolution of soil structure in response to the transport of (in-)organic soil constituents relates to specific hydraulic and osmotic events.
Assessment of climate change and human activities on vegetation development in Northeast China
Authors: Xue Lin , Kappas Martin , Wyss Daniel , Putzenlechner Birgitta
Published: March 2022

Vegetation in Northeast China (NEC) has faced dual challenges posed by climate change and human activities. However, the factors dominating vegetation development and their contribution remain unclear and cannot be precisely discussed. In this study, we conducted a comprehensive evaluation of the response of vegetation in different land cover types, climate regions, and time scales to water availability from 1990 to 2018 based on the relationship between normalized difference vegetation index (NDVI) and Standardized Precipitation-Evapotranspiration Index (SPEI). The effects of human activities and climate change on vegetation development were quantitatively evaluated using the residual analysis method. We showed that the area percentage with a positive correlation between NDVI and SPEI increases with the extension of time scales. NDVI of grass, sparse vegetation, rain-fed crop, and built-up land as well as sub-humid and semi-arid areas (drylands) correlated positively with SPEI, and the correlations increased with the extension of time scales. The negatively correlated area was concentrated in humid areas or areas covered by forests and shrubs. The maximum water surplus period for irrigated crops and forests, shrubs, wetlands, humid areas were 1-month and 6-months, respectively. Vegetation water surplus in humid areas weakens with warming, and vegetation water constraints in drylands enhance. Moreover, potential evapotranspiration had an overall negative effect on vegetation and precipitation is a controlling factor for vegetation development in semi-arid areas. Within the period of study, 53% of the vegetated area in NEC showed a trend of improvement, which is mainly attributed to human activities (93%), especially through the implementation of ecological restoration projects in NEC. The relative role of human activities and climate change in vegetation degradation areas were 56% and 44%, respectively. Our findings highlight that the government should more explicitly consider the spatiotemporal heterogeneity of the influence of human activities and water availability on vegetation under changing climate, and improve the resilience of regional water resources. The relative proportions and roles map of climate change and human activities in vegetation change areas provide a basis for government to formulate local-based management policies.
Dendroprovenancing instream wood at the watershed scale applying fingerprinting techniques
Authors: del Hoyo Gibaja Javier , Vennemann Torsten , Vauridel Marceline , Ruiz-Villanueva Virginia
Published: March 2022

Within the field of dendrochronology, different sub-disciplines arise using the information stored in the wood for a variety of purposes. In this study, we use dendroprovenance to develop a methodology that allows us to infer the source area of instream large wood (LW) at the river basin scale applying fingerprinting techniques.

LW is mainly supplied to fluvial ecosystems by riparian vegetation and nearby areas, and the presence of wood in a river determines its geomorphology and ecology; but also, it is associated with an increase in danger and risk to infrastructures and population. For this reason, research on the origin of LW is essential to better understand LW processes and to facilitate decision-making in the management of the forest and the river.

The tracers we have used so far are the stable isotopes coming from the water molecule: hydrogen (D/H) and oxygen (18O/16O). These isotopes show spatial variations depending on evaporation-precipitation processes and resulting isotopic fractionation. Subsequently, the water absorbed by a tree growing in a particular place stores this isotopic signal, and when that tree (or a piece of it) falls and becomes part of the river ecosystem, we can use this isotopic signal to infer the origin of the wood.

Our study site is a 50 km reach of the Rhone River between Lake Geneva and Genissiat dam (3000 km2 of catchment) in France, where all arriving wood is stored upstream from the dam. The goal is to differentiate the wood coming from the two main tributaries, the Arve and Valserine rivers (located in different mountain systems) since they are the main wood suppliers at Genissiat.  

Preliminary results show clear differences in the isotopic composition when comparing samples from one tributary and the other, with the most notable differences in the most recent tree rings.

Lastly, we plan to analyze other tracers such as minor and trace elements that are linked to the geology and combine them with the isotopic ratios in a multivariate analysis to determine the origin of the wood in a more accurate manner. Consequently, we will have developed a new dendroprovenance method that can be extrapolated to other fields, taking a step forward in the application of our knowledge about tree rings.
Linking litter decomposition characterized by the Tea Bag Index to soil microbial characteristics under long term manure and crop rotation management
Authors: Fu Yuting , Paradelo Marcos , Ravnskov Sabine , de Jonge Lis W. , Arthur Emmanuel
Published: March 2022

Soil microbiome is an important indicator of soil quality and it is related to various soil functions, including soil carbon cycling. Plant litter decomposition is a key process in carbon cycling, and the use of standardized plant litter for the comparison of decomposition rates between different conditions is a promising method. In this study, we aimed to investigate the difference in microbial community composition in long-term manure amended soils with different crop rotations, and its relationship with litter decomposition by using the Tea Bag Index (TBI) protocol. Green tea and rooibos tea bags were buried pairwise in three long-term experimental sites (LTEs) in Germany, Denmark and Sweden for three months. The TBI, i.e. decomposition rate and stabilization factor, was calculated from the weight loss of tea. The three LTEs have contrasting soil textures and had been manured between 20 and 127 years. The rotation elements in the LTEs include spring barley, winter wheat, winter oat, maize, and grass/clover. The microbial community composition was characterized by biomarkers (phospholipid fatty acids and neutral lipid fatty acids) and 16S and ITS sequencing. Enzyme activity was quantified by fluorescein diacetate hydrolysis analysis. The linkage between TBI and several microbial properties including microbial biomass, enzyme activity, the fungal:bacterial ratio, and the abundance and the diversity of the microbial community, will be discussed. The interactive effect of soil texture and management on the TBI and microbial properties will be addressed, which shall provide implications for soil quality and soil management.
A crevasse-depth calving law accounting for submarine melt undercutting
Authors: Slater Donald , Benn Doug
Published: March 2022

The impact of submarine melting on calving is thought to be central in the response of marine-terminating glaciers to climate, yet we currently have no settled parameterisation that can represent this process in ice sheet models. The crevasse-depth calving law has been widely applied with arguable success, but in its present form accounts only for depth-mean stresses. As such, it does not account for the bending stresses induced by undercutting that may be key to the impact of submarine melting on calving.

Here, we combine elastic beam theory with linear elastic fracture mechanics to study the propagation of surface and basal crevasses near the front of tidewater glaciers in response to melt undercutting. We check our results against a numerical approach involving 2D elastic simulations and the displacement correlation method for estimating fracture depth. Our results suggest that bending stresses can play a significant role in modifying crevasse depth, with undercutting promoting the opening of surface crevasses and protruding ‘ice feet’ promoting the opening of basal crevasses. Lastly, we seek a revised crevasse-depth calving law that accounts for these effects.
Decadal changes of the Adriatic sea level – exploring the combined effect of sea level rise and climate regime’s shift 
Authors: Pupić Vurilj Mia , Šepić Jadranka , Pilić Pave
Published: March 2022

In this study, an analysis of the observed Adriatic mean sea level time series has been carried out in order to determine the primary causes of the changes documented during the last 50 years.  Monthly sea level data were downloaded from the Permanent Service for Mean Sea Level for seven stations located along the northern and eastern Adriatic coast: Venice, Trieste, Rovinj, Bakar, Zadar, Split and Dubrovnik. Significant positive sea level trend, related to climate change, was detected at the majority of the stations. Further on, using Rodionov’s regime shift index algorithm, several regime shifts were detected. The first pronounced regime shift occurred in 1989 resulting with mean sea level lower than usual for an average of 4.37 cm; the second regime shift occurred in 1996 when mean sea level increased for an average of 2.07 cm; and the third regime shift, which is still on-going, started in 2009 when mean sea level abruptly increased to 5.3 cm above average.  A relationship between North Atlantic Oscillation (NAO) and sea level data has been explored, using both monthly and yearly data. High and significant correlation between the two was established for all data, and in particular for the winter season (December, January, February, March). All climate shifts were related to pronounced changes of NAO. The negative shift starting in 1989 was related to the positive phase of NAO, i.e. to weaker cyclonic activity over the Mediterranean and the Adriatic Sea. Oppositely, the two latter positive regime shifts were related to significant decrease and negative phases of NAO, with NAO reaching the most negative values of the entire observation period during the shift starting in 2009. Negative phase of NAO corresponds to stronger cyclonic activity over the Mediterranean and the Adriatic Sea. In conclusion, documented rise of the Adriatic sea level during the last 50 years, and in particular accelerated rise during the last 20 years represent a combination of mean sea level rise due to climate change and due to atmospherically induced shift of climate regimes.
Arctic Century 2021 – an interdisciplinary expedition to the Kara and Laptev Seas to study ocean, atmosphere and land processes in the changing Arctic
Authors: Schaepman-Strub Gabriela , Kassens Heidemarie , Jaccard Samuel L. , Makhotin Mikhail ,   Arctic Century science team
Published: March 2022

The region of the Kara and Laptev Seas in the Russian Arctic has been experiencing one of the highest warming rates globally during past decades. From 5 August – 6 September 2021, the Arctic Century science team gathered unique data during a research expedition, along marine transects and on seven high Arctic islands that are very rarely accessible. The aim of the expedition is to contribute to the understanding of the dynamics and interactions between the ocean, cryosphere, land and atmosphere in the face of global change. Here we provide an overview of the main research topics and investigations performed, including: dynamics of Atlantic water masses; biodiversity and ecosystem productivity in the ocean and on high Arctic islands, at the margin of life; dynamics of the atmosphere and interactions with the ocean and land; past climate change and sea level history reconstruction based on sediment and ice cores; and amount and flow of macro- and microplastic in the ocean and along the shoreline. First analyses of samples and data are currently being performed by the expedition consortium. After an initial moratorium, the data will be made openly accessible to the wider science community.
Dynamic 3D modelling of the unconfined aquifer of the River Marecchia alluvial fan (Rimini)
Authors: Delfini Ilaria , Montanari Alberto , Chahoud Andrea
Published: March 2022

Aquifers play a relevant role in the mitigation of the risk due to the occurrence of drought events in the Emilia-Romagna region. In fact, their capability to store relevant volumes of water and the long time span between meteorological and groundwater droughts make aquifers an essential resource during dry periods. To mitigate the risk induced by water scarcity, in 2014 a managed recharge experiment was carried out on the River Marecchia alluvial fan. In detail, an additional volume taken from the river was diverted into a quarry lake. The lake is an outcrop of the aquifer, therefore an increase in the lake water volume produces a corresponding increase of the piezometric level in the aquifer, and therefore larger groundwater availability.

Several international experiences on the management of aquifers for civil and agricultural water supply have shown the value of the information that can be derived by running groundwater simulation models. In particular, MODFLOW, an open access groundwater simulation model developed by the United States Geological Survey, is widely applied.

The purpose of this work is to apply MODFLOW to study solutions for managing artificial recharge in the River Marecchia alluvial fan. In particular, a previous application of MODFLOW by the Regional Agency for Prevention, Environment and Energy of Emilia-Romagna (ARPAE) has been repeated by using a different model interface, ModelMuse, and additional climatic scenarios.

The work confirms the potential benefits that can be provided by a groundwater simulation model for optimizing aquifer recharge. The application confirmed that recharge may be very successful in this specific case for mitigating the impact of water withdrawals.
Strain evolution on a submarine cable during the 2021 Etna eruption
Authors: Murphy Shane , Garreau Pierre , Palano Mimmo , Ker Stephan , Quetel Lionel , Jousset Philippe , Riccobene Giorgio , Aurnia Salvatore , Currenti Gilda , Gutscher Marc-Andre
Published: March 2022

On the 13th December 2020, a Strombolian eruption occurred on Mount Etna. We present a study of the temporal and spatial variation of strain measured at the underwater base of volcano during this event. 

As part of the FOCUS project, a BOTDR (Brillouin Optical Time Domain Reflectometry) interrogator has been connected to the INFN-LNS ( Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud) fibre optic cable that extends from the port of Catania 25km offshore to TTS (Test Site South) in a water depth of 2km. This interrogator has been continuously recording the relative strain changes at 2m spacing along the length of the cable every 2 hrs since May 2020. 

On preliminary analysis, a change in strain is observed at the around the time of the eruption, however this variation occurs close to the shore where seasonal variations in water temperatures are in the order of 5°C. As Brillouin frequency shifts are caused by both temperature and strain variations, it is necessary to remove this effect. To do so, numerical simulations of seasonal sea temperature specific to offshore Catania have used to estimate the change in temperature along the cable. This temperature change is then converted to a Brillouin frequency shift and removed from the frequency shift recorded by the interrogator before being converted to relative strain measurements. This processing produces a strain signature that is consistent with deformation observed by nearby geodetic stations on land.
A reduction of the plant carbon source postpones autumn leaf senescence in birch seedlings
Authors: Maschler Julia , Keller Jenna , Bialic-Murphy Lalasia , Zohner Constantin M. , Crowther Thomas W.
Published: March 2022

The length of the growing season in temperate and boreal forests has a strong effect on the global carbon balance. Yet, our current understanding of the drivers of phenological processes such as autumn leaf senescence in deciduous trees is not sufficient for making reliable estimates of future growing-season lengths under climate change. While temperature has been shown to be an important driver of autumn leaf senescence, recent evidence suggests that the concept of carbon sink limitation might help to reduce unexplained variation in leaf senescence predictions. According to the carbon sink limitation hypothesis, senescence is regulated by the balance of the plant carbon source and the plant carbon sink, so that senescence occurs later when carbon inputs (source) are low and earlier when there is a low carbon demand (sink). In our experiment, we manipulated carbon source–sink dynamics in birch seedlings (Betula pendula L.) to evaluate the evidence for an effect of carbon sink limitation on autumn leaf senescence in a widespread deciduous tree. Specifically, we removed leaves and/or buds from the seedlings and monitored the effects on autumn net photosynthesis and leaf senescence. In agreement with the carbon sink limitation hypothesis, we observed that a decrease in the carbon source through a high degree of leaf removal increased autumn leaf-level photosynthesis by ~14% and postponed senescence by 5.5 ± 2.4 days. Yet, we did not see significant effects of the lower- and medium-degree defoliation treatments. Further, we did not observe an effect of bud removal on either photosynthesis or senescence, which was likely caused by the fact that our bud removal treatment did not considerably change the plant carbon sink. At least partly, our results are in line with the hypothesis of carbon sink limitation as a driver of growing-season length and move the scientific field closer to narrowing a main uncertainty in climate change predictions.
Are avalanche models correct? An uncertain view on convergence
Authors: Tonnel Matthias , Wirbel Anna , Oesterle Felix , Fischer Jan-Thomas
Published: March 2022

At the core of many avalanche simulation tools, numerical kernels are utilized to solve flow model equations. Aside from trying to fit the models as best as possible to the current understanding of actual flow mechanisms, these kernels have to fulfill general mathematical requirements, such as convergence, stability and consistency. The precision of numerical solutions is limited and needs to be determined by appropriate uncertainty quantification approaches. It is also necessary to assess the impact of input variability propagating through the numerical kernel.

To allow kernel testing and uncertainty quantification, the AvaFrame framework provides a suite of test cases as well as analysis tools. This includes tests with known solutions usable to determine the kernel errors (ana1Tests) and idealized/real world topographies to estimate effects of varying simulation setups. By changing numerical settings, flow model setup or input data it is possible to show their effects on simulation results in a quantitative manner. It therefore allows us to relate input variations to the uncertainty in simulation results. Error and uncertainty quantification is done using modules for computing statistical measures (ana4Stats), indicators along an avalanche path (ana3AIMEC) and various visualization routines.

We showcase this for our com1DFA dynamical dense flow avalanche (DFA) module. The kernel of com1DFA is based on depth integrated governing equations (shallow water) and solved numerically using the smoothed particle hydrodynamics (SPH) method. Applying our analysis tools, we evaluate the convergence of the DFA kernel with regard to the numerical parameters time step, SPH kernel size and particles size. We investigate the accuracy and precision of the numerical solution using the similarity solution test, a test with a semi-analytic solution for depth integrated equations. It allows us to establish a suitable relation between time step, SPH kernel size and particles size for the com1DFA kernel.

Using the same approach for an avalanche setup, we can also vary selected input parameters like friction coefficients and/or release thickness and quantify the resulting uncertainties on simulation results, e.g. runout and peak flow variables.
Using cosmic-ray neutron sensors with machine learning to improve predictions of evapotranspiration and carbon fluxes
Authors: Power Daniel , Rico-Ramirez Miguel Angel , Gentine Pierre , McJannet David , da Rocha Humberto Ribeiro , Rosolem Rafael
Published: March 2022

Estimates of evapotranspiration and carbon fluxes across the globe are increasingly important to understand the impacts of climate change on global eco-hydrology. Soil moisture has a significant influence in these processes, and if we want to accurately predict energy and carbon fluxes good quality soil moisture data is ultimately needed. Flux towers can measure key atmospheric fluxes and often include traditional point-scale soil moisture sensors within the sensor footprint. However, the spatial mismatch between the flux tower footprint and in-situ point scale soil moisture sensors, as well as a lack of standardisation of these sensors, could lead to biases in this data source.

The Cosmic-Ray Neutron Sensor (CRNS) is a more recent technology that can provide field scale (~250m radius), root-zone depth soil moisture estimates at hourly intervals. This is possible through an indirect relationship between measured cosmic-ray neutrons scattered from the soil and the amount of hydrogen atoms contained in the soil. Recent efforts to harmonize around 200 publicly available CRNS sites across the globe, using a standardised and state-of-the-art methodology, now opens the possibility for global scale studies.

We have identified co-located flux tower and CRNS sites across the globe, covering the USA, Europe, Australia, and Brazil. We use established machine learning methods to train predictive models of evapotranspiration and carbon fluxes. We employ the NGBoost algorithm using a decision tree base learner. A key aspect of the NGBoost algorithm is that it gives a probability distribution of the prediction rather than a single point estimate. This will enable us to better understand not only the predictive power but also the uncertainty associated with the model. Our hypothesis is that the information gained when using a spatially consistent, standardised soil moisture estimate will be non-uniform across the globe. For example, it may be of more importance in transition periods, such as during seasonal changes to average soil moisture, as well as sites located in transition zones from dry to wet. This research will provide us with a better understanding of the value of soil moisture in the prediction of atmospheric fluxes across the globe when spatiotemporal scales among different environmental variables are more comparable
The influence of ice-contact lakes and supraglacial debris on glacier change in High Mountain Asia 
Authors: Scoffield Alex , Rowan Ann , Sole Andrew
Published: March 2022

The number and extent of glacial lakes in mountain regions worldwide has increased over recent decades as glaciers have lost mass. These ice-contact lakes modify the dynamic response of glaciers to climate change, presenting a challenge to projecting their future evolution. In High Mountain Asia (HMA) glacial lakes have expanded by more than 45% in the last 30 years. Previous studies have demonstrated the contrasting dynamic evolution of lake- and land-terminating glaciers in the Eastern Himalaya, although it was previously unclear if this was a localised phenomenon. Using existing and manually derived datasets, we observed glacier surface velocity, surface elevation, terminus position and glacial lake area change across HMA’s differing climatic regimes over a twenty-year period (2000–2020) to investigate the dynamic evolution of ~60 lake- and land-terminating glaciers.

 

Our results show that lake-terminating glaciers in the Himalaya, Karakoram and Pamir experienced faster ice flow in the ablation zone, significant surface thinning and extensive terminus recession in comparison to land-terminating glaciers over the same period. The majority of lake-terminating glacier population experienced a glacier-wide increase in velocity during the twenty-year observation period, including 58% of individual glaciers. In comparison, 62% of land-terminating glaciers experienced a decrease in velocity during the same period. This result suggests that lake-induced dynamic changes are occurring irrespective of the regional climatic regime. Our observations also revealed that lake-terminating debris-covered glaciers experienced a greater magnitude of change in velocity, surface elevation and terminus position, than their clean ice counterparts. These results are important for making projections of future glacier change in HMA where many debris-covered glaciers are pre-disposed to the development of terminal lakes in the next few decades.
Assessing the effects of climatic variables on soil and groundwater salinity in a low-lying agricultural field near the Venice Lagoon, Italy
Authors: Teatini Pietro , Ester Zancanaro , Francesco Morari
Published: March 2022

Costal reclaimed farmlands are commonly threatened by saltwater intrusion and peat-driven salinity, resulting in low and unstable agricultural productions. Climatic variables have a great effect on soil moisture and salinity influencing crop production during the various growing seasons. For this reason, monitoring soil water and salinity dynamics in the root zone during the crop growing season is fundamental to conceive mitigation strategies (e.g., precision irrigation techniques). To this end, a monitoring network was installed in an agricultural field located at the southern margin of the Venice Lagoon. Three soil-stations were placed along the main sandy paleochannel crossing the farmland southwest to northeast (stations S1, S2, and S3), while stations S4 and S5 were placed in two silty-loamy areas with high peat content. Each station was equipped with three T4e tensiometers (UMS GmbH, Munchen, Germany) at 0.3, 0.5, and 0.7 m, four Teros 12 sensors (METER Group, Inc., Pullman, WA, USA) measuring volumetric water content, temperature, and electrical conductivity (ECb) at 0.1, 0.3, 0.5, and 0.7 m. In addition, a 2 m deep piezometer was installed to monitor groundwater electrical conductivity (ECw) and depth to the water table. Soil samples were collected on each monitoring location and analyzed for texture, bulk density (BD), soil organic carbon (SOC), electrical conductivity (EC 1:5), pH, and cation exchange capacity (CEC). Moreover, a weather station was installed in the experimental field to accurately monitor the local meteorological conditions during the 2019 and 2020 growing seasons. The soil monitoring dataset shows that ECb increases with depth at all locations. Moreover, rainfall events higher than 10 mm/day caused an increase in the ECb at all layers and stations. The monitoring stations inside the paleochannel showed lower ECb if compared to station S4 and S5, probably due to the highest hydraulic conductivity and, consequently, the highest leaching capacity. S5 was characterized by the highest peat content and showed the highest salinity in both soil and groundwater. In general, soil ECb and groundwater ECw showed similar behavior in 2019 and 2020, except for S4 and S5 that were saltier in 2019. These preliminary analyses demonstrated a strong influence of rainfall events on salinity behavior and highlights how climatic variables, soil heterogeneity, and saltwater intrusion at depth play an important role in the complex salinity dynamics within the root zone.
Clustering and event similarity based fault characterization of post mining induced seismicity of Gardanne mine, France
Authors: Namjesnik Dalija , Niemz Peter , Kinscher Jannes , Cesca Simone , Contrucci Isabelle , Dominique Pascal , Aochi Hideo
Published: March 2022

In post-mining environments, seismic hazard is still not very well understood, as number of research studies remains limited. Seismicity is often considered in post-mining risk mitigation procedures as a precursory of failure initiation in rocks within the mining works leading to ground instabilities. However, flooding of the mines can also lead to perturbations of stress states and pore pressures within the rock mass leading to failure of pre-existing faults, which may have more important impact on public safety due to a potentially longer period of activity and possibly higher magnitudes of the induced seismic events depending on the fault size.  

In a former coal mine in Gardanne, France, which was abandoned in 2003 and flooded afterwards, seismicity started appearing and raising concerns since 2010, when flooding reached the center of the mining basin. The seismic activity has been occurring approximately every two years in the form of crises. Events were also felt by the local population. A sparse temporary monitoring network has been installed in 2013 in this seismically active area. Based on research results so far, seismicity originates from the reactivation of faults underlying the mining excavations and is influenced by flooding, pumping of the water, and seasonal meteorological conditions. 

We investigate the clustering behavior and multiplet occurrences within the seismic events recorded by the sparse temporary microseismic network between 2014 and 2017. Detailed cluster analyses, the spatio-temporal distribution, recurrence time patterns, and source parameters help to characterize seismically active structure(s) below the mining works. The triggering of the seismic activity in each cluster appears to be differently influenced by the hydro-meteorological conditions, with some clusters being more affected by rainfall, while other by dry period. The variations of the pumping rate strongly affect the rate of seismicity in this area as well. The analysis is complemented by incorporating a new dataset recorded by an enhanced monitoring network during 2019, which allows to follow the evolution of the cluster activity. 
Methane flux changes during irrigation experiment in boreal upland forest soil - lessons for future experiments
Authors: Määttä Tiia , Lohila Annalea , Luoto Miska , Korkiakoski Mika , Penttilä Timo
Published: March 2022

Boreal upland forests are generally considered methane (CH4) sinks due to high methane consumption rates. However, some studies have shown a boreal upland forest soil turning from a CH4 sink to a source after long-term abundant precipitation but the factors affecting this change remain largely unknown. In a simulated rainfall experiment, we investigated soil moisture effects on CH4 flux. We also evaluated the influence of simultaneous soil temperature increase, organic litter addition and root exclusion on CH4 flux.

The study was conducted in a northern boreal upland forest soil (Kenttärova forest in Kittilä, Finland) in summer 2018. Split-plot design was used in the experiment with soil moisture being the main treatment variable and soil warming (T), organic litter addition (A) and organic litter and root exclusion (E) subtreatment variables. The design included two main plots: irrigation (I) and control (C), within which each subtreatment was replicated three times. In  addition to the T, A and E manipulations, plots without additional manipulations (O) were included for the assessment of the effect of only soil moisture increase (n=4). CH4 flux was measured at least once a week using chambers. Soil moisture and temperature were also continuously measured.

Contrary to our expectation, the soil remained a CH4 sink after experimental rainfall increase but irrigation and control sites differed significantly in their CH4 fluxes, indicating a strong decreasing effect of soil moisture on soil CH4 sink. All treatments had lowest CH4 uptake rates in August, possibly as a result of high soil moisture. The IA treatment had the lowest uptake rates possibly due to a reduction in gas diffusion. The IE treatment had contrasting results to all other treatments and showed a positive relationship between uptake rate and soil moisture, but the causes remained unsolved and the results were highly uncertain. T treatment had no effect on uptake likely due to a failure to create soil temperature differences and thus the interactions were not reliably analyzed. Our results suggest that the CH4 flux response to soil moisture may have been more related to changes in CH4 consumption than production. Based on these results, future irrigation experiments should especially assess the combined effect of organic litter addition and soil moisture on soil CH4 sink over multiple years. Improvements in the manipulation methods, experimental design and sensors will also be needed.