Keynote Speakers

Dr. Vicenç Acuña, Catalan Institute for Water Research, Spain; Personal web page

Keynote: Session 12 : Intermittent streams and rivers

"Temporary streams in the 21st century - current scientific and management challenges"

Temporary streams and rivers support biodiversity and provide valuable goods and services, especially in arid and semi-arid landscapes. However, temporary streams and rivers are being degraded at alarming rates owing to development, hydromorphological alteration, and disposal of wastewater, among other stressors, and pressure will likely increase under global change. Within this context, it is key to manage temporary streams and rivers as a singular ecohydrological type and not as a permanent waterway or a terrestrial ecosystem. Nevertheless, two challenges hinder this overarching goal. First, data sets on flow intermittency and associated biotas are currently very scarce. As a consequence, flow-ecology relationships in temporary waterway networks are largely unknown, and appropriate metrics to define and monitor their ecological status are missing. Second, the ecological and social values of temporary streams and rivers are often widely underestimated, being regarded as secondary ecosystems relative to permanent-river main stems. To conserve temporary streams and rivers, ecologists must demonstrate the need to define them as unique ecosystems and conservation targets, and managers can contribute to this by systematically collecting biological and hydrological data. Additionally, innovative approaches at the intersection of ecology, citizen science, and management, can help to: map them (inventory); inform people about their ecological values by invoking the ecosystem services paradigm (educate); safeguard them from further human threats (protect); preserve their flow regime when managing reservoirs, wastewater treatment plants, and water abstraction activities (sustainably manage); and restore temporary reaches that may have been physically degraded (e.g. due to gravel mining and off-road use) or which have lost historical flows due to increasing droughts and overuse of water (restore).

Dr. Fabien Arnaud, EDYTEM, Chambéry, France; Personal web page

Keynote: Session 4: Temporal variability of CZ processes using high-resolution bio- and geoarchives

"Retro-observation of Earth Critical Zone Dynamics from Lake Sediment records"

The Earth Critical Zone (ECZ) is the active uppermost Earth layer in which occur matter and energy transfers that sustain life on our planet. In order to guaranty a satisfying functioning of the ECZ, it is of prime importance to understand how natural and anthropogenic factors influence the tight interrelations between all its compartments. In that aim, Humanity deployed an array of sensors that ongoing environmental changes, amongst which Long-Term Ecological Research infrastructures network is the most developed and structured example. However, environmental changes are affecting systems whom state was inherited from several centuries or millennia, i.e. much beyond the possibility of direct observation.

Pr. Dr. Friedhelm von Blanckenburg, GFZ German Research Centre for Geosciences, Potsdam, Germany Personal web site

Keynote: Session 16 : Mineral/biota interaction of the CZ

 "Uplifted, recycled, eroded. Budgeting the plant mineral nutrient balance by element fluxes and metal isotopes"

Dr. Bertrand Bonan, Centre National de Recherches Météorologiques (CNRM), Toulouse, France Personal web page

Keynote: Session 14 : Model data fusion : improving model predictionand process understandingntermittent streams and rivers

"Data Assimilation for Continuous Assessment of Severe Conditions Over Terrestrial Surfaces"

Monitoring accurately the evolution of land surface variables (LSVs) such as soil moisture, biomass or leaf area index (LAI) is critical for various applications such as weather predictions, climate change or agricultural practices. Powerful instruments in that context are Land Data Assimilation Systems (LDASs) as they combine information from numerical simulations from Land Surface Models (LSMs) and satellite observations using data assimilation. One of them is LDAS-Monde, the offline LDAS developed by Météo-France'sresearch centre (CNRM). LDAS-Monde is a global offline land data assimilation system (LDAS) that jointly assimilates satellite-derived observations of surface soil moisture (SSM) and leaf area index (LAI) into the ISBA (Interaction between Soil Biosphere and Atmosphere) land surface model (LSM).

This study demonstrates that LDAS-Monde is able to detect, monitor and forecast the impact of extreme weather on land surface states. Firstly, LDAS-Monde is run globally at 0.25∘ spatial resolution over 2010–2018. It is forced by the state-of-the-art ERA5 reanalysis (LDAS_ERA5) from the European Centre for Medium Range Weather Forecasts (ECMWF). The behaviour of the assimilation system is evaluated by comparing the analysis with the assimilated observations. Then the land surface variables (LSVs) are validated with independent satellite and in situ datasets Secondly, the global analysis is used to (i) detect regions exposed to extreme weather such as droughts and heatwave events and (ii) address specific monitoring and forecasting requirements of LSVs for those regions. This is performed by computing anomalies of the land surface states. They display strong negative values for LAI and SSM in 2018 for two regions: north-western Europe and the Murray–Darling basin in south-eastern Australia. For those regions, LDAS-Monde is forced with the ECMWF Integrated Forecasting System (IFS) high-resolution operational analysis (LDAS_HRES, 0.10∘ spatial resolution) over 2017–2018. Monitoring capacities are studied by comparing open-loop and analysis experiments, again against the assimilated observations. Forecasting abilities are assessed by initializing 4 and 8 d LDAS_HRES forecasts of the LSVs with the LDAS_HRES assimilation run compared to the open-loop experiment. The positive impact of initialization from an analysis in forecast mode is particularly visible for LAI that evolves at a slower pace than SSM and is more sensitive to initial conditions than to atmospheric forcing, even at an 8 d lead time. This highlights the impact of initial conditions on LSV forecasts and the value of jointly analysing soil moisture and vegetation states.

Pr. Phillip Brunner, Laboratory of Hydrogeological Processes, Centre for Hydrogeology and Geothermics, (CHYN), University of Neuchatel (Unine), Switzerland Personal web page

Keynote: Session 9 : Surface - groundwater interactions

"And what should we measure today? New approaches for observing and simulating surface water groundwater interactions."

It is an exciting time to be involved in studying surface water groundwater interactions. Recent developments in computational power now allow for the application of fully-coupled, physically based models to simulate surface water groundwater interactions. Moreover, in a parallel development, new field approaches can provide the observation data required to parametrize and calibrate these complex models. In this presentation, the development and integration of innovative and novel field methods in these modeling approaches is illustrated with several examples. Approaches to identify the most valuable observations are illustrated. Open questions and future research directions in modeling surface and subsurface flow processes in a holistic way are discussed.

Dr. Philippe Ciais, Laboratoire des Sciences du Climat et de l'Environnement (LSCE-IPSL), Gif-sur-Yvette, France Personal web page

Keynote: Session 10 : Earth systems models: water and carbon cycle

"Detection and attribution of water stress on plant photosynthesis"

Low soil water content and high atmospheric dryness, estimated from water vapor pressure deficit (VPD) both negatively affect terrestrial photosynthesis (GPP). The sensitivity of GPP to soil versus atmospheric dryness is difficult to disentangle, however, because of their strong covariation. I will present the results of a machine learning approach to GPP data derived from eddy-covariancemeasurements collected in a global network and a dense European network capturing the extreme drought of 2018[MOU3] , showing that a decrease in soil moisture is not universally associated with a reduction of GPP. Instead, GPP increases in response to decreasing moisture when soils are not dry. By contrast, the sensitivity of GPP to an increase of VPD is always negative across the full range of SWC variations. This is explained by a negative sensitivity of canopy conductance to increasing VPD (irrespective of soil moisture), consistent with stomatal closure responses documented at leaf scale. On the other hand, maximum carboxylation rates showed a more negative sensitivity to VPD when the atmosphere is humid, and a positive sensitivity to decreasing SWC when SWC is high. The second part of the presentation will focus on the detection of critical soil moisture thresholds of the appearance of plant water stress and land surface energy partitioning, to characterize the impact of drought and improve models for predicting future ecosystem condition and climate. Quantifying the these thresholds across biomes and climates is challenging because surface energy fluxes remain largely unobserved. Here, we used the latest database of eddy covariance measurements from the ICOS European network to estimate those thresholds across Europe by evaluating turning points in evaporative fraction. Prospects for estimating them using satellite observations will be addressed.

Pr. William E. Dietrich, University of California Berkeley (Earth Science Department), USA Personal web page

 Keynote: Session 15 : Rates and processes of the CZ formation

 "Controls on critical zone formation: lateral, top-down, and bottom-up."

 We are in the pioneering phase of discovering what the critical zone looks like and what processes predictably explain what we find. Many researchers have begun by focusing on upland landscapes of hills and valleys, taking what can be called a “unit hillslope” approach. This is rational, as watersheds are simply a collection of repeating hillslopes bordered by channels, and research on a single (or a few) individual (unit) hillslope is necessitated by the observational challenge of fully characterizing the subsurface architecture and documenting processes driving critical zone evolution. Theory is needed to generalize out from unit hillslopes findings to entire landscapes. Several theories have been proposed that make testable predictions regarding the structure under a hill of the transition from weathered, fractured bedrock to the underlying fresh bedrock. This transition in essence defines a bottom of the critical zone, i.e. the depth below the ground-surface in which fresh bedrock undergoes change as it enters the near- surface environment. These theories are not competing, rather in many ways are additive components of an inclusive general theory for controls on subsurface critical zone evolution. In a hill, stresses may arise in compressive (lateral) tectonic regimes that drive fracture opening to considerable depth, with the greatest depth under the hill crest. Hills may also be subject to penetrative freeze-thaw fracture. Infiltrating waters into fresh bedrock will react chemically and drive a downward propagating reactive front. The lower bound of this top-down process may be set by completion of reaction exchanges of the infiltrating water. If still reactive waters recharge a groundwater that laterally drains, then lateral chemical erosion processes will contribute to advancing the weathering front. A constraint on chemical evolution is the necessity for water contained within the fresh bedrock to be drained. Such drainage is induced by head gradients caused by the river incision at the base of the hillslope. This need for drainage effectively creates a “bottom-up” control on height of the fresh bedrock (critical zone bottom) beneath a hillslope. In all models, prediction of the depth to fresh bedrock under hillslopes also requires models for surface erosion and soil depth development. Here I describe four intensively-monitored unit hillslopes underlain by turbidite sequences (variably-deformed) developed in the summer dry coastal mountains of Oregon and California (Eel River CZO) (annual rain 534 to 2000 mm), in areas of uplift and channel incision of about 100 to 400 m/my. The extreme bottom-up case was found in the bedrock underlain by mélange, which effectively is churned mud with exceptionally low saturated conductivity. Fresh saturated bedrock lies within meters of the ground surface, and water drainage of the fresh bedrock may be driven primarily by transpiration uptake. In the other three cases the elevation of fresh bedrock above the channel progressively increases toward the hillslope divide in a manner consistent with a bottom-up theory. Reactive transport modeling is underway. In field studies major challenges include legacy effects of past climate, varying tectonic regimes and geomorphic evolution, and the quantification of process rates.

Dr. Thierry Lebel, Institut des géosciences de l'environnement de Grenoble (IGE), IRD, France

Keynote: Session 17 : Challenges in understanding CZ processes in Africa

 "Global change and the water cycle in the intertropical zone: scientific challenges and societal stakes"

Droughts and inundations are permanent threats for the populations of tropical regions, who are consequently extremely vulnerable to any rainfall regime change that may reinforce either one or both of these climatic perils. While temperatures in the tropics are displaying a much lower interannual variability than in mid-latitude regions, tropical rainfall is, at the opposite, characterized by a strong interannual and decadal variability. The poorest are those who are the most affected, by this unreliable rainfall and the big Sahelian drought of the 1970s-1980s generated massive displacement of populations across the region, some having never returned to their living place even though their living conditions in urban surroundings is often very difficult. Global change is likely to reinforce this vulnerability. For one the atmospheric warming is expected to intensify the water cycle, meaning persisting droughts coexisting with more intense rainfall associated with convective events, and thus an increased probability of damaging floods. In parallel, land use and land cover changes, whether induced by human practices or resulting from rainfall regime modifications also have a strong effect on the continental water cycle over a range of scales, from local (increased runoff coefficients due to more intense rain falling on degraded soils) to regional (land-surface feedbacks onto the regional climate dynamics).

In this presentation we will discuss and illustrate how the water cycle is interlinked with regional climate dynamics in the tropics, and what are the scientific challenges faced by researchers when trying to better understand these linkages in order to be able to anticipate changes to come in response to global warming. We will also present results about what seems to be the first manifestation of global warming in terms of hydro-climatic intensification and the deriving societal stakes.

Pr. Majken C. Looms Zibar, University of Copenhaguen, Dept of Geoscience and Natural Resource Management, Danemark Personal web page

Keynote: Session 11 : Hydrogeophysics (incl. ITN "ENIGMA")

"Delineating transport pathways in low permeable media using crosshole ground penetrating radar"

Dr. Michaël Mirtl, UFZ Leipzig, Umweltbundesamt Vienna Personal web page

Keynote: Session 2 : Long-term environmental and biodiversity observation - understanding of the Earth system in the Anthropocene

"Putting a Whole System Approach into practice – Implications for Standard Observations, network and site operations"

Dr. Nicola Montaldo, University of Cagliari, Italy Personal web page

Keynote: Session 3 : Integration of in-situ and remote sensing data for a better integration of the soil - vegetation - atmosphere and Earth system dynamics and services at the regional scale

"Data assimilation of remote sensing observations for soil water balance and vegetation growth predictions in heterogenous ecosystems under water-limited conditions"

Mediterranean basins under water-limited conditions are typically characterized by a rugged topography and a high spatial variability of physiographic properties. Tree cover, and its spatial patterns, are variable, producing the tree-grass mosaic on the landscape. For properly representing the land surface interactions in these ecosystems, there is the need of coupling ecohydrological modelling with advanced field and remote sensing observations at high spatial and temporal resolutions.

Land surface models (LSMs) have been developed to simulate mass and energy transfers between the land and atmosphere, and to evolve the soil moisture and thermal states through time from the integration of mass and energy balance equations. LSMs have been coupled with vegetation dynamic models (VDM) for modeling the dynamic interactions between land surface processes and vegetation (e.g., leaf area index, LAI).

Data assimilation techniques guide ecohydrological models with periodic observations of certain state variables with the observations coming from remote sensing platforms. In fact, recent efforts are leading to improvements in the mapping of key ecohydrological variables, like the soil moisture and LAI, from remote sensors.

The new constellation of synthetic aperture radar satellite, Sentinel-1, provides images at a high spatial resolution (up to 10 m) typical of radar sensors, but also at high time resolutions (6-12 revisit days), representing a major advance for the development of operational soil moisture mapping of heterogenous ecosystems. Vegetation cover attenuate radar signal, and its contribution needs to be accurately considered. A simplified approach for estimating a key parameter of retrieval methods, the surface roughness, from the normalized difference vegetation index (NDVI) derived by simultaneous Sentinel 2 optical observations is proposed.

At the same time, LAI mapping can be derived from observations of optical remote sensors operating in the visible and infrared bands, for estimating vegetation indexes, like the normalized difference vegetation index (NDVI), strictly related to LAI. Nowadays, a wide variety of optical remote sensors are available, with the Landsat 8 and Sentinel 2 being very attractive for heterogenous ecosystems thanks to their high spatial (10- 30 m), and time (7 days) resolutions.

In an heterogeneous Mediterranean ecosystem in Sardinia, characterized by wild olives and grass, an eddy-covariance – based tower is operating from 2003, and extended field measurements (soil moisture, LAI, etc.) have been performed. The coupled LSM-VDM has been applied at the field site, and data assimilation approaches based on the Ensemble Kalman filter (EnKF) have been developed, assimilating both Sentinel 1 observations for soil moisture estimate and NDVI observations from optical data for LAI predictions. This approach, as with other common data assimilation approaches, may fail when a key model parameter, e.g. the saturated hydraulic conductivity for soil moisture predictions, is estimated poorly. For overcoming this model bias an innovative multiscale assimilation system is developed, which accepts this violation in the early model run-times and dynamically calibrates the model parameter ensemble as a function of the persistent bias in the model, allowing to remove the model bias, restore the fidelity to the EnKF requirements and reduce the model uncertainty.

Dr. Estela Nadal Romero, CSIC Zaragoza Instituto Pirenaico de Ecologia, Spain Personal web page

Keynote: Session 8 : Monitoring and modelling water and solid transport during extreme events

"Monitoring and modelling water and solid transport during extreme events in Mediterranean mountain areas"

Dr. Antonello Provenzale, NRCI, Pisa, Italy Personal web page

Keynote: Session 13 :Mountain CZ and sustainability in a changing world

"Critical Zone and Ecosystem Observatories in mountain environments: laboratories for unravelling geosphere-biosphere interactions"

Geosphere-biosphere interactions dominate the functioning of our planet, and can be observed in any location on Earth. On the other hand, critical and extreme environments offer the opportunity for unravelling some of the essential aspects of such couplings (e.g., the role of ecosystem engineers, niche construction, biogeochemical cycling), owing to the difficult and harsh conditions that put severe constraints on organisms and communities and make the interactions more visible. For this reason, in 2016 we started establishing Critical Zone and Ecosystem observatories in a few critical mountain sites such as the high Nivolet plain in the Gran Paradiso National Park in Italy (2700 m a.m.s.l), the Bayelva catchment in Spitzbergen, Norway (78° N), and the area of Mt. Etna in Sicily, Italy. Future efforts will focus on another high-altitude location in the area of Monte Rosa, Italy, on the arid environment of Pianosa Island and on severely burned Mediterranean environments, and possibly on Antarctica. Here, we discuss in some detail the research ongoing in the environment of Col Nivolet in the Gran Paradiso National Park (GPNP). This area, covered with snow from November to June, is characterized by a complex environment of alpine pastures, oligotrophic lakes, peat bogs, rock outcrops and meandering streams, and it is the habitat of ibex, chamois, eagles and marmots. Domestic ungulates (cattle, sheep, goats) are brought up during the short summer. The geological substrate includes areas with gneiss, carbonates, glacial deposits and alluvial soil. Ongoing measurements include water and carbon fluxes using both portable and fixed flux chambers and Eddy Covariance installations, soil and water physical-chemical characteristics, stream discharge, vegetation characteristics and invertebrate biodiversity. Two weather stations provide daily records of temperature, precipitation and snow cover since more than 50 years. One added value of this high-altitude observatory is the possibility of comparing the dynamics of Alpine tundra CZ with the similar measurements we perform in Spitzbergen. Here, we discuss a simple empirical, data-driven model of carbon exchanges, able to identify the main drivers of carbon fluxes in the Alpine tundra. A general discussion on modelling CZ dynamics in critical environments, along the notion of Digital Twins, will conclude the presentation.

Pr. Daniella Rempe, Jackson School of Geosciences (Department of Geological Sciences), University of Texas at Austin, USA Persoal web page

Keynote: Session 5 : Measuring and modelling water storage dynamics

"The bedrock component of watershed storage: Advances and insights"

Dynamic water storage in the critical zone plays a central, but highly uncertain role, in determining how watersheds respond to change. Soil and groundwater hydraulics underpin the model frameworks used to predict watershed storage. However, across much of Earth's terrestrial surface, soils form only a thin mantle over meters of variably saturated bedrock, and overlying plant ecosystems can extend their roots into the pores and fractures of this bedrock. Relative to soils and groundwater, unsaturated water storage in bedrock is poorly characterized. Recent advances in monitoring the spatiotemporal hydrologic dynamics of bedrock are revealing how bedrock water storage mediates watershed fluxes. Geophysical techniques across a variety of spatial scales including nuclear magnetic resonance, neutron logging, superconducting gravity, flexible time-domain transmission sensing and ambient noise seismology are being used in a watershed mass balance framework to directly quantify the bedrock component of watershed storage. These direct measurements indicate that bedrock water storage (1) substantially contributes to transpiration fluxes across a range of rock types, biomes and climates (2) plays an important, but variable role in regulating the timing and volume of groundwater recharge and streamflow and (3) may require explicit treatment in distributed hydrologic models. While bedrock may have once been considered a last-resort water source for plants, new studies indicate that bedrock is accessed by plants both within and outside of drought periods. Together, these findings have consequences for how we conceptualize a wide array of critical zone processes.

Dr. Markus Reichstein, Max Planck Institute of Biogeochemistry (BGC), Jena, Germany Personal web page

Keynote: Session 6 : Biogeochemical processes at the soil and catchment scale

For a better understanding of the Earth system we need a stronger integration of observations and (mechanistic) models. Classical model-data integration approaches start with a model structure and try to estimate states or parameters via data assimilation and inverse modelling, respectively. Sometimes, several model structures are employed and evaluated, e.g. in Bayesian model averaging, but still parametric model structures are assumed which is avoided with  Recently, Reichstein et al. (2019) proposed a fusion of machine learning and mechanistic modelling approaches into so-called hybrid modelling. Ideally, this combines scientific consistency with the versatility of data driven approaches and is expected to allow for better predictions and better understanding of the system, e.g. by inferring unobserved variables. In this talk I will introduce this concept and illustrate its promise with examples on carbon and water cycles from the ecosystem to the global scale.

Pr. Hans-Jörg Vogel, UFZ, Germany Personal web page

Keynote: Session 1 : Innovative sensing methods for the Critical Zone

"The Legacy of Henry Lin and the future of Hydropedology"

In this presentation we build upon the original idea of hydropedology as an interdisciplinary approach in soil science. It is based on the fact that at a wide range of spatial scales, pedological processes are shaping subsurface structures that are of critical importance for water dynamics within soil and terrestrial systems, while, at the same time, water dynamics is shaping pedogenetic processes significantly through transport of solutes and solid materials. The concept of hydropedology was considerably inspired by the work and spirit of Henry Lin who made substantial contributions to improve the understanding and modelling of hydrological processes at different spatial scales from the local soil profile to the landscape. This was accompanied by his passionate appeal for systems thinking and his firm conviction that the classical concepts were not sufficient to adequately represent water dynamics in soils.

This is a formidable research challenge until today. With climate change, the research field of hydropedology will gain additional momentum since water shortage will become a highly critical issue for agriculture and the functioning of terrestrial ecosystems. This is true also in many regions that have rarely suffered from water shortages since. We will discuss possible avenues how to improve classical concepts for modelling water movement in soil by including soil structural characteristics at the scale of soil profiles and how to leverage our pedological knowledge to better parameterize the subsurface at the scale of landscapes for the sake of hydrologic modeling.

Dr. Christoph Wohner, Umweltbundesamt GmbH, Austria Personal web page

Keynote: Session 7 : Management and integration of environmental observation sites

"Conceptualising and designing a pan-European environmental data infrastructure using the example of the eLTER Research Infrastructure"

 One of the major goals of the European Long-Term Ecological Research (eLTER) and the upcoming eLTER Research Infrastructure (eLTER RI) is to provide reliable and quality-controlled long-term data for scientific analysis as well as the assessment of environmental policy impacts. For this purpose, eLTER has designed, implemented and operates a federated data infrastructure called the eLTER Information System. This e-infrastructure offers data stored in existing partner data systems, harmonised by a central discovery portal and federated data access components providing a common information management infrastructure for making environmental data available from distributed resources provided by the contributing LTER national networks.