DeFord Lecture Series

DeFord Lecture Series Speaker Schedule

The DeFord (Technical Sessions) lecture series has been a requirement and a tradition for all graduate students since the late 1940s. Once the official venue for disseminating DGS graduate student research, the DeFord Lecture series is now the forum for lectures by distinguished visitors and members of our community. Faculty and researchers from the Jackson School have invited prestigious researchers from around the world to present a lecture in this series. This is made possible only through a series of endowments.

The list below shows all the scheduled talks this semester. If you would like to meet with any of the speakers, please contact them or their hosts directly.

DeFord Lecture Series 2021-22 Speaker Schedule

All talks are Thursdays from 4-5PM (CST) and are available to the public through Zoom (Fall 2021 and Spring 2022 will continue to be online):

Recordings of past lectures are available on the Jackson School YouTube channel.

Date Speaker/
Apr 28 Malak Tfaily
University of Arizona, Environmental Science
Disentangling organisms’ metabolic responses and acclimation to environmental gradients through ecometabolomics

Abstract: Advances in different -omics technologies have revolutionized biological research by enabling high-throughput monitoring of biological processes at the molecular level and their responses to environmental perturbation. Metabolomics is a fast-emerging technology in systems biology that aims to profile small compounds within a biological system that are often end products of complex biochemical cascades. Thus, metabolomics can enable discovery of the genetic basis of metabolic variation by linking the genotype to the phenotype. Despite increasing accessibility of multi-omics technologies, integration of multi-omics data in analysis pipelines remains a challenge especially in the environmental field. In addition, there are still many associated bottlenecks to overcome in metabolomics before measurements will be considered robust. In this talk, I will go over current efforts in my lab that builds on ten years of analytical experience to develop comprehensive, open-source, command-line based pipeline for metabolomics data analysis. I will then spend the rest of the lecture describing how such data can help us disentangle organisms’ metabolic responses and acclimation to environmental gradients. This includes our work across three contrasting different ecosystems: the Tropical Rainforest Biome of Biosphere 2 (B2), Saguaro Desert National Park and peatland ecosystems.

Bayani Cardenas
May 2 Tianna Bruno Title: Environmental Injustice and Ecological Memory in the Biophysical Afterlife of Slavery

Abstract: This talk draws together concepts in Black geographies and critical physical geography to examine the linkages between racial and environmental histories in Black environmental justice communities along the U.S. Gulf Coast. Specifically, this talk considers the notion of ecological memory, a natural science concept that refers to how past states or processes influence present or future responses in ecological communities, and its compatibility with threads within Black geographies and Black studies, in particular the afterlife of slavery. The afterlife of slavery refers to the precarity and devaluation of Black life set in motion by chattel slavery. Heeding calls within critical physical geography to take seriously the biophysical and social co-constitution of landscapes, I put forth the concept of the biophysical afterlife of slavery to describe how the precarity and devaluation of Black life has impacted the natural environments in which these Black lives exist. In this talk, I will discuss a framework I have developed that draws together the reconstruction of environmental histories with analyses of the past, present, and future of the biophysical afterlife of slavery: using dendrochronology and trees as archives of the biophysical afterlife of slavery, as well as witnesses to Black life and sense of place in environmentally precarious spaces over time. This research focuses on a case study of Port Arthur, Texas, a historically Black community nestled in what the US Environmental Protection Agency calls “the largest oil refinery network in the world”.

Past lectures
Sep 2 Greg Stock
Yosemite National Park Geologist, National Park Service
Understanding and mitigating rockfall hazards in Yosemite National Park
Abstract:  Rockfalls are a defining feature of the cliffs of Yosemite National Park, with a rockfall occurring every five days on average.  Yosemite is an ideal natural laboratory to study rockfall processes, but it comes at a cost: rockfalls pose considerable hazard to the park’s 4-5 million annual visitors.  Combining traditional field mapping with remote sensing tools such as lidar, structure-from-motion photogrammetry and thermal imaging, this talk will summarize the findings from more than a decade of collaborative rockfall research, ranging from how rockfalls control long-term landscape evolution to the challenge of ensuring visitor safety in one of the world’s most popular parks.
Wade Aubin
Sep 9 Elizabeth Barnes
Colorado State University
Viewing Anthropogenic Change Through an AI Lens
Abstract: Humans are vastly modifying the earth system, with identifiable impacts across the land surface, cryosphere, ocean and atmosphere. Here, we will explore two example applications of how explainable AI (XAI) techniques can help us visualize and quantify these changes over time. Both parts of this talk serve as examples of how viewing our climate through an AI lens has the power to uncover new insights into anthropogenic change – allowing scientists to ask “why?” but now with the power of machine learning.
Geeta Persad
Sep 16 Akhilesh Gupta
India Department of Science and Technology
Climate Research in India: Progress and Vision for 2030Talk abstract and summary Dev Niyogi
Sep 23 Justin Filiberto
Lunar and Planetary Institute
Present Day Volcanism on Venus: Evidence from Oxidation Rate Experiments
Abstract: The surface of Venus is covered with some of the largest volcanoes in our Solar System, including some fresh and unweathered lava flows, based on orbital spectroscopic and radar measurements. However, rocks on Venus are in contact with its hot (~470° C) and caustic (CO2 with S) atmosphere, which should alter these rocks and produce coatings of iron-oxides and sulfates on the rocks surface. These coatings should be observable from orbital measurements. Therefore, unweathered lava flows are thought to be geologically very young. Future missions VERITAS, DAVINCI, and EnVision will fly in the next decade and will image these volcanoes. However, to constrain the age of these unweathered lava flows from current and future data sets, the rate of alteration and how alteration minerals affect orbital measurements are needed. Here I will discuss what is known about igneous petrology of Venusian lava flows and specifically focus on recent alteration experiments that suggest unweathered lava flows are only a few years or up to a decade old.
Chenguang Sun
Sep 30 Jessica Barnes
University of Arizona
Next-generation lunar sample science
Abstract: NASA had the foresight to lock away some material collected during the Apollo missions for future generations. NASA curation stored this material under special storage conditions, and it was unavailable for study by the science community. The premise was to save that material for a time when future generations would have access to analytical techniques beyond those available during the Apollo era. That time is now!
In preparation for future lunar missions anticipated in the 2020s it is important that we maximize the science derived from samples returned by the Apollo Program. Under NASA’s Apollo Next Generation Sample Analysis (ANGSA) program a selection of those specially stored samples is now available for study. Among those samples is Apollo 17 sample 71036. This lunar volcanic rock was stored frozen since its return in 1972. The release of sample 71036 presents a unique opportunity to study volatiles in a basalt that has been frozen and specially preserved since its arrival on Earth and to compare the results with basalts of similar bulk chemistries that have been stored at room temperature. This exceptional suite of basalts offers a chance to unravel the history of volatile loss on the Moon, from the onset of mineral crystallization through vesicle formation, sampling, and subsequent curation.
We are conducting a detailed study of the 3D mineralogy and textures; the major, minor, and volatile element chemistry of phases in the Apollo 17 basalts; and we are determining the exposure and eruption ages of the basalts. The work plan involves a consortium of institutions and coordination of a myriad of analytical techniques. Our goal is not only to better understand the origin and evolution of the Moon but to also address some outstanding questions regarding the long-term storage and handling of extraterrestrial materials.
Chenguang Sun
Oct 7 Marisa Palucis
Dartmouth University
Geomorphic response to climate change in the Arctic: Implications for early Mars
Abstract: Alluvial fans may represent one of the last widespread signs of significant fluvial activity on Mars’ surface. Understanding the climatic conditions during the formation of these features may provide key insights on habitability and climate change on Mars.Numerous studies have used data and theory from terrestrial fans from warm, arid, rainfall-dominated climates to estimate flow discharges, runoff rates, and total water volumes that likely built Martian fans. However, it has been suggested that Martian fans sourced water only from snowmelt, and perhaps under periglacial conditions. Thus, there is a knowledge gap about the dominant processes building fans under periglacial conditions, and importantly for Mars, a lack of understanding about the characteristic flow magnitudes during depositional events.

In this talk I will present results from a field-based terrestrial analog study involving characterization of the sedimentology and geomorphology of a periglacial alluvial fan in the Richardson Mountains, Northwest Territories, Canada. I will (1) qualitatively describe the range of sedimentary processes occurring on a periglacial alluvial fan and compare them to prior observations, (2) report measured flow discharges and runoff rates that occurred during a summer storm event, and (3) show that melt rates suggested for Mars are capable of entraining and transporting appreciable amounts of sediment by fluvial processes.

Tim Goudge
Oct 14 Claire Masteller
Washington University
How rivers remember: the effects of flow history on sediment mobility in gravel-bed rivers
Abstract: Rivers transmit environmental signals across landscapes.  In the wake of a changing climate, predicting river channel response to variations in flow magnitude and flood frequency is of significant importance for floodplain communities and ecosystems. As these environmental perturbations propagate across a drainage basin, it’s important to consider the role of prior flow history in a channel when predicting its future evolution. However, widely used models for fluvial sediment transport currently do not integrate these history effects. This omission represents a fundamental, outstanding knowledge gap in earth surface processes.
In this talk I will focus on the process of bedload sediment transport in gravel-bed rivers, where memory effects are observed over a variety of time-scales.  I will first discuss the origins of memory in gravel bed rivers, using results from a series of laboratory flume experiments.  I will then apply these new insights to a unique, continuous record of coarse sediment transport to quantify the thresholds for memory formation and destruction in a steep mountain stream. I will discuss the development and implementation of a history-dependent function to better describe sediment mobility by accounting for these memory effects.
Joel Johnson
Oct 21 Nandita Basu
University of Waterloo
Water Quality Challenges and Opportunities from the Local to the Global Scale
Abstract: Declining water quality is a growing global issue. As the human population increases, a multitude of factors, from intensive agricultural practices and widespread over-application of commercial fertilizers, to climate change and wildfires threatening our drinking water supplies, to emerging contaminants from rapid urbanization and concentrated livestock operations, threaten our water resources.Multiple new policies have been developed to improve water quality in our lakes and streams; however, water quality remains a persistent problem. In this talk, Nandita Basu will address the nature of water quality challenges, especially focusing on long term legacies of nutrients, and discuss opportunities for addressing some of these challenges through a combination of top-down analysis — using large geospatial datasets to identify watershed functional  traits — and mechanistic modeling, from the reach to the watershed scale. Through this discussion, she will highlight novel approaches for regional- and global-scale solutions to water quality challenges.
Bayani Cardenas
Oct28 Xiaowei Chen
University of Oklahoma
Multi-scale analyses reveals diverse triggering processes during induced earthquake sequences
Abstract: In the past decade, Oklahoma experienced a large-scale earthquake experiment with significant variations of seismicity rates that are strongly correlated with injection rates from wastewater disposal. In response to the increased seismicity rate, the seismic network has been significantly expanded, providing a rich dataset to better understand the earthquake triggering processes during fluid injection. The original view of induced seismicity was simple and straightforward – increase pore pressure reduces effective normal stress, promoting fault failure. However, observations in Oklahoma suggests that triggering processes of induced earthquake sequences can be very complex, and are strongly influenced by fault structure and stress state.In this presentation, I start with large-scale observation of seismicity migration and stress/fault distributions. Multi-scale analysis of seismicity migration allows us to derive hydraulic properties for the Arbuckle group and the crystalline basement. These parameters contributed to large-scale modeling that suggested the importance of poroelastic stress from fluid injection. With detailed analysis of the stress state of seismogenic faults, we find that fault stress state could strongly influence temporal evolution of earthquake sequences. Then, I discuss diverse triggering processes observed during several individual sequences. The Woodward sequence in western Oklahoma suggests that earthquake-to-earthquake triggering drives the fault activation. The Guthrie sequence in central Oklahoma occurred within a complex fault mesh network, and showed evidence of aseismic slip along a normal fault. These detailed observations provide a reference framework for future earthquake rupture simulations within different fault systems, and insights into the triggering processes during fluid-driven natural earthquake sequences.
Peter Flemings
Nov 4 Jacky Austermann
Columbia University, LDEO
How high was last interglacial sea level?Abstract: The Last interglacial (~125ka) was 0.5-1.5 ºC warmer than today, making it an interesting natural experiment for how ice sheets respond to modest warming. In this talk I will first describe past estimates for Last interglacial sea level and corresponding polar ice retreat before presenting our new assessment from sea level data in the Bahamas. I will show our field evidence and describe how we can leverage the spatial extent of the data to constrain the contribution of glacial isostatic adjustment to past sea level. Based on these data, we find that Last Interglacial sea level very unlikely exceeded ~5m, which is below the current estimate from the IPCC. Next, I will present new Last Interglacial sea level data from northwest Europe, and argue that these observations predominantly constrain the contribution from the Antarctic ice sheet during the Last interglacial. Combining both results (from the Bahamas and northwest Europe) allows us to not only produce a new time-varying estimate of Last Interglacial sea level, but also partition this melt between Greenland and the Antarctic ice sheet. I will end by speculating what these new results mean for future sea level rise.
Charles Kerans
Nov 11 Marissa Tremblay
Purdue University
From the Alps to Outer Space: Reconstructing Surface Temperatures Using Cosmogenic Noble Gases Catherine Ross
Nov 18 Kevin Mahan
University of Colorado
Rheological heterogeneity in deep continental crust: Examples from the Rocky Mountains, the Canadian Shield, and the European AlpsAbstract: This presentation will highlight three examples of rheological heterogeneity recorded in exhumed exposures of deep continental crust. The first two are examples where lithological contrasts influenced the rheological behavior of kilometer-scale ductile shear zones, and the third is an example of mechanical heterogeneity in the form of initial fractures that evolved to ductile shear zones. While the examples vary widely in scale and tectonic setting, a common observation is that heterogeneity (lithological and mechanical) and fluid availability (and fluid-rock interaction) played critical roles in promoting active deformation mechanisms and transient ductile and brittle behavior.
The Paleoproterozoic Hell Roaring Creek shear zone is a 3 km wide, steeply dipping amphibolite-facies structure exposed in the northern Madison Range of southwest Montana (~25 km paleodepths). Mineral assemblages and local evidence for metasomatism suggest deformation developed under relatively wet conditions. Stretching lineations within the shear zone have a bimodal geometry, with nearly down-dip orientations in most lithologies but shallowly plunging orientations in the most quartz-rich lithologies. Dextral shear sense indicators are consistently observed on subhorizontal surfaces. Observations within and adjacent to the shear zone suggest that the steep fabric elements are at least partly inherited from an earlier episode of deformation and were enhanced during subsequent shear zone activity. Thus, the shear zone exhibits strain partitioning during transpression due to rheological contrast among lithologies and heterogeneity from inherited structures.
PseudotachylyteThe Paleoproterozoic Cora Lake shear zone in the western Churchill Province of the Canadian Shield is a several km wide zone of granulite- to upper amphibolite-facies mylonite which hosts synkinematic pseudotachylyte (~30-25 km paleodepths). Limited evidence for hydrous fluids suggest relatively dry conditions. The shear zone is localized at a major lithological and terrane boundary, with the pseudotachylyte network centered on the more intensely deformed, finer-grained ultramylonitic core. We conclude that episodic brittle failure during lower-crustal ductile shear was most likely due to local stress amplification from a relatively common type of km-scale lithological heterogeneity.
Fracture systems in otherwise homogeneous granites in the Alps and in meta-gabbronorite dikes in Montana systematically evolved into outcrop-scale ductile shear zones under amphibolite- to eclogite-facies conditions, with strong influences from locally fluxing aqueous fluids. The interpreted shear zone evolution involved (1) initial strain localization by nucleation on pre-existing, or in some cases nearly co-eval, fractures that focused fluid infiltration, (2) grain-size reduction by microfracturing, dislocation creep, and synkinematic metamorphic reactions driven by chemical potential gradients, and (3) a switch to grain-size sensitive granular flow accommodated by fluid-assisted diffusion in ultramylonite.
Phil Orlandini
Dec 2 Steven Davis University of California, Irvine Global and regional drivers of land-use emissionsAbstract: Human uses of land have transformed and fragmented ecosystems, degraded biodiversity, disrupted carbon and nitrogen cycles and added prodigious quantities of greenhouse gases (GHGs) to the atmosphere. However, in contrast to fossil-fuel carbon dioxide (CO2) emissions, trends and drivers of GHG emissions from land use (including both land-use change and agriculture) have not been as comprehensively and systematically assessed. I’ll present recent work my group has done to analyze country-, process-, GHG- and product-specific inventories of global land-use emissions over the last half-century, including uncertainties and decomposition of key demographic, economic, and technical drivers. I’ll then present results of a related analysis of the land-use emissions embodied in international trade and discuss implications for mitigation efforts. Finally, I’ll briefly introduce the Carbon Monitor, an international collaboration hatched during the pandemic to estimate global, country, and U.S. state-level fossil emissions in near real time. Patrick Heimbach, Geeta Persad
Jan 27 Debbie-Ann Gordon-Smith
The University West Indies, at Mona
Investigation of water resources and nutrient biogeochemistry on the island of Jamaica using environmental tracersAbstract: Global water resources have been under severe stress due to various factors including poor management, pollution and changes in rainfall patterns due to climate variability. The small islands of the Caribbean, such as Jamaica, have not been spared; prolonged periods of drought, extreme weather events and increased urbanization have led to water shortages and impaired water quality.
Sustainable management of these natural water resources requires an understanding of the dynamics of their physical behavior and their chemical constituents. Environmental tracers have proven to be very effective tools for studying the transport and mixing of surface and subsurface water on regional and global scales.
This lecture will introduce the audience to the use of stable and radioactive isotopes as tracers in the investigation of the fresh and coastal waters of Jamaica. The talk will describe the analytical techniques used in these isotopic studies, present findings related to the sources, pathways and fate of nutrients and other inorganic contaminants, and suggest implications of these findings for the sustainable management of Jamaica’s water resources.
Rowan Martindale
Feb 3 Scott Jasechko

University of California, Santa Barbara

Global groundwater well water levels and drilling activitiesAbstract: Groundwater resources sustain human livelihoods and ecosystem health, but they are under pressure from overuse. Here we report on a continental-scale and locally relevant database of groundwater well construction reports. We analyze these data to (i) evaluate how groundwater users (i.e., humans) are responding to groundwater depletion in numerous areas around the globe, and (ii) to compare water levels in wells to water levels of nearby streams to map out which rivers may be leaking into the subsurface as they flow downstream. Bayani Cardenas
Feb 10 Mattheos Santamouris

University New South Wales

Urban Overheating, The impact on Energy and Health. State of the art and the potential of mitigation technologiesAbstract: Regional climate change in cities is the most documented phenomenon of climate change. Higher urban temperatures are documented experimentally for more than 450 major cities in the world. Numerous investigations demonstrate that the mean magnitude of the temperature increase may exceed 4-6 C, while at the peak it may exceed 10 C. The serious increase of the frequency and the strength of heat waves creates strong synergies between the global and regional climate change and intensify the magnitude of the overheating.
Urban overheating causes a serious impact both on the energy demand and generation sectors. It increases the cooling energy consumption of buildings, rises the peak electricity demand and obliges utilities to built additional power plants, it affects seriously health issues and in particular heat related mortality and morbidity, impacts the concentration of pollutants and damages the urban environmental quality, and finally deteriorates the levels of local vulnerability and thermal comfort.
To counterbalance the problem of urban overheating, numerous heat mitigation systems and technologies are proposed, and implemented in more than 250 large scale urban projects. Mitigation policies and technologies aim to strength the cooling potential of heat sinks and weaken the intensity of the heat sources. Among the developed mitigation technologies, the use of advanced, materials like the recently developed photonic components and the reflective, cool materials, the implementation of additional greenery in buildings and open spaces, the use of passive evaporative systems involving additional irrigation of urban zones and finally the dissipation of the excess heat into the ground seems to provide the higher mitigation potential.
Although mitigation seems to seriously counterbalance the impacts of urban overheating, there is a need to adapt the built environment to face the present and future climate challenges. Adaptation technologies involving advanced energy and environmental systems for buildings, may minimize the energy needs of buildings and provide indoor comfortable conditions with the minimum energy use.
The present lecture reviews and reports the recent progress and knowledge on the specific impact of current and projected urban overheating in energy, peak electricity demand, air quality, mortality and morbidity and urban vulnerability. In parallel, it discusses new findings related to the characteristics and the magnitude of urban overheating, and reports and analyse the recent knowledge on the synergies between urban heat island and heat waves. Finally, it presents the recent developments in the field of mitigation technologies for buildings and cities and provides inside information on the current and future potential.
Dev Niyogi
Mar 3 Natalie M. Mahowald
Cornell Engineering, Earth & Atmospheric Sciences
Constraining Atmospheric Micro PlasticsAbstract: Plastic pollution is one of the most pressing environmental and social issues of the 21st century. Recent work has highlighted the atmospheric role in transporting human-derived microplastics to remote locations (1, 2). Here we use in situ observations of microplastic deposition combined with an atmospheric transport model and optimal estimation techniques to test hypotheses of the most likely sources of atmospheric plastic. Results suggest that atmospheric microplastics are primarily derived from secondary re-emission sources including road, ocean, and soil sources. However, due to limited observations and understanding of the source processes, there are still large uncertainties in source attribution. In the western USA, the dominant sources of microplastic were from roads (84%), the ocean (11%) and agricultural dust (5%). Using our best estimate of plastic sources and modeled transport pathways, most continents were net importers of plastics from the marine environment, underscoring the cumulative role of legacy pollution in contributing to the atmospheric burden of plastic. This effort is the first to use high resolution spatial and temporal deposition data along with different hypothesized emission sources to constrain atmospheric plastic. Parallel to global biogeochemical cycles, plastics now spiral around the globe with distinct atmospheric, oceanic, cryospheric, and terrestrial lifetimes. Though advancements have been made on the manufacture of biodegradable polymers, our data suggest that the non-biodegradable polymers will continue to cycle through the surface Earth. Because of the limited observations and knowledge, there remain large uncertainties in the sources, transport and deposition of microplastics. Thus, we prioritize future research directions for understanding the plastic cycle. Paper: Geeta Persad
Mar 10 Anita Marshall
University of Florida
Accessible Geoscience Field Experiences
Abstract: Geosciences field work is valued for learning opportunities and research, as well as personal and professional growth for students. But exclusion from these formative learning experiences can negatively influence degree persistence and career prospects for students with disabilities. Based on an evaluation of disability-inclusive field courses, ongoing work designing a fully accessible field program, and personal experience undertaking field research with a physical disability, this presentation will explore ways to create field programs that support all students and best practices for building supportive learning communities in the field.
Julia Clarke
Mar 31 Christopher Bell
University of Texas at Austin
Austin’s Zero-Waste Initiative: Getting it Right with the Blue and Green Bins
Abstract: In 2011 The City of Austin adopted a master plan for materials (formerly ‘waste’) management and established goals for the diversion of materials from landfill and incineration.  Austin’s zero-waste initiative is an ambitious goal but requires effective participation by the residents of (and visitors to) the city.  A Universal Recycling Ordinance was adopted in a step-wise fashion for residential and food services properties across the city and is now in full effect.  The city uses three collecting bins to organize materials for trash, recycling, and composting.  Many residents, including many students on the UT campus are unfamiliar with what should and should not be placed in the various bins and why, and contamination can be a serious problem.  I will discuss the difference between what is conceptually recyclable, what is recyclable in Austin, and what should go in the blue and green bins.  Many of the materials in our ‘waste’ stream are valuable Earth resources, and are readily captured and sorted by semi-automated systems at a Material Recovery Facility (MRF).  Others are not readily captured, and require special handling.  Knowing the difference makes a difference!!  An active investigation of the trash and recycling bins of JGB will help illustrate the point.
John Lassiter
Apr 7 Julia Clarke
University of Texas at Austin
Shape, Size, and Sound: Inference of Extinct Dinosaur Vocalization John Lassiter
Apr 14 Ryan Smith
University of Missouri S&T

Sensing Groundwater from a Distance: Harnessing Satellite and Ground-based Geophysics to Model Hydrogeologic Fluxes and Their Impact on Natural and Human Systems

Climate change, population growth and land use change are increasing the scarcity of surface water supplies and driving greater demand for groundwater resources. This trend has led to the ongoing depletion of many of the world’s aquifers. While many have observed regional groundwater depletion, the processes driving this depletion, and its effect on aquifer dynamics, are poorly understood. One major barrier to improving understanding of these processes is a lack of data at appropriate resolution and scale. The booming satellite industry is providing petabytes of earth observational data that have the potential to answer many of these scale- and resolution- dependent questions, but relating these disparate datasets to hydrogeologic systems requires an improved fundamental understanding of the system properties linking aquifer processes to land surface dynamics. For example, Interferometric Synthetic Aperture Radar (InSAR) can be used to estimate earth deformation with cm- to mm- accuracy, but the mechanisms linking aquifer dynamics to ground deformation are complex, non-linear and vary with time. Evapotranspirative flux, a major component of groundwater use, can be modeled with thermal satellite imagery, but these models alone often do not adequately explain groundwater demand, indicating complex inter-relationships between evapotranspiration, precipitation, infiltration, groundwater use and surface water use. In this talk, I will discuss several ongoing projects that seek to address these challenges, including both process-based and data-driven models that integrate in-situ data, as well as ground-based and satellite geophysics to identify key, scale-dependent drivers of groundwater flux, explore how temporally varying hydrologic parameters can alter aquifer dynamics, and link groundwater over-use to impacts on water quality.

Ann Chen
Apr 21 Jesus Gomez-Velez
Vanderbilt University
Where does all the plastic go?

Abstract: Plastic pollution threatens the health of humans and aquatic and terrestrial ecosystems globally. Proposing coping strategies and solutions to this threat requires a clear understanding of the processes controlling the fate and transport of mismanaged plastics at multiple scales, going from watersheds to regions and even continents. River corridors are the primary conveyors and traps for mismanaged plastic produced within the landscape and eventually released into the ocean. During this talk, I explore the primary sources of plastic pollution globally and present the results of a new flow and transport model for plastic waste in riverine environments. We found that only a fraction of the mismanaged plastic entering rivers since the 1950s (roughly 0.25%) will be delivered to the ocean by 2100, with most of the plastic being sequestered in freshwater ecosystems. The patterns of plastic accumulation and its residence time are strongly controlled by the (i) topology and geometry of the river network and (ii) the relative location and trapping efficiency of flow regulation structures, primarily large dams. Our modeling results highlight the role of rivers as major sinks for plastic waste and the need for targeted remedial strategies that consider the river network structure and anthropogenic regulation when proposing intervention measures and sampling efforts to optimize the gains and set realistic expectations.

Bayani Cardenas