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Fall 2015 Colloquia Schedule

August 24: First day of term, no colloquium

August 31: Adam Ward, IU School of Public and Environmental Affairs. Title: Advancing the use of electrical geophysical techniques to characterize hyporheic and riparian transport.

Abstract: Stream solute tracers are a popular tool to quantify exchanges of water and solutes between the advection-dominated main channel and locations of temporary (commonly "transient") storage, such as hyporheic and riparian zones, which are ecologically important. Commonly, in-stream tracer time-series are interpreted with numerical models using assumed residence time distributions for the subsurface because the true distribution cannot be measured (the "Black Box"). Here, I demonstrate the use of time-series analysis on geophysical images of hyporheic solute transport to quantify transport along these subsurface flow paths and interpret dominant transport processes in the subsurface. The hyporheic transit time distribution is quantified in-situ, and used to parameterize a numerical model of solute transport and hyporheic exchange. A best-fit is determined by adjusting the maximum observed residence time to consider. In this way, we develop a threshold to differentiate locations in the subsurface that contributed to the in-stream breakthrough curve from those that were beyond the detection limits of the stream tracer alone, demonstrating the extent of transport (and therefore associated ecological function) that is not observed by in-stream tracers alone. In this study, I show that about 80% of hyporheic flowpaths are omitted if only considering the in-stream tracer, a result that has important implications for interpretations of biogeochemical processes (e.g., nutrient spiraling) at the scale of stream reaches. Finally, I map the flowpaths that are observed by the in-stream tracer to visualize the physical extent of the hyporheic zone that is traditionally measured using stream tracers alone, and contrast that domain to the full hyporheic extent. For the first time, the window of detection (a temporal limitation of tracer studies) is mapped onto a spatial domain. The under-sampling of slower hyporheic flowpaths has significant implications for estimates of ecosystem function that are based on stream solute tracer experiments and simulations.

September 7: Labor Day, no colloquium

September 14: Alan Fryar, University of Kentucky. Title: From Bourbon to Bacteria: Some Uses and Abuses of Kentucky Karst Springs.

Abstract: Karst landscapes form on relatively soluble rocks, particularly limestone, and are marked by integration of surface and subsurface drainage through features such as sinkholes, sinking streams, conduits, caves, and springs. Karst occupies ˜15% of the area of the contiguous USA and ˜38 to 55% of Kentucky. Because karstified limestone is heterogeneous, subsurface flow paths can be localized, spatially variable, and difficult to delineate. Karst groundwater (spring) basins do not necessarily coincide with surface watersheds. Because flow-path apertures can be relatively large (on the order of meters), groundwater velocities can be relatively rapid (on the order of 100 m/hr), and filtration of particulate contaminants, such as sediment and microbes, is limited. Therefore, karst aquifers are vulnerable to non-point-source pollution from runoff.

In Kentucky, many communities in karst terrain formed around springs, which provided water for various purposes, including drinking, milling, and cooling. This talk reviews the role of karst springs in the origin of bourbon, Kentucky’s native spirit, and provides a case study of sediment and bacteria movement through two spring basins, one primarily urban, the other agricultural. Sediment fluxes from the springs vary with sediment availability over seasonal or longer time scales. Bacterial indicators suggest that leakage from sanitary sewers augments baseflow for the urban spring. Differences in water-quality parameters between the springs appear to reflect differences in land use, basin size, conduit architecture, and spring modification (impoundment).

September 21: Jeremy Fein University of Notre Dame Department of Civil and Environmental Engineering and Earth Sciences. Title: Using Thermodynamics to Quantify Metal Adsorption and Bioavailability to Bacteria in Geologic Systems

Abstract: Determining the controls on metal bioavailability is crucial in order to understand the geomicrobiology of geologic systems with high metal concentrations, such as acid mine systems or contaminated soils, and in order to optimize bioremediation strategies aimed at remediating those types of systems. In addition, the controls on the rates of several environmentally significant metabolic processes, such as mercury methylation or bacterial reduction/oxidation of metals, are poorly understood. The key to improved models of all of these geomicrobiological processes is the ability to quantitatively model bacterial metal bioavailability. Metal adsorption onto bacterial cell walls represents the first interaction of a metal with the cell, and for this reason we hypothesize that accessibility of the metal to the cell is directly related to, and can be predicted by, cell wall metal speciation.

In the research that will be discussed, we test the hypothesis that bacterial surface speciation and concentration of heavy metals controls the bioavailability of those metals. Previous models of metal bioavailability (e.g., the Biotic Ligand Model) characterize metal binding onto a wide range of organisms using a generic, unspecified metal-binding biotic ligand that does not account for the many complexities of metal adsorption reactions onto biological surfaces. These models often fail because of these overlooked complexities in adsorption reactions. Over the past 15 years, we have learned much about the mechanisms involved in metal binding onto bacterial cell walls, and have developed quantitative surface complexation models based primarily on x-ray absorption spectroscopy and bulk adsorption measurements.

In this presentation, I will review my group’s work to improve surface complexation models of bacterial metal binding, and to use those models to quantify the controls on the bioavailability of aqueous metals to bacteria. We have shown that bacterial chemotactic response and the enzymatic reduction of U(VI) are two examples of adsorption-controlled processes. The extent and rate of both of these processes can be directly related to the concentration of metal adsorbed onto the bacterial cell wall. Therefore, improving the sophistication and accuracy of surface complexation models of metal adsorption onto bacteria will lead to improved quantitative models of bacterial processes in realistic complex systems.

September 28: No Colloquium.

October 5: Jennifer Druhan, Department of Geology, University of Illinois. Title: Reactive transport approaches to unraveling biogeochemical processes in groundwater systems

Abstract: Water is a basic necessity for life, and exerts a primary control on virtually all geological, chemical and biological processes occurring at or near the Earth’s surface. Because these water-rock-life interactions take place at interfaces, both fluid composition and the physical and chemical structure of porous media must be treated as coevolving phenomena. Such complex and interrelated processes can hinder both interpretation and prediction of key environmental processes. One avenue of addressing this complexity is the use of multicomponent numerical methods that combine the governing equations of flow, transport and reactivity. In this presentation I will demonstrate the construction and application of multi-component reactive transport models to address key hydrogeochemical problems, with an emphasis on the balance between simulations of complex reactivity versus highly heterogeneous hydrologic conditions. Examples include stable isotope fractionations during microbially-mediated redox cycling and reactivity in highly resolved permeability structures. The goal is to demonstrate how simulations can be used to interrogate complex field data and thus provide new insights into the processes governing hydrogeochemical systems.

October 12: Patrick O’Connor, Department of Biomedical Sciences Ohio University. Title: Cretaceous Terrestrial Vertebrates from Afro-Madagascar: New Perspectives on Birds and Crocodiles from the Age of Dinosaurs

Dr. O’Connor is a professor of Vertebrate Paleontology and Evolutionary Morphology in the Department of Biomedical Sciences (http://www.oucom.ohiou.edu/dbms-oconnor/) and serves to direct and collaborate on a number of paleontological and geological field projects focused on exploring for Cretaceous terrestrial and freshwater vertebrates from former southern (Gondwanan) landmasses. His current projects include exploratory efforts in Middle Cretaceous deposits in Tanzania, Campanian-Maastrichtian units in Egypt, the terminal Cretaceous of Madagascar, and Campanian-Paleocene rocks exposed in the James Ross Basin adjacent to the tip of Antarctic Peninsula.

Abstract: The Cretaceous terrestrial vertebrate record from Gondwanan landmasses has improved dramatically over the past two decades. Nonetheless, large gaps in our knowledge remain with present day Afro-Arabia among the most limited in terms of characterizing faunal diversity during the last stage of the Mesozoic. For example, whereas circum-Saharan Africa preserves Cretaceous sequences with vertebrates derived from both marine and continental facies, the southern half of the continent preserves very little in terms of backboned animals during this time. Indeed, much of southern Africa existed as a stable land surface with only minimal development of accommodation space during the Cretaceous, resulting in a relatively limited number of continental deposits and any associated fossils. Thus, any new information from this region will have an immediate impact for evaluating paleobiogeographic models, not to mention providing baseline data for conducting faunal comparisons with other parts of the continent and other regions of Gondwana. By contrast, terminal Cretaceous (Maastrichtian) deposits and an exquisitely preserved vertebrate fauna from the Mahajanga Basin in northwestern Madagascar have received significant attention over the past two decades. Yet the regional context of this new fauna has remained elusive due to the temporally-heterogenerous nature of faunas from nearby landmasses.

In an attempt to address one of the most notable geographic sampling biases in Gondwana, expeditions to the Rukwa Rift Basin in southwestern Tanzania have resulted in the recovery of a diverse Cretaceous terrestrial vertebrate fauna from the middle Cretaceous Galula Formation. These expeditions have recovered fossils representing all major vertebrate clades, including fishes, crocodyliforms, dinosaurs, and the most complete mammal yet recovered from Continental Africa. Other notable discoveries from the Galula Formation include four taxa each of saurischian dinosaurs and notosuchian crocodyliforms, both of which represent ideal groups for integration into current models aimed at understanding large-scale biogeographic patterns. The co-occurrence of both notosuchian crocodyliforms and titanosaurian sauropods with sister-taxa from the geographically proximate Dinosaur Beds of Malawi supports a regional endemism model during the middle Cretaceous. Ongoing work in Cretaceous units exposed in other regions of the former supercontinent (e.g., northern Africa, Antarctica) seeks fill in the patchwork of sampling voids, providing an opportunity for the development of more robust continent- and perhaps supercontinent-wide biogeographic models leading up to the K-Pg boundary.

October 19: Yutian Wu, Purdue University. Title: Hydrological cycle and climate change

Abstract: This talk will present an overview of the global hydrological cycle and how the hydrological cycle is projected to change in the future warming climate. The talk will review our current understanding of the hydrological cycle response to increased greenhouse warming, i.e., ’wet gets wetter, dry gets drier’ and the possible contributions from the changes in the atmospheric large-scale circulation. The talk will also discuss the possible influences from other climatic forcings such as the anticipated ozone recovery in the future climate.

October 26: Colin Amos, Department of Geology, Western Washington University Title: Earthquakes, groundwater, and uplift in the Sierra Nevada of California

Abstract: Groundwater use in California’s San Joaquin Valley exceeds replenishment of the aquifer, leading to substantial diminution of this resource and rapid subsidence of the valley floor. The volume of groundwater lost over the past century-and-a-half (˜160 km3) also represents a substantial reduction in mass and a large-scale unburdening of the lithosphere, with significant but unexplored potential impacts on crustal deformation and seismicity. Here we use vertical GPS measurements to show that a broad zone of rock uplift up to 3 mm yr-1 surrounds the southern San Joaquin Valley. The observed uplift matches well with predicted flexure from a simple elastic model of current rates of water-storage loss constrained by GRACE satellite data, the majority of which is caused by groundwater depletion. Height of the adjacent central Coast Ranges and Sierra Nevada is strongly seasonal and peaks during the dry late summer and fall, out of phase with inflation of the valley floor during wetter months. Our modeling suggests that long-term and late-summer flexural uplift of the Coast Ranges also affects stresses on faults paralleling the San Joaquin Valley. Estimated Coulomb stress evolution on the San Andreas Fault totals 1-2 kPa per decade, with seasonal variations of ˜1 kPa at seismogenic depths. The seasonal stress change provides a viable mechanism for observed seasonality in microseismicity at Parkfield, and the trend potentially affects long-term seismicity rates for fault systems adjacent to the valley. We also infer that observed contemporary uplift of the southern Sierra Nevada previously attributed to tectonic and/or mantle derived forces is partly a consequence of human-caused groundwater depletion. We are currently exploring constraints from seasonal and interannual vertical motion and a more realistic viscoelastic Earth model to estimate spatial and temporal patterns of groundwater unloading, as well as potential impacts on apparent fault slip rates estimated with horizontal GPS.

November 2: GSA week, no colloquium

November 9: No colloquium

November 16: Tom Knutson, Geophysical Fluid Dynamics Laboratory, NOAA. Title: Climate change in West Antarctica: Are we heading for a dramatic rise in sea level?

Abstract: A survey of past data on tropical cyclones, focusing on the Atlantic basin, reveals pronounced multidecadal variability but does not show strong evidence for long-term trends as occur with global mean temperature. It remains uncertain whether greenhouse gas-induced global warming has caused any detectable impact on tropical cyclone activity. Changes in aerosol forcing may have contributed to pronounced multidecadal variations in the Atlantic basin, but this issue also remains unresolved. Despite the lack of a clearly detectable signal in past observations, owing to certain observed characteristics of tropical cyclones it is prudent to consider whether substantial future global warming could lead to significant changes in their characteristics. We use models to explore this possibility. We first use a 50-km grid global atmospheric general circulation model developed at GFDL (HiRAM, C180) to simulate tropical storms and hurricanes under present-day and future climate conditions. This model has demonstrated capability to simulate the current climatology of tropical cyclone occurrence and can even simulate the interannual variability of tropical cyclone frequency in the Atlantic basin when run with observed sea surface temperatures (SSTs). This model simulates a global reduction in tropical storm frequency for warm climate conditions as projected for the late 21st century (CMIP5, RCP4.5 scenario).

We then downscale large samples of tropical storms from this model into the GFDL hurricane model, which has grid spacing near the storm of about 6 km, and includes ocean coupling (e.g., "cold wake" generation by the storms). Despite the reduced global number of tropical storms in the warmer climate, the model also simulates an increase in the average cyclone intensity, precipitation rates, and the number and occurrence days of very intense category 4 and 5 storms in the warmer climate. These changes, while present in global averages, are not present in all individual basins. Basins with a greater increase in storm activity tend to also have a projected SST warming (from the CMIP5 models) that is greater than in other tropical basins. For storm size, our framework can reproduce the observed global distribution of storm size (slight high bias) and can also reproduce the differences between basins in median storm size. The median storm size remains about the same globally in the warm climate simulations, with small increases in most basins offset by decreased size in the northwest Pacific basin.

November 23: Thanksgiving Holiday, no colloquium

November 30: Andy Wickert, University of Minnesota. Title: Reconstruction of North American drainage basins and water discharge since the Last Glacial Maximum

December 7: Stephen Kaczmarek, Western Michigan University. Title: The surprising simplicity of limestone microporosity

Abstract: Carbonate oil reservoirs host a large proportion of the conventional petroleum resources worldwide. A global investigation of microporous limestone reservoirs indicates that the most volumetrically significant microporosity is hosted among low-magnesium calcite microcrystals. Microcrystals are homogeneous in terms of size with >90% measuring 1-6 in diameter. Micropores are also homogeneous with >90% measuring between 1 and 3 µm in diameter. Most microcrystal assemblages fall into one of three major textural classes (granular, clustered, or fitted) that directly correlate to porosity and permeability, as well as the mean pore and pore throat size. The isotopic geochemistry of these microcrystals implies a relatively straightforward diagenetic paradigm, namely stabilization of metastable marine carbonate material and subsequent cementation during burial.

December 14: AGU Meeting, Finals week, no colloquium