REU 2013 Experiences
At the University of Arizona, we are building a program to bridge the gap between laboratory- and field-scale studies by utilizing the unique infrastructure of Biosphere 2. Biosphere 2 offers unique opportunities for the exploration of complex questions in earth sciences because of its ability to combine varying scales, precise manipulation and fine monitoring in controlled experiments. By building upon the large external scientific network at the University of Arizona in hydrology, geology, geochemistry, ecology, biology, physics, engineering and atmospheric sciences, we are developing a strong multidisciplinary team of researchers who are undertaking the design and deployment of top-notch science to address complex questions in environmental sciences. Projects for 2013 REU students include:
Coupling subsurface biogeochemistry to Critical Zone evolution, Jon Chorover, Soil, Water and Environmental Science Dept.. Students working in the Chorover lab would have the opportunity to work on geochemical aspects of a collaborative and multi-disciplinary Critical Zone Observatory (CZO) (NSF EAR 0724958: "Transformative Behavior of Energy, Water and Carbon in the Critical Zone: An Observatory to Quantify Linkages among Ecohydrology, Biogeochemistry, and Landscape Evolution"). The "Critical Zone" is defined as that portion of the Earth's terrestrial surface that extends from the outer periphery of the vegetation canopy to the lower limit of ground water penetration (National Research Council, 2001 "Basic Research Opportunities in Earth Sciences"). REU students would have an opportunity to work at one of two sites within the UA CZO, including the Santa Catalina Mountains (AZ) and the Jemez River Basin (NM). Projects in the Chorover lab would focus on coupling field work and laboratory studies to understand subsurface biogeochemical processes, particularly those related to the impacts of the carbon cycle on geochemical weathering, and the interaction of these processes with Critical Zone ecohydrology, stream water dynamics, and landform evolution.
Soil biogeochemistry in human dominated landscapes Mitchell Pavao-Zuckerman, Biosphere 2. Understanding the contribution of organisms to biogeochemical cycling is one of key points in linking across scales in ecosystems. The response of organisms to their local environment reflects one way in which ecosystems directly respond to land-use change, and climate. My lab focuses on the connections between the structure of soil food webs and biogeochemical cycling in human dominated landscapes and urbanized ecosystems. The B2 campus is being developed as a model city ecosystem for such studies using meso-scale experiments related to green infrastructure. I have been studying microbial and microfaunal diversity, carbon fluxes, and nutrient transformations at B2 and in wild and urbanized environments in southwestern Arizona. Research projects for REUs would focus on microcosm studies and observational studies in B2 experiments and real world settings to investigate the interactions between the biological structure of ecosystems and C and N transformations.
Mineral weathering, soil formation and carbon sequestration as influenced by water flow and biota. Katerina Dontsova, Biosphere 2. Students will have opportunity to participate in one of several ongoing projects at B2 that focus on soil formation processes. The projects range in scale from Landscape Evolution Observatory ( LEO) (340 m2 area, 1 m soil depth) to large mesocosms with mesquite and grasses ( 0.26 m2 area, 1 m depth) to smaller and more controlled systems (20 cm2area, 30 cm depth). Students will be looking at the changes that are happening in the rock during initial stages of soil formation as a result of water flow and biological activity. In the small mesocosms students will be working on establishing the role of root-mycorrhizae-bacterial associations on the extent of total weathering and chemical denudation. Specifically, to what extent does biota (plants and microbes) contribute to weathering rock to form high surface area secondary solids while also diminishing the loss of weathering products in solution due to lithogenic nutrient uptake into biomass and the nucleation and co-precipitation of colloids and natural organic polymers. They would use direct measurements and geochemical modeling. We hypothesize that plant and microbial/fungal effects are synergistic and not simply additive. In larger mesocosms we will be linking measured weathering, denudation, and carbon sequestration in the soil to water transpiration, plant photosynthesis and plant and soil respiration; while LEO research will focus on development of subsurface heterogeneity through hydrologic-geochemical coupling.
Abiotic effects and dynamics of woody plant cover David Breshears, School of Natural Resources and Environment. The overall theme of the research for this project will be related to gradients of woody plant cover, which can span from grassland to forest. More specifically, key questions focus on abiotic effects of woody plants and their responses to changes in climate and land use. Specifically projects could include assessments of changes in near ground microclimate conditions associated with different densities of woody plant cover, spatial variation in dust production as a function of woody plant cover, and or plant water stress preceding tree mortality along vegetation gradients. Approaches would include hemispherical photography and computational assessments of solar radiation regimes, measurements of dust production using a variety of instruments, and/or measurements of plant water stress and related physiological metrics.
Ecohydrology in semiarid mountain ecosystems Dr. Greg Barron-Gafford, Biosphere 2 Our research within this project involves measuring leaf and soil carbon and/or water fluxes with the goal of better understanding how mixed conifer forests in semiarid environments will respond to climatic stresses of temperature, summer drought, and reduced snow input. We will estimate the component fluxes within sub-canopy and canopy species in the Santa Catalina Mountains that border north Tucson. Potential projects include measuring carbon and water exchange with the atmosphere in individual trees or whole sub-canopy plots to capture variation due to canopy cover (a biological influence), slope and/or aspect (a physical driver) and changing climate (atmospheric influences). Methods will include measures of plant water status, hemispherical photography (to quantify incoming solar radiation), and leaf/plot/soil gas exchange with the atmosphere. We are interested in how these ecosystems will perform under projected climate change scenarios, which species might begin dominating the ecosystem, and how tightly coupled carbon uptake is to water availability in this semiarid sky island setting.
Solute fluxes in surface water, Jennifer McIntosh, Hydrology and Water Resources Dept. REU students would be involved in Critical Zone Observator research in the Santa Catalina Mountains and Jemez River Basin. Potential student research questions include: How do solute fluxes in surface waters vary as a function of bedrock lithology and age? How do weathering rates vary as a function of hillslope aspect and water transit times? What are the dominant sources of organic carbon to surface streams, and how do these inputs vary across the landscape? Student research would involve field sample collection, laboratory analyses, and interpretation of data.
Modeling of soil water dynamics; Marcel Schapp, Soil Water and Environmental Sciences Dept. Students would participate in modeling and computer simulation of soil-water dynamics in selected soils in the CZO project or the B2 LEO hillslope project. In particular, they would study the relation between soil (geo)morphology and drainage and vegetation dynamics. The students would obtain knowledge on how to implement dynamic eco-hydrological systems in computer models and interpret simulation results. Alternatively, students would participate in measurement of water dynamics in B2 hillslope soils. In particular students would use an existing 1-Dimensional representation of the B2 hillslope soils to determine soil water dynamics, but also soil chemical weathering rates. The students would obtain experience with complex measurement and control systems.
Using digital images to link the hydrologic cycle and ecosystem phenology Shirley Papuga, School of Natural Resources and Environment. Climate change induced shifts in precipitation alter the pulses of soil moisture that drive basic phenological activity in water-limited ecosystems, such as flowering and green up. We use digital images to understand phenological triggers in water-limited ecosystems caused by precipitation induced variability in soil moisture, which characterize phenological changes within the ecosystem at a daily scale. Using MATLAB image-processing tools, we can develop a quantitative measure of phenology from these images which can be directly linked to meteorological and flux data collected at the tower. Students would select a focal plant species, develop hypotheses about the phenological triggers (e.g. temperature, rainfall) for their species, and inspect images by eye to determine the timing of phenological events. Using modules (developed by Dr. Papuga), a student can quickly learn to process the images in MATLAB and develop an index to automatically detect their phenological phases, and compare their index to results from their visual inspection. Finally, the student will use meteorological data and flux tower data to explain the timing of their phenological events to determine if their hypotheses were correct.
Interaction of landscapes, pedogenesis and mass fluxes Craig Rasmussen, Soil Water and Environmental Sciences Dept.. The proposed REU project would include quantifying the interaction among landscape position, soil formation and elemental mass flux. Landscape scale variation in chemical and physical weathering has emerged as a key component modulating terrestrial biogeochemistry. In particular, CO2 consumption associated with mineral weathering and the interaction of this process with pedogenesis and erosion appear to be significant factors controlling long-term patterns in atmospheric CO2 concentration. The REU project would specifically focus on the hypothesis that weathering and mass flux vary predictably with landscape position and climate forcing. Testing of this hypothesis will be accomplished by quantifying the mass flux of elements such as Na and Si from soil profiles located at various landscape positions on north facing slopes embedded within various ecosystems along the environmental gradient encompassed by the Santa Catalina Mountains. The project would include a combination of field sampling, physical and chemical laboratory analyses, and data synthesis with the goal of generating a dataset suitable for publication and/or the pursuit of further funding to address broader scale biogeochemical processes.
Water transit time at catchment scales. Peter Troch, Hydrology and Water Resources Dept.& Biosphere 2. My research aims at a better understanding of catchment scale hydrological processes through advanced measurement, modeling and synthesis methods. The objectives of this research in general are: (1) Developing, testing and applying advanced observation methods for hydrological fluxes and states at a range of spatial and temporal scales; (2) Developing hillslope to catchment scale hydrological models for water and solute transport; and (3) Hydrological synthesis at the catchment scale with special attention to hydrological extremes. The motivation of this work is to contribute to improved water resources management in the light of climate change and other human influences on the hydrological cycle. Students working in my lab will work on water transit time estimation using stable isotope data from rain and streamflow samples. The training I can provide is field work, lab work including running the laser spec in my lab and mathematical modeling of flow and transport processes at catchment scales.
Quantifying rapid landscape evolution. Jon Pelletier, Geosciences Dept. Landscape evolution usually occurs too slowly to be measured. However, by focusing on experimental landscapes (such as in the B2 Landscape Evolution Observatory), or by visiting landform types known to evolve rapidly (e.g. sand dunes, which migrate ~ 10 m/day on windy days) landscape evolution can be quantified in real time (using terrestrial laser scanning) and used to test computer-based models for how Earth’s surface is modified by gravity, wind, and flowing water. In this proposed REU project, students will collect data on landscape evolution occurring in real time, and will work with mentor Jon Pelletier to test existing computer-based models (developed by Pelletier) to test the efficacy of those models and identify ways that they can be improved. The ultimate goal of computer-based modeling is to predict the future evolution of Earth’s surface at a variety of scales, including under scenarios of changing climate. This project will include a combination of field measurements, computer modeling, and data analysis with the goal of generating a journal publication.
Seasonal changes in growth physiology in Cottonwood trees. David Moore, SNRE Plants take up about half of all the carbon produced by humanity through the process of photosynthesis but there are many unanswered questions about how long this will continue especially as we see earlier springs and later falls in some plant species. This project aims to discover the environmental triggers for major phenological events in cottonwood trees by studying patterns of leaf development, plant photosynthesis and growth. The project will take place at B2 using an experimental stand of trees. Depending on their interests students will learn how to carry out physiological measurements, image analysis, spectral measurements of leaves and laboratory techniques.