REU Projects 2013
The following projects are availble:
- Microbial ecology and biogeochemistry in mountain lakes.
- Rising Snowlines and Water Availability for Park Resources in a Warming Climate.
- Hydro-ecological implications of buried volcanic ash (tephra) in meadows of Yosemite.
- Effect of physical perturbations in the environment on soil organic matter dynamics.
- Role of biotic and abiotic controls over conifer seedling establishment in subalpine meadows in Yosemite National Park.
- Interdisciplinary Assessment of Yosemite Valley's Riparian Habitat.
- Giant sequoia population demographic structure and impacts of fire.
- Soil biology and nutrient cycling in giant sequoia groves.
- Understanding anthropogenic and biogenic fluxes of greenhouse gases in YNP.
Lakes are climate sentinels that will be rapidly and substantially altered by anthropogenic climate change. Among the predicted effects of warming is disruption of lake carbon balance, including elevated microbial respiration rates in sediments and the water column—changes that are globally significant because lakes and other inland waters play a disproportionate role in the carbon cycle. At the same time, increasing deposition of atmospheric pollutants has prompted reexamination of nutrient limitation of lake microbial processes and communities. Yet these changes take place against a backdrop of limited knowledge regarding lake microbial community ecology and biogeochemistry; ‘typical’ freshwater bacteria and their phenology were identified within only the past decade, and relationships between community composition and activity, and responses to nutrient additions, are varied. REU participants will be involved in examining microbial community ecology and biogeochemistry across environmental gradients in YNP mountain lakes. They will use natural gradients in conjunction with experimental manipulation to quantify environmental controls on microbial community composition, diversity, and activity, with a particular focus on the processes of respiration and nitrification.
Snow comprises 90% of YNP’s precipitation. This natural reservoir accumulates each winter and its subsequent melt nourishes ecosystems through the warm dry summer. However, climate warming will result in less snow and more rain, dramatically altering moisture availability and timing in the coming decades. Several studies have attempted to evaluate moisture stress in current and future climates using understandably limited datasets, but improved data availability (including satellite-based detection of snow cover, soil moisture and snow depth measurements, and improved understanding of forest canopy-snow relationships) now make it possible to build a better understanding of snow accumulation and melt and the subsequent partitioning of melt into runoff and plant-available soil moisture. Advances in our understanding of the snow – soil nexus will be essential to future management of forests and fire, water resources, and plant and animal refugia (e.g., Yosemite Toad habitat protection, potential for Wolverine introduction, and protection of rare plant communities). The central goal of this project is establish a quantitative means of estimating forest soil-moisture deficit across YNP. REU students will be involved in measuring and modeling moisture deficit at different elevations using state-of-the-art instrumentation, satellite products, and a robust snowpack energy balance model.
The most recent volcanic eruptions in the Mono-Inyo chain of craters in the Sierra Nevada, which occurred ~760 and ~1200 years ago, commenced with violent pyroclastic eruptions of pumice that was later carried by wind and deposited over large areas. Today, layers of pumiceous fragments (tephra) are visible in meadow topsoils of the southern Sierra Nevada, from YNP south to the Kern River drainage. In contrast to the overlying (younger) and underlying (older) meadow soils, the tephra layer has very low organic matter content and is made up of coarser particles. Consequently, the ability of the tephra to retain moisture against desiccation (by evaporation, drainage, and/or plant uptake) is significantly lower. We established arrays of buried sensors and gas wells in Dana Meadows of YNP to analyze the effect of the tephra on the moisture dynamics and associated ecological functioning of meadows. REU students will participate in field acquisition of soil moisture, soil water potential, and temperature data from multiple arrays of buried sensors using electronic data-loggers, collection of gas samples, and analysis of gas and soil samples in the laboratory.
Identification and quantification of ecosystem variables that regulate how and why organic matter persists in soil for long periods of time (up to millennia) is critical area of research, with important implications for our understanding of the role of soils in regulating the climate system. Previous work by Berhe’s research group in YNP has centered on determining soil organic matter stocks and fluxes in a series of alpine and subalpine meadows, and developing empirical relationships and predictive models of C turnover in these ecosystems. REU students will contribute to the experimental design of similar efforts within new meadows in YNP, and learn multiple field and laboratory techniques in soil science and biogeochemistry, including: field soil characterization, elemental analysis, trace gas flux analysis using static chambers and gas chromatography, and data analysis.
High-elevation Sierran meadows are being encroached by conifers, and the loss of these meadows may mean loss of important ecosystem services (such as water storage and release) that they provide. Our current project integrates topics in ecology and hydrology on a landscape scale to explore the causes of meadow encroachment. Potential field projects include investigating the effects of small mammals, microsite soil moisture, and seed availability on tree seedling establishment in meadows. This project required extended hiking or short backpacking trips, so students must be in good physical condition.
This research experience links vegetation and wildlife studies with social science to assess the condition of riparian habitat in Yosemite Valley. The student(s) will quantify wildlife habitat using a standardized vegetation sampling technique involving the collection of vegetation structure and plant species composition data at multiple locations in the Merced River corridor. Student(s) will integrate a social science component by assisting with development and implementation of an index to capture extent of visitor use and associated impacts within the same sampling locations. Student(s) will then use the vegetation data and human use index to evaluate what factors might be influencing habitat use by birds. Ultimately, these data will provide insight on patterns of habitat use by riparian breeding birds in Yosemite Valley in support of Yosemite's Merced River Plan. This project is best suited for two student researchers. Experience with vegetation sampling, plant identification, GPS, and statistical analyses is preferred but not required.
Yosemite contains three giant sequoia groves, each with a unique history of natural and prescribed fires. Giant sequoias are dependent upon fire for new seedling establishment. Lack of fire greatly reduces natural seedling development (recruitment) and skews populations to older adults. All three groves had fire largely excluded as a natural process beginning in the mid-1800s. Beginning in 1970, fire was reintroduced to the groves as a management tool, but each grove has experienced widely different burn regimes. The research will involve a mix of field work (day trips) and office time. Students will collect field data in the sequoia groves in sometimes rugged terrain using GPS technology and vegetation plot sampling methods. The field data will then be used to examine the spatial relationships between fire history and severity and recruitment patterns and population structure using GIS. Experience with vegetation plot sampling, GPS, and ArcGIS preferred but not required.
Yosemite contains three giant sequoia groves, however very little is known about how the presence of these massive and majestic trees influence soil in the Sierra mixed-confer zone. In collaboration with a giant sequoia population demographic study, this project will involve a paired-comparison of soil properties and processes within the giant sequoia groves and adjacent mixed-conifer forests. In-field measurements of soil respiration (CO2 evolution from biological activity in the soil) and laboratory analyses of soil chemical and biological properties will be conducted to help elucidate the influence of these plant dominants on ecosystem function.
The NPS has ambitious goals for reductions in greenhouse gas emissions, but there is a limited understanding of what the current emissions are and what management approaches would therefore allow for the targeted emissions reductions. This REU project will explore integrated methods in ecosystem modeling, atmospheric analysis, and industrial ecology to develop fundamental insights on the current anthropogenic and biogenic emissions of greenhouse gases in YNP, as well explore potential emission mitigation strategies (e.g., increased energy efficiency, renewable energy production, and improved waste management and transportation services). Industrial ecology provides fundamental methods for understanding anthropogenic emissions but often lacks a robust representation of co-located ecological effects (e.g., soil carbon sequestration, forest wildfire). The mentors leading this project seek to integrate their expertise in both traditional and industrial ecology in order to provide a unique student research experience at the frontiers of carbon management.