Current Research


Environmental controls on soil carbon storage and turnover in the Caribbean

DSCN1306The primary research objectives of this project are to: 1)  Quantify soil carbon under different land uses across environmental gradients in Puerto Rico to determine the role of land use and state factors on soil C storage, 2) Evaluate the magnitude and persistence of legacy effects of historical land use on soil carbon with time since conversion across different soil types, and 3) Determine the effect of soil type, climate and land use on the relative importance of different physical, chemical and biological processes contributing to carbon sequestration in tropical soils. In collaboration with the USDA NRCS Rapid Carbon Assessment and funded by NSF CAREER award. Collaborators: Carmen Santiago, Manuel Matos, Samuel Rios. Read more about this project here.




Soil resource heterogeneity and tree species diversity in tropical secondary forestsDSCN3174

PhD Student: Ricardo Rivera

The objective of this research is to measure the heterogeneity of soil nutrient pools and availability through successional stages in post-agricultural forests. Characterizing these spatial patterns through succession will elucidate the importance of patterns over community assembly processes. For example, it is thought that deterministic processes dominate species establishment in early succession while stochastic processes dominate later stages of succession, but how important is the spatial arrangement of soil properties in deterministic or stochastic processes. This research will explore how important are the initial spatial patterns of soil nutrients in determining establishment of species in early succession and how they change through later stages of succession. This data will be incorporated into spatially explicit models of community assembly following changes in land-use in the tropics. Collaborator: Dr. Maria Uriarte.




Carbon cycling in biofuel energy cropping systems: measurements and mechanisms of soil organic carbon sequestration

PhD Student: Adam von HadenGE DIGITAL CAMERA

Biofuels are anticipated to become an increasing portion of U.S. agriculture, but the ecological ramifications of such widespread land use change are relatively uncertain. The overall goal of my research is to generate an improved understanding of the controls on carbon loss, storage, and stabilization in model biofuel cropping systems in order to inform environmental, economic, and policy decisions related to bioenergy. My research examines annual net ecosystem primary productivity and explores the drivers of in situ ecosystem carbon losses via heterotrophic and autotrophic respiration in bioenergy cropping systems. In addition, my research seeks to elucidate the mechanisms of soil organic carbon accrual by comparing changes in soil carbon pools following five years of biofuel cropping system establishment. My research is being conducted at the University of Wisconsin-Madison Arlington Agricultural Research Station with additional archived soils from Kellogg Biological Station in Michigan. This work is funded by the Great Lakes Bioenergy Research Center in collaboration with my co-advisors: Dr. Chris Kucharik and Dr. Randy Jackson.



The effects of land use and environmental factors on soil carbon storage in Puerto RicoIMG_0115

MS Student: Elliot Vaughan

My thesis is looking at different factors that affect soil carbon (C) and nitrogen (N) storage in Puerto Rico. I am particularly interested in how human land use influences soil biogeochemical processes and how land use interacts with environmental factors to determine site-specific responses. I am using samples collected by the Natural Resource Conservation Service (NRCS) at 20 sites across the island. The sites include forest and pasture sites on three different soil types, spanning a range of climate variables. I will be analyzing the data to see which of these variables is most important in determining soil C and N storage.





Vulnerability of carbon in buried soils to climate change and landscape disturbance

PhD student: Laura SzymanskiBrady soil Marin-Spiotta

This project will test the potential for deep buried soil organic matter to become a carbon source in response to changes in climate or land use that affect the connectivity of buried soils to the atmosphere. The research aims to understand (1) how soil burial contributes to the persistence of carbon in the form of soil organic matter and (2) whether exposure to surface conditions can trigger the decomposition of ancient carbon. The proposed study site is located in the U.S. Great Plains, where climate-driven loess deposition during the late Pleistocene and Holocene resulted in sequences of buried soils in thick loess deposits. The vulnerability of ancient organic matter to changing environmental conditions will be measured in two ways. First, changes in organic matter age, composition and bioavailability will be quantified along eroding and depositional field toposequences, where the paleosol exists at varying degrees of isolation from the modern landscape surface. Second, laboratory manipulations will measure the effects of carbon substrates, nitrogen availability, and microbial composition on ancient organic matter decomposition and mobilization in gaseous and dissolved forms. This study combines a geomorphic approach drawing from paleoclimatic reconstructions with advanced geochemical, spectroscopic and metagenomic techniques to generate new knowledge on environmental controls on carbon biogeochemistry. Funded by NSF Geobiology and Low Temperature Geochemistry. Collaborators: Dr. Joe Mason, Dr. Asmeret Berhe and Dr. Marie-Anne de Graaff.


Nitrogen cycling during tropical forest succession

Student: Sanober Mirza, Holstrom Environmental Scholar

The objective of this project is to quantify the variation in different nitrogen (N) cycling processes with forest succession. Nitrogen plays two important roles in Earth’s climate. As a plant nutrient, the availability of N affects plant growth and the uptake of carbon (C) from the atmosphere into plant biomass. The accumulation of C in long-lived biomass and in soils contributes to reducing the amount of CO2 in the atmosphere. Secondly, excess N can lead to the production of N2O, which is a more potent greenhouse than CO2. Land-use change, specifically deforestation and reforestation, can affect N availability for plant growth and N2O production. Long-term agricultural use can deplete nitrogen sources, even in tropical soils where N is not expected to limit productivity. Through the evaluation of nitrogen-fixing tree species, N in litterfall, soil N, and N mineralization, we will gain a comprehensive picture of tropical N-cycle variation. Soils have been sampled from a well-replicated chronosequence in Puerto Rico with pastures, 29-year-old forests, 69-year-old forests, and primary forest. The results from this study can be applied to forest management and land-use decisions, with implications for the global climate.



Garden archeology in a Japanese American internment camp 

This interdisciplinary research aims to reconstruct gardening practices in a former WWII Japanese American internment camp in order to better understand how displaced interns used local resources to transform military enclosures into productive social and natural spaces. We are using elemental analysis, spectroscopy, and mass spectrometry to better understand how interns influenced the physical properties of historical garden soils within encampments. Funded by WARF. Collaborators: Dr. Bonnie Clark. Project page at DU.


ADVANCE Partnership: From the Classroom to the Field: Improving the Workplace in the Geosciences

The geosciences is one of the least diverse disciplines in STEM. One reason for this is the hostile climate experienced by many women and people of color in the geosciences due to sexual and racial harassment. This collaborative project with the Earth Science Women’s Network, the Association for Women Geoscientists and the American Geophysical Union aims to improve work climate conditions and increase gender equity in the geosciences by developing bystander intervention workshops for department heads, chairs, and faculty to appropriately respond to, prevent, and eliminate sexual harassment. Goals include sexual harassment awareness and prevention training in the teaching of ethical conduct in research guidelines; developing and incorporating geoscience-relevant scenarios in training and teaching materials, including field research and educational settings; incorporating experiences of community members with intersectional identities who may face sexual, racial and gender harassment, and collaborating with professional society partners for national dissemination, implementation, and sustainability. Funded by NSF ADVANCE Partnership program. Team members include: Billy Williams, American Geophysical Union; Blair Schneider, Association for Women Geoscientists; Allison Mattheis, California State University, Los Angeles; and leaders from the Earth Science Women’s Network: Rebecca Barnes, Colorado College; Asmeret Berhe, University of California, Merced; and Meredith Hastings, Brown University. Project assistants on the team are Haley Burkhardt and Sunita NandihalliHaley is a second year graduate student in Biological Anthropology who has been a critical part of the PEOPLE program serving new students to campus, and especially Native students. Sunita is a new masters student in the Counseling Psychology program with research experience on cross-cultural studies.