Lewis Lab at USF

Welcome!

lewislab — Fri, 31 May 2013 16:45:13 +0000

Welcome to the site of David Lewis’ research group at the University of South Florida. This front page is our lab news feed. Please see other tabs to discover who we are and what we do.

Nitrogen retention in the soil of old-growth forests

lewislab — Fri, 31 May 2013 16:42:48 +0000

The widespread use of fossil fuels and combustion engines, along with several particular agricultural practices, have transformed a lot of nitrogen from unavailable forms (atmospheric dinitrogen) into biologically usable (or “reactive”) forms. This process is called nitrogen fixation. Worldwide, human activities have tripled the rate of nitrogen fixation, compared to background rates prior to the Industrial Revolution. This accelerated conversion of nitrogen (N) into reactive forms has damaged air and water quality, created human health risks, and upended ecological communities composed of species adapted to low-nitrogen conditions.

Fortunately, soil organic matter has the capacity to capture and retain large masses of reactive N, potentially mitigating the problems of excess N. Soil organic matter is the decaying, non-living material that came from organisms (fallen leaves, dead microbial cells, molecules exuded by plant roots, etc). This organic matter is abundant in soil, but there is little information on exactly how it retains N, and on which forms of N it best retains. We recently published a paper in which we compared the retention of three forms of nitrogen (NH4, NO2, and NO3) by both biological and non-biological (abiotic) mechanisms. We added a stable isotope of nitrogen (15N) in each N form to both live and sterilized soil. We conducted this research using soils from old-growth forests, which were once thought not to retain N because their plants had stopped growing. But our renewed focus on the soils of these ancient places shows that they may indeed retain large quantities of N. This research was conducted out of Jason Kaye’s lab at Penn State.

Jimenez in the spotlight!

lewislab — Fri, 01 Mar 2013 21:00:31 +0000

Kristine’s study of wetland-atmosphere CO2 exchange and its sensitivity to wetland hydroperiod was recently highlighted in the “Research Spotlight” in Eos, a weekly newspaper of the Earth and space sciences published by the American Geophysical Union. The “Spotlight” emphasized the potentially controversial implication of Kristine’s research that “restoring the Everglades will likely diminish the potential of the region to serve as a carbon sink.” Kristine conducted this work while a Master’s student in Greg Starr’s lab at the U. of Alabama. Read the full Spotlight, and find her research here.

How does soil hydrology fit into the organic matter-nitrogen relationship?

lewislab — Fri, 01 Mar 2013 20:58:36 +0000

Nitrogen is perhaps the most limiting nutrient in the biosphere, and human acceleration of the nitrogen cycle causes havoc in ecological systems, where organisms are adapted to low-nitrogen conditions. Accelerated nitrogen cycling also adversely impacts air and water quality – it functions as a greenhouse gas, generates smog, depletes ozone, and causes algae blooms and fish kills. Much biogeochemical research has thus focused on the role of soil organic matter (the massive reservoir of decomposing remains of once-living biomass) in retaining nitrogen, dramatically slowing its cycling through the environment. Historically, however, nitrogen retention theories have focused on the role of soil organic matter in the absence of soil hydrology. In a new paper led by our colleague Michael Castellano at Iowa State, we contrast coarse vs. fine textured soil along a hillslope in Maryland to test hypotheses that nitrogen retention in soil organic matter is regulated by soil texture and the ease with which water transports organic matter and nitrogen through different types soil. This research was conducted out of Jason Kaye’s lab at Penn State. See the paper here.

Sharon Feit – from degree straight to job!

lewislab — Thu, 31 Jan 2013 14:22:06 +0000

Congratulations to Sharon Feit on her new job. Sharon is a Natural Resource Specialist, with the Natural Resource Group in Minneapolis. Her primary roles are to make sure that oil and gas pipelines avoid federally-protected wetlands and endangered-species habitats, and to assist with wetland delineations and compliance with environmental regulations. Notably, Sharon got this job straight from doing her master’s thesis on wetland soils and hydrology as a valuable member of our lab. She had to rush out of town without delay. Her lifetime of hard work and robust science clearly paid off in the job market!

New publication by Ken Nilsson on the ULTRA project

lewislab — Fri, 14 Dec 2012 14:39:56 +0000

A new publication by Ken Nilsson and co-authors just came out in the journal Wetlands Ecology and Management. The research models the frequency distribution of the water table elevation and the probability of wetland inundation in 56 isolated, depressional basin wetlands in the north Tampa Bay region. This study is an important link between the ecological outcomes of hydrological change, and the hydrological consequences of regional urban water policy, which are other facets of our water and society research program (the ULTRA project). Dr. Nilsson has been a post-doc on the ULTRA project. Good job Ken!

Congratulations Sharon!

lewislab — Wed, 24 Oct 2012 20:31:13 +0000

Sharon Feit defended her Masters thesis today, en route to graduating with her M.S. degree this fall. Her thesis is titled “Variability in Hydrology and Ecosystem Properties and their Role in Regulating Soil Organic Matter Stability in Wetlands of West-Central Florida.” Sharon joined the lab in the summer of 2010. Her research examined the roles that wetland vegetation community and hydrology play in regulating the size of soil carbon and nitrogen pools, and the partitioning of these pools into labile (bioavailable) and stable fractions. Perhaps of greatest importance, her work suggests that under the oxidizing conditions of suppressed wetland hydroperiods, wetland soils appear to lose even their stable C and N fractions. Given the extremely large size of wetland C and N pools, these results have important implications for mineral C and N release to air and water, and for groundwater management. Great job Sharon!!!

Congratulations Kristine!

lewislab — Wed, 17 Oct 2012 00:50:33 +0000

Congratulations to Kristine Jimenez, manager of our lab and much of our coastal soils research. Kristine’s Masters research was just published in JGR-Biogeosciences. Kristine recently conducted this research while pursuing her M.S. at the University of Alabama, prior to joining our lab. Her research investigated wetland-atmosphere carbon exchange in the Everglades, comparing marshes of distinctly different hydroperiods. Kristine’s experience has proven helpful to our lab, where we also investigate the role of hydrology in wetland carbon cycling. Check out her paper here.

Recent ecohydrology publication

lewislab — Tue, 07 Aug 2012 21:33:39 +0000

With our colleague Michael Castellano, at Iowa State, we recently co-authored a book chapter that develops conceptual models linking biogeochemistry with hydropedology (or the fine-scale movement of water through soil). Please contact us for a copy of the chapter. Here is the full citation:
Castellano, M.J., Lewis, D.B., Andrews, D.M., McDaniel, M.D., 2012. Coupling biogeochemistry and hydropedology to advance carbon and nitrogen cycling science. In: Lin, H. (Ed.), Hydropedology: Synergistic Integration of Soil Science and Hydrology. Academic Press, Elsevier B.V., pp. 711–735.

ESA presentation

lewislab — Mon, 06 Aug 2012 21:22:54 +0000

We recently gave a presentation on our coastal soils project, highlighting results both from the core project and from honors thesis research by Jewel Brown, one of our recent undergraduate alums.

See the abstract for the talk here:
http://eco.confex.com/eco/2012/webprogram/Paper37807.html