Ecosystems Lab at USF

Viviana Penuela received a McKnight Doctoral Fellowship award, for tuition and stipend support for three years. Viviana’s successful proposal described her plan to investigate how the growing use of reclaimed water alters the chemical composition of soil, and may thereby affect soil microbiology, physics, and ultimately carbon and nitrogen sequestration. The title of her project was “Influences of reclaimed water irrigation on microbial processes and aggregates formation in urban soils,” an example of basic biogeochemistry set in an urban context. Viviana will conduct a comparative study between lawn management strategies (reclaimed vs. aquifer water irrigation) in urban soils. The samples will be taken from residential lawns irrigated with reclaimed water and from those irrigated with potable water. She will compare physical and microbial properties of the soil to better understand the effect of reclaimed water irrigation soil carbon and nutrient storage.

Check out our latest paper on the mineralization of soil organic matter in coastal wetlands. Coastal wetlands are mangrove forests and salt marshes at the interface where land meets the sea. Mangrove forests are located in the tropics, salt marshes with primarily herbaceous vegetation are found at cooler latitudes, and the two habitat types intergrade in the subtropics. These ecosystems store massive amounts of soil organic matter, the decaying remains of once-living material. The mineralization (i.e., complete decomposition) of this organic matter results in the loss of soil mass and a decline in soil elevation, rendering these ecosystems more vulnerable to sea level rise; releases carbon- and nitrogen-based greenhouse gases and pollutants to air and seawater; and yet supplies nutrients to coastal wetland vegetation.

Given these important roles played by soil organic matter mineralization, we are interested in how mineralization in Florida’s subtropical coastal wetlands might respond to climate change. Climate change results in sea level rise and an increase in coastal soil inundation, warming, and the redistribution of plant species (the encroachment of mangrove forests into herbaceous salt marshes). An understanding of how climate change might affect organic matter mineralization must account for the response of mineralization to these three factors: increased tidal inundation (which should increase anoxia that suppresses mineralization), warming (which should stimulate mineralization), and changes in the plant species that produce organic matter.

Our new paper investigates how these factors interactively affect carbon (C) and nitrogen (N) mineralization in coastal wetland soils. Using both a field survey and laboratory experiment, we found C mineralization was increased by warming, but suppressed by soil saturation and prolonged inundation. However, C mineralization in inundated soil was extraordinarily sensitive to temperature, so the stimulation of C mineralization by warming may “win out” over the protection of soil C by prolonged inundation and soil saturation. Ecosystem type was important, too, as mangrove forest soil had higher “carbon quality” (more mineralization for a given amount of organic matter), while N mineralization was higher in salt marshes. The take-home message is that C and N mineralization in coastal wetlands will change with the alterations in soil water regime, temperature, and plant composition that accompany climate change.

We presented our latest wetlands research at the annual meeting of the South Atlantic Chapter of the Society of Wetlands Scientists. Wetlands provide many services, including groundwater recharge and flood mitigation, habitat for species adapted to life in seasonally wet environments, and recreational and even spiritual opportunities. Two biogeochemical services that wetlands provide are carbon and nitrogen storage, which mitigate greenhouse gas loading to the atmosphere and protect downstream water quality.

In this presentation, we asked: How important is wetland hydrology for these biogeochemical services? Depressional basin wetlands in the northern Tampa Bay region are flooded when the water table rises in response to the rainy season. Some wetlands, however, stay inundated for many months each years, whereas others generally fail to hold surface water. Soil inundation impedes decomposition of soil carbon by microorganisms, and soil carbon is an important substrate for “fueling” the immobilization of mineral nitrogen (the type in fertilizers and fallout from air pollution) in soil organic matter. We thus tested the prediction that well-inundated wetlands (compared with their highly-drained counterparts) would hold larger soil carbon pools and have a greater nitrogen immobilization capacity. We tested this prediction using a combination of isotopic (15N) labeling of soil, and long-term soil incubations. Our results were generally what we expected, but held a few surprises, too!

Along with teaching and research, outreach forms one of the priorities of the Lewis Lab. Outreach efforts include sharing discoveries with professional environmental managers, information sessions with the public, and educational opportunities for school groups outside USF. Over the past two years, lab member Kristine Jimenez, along with Dr. Ankur Desai (Univ of Wisconsin – Madison), has been holding an outreach program called Forest and Climate Leaders In Menominee and the Environment (ForCLIMATE) aimed at providing students at the College of Menominee Nation (CMN) new opportunities to explore scientific methods of studying global change. This summer the class included CMN’s Sustainable Development Institute and high school students in the highly selective Sustainability Leadership Cohort. This program ignites interest in sustainability through the STEM fields, and builds leadership skills that respect other cultural values and shape innovative leaders. During this 4-day retreat at the Univ. of Wisc. Kemp Natural Resources Station, students participated in methods that scientists use to study the environment and the earth-atmosphere system. Kristine designed a module where students used field methods to determine soil texture and measure soil nutrients and pH, and facilitated discussions about climate change, renewable energy, indigenous knowledge, and culture.

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.

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.

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.

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!

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!