On to candidacy!


Congratulations to Bert Anderson, who just passed the PhD proposal examination, and has advanced to the status of PhD candidate. Bert’s research will examine how biogenic habitat modification alters organic matter dynamics in hypersaline coastal salt pans. Now the real work begins!

Viviana defends her MS!

Viviana...from MS on to PhD.

Viviana…from MS on to PhD.

Congratulations to Viviana Penuela! She recently defended her Master’s degree research, and has now deposited her approved thesis, thus successfully completing her M.S. degree. Viviana’s research addressed the link between land management policy and soil biogeochemistry. In particular, she examined how soil organic matter and nutrient pools in residential lawns were affected by different lawn system management strategies. These different strategies arise from an interaction between municipal-level policies and  the yard-care behaviors of individual home residents. Distinct high-amendment and low-amendment strategy types were evident, and corresponded with the use of reclaimed water. Viviana’s work identified important implications for soil chemistry and microbiology, and contributes to understanding ecological variability in urban systems. Good work Viviana!

Benefits of age – services provided by older forests

How do ecosystems change as they age? It’s a question we address in our most recent article – read it here! We identify how ecosystems might continue accumulating nitrogen even after they stop growing.

Oak forests in central Pennsylvania. Young forest stand (about 10 years old) on the left, and older forest stand (over 100 years old) on the right. The older forest has accumulated abundant soil organic matter, and has great potential for capturing nitrogen and holding it in a stable form.

Oak forests in Pennsylvania. Young forest stand (about 10 years old) on the left, and older forest stand (over 100 years old) on the right. The older forest has accumulated abundant soil organic matter, and has great potential for capturing nitrogen and holding it in a stable form.

Succession, or the progressive change in ecological systems as they age, has long been an important concept in ecology that helps organize the discipline. For example, ecologists who focus on the cycling of energy and essential nutrients might investigate how these cycles change as an ecosystem ages. Ecologists know that young, growing ecosystems can increase their stockpile of nutrients (such as nitrogen) by storing it in accumulating plant matter. We also know that soils are a huge reservoir for storing nitrogen, and that even old ecosystems can continue to accumulate nitrogen in soil even after the plants have stopped growing. Our research, conducted with Jason Kaye at Penn State and Michael Castellano at Iowa State, suggests a couple mechanisms by which nitrogen can continue to accumulate in the soil of old forests. First, we show that new inputs of nitrogen are captured by soil organic matter much faster than are released, meaning the soil must accumulate nitrogen over time. Second, we found that the potential for this accumulation was greater in older forests because those forests had more soil organic matter. This research helps us understand the link between ecosystem succession and the nutrient economy of ecosystems, and highlights a significant ecosystem service—the capture of nitrogen, which can severely impair air and water quality—of mature ecosystems.

Big strides ahead

As we move into the second half of the semester, members of the lab are preparing to take important steps forward in their careers as ecologists. PhD student Bert Anderson will be defending his dissertation proposal in efforts to move forward to candidacy status. Likewise, Viviana Penuela will be defending her Master’s thesis that reports her studies of urban soil responses to the use of reclaimed water. Best wishes to them!!!

History is alive in your front yard

Was your yard once a farm? It matters! Check out our recent paper here.

This farm will affect the yards soon to replace it long after it is gone (Photo: Central Arizona-Phoenix LTER).

This farm will affect the yards soon to replace it long after it is gone (Photo: Central Arizona-Phoenix LTER).

The natural world today bears marks of the  past. These legacies may seem obvious—clearly coastlines remain affected by hurricanes and oil spills long after these disturbances have ended. However, conclusively linking a particular bit of history to specific conditions today turns out to be tricky. In our recent paper with Ann Kinzig at Arizona State and Jason Kaye at Penn State, we investigated whether the amount of carbon and nitrogen stored in soil was different in lawns that had been farms a century ago than in lawns carved out of previously undisturbed Sonoran Desert ecosystem. It did matter! It also mattered how old the lawn was. Thus two ecosystems (for example, two lawns) that look similar on the surface may function quite differently because they have different histories. (So don’t judge a book by its cover!) Globally, explosive urban growth gobbles up both farmland and natural ecosystems alike. So the habitat for billions of urban people will depend on what their neighborhood used to be. Moreover, carbon and nitrogen are two chemical elements that dramatically alter the energy balance of the atmosphere and the water quality of lakes, streams, and bays. So, the sequestration, or storage, or carbon and nitrogen in soil is of widespread interest. (This work was funded by a McDonnell Foundation grant to Ann Kinzig, and a NSF grant to the CAP-LTER.)

Remote sensing of soil ecosystem services

remotesensing2Wetland carbon and nitrogen storage detected by satellite…check it out here! Naveen Anne and his advisor Dr. Amr Abd-Elrahman at the University of Florida turned their remote sensing expertise to ecosystem services provided by the soils of coastal wetlands. Ecosystem services are the free benefits that society gets from nature, and coastal wetlands like mangrove forests and salt marshes provide them in abundance. In particular, coastal wetlands store massive amounts of carbon and nitrogen in rich deposits of soil organic matter, thereby protecting the quality of the atmosphere and ocean water. The Lewis Lab at USF collaborated with Naveen and Amr to develop spectral models of organic matter, carbon, and nitrogen storage in coastal soils. Spectral models predict features of the Earth’s surface based on light detected by remote-sensing instruments such as satellites. These technologies are particularly useful because coastal wetlands are hard to access on foot, but their important services may be sensitive to disturbances ranging from habitat destruction and oil spills to climate change and sea level rise. In this paper, we took remote sensing of soil one step further than past work, by focusing on soil attributes that are particular to the service of carbon and nitrogen storage. Namely, we developed spectral models of portions of organic matter, carbon, and nitrogen that are easily lost from soils. These models could be used to prioritize coastal areas for protection. This work was supported with funds from the US National Science Foundation.

Congratulations Viviana!

VivianaViviana 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.

Farming stratgies when going organic


Study lead Meagan Schipanski and co-author Jason Kaye.

Study lead Meagan Schipanski and co-author Jason Kaye.

In the environment, everything affects everything else, prompting someone to once say, “ecology isn’t rocket science, it’s much harder.” This complexity is especially true in agricultural systems. Farmers make many management decisions: go organic or not, use full or reduced plowing, decide what mixture of crops to rotate. These decisions then affect soil quality and weed and insect abundance, which in turn affect crop production. This complexity makes it difficult to determine which management strategies really work, and why. To help resolve this challenge, the Lewis Lab collaborated in a recent study that compared soil, weed, insect, and crop responses to different cropping system strategies. The study was conducted at Penn State, led by Meagan Schipanski at Colorado State University. It was set in Pennsylvania at experimental farmland undergoing a three-year transition from conventional to organic production. Farm plots were plowed using either full or reduced tillage, and either included perennial sod-forming or annual cover crops prior to cultivating soy and corn. We used statistical approaches that are relatively new to agroecology in order to determine how these management strategies impacted interactions among soils, weeds, and insects, and how those factors in turn influenced crop yields. We found that managing weed populations through full tillage in organic farm systems can improve crop yields. However, these short-term profits come at the expense of a loss in soil quality and beneficial insect conservation when soils are heavily plowed. Check out the paper here!

Coastal wetlands and climate change

Graphical abstractCheck 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.

Services provided by wetlands – is hydrology important?

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 forcypressdome_inside_flooded 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!