Research

A sampling of some of our ongoing and recently completed projects:

The role of iron redox dynamics in carbon losses from tropical forest soils

(NSF Ecosystems project with Whendee Silver and Aaron Thompson) Bisley worm castings

We seek to understand how fluctuations in moisture and soil oxygen availability driven by climate change feed back on coupled interactions among soil microbial and geochemical processes that control carbon turnover. Sequential iron reduction and oxidation appear to have a significant but poorly-described role in driving the decomposition of biochemically recalcitrant (and likely old) organic matter.

Postdoc Wenjuan Huang is leading the charge on this project.

 

Prairie pothole soils: hotspots of nitrogen losses from agricultural landscapes?

This work is funded by the USDA, EPA, the Iowa Nutrient Research Center, and the Leopold Center for Sustainable Agriculture. Soil moisture is a key factor regulating both nitrate leaching losses and nitrous oxide production. Moisture varies predictably over space in the Des Moines lobe region of Iowa, where depressions known as prairie potholes (former wetlands)

IMG_0085

are consistently wetter than adjacent upland soils. Potholes may contribute disproportionally to nitrate losses and nitrous oxide emissions, implying that targeted conversions of potholes under corn/bean cultivation to perennial vegetation could yield substantial reductions in these impacts. PhD student Nate Lawrence and Carlos Tenesaca are leading this work.

 

Impacts of iron biogeochemical cycling on soil carbon stabilization in Iowa agroecosystems

This work is funded in part by the Center for Global and Regional Environmental Research (CGRER). Perennial cropping systems offer important opportunities for improving agroecosystem sustainability, and soil C sequestration and related fertility enhancement are chief among potential benefits. We seek to understand the mechanisms by which mineral-associated C is accrued or lost, using the Comparison of Biofuels Study (COBS) led by ISU colleague Matt Liebman. We will use  measurements of Fe dynamics and C stable isotopes to tease apart these questions.  Grad student Chenglong Ye and undergrad Anthony Mirabito are leading this work.

Controls on lignin degradation: bridging old and new paradigms of soil organic matter:

Collaboration with Ken Hammel, USDA Forest Products Lab and University of Wisconsin-Madison. Lignin is difficult to decompose, but recent work suggests that it may be degraded relatively rapidly in natural soils. The question remains: how important is lignin as a constituent of soil organic matter, and what are the biogeochemical controls on lignin losses and stabilization? We are addressing these questions using incubations of a broad spectrum of soils with 13C-labeled lignins and litter.

utah sheep in high countryRecent projects: Tracing nitrogen inputs, transformations, and losses across wildland / agricultural / urban transitions

(NSF-EPSCOR project with many collaborators at the University of Utah and Utah State University)

Our research explores the patterns and processes controlling N dynamics across wildland to urban land use gradients spanning mountains to valleys in northern Utah. This work has revealed that wildland and urban ecosystems adjacent to the Wasatch Mountains have a strong capacity for retaining nitrogen deposition, yet N cycling in wildland areas can be 131220_SagePointDormsperturbed by relatively subtle land use changes (e.g. roads, dogs, low-intensity grazing). Multiple lines of inference suggest that leaking municipal sewers may be a primary N source to urban streams in this region.