Research & Publications

As a postdoc with Whendee Silver, I studied how carbon storage in soils is affected by soil characteristics and management practices. This is important because the more carbon that’s stored in the soil, the less that is in the atmosphere trapping heat and causing global warming. A good place to study this is on dairies. In California we have over 1.7 million dairy cows which produce more than 70 billion pounds of manure each year. This is a big source of carbon and, while some of that carbon is being stored in soil, I investigated how we can increase that amount.

My project had three parts:

1. Greenhouse gas emissions from livestock manure management

I wanted to know the state-of-the-science of greenhouse gas emissions from livestock agriculture. I did a comprehensive literature search of field-scale greenhouse gas flux measurements from dairy manure management globally. Surprisingly, less than 40 studies met my qualifications and, when I compared their results to estimates based on the most recent IPCC models, some had much higher fluxes than the estimates predicted.

- Related paper in Global Change Biology. Open access preprint available here.

2. Long-term impacts of manure additions to rangelands

I collected and analyzed soils from pastures on organic dairies in California. Some of these pastures have had manure spread on them for decades, while others haven’t so the only manure that’s been added has been the relatively small amount that “falls” during grazing. The difference in carbon content between these fields indicates how much carbon can be stored in these types of grassland soils. Using the DAYCENT biogeochemical model, I modeled these fields to explore the net greenhouse gas impact of manure additions.

- Related paper in Global Change Biology.

3. Field measurements of greenhouse gas fluxes from dairy manure management

I measured greenhouse gas fluxes in a corral, a manure pile, and a field on a pasture-based dairy in California monthly for almost 2 years. This is one of the longest field measurement campaigns of this kind yet. This data will help test biogeochemical models and identify the best management practices to mitigate climate change.

- Related paper in Ecological Applications.

I explored the relationship between soils, geomorphology, and climate in the Atacama Desert, Chile. I compiled soil data, erosion rates and exposure ages from cosmogenic radionuclide measurements, and dust input rates from passive dust traps. This work provides a field test of some geomorphic models, paving the way for a better understanding of what's going on on Mars as well as other arid systems on Earth. My sites spanned a gradient from biotic landscapes to abiotic ones, thus precipitation is a key variable and its effects are more evident than in more humid regions.

- Related paper in Earth Surface Processes and Landforms.

If you go to -24.131691 S and -69.971654 W in Google, and zoom in close to the hills there, you'll see the hillslopes are covered with stripes that run parallel to contour. I like to call them zebra stripes. Except for one researcher in 1982, no one has really studied these surface features but there is a lot that we might be able to learn from them. In the summer of 2006, I did some sprinkling experiments and some infiltration measurements, as well as a little survey work, to start to quantify the zebra stripes. I'm determining their extent and what controls their appearance - likely a combination of topography, bedrock, and precipitation.

The zebra stripes are probably formed by surface wash - a rare event in the Atacama. From the data I've gathered, I'm attempting to quantify how big the precipitation events must be to mobilize and sort the gravels. Given that there is almost no historical climate data for the core of the desert, this could be useful information for interpreting the landscape and soils.

- Related paper in Geomorphology.

I've been down to Chile three times now and have quite a few Atacama photos.