Welcome to GeoUnion, the graduate student body of the Department of Earth, Environmental and Planetary Sciences. GeoUnion strives to supplement the overall graduate student experience at Rice and DEEPS. GeoUnion represents DEEPS in the overall Rice grad student community, acts as a liaison between students and faculty and organizes a number of intra- and inter-departmental events throughout the academic year.
In 1842, Darwin identified three types of reefs: fringing reefs, which are directly attached to volcanic islands; barrier reefs, which are separated from volcanic islands by lagoons; and ring reefs, which enclose only a lagoon and are defined as atolls. Moreover, he linked these reef types through an evolutionary model in which an atoll is the logical end point of a subsiding volcanic edifice, as he was unaware of Quaternary glaciations. As an alternative, starting in the 1930s, several authors proposed the antecedent karst model; in this model, atolls formed as a direct interaction between subsidence and karst dissolution that occurred preferentially in the bank interiors rather than on their margins through exposure during glacial lowstands of sea level. Atolls then developed during deglacial reflooding of the glacial karstic morphologies by preferential stacked coral-reef growth along their margins. Here, a comprehensive new model is proposed, based on the antecedent karst model and well-established sea-level fluctuations during the last 5 million years, by demonstrating that most modern atolls from the Maldives Archipelago and from the tropical Pacific and southwest Indian Oceans are rooted on top of late Pliocene flat-topped banks. The volcanic basement, therefore, has had no influence on the late Quaternary development of these flat-topped banks into modern atolls. During the multiple glacial sea-level lowstands that intensified throughout the Quaternary, the tops of these banks were karstified; then, during each of the five mid-to-late Brunhes deglaciations, coral reoccupied their raised margins and grew vertically, keeping up with sea-level rise and creating the modern atolls.
Expected final online publication date for the Annual Review of Marine Science, Volume 13 is January 4, 2021.
André W. Droxler1 and Stéphan J. Jorry2
2Marine Geosciences Unit, IFREMER, 29280 Plouzané, France
– OCTOBER 19, 2020
The abstract benefits of biochar for long-term storage of carbon and nitrogen on American farms are clear, and now new research from Rice University shows a short-term, concrete bonus for farmers as well.
That would be money. To be precise, money not spent on irrigation.
In the best-case scenarios for some regions, extensive use of biochar could save farmers a little more than 50% of the water they now use to grow crops. That represents a significant immediate savings to go with the established environmental benefits of biochar.
The open-access study appears in the journal GCB-Bioenergy.
Biochar is basically charcoal produced through pyrolysis, the high-temperature decomposition of biomass, including straw, wood, shells, grass and other materials. It has been the subject of extensive study at Rice and elsewhere as the agriculture industry seeks ways to enhance productivity, sequester carbon and preserve soil.
The new model built by Rice researchers explores a different benefit, using less water.
“There’s a lot of biochar research that focuses mostly on its carbon benefits, but there’s fairly little on how it could help stakeholders on a more commercial level,” said lead author and Rice alumna Jennifer Kroeger, now a fellow at the Science and Technology Policy Institute in Washington, D.C. “It’s still an emerging field.”
The study co-led by Rice biogeochemist Caroline Masiello and economist Kenneth Medlock provides formulas to help farmers estimate irrigation cost savings from increased water-holding capacity (WHC) with biochar amendment.
The researchers used their formulas to reveal that regions of the country with sandy soils would see the most benefit, and thus the most potential irrigation savings, with biochar amendment, areas primarily in the southeast, far north, northeast and western United States.
The study analyzes the relationship between biochar properties, application rates and changes in WHC for various soils detailed in 16 existing studies to judge their ability to curtail irrigation.
The researchers defined WHC as the amount of water that remains after allowing saturated soil to drain for a set period, typically 30 minutes. Clay soils have a higher WHC than sandy soils, but sandy soils combined with biochar open more pore space for water, making them more efficient.
WHC is also determined by pore space in the biochar particles themselves, with the best results from grassy feedstocks, according to their analysis.
In one comprehensively studied plot of sandy soil operated by the University of Nebraska-Lincoln’s Agricultural Water Management Network, Kroeger calculated a specific water savings of 37.9% for soil amended with biochar. Her figures included average rainfall and irrigation levels for the summer of 2019.
The researchers noted that lab experiments typically pack more biochar into a soil sample than would be used in the field, so farmers’ results may vary. But they hope their formula will be a worthy guide to those looking to structure future research or maximize their use of biochar.
More comprehensive data for clay soils, along with better characterization of a range of biochar types, will help the researchers build models for use in other parts of the country, they wrote.
“This study draws attention to the value of biochar amendment especially in sandy soils, but it’s important to note that the reason we are calling out sandy soils here is because of a lack of data on finer-textured soils,” Masiello said. “It’s possible that there are also significant financial benefits on other soil types as well; the data just weren’t available to constrain our model under those conditions.”
“Nature-based solutions are gaining traction at federal, state and international levels,” Medlock added, noting the recently introduced Growing Climate Solutions Act as one example. “Biochar soil amendment can enhance soil carbon sequestration while providing significant co-benefits, such as nitrogen remediation, improved water retention and higher agricultural productivity. The suite of potential benefits raises the attractiveness for commercial action in the agriculture sector as well as supportive policy frameworks.”
Rice alumna Ghasideh Pourhashem, a nonresident faculty scholar at the Center for Energy Studies (CES) at Rice’s Baker Institute for Public Policy, is co-author of the paper. Masiello is the W. Maurice Ewing Professor, a professor of Earth, environmental and planetary sciences and a faculty scholar at the CES. Medlock is the James A. Baker, III, and Susan G. Baker Fellow in Energy and Resource Economics at the Baker Institute, senior director of the CES and an adjunct assistant professor of economics.
The Rice Department of Earth, Environmental and Planetary Sciences and the Rice Shell Center for Sustainability supported the research.
Department of Earth, Environmental and Planetary Sciences
6100 Main Street
Houston, TX 77005 USA