The Formation of Clay-Enriched Horizons by Lessivage
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©2018. American Geophysical Union. All Rights Reserved. Soils with argillic horizons comprise more than 25% of the Earth's surface. Although their origin is still debated, lessivage is often invoked to explain them, but the long timescales involved hinder its direct experimental verification. We present a parsimonious model of clay transport, formulated for long timescales over which lessivage is modeled stochastically, complemented by detailed field observations. This probabilistic description allows us to predict the clay profile, the depth of the Bt horizon from the surface, and the mean clay residence time. The results are tested with field measurements at different locations in the Calhoun Critical Zone Observatory. Dimensional analysis unveils two dimensionless parameters governing lessivage dynamics, leading to a classification based on erosion rates and lessivage characteristics. We identify static and eluviated regimes, in which erosion or eluviation prevails, and an illuviated regime, in which the balance between lessivage and erosion brings about the formation of a Bt horizon.
Published Version (Please cite this version)
Calabrese, S, DD Richter and A Porporato (2018). The Formation of Clay-Enriched Horizons by Lessivage. Geophysical Research Letters, 45(15). pp. 7588–7595. 10.1029/2018GL078778 Retrieved from https://hdl.handle.net/10161/21231.
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Richter’s research and teaching links soils with ecosystems and the wider environment, most recently Earth scientists’ Critical Zone. He focuses on how humanity is transforming Earth’s soils from natural to human-natural systems, specifically how land-uses alter soil processes and properties on time scales of decades, centuries, and millennia. Richter's book, Understanding Soil Change (Cambridge University Press), co-authored with his former PhD student Daniel Markewitz (Professor at University of Georgia), explores a legacy of soil change across the Southern Piedmont of North America, from the acidic soils of primary hardwood forests that covered the region until 1800, through the marked transformations affected by long-cultivated cotton, to contemporary soils of rapidly growing and intensively managed pine forests. Richter and colleagues work to expand the concept of soil as the full biogeochemical weathering system of the Earth’s crust, ie, the Earth’s belowground Critical Zone, which can be tens of meters deep. The research examines decadal to millennial changes in the chemistry and cycling of soil C, N, P, Ca, K, Mg, and trace elements B, Fe, Mn, Cu, Be, Zr, and Zn across full soil profiles as deep at 30-m. Since 1988, Richter has worked at and directed the Long-Term Calhoun Soil-Ecosystem Experiment (LTSE) in the Piedmont of South Carolina, a collaborative study with the USDA Forest Service that quantifies how soils form as natural bodies and are transformed by human action, and a study that has grown to become an international model for such long-term soil and ecosystem studies. In 2005, Richter and students initiated the first comprehensive international inventory project of the world’s LTSEs, using an advanced-format website that has networked metadata from 250 LTSEs. The LTSEs project has held three workshops at Duke University, NCSU's Center for Environmental Farming Systems, and the USDA Forest Service's Calhoun Experimental Forest and Coweeta Hydrologic Laboratory, hosting representatives from Africa, Asia, Australia, Europe, and the Americas. Richter's 60-year old Long Term Calhoun Soil and Ecosystem Experiment is linked to similar experiments and platforms around the world via the ‘Long-Term Soil-Ecosystem Experiments Global Inventory’, assembled by Dan Richter, Pete Smith, and Mike Hofmockel."He is an active member of the International Commission on Stratigraphy’s Working Group on the Anthropocene. Richter has written in the peer-reviewed literature about all of these projects, and in November 2014 his soils research at the Calhoun and his soils teaching were featured in Science magazine.
Amilcare Porporato earned a Master Degree in Civil Engineering (summa cum laude) in 1992 and his Ph.D. in 1996 from Polytechnic of Turin. He was appointed Assistant Professor in the Department of Hydraulics of the Polytechnic of Turin, and he moved to Duke University in 2003, where he is now Full Professor in the Department of Civil and Environmental Engineering with a secondary appointment with the Nicholas School of the Environment.
In June 1996, Porporato received the Arturo Parisatti International Price, awarded by the Istituto Veneto di Scienze, Lettere e Arti. He was Research Associate at the Texas A&M University (USA) in 1998 and Visiting Scholar at Princeton University (USA), Department of Civil and Environmental Engineering, from 1999 to 2001. In 2008-2009 he was the first Landolt & Cie Visiting Chair in “Innovative Strategies for a sustainable Future” at Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland. He was awarded the 2007 Professor Senol Utku’ award, the 2010 Earl Brown II Outstanding Civil Engineering Faculty Award, and in 2011 he received a Lagrange fellowship from the Polytechnic of Turin, the CRT bank and the ISI (Institute for Scientific Interchange). In 2012 he was elected an AGU fellow.
His main research interests regard nonlinear and stochastic dynamical systems, hydrometeorology and soil-atmosphere interaction, soil moisture and plant dynamics, soil biogeochemistry, and ecohydrology.
Porporato has been Editor of Water Resources Research (AGU) (2004-2009), and he is currently editor for Hydrological Processes. He is also member of the editorial board of Advances in Water Resources and the Hydrologic Science Journal. Among other things, he was chairman and convener of the Ecohydrology sessions of the AGU Spring Meeting in 2001 and 2002 and of the EGU in 2004-2006. Porporato has been part of the Italian research groups of Turbulence and Vorticity and of Climate, Soil and Vegetation Interaction, an adviser for real-time forecasting in the Piedmont Region (Italy), and ecohydrology (US National Academy).
Porporato's didactic experience comprises courses in Environmental Fluid Mechanics, Hydraulics, Hydraulic Constructions, Statistical and Physical Hydrology, Ecohydrology, Nonlinear Dynamics and Stochastic Processes. He has also been the didactic coordinator for the International School "Hydroaid: Water for Development", co-organized by the Polytechnic of Turin and the Italian Ministry of Foreign Affairs.
Porporato is author of more than 140 peer-reviewed papers, several publications presented at national and international conferences and invited talks. He is also co-author of the book "Ecohydrology of water controlled ecosystems" (Cambridge Univ. Press, 2004) and the edited the book "Dryland Ecohydrology" (Springer, 2005).
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