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Rates of soil mixing and associated carbon fluxes in a forest vs. tilled agricultural field:  Implications for modeling the soil carbon cycle
Department of Soil, Water, and Climate, University of Minnesota–Twin Cities, St. Paul, Minnesota, USA.
Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware, USA.
Stroud Water Research Center, Avondale, Pennsylvania, USA.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2011 (English)In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 116, no G01014Article in journal (Refereed) Published
Abstract [en]

In natural ecosystems, bioturbation is an essential component of soil formation, whereas tillage drives soil mixing in agricultural soils. Yet soil mixing is commonly neglected in modeling soil organic carbon (SOC) as it responds to land use changes. Here, in order to determine mixing-driven carbon fluxes, we combine a mass balance model with measurements of 210Pb activities and SOC contents. Soil mixing rates by tillage decrease from 3.4 ± 2.3 cm yr−1 at the surface to 0.8 ± 0.2 cm yr−1 at a depth of ∼20 cm, causing the SOC stored in the upper 25 cm of the soil to be physically turned over via mixing annually. In contrast, the bioturbation-driven soil mixing velocity at the forest increases from 0.6 ± 0.1 cm yr−1 at the surface to 2.7 ± 0.5 cm yr−1 at a depth of ∼10 cm, which results in physically turning over SOC in the A horizon via mixing on years to decadal time scales. Therefore, SOC fractions with different susceptibilities to decomposition may have significantly different physical trajectories within the soils over their lifespans, and thus the assumption of C-cycling models that all SOC fractions experience identical environmental conditions is unlikely to be realistic. Carbon sinks, excesses of plant carbon inputs over decomposition carbon losses, are found within the top portion of the A horizons. These carbon excesses are transferred, via mixing, to the lower portion of the A horizon, where they are decomposed. By quantifying mixing-derived SOC fluxes, this study shows a previously unrecognized complexity in understanding SOC dynamics associated with land use changes.

Place, publisher, year, edition, pages
2011. Vol. 116, no G01014
National Category
Ecology Earth and Related Environmental Sciences
Research subject
Earth Sciences with Specialization Environmental Analysis
URN: urn:nbn:se:umu:diva-46317DOI: 10.1029/2010JG001304OAI: diva2:437803
Available from: 2011-08-30 Created: 2011-08-30 Last updated: 2011-09-26Bibliographically approved

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