2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 1
Presentation Time: 3:05 PM

Environmental and Geological Controls on the Soil Carbon Cycle In a Changing World

AMUNDSON, Ronald, Division of Ecosystem Sciences, University of California, Berkeley, 137 Mulford Hall, #3114, Berkeley, CA 94720-3114, SANDERMAN, Jonathan, Earth and Planetary Sciences, UC Santa Cruz, 800 Buchanan Street, Room 2125, Albany, CA 94710 and YOO, Kyungsoo, Soil, Water, and Climate, University of Minnesota, 1991 Upper Buford Circle, St. Paul, MN 55108, earthy@nature.berkeley.edu

Soil C is the balance between plant inputs and biological and physical losses. Nearly 20% of anthropogenic CO2 emissions are from land use changes, but reducing this loss requires understanding the natural and management-specific impacts on soil C. The main control on the soil C cycle is climate. Radiocarbon measurements have shown that decomposition accelerates with increasing temperature and that under projected warming scenarios soils should release CO2 and provide a positive feedback to warming. Ecosystem-scale C fluxes also reveal a strong temperature effect on soil C residence times. Recently-assessed reductions in soil C storage in Great Britain provide support for the concern about positive feedbacks to warming. Recent research has refined the rates of C erosion and its fate in both cultivated and undisturbed upland ecosystems. Briefly, soil C on actively eroding hillslopes is in a perpetual non-steady state due to ongoing erosion and deposition. Additionally, vegetated upland watersheds act as filters for large annual fluxes of DOC, ultimately releasing small refractory C pools to aqueous systems. In cultivated soils, the changes in soil C are further impacted by climate. Comparative studies of cultivated and non-cultivated soils in the Great Plains and India show that fractional losses of soil C during cultivation are greater under humid climates. Recent 14C work shows that large-scale soil structure significantly controls soil C storage, and that disruption of this structure by tillage can rapidly release pools of C that have been stored for millennia. While improved and scientifically-informed management of agricultural ecosystems is an important tool in mitigating anthropogenic greenhouse gas emissions, the most significant impact on C emissions can be achieved by reducing the rates of global land conversion.
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