Long-term modeling of soil C erosion and sequestration at the small watershed scale |
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Authors: | R C Izaurralde J R Williams W M Post A M Thomson W B McGill L B Owens R Lal |
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Institution: | (1) The Joint Global Change Research Institute, 8400 Baltimore Avenue, Suite 201, College Park, MD 20740-2496, USA;(2) Blacklands Research Center, Texas A&M University, 808 East Blacklands Road, Temple, TX 76502, USA;(3) Oak Ridge National Laboratory, Building 1509, Bethel Valley Road, PO Box 2008 MS6335, Oak Ridge, TN 537831-6335, USA;(4) College of Science and Management, University of Northern British Columbia, 3333 University Way, Prince George, BC V2N 4Z9, Canada;(5) North Appalachian Experimental Watershed, USDA-Agricultural Research Station, 28850 SR 621, Coshocton, OH 43812-0488, USA;(6) School of Natural Resources Food, Agricultural and Environmental Sciences, The Ohio State University, 422B Kottman Hall, 2021 Coffey Road, Columbus, OH 43210, USA |
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Abstract: | The soil C balance is determined by the difference between inputs (e.g., plant litter, organic amendments, depositional C)
and outputs (e.g., soil respiration, dissolved organic C leaching, and eroded C). There is a need to improve our understanding
of whether soil erosion is a sink or a source of atmospheric CO2. The objective of this paper is to discover the long-term influence of soil erosion on the C cycle of managed watersheds
near Coshocton, OH. We hypothesize that the amount of eroded C that is deposited in or out of a watershed compares in magnitude
to the soil C changes induced via microbial respiration. We applied the erosion productivity impact calculator (EPIC) model to evaluate the role of erosion–deposition
processes on the C balance of three small watersheds (∼1 ha). Experimental records from the USDA North Appalachian Experimental
Watershed facility north of Coshocton, OH were used in the study. Soils are predominantly silt loam and have developed from
loess-like deposits over residual bedrock. Management practices in the three watersheds have changed over time. Currently,
watershed 118 (W118) is under a corn (Zea mays L.)–soybean (Glycine max L.] Merr.) no till rotation, W128 is under conventional till continuous corn, and W188 is under no till continuous corn.
Simulations of a comprehensive set of ecosystem processes including plant growth, runoff, and water erosion were used to quantify
sediment C yields. A simulated sediment C yield of 43 ± 22 kg C ha−1 year−1 compared favorably against the observed 31 ± 12 kg C ha−1 year−1 in W118. EPIC overestimated the soil C stock in the top 30-cm soil depth in W118 by 21% of the measured value (36.8 Mg C
ha−1). Simulations of soil C stocks in the other two watersheds (42.3 Mg C ha−1 in W128 and 50.4 Mg C ha−1 in W188) were off by <1 Mg C ha−1. Simulated eroded C re-deposited inside (30–212 kg C ha−1 year−1) or outside (73–179 kg C ha−1 year−1) watershed boundaries compared in magnitude to a simulated soil C sequestration rate of 225 kg C ha−1 year−1 and to literature values. An analysis of net ecosystem carbon balance revealed that the watershed currently under a plow
till system (W128) was a source of C to the atmosphere while the watersheds currently under a no till system (W118 and W188)
behaved as C sinks of atmospheric CO2. Our results demonstrate a clear need for documenting and modeling the proportion of eroded soil C that is transported outside
watershed boundaries and the proportion that evolves as CO2 to the atmosphere. |
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