HR: 10:20h
AN: B22C-01 INVITED    [Abstracts]
TI: Soil carbon as a metric for longterm ecosystem function
AU: * Harden, J W
EM: jharden@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd, Menlo Park, CA 94025, United States
AU: Neff, J C
AF: Geological Sciences Dept. & Environmental Studies, Univ. Colorado, Boulder, CO 80309, United States
AB: Soils are responsible for the processing of carbon, water, nutrients, and toxins and as such are a key component of ecosystem resilience. It follows, then, that ecosystem recovery from disturbances by geomorphic, fire, cultivation or urbanization processes should be controlled in part by soil carbon storage and turnover. Soils however, are also highly heterogeneous and are composed of a range of SOM pools with varying turnover times. We suggest that the relative distribution of carbon through these pools is a key characteristic of ecosystems that are more or less resilient following disturbance. Based on a number of soil types around the world, we propose that the most resilient systems are those with large stocks of carbon that turn over in decadal to century time scales. These systems are typically found on early Holocene to late Pleistocene geomorphic surfaces in a wide range of climatic settings. Using this paradigm for soils and ecosystems, we can generalize as to the vulnerability of soil systems across a number of ecosystems. In boreal forest ecosystems, changes in climate, and fire disturbance make ecosystems highly vulnerable to loss of decade-to-century soil carbon, which resides near the soil surface as free light fraction. In these settings, near to complete loss of the intermediate turnover pools is possible because of limited physical protection of the SOM and has repercussions that range from ecological successional dynamics to global C cycling. Dryland soils are similarly vulnerable to change because, like boreal systems, the bulk of SOM is located in pools of light density carbon that are prone to loss following disturbances such as fire and grazing. This paradigm can also be applied to understanding specific mechanisms that destabilize or stabilize this decade-to-century soil carbon. Combustion, erosion, and physical disaggregation (such as by tillage) destabilize while ponding, erosion mitigation, and no-till aggregation help to stabilize this important pool. These examples help to establish a generalized understanding of ecosystem resilience under various disturbance events.
DE: 0428 Carbon cycling (4806)
DE: 0429 Climate dynamics (1620)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting