Friday, 14 July 2006 - 8:00 AM
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A Paradigm for Soil Resilience.

Jennifer W. Harden, U.S. Geological Survey, 345 Middlefield Road, ms 962, Menlo Park, CA 94025

Soil degradation is a disturbance risk facing all nations today, with climate change, land management, urbanization, and pollution exerting disturbances from which recovery and resilience are uncertain and, in most cases, not quantified. Underlying mechanisms for ecosystem resilience to soil disturbance rely fundamentally on soils, soil properties, and dynamics between soils and contiguous systems. Organic matter provides substrate for biotic reactions, regulates biotic diversity, nutrient turnover and nutrient retention, permeability of gas and water, and wind and water erosion. It therefore follows that soil carbon storage and turnover could provide an index for soils' resilience and vulnerability to disturbance. Several paradigms from Quaternary geology, soil classification, and ecology can be combined into one over-arching index of soil resilience to disturbance centered on the soil chronosequence. Young landforms underlain by deposits 1 to 102 yrs in age, are postulated to be potentially rich in nutrients but limited by soil water-holding capacity and nitrogen colonizers. “Juvenile landforms” underlain by deposits 102 to 104 yrs in age are likely most resilient as a result of abundant primary minerals, secondary oxides and clays that hold but do not restrict water flow, abundant organic matter storage, and abundant plant-available nutrients. “Old Landforms” underlain by deposits 104 to 106 yrs are least resilient to disturbance as a result of depleted primary minerals, occlusion of nutrients by secondary minerals, and restricted hydrologic flow that inhibits ideal use of available water. Resilience to soil disturbance induced by climatic change, land use, and pollution therefore depends fundamentally on landform age in context of climatic and vegetation history which vary regionally and in context of erosion and re-deposition (such as eolian inputs and exports) which vary locally and regionally. To test this paradigm, soil radiocarbon is used as a proxy for soil carbon turnover and soils' resilience to change.

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