USGS - science for a changing world
Winter coring of soil

NOTE: This project has sunset and is superceded by Fate of Carbon in Soil Systems. Because this page is no longer maintained, all links below have been removed.

The Alaskan interior contains enormous carbon reserves in vegetation and soils. We are assessing carbon reservoirs and their interaction with fire, permafrost and surface-water interactions. We are testing a number of hypotheses through field research and modeling. Specifically, we hypothesize that:

  1. Soil drainage exerts a major control over carbon exchange at the landscape scale and is closely associated with (i) decomposition rates, (ii) fuel structure and storage, (iii) fire severity, and (iv) rates of permafrost degradation and recovery.
  2. Gradual warming, fire disturbance, and permafrost/active layer changes will influence interactions among soils, nutrients, and hydrology that control the uptake and release of carbon dioxide, dissolved carbon and nutrients, and methane.
  3. A regional understanding of the carbon budget can be constructed from process-based ecosystem models and detailed site measurements of fire extent and severity, permafrost, and hydrology.

fieldwork

Our field strategy involves a process-oriented study of upland and wetland systems using chronosequences of stand-age (time since fire). Across these chronosequences, we are determining carbon inputs by plants as well as carbon losses due to fire and decomposition. Our site matrix includes well drained (no permafrost) to poorly drained (with permafrost and high water tables) conditions. Fire emissions and the effects of fire on carbon and nutrient availability are also being addressed through work on wildland and experimental burns.

Together with non-USGS collaborators, we are measuring site conditions, inputs to soil carbon, mechanisms of soil carbon loss, and fire emissions. The US Geological Survey is actively playing a role in the following studies:

Specific measurements of foliar, moss, woody, and soil components include extensive analyses of C, N, 13C, and 15N as well as selected sample analysis of 14C, P, and Hg. Such isotopic measurements allow us to refine models of CO2 emissions over the fire cycle. Our models then can be compared directly to carbon losses due to fire and carbon inputs by net primary production. Our collaborators also studied:

  • Respiration and net CO2 budgets: Jim Randerson (UC Irvine)
  • Heterotrophic and autotrophic respiration: Ted Schuur (University of Florida)
  • Role of fungi in nutrient cycling: Kathleen Treseder (UC Irvine)
  • Remote sensing of fire chronosequence attributes: Eric Kasischke (University of Maryland)
  • modeling

    Coring frozen soilGIS-based drainage types of Alaska. Light colors are excessively well drained, dark colors are very poorly drained. Click here for a paper on soil drainage and carbon in Alaska.

    Our primary modeling objective is to establish a strategy for the regionalization of field measurements in order to both maximize the utility of and insights gained from our field data and strengthen existing carbon models by introducing a process-level understanding of carbon exchange.

    Previous work has demonstrated the importance of including soil drainage and fire disturbance as key parameters in defining the fate of carbon due to their effect on fire severity, decomposition, and vegetation structure/function. Our modeling efforts include:

  • The Terrestrial Ecosystem Model (TEM). Work by the group of David McGuire (USGS/Univ. of Alaska) has expanded TEM to include important environmental factors such as moss and snow thermal conductivity and thickness (all of which impact soil temperatures in organic soil layers), soil factors such as soil carbon lability and carbon-nitrogen interactions, and disturbances such as fire.
  • A site-specific process model aimed at determining the key soil mechanisms that must be represented when scaling from the site to the regional level. This model is being developed by Jason Neff.
  • GIS-based modeling of soil drainage and fire history combined with long-term carbon mass balance.
  • Modeling efforts are breaking new ground by dealing with both soil drainage (from a spatial perspective) and fire (from both a spatial and temporal perspective). Process-based models will help test the sensitivity of carbon to factors such as fire combustion, plant structure, permafrost, and mineral/organic complexation. Spatially explicit process-based models are being used to produce carbon exchange estimates that, in addition to soil drainage and fire occurrence, will incorporate spatial and temporal variation in climate and atmospheric CO2.

    Future modeling collaborations will be within the scope of the new permafrost research with both Vladimir Romanovsky at the University of Alaska, Fairbanks and Qianlai Zhuang at Purdue University.

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