Modeling Soil Biogeochemistry

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Modeling Soil Biogeochemistry Yude Pan USDA
Forest Service Northern Global Change
Program Newtown Square, PA 19073, USA
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• Biogeochemistry Models
• Process-based, mechanistic models, and
  different from
• classic statistical based empirical
  relationships
• Feedbacks and constraints on fluxes and pools
  affect the
• ecosystem as a whole.
• If we can adequately describe the dependence
  of
• processes on environmental factors, we can
  estimate these
• processes anywhere as data available.
• It combines information from field sites with
  large scale
• information on climate, soils and vegetation.

• General features
• Simulation model of C, N and H2O cycles, pools
  and fluxes
• GIS-referenced (GIS), grid-cell based spatial
  model
• Temporal and seasonal patterns at daily or
  monthly time step
• Plant functional types
• Ecosystem function and mass-balance
• Large scale (regional, continental, or global)

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Carbon Cycle Fluxes GPP, NPP, NEP, NBP, Ra,
litter, Rh Pools vegetation C, soil C
Nitrogen Cycle Fluxes N uptake, N
resorption, N mobilization, litter N
N mineralization, N losses Pools
vegetation N, soil inorganic N, soil organic
N Water Cycle Fluxes precipitation,
evaporation, transpiration, snowmelt,
runoff, drainage Pools available soil
water
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Two way processes Inorganic N produced
during decomposition, and N immobilization by
decomposer organisms Decomposition rate a
function of soil moisture, temperature available
N, and C/N ratio in SOM
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Biome-BGC Simple flowchart
Soil processes

• Similar processes with TEM
• but have three soil components
• forest floor, top soil layer
• and mineral soil
• C respired from soils, but no
• N leaching loss

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• Century has the most complicated soil processes
  mainly including more details of
• soil features and components forest floor,
  active pool, slow pool and passive pool
• Different decomposition rates for different
  pools. Decomposition is a function of
• soil temperature, moisture, and soil C for all
  pools, but related to lignin content for
• structural C, and to soil texture for active SOM.

Century
Belowground C dynamics
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• Soil processes net N mineralization,
• immobilization, nitrification, plant N uptake
• and leaching losses.
• Single SOM pool (equivalent to all pools in
• Century except passive pool).
• N mineralization is a function of C/N ratio,
• temperature and soil moisture but different
• tissues have different turnover rates

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Soil variables and processes

• Inputs from above- belowground plant residues
• Initial soil C pools (based on field data or
  calibrating to soil texture)
• Soil profile differentiation or single pool
  (issue of soil depth)
• Key process decomposition (function of
  temperature and moisture)
• Leaching losses (N, C)

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A case study using Pnet-CN
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Urban
Agr
Forests

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Patterns of Nitrogen Deposition and Ground-level
Ozone for the Mid-Atlantic Region
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Model Input Data Layers
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Climatic Trends in the Mid-Atlantic Region
Average annual temperature 1oF
Average annual precipitation 10
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Comparison among Remote Sensing, Modeling and
Inventory
Forest inventory plots
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SOM
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Annual NEP under Average and Historical Climate
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