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Conceptual Process Model for Basin-type Wetlands of the Prairie Pothole Region

by Paul R. Adamus*

December 1992

The following report was originally published by EPA under the title, "A Process For Regional Assessment Of Wetland Risk. Appendix C:"Conceptual Process Model for Basin-type Wetlands of the Prairie Pothole Region (EPA/600/R-92/249). It is a relatively detailed, qualitative portrayal of the known linkages among ecosystem processes and variables in Prairie depressional wetlands. Preparation of the document was supported by EPA's Wetlands Research Program through contract #68-C8-0006 to ManTech Environmental Technology, Inc. The document was subjected to EPA's peer and administrative review and approved for publication. The opinions expressed herein are those of the author and do not necessarily reflect those of EPA. The official endorsement of the Agency should not be inferred.

* As of June 1998, the author can be contacted at:

Adamus Resources Assessment, Inc.
6028 NW Burgundy Dr.
Corvallis, OR 97330




The conceptual model on the following pages was prepared as an aid in identifying appropriate indicators of wetland functions. The indicators that resulted partly from consideration of this model are discussed and documented with citation of published literature in a related document ("Condition, Values, And Loss Of Natural Functions Of Prairie Wetlands Of The North-Central United States") posted on the EPA's wetlands web page. This conceptual model is organized hierarchically and is intended to show qualitative linkages among major processes or forcing functions (I., II., etc.) and their supporting processes and/or indicators. The model was constructed from literature, theory, and experience. Its purpose is to help identify important indicators and forcing functions, for possible use in landscape function studies. It is not intended to show all possible linkages. Portions of the model are described narratively in:

Rosen, B.H., P.R. Adamus, and H. Lal. 1995. A conceptual model for the assessment of depressional wetlands in the prairie pothole region. Wetlands Ecology and Management 3(4):195-208.

Unless otherwise noted, the model is read from top to bottom and from left to right. For example, the lines at the beginning of the model (part I.) show that Runoff Volume and Timing is affected partly by runoff event seasonal timing, which is partly affected by temperature (A.3.b), which is affected partly by latitude (A.3.b.2). The major forcing functions and processes that are considered are as follows:

  1. Runoff Volume and Timing
  2. Groundwater Exchange
  3. Sedimentation
  4. Adsorption/Desorption
  5. Denitrification
  6. Biological Uptake/Storage/Dispersal (of Nutrients/ Chemicals)
  7. Ecosystem Production

In part VIII., specific PPR stressors are listed and connected to other model components, allowing qualitative assessment of potential impacts to wetland forcing functions.

  1. RUNOFF VOLUME and TIMING (peak flows, low flows, desynchronization)

    Affects the following: I.D.1.a.(1)(b), I.D.1.a.(2), I.D.2.a, I.D.2.d.(4)(b)(i), II.A, III.A.2, III.A.5, III.C, III.F.2.d, III.F.10, IV.C.2.c, IV.F, V.A.3.b.(5), V.A.5.b.(3)(a), V.A.5.b.(6), V.B.2.f, V.C.1, V.G, VI.A, VI.B.1, VII.B.7

    Is affected by the following:

      1. Precipitation
      2. Runoff Event Intensity (seasonal and hourly distributions)
        1. Region
        2. Elevation
      3. Runoff Event Seasonal Timing
        1. Snow/ice as % of annual precipitation
        2. Temperature (seasonal pattern; snowmelt/icemelt sequencing)

          (1) Light (intensity, seasonal and daily duration) (Affected by: VII.B.2)
          (2) Latitude
          (3) Elevation
          (4) Wind (Affected by: I.C.1.d)
          (5) Salinity/Specific Conductivity

          (a) Groundwater inputs (Affected by: II)
          (b) Soil type (calcite, gypsum, etc.)
          (c) Evapotranspiration (Affected by: I.D.1)
          (d) Extent of drainage/vegetation removal
          (e) Input from irrigation return waters
          (6) Artificial drainage
          (7) Groundwater inputs (Affected by: II)
          (8) Reflectance (heat sink, albedo)
          (a) Soil type/color
          (b) Vegetation type and density (Affected by: VII)
          (c) Topography
  2. LANDSCAPE FACTORS (upslope from wetland):
    1. Input Runoff Volume (per unit time)
      1. Catchment area (i.e., basin position in catchment)
      2. Artificial water subsidies (e.g., transbasin or transcatchment pumping)
      3. Extent of upslope catchment storage (Affected by: I.D.3)
      4. Catchment shape
      5. Drainage density
      6. Linearity of delivery channels
      7. And all factors in C and D below, accumulated over all areas draining to the wetland.
  3. SITE-SPECIFIC (within wetland) INPUTS:
    1. Condensation (fog drip, dew)
      1. Vegetation Surface Area
        (1) Vegetation density (Affected by: VII)
        (2) Number of vertical strata
      2. Edge/area ratio of vegetated portion of wetland
      3. Vegetation edge contrast
      4. Wind or Air Movement (duration, velocity, seasonality)
        (1) Region
        (2) Basin position relative to prevailing wind direction
        (3) Fetch
        (4) Vegetation density (Affected by: VII)
        (5) Vegetation height (Affected by: VII)
        (6) Vegetation vertical roughness (height variation, layering)
        (7) Topographic vertical roughness
    2. Horizontal Interception (e.g., snowdrift accumulation)
      1. Slope
      2. Surface Roughness
        (1) Topographic irregularity
        (2) Soil surface irregularity
        (3) Vegetation density (Affected by: VII)
        (4) Vegetation height relative to runoff depth
    3. Vertical Interception
      1. Vegetation Surface Area
        (1) Vegetation density (Affected by: VII)
        (2) Number of vertical strata
      2. Seasonal duration of foliage (evergreen vs. deciduous; annual vs. perennial)
      3. Antecedent saturation status of foliage
        (1) Precipitation amounts
        (2) Precipitation seasonal timing
        (3) Precipitation intensity
  4. SITE-SPECIFIC (within-wetland) OUTPUTS/STORAGE:
    1. Evapotranspiration
      1. Transpiration Efficiency
        (1) Water Table Position (relative to plant roots) (field capacity, wilting coefficient)
        (a) Groundwater exchange (Affected by: II)
        (b) Runoff inputs (Affected by: I )
        (c) Infiltration (Affected by: I.D.2)
        (d) Evapotranspiration (Affected by: I.D.1)
        (2) Runoff timing (runoff inputs peak during the season of maximum plant growth)(Affected by:I)
        (3) Foliage biomass (Affected by: Ecosystem Production, VII)
        (4) Rooting depth and total root mass biomass (Affected by: III.E.1)
      2. Evaporation Efficiency
        (1) Basin's Depth-to-Volume Ratio (or edge/area index)
        (a) Basin size
        (b) Basin shape
        (c) Depth factors (see III.F.2)
        (2) Salinity/specific conductivity (Affected by: I.A.3.b.(5))
        (3) Wind (Affected by: I.C.1.d) (4) Temperature
        (a) Factors listed in I.A.3.b
        (b) Mean depth (Affected by: III.F.2)
        (5) Ground Cover Density (% cover including plant litter)
        (a) Ecosystem production (Affected by: VII)
        (b) Prior decomposition (Affected by: V.B.2)
    2. Infiltration (in some cases, aquifer recharge as well)
      1. Antecedent Saturation Status
      2. Land slope
      3. Pumping (wellheads)
      4. Permeability or Conductivity
        (1) Soil/Subsurface Type (Affected by: III)
        (a) Clay %
        (b) Organic matter, % or density (Affected by: V, V.B)
        (c) Other impermeable aquicludes
        (2) Freezing (probability, extent, duration, depth) (Affected by: Temperature, I.A.3.b)
        (3) Compaction
        (a) Animal density (trampling)
        (b) Paving
        (c) Ground cover and foliage biomass (Affected by: I.D.1.b.(5))
        (d) Freeze/thaw (frequency, magnitude) (Affected by: I.A.3.b)
        (e) Tillage practices
        (4) "Piping"
        (a) Rooting depth and total root mass biomass (Affected by: III.E.1)
        (b) Burrowing vertebrate density (e.g., moles, prairie dogs)
        (i) Soil saturation (Affected by: Runoff Volume and Timing, I)
        (ii) Soil texture (Affected by: V.D.1)
        (c) Artificial drainage
      5. Surface Storage
        1. Basin Volume
          (1) Basin area
          (2) Mean depth (Affected by: III.F.2)
          (3) Volume reduction by ice (extent, duration)
          (a) Temperature (Affected by: I.A.3.b)
          (b) Salinity (Affected by: I.A.3.b.(5))
        2. Outlet Cross-sectional Area and Shape
          (1) Height relative to high water level
          (2) Width at high water level
          (3) Blockage by ice (extent, duration)
          (a) Temperature (Affected by: I.A.3.b)
          (b) Salinity (Affected by: I.A.3.b.(5))
        3. Capillarity of Soils/Sediments
          (1) Soil particle size (clay %) (Affected by: III)
          (2) Organic matter % (Affected by: V, V.B)
          (3) Organic matter type
          (4) Duration of frost-free season
  5.  GROUNDWATER EXCHANGE (recharge, discharge, lateral flow, low flow augmentation, soil water conservation)

    Affects: I.A.3.b.(5)(a), I.A.3.b.(7), I.D.1.a.(1)(a), V.A.2

    Affected by the following:

    1. Runoff Volume and Timing (Affected by: I)
    2. Water Table Slope
      1. Regional
      2. Local
    3. Infiltration (Affected by: I.D.2)
  6. SEDIMENTATION (particle deposition, stabilization, entrapment, agglomeration, precipitation)

    Affects: I.D.2.d.(1), I.D.3.c.(1), III.E.1.b, IV.B, V.C.2, V.D.1.a, IV.A, V.B.3, VII.B.3.c.(1)

    Affected by:

    1. Incoming Sediment Concentration
      1. Erosion in Catchment (proximity of wetland to)
        1. Sediment/soil type
        2. Wind (Affected by: I.C.1.d)
        3. Ice (Affected by: I.A.3.b)
        4. Precipitation intensity and form (rain vs. snow, storm vs. drizzle)
        5. Tillage practices
        6. Artificial ditching or drainage
        7. Human visitation (machinery, trampling)
        8. Animal activities (e.g., grazing) (extent, duration, seasonality)
      2. Runoff volume and timing (Affected by: I)
      3. Presence of input channels
      4. Dry Deposition
        1. Proximity to sources
        2. Wind (Affected by: I.C.1.d)
      5. Extent of upslope runoff retention (Affected by: Runoff Volume and Timing, I)
    2. Velocity (Wave Height) Reduction in Wetland
      1. Plant community composition
        1. Vegetation height relative to water depth or wave height
        2. Vegetation rigidity
        3. Vegetation seasonal persistence (annual vs. perennial)
      2. Vegetation density (Affected by: Ecosystem Production, VII)
      3. Vertical roughness (e.g., microtopographic variation)
    3. Hydraulic Residence Time (Affected by: Runoff Volume and Timing, I)
    4. Settling Time
      1. Gravity Settling
        1. Sediment particle type (mass, shape, size, charge)
        2. Temperature (Affected by: I.A.3.b)
      2. Flocculation
        1. Salinity/specific conductivity (Affected by: I.A.3.b.(5))
        2. Sediment particle type (mass, shape, size, charge)
        3. Ecosystem Production (Affected by: VII)
          (1) Filter-feeder density at season of sediment input (flocculation via fecal pellets)
          (2) Microbial density at season of sediment input (flocculation via agglomerates)
      3. Physicochemical Precipitation (e.g., calcitic)
        1. Temperature (Affected by: I.A.3.b)
        2. Photosynthesis (Affected by: Ecosystem Production, VII)
        3. Acidity/pH (Affected by: IV.D)
    5. Stabilization by Plant Community
      1. Root Biomass and Rooting Depth
        1. Plant community species composition (typical root length)
        2. Soil hydrologic regime: anaerobiosis limitation (Affected by: III)
        3. Soil type: penetrability
          (1) Texture (Affected by: V.D.1)
          (2) Compaction (Affected by: I.D.2.d.(3))
      2. Mat- or Sod- forming Ability
        1. Plant community species composition
        2. Wave or current velocity (Affected by: Wind, I.C.1.d)
    6. Erosion, Resuspension, and Mixing (within-wetland)
      1. Sediment/soil type
      2. Water depth
        1. Original landform
        2. Sedimentation (all of III)
        3. Subsidence
          (1) Artificial drainage
          (2) Soil type
          (3) Soil organic matter (Affected by: Carbon, V, V.B)
        4. Runoff volume (Affected by: I)
      3. Wind (Affected by: I.C.1.d)
      4. Ice (Affected by: I.A.3.b)
      5. Precipitation intensity and form (rain vs. snow, storm vs. drizzle)
      6. Tillage practices
      7. Artificial ditching or drainage
      8. Human visitation (machinery, trampling)
      9. Animal activities/bioturbation (e.g., presence of carp, ducks) (Affected by: Ecosystem Production, VII)
      10. Runoff volume and timing (Affected by: I)
      11. Boat wakes (magnitude, extent, frequency)
  7.  ADSORPTION/DESORPTION (cation exchange, anion exchange)

    Affects: V.A, VI.B.2, VII.B.1

    Is affected by:

    1. Hydraulic Residence Time (Affected by: Sedimentation, III)
    2. Soil/sediment type (Affected by: Sedimentation, III)
    3. Aluminum-iron-calcium content
      1. Geologic parent material
      2. Degree of weathering
        1. Wind (Affected by: I.C.1.d)
        2. Ice (Affected by: I.A.3.b)
        3. Water level fluctuations (Affected by: Runoff Volume, I)
      3. Particle size
      4. Organic matter % (Affected by: V, V.B)
    4. Acidity/pH
      1. Geologic parent material
      2. Anaerobiosis (Affected by: V.C)
      3. Contaminated precipitation
      4. Runoff exposure to mining activities (Affected by: I)
      5. Fire (frequency, type, probability)
    5. Anaerobiosis (Affected by: V.C)
    6. Fluctuating Hydrologic Conditions
      1. Extent (Affected by: Runoff Timing and Volume, I)
      2. Season of Fluctuation
    7. Ambient concentration of nutrient or chemical substance (Affected by V, VI)
  8.  DENITRIFICATION (rate and proportional amount of N2 or N20 release)

    Affects: I.D.2.d.(1)(b), I.D.3.c.(2), III.F.2.c.(3), IV.C.4, V.C.3, V.D.1.b, VI.B.2, VII.B.1

    Is affected by:

    2. Available Nutrients
      1. Geologic erosional sources
      2. Groundwater sources (Affected by: II)
      3. Land Use Sources
        1. Dry deposition
          (1) Wind (Affected by: I.C.1.d)
          (2) Soil wind-erodibility (rating, proximity)
        2. Runoff
          (1) Soil erodibility (rating, proximity) (Affected by: Erosion, III.A.1)
          (2) Animal density (seasonality, proximity)
          (3) Fertilizer extent (seasonality, proximity)
          (4) Subsidence/mineralization following drainage
          (5) Runoff volume (Affected by: I)
      4. Animal immigration
      5. Internal Sources
        1. Fixation
          (1) Plant community composition (bluegreen algae)
        2. Mineralization/remobilization
          (1) Fire (extent, frequency, type, probability) (2) Decomposition (Affected by: V.B.2) (3) Fluctuating hydrologic regime
          (a) Extent (Affected by: Runoff Timing and Volume, I) (b) Season of fluctuation
        3. "Pumping" from sediments and release to water column
          (Affected by: Community Uptake, Storage, and Dispersal VI)
        4. Concentrating Effects
          (1) Evapotranspiration (Affected by: I.D.1)
          (2) Freezing (Affected by: I.A.3.b)
      6. Upslope Uptake/Removal (Affected by: Runoff Volume and Timing, I; also VI and B-G below)
    3. Carbon (amount, type, seasonality)
      1. Plant and animal production (Affected by: VII)
      2. Decomposition (decay rates)
        1. Vegetation type
        2. Salinity (Affected by: I.A.3.b.(5))
        3. Invertebrate density (Affected by: Ecosystem Production, VII)
        4. Anaerobiosis (Affected by: V.C)
        5. Hydrologic fluctuation
        6. Extent (Affected by: Runoff Volume and Timing, I)
        7. Season of fluctuation
      3. Sedimentation (Affected by: III)
      4. Fire History
    4. Anaerobiosis/Reducing Conditions (extent, duration, frequency, probability):
      1. Hydrologic regime (Affected by: Runoff Volume and Timing, I)
      2. Soil pore space and volume (Affected by: III, V.D)
      3. Organic load (Affected by: V, V.B)
      4. Temperature and ice (extent, duration, frequency, probability) (Affected by: I.A.3.b)
      5. Chemical input (chemical oxygen demand)
      6. Subsurface oxidation of anaerobic zones by plant roots (Affected by: V.C)
    5. Pore Space and Volume
      1. Soil Texture (bulk density, porosity)
        1. Clay % (Affected by: III)
        2. Organic matter % and type (Affected by: V, V.B)
        3. Tillage practices (tillage generally increases porosity)
        4. Burrowing invertebrate density (Affected by: Ecosystem Production, VII)
        5. Compaction/trampling (Affected by: I.D.2.d.(3))
    6. Salinity/specific conductivity (Affected by: I.A.3.b.(5))
    7. Acidity/pH (Affected by: IV.D)
    8. Hydraulic retention time in upper soil layer (Affected by: Runoff Volume and Timing, I)
    9. Temperature (Affected by: I.A.3.b)
    10. Sulfur availability

    Affects: V.A.5.c, V.A, VI.B.2, VII.B.1

    Is affected by:

    1. Hydraulic retention times of substances in upper soil layer (Affected by: Runoff Volume and Timing, I)
    2. Concentration of substance (during season of maximum organism growth/uptake)
      1. Runoff volume and timing (Affected by: I)
      2. Available nutrients/chemicals (Affected by: V.A)
    3. Ecosystem production (Affected by: VII)
    4. Organism Types
      1. Proximity of usual microhabitats to spatial maxima of the substance
      2. Food habits
      3. Intrinsic growth rates
      4. Modes of uptake
      5. Tenacity of Uptake
        1. Lifespans of organisms comprising the community
        2. Anatomical locus of accumulation
      6. Emigration rates
  10. ECOSYSTEM PRODUCTION (respiration, photosynthesis)

    Affects: I.D.1.a.(3), I.D.1.b.(5)(a), III.B.2, III.D.2.c, III.D.3.b, III.F.9, V.B.1, V.B.2.c, V.D.1.d, VI.C, VII.B.3.c.(2), VII.H.4

    Is affected by:

    1. Organism Types (species composition)
      1. Intrinsic growth rates
      2. Tolerance for crowding (size, metabolic needs, etc.)
    2. Food and Substrate Conditions (required by component organisms)
      1. Nutrients (Affected by: V.A)
      2. Temperature (Affected by: I.A.3.b)
      3.  Light Availability
        1. Depth (Affected by: III.F.2)
        2. Shade (from topographic relief, vegetation, clouds/fog)
        3. Transmissivity of air/water (e.g., turbidity)
          (1) Sedimentation (Affected by: III)
          (2) Plankton blooms (Affected by: Ecosystem Production, VII)
          (3) Snow covering ice
        4. Latitude
        5. Aspect
        6. Elevation
      4. Dissolved oxygen (Affected by: Anaerobiosis, V.C)
      5. Acidity/pH (Affected by: IV.D)
      6. Salinity/specific conductance (Affected by: I.A.3.b.(5))
      7. Hydrologic regime (Affected by: Runoff Volume and Timing, I)
      8. Spatial/temporal interspersion of above, as optimal for most productive combination of species
    3. Extent of contamination (Affected by: Available Nutrients, V.A -- the processes are similar).
    4. Extent of disturbance by human visitation
    5. Competition
    6. Biological Removal/Recycling Processes
      1. Predation/harvest
      2. Herbivory (e.g., muskrat, livestock)
    7. Physical Removal Processes
      1. Fire (extent, frequency, type, probability)
      2. Wind (Affected by: I.C.1.d)
      3. Ice scour (Affected by: I.A.3.b)
      4. Geological phenomena (e.g., subsidence)
      5. Tillage
    8. Immigration/Emigration
      1. Intrinsic characteristics related to seed dispersal or behavioral mobility of species
      2. Suitability of core habitat area
        1. Size
        2. Habitat quality
      3. Suitability of connections to similar habitat patches
        1. Permeability of surrounding landscape matrix vs. corridors
        2. Distance to nearest other suitable habitat patch
      4. Suitability of target habitat patch (Affected by: Ecosystem Production, VII)

    Direct effects of stressors are listed below. The theoretical, secondary effects of these activities can be traced by turning to the cited entries, then tracing relationships to other functional components by searching leftwards in the hierarchical arrangement of processes and/or in their referenced processes. When a major process heading (roman numeral) is reached, continue the chain by branching to each of the entries listed following the subheading, "Affects:".

      1. Artificial Drainage (I.A.3.b.(6), I.D.2.d.(4)(c), III.A.1.f, III.F.2.c.(1), III.F.7)
      2. Surface Storage (I.D.3)
      1. Groundwater Exchange (II.)
      2. Surface Storage, Infiltration, Evapotranspiration (I.D, I.E, I.F)
      1. Groundwater Exchange (II.)
      2. Runoff Volume and Timing (I.)
    4. GRAZING
      1. Herbivory (VII.F.2)
      2. Compaction (I.D.2.d.(3))
    5. MOWING
      1. Vegetation Density (I.A.3.b.(8)(b), I.C.1.a.(1), I.C.1.d.(4), I.C.2.b.(3), I.C.3.a.(1), I.D.1.a.(3), I.D.1.b.(5)(a), III.B.2, III.D.2.c, III.D.3.b, III.F.9, V.B.1, V.B.2.c, V.D.1.d, VI.C, VII.B.3.c.(2), VII.H.4)
      2. Compaction (I.D.2.d.(3))
      1. Tillage (I.D.2.d.(3)(e), III.A.1.e, III.F.6, V.D.1.c)
      2. Topographic vertical roughness (I.C.2.b.(1), III.B.3)
    7. BURNING
      1. Fire (IV.D.5, V.A.5.b.(1), V.B.4, VII.G.1)
      1. Contaminants (for protection of crops from weeds or insects) (VII.C)
      1. Nutrients (V.A, VI.B.2, VII.B.1)
      1. Human Visitation (III.A.1.g, III.F.8, VII.D)
      2. Compaction (I.D.2.d.(3))