Skip Navigation

FAM for Slope Linear Wetlands of the Prairie Pothole Region in Eastern SD

INITIAL REVIEW DRAFT

INTERIM FUNCTIONAL ASSESSMENT MODEL FOR SLOPE (LINEAR) WETLANDS OF THE PRAIRIE POTHOLE REGION IN EASTERN SOUTH DAKOTA

CONTENTS

1.0 MODERATION OF GROUNDWATER FLOW

2.0 Velocity Reduction of Surface Water Flow

3.0 RETENTION, CONVERSION, AND RELEASE OF ELEMENTS AND COMPOUNDS


4.0 Retention of Particulates

5.0 ORGANIC CARBON EXPORT

6.0 MAINTENANCE OF CHARACTERISTIC PLANT COMMUNITY

7.0 MAINTENANCE OF HABITAT INTERSPERSION AND CONNECTIVITY AMONG WETLANDS

8.0 MAINTAIN DISTRIBUTION AND ABUNDANCE OF VERTEBRATES AND INVERTEBRATES


Variables Used in the Hydrogeomorphic Assessment of Slope Wetlands in the Prairie Pothole Region of Eastern South Dakota

 1.0 MODERATION OF GROUNDWATER FLOW

 DEFINITION: The capacity of the wetland to regulate the outflow of groundwater.

Effects On Site: Contributes to the maintenance of characteristic soils, vegetation, invertebrate and vertebrate communities, and provides for the moderation of groundwater flow.

Effects Off-Site: Modifies off-site hydrology of wetland and riverine systems within the groundwater and surface water flow net.

Discussion of Function

A combination of geological material and regional water balance affects the groundwater and surface water flow within the wetlands. The principal water sources for these sloped wetlands are from groundwater and precipitation and the principal water losses are through evapotranspiration and surface runoff. These hydrological elements produce an inter- and intra-annual cycle of water storage within the wetland boundaries. This cycle supports the diverse plant and animal habitats as well as biogeochemical processes. These sloped wetlands sustain the hydrological cycle. The hydrological dynamics of the Prairie Pothole Region are addressed by Stewart and Kantrud (1972), Winter (1989) and Kantrud et al. (1989).

Discussion of Variables

The variables associated with the performance of this function focus on land use and on the physical integrity of soil conditions. Human activities at nearby lower elevations and above or within the wetland affect the rate and quantity of surface and subsurface water entering and leaving the wetland. Vupuse, Vwetuse, and Vsource are used to describe potential alterations of water flow to the wetlands. Land use activities also affect erosion and sediment import into the wetlands by water and wind. Undisturbed soil conditions within the wetland are closely related to water storage through the ability of the soil to transmit and hold water interstitially. This soil condition is described in the Vpore variable. Finally, constructed drainage features in and adjacent to the wetland directly impacts the subsurface flow of water to and from the wetland. The Vhydalt variable reflects this aspect of the function.

1.0 MODERATION OF GROUNDWATER FLOW

Model Variable Measurement or Condition Index
Vupuse: Upland Land Use

Definition: Dominant land use or condition of the upland watershed that contributes to the wetland. The entire watershed area should be considered when determining the functional index of this variable.

Logic: Upland land use influences or moderates ground water flow through the evapotranspiration process.

 

Well managed, permanently vegetated native prairie. Management allows for adequate plant recovery time between grazing periods.

Permanent vegetation under a system of management such as,

native species under season long grazing with moderate use;

-OR-

idle non-native grassland cover;

-OR-

permanent native or non-native hayland.

Permanent native or non-native pasture which has been historically over-grazed, with some (<50 percent) bare ground, low plant vigor;

-OR-

no-till small grain;

-OR-

minimum till small grain in a grass/legume rotation.

Permanent native or non-native pasture which has been severely over-grazed, with significant (>50 percent) bare ground, low plant vigor, and evidence of soil erosion;

-OR-

no-till or minimum till row crop, minimum till small grain.

Conventional tillage small grain or row crop;

-OR-

inputs/overflow from cultural activities (industrial, urbanization, etc.).

Urban, semi-pervious, or impervious surface (this condition will result in maximum overland flow and a high rate of delivery to wetland). If best management practices employed, the impact may be somewhat less.

 

1.0

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

0.25

 

 

 

 

0.1

 

 

 

0.0

 

1.0 MODERATION OF GROUNDWATER FLOW

Model Variable Measurement or Condition Index
Vwetuse: Wetland Land Use

DEFINITION: Dominant land use and condition of the wetland.

LOGIC: Land use in the wetland affects soil pore space and the vegetation/

evapotranspiration relationship that results in the characteristic hydrologic regime.

No evidence of tillage in the wetland (adapted vegetation intact);

-OR-

if previously tilled, outermost (temporary) wetland zone presently

intact,

-AND/OR-

if some use in the wetland (haying, grazing), no evidence of disruption to the wetland system (such as by compaction or rutting by equipment, or excessive trampling by livestock).

No evidence of tillage through innermost part of wetland (zones wetter than the temporary zone),

-AND-

some evidence of disturbance (grazing, haying, or tillage) in a portion of the outermost part of wetland (temporary zone),

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) tilled or over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) are rarely tilled or are intact,

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) is tilled or severely over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) is tilled or over-grazed most years,

-AND-

visual evidence of ephemeral gullies present in wet zone.

Wetland receives conventional tillage in all zone(s) most years. If recently tilled, crop and wetland vegetative remnants can be observed in area.

Wetland more severely disturbed than indicated above (no vegetation, rutted, pig farm, feedlot, urban fill, etc.).

 

1.0

 

 

 

 

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

 

0.25

 

 

 

 

0.1

 

0.0

 

1.0 mODERATION OF GROUNDWATER FLOW

Model Variable Measurement or Condition Index
Vpore: Soil Pores

DEFINITION: The physical integrity of the soil in the surface layer and the upper part of the subsoil. This includes the number and continuity of pores and the type, grade, and size of soil structure.

LOGIC: Saturated hydraulic conductivity is directly related to pores and other voids in the soil. Reduced hydraulic conductivity results in a decrease of the hydraulic discharge function.

Many medium, fine, and/or very fine, continuous pores,

-AND-

structure is weak or moderate prismatic,

-AND/OR-

moderate or strong, medium and fine, angular or subangular blocky,

-AND/OR-

moderate or strong granular,

-AND-

consistence is friable or very friable.

Common fine and very fine, none or few medium, continuous and discontinuous pores,

-AND-

structure is weak or moderate, medium and/or fine angular or subangular blocky,

-AND/OR-

weak or moderate granular,

-AND-

consistence is firm.

Few fine and very fine discontinuous pores,

-AND-

structure is weak coarse subangular blocky or massive (coarse, cloddy or structureless),

-AND-

consistence is very firm or harder,

-AND/OR-

plow pan present in this zone, evidenced by roots growing horizontally along pan.

The substrate is a non-porous medium (asphalt, concrete, etc.).

 

 

 

 

1.0

 

 

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

0.1

 

 

 

 

0.0

 

1.0 MODERATION OF GROUNDWATER FLOW

Model Variable Measurement or Condition Index
Vhydalt: Hydrology Alterations

Definition: Presence of a constructed subsurface and/or surface outlet below the wetland boundary. Depth of fill, changes in depth of the subsurface or surface drain, and distance from the wetland impacts wetland ground water surface elevation.

Logic: Presence of surface outlets, subsurface drains, or fill material impacts ground water surface elevations and maintenance of saturated anaerobic conditions throughout the wetland.

 

No subsurface drain present and subsurface flow is not impacted;

-OR-

if there is a nearby subsurface drainage feature with an invert elevation 3 feet or more lower than the wetland boundary, the distance to such feature corresponds to that identified in Table 1 for the soil texture (subsoil, 2 to 3 foot depth) in the wetland. No fill in wetland.

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1. No fill in wetland.

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1;

-OR-

presence of a shallow surface ditch (<1 foot deep) through wetland with saturated conditions still present;

-OR-

fill present in wetland;

-OR-

additional surface water added to system (as from irrigation return, drainage outlets, etc.).

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1;

-OR-

presence of a surface ditch (>1 foot deep) through wetland; saturated conditions have been impacted but ineffectively removed;

-OR-

fill present in wetland.

Surface or subsurface drainage feature within wetland or fill present:; saturated conditions have been severely impacted but still occur seasonally.

Saturated conditions non-existent (completely drained);

-OR-

non-wetland (upland) area (mitigation purposes).

 

 

 

1.0

 

 

 

 

 

0.75

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

 

 

0.25

 

 

 

 

 

 

0.1

 

 

0.0

 

1.0 mODERATION OF GROUNDWATER FLOW

Model Variable Measurement or Condition Index
Vsource: Source Area of Flow Intercepted by Wetland

DEFINITION: The area surrounding a wetland that defines the catchment or watershed of that wetland. The entire watershed area should be considered when determining the functional index for this variable.

LOGIC: Altering drainage patterns within and among wetlands will impact ground water and surface water flow to the wetland.

No alteration of upland watershed source area through surface alterations (such as water impoundment structures, terraces, or roads), subsurface alterations (such as tile drains or ditches), or additions (such as irrigation and associated practices or terrace outlets).

Presence of surface alterations within upland watershed source area which impacts overland flow into wetland (such as terraces or roads); however, no subsurface alterations (such as tile drains), or additions (such as irrigation and associated practices or terrace outlets) present. Less than 20 percent of watershed area is impacted.

The dominant surface and subsurface flow paths of water in the upland watershed source area has been altered, thus affecting the flow of water to the wetland (such as by drainage, terraces, or irrigation return). 20 to 50 percent of the watershed area is impacted,

-AND-

the alteration(s) does not change the wetland subclass.

The dominant surface and subsurface flow paths of water in the upland watershed source area has been altered, thus affecting the flow of water to the wetland (such as by drainage, terraces, or irrigation return),

-AND-

the alteration(s) changes the wetland subclass.

Upland watershed source area extremely altered such that almost all water flow to wetland has been eliminated (such as from urbanization).

 

1.0

 

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

0.1

 

 

 

 

0.0

INDEX OF FUNCTION:

={Vhydalt x [(Vsource + Vupuse)/2 + (Vpore + Vwetuse)/2] /2}1/2

2.0 VELOCITY REDUCTION OF SURFACE WATER FLOW

DEFINITION: Reduces the velocity of surface runoff from storm events and/or snowmelt runoff.

Effects On-Site: Maintains characteristics soils, vegetation, invertebrate and vertebrate communities, and provides for erosion reduction and to the nutrient and chemical cycling process.

Effects Off-Site: Erosion reduction and retention of elements and compounds on site decreases probability of export to aquatic ecosystems downstream.

Discussion of Functions

A combination of vegetation and microtopographic changes within the wetland provide a structural roughness to reduce the velocity of overland flow in and out of the wetland. Reduction of overland flow within the wetland allows time for the settlement of water-born sediments and nutrients within the wetland. The vegetation within the wetland also provides for erosion control.

Discussion of Variables

The variables within this function reflect the land use and the physical condition of watershed or catchment area. Land use is reflected by upland land use, wetland land use, sediment delivery, and vegetation density variables (Vupuse, Vwetuse, Vsed, and Vpcover respectively). The physical conditions for this function are reflected by the Vsource and Vmicro variables.

2.0 VELOCITY REDUCTION OF SURFACE WATER FLOW

Model Variable Measurement or Condition Index
Vsource: Source Area of Flow Intercepted by Wetland

DEFINITION: The area surrounding a wetland that defines the catchment or watershed of that wetland. The entire watershed area should be considered when determining the functional index for this variable.

LOGIC: Altering drainage patterns within and among wetlands will impact ground water and surface water flow into and out of the wetland.

No alteration of upland watershed source area through surface alterations (such as water impoundment structures, terraces, or roads), subsurface alterations (such as tile drains or ditches), or additions (such as irrigation and associated practices or terrace outlets).

Presence of surface alterations within upland watershed source area which impacts overland flow into wetland (such as terraces or roads); however, no subsurface alterations (such as tile drains), or additions (such as irrigation and associated practices or terrace outlets) present. Less than 20 percent of watershed area is impacted.

The dominant surface and subsurface flow paths of water in the upland watershed source area has been altered, thus affecting the flow of water to the wetland (such as by drainage, terraces, or irrigation return). 20 to 50 percent of the watershed area is impacted,

-AND-

the alteration(s) does not change the wetland subclass.

The dominant surface and subsurface flow paths of water in the upland watershed source area has been altered, thus affecting the flow of water to the wetland (such as by drainage, terraces, or irrigation return),

-AND-

the alteration(s) changes the wetland subclass.

Upland watershed source area extremely altered such that almost all water flow to wetland has been eliminated (such as from urbanization).

 

1.0

 

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

0.1

 

 

 

 

0.0

 

2.0 VELOCITY REDUCTION OF SURFACE WATER FLOW

Model Variable Measurement or Condition Index
Vupuse: Upland Land Use

Definition: Dominant land use or condition of the upland watershed that contributes to the wetland. The entire watershed area should be considered when determining the functional index of this variable.

Logic: Upland land use influences or moderates ground water flow through the evapotranspiration process.

 

Well managed, permanently vegetated native prairie. Management allows for adequate plant recovery time between grazing periods.

Permanent vegetation under a system of management such as,

native species under season long grazing with moderate use;

-OR-

idle non-native grassland cover;

-OR-

permanent native or non-native hayland.

Permanent native or non-native pasture which has been historically over-grazed, with some (<50 percent) bare ground, low plant vigor;

-OR-

no-till small grain;

-OR-

minimum till small grain in a grass/legume rotation.

Permanent native or non-native pasture which has been severely over-grazed, with significant (>50 percent) bare ground, low plant vigor, and evidence of soil erosion;

-OR-

no-till or minimum till row crop, minimum till small grain.

Conventional tillage small grain or row crop;

-OR-

inputs/overflow from cultural activities (industrial, urbanization, etc.).

Urban, semi-pervious, or impervious surface (this condition will result in maximum overland flow and a high rate of delivery to wetland). If best management practices employed, the impact may be somewhat less.

 

1.0

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

0.25

 

 

 

 

0.1

 

 

 

0.0

 

2.0 velocity reduction of surface water flow

Model Variable Measurement or Condition Index
Vmicro: Microtopographic Complexity

DEFINITION: The microtopographic surface roughness of wetland.

LOGIC: Microtopographic complexity, or surficial roughness of the wetland, influences the rate at which surface water flows through the wetland. The more complex the wetland surface is, the greater the potential for deposition of sediment.

 

 

Natural conditions occur within wetland (predominantly well managed native vegetation with little or no anthropogenic disturbances evident as from livestock or machinery).

Vegetation consists predominantly of well managed, non-native species,

-AND-

average annual storm-based peak discharge depth does not exceed the average annual height of the vegetation,

-AND-

main flow frequently shifts from side to side due to changes in cross-sectional shape of the flood plain, changes in frequency and distribution of hummocks, or changes in slope.

Area is tilled infrequently (no greater than 2 years out of 5);

-OR-

area consists of severely over-grazed native or non-native species,

-AND-

average annual storm-based peak discharge depth exceeds the average annual height of the vegetation,

-AND-

main flow occasionally shifts from side to side due to changes in channel and flood plain cross-section, changes in frequency and distribution of hummocks, or changes in slope.

Area is tilled occasionally (no greater than 3 years out of 5);

-OR-

area is fall hayed or burned to remove current seasons plant growth,

-AND-

size and shape of channel cross-sections change gradually.

Area is tilled most years (4 years out of 5 or more);

-OR-

area has been channeled and is vegetated;

-OR-

area consists of a non-wetland (i.e. upland) site.

 

Area has been channeled and is not vegetated, or has been obliterated by urbanization (i.e. paved, filled and leveled for construction, etc.).

 

 

1.0

 

 

 

 

 

0.75

 

 

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

0.25

 

 

 

 

 

0.1

 

 

 

 

0.0

 

2.0 VELOCITY REDUCTION OF SURFACE WATER FLOW

Model Variable Measurement or Condition Index
Vpcover: Vegetation Density

DEFINITION: The abundance of woody and herbaceous plants in all vegetation zones within the wetland.

LOGIC: Density of the vegetation present within and adjacent to the wetland influences rate of surface water flow, and influences the rate of erosion and deposition of sediment.

Canopy coverage is 75 to 125 percent of reference standard.

Canopy coverage is 25 to 74 percent, or >125 percent, of reference standard.

Canopy coverage is 1 to 24 percent of reference standard;

-OR-

vegetation and/or clods in furrows, etc.

Plants absent, no canopy coverage.

1.0

 

0.5

 

0.1

 

0.0

 

2.0 VELOCITY REDUCTION OF SURFACE WATER FLOW

Model Variable Measurement or Condition Index
Vsed: Sediment Delivery to Wetland

DEFINITION: Extent of sediment delivered to wetland from human activities, including agriculture.

LOGIC: Land use and erodibility characteristics of the soil affect the potential for sediment delivery to the wetland. If the wetland fills with sediment, the capacity of the wetland to perform erosion control is reduced.

 

No visual evidence of accelerated sediment delivery to wetland.

Visual evidence of historic and/or recent, culturally-accelerated sediment delivery to the wetland (such as minor accumulations of sediment in the form of small, stabilized deltas, sediment fans, drift deposits from windblown sediments, etc.),

-AND/OR-

visual observation indicates average deposition depth in wetland at <3 inches.

Visual evidence of recent and historic sediment delivery to the wetland in the form of sediment staining of detritus, thin silt deposits on detritus, and/or slight accumulations of sediment along plant stems;

-OR-

tillage through buffer to the outer edge of wetland,

-AND/OR-

visual observation indicates average deposition depth in wetland at about 3 to 6 inches.

Visual evidence of recent and historic sediment delivery to the wetland, as indicated by partial burial (25 to 75 percent) of detritus, or partial burial of plant crowns and stems;

-OR-

tillage through buffer and partial or complete tillage through wetland,

-AND/OR-

visual observation indicates average deposition depth in wetland at about 6 to 9 inches.

Visual evidence of significant sediment delivery to the wetland, as indicated by nearly complete (>75 percent) burial of detritus and/or vegetation in wetland. Presence of zones of sediment deposition, such as deltas, sediment fans, or drift deposits, common throughout wetland. Ephemeral or perennial gullies may be present on uplands adjacent to wetland. Best management practices lacking to control sediment delivery,

-AND/OR-

visual observation indicates average deposition depth in wetland at about 9 to 12 inches.

Pronounced rise in bottom elevation of wetland due to accelerated sediment delivery from cultural sources such as agriculture and urbanization. Typical average deposition depth in wetland is >12 inches.

1.0

 

 

 

0.75

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

0.25

 

 

 

 

 

 

 

 

 

0.1

 

 

 

 

 

0.0

 

2.0 VELOCITY REDUCTION OF SURFACE WATER FLOW

Model Variable Measurement or Condition Index
Vwetuse: Wetland Land Use

DEFINITION: Dominant land use and condition of the wetland.

LOGIC: Land use in the wetland affects soil pore space, the vegetation/

evapotranspiration relationship, and surface roughness that results in a characteristic hydrologic regime.

No evidence of tillage in the wetland (adapted vegetation intact);

-OR-

if previously tilled, outermost (temporary) wetland zone presently

intact,

-AND/OR-

if some use in the wetland (haying, grazing), no evidence of disruption to the wetland system (such as by compaction or rutting by equipment, or excessive trampling by livestock).

No evidence of tillage through innermost part of wetland (zones wetter than the temporary zone),

-AND-

some evidence of disturbance (grazing, haying, or tillage) in a portion of the outermost part of wetland (temporary zone),

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) tilled or over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) are rarely tilled or are intact,

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) is tilled or severely over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) is tilled or over-grazed most years,

-AND-

visual evidence of ephemeral gullies present in wet zone.

Wetland receives conventional tillage in all zone(s) most years. If recently tilled, crop and wetland vegetative remnants can be observed in area.

Wetland more severely disturbed than indicated above (no vegetation, rutted, pig farm, feedlot, urban fill, etc.).

 

1.0

 

 

 

 

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

 

0.25

 

 

 

 

0.1

 

0.0

INDEX OF FUNCTION:

= [(Vsource + Vupuse + Vmicro + Vpcover)/4 + (Vsed + Vwetuse)/2] /2

3.0 RETENTION, CONVERSION, AND RELEASE OF ELEMENTS AND COMPOUNDS

DEFINITION: Short- and long-term cycling and removal of elements and compounds on-site through the abiotic and biotic processes that convert elements from one form to another.

Effects On-Site: Net effects of retention, conversion, and release are balanced between gains through import processes and losses through hydrologic export, efflux to the atmosphere, and long term retention in persistent biomass and sediments.

Effects Off-Site: Retention of elements and compounds on-site decreases probability of export to aquatic ecosystems down-gradient and consequent nutrient loading.

Discussion of Functions

The use of the term cycling refers to the annual turnover of nutrients and retention refers to the relatively long term accumulation or loss through conversion or removal of elements and compounds from incoming water sources. Elements include macronutrients essential to plant growth (nitrogen, phosphorous, potassium) and other elements such as heavy metals (zinc, chromium, etc.) that can be toxic at high concentrations. Compounds include herbicides, pesticides, and other imported materials. Mechanisms of cycling, retention, conversion, release and removal include sorption, sedimentation, denitrification, burial, decomposition to inactive forms, decay, uptake and incorporation into short and long lived annual and perennial herbaceous biomass, and similar processes [Brinson et al. (1985)].

Discussion of Variables

The variables within this function reflect land use, abiotic, and biotic components. Land use activities impact the magnitude of elements and compounds entering the system and the natural cycling and removal processes of the elements and compounds. Land use is reflected by the upland land use and wetland land use variables (Vupuse and Vwetuse, respectively).

Biotic components of the wetland ecosystem cycle and retain elements and compounds through biomass accumulation and litter production. Elements and compounds are recycled annually through decay and decomposition. Neely and Baker (1989) report decay rates for some emergent plants in the Prairie Pothole region to be greater than one year, indicating retention. These decomposition rates facilitate both cycling on an annual basis and retention on a longer than one year basis within the wetland. Biotic components consist of the vegetative cover and detritus variables (Vpcover and Vdetritus, respectively).

The abiotic components assist reduction and oxidation processes that biogeochemically cycle and retain elements and compounds. Abiotic components are represented by sorptive properties of the soil (Vsorpt), soil integrity (Vpore), and by the amount and presence of water (represented by the Vhydalt and Vsource variables).

3.0 RETENTION, CONVERSION, AND RELEASE OF ELEMENTS AND COMPOUNDS

Model Variable Measurement or Condition Index
Vsource: Source Area of Flow Intercepted by Wetland

DEFINITION: The area surrounding a wetland that defines the catchment or watershed of that wetland. The entire watershed area should be considered when determining the functional index for this variable.

LOGIC: Altering drainage patterns within and among wetlands will impact surface water flow to the wetland.

No alteration of upland watershed source area through surface alterations (such as water impoundment structures, terraces, or roads), subsurface alterations (such as tile drains or ditches), or additions (such as irrigation and associated practices or terrace outlets).

Presence of surface alterations within upland watershed source area which impacts overland flow into wetland (such as terraces or roads); however, no subsurface alterations (such as tile drains), or additions (such as irrigation and associated practices or terrace outlets) present. Less than 20 percent of watershed area is impacted.

The dominant surface and subsurface flow paths of water in the upland watershed source area has been altered, thus affecting the flow of water to the wetland (such as by drainage, terraces, or irrigation return). 20 to 50 percent of the watershed area is impacted,

-AND-

the alteration(s) does not change the wetland subclass.

The dominant surface and subsurface flow paths of water in the upland watershed source area has been altered, thus affecting the flow of water to the wetland (such as by drainage, terraces, or irrigation return),

-AND-

the alteration(s) changes the wetland subclass.

Upland watershed source area extremely altered such that almost all water flow to wetland has been eliminated (such as from urbanization).

 

1.0

 

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

0.1

 

 

 

 

0.0

 

3.0 Retention, conversion, and release of Elements and compounds
Model Variable Measurement or Condition Index
Vhydalt: Hydrology Alterations

Definition: Presence of a constructed subsurface and/or surface outlet below the wetland boundary. Depth of fill, changes in depth of the subsurface or surface drain, and distance from the wetland impacts wetland ground water surface elevation.

Logic: Presence of surface outlets, subsurface drains, or fill material impacts ground water surface elevations and maintenance of saturated anaerobic conditions throughout the wetland. In addition, outlets provide vectors for the transport of elements and compounds to off-site aquatic systems.

 

No subsurface drain present and subsurface flow is not impacted;

-OR-

if there is a nearby subsurface drainage feature with an invert elevation 3 feet or more lower than the wetland boundary, the distance to such feature corresponds to that identified in Table 1 for the soil texture (subsoil, 2 to 3 foot depth) in the wetland. No fill in wetland.

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1. No fill in wetland.

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1;

-OR-

presence of a shallow surface ditch (< 1 foot deep) through wetland with saturated conditions still present;

-OR-

fill present in wetland;

-OR-

additional surface water added to system (as from irrigation return, drainage outlets, etc.).

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1 (below);

-OR-

presence of a surface ditch (> 1 foot deep) through wetland; saturated conditions have been impacted but have ineffectively removed;

-OR-

fill present in wetland.

Surface or subsurface drainage feature within wetland or fill present:; saturated conditions have been severely impacted but still occur seasonally.

Saturated conditions non-existent (completely drained);

-OR-

non-wetland (upland) area (mitigation purposes).

 

 

 

1.0

 

 

 

 

 

0.75

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

 

 

0.25

 

 

 

 

 

 

0.1

 

 

0.0

 

3.0 RETENTION, CONVERSION, AND RELEASE OF ELEMENTS AND COMPOUNDS
Model Variable Measurement or Condition Index
Vupuse: Upland Land Use

Definition: Dominant land use or condition of the upland watershed that contributes to the wetland. The entire watershed area should be considered when determining the functional index of this variable.

Logic: Upland land use influences or moderates ground water flow through the evapotranspiration process.

 

Well managed, permanently vegetated native prairie. Management allows for adequate plant recovery time between grazing periods.

Permanent vegetation under a system of management such as,

native species under season long grazing with moderate use;

-OR-

idle non-native grassland cover;

-OR-

permanent native or non-native hayland.

Permanent native or non-native pasture which has been historically over-grazed, with some (<50 percent) bare ground, low plant vigor;

-OR-

no-till small grain;

-OR-

minimum till small grain in a grass/legume rotation.

Permanent native or non-native pasture which has been severely over-grazed, with significant (>50 percent) bare ground, low plant vigor, and evidence of soil erosion;

-OR-

no-till or minimum till row crop, minimum till small grain.

Conventional tillage small grain or row crop;

-OR-

inputs/overflow from cultural activities (industrial, urbanization, etc.).

Urban, semi-pervious, or impervious surface (this condition will result in maximum overland flow and a high rate of delivery to wetland). If best management practices employed, the impact may be somewhat less.

 

1.0

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

0.25

 

 

 

 

0.1

 

 

 

0.0

 

3.0 RETENTION, CONVERSION AND RELEASE OF ELEMENTS AND COMPOUNDS
Model Variable Measurement or Condition Index
Vwetuse: Wetland Land Use

DEFINITION: Dominant land use and condition of the wetland.

LOGIC: Land use in the wetland affects soil pore space, vegetation, and detrital biomass that results in characteristic removal of elements and compounds.

No evidence of tillage in the wetland (adapted vegetation intact);

-OR-

if previously tilled, outermost (temporary) wetland zone presently

intact,

-AND/OR-

if some use in the wetland (haying, grazing), no evidence of disruption to the wetland system (such as by compaction or rutting by equipment, or excessive trampling by livestock).

No evidence of tillage through innermost part of wetland (zones wetter than the temporary zone),

-AND-

some evidence of disturbance (grazing, haying, or tillage) in a portion of the outermost part of wetland (temporary zone),

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) tilled or over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) are rarely tilled or are intact,

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) is tilled or severely over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) is tilled or over-grazed most years,

-AND-

visual evidence of ephemeral gullies present in wet zone.

Wetland receives conventional tillage in all zone(s) most years. If recently tilled, crop and wetland vegetative remnants can be observed in area.

Wetland more severely disturbed than indicated above (no vegetation, rutted, pig farm, feedlot, urban fill, etc.).

 

1.0

 

 

 

 

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

 

0.25

 

 

 

 

0.1

 

0.0

 

3.0 RETENTION, CONVERSION, AND RELEASE OF ELEMENTS AND COMPOUNDS
Model Variable Measurement or Condition Index
Vpcover: Vegetation Density

DEFINITION: The abundance of woody and herbaceous plants in all vegetation zones within the wetland.

LOGIC: Living plant biomass cycles nutrients through (1) soil and water nutrient uptake, (2) biomass accumulation, and (3) litter production.

Canopy coverage is 75 to 125 percent of reference standard.

Canopy coverage is 25 to 74 percent, or >125 percent, of reference standard.

Canopy coverage is 1 to 24 percent of reference standard;

-OR-

vegetation and/or clods in furrows, etc.

Plants absent, no canopy coverage.

1.0

 

0.5

 

0.1

 

0.0

 

3.0 RETENTION, CONVERSION, AND RELEASE OF ELEMENTS AND COMPOUNDS
Model Variable Measurement or Condition Index
Vdetritus: Detritus

DEFINITION: The presence of litter in various stages of decomposition. Only plant debris that is prostrate and in direct contact with the soil surface should be considered.

LOGIC: Litter provides an energy source and increased surface area for microbial processing of nutrients.

Litter layer (consisting of herbaceous, shrub, and/or tree debris in various stages of decomposition, overlying and in direct contact with the soil surface) is 75 to 125 percent of reference standard. Direct measurement is 8 to 12 centimeters thickness.

Litter layer is 50 to 74 percent or >125 percent of reference standard. Direct measurement is 5 to <8 centimeters or >12 centimeters thickness.

Litter layer is 25 to 49 percent of reference standard. Direct measurement is 2 to <5 centimeters thickness.

Litter layer is 10 to 24 percent of reference standard. Direct measurement is 1 to <2 centimeters thickness;

-OR-

if cultivated, no-till fields.

Litter layer is 1 to 9 percent of reference standard. Direct measurement is 0 to <1 centimeter thickness;

-OR-

if cultivated, minimum or conventionally tilled fields.

Litter layer is absent (bare ground, paved surface).

 

 

1.0

 

 

0.75

 

0.5

 

 

 

0.25

 

 

 

0.1

 

0.0

 

3.0 RETENTION, CONVERSION, AND RELEASE OF ELEMENTS AND COMPOUNDS
Model Variable Measurement or Condition Index
Vsorpt: Sorptive Properties of Wetland Soils

DEFINITION: The physical ability of wetland soils to retain and release elements and compounds.

LOGIC: Soil physical properties (texture, organic carbon content, and occurrence of redoximorphic features) of the surface layer and upper part of the subsoil influence, and therefore can be used to indicate, the soils ability to retain and release elements and compounds.

Physical properties of soils similar to the reference standard.

Soil texture is medium or moderately fine (L, CL, SIL, SICL, SCL with 20 to 40 percent clay),

-AND-

organic carbon is >2 percent (measured or from soil survey report); or if not measured, Munsell color value is <3,

-AND-

common or many redox features present (Fe and/or Mn concretions, and/or reduced or depleted matrix) from 0 to 12 inches.

Physical properties of soils differ somewhat from reference standard. Soil texture is moderately coarse (L, SIL, VFSL with

<20 percent clay), or fine or very fine (C, SIC, SC with >40 percent clay),

-AND-

organic carbon is >2 percent (measured or from soil survey report); or if not measured, Munsell color value is <3,

-AND-

common or many redox features present (Fe and/or Mn concretions, and/or reduced or depleted matrix) from 0 to 12 inches.

Physical properties of soils differ from reference standard.

Soil texture is moderately coarse (VFSL with <15 percent clay; SL or FSL with 10 to 20 percent clay; or SI or LVFS),

-AND-

organic carbon is 1 to 2 percent (measured or from soil survey report); or if not measured, Munsell color value is 4 or 5,

-AND-

few redox features present (Fe and/or Mn concretions, and/or reduced or depleted matrix) from 0 to 12 inches.

Major departure in physical properties of soils from reference standards.

Soil texture is coarse (CoSL; SL or FSL with <10 percent clay; or textures coarser than LVFS),

-AND/OR-

organic carbon is <1 percent (measured or from soil survey report); or if not measured, Munsell color value is >5,

-AND/OR-

no redox features present, or redox features present below 12 inches.

The surface lacks soil or natural substrate properties (i.e. asphalt, concrete, buildings).

 

 

 

1.0

 

 

 

 

 

 

 

 

 

0.75

 

 

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

 

0.1

 

 

 

 

 

0.0

 

3.0 RETENTION, CONVERSION, AND RELEASE OF ELEMENTS AND COMPOUNDS
Model Variable Measurement or Condition Index
Vpore: Soil Pores

DEFINITION: The physical integrity of the soil in the surface layer and the upper part of the subsoil. This includes the number and continuity of pores and the type, grade, and size of soil structure.

LOGIC: Soil pores provide surface area for soil/ water/air contact and, therefore, increased surface area for microbial activity.

Many medium, fine, and/or very fine, continuous pores,

-AND-

structure is weak or moderate prismatic,

-AND/OR-

moderate or strong, medium and fine, angular or subangular blocky,

-AND/OR-

moderate or strong granular,

-AND-

consistence is friable or very friable.

Common fine and very fine, none or few medium, continuous and discontinuous pores,

-AND-

structure is weak or moderate, medium and/or fine angular or subangular blocky,

-AND/OR-

weak or moderate granular,

-AND-

consistence is firm.

Few fine and very fine discontinuous pores,

-AND-

structure is weak coarse subangular blocky or massive (coarse, cloddy or structureless),

-AND-

consistence is very firm or harder,

-AND/OR-

plow pan present in this zone, evidenced by roots growing horizontally along pan.

The substrate is a non-porous medium (asphalt, concrete, etc.).

 

 

 

 

1.0

 

 

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

0.1

 

 

 

 

0.0

INDEX OF FUNCTION:

= [(Vsource + Vhydalt)/2 + (Vupuse + Vwetuse )/2 + (Vpcover + Vdetritus)/2 + (Vsorpt + Vpore)/2] /4

4.0 RETENTION OF PARTICULATES

 DEFINITION: Deposition and retention of inorganic and organic particulates (>.45 um) from the water column, primarily through physical processes.

Effects On-Site: Sediment accumulation contributes to the nutrient capital of the ecosystem. Deposition increases surface elevation and changes topographic complexity. Natural rates of accumulation are slow. Organic matter may also be retained for decomposition, nutrient recycling, and detrital food web support.

Effects Off-Site: Reduces potential export of sediment to downstream wetland and aquatic ecosystems and groundwater systems.

 Discussion of Function

Retention applies to particulates arising from both on-site and off-site sources, but excludes in situ production of peat. The Retention of Particulates function contrasts with the Retention, Conversion, and Release of Elements and Compounds function in that the emphasis is more dependent on physical processes such as sedimentation and particulate removal. Sediment retention occurs through burial and chemical precipitation (i.e. removal of phosphorous by Fe+++). Dissolved forms may be transported as particles after undergoing sorption and chelation (heavy metals mobilized with humic and fulvic compounds). Imported sediment can undergo renewed pedogenesis on-site, which potentially involves weathering and release of elements that were previously inaccessible to mineral cycling (Brinson, 1995).

Discussion of Variables

The variables associated with the performance of this function focus primarily on components of the system that affect the physical processes of particulate removal and sedimentation. Because of the position on the landscape occupied by these wetlands, a primary source of sediment would be from uplands as particulates transported in overland flow. Therefore, use of the uplands (Vupuse) has a direct influence on the potential delivery of sediment to these ecosystems. The presence and condition of the buffer zone (Vbwidth and Vbcond, respectively) around the margin of the wetland affects surface flow into the wetland from adjacent uplands. Use of the wetland (Vwetuse) will affect the ability of the wetland ecosystem to perform this function, and will have an influence on the variability of related functional indices. As water flows over surfaces, friction and shear forces create turbulent flow and reduce velocities, both of which are conducive to sediment deposition. The variables used to determine sediment deposition as related to reduced velocities include the density of the vegetative cover (Vpcover ), and the microtopographic complexity or roughness (Vmicro) of the ground. Sedimentation is represented by direct evidence (Vsed).

4.0 RETENTION OF PARTICULATES

Model Variable Measurement or Condition Index
Vupuse: Upland Land Use

Definition: Dominant land use or condition of the upland watershed that contributes to the wetland. The entire watershed area should be considered when determining the functional index of this variable.

Logic: Upland land use influences or moderates ground water flow through the evapotranspiration process.

 

Well managed, permanently vegetated native prairie. Management allows for adequate plant recovery time between grazing periods.

Permanent vegetation under a system of management such as,

native species under season long grazing with moderate use;

-OR-

idle non-native grassland cover;

-OR-

permanent native or non-native hayland.

Permanent native or non-native pasture which has been historically over-grazed, with some (<50 percent) bare ground, low plant vigor;

-OR-

no-till small grain;

-OR-

minimum till small grain in a grass/legume rotation.

Permanent native or non-native pasture which has been severely over-grazed, with significant (>50 percent) bare ground, low plant vigor, and evidence of soil erosion;

-OR-

no-till or minimum till row crop, minimum till small grain.

Conventional tillage small grain or row crop;

-OR-

inputs/overflow from cultural activities (industrial, urbanization, etc.).

Urban, semi-pervious, or impervious surface (this condition will result in maximum overland flow and a high rate of delivery to wetland). If best management practices employed, the impact may be somewhat less.

 

1.0

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

0.25

 

 

 

 

0.1

 

 

 

0.0

 

4.0 RETENTION OF PARTICULATES

Model Variable Measurement or Condition Index
Vbwidth: Grassland Buffer Width

Definition: Width of grassland buffer surrounding outermost edge of wetland.

Logic: Width of the wetland buffer zone influences the delivery of sediment and nutrients to the wetland.

 

 

Buffer is >50 feet wide.

Buffer is 37.5 to <50 feet wide.

 

Buffer is 25 to <37.5 feet wide.

 

Buffer is 12.5 to <25 feet wide.

 

Buffer is 1 to <12.5 feet wide.

 

There is no buffer.

1.0

0.75

 

0.5

 

0.25

 

0.1

 

0.0

 

 

4.0 RETENTION OF PARTICULATES

   
Model Variable Measurement or Condition Index
Vbcond: Grassland Buffer

Condition

Definition: Dominant land use condition within 50 feet of the outermost edge of the wetland.

Logic: The condition of the wetland/upland buffer determines the ability of the buffer to filter sediments and nutrients traveling from sources to the wetland.

No alteration to wetland buffer.

Tillage disrupts 1 to 25 percent of wetland buffer area,

-AND/OR-

Visual Obstruction Measurement (VOR) is 75 to 99 percent of reference standard.

Tillage disrupts 26 to 50 percent of wetland buffer area,

-AND-

no-till or minimum till practices are used on buffer area,

-AND/OR-

VOR is 50 to 76 percent of reference standard.

Tillage disrupts 51 to 75 percent of buffer area,

-AND-

no-till or minimum till practices are used on buffer area,

-OR-

VOR is 25 to 49 percent of reference standard.

Tillage has disrupted >75 percent of buffer area; conventional tillage used; best management practices (BMP’s) are used in area adjacent to wetland;

-OR-

VOR is 1 to 24 percent of reference standard.

No buffer and no BMP’s used in area adjacent to wetland.

 

1.0

 

0.75

 

 

 

 

0.5

 

 

 

 

0.25

 

 

 

 

0.1

 

 

0.0

 

4.0 RETENTION OF PARTICULATES

Model Variable Measurement or Condition Index
Vwetuse: Wetland Land Use

DEFINITION: Dominant land use and condition of the wetland.

LOGIC: Land use in the wetland affects the ability of the wetland ecosystem to perform this function. It will also influence the variability of related functional indices.

No evidence of tillage in the wetland (adapted vegetation intact);

-OR-

if previously tilled, outermost (temporary) wetland zone presently

intact,

-AND/OR-

if some use in the wetland (haying, grazing), no evidence of disruption to the wetland system (such as by compaction or rutting by equipment, or excessive trampling by livestock).

No evidence of tillage through innermost part of wetland (zones wetter than the temporary zone),

-AND-

some evidence of disturbance (grazing, haying, or tillage) in a portion of the outermost part of wetland (temporary zone),

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) tilled or over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) are rarely tilled or are intact,

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) is tilled or severely over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) is tilled or over-grazed most years,

-AND-

visual evidence of ephemeral gullies present in wet zone.

Wetland receives conventional tillage in all zone(s) most years. If recently tilled, crop and wetland vegetative remnants can be observed in area.

Wetland more severely disturbed than indicated above (no vegetation, rutted, pig farm, feedlot, urban fill, etc.).

 

1.0

 

 

 

 

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

 

0.25

 

 

 

 

0.1

 

0.0

 

4.0 retention of particulates
Model Variable Measurement or Condition Index
Vsed: Sediment Delivery to Wetland

DEFINITION: Extent of sediment delivered to wetland from human activities, including agriculture.

LOGIC: Land use, percent slope of the upland watershed, and erodibility characteristics of the soil affect the potential for sediment delivery to the wetland. If the wetland fills with sediment, the capacity of the wetland to retain additional sediment is reduced.

 

No visual evidence of accelerated sediment delivery to wetland.

Visual evidence of historic and/or recent, culturally-accelerated sediment delivery to the wetland (such as minor accumulations of sediment in the form of small, stabilized deltas, sediment fans, drift deposits from windblown sediments, etc.),

-AND/OR-

visual observation indicates average deposition depth in wetland at <3 inches.

Visual evidence of recent and historic sediment delivery to the wetland in the form of sediment staining of detritus, thin silt deposits on detritus, and/or slight accumulations of sediment along plant stems;

-OR-

tillage through buffer to the outer edge of wetland,

-AND/OR-

visual observation indicates average deposition depth in wetland at about 3 to 6 inches.

Visual evidence of recent and historic sediment delivery to the wetland, as indicated by partial burial (25 to 75 percent) of detritus, or partial burial of plant crowns and stems;

-OR-

tillage through buffer and partial or complete tillage through wetland,

-AND/OR-

visual observation indicates average deposition depth in wetland at about 6 to 9 inches.

Visual evidence of significant sediment delivery to the wetland, as indicated by nearly complete (>75 percent) burial of detritus and/or vegetation in wetland. Presence of zones of sediment deposition, such as deltas, sediment fans, or drift deposits, common throughout wetland. Ephemeral or perennial gullies may be present on uplands adjacent to wetland. Best management practices lacking to control sediment delivery,

-AND/OR-

visual observation indicates average deposition depth in wetland at about 9 to 12 inches.

Pronounced rise in bottom elevation of wetland due to accelerated sediment delivery from cultural sources such as agriculture and urbanization. Typical average deposition depth in wetland is >12 inches.

1.0

 

 

 

0.75

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

0.25

 

 

 

 

 

 

 

 

 

0.1

 

 

 

 

 

0.0

 

4.0 retention of particulates

Model Variable Measurement or Condition Index
Vmicro: Microtopographic Complexity

DEFINITION: The microtopographic surface roughness of wetland.

LOGIC: Microtopographic complexity, or surficial roughness of the wetland, influences the rate at which surface water flows through the wetland. The more complex the wetland surface is, the greater the potential for deposition of sediment.

 

 

Natural conditions occur within wetland (predominantly well managed native vegetation with little or no anthropogenic disturbances evident as from livestock or machinery).

Vegetation consists predominantly of well managed, non-native species,

-AND-

average annual storm-based peak discharge depth does not exceed the average annual height of the vegetation,

-AND-

main flow frequently shifts from side to side due to changes in cross-sectional shape of the flood plain, changes in frequency and distribution of hummocks, or changes in slope.

Area is tilled infrequently (no greater than 2 years out of 5);

-OR-

area consists of severely over-grazed native or non-native species,

-AND-

average annual storm-based peak discharge depth exceeds the average annual height of the vegetation,

-AND-

main flow occasionally shifts from side to side due to changes in channel and flood plain cross-section, changes in frequency and distribution of hummocks, or changes in slope.

Area is tilled occasionally (no greater than 3 years out of 5);

-OR-

area is fall hayed or burned to remove current seasons plant growth,

-AND-

size and shape of channel cross-sections change gradually.

Area is tilled most years (4 years out of 5 or more);

-OR-

area has been channeled and is vegetated;

-OR-

area consists of a non-wetland (i.e. upland) site.

 

Area has been channeled and is not vegetated, or has been obliterated by urbanization (i.e. paved, filled and leveled for construction, etc.).

 

 

1.0

 

 

 

 

 

0.75

 

 

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

0.25

 

 

 

 

 

0.1

 

 

 

 

0.0

 

4.0 RETENTION OF PARTICULATES

Model Variable Measurement or Condition Index
Vpcover: Vegetation Density

DEFINITION: The abundance of woody and herbaceous plants in all vegetation zones within the wetland.

Logic: Density of the herbaceous layer influences the rate at which surface water flows through the wetland, thus influencing the rate and amount of sediment deposition.

Canopy coverage is 75 to 125 percent of reference standard.

Canopy coverage is 25 to 74 percent, or >125 percent, of reference standard.

Canopy coverage is 1 to 24 percent of reference standard;

-OR-

vegetation and/or clods in furrows, etc.

Plants absent, no canopy coverage.

1.0

 

0.5

 

0.1

 

0.0

INDEX OF FUNCTION:

= { Vsed x [(Vupuse + Vwetuse)/2 + (Vbwidth + Vbcond)/2 + (Vpcover + Vmicro)/2] /3}1/2

 5.0 ORGANIC CARBON EXPORT

 DEFINITION: Export of dissolved and particulate organic carbon and detritus from the wetland. Mechanisms include processes such as leaching, flushing, displacement, and erosion.

Effects On-Site: The removal of organic matter from living biomass, detritus, and soil organic matter contributes to carbon turnover (plant storage) and food web support.

Effects Off-Site: Provides support for food webs and biogeochemical processing from the wetland ecosystem.

 Discussion of Function

Wetlands export organic carbon at higher rates per unit area than terrestrial ecosystems (Mulholland and Kuenzler, 1979) in part because surface water has greater contact time with organic matter in litter and surface soil. While the molecular structure of most organic material is not well known because of its chemical complexity (Stumm and Morgan, 1981), organic matter nevertheless plays important roles in geochemical and food web dynamics. For example, organic carbon complexes with a number of relatively immobile metallic ions which facilitates transport in soil (Schiff et al., 1990). Organic carbon is a primary source of energy for microbial food webs (Dahm, 1981; Edwards, 1987; Edwards and Meyer, 1986) which form the base of the detrital food web in aquatic ecosystems. These factors, in combination with the proximity of wetlands to aquatic ecosystems, make wetlands critical sites for supplying both dissolved and particulate organic carbon.

 Discussion of Variables

Two factors are required in order for slope wetlands to function as a source of organic carbon for export. These factors are a source of organic material and water flow for transport. The density of the plant community within and surrounding the wetland influences the input of organic material (Vpcover) into the wetland. This input is in the form of both the living and dead vegetation (Vdetritus). The plant community present and the organic material it supplies to the wetland ecosystem is a direct function of the use and condition of the wetland (Vwetuse). Water movement into and through the wetland can be characterized by wetland surficial complexity (Vmicro) and by restrictions in or alterations to hydrology (Vhydalt). When precipitation rates exceed soil infiltration rates, overland flow in uplands adjacent to slope wetlands can transport both dissolved and particulate organic carbon into and through a wetland. Subsurface inflow contributes to organic carbon export. Displacement of existing soil water within alluvium may create outflow through surface and subsurface pathways to downstream localities.

5.0 ORGANIC CARBON EXPORT

Model Variable Measurement or Condition Index
Vpcover: Vegetation Density

DEFINITION: The abundance of woody and herbaceous plants in all vegetation zones within the wetland.

LOGIC: Living plant biomass cycles nutrients through (1) soil and water nutrient uptake, (2) biomass accumulation, and (3) litter production.

Canopy coverage is 75 to 125 percent of reference standard.

Canopy coverage is 25 to 74 percent, or >125 percent, of reference standard.

Canopy coverage is 1 to 24 percent of reference standard;

-OR-

vegetation and/or clods in furrows, etc.

Plants absent, no canopy coverage.

1.0

 

0.5

 

0.1

 

0.0

 

5.0 ORGANIC CARBON EXPORT

Model Variable Measurement or Condition Index
Vdetritus: Detritus

DEFINITION: The presence of litter in various stages of decomposition. Only plant debris that is prostrate and in direct contact with the soil surface should be considered.

LOGIC: Litter provides an energy source and increased surface area for microbial processing of nutrients.

Litter layer (consisting of herbaceous, shrub, and/or tree debris in various stages of decomposition, overlying and in direct contact with the soil surface) is 75 to 125 percent of reference standard. Direct measurement is 8 to 12 centimeters thickness.

Litter layer is 50 to 74 percent or >125 percent of reference standard. Direct measurement is 5 to <8 centimeters or >12 centimeters thickness.

Litter layer is 25 to 49 percent of reference standard. Direct measurement is 2 to <5 centimeters thickness.

Litter layer is 10 to 24 percent of reference standard. Direct measurement is 1 to <2 centimeters thickness;

-OR-

if cultivated, no-till fields.

Litter layer is 1 to 9 percent of reference standard. Direct measurement is 0 to <1 centimeter thickness;

-OR-

if cultivated, minimum or conventionally tilled fields.

Litter layer is absent (bare ground, paved surface).

 

 

1.0

 

 

0.75

 

0.5

 

 

 

0.25

 

 

 

0.1

 

0.0

 

5.0 ORGANIC CARBON EXPORT

Model Variable Measurement or Condition Index
Vwetuse: Wetland Land Use

DEFINITION: Dominant land use and condition of the wetland.

LOGIC: Land use in the wetland affects soil pore space, microbial activity, vegetation, and detrital biomass that results in organic decomposition and characteristic nutrient cycling processes.

No evidence of tillage in the wetland (adapted vegetation intact);

-OR-

if previously tilled, outermost (temporary) wetland zone presently

intact,

-AND/OR-

if some use in the wetland (haying, grazing), no evidence of disruption to the wetland system (such as by compaction or rutting by equipment, or excessive trampling by livestock).

No evidence of tillage through innermost part of wetland (zones wetter than the temporary zone),

-AND-

some evidence of disturbance (grazing, haying, or tillage) in a portion of the outermost part of wetland (temporary zone),

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) tilled or over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) are rarely tilled or are intact,

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) is tilled or severely over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) is tilled or over-grazed most years,

-AND-

visual evidence of ephemeral gullies present in wet zone.

Wetland receives conventional tillage in all zone(s) most years. If recently tilled, crop and wetland vegetative remnants can be observed in area.

Wetland more severely disturbed than indicated above (no vegetation, rutted, pig farm, feedlot, urban fill, etc.).

 

1.0

 

 

 

 

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

 

0.25

 

 

 

 

0.1

 

0.0

 

 

5.0 ORGANIC CARBON EXPORT

Model Variable Measurement or Condition Index
Vhydalt: Hydrology Alterations

Definition: Presence of a constructed subsurface and/or surface outlet below the wetland boundary. Depth of fill, changes in depth of the subsurface or surface drain, and distance from the wetland impacts wetland ground water surface elevation.

Logic: Presence of surface outlets, subsurface drains, or fill material impacts ground water surface elevations and maintenance of saturated anaerobic conditions throughout the wetland. Displacement of existing soil water through subsurface water movement contributes to organic carbon export by creating outflow through surface and subsurface pathways to downstream localities.

 

No subsurface drain present and subsurface flow is not impacted;

-OR-

if there is a nearby subsurface drainage feature with an invert elevation 3 feet or more lower than the wetland boundary, the distance to such feature corresponds to that identified in Table 1 for the soil texture (subsoil, 2 to 3 foot depth) in the wetland. No fill in wetland.

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1. No fill in wetland.

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1;

-OR-

presence of a shallow surface ditch (<1 foot deep) through wetland with saturated conditions still present;

-OR-

fill present in wetland;

-OR-

additional surface water added to system (as from irrigation return, drainage outlets, etc.).

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1;

-OR-

presence of a surface ditch (>1 foot deep) through wetland; saturated conditions have been impacted but ineffectively removed;

-OR-

fill present in wetland.

Surface or subsurface drainage feature within wetland or fill present:; saturated conditions have been severely impacted but still occur seasonally.

Saturated conditions non-existent (completely drained);

-OR-

non-wetland (upland) area (mitigation purposes).

 

 

 

1.0

 

 

 

 

 

0.75

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

 

 

0.25

 

 

 

 

 

 

0.1

 

 

0.0

 

5.0 ORGANIC CARBON EXPORT

Model Variable Measurement or Condition Index
Vmicro: Microtopographic Complexity

DEFINITION: The microtopographic surface roughness of wetland.

LOGIC: Microtopographic complexity, or surficial roughness of the wetland, influences the rate at which surface water flows through the wetland. The more complex the wetland surface is, the greater the potential for deposition of sediment and retention of detritus.

 

 

Natural conditions occur within wetland (predominantly well managed native vegetation with little or no anthropogenic disturbances evident as from livestock or machinery).

Vegetation consists predominantly of well managed, non-native species,

-AND-

average annual storm-based peak discharge depth does not exceed the average annual height of the vegetation,

-AND-

main flow frequently shifts from side to side due to changes in cross-sectional shape of the flood plain, changes in frequency and distribution of hummocks, or changes in slope.

Area is tilled infrequently (no greater than 2 years out of 5);

-OR-

area consists of severely over-grazed native or non-native species,

-AND-

average annual storm-based peak discharge depth exceeds the average annual height of the vegetation,

-AND-

main flow occasionally shifts from side to side due to changes in channel and flood plain cross-section, changes in frequency and distribution of hummocks, or changes in slope.

Area is tilled occasionally (no greater than 3 years out of 5);

-OR-

area is fall hayed or burned to remove current seasons plant growth,

-AND-

size and shape of channel cross-sections change gradually.

Area is tilled most years (4 years out of 5 or more);

-OR-

area has been channeled and is vegetated;

-OR-

area consists of a non-wetland (i.e. upland) site.

 

Area has been channeled and is not vegetated, or has been obliterated by urbanization (i.e. paved, filled and leveled for construction, etc.).

 

 

1.0

 

 

 

 

 

0.75

 

 

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

0.25

 

 

 

 

 

0.1

 

 

 

 

0.0

INDEX OF FUNCTION:

= [(Vpcover + Vdetritus + Vwetuse)/3 + (Vmicro + Vhydalt)/2] /2

6.0 MAINTENANCE OF CHARACTERISTIC PLANT COMMUNITY

DEFINITION: The species composition and physical characteristics of living plant biomass. Characteristic plant communities are not dominated by exotic or nuisance species. Vegetation is maintained by mechanisms such as seed dispersal, seed banks, and vegetative propagation which respond to variations in hydrology and disturbances such as fire and herbivores. The emphasis is on the temporal dynamics and structure of the plant community as revealed by species composition and abundance.

Effects On-Site: Creates microclimatic conditions that support the life histories of plants and animals. Converts solar radiation and carbon dioxide into complex organic carbon that provides energy to drive food webs. Provides habitat for feeding, and cover for nesting, resting refuge, escape, and breeding for resident and migratory animals.

Effects Off-Site: Provides a source of vegetative propagules for adjacent ecosystems which assists in revegetation following drought or disturbance and provides for gene flow between populations. Provides habitat for animals from adjacent ecosystems and for migrating birds (waterfowl, waders, etc.).

Discussion of Functions

Vegetation accounts for most of the biomass of prairie wetland systems. The physical characteristics of living and dead plants are closely related to ecosystem functions associated with hydrology, nutrient cycling, and the abundance and diversity of animal species (Lillie and Evard, 1994). Vegetation is not static, however, and species composition and physical characteristics can change in space and time in response to natural and anthropogenic influences (Weller, 1987).

Discussion of Variables

The variables within this functional index address plant community characteristics and potential anthropogenic disturbance.

Plant community characteristics alter with various types of perturbation. The ratio of native to non-native plant species (Vpratio) indicates the health of a plant community. A healthy plant community is comprised of a high percentage of native noninvasive plants. As a system becomes perturbed, invasive native and non-native species out compete sensitive native species. Plant abundance, as measured by percent cover (Vpcover), captures the ability of the system to remain self-sustaining. Detritus (Vdetritus) maintains thermal regulation of rhizospheres and propagules, and is essential for nutrient cycling.

The elements of a healthy plant community may be compromised by anthropogenic activities. Land use within the wetland (Vsed and Vwetuse) directly impacts plant communities by burying or disrupting detritus, seed banks, rhizomes, etc. Finally, hydrophilic plants are directly affected by water level and soil moisture regime which may be affected by the presence of an outlet. The presence and degree of impact of an outlet is reflected in the (Vhydalt ) variable.

6.0 MAINTENANCE OF CHARACTERISTIC PLANT COMMUNITY

Model Variable Measurement or Condition Index
Vwetuse: Wetland Land Use

DEFINITION: Dominant land use and condition of the wetland.

LOGIC: Disturbances within the wetland can have an influence on the maintenance of native plant populations.

 

No evidence of tillage in the wetland (adapted vegetation intact);

-OR-

if previously tilled, outermost (temporary) wetland zone presently

intact,

-AND/OR-

if some use in the wetland (haying, grazing), no evidence of disruption to the wetland system (such as by compaction or rutting by equipment, or excessive trampling by livestock).

No evidence of tillage through innermost part of wetland (zones wetter than the temporary zone),

-AND-

some evidence of disturbance (grazing, haying, or tillage) in a portion of the outermost part of wetland (temporary zone),

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) tilled or over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) are rarely tilled or are intact,

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) is tilled or severely over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) is tilled or over-grazed most years,

-AND-

visual evidence of ephemeral gullies present in wet zone.

Wetland receives conventional tillage in all zone(s) most years. If recently tilled, crop and wetland vegetative remnants can be observed in area.

Wetland more severely disturbed than indicated above (no vegetation, rutted, pig farm, feedlot, urban fill, etc.).

 

1.0

 

 

 

 

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

 

0.25

 

 

 

 

0.1

 

0.0

 

6.0 MAINTENANCE OF CHARACTERISTIC PLANT COMMUNITY

Model Variable Measurement or Condition Index
Vsed: Sediment Delivery to Wetland

DEFINITION: Extent of sediment delivered to wetland from human activities, including agriculture.

LOGIC: Land use, percent slope of the upland watershed, and erodibility characteristics of the soil affect the potential for sediment delivery to the wetland which can affect the capacity of the wetland to maintain native plant populations.

 

No visual evidence of accelerated sediment delivery to wetland.

Visual evidence of historic and/or recent, culturally-accelerated sediment delivery to the wetland (such as minor accumulations of sediment in the form of small, stabilized deltas, sediment fans, drift deposits from windblown sediments, etc.),

-AND/OR-

visual observation indicates average deposition depth in wetland at <3 inches.

Visual evidence of recent and historic sediment delivery to the wetland in the form of sediment staining of detritus, thin silt deposits on detritus, and/or slight accumulations of sediment along plant stems;

-OR-

tillage through buffer to the outer edge of wetland,

-AND/OR-

visual observation indicates average deposition depth in wetland at about 3 to 6 inches.

Visual evidence of recent and historic sediment delivery to the wetland, as indicated by partial burial (25 to 75 percent) of detritus, or partial burial of plant crowns and stems;

-OR-

tillage through buffer and partial or complete tillage through wetland,

-AND/OR-

visual observation indicates average deposition depth in wetland at about 6 to 9 inches.

Visual evidence of significant sediment delivery to the wetland, as indicated by nearly complete (>75 percent) burial of detritus and/or vegetation in wetland. Presence of zones of sediment deposition, such as deltas, sediment fans, or drift deposits, common throughout wetland. Ephemeral or perennial gullies may be present on uplands adjacent to wetland. Best management practices lacking to control sediment delivery,

-AND/OR-

visual observation indicates average deposition depth in wetland at about 9 to 12 inches.

Pronounced rise in bottom elevation of wetland due to accelerated sediment delivery from cultural sources such as agriculture and urbanization. Typical average deposition depth in wetland is >12 inches.

1.0

 

 

 

0.75

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

0.25

 

 

 

 

 

 

 

 

 

0.1

 

 

 

 

 

0.0

 

6.0 MAINTENANCE OF CHARACTERISTIC PLANT COMMUNITY

Model Variable Measurement or Condition Index
Vhydalt: Hydrology Alterations

Definition: Presence of a constructed subsurface and/or surface outlet below the wetland boundary. Depth of fill, changes in depth of the subsurface or surface drain, and distance from the wetland impacts wetland ground water surface elevation.

Logic: Presence of surface outlets, subsurface drains, or fill material impacts ground water elevations and maintenance of saturated anaerobic conditions throughout the wetland and can control the assemblage of aquatic/nonaquatic vegetation. In addition, outlets provide vectors for the transport of elements and compounds to off-site aquatic systems.

No subsurface drain present and subsurface flow is not impacted;

-OR-

if there is a nearby subsurface drainage feature with an invert elevation 3 feet or more lower than the wetland boundary, the distance to such feature corresponds to that identified in Table 1 for the soil texture (subsoil, 2 to 3 foot depth) in the wetland. No fill in wetland.

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1. No fill in wetland.

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1;

-OR-

presence of a shallow surface ditch (<1 foot deep) through wetland with saturated conditions still present;

-OR-

fill present in wetland;

-OR-

additional surface water added to system (as from irrigation return, drainage outlets, etc.).

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1;

-OR-

presence of a surface ditch (>1 foot deep) through wetland; saturated conditions have been impacted but ineffectively removed;

-OR-

fill present in wetland.

Surface or subsurface drainage feature within wetland or fill present:; saturated conditions have been severely impacted but still occur seasonally.

Saturated conditions non-existent (completely drained);

-OR-

non-wetland (upland) area (mitigation purposes).

 

 

 

1.0

 

 

 

 

 

0.75

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

 

 

0.25

 

 

 

 

 

 

0.1

 

 

0.0

 

6.0 MAINTENANCE OF CHARACTERISTIC PLANT COMMUNITY

Model Variable Measurement or Condition Index
Vpratio: Ratio of Native to Non-Native Species

Definition: The ratio of native to non-native plant species present in wetland zones as indicated by the top 4 dominants or by a more extensive species survey.

Logic: The presence of a high ratio of non-invasive native to invasive native and non-native plant species indicates that disturbances which interrupt naturally occurring cycles and other vegetative dynamics are minimal.

Native species comprise 100 percent of the species in the wetland.

Native species comprise 75 to <100 percent of the canopy in each zone.

Native species comprise 50 to <75 percent of the canopy in each zone.

Native species comprise 25 to <50 percent of the canopy in each zone.

Native species comprise 0 to <25 percent of the canopy in each zone;

-OR-

Lythrum salicaria (Purple Loosestrife) is among the dominant species present;

-OR-

single dominant plant specie (native or non-native) comprise a monotypic invasive stand within any wetland zone (such as cattails, reed canarygrass, etc.).

Wetland unvegetated.

1.0

 

0.75

 

0.5

 

0.25

 

 

 

 

 

0.1

 

 

 

 

0.0

 

6.0 MAINTENANCE OF CHARACTERISTIC PLANT COMMUNITY

Model Variable Measurement or Condition Index
Vpcover: Vegetation Density

DEFINITION: The abundance of woody and herbaceous plants in all vegetation zones within the wetland.

LOGIC: Characteristic plant densities of native prairies influence a suite of plant community components: seed/rhizome source, nutrient cycling processes, microclimate conditions, etc.

Canopy coverage is 75 to 125 percent of reference standard.

Canopy coverage is 25 to 74 percent, or >125 percent, of reference standard.

Canopy coverage is 1 to 24 percent of reference standard;

-OR-

vegetation and/or clods in furrows, etc.

Plants absent, no canopy coverage.

1.0

 

0.5

 

0.1

 

0.0

 

6.0 MAINTENANCE OF CHARACTERISTIC PLANT COMMUNITY

Model Variable Measurement or Condition Index
Vdetritus: Detritus

DEFINITION: The presence of litter in various stages of decomposition. Only plant debris that is prostrate and in direct contact with the soil surface should be considered.

LOGIC: Detrital biomass impacts nutrient cycling processes and disturbance regimes (e.g. fire) and thereby influences plant assemblages.

Litter layer (consisting of herbaceous, shrub, and/or tree debris in various stages of decomposition, overlying and in direct contact with the soil surface) is 75% to 125% of reference standard. Direct measurement is 8 to 12 centimeters thickness.

Litter layer is 50% to <75% or >125% of reference standard. Direct measurement is 5 to <8 centimeters or >12 centimeters thickness.

Litter layer is 25% to <50% of reference standard. Direct measurement is 2 to <5 centimeters thickness.

Litter layer is 10% to <25% of reference standard. Direct measurement is 1 to <2 centimeters thickness;

-OR-

if cultivated, no-till fields.

Litter layer >0% to 10% of reference standard. Direct measurement is 0 to <1 centimeter thickness;

-OR-

if cultivated, minimum or conventionally tilled fields.

Litter layer is absent (bare ground, paved surface).

 

 

1.0

 

 

0.75

 

0.5

 

 

 

0.25

 

 

 

0.1

 

0.0

INDEX OF FUNCTION:

= (Vwetuse + Vsed + Vhydalt + Vpratio + Vpcover + Vdetritus) /6

7.0 MAINTENANCE OF HABITAT INTERSPERSION AND CONNECTIVITY AMONG WETLANDS

DEFINITION: The spatial relationship of an individual wetland with respect to adjacent wetlands in the complex.

Effects On-Site: The assessed wetland contributes to habitat features of the wetland complex by virtue of its position in the landscape.

Effects Off-Site: Contributes to overall landscape diversity of habitat for aquatic and terrestrial organisms.

Discussion of Functions

Wetlands provide water and other life requirements for motile species that primarily exploit upland habitats. In addition, all vegetative strata in wetlands, from herbaceous layer to tree canopy, provide wildlife corridors (connections) between different wetland types, between uplands and wetlands, and between uplands (Sedell et al., 1990). Such connections between habitats were more isolated from one another (Brinson, 1995).

Discussion of Variables

Uninterrupted corridors are critical for movement of animals within and between wetlands. The integrity of these corridors may be disturbed through human-induced perturbations both within and around the assessment area. The extent of these perturbations is represented by the variables Vupuse, Vwetuse, Vhydalt, Vbcont, Vbcond, and Vbwidth. Vupuse represents the land use within the watershed above the wetland. Vwetuse represents the land use within the wetland. Vhydalt represents the maintenance of water levels within the wetland and alterations which impact this maintenance. Vbwidth represents the vegetative buffer width along the wetland. Vbcont represents the continuity of the vegetative buffer along the wetland. Vbcond represents the condition of the buffer along the outermost edge of the wetland.

The pattern of different types of wetlands in the landscape, and their contribution to habitat and the frequency of distribution of wetland sizes within a radius of one mile relates to the animal guilds that use the wetlands. Wetlands are dynamic, integrated systems that provide habitat for migratory ducks and geese. If a wetland is accessible and provides a high quality food source, waterfowl will seek it out. Waterfowl dynamics as they are related to wetland types are explained in Gersib et al. (1989).

7.0 MAINTENANCE OF HABITAT INTERSPERSION AND CONNECTIVITY AMONG WETLANDS

Model Variable Measurement or Condition Index
Vupuse: Upland Land Use

Definition: Dominant land use or condition of the upland watershed that contributes to the wetland. The entire watershed area should be considered when determining the functional index of this variable.

Logic:

Well managed, permanently vegetated native prairie. Management allows for adequate plant recovery time between grazing periods.

Permanent vegetation under a system of management such as,

native species under season long grazing with moderate use;

-OR-

idle non-native grassland cover;

-OR-

permanent native or non-native hayland.

Permanent native or non-native pasture which has been historically over-grazed, with some (<50 percent) bare ground, low plant vigor;

-OR-

no-till small grain;

-OR-

minimum till small grain in a grass/legume rotation.

Permanent native or non-native pasture which has been severely over-grazed, with significant (>50 percent) bare ground, low plant vigor, and evidence of soil erosion;

-OR-

no-till or minimum till row crop, minimum till small grain.

Conventional tillage small grain or row crop;

-OR-

inputs/overflow from cultural activities (industrial, urbanization, etc.).

Urban, semi-pervious, or impervious surface (this condition will result in maximum overland flow and a high rate of delivery to wetland). If best management practices employed, the impact may be somewhat less.

 

1.0

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

0.25

 

 

 

 

0.1

 

 

 

0.0

 

7.0 MAINTENANCE OF HABITAT INTERSPERSION AND CONNECTIVITY AMONG WETLANDS

Model Variable Measurement or Condition Index
Vwetuse: Wetland Land Use

DEFINITION: Dominant land use and condition of the wetland.

LOGIC: Land use in the wetland affect the capacity of the wetland complex to maintain native faunal populations.

No evidence of tillage in the wetland (adapted vegetation intact);

-OR-

if previously tilled, outermost (temporary) wetland zone presently

intact,

-AND/OR-

if some use in the wetland (haying, grazing), no evidence of disruption to the wetland system (such as by compaction or rutting by equipment, or excessive trampling by livestock).

No evidence of tillage through innermost part of wetland (zones wetter than the temporary zone),

-AND-

some evidence of disturbance (grazing, haying, or tillage) in a portion of the outermost part of wetland (temporary zone),

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) tilled or over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) are rarely tilled or are intact,

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) is tilled or severely over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) is tilled or over-grazed most years,

-AND-

visual evidence of ephemeral gullies present in wet zone.

Wetland receives conventional tillage in all zone(s) most years. If recently tilled, crop and wetland vegetative remnants can be observed in area.

Wetland more severely disturbed than indicated above (no vegetation, rutted, pig farm, feedlot, urban fill, etc.).

 

1.0

 

 

 

 

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

 

0.25

 

 

 

 

0.1

 

0.0

 

7.0 MAINTENANCE OF HABITAT INTERSPERSION AND CONNECTIVITY AMONG WETLANDS

Model Variable Measurement or Condition Index
Vhydalt: Hydrology Alterations

Definition: Presence of a constructed subsurface and/or surface outlet below the wetland boundary. Depth of fill, changes in depth of the subsurface or surface drain, and distance from the wetland impacts wetland ground water surface elevation.

Logic: Presence of surface outlets, subsurface drains, or fill material impacts ground water surface elevations and maintenance of saturated anaerobic conditions throughout the wetland. Changes in the water surface elevations can alter the surface connections among wetlands, change productivity and habitat structure, and change hydroperiod.

No subsurface drain present and subsurface flow is not impacted;

-OR-

if there is a nearby subsurface drainage feature with an invert elevation 3 feet or more lower than the wetland boundary, the distance to such feature corresponds to that identified in Table 1 for the soil texture (subsoil, 2 to 3 foot depth) in the wetland. No fill in wetland.

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1. No fill in wetland.

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1;

-OR-

presence of a shallow surface ditch (<1 foot deep) through wetland with saturated conditions still present;

-OR-

fill present in wetland;

-OR-

additional surface water added to system (as from irrigation return, drainage outlets, etc.).

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1;

-OR-

presence of a surface ditch (>1 foot deep) through wetland; saturated conditions have been impacted but ineffectively removed;

-OR-

fill present in wetland.

Surface or subsurface drainage feature within wetland or fill present:; saturated conditions have been severely impacted but still occur seasonally.

Saturated conditions non-existent (completely drained);

-OR-

non-wetland (upland) area (mitigation purposes).

 

 

 

1.0

 

 

 

 

 

0.75

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

 

 

0.25

 

 

 

 

 

 

0.1

 

 

0.0

 

7.0 MAINTENANCE OF HABITAT INTERSPERSION AND CONNECTIVITY AMONG WETLANDS

Model Variable Measurement or Condition Index
Vbwidth: Grassland Buffer Width

Definition: Width of grassland buffer surrounding outermost edge of wetland.

Logic: The width of an intact wetland/upland ecotone influences the availability of food sources for aquatic fauna (e.g. terrestrial invertebrates and upland seeds for water fowl). Additionally, this wetland/upland interface offers habitat for edge species (e.g. amphibians).

Buffer is >50 feet wide.

Buffer is 37.5 to <50 feet wide.

 

Buffer is 25 to <37.5 feet wide.

 

Buffer is 12.5 to <25 feet wide.

 

Buffer is 1 to <12.5 feet wide.

 

There is no buffer.

1.0

0.75

 

0.5

 

0.25

 

0.1

 

0.0

 

 

7.0 MAINTENANCE OF HABITAT INTERSPERSION AND CONNECTIVITY AMONG WETLANDS

Model Variable Measurement or Condition Index
Vbcont: Grassland Buffer Continuity

Definition: Continuity of the grassland within 50 feet of the outermost edge of the wetland.

Logic: The continuity of an intact wetland/upland ecotone influences the availability of food sources for aquatic fauna (e.g. terrestrial invertebrates and upland seed sources for waterfowl).

Continuity is >75% to 100%.

 

Continuity is >50% to 75%.

 

Continuity is >25% to 50%.

 

Continuity is >0% to 25%.

 

No continuity; however, there is potential for recovery.

 

No continuity, and no potential for recovery.

 

1.0

 

0.75

 

0.5

 

0.25

 

0.1

 

0.0

 

7.0 MAINTENANCE OF HABITAT INTERSPERSION AND CONNECTIVITY AMONG WETLANDS

Model Variable Measurement or Condition Index
Vbcond: Grassland Buffer

Condition

Definition: Dominant land use condition within 50 feet of the outermost edge of the wetland.

Logic: The condition of an intact wetland/upland ecotone influences the availability of food sources for aquatic fauna (e.g. terrestrial invertebrates and upland seed sources for waterfowl).

No alteration to wetland buffer.

Tillage disrupts 1 to 25 percent of wetland buffer area,

-AND/OR-

Visual Obstruction Measurement (VOR) is 75 to 99 percent of reference standard.

Tillage disrupts 26 to 50 percent of wetland buffer area,

-AND-

no-till or minimum till practices are used on buffer area,

-AND/OR-

VOR is 50 to 76 percent of reference standard.

Tillage disrupts 51 to 75 percent of buffer area,

-AND-

no-till or minimum till practices are used on buffer area,

-OR-

VOR is 25 to 49 percent of reference standard.

Tillage has disrupted >75 percent of buffer area; conventional tillage used; best management practices (BMP’s) are used in area adjacent to wetland;

-OR-

VOR is 1 to 24 percent of reference standard.

No buffer and no BMP’s used in area adjacent to wetland.

 

1.0

 

0.75

 

 

 

 

0.5

 

 

 

 

0.25

 

 

 

 

0.1

 

 

0.0

INDEX OF FUNCTION:

= [Vupuse + Vwetuse + Vhydalt + (Vbwidth + Vbcont + Vbcond) /3] /4

8.0 MAINTAIN DISTRIBUTION AND ABUNDANCE OF VERTEBRATES AND INVERTEBRATES

DEFINITION: The capacity of a wetland to maintain characteristic density and spatial distribution of vertebrates and invertebrates (aquatic, semi-aquatic, and terrestrial) that utilize wetlands for food, cover, rest, and reproduction.

Effects On-Site: Vertebrates and invertebrates distribute seeds throughout a wetland site, pollinate flowers, aerate the soil, aerate and aid in the decomposition of coarse woody debris, alter the hydroperiod and light regimes, and contribute to biodiversity.

Effects Off-Site: Vertebrates and invertebrates distribute seeds between wetland sites, pollinate flowers, provide food for predators, aerate the soil, aerate and aid in the decomposition of coarse woody debris, alter the hydroperiod and light regimes, and contribute to biodiversity.

Discussion of Functions

Maintenance of biodiversity, in part, depends on the total wetland area and on the types of wetlands within regions, in addition to local resource management approaches. Individual wetlands function in part through interaction with the adjacent portions of the landscape and with other wetlands. The connections between individual wetlands, aquatic systems, and terrestrial systems are critical to the support of many organisms. Thus, the landscape gives proper context for the evaluation of some wetland functions.

Maintaining characteristic density and spatial distribution of vertebrates and invertebrates in wetlands contributes to biodiversity. A large number of vertebrates and invertebrates show some association with wetlands, but species vary widely in the nature of their association. Some species may be confined to wetlands or be dependent upon them for specific activities or stages of their life cycle. Other species have a range of dependencies on wetlands for food and habitat. For individual species, the suitability of a particular wetland for habitat or for food may be critically dependent on the duration and time of year at which the wetland is inundated or saturated with water.

Discussion of Variables

The variables associated with maintaining characteristic density and spatial distribution of vertebrates and invertebrates focus primarily on the role wetlands play in maintenance of biodiversity. Variables associated with vertebrate species (Vvert), and those associated with invertebrate species (Vinvt), are measured directly by observation, by physical evidence (some sort of sign) their presence left behind, or by other surrogate measures.

8.0 MAINTAIN DISTRIBUTION AND ABUNDANCE OF VERTEBRATES AND INVERTEBRATES

Model Variable Measurement or Condition Index
Vvert: Distribution and Abundance of Resident and Migratory Vertebrates

Definition: The capacity of a wetland to maintain characteristic density and spatial distribution of vertebrates.

Logic: Maintenance of biodiversity depends on management of the wetland itself, adjacent upland resources, and diversity of the wetlands within a given area.

Presence of vertebrates (amphibians, birds, fish, reptiles, and/or mammals) in the wetland. Indicators include direct observation of vertebrates,

-AND/OR-

indirect observations (evidence such as, but not limited to, nests, tracks, calls, skeletons, skins, feathers, trails, scat, kills, burrows, browsed plants, egg masses, larvae),

-AND-

high vertebrate diversity is implied by the presence of 14 or more indicators.

Above average diversity of vertebrates is implied by the presence of 9 to 13 of the above-referenced indicators.

Average diversity of vertebrates is implied by the presence of 5 to 8 of the above-referenced indicators.

Below average diversity of vertebrates is implied by the presence of 1 to 4 of the above-referenced indicators.

None of the above-referenced indicators present implies no vertebrates present,

-AND-

wetland has not been eliminated (such as by development), thus with the potential for recovery.

None of the above-referenced indicators present implies no vertebrates present,

-AND-

wetland has been eliminated (such as by development), thus with no potential for recovery.

 

 

1.0

 

 

 

 

 

0.75

 

0.5

 

0.25

 

 

0.1

 

 

 

 

0.0

 

8.0 MAINTAIN DISTRIBUTION AND ABUNDANCE OF VERTEBRATES AND INVERTEBRATES

Model Variable Measurement or Condition Index
Vinvt: Distribution and Abundance of Wetland Invertebrates in Aquatic Habitats (Soil, Leaf Litter, and Coarse Woody Debris)

Definition: The capacity of a wetland to maintain characteristic density and spatial distribution of invertebrates.

Logic: Maintenance of biodiversity depends on management of the wetland itself, adjacent upland resources, and diversity of the wetlands within a given area.

Presence of invertebrates such as aquatic worms, leeches, insects (e.g. mayflies, dragon flies, damselflies), other crustaceans (e.g. crayfish, amphipods), and mollusks (e.g. snails, clams) in the wetland. Indicators include direct observation of invertebrates,

-AND/OR-

indirect observations (evidence such as, but not limited to, shells or fragments, exudate, tunnels, casts, holes, galleries in logs and twigs, trails),

-AND-

high invertebrate diversity is implied by the presence of 9 or more indicators.

Above average diversity of invertebrates is implied by the presence of 6 to 8 of the above-referenced indicators.

Average diversity of invertebrates is implied by the presence of 3 to 5 of the above-referenced indicators.

Below average diversity of invertebrates is implied by the presence of 1 or 2 of the above-referenced indicators.

None of the above-referenced indicators present (as in continuously cropped fields, for example),

-AND-

wetland has not been eliminated (such as by development), thus with the potential for recovery.

None of the above-referenced indicators present,

-AND-

wetland has been eliminated (such as by development), thus with no potential for recovery.

 

 

 

1.0

 

 

 

 

 

0.75

 

0.5

 

0.25

 

 

 

0.1

 

 

 

0.0

INDEX OF FUNCTION:

= (Vvert + Vinvt ) /2

Variables Used in the Hydrogeomorphic Assessment of Slope Wetlands in the Prairie Pothole Region of Eastern South Dakota

Initial Review Draft

November, 1997 

Vbcond: Grassland Buffer Condition

Model Variable Measurement or Condition Index
Definition: Dominant land use condition within 50 feet of the outermost edge of the wetland.

Logic: The condition of an intact wetland/upland ecotone influences the availability of food sources for aquatic fauna (e.g. terrestrial invertebrates and upland seed sources for waterfowl).

No alteration to wetland buffer.

Tillage disrupts 1 to 25 percent of wetland buffer area,

-AND/OR-

Visual Obstruction Measurement (VOR) is 75 to 99 percent of reference standard.

Tillage disrupts 26 to 50 percent of wetland buffer area,

-AND-

no-till or minimum till practices are used on buffer area,

-AND/OR-

VOR is 50 to 76 percent of reference standard.

Tillage disrupts 51 to 75 percent of buffer area,

-AND-

no-till or minimum till practices are used on buffer area,

-OR-

VOR is 25 to 49 percent of reference standard.

Tillage has disrupted >75 percent of buffer area; conventional tillage used; best management practices (BMP’s) are used in area adjacent to wetland;

-OR-

VOR is 1 to 24 percent of reference standard.

No buffer and no BMP’s used in area adjacent to wetland.

 

1.0

 

0.75

 

 

 

 

0.5

 

 

 

 

0.25

 

 

 

 

0.1

 

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Vbcont: Grassland Buffer Continuity

Model Variable Measurement or Condition Index
Definition: Continuity of the grassland within 50 feet of the outermost edge of the wetland.

Logic: The continuity of an intact wetland/upland ecotone influences the availability of food sources for aquatic fauna (e.g. terrestrial invertebrates and upland seed sources for waterfowl).

Continuity is >75% to 100%.

 

Continuity is >50% to 75%.

 

Continuity is >25% to 50%.

 

Continuity is >0% to 25%.

 

No continuity; however, there is potential for recovery.

 

No continuity, and no potential for recovery.

 

1.0

 

0.75

 

0.5

 

0.25

 

0.1

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Vbwidth: Grassland Buffer Width

Model Variable Measurement or Condition Index
Definition: Width of grassland buffer surrounding outermost edge of wetland.

Logic: Width of the wetland buffer zone influences the delivery of sediment and nutrients to the wetland.

 

 

Buffer is >50 feet wide.

 

Buffer is 37.5 to <50 feet wide.

 

Buffer is 25 to <37.5 feet wide.

 

Buffer is 12.5 to <25 feet wide.

 

Buffer is 1 to <12.5 feet wide.

 

There is no buffer.

1.0

 

0.75

 

0.5

 

0.25

 

0.1

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Vdetritus: Detritus

Model Variable Measurement or Condition Index
DEFINITION: The presence of litter in various stages of decomposition. Only plant debris that is prostrate and in direct contact with the soil surface should be considered.

LOGIC: Litter provides an energy source and increased surface area for microbial processing of nutrients.

Litter layer (consisting of herbaceous, shrub, and/or tree debris in various stages of decomposition, overlying and in direct contact with the soil surface) is 75 to 125 percent of reference standard. Direct measurement is 8 to 12 centimeters thickness.

Litter layer is 50 to 74 percent or >125 percent of reference standard. Direct measurement is 5 to <8 centimeters or >12 centimeters thickness.

Litter layer is 25 to 49 percent of reference standard. Direct measurement is 2 to <5 centimeters thickness.

Litter layer is 10 to 24 percent of reference standard. Direct measurement is 1 to <2 centimeters thickness;

-OR-

if cultivated, no-till fields.

Litter layer is 1 to 9 percent of reference standard. Direct measurement is 0 to <1 centimeter thickness;

-OR-

if cultivated, minimum or conventionally tilled fields.

Litter layer is absent (bare ground, paved surface).

 

 

1.0

 

 

0.75

 

0.5

 

 

 

0.25

 

 

 

0.1

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Vhydalt: Hydrology Alterations

Model Variable Measurement or Condition Index
Definition: Presence of a constructed subsurface and/or surface outlet below the wetland boundary. Depth of fill, changes in depth of the subsurface or surface drain, and distance from the wetland impacts wetland ground water surface elevation.

Logic: Presence of surface outlets, subsurface drains, or fill material impacts ground water surface elevations and maintenance of saturated anaerobic conditions throughout the wetland.

 

No subsurface drain present and subsurface flow is not impacted;

-OR-

if there is a nearby subsurface drainage feature with an invert elevation 3 feet or more lower than the wetland boundary, the distance to such feature corresponds to that identified in Table 1 for the soil texture (subsoil, 2 to 3 foot depth) in the wetland. No fill in wetland.

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1. No fill in wetland.

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1;

-OR-

presence of a shallow surface ditch (<1 foot deep) through wetland with saturated conditions still present;

-OR-

fill present in wetland;

-OR-

additional surface water added to system (as from irrigation return, drainage outlets, etc.).

A nearby subsurface drainage feature is present with an invert elevation 3 feet or more lower than the wetland boundary, and within the distance and corresponding soil texture (subsoil, 2 to 3 foot depth) in the wetland, from Table 1;

-OR-

presence of a surface ditch (>1 foot deep) through wetland; saturated conditions have been impacted but ineffectively removed;

-OR-

fill present in wetland.

Surface or subsurface drainage feature within wetland or fill present:; saturated conditions have been severely impacted but still occur seasonally.

Saturated conditions non-existent (completely drained);

-OR-

non-wetland (upland) area (mitigation purposes).

 

 

 

1.0

 

 

 

 

 

0.75

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

 

 

0.25

 

 

 

 

 

 

0.1

 

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Vinvt: Distribution and Abundance of Wetland Invertebrates in Aquatic Habitats

Model Variable Measurement or Condition Index
Definition: The capacity of a wetland to maintain characteristic density and spatial distribution of invertebrates. Aquatic habitats include soil, leaf litter, and coarse woody debris.

Logic: Maintenance of biodiversity depends on management of the wetland itself, adjacent upland resources, and diversity of the wetlands within a given area.

Presence of invertebrates such as aquatic worms, leeches, insects (e.g. mayflies, dragon flies, damselflies), other crustaceans (e.g. crayfish, amphipods), and mollusks (e.g. snails, clams) in the wetland. Indicators include direct observation of invertebrates,

-AND/OR-

indirect observations (evidence such as, but not limited to, shells or fragments, exudate, tunnels, casts, holes, galleries in logs and twigs, trails),

-AND-

high invertebrate diversity is implied by the presence of 9 or more indicators.

Above average diversity of invertebrates is implied by the presence of 6 to 8 of the above-referenced indicators.

Average diversity of invertebrates is implied by the presence of 3 to 5 of the above-referenced indicators.

Below average diversity of invertebrates is implied by the presence of 1 or 2 of the above-referenced indicators.

None of the above-referenced indicators present (as in continuously cropped fields, for example),

-AND-

wetland has not been eliminated (such as by development), thus with the potential for recovery.

None of the above-referenced indicators present,

-AND-

wetland has been eliminated (such as by development), thus with no potential for recovery.

 

 

 

1.0

 

 

 

 

 

0.75

 

0.5

 

0.25

 

 

 

0.1

 

 

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Vmicro: Microtopographic Complexity

Model Variable Measurement or Condition Index
DEFINITION: The microtopographic surface roughness of wetland.

LOGIC: Microtopographic complexity, or surficial roughness of the wetland, influences the rate at which surface water flows through the wetland. The more complex the wetland surface is, the greater the potential for deposition of sediment.

 

 

Natural conditions occur within wetland (predominantly well managed native vegetation with little or no anthropogenic disturbances evident as from livestock or machinery).

Vegetation consists predominantly of well managed, non-native species,

-AND-

average annual storm-based peak discharge depth does not exceed the average annual height of the vegetation,

-AND-

main flow frequently shifts from side to side due to changes in cross-sectional shape of the flood plain, changes in frequency and distribution of hummocks, or changes in slope.

Area is tilled infrequently (no greater than 2 years out of 5);

-OR-

area consists of severely over-grazed native or non-native species,

-AND-

average annual storm-based peak discharge depth exceeds the average annual height of the vegetation,

-AND-

main flow occasionally shifts from side to side due to changes in channel and flood plain cross-section, changes in frequency and distribution of hummocks, or changes in slope.

Area is tilled occasionally (no greater than 3 years out of 5);

-OR-

area is fall hayed or burned to remove current seasons plant growth,

-AND-

size and shape of channel cross-sections change gradually.

Area is tilled most years (4 years out of 5 or more);

-OR-

area has been channeled and is vegetated;

-OR-

area consists of a non-wetland (i.e. upland) site.

 

Area has been channeled and is not vegetated, or has been obliterated by urbanization (i.e. paved, filled and leveled for construction, etc.).

 

 

1.0

 

 

 

 

 

0.75

 

 

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

0.25

 

 

 

 

 

0.1

 

 

 

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Vpcover: Vegetation Density

Model Variable Measurement or Condition Index
DEFINITION: The abundance of woody and herbaceous plants in all vegetation zones within the wetland.

LOGIC: Density of the vegetation present within and adjacent to the wetland influences rate of surface water flow, and influences the rate of erosion and deposition of sediment.

Canopy coverage is 75 to 125 percent of reference standard.

Canopy coverage is 25 to 74 percent, or >125 percent, of reference standard.

Canopy coverage is 1 to 24 percent of reference standard;

-OR-

vegetation and/or clods in furrows, etc.

Plants absent, no canopy coverage.

1.0

 

0.5

 

0.1

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Vpore: Soil Pores

Model Variable Measurement or Condition Index
DEFINITION: The physical integrity of the soil in the surface layer and the upper part of the subsoil. This includes the number and continuity of pores and the type, grade, and size of soil structure.

LOGIC: Saturated hydraulic conductivity is directly related to pores and other voids in the soil. Reduced hydraulic conductivity results in a decrease of the hydraulic discharge function.

Many medium, fine, and/or very fine, continuous pores,

-AND-

structure is weak or moderate prismatic,

-AND/OR-

moderate or strong, medium and fine, angular or subangular blocky,

-AND/OR-

moderate or strong granular,

-AND-

consistence is friable or very friable.

Common fine and very fine, none or few medium, continuous and discontinuous pores,

-AND-

structure is weak or moderate, medium and/or fine angular or subangular blocky,

-AND/OR-

weak or moderate granular,

-AND-

consistence is firm.

Few fine and very fine discontinuous pores,

-AND-

structure is weak coarse subangular blocky or massive (coarse, cloddy or structureless),

-AND-

consistence is very firm or harder,

-AND/OR-

plow pan present in this zone, evidenced by roots growing horizontally along pan.

The substrate is a non-porous medium (asphalt, concrete, etc.).

 

 

 

 

1.0

 

 

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

0.1

 

 

 

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Vpratio: Ratio of Native to Non-Native Species

Model Variable Measurement or Condition Index
Definition: The ratio of native to non-native plant species present in wetland zones as indicated by the top 4 dominants or by a more extensive species survey.

Logic: The presence of a high ratio of non-invasive native to invasive native and non-native plant species indicates that disturbances which interrupt naturally occurring cycles and other vegetative dynamics are minimal.

Native species comprise 100 percent of the species in the wetland.

Native species comprise 75 to <100 percent of the canopy in each zone.

Native species comprise 50 to <75 percent of the canopy in each zone.

Native species comprise 25 to <50 percent of the canopy in each zone.

Native species comprise 0 to <25 percent of the canopy in each zone;

-OR-

Lythrum salicaria (Purple Loosestrife) is among the dominant species present;

-OR-

single dominant plant specie (native or non-native) comprise a monotypic invasive stand within any wetland zone (such as cattails, reed canarygrass, etc.).

Wetland unvegetated.

1.0

 

0.75

 

0.5

 

0.25

 

 

 

 

 

0.1

 

 

 

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

 

Vsed: Sediment Delivery to Wetland

Model Variable Measurement or Condition Index
DEFINITION: Extent of sediment delivered to wetland from human activities, including agriculture.

LOGIC: Land use and erodibility characteristics of the soil affect the potential for sediment delivery to the wetland. If the wetland fills with sediment, the capacity of the wetland to perform erosion control is reduced.

 

No visual evidence of accelerated sediment delivery to wetland.

Visual evidence of historic and/or recent, culturally-accelerated sediment delivery to the wetland (such as minor accumulations of sediment in the form of small, stabilized deltas, sediment fans, drift deposits from windblown sediments, etc.),

-AND/OR-

visual observation indicates average deposition depth in wetland at <3 inches.

Visual evidence of recent and historic sediment delivery to the wetland in the form of sediment staining of detritus, thin silt deposits on detritus, and/or slight accumulations of sediment along plant stems;

-OR-

tillage through buffer to the outer edge of wetland,

-AND/OR-

visual observation indicates average deposition depth in wetland at about 3 to 6 inches.

Visual evidence of recent and historic sediment delivery to the wetland, as indicated by partial burial (25 to 75 percent) of detritus, or partial burial of plant crowns and stems;

-OR-

tillage through buffer and partial or complete tillage through wetland,

-AND/OR-

visual observation indicates average deposition depth in wetland at about 6 to 9 inches.

Visual evidence of significant sediment delivery to the wetland, as indicated by nearly complete (>75 percent) burial of detritus and/or vegetation in wetland. Presence of zones of sediment deposition, such as deltas, sediment fans, or drift deposits, common throughout wetland. Ephemeral or perennial gullies may be present on uplands adjacent to wetland. Best management practices lacking to control sediment delivery,

-AND/OR-

visual observation indicates average deposition depth in wetland at about 9 to 12 inches.

Pronounced rise in bottom elevation of wetland due to accelerated sediment delivery from cultural sources such as agriculture and urbanization. Typical average deposition depth in wetland is >12 inches.

1.0

 

 

 

0.75

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

0.25

 

 

 

 

 

 

 

 

 

0.1

 

 

 

 

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________ 

Vsorpt: Sorptive Properties of Wetland Soils

Model Variable Measurement or Condition Index
DEFINITION: The physical ability of wetland soils to retain and release elements and compounds.

LOGIC: Soil physical properties (texture, organic carbon content, and occurrence of redoximorphic features) of the surface layer and upper part of the subsoil influence, and therefore can be used to indicate, the soils ability to retain and release elements and compounds.

Physical properties of soils similar to the reference standard.

Soil texture is medium or moderately fine (L, CL, SIL, SICL, SCL with 20 to 40 percent clay),

-AND-

organic carbon is >2 percent (measured or from soil survey report); or if not measured, Munsell color value is <3,

-AND-

common or many redox features present (Fe and/or Mn concretions, and/or reduced or depleted matrix) from 0 to 12 inches.

Physical properties of soils differ somewhat from reference standard. Soil texture is moderately coarse (L, SIL, VFSL with

<20 percent clay), or fine or very fine (C, SIC, SC with >40 percent clay),

-AND-

organic carbon is >2 percent (measured or from soil survey report); or if not measured, Munsell color value is <3,

-AND-

common or many redox features present (Fe and/or Mn concretions, and/or reduced or depleted matrix) from 0 to 12 inches.

Physical properties of soils differ from reference standard.

Soil texture is moderately coarse (VFSL with <15 percent clay; SL or FSL with 10 to 20 percent clay; or SI or LVFS),

-AND-

organic carbon is 1 to 2 percent (measured or from soil survey report); or if not measured, Munsell color value is 4 or 5,

-AND-

few redox features present (Fe and/or Mn concretions, and/or reduced or depleted matrix) from 0 to 12 inches.

Major departure in physical properties of soils from reference standards.

Soil texture is coarse (CoSL; SL or FSL with <10 percent clay; or textures coarser than LVFS),

-AND/OR-

organic carbon is <1 percent (measured or from soil survey report); or if not measured, Munsell color value is >5,

-AND/OR-

no redox features present, or redox features present below 12 inches.

The surface lacks soil or natural substrate properties (i.e. asphalt, concrete, buildings).

 

 

 

1.0

 

 

 

 

 

 

 

 

 

0.75

 

 

 

 

 

 

 

 

 

0.5

 

 

 

 

 

 

 

 

 

0.1

 

 

 

 

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Vsource: Source Area of Flow Intercepted by Wetland

Model Variable Measurement or Condition Index
DEFINITION: The area surrounding a wetland that defines the catchment or watershed of that wetland. The entire watershed area should be considered when determining the functional index for this variable.

LOGIC: Altering drainage patterns within and among wetlands will impact ground water and surface water flow to the wetland.

No alteration of upland watershed source area through surface alterations (such as water impoundment structures, terraces, or roads), subsurface alterations (such as tile drains or ditches), or additions (such as irrigation and associated practices or terrace outlets).

Presence of surface alterations within upland watershed source area which impacts overland flow into wetland (such as terraces or roads); however, no subsurface alterations (such as tile drains), or additions (such as irrigation and associated practices or terrace outlets) present. Less than 20 percent of watershed area is impacted.

The dominant surface and subsurface flow paths of water in the upland watershed source area has been altered, thus affecting the flow of water to the wetland (such as by drainage, terraces, or irrigation return). 20 to 50 percent of the watershed area is impacted,

-AND-

the alteration(s) does not change the wetland subclass.

The dominant surface and subsurface flow paths of water in the upland watershed source area has been altered, thus affecting the flow of water to the wetland (such as by drainage, terraces, or irrigation return),

-AND-

the alteration(s) changes the wetland subclass.

Upland watershed source area extremely altered such that almost all water flow to wetland has been eliminated (such as from urbanization).

 

1.0

 

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

0.1

 

 

 

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Vupuse: Upland Land Use

Model Variable Measurement or Condition Index
Definition: Dominant land use or condition of the upland watershed that contributes to the wetland. The entire watershed area should be considered when determining the functional index of this variable.

Logic: Upland land use influences or moderates ground water flow through the evapotranspiration process.

 

Well managed, permanently vegetated native prairie. Management allows for adequate plant recovery time between grazing periods.

Permanent vegetation under a system of management such as,

native species under season long grazing with moderate use;

-OR-

idle non-native grassland cover;

-OR-

permanent native or non-native hayland.

Permanent native or non-native pasture which has been historically over-grazed, with some (<50 percent) bare ground, low plant vigor;

-OR-

no-till small grain;

-OR-

minimum till small grain in a grass/legume rotation.

Permanent native or non-native pasture which has been severely over-grazed, with significant (>50 percent) bare ground, low plant vigor, and evidence of soil erosion;

-OR-

no-till or minimum till row crop, minimum till small grain.

Conventional tillage small grain or row crop;

-OR-

inputs/overflow from cultural activities (industrial, urbanization, etc.).

Urban, semi-pervious, or impervious surface (this condition will result in maximum overland flow and a high rate of delivery to wetland). If best management practices employed, the impact may be somewhat less.

 

1.0

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

0.25

 

 

 

 

0.1

 

 

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Vvert: Distribution and Abundance of Resident and Migratory Vertebrates

Model Variable Measurement or Condition Index
Definition: The capacity of a wetland to maintain characteristic density and spatial distribution of vertebrates.

Logic: Maintenance of biodiversity depends on management of the wetland itself, adjacent upland resources, and diversity of the wetlands within a given area.

Presence of vertebrates (amphibians, birds, fish, reptiles, and/or mammals) in the wetland. Indicators include direct observation of vertebrates,

-AND/OR-

indirect observations (evidence such as, but not limited to, nests, tracks, calls, skeletons, skins, feathers, trails, scat, kills, burrows, browsed plants, egg masses, larvae),

-AND-

high vertebrate diversity is implied by the presence of 14 or more indicators.

Above average diversity of vertebrates is implied by the presence of 9 to 13 of the above-referenced indicators.

Average diversity of vertebrates is implied by the presence of 5 to 8 of the above-referenced indicators.

Below average diversity of vertebrates is implied by the presence of 1 to 4 of the above-referenced indicators.

None of the above-referenced indicators present implies no vertebrates present,

-AND-

wetland has not been eliminated (such as by development), thus with the potential for recovery.

None of the above-referenced indicators present implies no vertebrates present,

-AND-

wetland has been eliminated (such as by development), thus with no potential for recovery.

 

 

1.0

 

 

 

 

 

0.75

 

0.5

 

0.25

 

 

0.1

 

 

 

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Vwetuse: Wetland Land Use

Model Variable Measurement or Condition Index
DEFINITION: Dominant land use and condition of the wetland.

LOGIC: Land use in the wetland affects soil pore space and the vegetation/

evapotranspiration relationship that results in the characteristic hydrologic regime.

No evidence of tillage in the wetland (adapted vegetation intact);

-OR-

if previously tilled, outermost (temporary) wetland zone presently

intact,

-AND/OR-

if some use in the wetland (haying, grazing), no evidence of disruption to the wetland system (such as by compaction or rutting by equipment, or excessive trampling by livestock).

No evidence of tillage through innermost part of wetland (zones wetter than the temporary zone),

-AND-

some evidence of disturbance (grazing, haying, or tillage) in a portion of the outermost part of wetland (temporary zone),

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) tilled or over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) are rarely tilled or are intact,

-AND-

no evidence of ephemeral gullies in wet zone.

Outermost part of wetland (temporary zone) is tilled or severely over-grazed most years,

-AND-

innermost part of wetland (zones wetter than the temporary zone) is tilled or over-grazed most years,

-AND-

visual evidence of ephemeral gullies present in wet zone.

Wetland receives conventional tillage in all zone(s) most years. If recently tilled, crop and wetland vegetative remnants can be observed in area.

Wetland more severely disturbed than indicated above (no vegetation, rutted, pig farm, feedlot, urban fill, etc.).

 

1.0

 

 

 

 

 

 

 

0.75

 

 

 

 

 

 

0.5

 

 

 

 

 

 

0.25

 

 

 

 

0.1

 

0.0

FUNCTIONAL INDEX:

Pre-Project/Mitigation __________ Post-Project/Mitigation __________

Calculation of Functional Indices for Slope Wetlands in the Prairie Pothole Region of Eastern South Dakota

1.0 Moderation of Groundwater Flow

Index of Function = {Vhydalt x [(Vsource + Vupuse) /2 + (Vpore + Vwetuse) /2] /2}1/2

 (Pre-Project/

Mitigation) = {_______ x [(_______ + _______) /2 + (_______ + _______) /2] /2}1/2

(Post-Project/

Mitigation) = {_______ x [(_______ + _______) /2 + (_______ + _______) /2] /2}1/2

 

INDEX OF FUNCTION:

[Pre-Project/Mitigation (a)] = __________ [Post-Project/Mitigation (b)] = __________

Net Change Due to Project (a - b) = __________


2.0 Velocity Reduction of Surface Water Flow

Index of Function = [(Vsource + Vupuse + Vmicro + Vpcover) /4 + (Vsed + Vwetuse) /2] /2

 

(Pre-Project/

Mitigation) = [(_______ + _______ + _______ + _______) /4 + (_______ + _______) /2] /2

(Post-Project/

Mitigation) = [(_______ + _______ + _______ + _______) /4 + (_______ + _______) /2] /2

 

INDEX OF FUNCTION:

[Pre-Project/Mitigation (a)] = __________ [Post-Project/Mitigation (b)] = __________

Net Change Due to Project (a - b) = __________

  

3.0 Retention, Conversion, and Release of Elements and Compounds

Index of Function = [(Vsource + Vhydalt) /2 + (Vupuse + Vwetuse) /2 + (Vpcover + Vdetritus) /2 +

(Vsorpt + Vpore) /2] /4

 (Pre-Project/

Mitigation) = [(_______ + _______) /2 + (_______ + _______) /2 + (_______ +

_______) /2 + (_______ + _______) /2] /4

(Post-Project/

Mitigation) = [(_______ + _______) /2 + (_______ + _______) /2 + (_______ +

_______) /2 + (_______ + _______) /2] /4

  

INDEX OF FUNCTION:

[Pre-Project/Mitigation (a)] = __________ [Post-Project/Mitigation (b)] = __________

Net Change Due to Project (a - b) = __________

 

4.0 Retention of Particulates

Index of Function = {Vsed x [(Vupuse + Vwetuse) /2 + (Vbwidth + Vbcond +) /2 + (Vpcover +

Vmicro) /2] /3} 1/2

 

(Pre-Project/

Mitigation) = {_______ x [(_______ + _______) /2 + (_______ + _______) /2 + (_______ +

_______) /2] /3} 1/2

(Post-Project/

Mitigation) = {_______ x [(_______ + _______) /2 + (_______ + _______) /2 + (_______ +

_______) /2] /3} 1/2

 

INDEX OF FUNCTION:

[Pre-Project/Mitigation (a)] = __________ [Post-Project/Mitigation (b)] = __________

Net Change Due to Project (a - b) = __________

5.0 Organic Carbon Export

Index of Function = [(Vpcover + Vdetritus + Vwetuse) /3 + (Vmicro + Vhydalt) /2] /2

 

(Pre-Project/

Mitigation) = [(_______ + _______ + _______) /3 + (_______ + _______) /2] /2

(Post-Project/

Mitigation) = [(_______ + _______ + _______) /3 + (_______ + _______) /2] /2

 

INDEX OF FUNCTION:

[Pre-Project/Mitigation (a)] = __________ [Post-Project/Mitigation (b)] = __________

Net Change Due to Project (a - b) = __________

 

6.0 Maintenance of Characteristic Plant Community

Index of Function = (Vwetuse + Vsed + Vhydalt + Vpratio + Vpcover + Vdetritus) /6

 

(Pre-Project/

Mitigation) = (_______ + _______ + _______ + _______ + _______ + _______) /6

(Post-Project/

Mitigation) = (_______ + _______ + _______ + _______ + _______ + _______) /6

 

INDEX OF FUNCTION:

[Pre-Project/Mitigation (a)] = __________ [Post-Project/Mitigation (b)] = __________

Net Change Due to Project (a - b) = __________


7.0 Maintenance of Habitat Interspersion and Connectivity Among Wetlands

Index of Function = [Vupuse + Vwetuse + Vhydalt + (Vbwidth + Vbcont + Vbcond) /3] /4

 

(Pre-Project/

Mitigation) = [_______ + _______ + _______ + (_______ + _______ + _______) /3] /4

(Post-Project/

Mitigation) = [_______ + _______ + _______ + (_______ + _______ + _______) /3] /4

 

INDEX OF FUNCTION:

[Pre-Project/Mitigation (a)] = __________ [Post-Project/Mitigation (b)] = __________

Net Change Due to Project (a - b) = __________

 

8.0 Maintain Distribution and Abundance of Vertebrates and Invertebrates

Index of Function = (Vvert + Vinvt) /2

 

(Pre-Project/

Mitigation) = (_______ + _______) /2

(Post-Project/

Mitigation) = (_______ + _______) /2

 

INDEX OF FUNCTION:

[Pre-Project/Mitigation (a)] = __________ [Post-Project/Mitigation (b)] = __________

Net Change Due to Project (a - b) = __________