Value of Soil Morphology to Wetland Restoration: Using Soils to Characterize

Historic Hydrology Patterns

Bruce Vasilas Department of Plant & Soil Sciences

University of Delaware

Areas of Expertise

• Not wetland restoration • Hydrologic characteristics of freshwater wetlands in

the Mid-Atlantic Region • Rapid assessment of hydrologic characteristics • Correlation of soil morphology with water quality

services

National Research Council (1992) defined restoration as the "return of an ecosystem to a close approximation of its condition

prior to disturbance."

Should wetland restoration prioritize a return to a close approximation of the historic hydrologic condition?

For hydrologic services (including water quality)-Yes

How do we return when we don’t know where we where?

Where’s the Water?

Soil Morphology

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Excavate and Compact

2007 2013

UD Wetland Restoration for Water Quality Services

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UD Wetland Restoration-Hydrologic Isolation

Value of Soil Morphology: Characteristics assessed by sight or touch

• Color • Structure: arrangement of primary particles into

larger, secondary particles • Horizonation: presence & sequence of distinct layers • Texture: particle size distribution

Soil morphology can be used to characterize wetland hydrology

• Hydroperiod • Hydrodynamics • Hydrologic inputs • Episaturation vs. endosaturation • Recharge systems vs. discharge systems

Hydric Soils

Hydric soils are defined as soils that formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part. (Federal Register, 7/13/94)

A drained soil is considered hydric if it was hydric prior to drainage.

Soil morphology reflects long-term hydrologic conditions.

Soil morphology responds very

slowly to altered hydrology.

Today’s morphology reflects historic hydrologic conditions.

Horizons: distinct soil layers

Sunken Series

E

Bt

Soil Structure

• Definition: The grouping or arrangement of primary particles into larger, secondary particles (peds)

• Importance – Reflects historic hydrology – Identification of confining layers – Identification of artesian systems

Platy Structure-Develops in response to pressure from above (perched systems)

Blocky Structure-Develops in clay enriched horizons in response to wetting/drying cycles

(dynamic water tables)

Massive Structure-Develops in subsurface horizons that are continuously wet

Confining Layer: Geologic material with little or no permeability; restricts water movement

Traffic pans Fragipans Confining layer Cemented layers Confined aquifer

Artesian Systems

Artesian water is ground water confined under pressure between layers of relatively impermeable geologic strata-a confined aquifer.

Fragipan: Confining layer with prismatic structure

Soil color indicates long-term soil moisture conditions.

Soil Color Munsell Soil Color Book, 7.5YR page

Short Term Saturation-Iron Segregation (Redoximorphic Features)

Long Term Saturation Black & brown-Organic matter accretion

Greys-Stripped mineral grains

Long-Term Inundation (Great Dismal Swamp)

Mineral Soil Flat; Seasonally Saturated

Episaturation vs. Endosaturation

• Endosaturation: Zone of saturation is continuous within the top 2 m of soil.

• Episaturation (Perched): 2 saturated layers are separated by an unsaturated zone within the top 2 m of soil.

• Why it matters: During the ‘dry season’ episatd. systems are more likely to go anaerobic in the root zone than endosatd. systems.

unsaturated

saturated

saturated

unsaturated

saturated

Endosaturated Episaturated (perched)

Loamy sand Loamy sand

Endosaturated Episaturated (Perched)

Silt loam

Loamy sand

Color & Texture

Using Soil Color Patterns to Characterize the Seasonal High Water Table & Water Table Fluctuations

Oxidized iron: high chroma Iron segregation: low chroma matrix, high chroma mottles No oxidized iron: no mottles

Rarely wet Wet for short duration Wet most of the time

Seasonal High WT

Identifying the Seasonal High Water Table

Dynamic Relatively

Static Static

Water Table Fluctuations

Field Indicators are soil morphological features used to identify hydric soils. Developed to assist in jurisdictional determinations of wetlands. Part of the 3-pronged approach dictated in the 87 Manual.

F3. Depleted Matrix

Can the Field Indicators be used to characterize hydrology beyond the standard jurisdictional criteria? They can also be used to: a. Distinguish recharge systems from

discharge systems b. Identify the median water table depth c. Characterize duration of inundation d. Characterize water table fluctuations

Field Indicators of Hydric Soils

Wet Wettest

F3 A11 A9 A3

Use of Field Indicators to Distinguish Recharge Sites vs. Discharge Sites

• Discharge systems release groundwater to the land surface (seeps, springs). – Flow path is horizontal and narrow.

• Recharge systems transmit water to the groundwater. – Flow path is vertical and wide.

Discharge Wetland

F12 F12

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Recharge Wetland

A3

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Use of Field Indicators to Characterize Hydroperiods

• Median water table depth • Duration of inundation • # water table fluctuations with respect to soil

surface and root zone

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Static Water Table, Permanently Inundated (3 years); A3. Black Histic

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Relationship Between Field Indicators & Median Water Table Depth (cm) (21 slope wetlands)

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Relationship between median WT depth (cm)

& Field Indicators in 21 slope wetlands.

a a

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F3/A11 F3/F2 F6 A3

Relationship Between Field Indicators and Inundation(% year)

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Relationship between Field Indicators and Water Table Fluctuations (no./yr.) at

15 cm Depth

Summary

• Soil morphology is a powerful tool for characterizing historic hydrology.

• Field Indicators of Hydric Soils can be used to characterize historic hydrology.

• These characteristics include: – Median water table depth – Duration of inundation – Water table fluctuations – Episaturation vs. endosaturation – Discharge vs. recharge systems

Questions