value of soil morphology to wetland restoration: using ... · value of soil morphology to wetland...
TRANSCRIPT
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 Restored Wetland Water Table Depth
2007 2013
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
A5
Recharge Wetland
A3
F2
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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Dynamic Water Table, Seasonally Saturated, (3 years); F3. Depleted Matrix
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F3/A11 F3/F2 F6 A3
Relationship Between Field Indicators & Median Water Table Depth (cm) (21 slope wetlands)
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F3/A11 F3/F2
F6 A3
Relationship between median WT depth (cm)
& Field Indicators in 21 slope wetlands.
a a
b b
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F3/A11 F3/F2 F6 A3
Relationship Between Field Indicators and Inundation(% year)
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F3/A11 F3/F2 F6 A3
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