1. No category

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
Where’s the Water?
How do we return when we don’t know
where we where?
Soil Morphology
Depth to WT (cm)
50
Original
25
0
-25
-50
Depth to WT (cm)
50
25
0
-25
-50
Restored
Excavate and Compact
UD Wetland Restoration for Water Quality Services
2007
2013
UD Restored Wetland Water Table
Depth
20
15
INCHES
10
5
0
-5
-10
UD Wetland Restoration-Hydrologic Isolation
2007
2013
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
Confining layer
Confined aquifer
Traffic pans
Fragipans
Cemented layers
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.
Endosaturated
Episaturated (perched)
unsaturated
saturated
unsaturated
saturated
saturated
Color & Texture
Endosaturated
Episaturated (Perched)
Loamy sand
Silt loam
Loamy sand
Loamy sand
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
Identifying the Seasonal High Water Table
Rarely wet
Wet for short duration
Wet most of the time
Seasonal
High WT
Water Table Fluctuations
Dynamic
Relatively
Static
Static
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
Field Indicators of Hydric Soils
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
Wet
F3
Wettest
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
Static Water Table, Permanently Inundated
(3 years); A3. Black Histic
Depth to WT (cm)
50
25
0
-25
-50
Date
Dynamic Water Table, Seasonally Saturated,
(3 years); F3. Depleted Matrix
Depth to WT (cm)
50
25
0
-25
-50
Date
Relationship Between Field Indicators &
Median Water Table Depth (cm) (21 slope wetlands)
20
10
0
-10
-20
-30
-40
F3/A11
F3/F2
F6
A3
10
5
0
-5
-10
-15
-20
Relationship between median WT depth (cm)
& Field Indicators in 21 slope wetlands.
F3/A11
F3/F2
a
a
b
b
F6
A3
Relationship Between Field Indicators
and Inundation(% year)
90
80
70
60
50
40
30
20
10
0
F3/A11
F3/F2
F6
A3
Relationship between Field Indicators
and Water Table Fluctuations (no./yr.) at
15 cm Depth
10
8
6
4
2
0
F3/A11
F3/F2
F6
A3
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