An Introduction to Hydric Soils

and Hydric Soil Terminology • Based on deliberations of:

The National Technical

Committee for Hydric

Soils (NTCHS).

A word about the NTCHS

• The National Technical Committee for Hydric Soils is a committee

with the following representation:

– Seven representatives from the various universities.

– Five representatives from the USDA, Natural Resources Conservation

Service (NRCS).

– One representatives from each the following federal agencies: USDA,

Forest Service, US Army Corps of Engineering, EPA, US Fish and

Wildlife Service, and Bureau of Land Management.

• The NTCHS make all decisions concerning hydric soils. Decision are

by majority vote. The only agency bound by NTCHS decisions is

NRCS.

• By relying heavily on the scientific and technical communities for its

membership, most NTCHS decisions are quite sound.

Wetlands

Wetlands

• In most cases (previous slide) there are three technical

criteria that must be met before an area can be called a

wetland: Wetland Hydrology, Wetland Vegetation, and

Hydric Soils.

• Throughout this lecture and all remaining lectures we are

not going to concern ourselves with Wetland Hydrology

and Wetland Vegetation. We are going to concentrate our

efforts on learning about Hydric Soils.

Hydric Soil Topics

• Hydric Soil Definition

• Hydric Soil Lists

• Hydric Soil Indicators

• Hydric Soil

– The definition provides up the basis for this lecture, the hydric soil lists are for off-site (office use), and the indicators provide us the best method of field identifying and delineating hydric soils. The ultimate goal of this lecture series is for you to fully understand hydric soils.

Hydric Soil Definition

• A soil 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. July 13, 1994).

• The definition sets the stage for this and future lectures and parts of the definition

will be referenced often.

– “that formed under” means that there are such things as drained hydric soils; that the

presence of ditches do not alter the status of a hydric soil.

– “saturation, flooding, and ponding” tells us there are three conditions for wetness. These

3 conditions of wetness are utilized differently.

– “during the growing season” will be applied differently for different applications.

– “develop anaerobic conditions” tell us that a hydric soil need not be reduced but only

lack oxygen.

– “in the upper part” is vague enough to allow interpretations that vary from region to

region and from climate to climate.

• This definition has many different forms in the 1 1/2 decades prior to 1994; the

NTCHS does not anticipate changing this (1994) version.

Special consideration: Flooded and

Ponded Soils

• The NTCHS has deliberated that a soil that is frequently flooded or ponded for long or very long duration (longer than 7 days) during the growing season is a Hydric Soil.

• However; Anaerobic conditions (as defined in the Hydric Soil Technical Standard) must exist also.

• This (meaning inundation)) provides us the first method of identifying a hydric soil (there will be two others).

• This method of identifying a hydric soil requires use of “during the growing season” data.

Growing Season

• Growing Season: The portion of the year when soil temperatures are above biologic zero 5 degrees C

(41 degrees F) at 50 cm (19.7"). The following growing season months are assumed for each of the

actual mean annual soil temperatures and soil temperature regimes of Soil Taxonomy:

• No Permafrost and

– 22 0 C or higher Isohyperthermic: January-December

– 22 0 C or Higher Hyperthermic: February-December

– 15 to 22 0 C Isothermic: January-December

– 15 to 22 0 C Thermic: February-October

– 8 to 15 0 C Isomesic: January-December

– 8 to 15 0 C Mesic: March-October

– Lower than 8 0 C Frigid: May-September

– Lower than 8 0 C Isofrigid: May-September

– Soil Taxonomy Requirements Cryic: May -August

• Permafrost and

– -10 0 C or lower Hypergelic: July-August

– -4 to -10 0 C Pergelic: July-August

– +1 to -4 0 C Subgelic: July-August

Hydric Soil

List: Most

hydric soil

lists are

created by a

soil scientist

based on local

experience

and

knowledge.

Clay County, Florida

_____________________________________________________________________________________________

| | | |

Map symbol and | Component |Percent | Landform | Hydric

map unit name | | of map | | rating

| | unit | |

_______________________________|_______________________|________|_________________|________

8: | | | |

Sapelo fine sand |Sapelo, hydric | 20 | Flats | Yes

|Rutlege | 3 | Depressions | Yes

|Albany | 10 | Knolls | No

|Sapalo, nonhydric | 67 | Flatwoods | No

9: | | | |

Leon fine sand |Leon, hydric | 10 | Flats | Yes

|Lynn Haven | 3 | Flats | Yes

|Sapelo, hydric | 3 | Flats | Yes

|Leon, nonhydric | 70 | Flatwoods | No

|Sapelo, nonhydric | 14 | Flatwoods | No

11: | | | |

Allanton and Rutlege mucky fine |Allanton | 45 | Depressions | Yes

sands, depressional | | | |

|Rutlege | 35 | Depressions | Yes

|Surrency | 5 | Depressions | Yes

|Sapelo, hydric | 5 | Flats | Yes

|Leon, nonhydric | 10 | Flatwoods | No

12: | | | |

Surrency fine sand, depressional|Surrency | 80 | Depressions | Yes

|Leon, hydric | 3 | Flats | Yes

|Meggett | 3 | Flats | Yes

|Rutlege | 3 | Depressions | Yes

|Santee | 2 | Flood plains | Yes

|Plummer | 9 | Flatwoods | No

13: | | | |

Meggett fine sandy loam |Meggett | 85 | Flats | Yes

|Goldhead, nonhydric | 15 | Flatwoods | No

17: | | | |

Plummer fine sand |Plummer, hydric | 20 | Flats | Yes

|Pelham, nonhydric | 15 | Flatwoods | No

|Plummer, nonhydric | 65 | Flatwoods | No

19: | | | |

Osier fine sand |Osier, hydric | 15 | Flats | Yes

|Rutlege | 2 | Depressions | Yes

|Osier, nonhydric | 65 | Flatwoods | No

|Albany | 10 | Knolls | No

|Hurricane | 8 | Knolls | No

20: | | | |

Scranton fine sand |Scranton, hydric | 15 | Flats | Yes

|Leon, hydric | 3 | Flats | Yes

|Rutlege | 2 | Depressions | Yes

|Scranton | 68 | Flatwoods | No

|Ridgewood | 5 | Knolls | No

|Ona, nonhydric | 3 | Flatwoods | No

Inherent Problems with Hydric Soil Lists

• There is a problem with hydric soil lists which may

confuse users (Hurt and Carlisle. 1997).

– The presence of a soil on a hydric soil list does not mean that the

soil is in fact hydric. This is only an interpretive rating. Just as is

the case with all interpretations based on information in a

published soil survey or other sources of estimated soil properties,

hydric soil interpretations are confirmed by on-site investigations.

• Hydric soil indicators (Hurt and Vasilas. 2006) provides

us a method of on-site confirmation of the presence or

absence of a hydric soil.

Hydric Soil Indicators

• Field Indicators of Hydric Soils in the US (Vasilas,

et.al. 2006) has been approved as the sole source

document for hydric soil identification and

delineation by the NRCS, US Army COE, EPA,

and US Fish and Wildlife Service. It has also been

approved as the sole source document for hydric

soil identification and delineation by the State of

Florida (DEP and Water Management Districts).

The beauty of the

hydric soil indicators is

that they provide us a

method to prove or

disproved the presence

of a hydric soil based

on something felt, seen,

or smelled and not

estimated or guessed.

Indicators are based on biogeochemical processes

that occur when a soil is saturated or inundated.

Biogeochemical Processes

• Biogeochemical processes are processes that alter soil due to the interaction of its

chemical composition and the animal and plant life it supports.

• Hydric soil indicators are based on several biogeochemical processes (Vepraskas. 1994)

that occur when soils are saturated or inundated (this subject will be covered thoroughly

in the lecture of redoximorphic features).

– Iron

– Carbon

– Carbon and Iron

– Carbon and/or Iron

– Carbon and Iron/Manganese

– Iron/Manganese

– Sulfur

– Algae

• The processes and the hydric soil indicator that result from the processes are reviewed in

the next few slides. The indicators will be covered in depth during a later lecture.

Ignore their being referenced for now; you may need to refer back after the next lecture.

Iron

• Twelve indicators are

based on iron

reduction,

transformation, and

differential

accumulation:

– A13, A14, A15, S4, S5,

F2, F3, F8, F9, F18,

F19 and F20.

Carbon

• Nineteen indicators

are based on carbon

accumulation and

differential

decomposition:

– A1, A2, A3, A5, A6,

A7, A8, A9, A10, S1,

S2, S3, S7, S8, S9, F1,

F11, F13, and F17.

Carbon and Iron

• Four indicators are based

on carbon accumulation

and differential

decomposition and iron

reduction, translocation,

and differential

accumulation:

– A11, A12, F6, and F7.

Carbon and/or Iron

• One indicator is based on

carbon accumulation and

differential decomposition

and/or iron reduction,

translocation, and

differential accumulation:

– S6.

Carbon and Iron/Manganese

• One indicator is based on

carbon accumulation and

differential decomposition

and iron/manganese

reduction, translocation,

and differential

accumulation:

– F16.

Iron/Manganese

• One indicator is based

on iron/manganese

reduction,

transformation, and

differential

accumulation:

– F12.

Sulfur

• One indicator is based

on sulfur reduction:

– A4.

Algae

• One indicator is based

on precipitation of

calcium carbonate by

algae:

– F10.

Where do we begin our

observations? • To determine whether an

indicator is present or not it is

critical to know where to begin

looking. To determine whether

a hydric soil indicator is present

we would begin our observation

of the soil in the photo to the

right beneath the knife blade

(below the fibric and hemic

material) in most LRRs but

where we begin our

observations varies from region

to region (next slide).

Where to look for an Indicator by

LRR (see slide 31) • The soil surface is the very top of the material upon which standing

– nationwide when applying indicators A1 and A2 and

– in LRRs F, G, H, and M if the material beneath any mucky peat

and/or peat is sandy.

• In LRR R the soil surface is the top of the mineral surface (underneath

any and all fibric, hemic, and/or sapric material) except for application

of A1 and A2.

• In the remaining LRRs and in LRRs F, G, H, and M if the material

beneath any mucky peat and/or peat is not sandy the soil surface is the

top of the muck or mineral surface (underneath any fibric and/or hemic

material) except for application of A1 and A2.

Field Indicators of Hydric Soils in the US http://www.statlab.iastate.edu/soils/hydric/fieldind/fieldind.html

• The remain portion of this

lecture pertains to the

publication Field

Indicators of Hydric Soils

in the US (Hurt and

Vasilas 2006)

• The current version is

Version 6.0; the picture to

the right is of the cover to

Version 3.2 (Hurt, et al.

1996)

Regionalization of Hydric Soil Indicators

• The NTCHS has approved each of the indicators for use in specific regions of the US (USDA, SCS. 1981). Most are based on Land Resource Regions (LRRs, next slide). Some are based on the smaller Major Land Resource Areas (MLRAs).

• Appendix 1 in Field Indicators of Hydric Soils in the US is a listing of the indicators approved for use in each LRR.

• A prime example of regionalization: Only the “presence” of muck is required in south Florida, as one goes North thicker layers are required. In New England (and other areas) muck (sapric material) occurs on upland soils so this indicator is not used in LRR R.

Basic Terms

• There are some basic terms used throughout that need explaining. These terms are defined here because they are used in the definitions of many of the indicators. – Depleted Matrix - Indicators A11, A12, F3, F9, and

F12.

– Gleyed Matrix – Indicators A11, A12, A14, S4, and F2.

– Reduced Matrix – Indicators A11,A12, A14, S4, F2, F3, F9, and F12.

– 70% masked by organic matter- Indicators A5, A11, A12, S7, S8, and S9.

Depleted Matrix

• For loamy and clayey soil material (and sandy soil material for application of Indicators A11 and A12), a depleted matrix refers to the volume of a soil horizon or subhorizon from which iron has been removed or transformed by processes of reduction and translocation to create colors of low chroma and high value. A, E and calcic horizons may have low chromas and high values and may therefore be mistaken for a depleted matrix; however, they are excluded from the concept of depleted matrix unless common or many, distinct or prominent redox concentrations as soft masses or pore linings are present. In some places the depleted matrix may change color upon exposure to air (Reduced Matrix), this phenomena is included in the concept of depleted matrix.

Depleted Matrix

• The following combinations of value and chroma identify a

depleted matrix:

– 1. Matrix value 5 or more and chroma 1 with or without

redox concentrations as soft masses and/or pore linings; or

– 2. Matrix value 6 or more and chroma 1 or 2 with or

without redox concentrations as soft masses and/or pore

linings; or

– 3. Matrix value 4 or 5 and chroma 2 and has 2 percent or

more distinct or prominent redox concentrations as soft

masses and/or pore linings; or

– 4. Matrix value 4 and chroma 1 and has 2 percent or more

distinct or prominent redox concentrations as soft masses

and/or pore linings.

Gleyed Matrix

• Soils with a gleyed matrix have the following combinations of

hue, value, and chroma and the soils are not glauconitic:

– 1. 10Y, 5GY, 10GY, 10G, 5BG, 10BG, 5B, 10B, or 5PB

with value 4 or more and chroma is 1; or

– 2. 5G with value 4 or more and chroma is 1 or 2; or

– 3. N with value 4 or more; or

– In some places the gleyed matrix may change color upon

exposure to air (reduced matrix). This phenomena is

included in the concept of gleyed matrix.

Depleted Depleted Gleyed

4/2, 5/2, 4/1 >5/1, >6/2 value >4, with 2% or more with or gley pages redox without redox of color concentrations concentrations charts

Depleted Matrix

• The range of colors for

the depleted matrix is

value 4 or more and

chroma 1 or 2;

however, colors of

value 4 and chroma 1

or 2 and value 5 and

chroma 2 must have

redox concentrations.

Matrix Color 10YR 4/2

Faint

Distinct

Prominent

Faint

Distinct

Prominent

Distinct

Prominent

Faint

Gleyed Matrix

• The range of colors for

the gleyed matrix is

value 4 or more on

either of the two gley

color charts.

Reduced Matrix

• A reduced matrix is a matrix that upon initial exposure fits

the color requirements of either a depleted matrix or a gleyed

matrix but changes color (redder hue) when exposed to air for

about 30 minutes (Vepraskas. 1994).

• In the next slide a soil (left photo) with a depleted/gleyed

matrix upon initial exposure was air dried for 7 days (right

photo). This is a classic example of a “reduced matrix.” The

most reduced areas turned the reddest after exposure. Some

hue changes occurred after 30 minutes but the change was

more dramatic after 7 days. The white bar in both photos is 1

cm long.

Reduced Matrix

70% Masked

• The picture on the right

is sandy soil material

with (clockwise from

top) 50, 60, and 70%

masked with organic

material. Organic carbon

content of the samples

are about 2, 3, and 4 %

respectively.

Moist Color

• All color requirements (hue,

value, and chroma) are for

moist color. If dry, moisten

to record color; if wet, allow

to dry to moist state. This

picture shows moist soil (L)

and dry soil (R). Features

are usually more readily

identifiable in moist state;

they may be missing if soil is

too wet (let dry).

Chroma

• Soil colors specified in the Indicators

do not have decimal points listed;

however, colors do occur between

Munsell (Gretag/Macbeth. 2000)

chips. Soil colors should not be

rounded to qualify as meeting an

indicator. For example: a soil matrix

with a chroma between 2 and 3 should

be listed as having a chroma of 2+.

This soil material does not have a

chroma 2 and would not meet any

indicator that requires a chroma 2 or

less.

2 2+

Summary

• We have explained the Hydric Soil Definition, Hydric Soil Lists.

Hydric Soil Indicators, and introduced Hydric Soil.

– The definition provides up the basis for this lecture, hydric

soil lists are for off-site (office use), and the indicators

provide us the best method of identifying and delineating

hydric soils (field use).

– Evidence of flooding and ponding can be used as the sole

source of evidence that an area has hydric soils if it has been

shown that anaerobic conditions have been met but really

should not be invoked.

– The presence of a soil on a hydric soil list does not mean that

the soil is in fact hydric; it is only an interpretive rating.

Summary (cont.)

– Hydric soil indicators are based on several biogeochemical

processes that occur when soils are saturated or inundated:

Iron, Carbon, Carbon and Iron, Carbon and/or Iron, Carbon

and Iron/Manganese, Iron/Manganese, Sulfur, and Algae.

– Field Indicators of Hydric Soils in the US (Hurt and Vasilas)

provides the structure of the regionalization of hydric soil

indicators and defines the terms depleted matrix, gleyed

matrix, and reduced matrix.

– Moist colors should be recorded and, although colors do

occur between Munsell chips, soil colors should not be

rounded to qualify as meeting an indicator.

Literature Cited

• Environmental Laboratory. 1987. Corps of Engineers Wetland Delineation Manual - Technical Report Y-87-1. US Army Engineers Waterways Experiment Station, Vicksburg, MS. http://www.wes.army.mil/el/wetlands/pdfs/wlman87.pdf

• Federal Register. July 13, 1994. Changes in Hydric Soils of the United States. Washington, DC. (current Hydric Soil Definition). http://soils.usda.gov/use/hydric/intro.htm#definition

• Hurt, G.W., and V.W. Carlisle. 1997. Proper use of hydric soil terminology. Soil Survey Horizons, Vol. 38, No. 4, Madison, WI. http://soils.usda.gov/use/hydric/hstn.htm#note1

Literature Cited (cont.)

• Vasilas, L.M., G.W. Hurt, and C.V. Noble. 2010. Field indicators of hydric soils in the United States (Version 7.0), USDA, NRCS, Fort Worth, TX. http://soils.usda.gov/soil_use/hydric/field_ind.pdf

• Xrite. 2009. Munsell® Color. New Windsor, NY.

• USDA, SCS. 1981. Land Resource Regions and Major Land Resource Areas of the United States. USDA-SCS Agricultural Handbook 296. US Govt. Printing Off., Washington, DC.

• Vepraskas, M. J. 1994. Redoximorphic Features for Identifying Aquic Conditions. Tech. Bulletin 301. North Carolina Ag. Research Service, North Carolina State Univ., Raleigh, North Carolina.