Title Slide

Organic Soils

Organic Soils

What are they?How are they formed?Where can they be found?How are they identified?How do they influence the soil?

Talk OutlineAsk the group how they can tell if a soil is organic. Stress that color is not the only way or the best way.

Section .1935 (21) defines organic soils as those

organic mucks and peats consisting of more than 20%

organic matter by weight and 18 inches (45 cm) or

greater in thickness.

Definition

Definition

Rule .1941 a4Organic soils shall be

considered unsuitable for the installation of on-site sanitary sewage systems.

Why are organic soils unsuitable?

What do you think of when you say muck?

WATER or WETTNESS

Most importantly organic soils are wet.

How does water move through organic soil?

What do organic soils and wood have in common?

They both burn!

Peat fire in Blacklands in 1980’s. The fire burned for months and was only put out by flooding the area by closing ditches and pumping water into the area.

SLIDE-Results of peat fire

High temps consumed forests…what about septic systems?

So how does this make organic soil unsuitable?

Here’s a tank and drainfield before a fire.

SLIDE-Septic tank after fire

After the fire the tank remained but the PVC was gone as was several inches to feet of organic soil.

What happens when you drive in a swamp?

Low strength makes construction problematic at times.

Why are organic soils unsuitable?

WetLow permeabilityFire hazardLow strength

Problems with organic soils. Note that for treatment of wastewater organic soils are actually very good.

NRCS definition…. Compare to DENR definition.

Histosol: Organic Soil

< 40 cm (16 in.) of organic surface>20% organic matter depending on clay contentTerric: 40-125 cm (16-51 in.) thickTypic: >125 cm (>51 in.) thick

Histic EpipedonSurface horizon containing more

than 20% OM, depending on clay content. Greater than 30

cm (12 in.) if drained, 45 cm (18 in.) if undrained.

Histic epipedon (or surface layer) may in some cases be suitable for OSWW, however usually it is not.

SLIDE-Histic epipedon, mineral below

Ask where the organics end.

SLIDE-Histic epipedon, thick

organic

Ask where the organics end. Note this is all organic. Stress that some organics are not black.

0369

12151821

0 30 60

% Clay

% O

rgan

ic C

arbo

n Muck

Mucky Mineral

Mineral

NRCS organic classes. Note that OC is roughly 1/2 of OM

Typical muck in the blacklands. Generally it is less permeable than clay.

Colloidal Muck

Very finely divided muck (sapric) organic materialMassive structureVery high moisture contentpH 3.5-4.0Very low permeabilitySticky with little fiber

SLIDE-Surface organic after ripening in Blacklands

Photo… looks like coffee grounds

Organic Soil

Strong granular structure develops when massive “colloidal”muck is tilled and oxidized

Why OM occurs. Go over each point.

Factors causing organic matter accumulation

High rainfallFlat or depressional landscapeLarge distances between streamShallow depth to impermeable subsurface layersHydrology-high water tableCool/Cold temperatures

Areas of organic soils to be discussed

Areas of organic soils

Organic soil flats Forested wetlandsDepressional wetlandsMarshes

SLIDE-Map eastern NC: Blacklands most extensive

Use map to illustrate location. Organic soils can also be found in the mountains but a less common.

Organic soil flats - Pocosins

High pocosinLow pocosin

Pocosin is Algonquian Indian for “Swamp on a Hill”

SLIDE-Schematic

Schematic

SLIDE-Pocosin

SLIDE-Woody material in pocosin soil

Some of the logs preserved in the pocosin are good enough to bring to a saw mill for lumber.

Text

Forested wetlands

Bottomland hardwood swampNon-riverine hardwood swampNon-riverine wet hardwood forest

SLIDE-Bottomland hardwood-Tyrell Co.

Obvious as there is standing water

SLIDE-Juniper swamp

SLIDE-Wet hardwood soil

Text

Depressional wetlands

Carolina BaysBogsVernal pools

SLIDE-Cross section

Carolina Bays

1930, Near Myrtle Beach, SCFirst photo-mosaic showing

depressions later called Carolina Bays.N

1.6 km(1 mile)

SLIDE-Landscape-not always extreme

SLIDE-Bog

Slide Vernal pool

Text

Marshes

EstuarineLacustrine

SLIDE-Estuary-Salt marsh

Generally obvious

SLIDE-Estuary

soil

All organic

SLIDE-Inland marsh

Look for wetland vegetation to help

Text…note color is not the only way to ID organics

Field Identification

ColorBulk densityGreasy feelFibersLow strength

Organic (O) Horizons

O horizons or layers: Layers dominated by organic material.Field Criteria

12% or more organic carbonDark color (never used by itself)Low strength, light dry weight, high fiber contentTypically a surface horizon-if buried may indicate disturbance

Subordinate Distinctions of O HorizonOa-Highly decomposed organic material (Muck)Oe-Moderately decomposed organic material (Muck and Peat)Oi-Slightly decomposed organic material (Peat)

NRCS O horizons

SLIDE-Example--All organic-

Estuary

Ask the group to ID the Organic layers on all the next few slides

SLIDE-Example--Upper

organic-Blacklands NC

SLIDE-Example--

All organic-Dismal Swamp

NC

SLIDE-Example

--Non-organic-Cummul

ic

SLIDE-Example--Non-organic-Spodic

Organic matter influence on soil properties

Soil colorbrown or black if aeratedreddish if reduced

Physical propertiesincrease structureincrease water holdingreduce bulk density

Chemical propertiesincrease CEClower pH