Organic Soils Title Slide

Organic Soils ¾ What

are they? ¾ How are they formed? ¾ Where can they be found? ¾ How are they identified? ¾ How do they influence the soil?

Talk Outline Ask 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

Rule .1941 a4 Organic soils shall be considered unsuitable for the installation of on-site sanitary sewage systems.

Definition

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? ¾ Wet ¾ Low

permeability ¾ Fire hazard ¾ Low strength

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

Histosol: Organic Soil ¾
20% organic matter depending on clay content ¾ Terric: 40-125 cm (16-51 in.) thick ¾ Typic: >125 cm (>51 in.) thick

NRCS definition…. Compare to DENR definition.

Histic Epipedon Surface 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.

% Organic Carbon

21 Muck

18 15 12

Mucky Mineral

9 6

Mineral

3 0 0

30 % Clay

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

60

Colloidal Muck ¾ Very

finely divided muck (sapric) organic material ¾ Massive structure ¾ Very high moisture content ¾ pH 3.5-4.0 ¾ Very low permeability ¾ Sticky with little fiber

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

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

Factors causing organic matter accumulation ¾ High

rainfall ¾ Flat or depressional landscape ¾ Large distances between stream ¾ Shallow depth to impermeable subsurface layers ¾ Hydrology-high water table ¾ Cool/Cold temperatures

Why OM occurs. Go over each point.

Areas of organic soils ¾ Organic

soil flats ¾ Forested wetlands ¾ Depressional wetlands ¾ Marshes

Areas of organic soils to be discussed

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 ¾ High

pocosin ¾ Low 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.

Forested wetlands ¾ Bottomland

hardwood swamp ¾ Non-riverine hardwood swamp ¾ Non-riverine wet hardwood forest

Text

SLIDE-Bottomland hardwoodTyrell Co.

Obvious as there is standing water

SLIDE-Juniper swamp

SLIDE-Wet hardwood soil

Depressional wetlands ¾ Carolina

Bays

¾ Bogs ¾ Vernal

Text

pools

SLIDE-Cross section

Carolina Bays 1.6 km (1 mile)

1930, Near Myrtle Beach, SC First photo-mosaic showing depressions later called Carolina Bays.

N

SLIDE-Landscape-not always extreme

SLIDE-Bog

Slide Vernal pool

Marshes ¾ Estuarine ¾ Lacustrine

Text

SLIDE-Estuary-Salt marsh

Generally obvious

SLIDEEstuary soil

All organic

SLIDE-Inland marsh

Look for wetland vegetation to help

Field Identification ¾ Color ¾ Bulk

density ¾ Greasy feel ¾ Fibers ¾ Low strength

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

Organic (O) Horizons ¾

O horizons or layers: Layers dominated by organic material. ¾ Field Criteria z 12% or more organic carbon z Dark color (never used by itself) z Low strength, light dry weight, high fiber content z Typically a surface horizon-if buried may indicate disturbance ¾ Subordinate Distinctions of O Horizon z Oa-Highly decomposed organic material (Muck) z Oe-Moderately decomposed organic material (Muck and Peat) z Oi-Slightly decomposed organic material (Peat)

NRCS O horizons

SLIDE-Example-All organicEstuary

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

SLIDEExample--Upper organicBlacklands NC

SLIDEExample-All organicDismal Swamp NC

SLIDEExample --NonorganicCummul ic

SLIDE-Example--Non-organicSpodic

Organic matter influence on soil properties ¾

¾

¾

Soil color z brown or black if aerated z reddish if reduced Physical properties z increase structure z increase water holding z reduce bulk density Chemical properties z increase CEC z lower pH