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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