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 < 40 cm (16 in.) of organic surface 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. 21 18 Muck 15 12 Mucky Mineral 9 6 Mineral
% Organic Carbon Organic % 3 0 03060 % Cl ay
NRCS organic classes. Note that OC is roughly 1/2 of OM 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 hardwood- Tyrell Co.
Obvious as there is standing water SLIDE-Juniper swamp SLIDE-Wet hardwood soil Depressional wetlands
¾ Carolina Bays ¾ Bogs ¾ Vernal pools
Text SLIDE-Cross section Carolina Bays
1.6 km (1 mile)
1930, Near Myrtle Beach, SC First photo-mosaic showing N depressions later called Carolina Bays.
SLIDE-Landscape-not always extreme SLIDE-Bog Slide Vernal pool Marshes
¾ Estuarine ¾ Lacustrine
Generally obvious SLIDE- Estuary 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 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
¾ Soil color
z brown or black if aerated
z reddish if reduced ¾ Physical properties
z increase structure
z increase water holding
z reduce bulk density ¾ Chemical properties
z increase CEC
z lower pH