Organic Soils. Title Slide

Transcription

1 Organic Soils Title Slide

2 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 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.

3 Definition 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.

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

5 Why are organic soils unsuitable?

6 What do you think of when you say muck? WATER or WETTNESS Most importantly organic soils are wet.

7 How does water move through organic soil?

8 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.

9 SLIDE-Results of peat fire High temps consumed forests what about septic systems?

10 So how does this make organic soil unsuitable? Here s a tank and drainfield before a fire.

11 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.

12 What happens when you drive in a swamp? Low strength makes construction problematic at times.

13 Wet Why are organic soils unsuitable? Low permeability Fire hazard Low strength Problems with organic soils. Note that for treatment of wastewater organic soils are actually very good.

14 Histosol: Organic Soil < 40 cm (16 in.) of organic surface >20% organic matter depending on clay content Terric: cm (16-51 in.) thick Typic: >125 cm (>51 in.) thick NRCS definition. Compare to DENR definition.

15 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.

16 SLIDE-Histic epipedon, mineral below Ask where the organics end.

17 SLIDE-Histic epipedon, thick organic Ask where the organics end. Note this is all organic. Stress that some organics are not black.

18 % Organic Carbon Muck Mucky Mineral Mineral % Clay NRCS organic classes. Note that OC is roughly 1/2 of OM

19 Colloidal Muck Very finely divided muck (sapric) organic material Massive structure Very high moisture content ph Very low permeability Sticky with little fiber Typical muck in the blacklands. Generally it is less permeable than clay.

20 SLIDE-Surface organic after ripening in Blacklands Photo looks like coffee grounds

21 Organic Soil Strong granular structure develops when massive colloidal muck is tilled and oxidized

22 Factors causing organic matter accumulation High rainfall Flat or depressional landscape Large distances between stream Shallow depth to impermeable subsurface layers Hydrology-high water table Cool/Cold temperatures Why OM occurs. Go over each point.

23 Areas of organic soils Organic soil flats Forested wetlands Depressional wetlands Marshes Areas of organic soils to be discussed

24 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.

25 Organic soil flats - Pocosins High pocosin Low pocosin Pocosin is Algonquian Indian for Swamp on a Hill

26 Schematic SLIDE-Schematic

27 SLIDE-Pocosin

28 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.

29 Forested wetlands Bottomland hardwood swamp Non-riverine hardwood swamp Non-riverine wet hardwood forest Text

30 SLIDE-Bottomland hardwood- Tyrell Co. Obvious as there is standing water

31 SLIDE-Juniper swamp

32 SLIDE-Wet hardwood soil

33 Depressional wetlands Carolina Bays Bogs Vernal pools Text

34 SLIDE-Cross section

35 Carolina Bays 1.6 km (1 mile) 1930, Near Myrtle Beach, SC First photo-mosaic showing depressions later called Carolina Bays. N

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37 SLIDE-Landscape-not always extreme

38 SLIDE-Bog

39 Slide Vernal pool

40 Marshes Estuarine Lacustrine Text

41 Generally obvious SLIDE-Estuary-Salt marsh

42 All organic SLIDE- Estuary soil

43 Look for wetland vegetation to help SLIDE-Inland marsh

44 Color Bulk density Greasy feel Fibers Low strength Field Identification Text note color is not the only way to ID organics

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

46 SLIDE-Example- -All organic- Estuary Ask the group to ID the Organic layers on all the next few slides

47 SLIDE- Example--Upper organic- Blacklands NC

48 SLIDE- Example-- All organic- Dismal Swamp NC

49 SLIDE- Example --Non- organic- Cummul ic

50 SLIDE-Example--Non-organic- Spodic

51 Soil color Organic matter influence on soil properties brown or black if aerated reddish if reduced Physical properties increase structure increase water holding reduce bulk density Chemical properties increase CEC lower ph

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