1. Wetland Soils

2. Definition of Soil
A collection of natural bodies, made up of mineral and organic materials, that supports or is capable of supporting the growth of land plants ‘out of doors.’
Soil is different from substrate
Upper limit of soil is air or shallow water

3. Composition Inorganic material Organic matter Water Gasses (air)
Sand
Silt
Clay
Gravel, stones, rock
Organic matter
Water
Gasses (air)
The percentages of each are highly variable across space. For example, 10% to 60% of the volume of soils supporting upland plants is gas.

4. Soil Texture

5. Pedogenesis Five soil forming factors Parent material Climate
Topography
Organic activity
Time

7. Soil Classifications
Wetland soils can be either primarily mineral or organic
Organic
High in plant remains
Mineral
High in inorganic material

10. Soil properties Porosity Infiltration Erodibility
Available Water Holding Capacity
Shrink-Swell
Permeability
Soil Texture (used more with Mineral soils)
Based on percentages of sand, silt, and clay
Loam is soil with relatively even mixtures of sand, silt, and clay
Best for conductivity AND water holding capacity

12. Soil Orders

13. Hydric Soils
Soils that experience flooded conditions which lead to anaerobic conditions during at least part of the year.
Features
Flooding creates anaerobic conditions; lack of oxygen
Organic materials accumulate
Hydrarch succession; peat buildup
Drainage classes
excessively drained
somewhat excessively drained
well drained
moderately well drained
somewhat poorly drained
poorly drained: saturated for extended time
very poorly drained: waterlogged

14. Mineral Hydric Soils
“Mineral soils, when flooded for extended periods, develop certain characteristics that allow for their identification” (Mitsch & Gosselink, 1993, p.119).
Organic content is typically less than 20% to 35%.
Porosity between 45% and 55%.
They typically have relatively low water holding capacity due to high hydraulic conductivity (the speed with which water passes through soil).
Nutrient availability for plants in these soils is relatively low
Mineral soils in wet environments frequently are blue-grey in color due to chemical changes as a result of water.

15. Gleization Development of a blue-gray or greenish color
Gleying: result of chemical reduction of iron

16. Mottle Formation Alternate wetting and drying
Spots of orange/reddish-brown (iron) or dark reddish-brown/black (manganese) spots in a gray (gleyed) soil matrix
Intermittently exposed soils in an otherwise reduced environment

17. Formation of Hydric Mineral Soils
Depends on:
presence of anaerobic conditions
sufficient soil temperature (> 5° C)
presence of organic matter

18. Organic Hydric Soils
Most hydric soils, however, have a high percentage of organic matter.
Heavily organic soils are called histosols because they contain at least 78% (by volume) water, which is filling the very large amount of pore space
“Organic soil is composed primarily of the remains of plants in various stages of decomposition and accumulates in wetlands as a result of anaerobic conditions created by standing water or poorly drained conditions” (Mitsch & Gosselink, 1993, p.117).
Anaerobic conditions greatly reduce decomposition because decomposers in this environment are fewer in number and far less efficient than their aerobic brethren.

19. Characteristics
Determined by the botanical origin of organic material and the degree of decomposition
Porosity is about 80%
Bulk density is low (dry weight of soil material per unit volume)
Water holding capacity is relatively high
Hydraulic conductivity can be either high or low (depending on the degree of decomposition of the plant material).
High cation exchange capacity, dominated by Ca, Mg, K, and Na
But since many nutrients are tied up in organic material, nutrient availability to plants is often low
Organic soils are generally colored dark, from dark black to dark brown

20. Basic Sources of Organic Material
1- Mosses
Sphagnum

21. Basic Sources of Organic Material
2- Herbaceous material
Grasses
Reed grass (Phragmites)
Wild rice (Zizania)
Salt marsh cord grass (Spartina)
Sedges
Carex
Cladium
Cattails (Typha)
Water lilies (Nymphaea)

22. Basic Sources of Organic Material
3- Wood and leaf litter
Birch (Betula)
Pine (Pinus)
Tamarack (Larix)
Cypress (Taxodium)
Water tupelo (Nyssa)

23. Decomposition
Soil scientists distinguish suborders of histosols based on the amount of organic decay.
Fibrists (also called peat)
less than one-third of the organic material is decomposed and more than two-thirds of the plant material is identifiable.
Saprists (muck)
at least two-thirds of the material is decomposed and less than one-third of the plants fibers are identifiable.
Hemists (mucky peat)
conditions of decomposition between saprists and fibrists.
Folist: organic soils caused by excessive moisture that accumulate in tropical and boreal mountains

25. Identifying Hydric Soils
Organic soils
Hydric organic soils are typified by only one layer: O-horizon
decomposed remains of plants
peat, muck, or combination
Identified by black muck or black to orange-brown peat, usually thicker than 16 inches
Form in:
waterlogged depressions
cold, wet climates
low-lying areas along coastal waters

26. Identifying Mineral Hydric Soils
Indicators
Histic epipedon: layer of organic material on the surface 8-16” thick
Smell of rotten eggs (hydrogen sulfide)
Mottles- lenses of non-dominant soil type
Abundance, size, and color of mottles reflects duration of saturation period and whether soil is hydric
Stratified layers within 6 inches of the soil surface
Presence of 2% or more organic bodies of muck or mucky material within 6” of soil surface
Mucky modified mineral surface layer 2” or thicker within 6” of soil surface
Muck layer 0.5” or thicker with 6” of soil surface
Loamy mucky material 4” or thicker within 6” of soil surface

27. Identifying Mineral Hydric Soils
Organic layer
Oa- mucky material (sapric)
Organic matter that breaks down into a greasy mass upon rubbing
Oi- peaty material (fibric)
More than 2/3s of the organic material is identifiable (leaves, stems, roots)
Oe- peaty muck or mucky peat
Folists- nonhydric organic soil forming in high mountains and boreal/arctic regions
Dark A-horizon from organic matter
Spodic horizon in evergreen forests