EVR4027 Wetland Environments Module 3 Quiz

Define “soil science”

Science concerned with the formation, nature, ecology, and classification of soil

What are the four components of soil?

Minerals, organic matter, water, and air

Define “minerals” as a soil component

A solid inorganic substance of natural occurrence.

How do minerals end up in soil?

Rocks, which are composed of minerals, break down into the soil over time

What amount of soil content is comprised of minerals?

½ of soil content

What determines soil texture?

Mineral presence/abundance

Define “organic matter” as a soil component.

What are the three types of benefits it brings to soil?

Tissues of plants, animals, or other organisms in decomposition at all stages: living, detritus (partially decomposed), and humus (fully decomposed).

Physical, chemical, and biological benefits

What are the physical benefits of organic matter in soil?

Enhances soil stability, improves water filtration, and increases water holding capacity

What are the chemical benefits of organic matter in soil?

Increases nutrient supply, increases pH stability, and increases decomposition rates

What are the biological benefits of organic matter in soil?

Serve as food for microbes, enhance pore space for microorganisms, and suppress diseases/pests through increased microbe diversity

What amount does water comprise of soil?

This varies widely, but often water comprises 25% of soil

Where is air found in soil?

In the soil poresW

What is the main benefit air provides in soil?

It enables the presence of oxygen and other gas in soil which aids chemical processes

What are the 4 groups of mineral particles (and their sizes) that determine soil texture?

Gravel (>2mm), Sand (>1mm), Silt (»), and Clay (invisible)

Define “porosity”

Describes the number, size, and connectedness of soil pores (air spaces)

What 2 components control/determine porosity of soil?

The texture (larger particles tend to create more porous soils) and compaction (agricultural soils are more compacted from heavy equipment repeatedly running on top)

What does soil porosity directly affect?

Water and air availability and therefore the chemical processes that occur there (e.g., soil moisture potential)

What three textures are measured by the texture triangle?

Percent clay, percent silt, and percent sand

Define “soil moisture potential”

The measure of water content in soil

What are the 3 important conditions that define plant available water and drainable porosity in soil?

Permanent wilting point, field capacity, and saturation

Define “permanent wilting point” as a condition of soil moisture potential

When the water content of a soil causes most plants growing to wilt and fail to recover their turgor upon rewetting. Water is strongly retained, trapped in smaller pores, and doesn’t readily flow

Define “field capacity” as a condition of soil moisture potential

The amount of water remaining in soil a few days after being wetted and free drainage has ceased

Define “saturation” as a condition of soil moisture potential

When the soil pores are holding the maximum amount of water and plants can’t uptake anymore water either

Define “plant available water” or “holding capacity”

[The portion of water able to be absorbed by plant roots.] By definition, it is the amount of water available, stored, or released between field capacity and the permanent wilting point water contents

Define “color” in terms of soil.

What is it influenced by?

A measure of hue, chroma, and value; an indicator of different properties as it is influenced by organic matter, minerals, and water content

What is a Munsell chart?

A chart used to measure soil color. Color can be indicative of wetland soil

Define “soil profile”

A cross-section of the soil that allows us to see the soil horizons

What are the 5 main soil horizons in order from top to bottom?

O, A, B, C, R

What defines the “O” horizon of a soil profile?

It is a litter layer containing organic matter (e.g., leaves) and is very dark in color (if present)

What defines the “A” horizon of a soil profile?

It is the topsoil layer containing mineral soil mixed with some organic matter. Generally dark in color due to humidified organic matter. It is the most productive layer with an abundance of plant roots

What defines the “B” horizon of a soil profile?

The subsoil layer, predominately mineral soil (a combination of parent material and accumulations from upper layers). Lighter color than the O and A horizons. Leached materials accumulate here

What defines the “C” horizon of a soil profile?

The parent material layer, composed of mineral soil, little affected from soil processes (no accumulation of minerals or materials from upper layers). Even lighter in color.

What defines the “R” horizon of a soil profile?

The bedrock layer composed of solid bedrock such as limestone, sandstone, or granite

How are hydric soils formed?

Formed under conditions of saturation, flooding, or ponding long enough during growing season to develop anaerobic conditions in the upper part

What are the 5 purposes of water? (i.e., what is it necessary for?)

Plant growth, chemical reactions, assistance in mixing soil particles as it moves through substrate, affecting decomposition of organic materials, and dissolving nutrients and minerals

*Although water serves these necessary functions, soil properties change when they become completely saturated

When do anaerobic conditions occur in soil?

What conditions do normal soils have?

Occur when there is a complete lack of oxygen in soil because pores are saturated with water. Normal soils have aerobic or oxygen-rich conditions.

What do anaerobic conditions cause in soils with these conditions?

Stress to plants due to a lack of oxygen roots need to function

What are anaerobic conditions characterized by?

A lack of oxygen which leads to different chemical processes in soil

What are the 6 biogeochemical processes that affect soil?

Oxidation, reduction, iron interactions with anaerobic bacteria, nitrogen cycle, cation exchange, and sulfur cycle

Define “oxidation” in terms of soil

Occurs during oxygen uptake by soils or when they’re oxygen-rich

Define “reduction” in terms of soil

Occurs when soils are releasing oxygen or are oxygen-deficient. Wetland soils show signs of reduction.

How does anaerobic bacteria interact with Fe3+ in soil?

Anaerobic bacteria add an electron to Fe3+, reducing it to Fe2+.

What color are iron oxides containing Fe3+ and what is their solubility in water?

They are yellow or red in color and insoluble in water

What color are iron oxides containing Fe2+ and what is their solubility in water?

They are colorless (grey/white) and water soluble

What color are saturated soils based on what we know of how iron oxides appear in color? Why?

Saturated soils are grey or white because the saturation creates anaerobic conditions, supporting anaerobic bacteria to form Fe2+ and result in a grey/white color

What color are drier soils based on what we know of how iron oxides appear in color? Why?

Drier soils are yellow or red in color because the increased air space in the soil creates aerobic conditions that supports the maintenance of Fe3+ in iron oxides which is red/yellow in color.

What does the presence of grey mottles near the surface in soil indicate?

Wetland soils

What does the presence of grey, yellow, and red mottles in subsoil indicate?

A fluctuating water table that creates saturated and unsaturated conditions

What are the two components of the Nitrogen cycle?

Nitrogen fixation and denitrification

Define “Nitrogen fixation” in terms of the nitrogen cycle

What conditions does it occur in?

What is the result for the soil?

During aerobic conditions, nitrogen fixation occurs where inorganic nitrogen is converted to organic forms by bacteria and/or algae. Soil then becomes a nitrogen sink.

Define “denitrification” in terms of soil.

What conditions does it occur in?

What is the result for the soil?

During anaerobic conditions, denitrification occurs where anaerobic bacteria convert ammonia to N2O and N2. Nitrogen is lost from a wetland during this process (released into the atmosphere)

How does high clay content of wetlands affect cation exchange?

What does this cause?

Some nutrients and heavy metals/pollutants exist as cations and absorb to negatively charged places on clay particles. This process causes wetlands to become a sink for nutrients, pollutants, and sediments which become attached to the clay particles

What is the “sulfur cycle” in terms of soil conditions?

Anaerobic bacteria reduce sulfate to hydrogen sulfide which makes wetland soil acidic and produces the “rotten egg” odor

Do biogeochemical processes make wetland soils more basic or more acidic?

Often make wetland soils more acidic

Why are wetlands often high in organic matter?

How does this manifest in soil?

Anaerobic conditions slow down decomposition which leaves a thick layer of organic litter.

They often have a pronounced O horizon and deep, dark A horizon. Sometimes wetlands have ‘muck’ soils which are black and spongy

What are the 6 important physical geochemical properties of hydric soil?

High quantities of organic matter (often dark), saturated soils, anaerobic conditions, reduced soils, acidic pH, texture often high in silt and clay (although wetlands sometimes occur in sandy soils)

What are the two main methods of soil sampling?

Using a soil probe/auger to extract samples or digging a soil pit

What are the 6 field indicators of hydric soils?

Soft, mushy, or water-logged soil, rotten egg smell (indicates sulfur has been reduced/anaerobic soils are present), peat and muck (slowed decomp causes buildup of organic matter), mottles (irregularly shaped blotches of color or texture within a soil matrix. Red indicates anaerobic conditions which results in reduction of iron), gleying (soil changing color due to water logging/anaerobic conditions, results in grey-blue colors), and stratified layers (top 6 inches, indicates repeated flood events)

Define “gleying” in terms of soil

The process of soil changing color due to water logging/anaerobic conditions, results in grey-blue colors

Define “mottles” in terms of soil.

What does red indicate?

Irregularly shaped blotches of color or texture within a soil matrix. Red indicates anaerobic conditions which results in reduction of iron

What causes the formation of peat and muck?

Anaerobic conditions slow down decomposition which causes increased buildup of organic matter