Hydric Soils Biogeochemistry

Question 1

Define a hydric soil

Answer 1

A soil formed under saturated conditions, such as ponding or seasonal flooding, that exhibits anerobic characteristics in the upper portion allowing characteristic biogeochemical processes to occur

Question 2

What are the primary characteristics of a hydric soil?

Answer 2

• Accumulation of organic carbon in the A horizon due to greatly reduced decomposition rates of OM
• Grey-colored subsoil horizons
• Production of gasses such as H2S and CH4

Question 3

How are soil drainage classes connected to wetlands?

Answer 3

Most hydric soils will be classified as poorly or very poorly drained (rarely somewhat poorly drained)

Question 4

How do you determine depth to seasonal saturation?

Answer 4

Fine the depth to low chroma (2 or less) or gleyed soil colors. These colors along with IRON (Fe) redox features indicate the depth to the SHWT

Question 5

How do hydric soils form?

Answer 5

Hydric soils form through prolonged water saturation, creating anaerobic conditions that trigger unique soil-forming processes. Continuous water presence limits oxygen infiltration, causing reduction reactions and distinctive mineral transformations.

Question 6

Classify the 5 drainage classes.

Answer 6

Question 7

What are the characteristics of organic hydric soils (peat)?

Answer 7

Highly organic substrate composed of
partially decomposed plant materials,
predominantly formed in anaerobic,
waterlogged environments with extremely low decomposition rates. Characterized by high water retention and low bulk density.

Question 8

What are the characteristics of mineral hydric soils (muck)?

Answer 8

Heavily organic mineral soils formed
through advanced decomposition of plant
materials, containing significant inorganic
components. Exhibit dark coloration, high
nutrient content, and important carbon
sequestration capabilities in wetland
ecosystems

Question 9

What is the color of a hydric soil influenced by?

Answer 9

OM content, amount and type of Fe minerals, Mn minerals, and moisture

Question 10

How do gley colors form?

Answer 10

• Fe materials that contain Fe in its “reduced” form. Reduced Fe has a valence state of +2 and is written as Fe(II).
• Fe(II) is colorless and soluble in water, MOVES with the soil water
• Forms gley colors when it combines with anions such as CO3, SO4, and PO4
• Colors are only visible while anaerobic; will reoxidize if exposed

Question 11

What are the two important “things” to color in soils?

Answer 11

Question 12

What are the unique characteristics that influence BGC cycles in wetlands?

Answer 12

Question 13

What are the 4 key BGC processes in wetlands?

Answer 13

1. C sequestration and storage
2. Decomposition and OM turnover
3. CH4 production and emission mechanisms
4. Interactions with C, N, and P cycles

Question 14

How do wetlands impact C cycling?

Answer 14

Wetlands act as important carbon sinks, sequestering CO2 from the atmosphere. Additionally, the unique anaerobic conditions influence carbon transformation and storage mechanisms.

Question 15

DOC is . . . ?

Answer 15

Dissolved Organic Carbon, dissolved within the WATER fraction

Question 16

Draw the Carbon cycle between the water column, anerobic, aerobic, and atmosphere

Answer 16

Question 17

How do wetlands impact decomposition and OM turnover?

Answer 17

Wetland soils experience slower decomposition due to anaerobic conditions, affecting OM accumulation

• Significantly more OM accumulation, vital to ecosystem health
• Decomposition and OM turnover impact nutrient cycling heavily

Question 18

How do wetlands impact CH4 emissions?

Answer 18

Wetlands are significant contributors to methane missions making them crucial in greenhouse gas studies.

Methanogenic microbes thrive in the anaerobic environments, facilitating the production of CH4. CH4 that then escapes is emitted to the atmosphere contributing to global climate change. CH4 emissions peak in summer.

Question 19

Define nitrogen fixation

Answer 19

The process where atmospheric N is converted into ammonia by certain bacteria, making it available for plant use.

Question 20

Define nitrification

Answer 20

The biological oxidation of ammonia into nitrites THEN nitrates, which plants can then readily absorb as nutrients.

Question 21

Define denitrification

Answer 21

The process where nitrates are reduced into N2 gas, returning to the atmosphere and preventing nutrient overload in wetlands.

Question 22

Define ammonification

Answer 22

The transformation of organic N from decomposed matter back into replenishing the N pool for plants.

Question 23

N fixation and denitrification are _________ prominent in wetlands due to . . . ?

Answer 23

More
the presence of specialized microbes and low O2 environments

Question 24

Nitrification and Ammonification are generally _______ in wetlands because . . . ?

Answer 24

Slower
aerobic conditions support faster nutrient cycling

Question 25

N cycling is vital for . . . ?

Answer 25

* nutrient availability * waste decomposition * water quality * greenhouse gas regulation

Question 26

Draw a diagram of the nitrogen cycle.

Answer 26

Question 27

___________ plays a crucial role in the P cycle by trapping and releasing P in wetland soils

Answer 27

sedimentation

Question 28

_____________ is vital for incorporating P into the food web

Answer 28

plant uptake

Question 29

What are potential P sources for wetlands?

Answer 29

* Ag. runoff with fertilizers * natural processes such as sedimentation * decomposition

Question 30

Draw a diagram of the phosphorous cycle.

Answer 30

Question 31

What are the 7 P transformations?

Answer 31

1. P input from a P source 2. Plant uptake of inorganic P 3. Decomposition and release of P 4. Microbia activity to mineralize organic P back into inorganic P OR immobilization 5. Adsorption to soil particles 6. Release back into water column via mineralization 7. Retention of P in wetlands preventing downstream eutrophication

Question 32

Compare wetland and terrestrial P cycling

Answer 32

**P Cycling in Wetlands** * Trap P through sedimentation, enhancing nutrient availability * Decomposition in wetlands releases P slowly * P retention in wetlands supports diverse plant and microbial life **P Cycling in NON-Wetlands** * Faster P cycling due to aerobic conditions * Face risks of P runoff, leading to downstream eutrophication

Question 33

How are the C, N, and P cycles interrelated?

Answer 33

The C, N, and P cycles are interconnected through various BGC processes: * The decomposition of OM (C cycle) releases nutrients like N and P which can then be taken up by plants (N and P cycles) * Availability of N and P can influence plant growth and consequently the amount of C that is stored in plant biomass and soil The RATIOS of C:N:P has a large impact on plant growth, microbial action, and nutrient cycling through the wetland ecosystem.

Question 34

What are the types of GHG produced by wetlands?

Answer 34

Methane (CH4) and Nitrous Oxide (N2O)

Question 35

What 4 factors influence GHG in wetlands?

Answer 35

**I. Water level** Influence of water level dictates anaerobic conditions and microbial activity **II. Temperature** Variations impact the rate of OM decomposition in wetlands, subsequently impacting GHG emissions **III. Soil Type** Different types of soils in wetlands have different district properties that influence GHG due to variations in nutrient availability and water retention **IV. Vegetation** The type and density of vegetation cover can greatly influence GHG by affecting photosynthesis and OM decomposition

Question 36

How does the Munsell Color Chart help in the identification of hydric soils?

Answer 36

Soil features (matrix, mottles) which exhibit a sufficiently low chroma (2 or less) below the A horizon can indicate a depth at which SHWT occurs. This determined drainage class can indicate if a soil is hydric or not i.e. those poorly and very poorly drained