Wetlands Midterm

3 key features used to define wetlands

Hydrology, soils, and hydrophylic vegetation

Threats to wetlands

Industrial development, climate change, and pollution

Ecosytem services provided by wetlands

Carbon sequestration and toxin removal

Wetlands that only have sedges and grasses

Marshes

Wetlands that only have trees

Swamps

Wetlands along __ margins are referred to as lacustrine

Lake

The seasonal variation of water levels in a wetland is also referred to as its

Hydroperiod

Bogs are sustained by groundwater inputs

False

Scientific and legal definitions of wetlands are the same

False

Wetlands with variable hydrologic conditions have higher species diversity

True

Discharge wetlands are created by inflowing groundwater

True

Wetlands along the margins of rivers, streams, or lakes

Riparian ecosystems

Obligate Wetland Plant

Species that almost always grows in wetlands under natural conditions

Facultative Wetland Plant

Plant species that usually occur in wetlands but are occasionally found in non-wetland areas

3 obligate wetland plants

• Buttonbush

• Alder

• Cattail

Geomorphology

Topography, flat versus steep gradients, inflows and outflows

Discharge wetlands

Wetlands created due to inflowing groundwater

Recharge wetlands

Wetlands that lose water to the water table (need a lot of precipitation)

Flow-through wetlands

Wetlands that receive and release groundwater

Primary productivity

• productivity increases with increase in flowthrough

• greater amounts of nutrients

• fresh sediment

• new propagules

• removal of toxins

Four major components of soil

Air (25%)

Water (25%)

Mineral Matter (45%)

Organic matter (5%)

Soil texture

size distribution of soil particles

Soil structure

soil particles are arranged together

Soil Color

Hue, Value (lightness or darkness), chroma (intensity or brightness)

12-18% or more of organic carbon or greater than 20-30% organic matter

Organic soils

Organic wetland soils

Histosols

Organic soil origins

• Mosses

• Herbaceous material: such as reed grasses

• wood and leaf litter

Types of organic soils (Histosols)

• Saprists: two thirds or more material is decomposed and less than one-third of the plant fibers are identifiable

• Fibrists: less than one-third of material is decomposed and more than two-thirds of the plant fibers are identifiable

• Hemists: conditions between saprist and fibrist soil

• Folists: organic soils caused by excessive moisture

Oxygen content in the soil

20% to less than 5%

High to moderate oxygen content

aerobic condition

Low or negligible oxygen content

anaerobic condition

Two drainage conditions characteristic of wetland soils

• poorly drained (PD)

• Very poorly drained (VPD)

Loss of electrons

Oxidation

Gain of electrons

Reduction

MEMORIZE THIS

Hydrophyte

Water plant

Xerophyte

Dry plant

Mesophyte

no specific adaptations to too much or not enough water

Tolerators

Possess functional modification enabling them to survive inundation

Regulators

Avoid water stress or modify it to minimize effects

Species richness often increases as water flow or pulsing hydrology increases

true

Spatial heterogeneity creates additional ecological niches and enhances diversity

true

Structural (or morphological) adaptations to flooding

• Aerenchyma tissue in roots and stem

• adventitious roots

• stem hypertrophy

• fluted trunks

• shallow root systems

• lenticles (gas exchange)

• cypress knees

Normal air space is - % of plant volume, while wetland roots may be up to __% air

• 2-7%

• 60%

• due to aerenchyma tissue acting as a vent

difference between sedges, rushes, and grasses

• Sedges have edges, rushes are round, grasses are hollow

Physiological adaptations to flooded areas

• pressurized gas flow

• rhizospheric oxygenation

• decreased water uptake

• altered nutrient absorption

• sulfide avoidance

• anaerobic respiration

Whole plant adaptation to flooded conditions

• carnivory

• floating seeds

• timing of seed drop

• asexual growth

• vivipary (seeds germinate while fruit is still on the tree)

Wetland plant life forms

• rooted floating: roots are in the substrate, but most leaves and flowers float on the water surface

• rooted submerged: roots are in the substrate, and most leaves and stems are underwater

• non-rooted floating: plant is not rooted at all

• emergent: plant is rooted and most growth arises above the water surface

• Persistent: plant form remains intact following winter dormancy

• non- persistent: does not remain intact following winter dormancy

Natural sources of nitrogen

• lightning

• biological nitrogen fixation

Anthropogenic sources of nitrogen

• burning of fossil fuels

• widespread cultivation of N-fixing crops

• use of fertilizers in agriculture— synthetic and animal manures

• urban, suburban, rural sources— wastewater, lawn fertilizers, septic tanks

*Wetlands are referred to as the “kidneys” of the landscape

Because they help remove excess nitrogen from the soil and water

Key nitrogen polluter (difficult to control)

NO₃

Available inorganic N forms

• Nitrate

• Ammonium

Mineralization

Conversion or organic N into inorganic N forms ( NH₄⁺, NO₃^-) via processes like decomposition

Immobilization

Conversion of inorganic N forms to organic N forms (via processes like plant & biological uptake)

Nitrification

• Aerobic only; microbial

• conversion of ammonium —> nitrate

• occurs in oxic soils- not in anoxic wetlands, therefore ammonium accumulates in wetlands because this process is shut off

Denitrification

• anaerobic; facultative bacteria

• process of conversion of nitrite and nitrate to nitrogen gas N₂

• Typically occurs in saturated soils

• MAJOR ecosystem service by wetlands

Iron and Manganese Transformation

• occur after nitrate on the redox scale

• both Fe and Mn are reduced/oxidized by bacteria

• Fe and Mn in their reduced forms are mobile and soluble

• Ferrous causes grey-green coloring

• Ferric causes reddish brown color

Sulfur reductions occur after Fe and Mn on the redox scale

True

S forms in wetlands:

• Organic S (>70%)

• Reduced inorganic sulfides such as pyrite (<10%)

• Dissolved sulfate (<20%)

• Gases (<5%)

Aerobic zone sulfur processes

• immobilization

• oxidation of inorganic sulfide and elemental sulfur

• mineralization of organic S to sulfate

Anaerobic zone Sulfur processes

• conversion of sulfate to H₂S by reducing bacteria

• H₂S can be released to the atmosphere or can react with organic matter to form organic S

Biggest elements used by plants

nitrogen and phosphorus

3 main P forms

• organic P

• fixed mineral P

• ortho-phosphate P

80-90% of the P in soils is in organic or fixed form

True

*In organic soils >95% of P is organic

Wetlands work very good for nitrogen removal but not as well for phosphorus

• because organic soils cannot remove P; you need mineral soils rich in iron oxides (phosphorus binds to iron)

Last stage in redox sequence

carbon

Sources

• when wetlands release more nutrients than they receive

• Output > input

Transformers

• when the nutrient form is converted. the ouput may not necessarily be reduced

• inorganic N —> organic N

• Inorganic P —> organic P

Sinks

• when wetlands reduce the nutrient amount

• (output < input)

Fermentation

organic matter broken down to produce lower acids, alcohol and CO2. by facultative or obligate anaerobes

Methanogenesis

when certain bacteria use CO₂ as the electron acceptor and generate methane gas (CH₄)

Methane oxidation

methane conversion to CO₂ by methanotrophs under oxic conditions