Environmental Resources IIIWetlands Ecology and Management

Mr V Zungu

Environmental Management

08 April 2011

Topics covered in this lecture

• Wetland status and trends, causes of losses.

• Definitions and criteria used to identify and

delineate wetlands.

• Wetlands functions and values.

• Overarching theme:

– the interplay of science, public policy and

natural resource values

The way that wetlands are

viewed has evolved over time:

• During settlement of the

U.S., wetlands were

considered ―bug-

infested, disease- ridden

wastelands that impeded

settlement and economic

development.

Federal policies toward wetlands has evolved

from policies and programs that encouraged

drainage and filling of wetlands……

The way that wetlands are

viewed has evolved over time:

• The public, especially user groups, began to

recognize the resource values of wetlands.

• Concern began to grow in the 1950’s and 1960’s

over an alarming rate of wetland loss in the U.S.

• Consequently, appreciation of wetlands

increased…

– ‖don’t it always seem to go you don’t know what you’ve

got ‘til its gone‖—Joni Mitchell, Big Yellow Taxi

More recent programs and legislation

provide indirect protection and incentives to

conserve and restore wetlands;

• Section 404 of the Clean Water Act

• Conservation provisions of the 1985-2000 Farm Bills (Food Security Acts)

• Coastal Zone Management Act

• No net loss policies (executive orders)

• North American Wetlands Conservation Act

Wait a minute…

what are wetlands anyway?

• Until the 1980’s, wetlands were mostly

viewed as a transitional stage in a sequence of

ecosystem development (i.e. succession) from

pond/lake to climax grassland or forest.

• Wetland science emerged as a subdiscipline

of ecology in the late 1970’s;

– conservation groups became concerned over

wetlands losses,

– public began to appreciate the unique

ecological functions and social values that

wetlands provide,

– driven by policy debate, managers needed a

scientifically-based definition and criteria to

delineate and classify wetlands.

Wetland scientists and others now recognize

wetlands as distinct ecosystems that are

highly connected with, but distinct from

aquatic and terrestrial ecosystems.

Nevertheless, delineating

the boundaries between

wetlands and aquatic and

terrestrial systems

involves drawing a

somewhat arbitrary (but

scientifically defensible)

line along an ecological

continuum.

Definition and delineation of

wetlands is difficult and highly

contentious:

We would like to have a clear

black and white definition of wetlands,

with criteria that can be unambiguously

applied in any situation.

Our definition and criteria are used to

make decisions about what is right and

wrong with respect to how society

protects and utilizes wetlands.

Definition and delineation of

wetlands is difficult and highly

contentious:

What we have instead are somewhat

complicated and highly nuanced

definitions and criteria for wetlands

delineation that are difficult to apply

unambiguously in any situation.

Wetlands definition and criteria,

although grounded in science seek

some balance among competing social

demands (protection vs. utilization).

How do we define (delineate)

wetlands? Wetland scientists

provide the answer (3-legged stool).

• Hydrology

• Hydric soils

• Hydrophytes

Let’s briefly examine each of these criteria:

Hydrology Criterion

• Lands that are inundated or saturated to within 18‖ of the soil surface for > 7 consecutive days during the growing season.

Hydric Soil Criterion

• Soils, recognizable by their color, physical structure, and chemical characteristics, that have developed under anoxic conditions associated with saturation or inundation by water.

Hydrophytic Vegetation Criterion

• Lands that support a preponderance of

plants that are adapted to growing under

conditions of substrate inundation or

saturation.

The devil is in the details:

specific criteria to satisfy different

purposes:

Scientific definition (USFWS)

• serves an heuristic purpose

• objectively broad

• one or more criteria must be present

• generally liberal

• Parameters tied to function (e.g. 7 days inundation.

Regulatory definition (USACE)

• serves social, political, or economic purposes

• subjectively narrowed

• all three criteria must be present

• more restrictive parameters (e.g. 21 days inundation)

• The issue of wetlands definition and delineation illustrates the interplay of science, public policy and values.

– liberal, strictly scientifically-based definition provides maximal protection of wetlands, but with social, economic, and political costs.

– USFWS definition describes the unique conditions under which wetlands perform ecological functions that humans value.

– more restrictive definition preserves individual property rights, allows more flexibility to accommodate social and economic pressures, but at the cost of certain ecological services and resource values that are not accounted for in our economic system.

OK, makes sense, but why these

three criteria?

• Let’s look at what happens when a soil is

saturated or inundated:

– water acts as a barrier to diffusion of O2 into

pore space from the atmosphere

– aerobic respiration by soil organisms depletes

O2 within 7 days when the temperature is above

biological zero

• Respiration continues via alternative

pathways in which soil microbes oxidize

organic matter by using a sequence of

different molecules as electron acceptors.

– oxidation-reduction potential declines as soil

becomes more anoxic and alternative electron

acceptors are used in anaerobic respiration

– this changes the chemical and physical

properties of the soil (leaching of ferrous

compounds, accumulation of nitrous and

sulfurous compounds, methane, etc.)

OK, so what happens to terrestrial

plants and animals?

• Macrophytes and metazoan animals respire

aerobically (O2 is final e- acceptor in

respiration).

• Reduced compounds are generally more

toxic than oxidized compounds.

• So lack of O2 is a stressor that wetland-

dependent species must be adapted to.

Some adaptations of wetlands-

dependent species

Plants

• rigid, highly vascularized

stems

• active diffusion of O2 to roots

• carbohydrate storage

• alternative metabolic

pathways

• reproductive strategies—

seed dispersal, germination

and growth requirements

Animals

• morphology-locomotion in

water

• morphology-feeding in water

• anaerobic respiration (diving

reflex)

• seasonal movement and/or

aestivation strategies

• reproductive strategies—

oviposition and development

and care of young

What are the ecological

functions (services) and resource

values that wetlands provide?

Wetlands dogma:

…wetlands are among the most productive

ecosystems in the world…

…wetlands act as ―sponges‖ on the landscape…

…wetlands are the ―kidneys‖ of the landscape…

…wetlands are hotspots of biodiversity…

A caveat and caution

…..’believe none of what you hear and only half of what you see’…..

(including this lecture)

Purported ecological functions

and values of wetlands:• Hydrology: discharge and

recharge groundwater, regulate surface water flows and sedimentation;

• Nutrient cycling: transform or sequester nutrients and chemical contaminants;

• Habitat: support biological diversity, recreation;

• Trophic support: provide food and fiber products.

Hydrology Functions:

regulation of surface water flow

and sedimentation:

Hydrology Functions:

groundwater recharge:

Water Quality Functions:

biogeochemical cycling:

Habitat and trophic support

functions:

Wetlands are detrital-

based systems.

Decaying plant

matter supports

invertebrates that

are utilized by

consumers.

Habitat and trophic support

functions:

Moist Shallow Deep Open

soil marsh marsh water

Plant diversity 2 1 3 4

Invasive species 1 2 3 4

Wildlife diversity 3 1 2 4

Migratory birds 1 2 3 4

Resident birds 3 2 1 4

Herptiles 2 1 3 4

Furbearers 3 2 1 4

Fish 4 3 2 1

1 = high, 4 = low