Principles of Wetlands Ecology

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……

…. to a federal policy of “no net loss” of wetlands, including subsidy and technical assistance to restore and create wetlands.

Estimated rate of wetlands loss

1950s – 1990s

Wetlands Status and Trends 2000

458,000

Average annual net wetland loss for the Average annual net wetland loss for the conterminous United Statesconterminous United States

1950s – 70s1950s – 70s 1980s – 90s1980s – 90s1970s – 80s1970s – 80s

290,000

58,500

Acres

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 toconserve 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 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

• Plants

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.

Vegetation Criterion

• Lands that support a preponderance of plants that are adapted to growing under conditions of substrate inundation or saturation.

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 freezing

• 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…