Environmental Resources III · •Wetland science emerged as a subdiscipline of ecology in the late...
Transcript of Environmental Resources III · •Wetland science emerged as a subdiscipline of ecology in the late...
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Environmental Resources IIIWetlands Ecology and Management
Mr V Zungu
Environmental Management
08 April 2011
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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
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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.
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Federal policies toward wetlands has evolved
from policies and programs that encouraged
drainage and filling of wetlands……
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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
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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
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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.
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• 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.
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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.
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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.
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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).
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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:
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Hydrology Criterion
• Lands that are inundated or saturated to within 18‖ of the soil surface for > 7 consecutive days during the growing season.
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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.
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Hydrophytic Vegetation Criterion
• Lands that support a preponderance of
plants that are adapted to growing under
conditions of substrate inundation or
saturation.
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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)
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• 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.
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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
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• 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.)
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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.
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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
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What are the ecological
functions (services) and resource
values that wetlands provide?
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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…
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A caveat and caution
…..’believe none of what you hear and only half of what you see’…..
(including this lecture)
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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.
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Hydrology Functions:
regulation of surface water flow
and sedimentation:
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Hydrology Functions:
groundwater recharge:
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Water Quality Functions:
biogeochemical cycling:
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Habitat and trophic support
functions:
Wetlands are detrital-
based systems.
Decaying plant
matter supports
invertebrates that
are utilized by
consumers.
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Habitat and trophic support
functions:
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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
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