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ECOLOGY OF WETLANDS

by

Prof. A. Balasubramanian

Centre for Advanced Studies in Earth Science

University of Mysore, India

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Introduction:

Earth’s surface has uneven topography. The

elevations and depressions form a wide

variety of landscapes and ecosystems.

Topography, water availability and climatic

conditions control almost all the ecosystems

in the world. Among all terrestrial

ecosystems, like Mountains, Deserts, and

forests, we have yet another ecosystem to be

studied that is the wetland ecosystem.

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As the names implies, these are wet lands.

Such lands exist along the borders of water

courses and water bodies, in topographically

low lying areas. Wetlands are the interfaces

between land and water. Some good

watersheds may have large undeveloped

wetlands that store the flood waters and

help a lot of fauna and flora to survive.

Once upon a time, these lands were

considered as wastelands.

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Gradually, due to urbanization, most of them

are getting converted into urban, agricultural

or industrial lands.

Recenlty, their importance as a highly

productive ecosystem has been recognized

by the people in several countries.

Degrading wetlands are to be restored.

Hence, it is necessary to understand the

environmental conditions of wetlands.

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In this episode. the following aspects are

discussed::

1. An overview of Wetlands

2. Types of wetlands

3. Hydrological conditions

4. Biological functions

5. Site-specific conditions

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1. AN OVERVIEW OF WETLANDS

Wetlands are defined as "lands in low-lying

plains, Dominated by hydric soils;

inundated or saturated by surface water or

ground water and promoting only

hydrophytic vegetation”.

These zones are found between dry land and

waterlogged zones along the edges of

streams, rivers, lakes, and coastlines.

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Wetlands are integral parts of a watershed.

Their position in the landscape is influenced

by and influences the characteristics of a

watershed. Wetlands are characterized by

the following factors:

a. Topographically low land

b. Permanent inundation

c. Hydric soils

d. Reducing environment (absence of free

oxygen within the soil profile)

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e. Hydrophytic vegetation at shallow and

deep waters

Wetlands can function as

nutrient sinks, temporary water storage

areas, groundwater recharge areas, and

critical wildlife habitat.

Natural and anthropogenic (human-induced)

activities within a watershed influence the

functions of natural wetlands.

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For example, by changing the hydrology of

a wetland, the water retention and sediment

attenuation functions can be lost, resulting in

downstream hydrological and water quality

impacts; or vegetative species and

composition within and surrounding a

wetland might change, resulting in habitat

quality changes.

Topographically, they are saucer or bowl

shaped depressions.

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The surface area will change as water is

added through rainfall and runoff or lost due

to evaporation, plant transpiration and deep

seepage.

Saucer-shaped features tend to be temporary

and seasonal with large areas exposed as

water is lost (wading bird habitat).

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Bowl shaped features tend to be semi-

permanent to permanent with smaller

exposed areas as water is lost, but providing

long-term water to support bird species and

amphibians.

Wetlands are inundated or saturated within

major portions of the root zone (usually

within 12 inches of the surface) during the

growing season.

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The prolonged presence of water creates

conditions that favor the growth of specially

adapted plants called hydrophytes and

promote the development of characteristic

wetland soils called hydric soils.

Wetlands can be found in nearly every

county and climatic zone.

Some are wet all of the time and some may

appear to be dry most of the time.

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2. TYPES OF WETLANDS

All Wetlands are not alike. They vary

depending upon the location in a watershed

and also with reference to their abiotic

factors.

Differences in the characteristics like

hydrology, water chemistry,biological

functions, vegetation,site-specific factors,

the climate and geology of the region,

landscape position, and soils.

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create more type of wetlands.

These factors are not independent, but form

a complex interrelationship to make each

wetland type a unique one.

Based on their physical, i.e.

geomorphological conditions, chemical, and

biological characteristics wetlands are

classified into various types.

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In general,

Two major categories of wetlands are

recognized as:

a) Inland wetlands.

b) Coastal wetlands.

Inland wetlands are non-tidal environments

and coastal wetlands may have a tidal

influence.

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The Inland wetlands include:

a. Inland freshwater marshes

b. Peatlands

c. Deepwater swamps

d. Riparian wetlands

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The Coastal wetlands include:

e. Tidal salt marshes

f. Tidal freshwater marshes

g. Mangrove wetlands

Inland wetlands are most common

on floodplains along rivers and streams, and

also in isolated depressions surrounded by

dry land.

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They are found along the margins of lakes

and ponds, and in other low-lying areas

where the groundwater intercepts the soil

surface or where the precipitation is more to

saturate the soil always.

Inland wetlands include marshes and wet

meadows dominated by herbaceous plants,

swamps dominated by shrubs, and wooded

swamps dominated by trees.

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These areas are characterized by sluggish or

standing water that can create an open-water

habitat for some wildlife.

Coastal wetlands are areas bordering

coastlines.

They are closely linked to some estuaries,

where the sea water mixes with the fresh

water bodies to form an environment of

varying salinities.

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The salt water and the fluctuating water

levels (due to tidal action) combine to create

a rather difficult environment for most

plants.

Many shallow coastal areas are unvegetated

mud flats or sand flats.

The Cowardin classification system uses a

salinity criterion of 0.5 ppt ocean-derived

salinity to differentiate between estuarine

and freshwater wetlands.

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The differences in salinity will be reflected

in the species composition of plants and

animals.

Wetlands are further divided into different

types based on the soil type and plant life.

They are:

bogs, Fens

swamps, and marshes.

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A bog is an acidic peat land (peat bog).

Bogs are freshwater wetlands, often formed

in old glacial lakes, characterized by spongy

peat deposits, evergreen trees and shrubs,

and a floor covered by a thick carpet of

sphagnum moss.

A fen is a freshwater peat land with

chemically basic (which roughly means

alkaline) ground water. This means that it

contains a moderate or high proportion of

hydroxyl ions (pH value greater than 7).

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Fens are covered mostly by grasses, sedges,

reeds, and wildflowers.

A fresh-water marsh's main feature is its

openness, with only low-growing or

"emergent" plants.

It may include grasses, rushes, reeds, typhas,

sedges, and other herbaceous plants

(possibly with low-growing woody plants)

in a context of shallow water.

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A coastal salt marsh may be associated with

estuaries and along waterways between

coastal barrier islands and the inner coast.

The plants may extend from reed in mildly

brackish water to salicornia on otherwise

bare marine mud.

It may be converted to human use as pasture

(salting) or for salt production (saltern).

A swamp is wetland with more open water

surface and deeper water than a marsh.

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In some countries like, it is dominated by

trees and woody bushes rather than grasses

and low herbs.

In Africa, swamps may be dominated by

papyrus.

A mangrove swamp or mangal is a salt or

brackish water environment dominated by

the mangrove species of tree, such as

Sonneratia.

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The Intertidal wetlands provide an excellent

example of invasion, modification and

succession. The invasion and succession

process is establishment of seagrasses.

These help stabilize sediment and increase

sediment capture rates. The trapped

sediment gradually develops into mud flats.

Mud flat organisms become established

encouraging other life forms changing the

organic composition of the soils.

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Tidal wetlands are further classified into:

1. Sub-tidal - The substrate is

permanently flooded with tidal water.

2. Irregularly Exposed- The land surface

is exposed by tides less often than sub-tidal.

3. Regularly Flooded- Tidal water

alternately floods and exposes the land

surface at least once a day.

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4. Irregularly Flooded- Tidal water

floods the land surface less often than the

previous type.

Non-tidal Wetlands

1. Permanently Flooded- Water covers

the land surface throughout the year in all

years. Vegetation is composed of obligate

hydrophytes.

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2. Intermittently Exposed-. Surface

water is present throughout the year, except,

in years of extreme drought.

3. Semi-permanently Flooded- Surface

water persists throughout the growing

season in most years.

When surface water is absent, the water

table is usually at or very near the land

surface.

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4. Seasonally Flooded- Surface water is

present for extended periods, especially

early in the growing season, but is absent by

the end of the season in most years.

When surface water is absent, the water

table is often near the land surface.

5. Saturated- The substrate is fully

saturated upto the surface during the

growing season, but no surface water is

seen.

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6. Temporarily Flooded- Surface water

is present for brief periods during the

growing season, but the water table usually

lies well below the soil surface for most of

the season.

7. Intermittently Flooded- The substrate

is usually exposed, but surface water is

present for variable periods without

detectable seasonal periodicity. Weeks,

months, or even years may intervene

between periods of inundation.

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The dominant plant communities under this

regime may change with reference to the

change in soil moisture.

8. Artificially Flooded- The amount and

duration of flooding are controlled by means

of pumps or siphons in combination with

dikes or dams. Vegetation present cannot be

considered a reliable indicator of the water

regime.

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Wetlands are permanent in some places or

seasonal in some places.

They may be wet only periodically.

The quantity of water present and the timing

of its presence in part determine the

functions of a wetland and its role in the

environment.

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5. HYDROLOGICAL CONDITIONS

The hydrologic conditions in a wetland

affect the abiotic factors such as

salinity, soil oxygen availability, and

nutrient availability.

These factors in turn greatly influence the

flora and fauna present in a wetland.

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Water depth and the natural hydroperiod in

a wetland also directly influence

vegetative composition and density,

primary productivity, organic accumulation,

nutrient cycling and availability, and

the types and density of aquatic and

terrestrial fauna in a wetland.

Stormwater inflows into wetlands can

directly affect the natural hydrology of

wetlands by changing water depths and

altering the hydroperiod of the ecosystems.

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The impacts of stormwater runoff on the

water quality in a wetland are dependent on

the volume and composition of the

stormwater.

Pollutants found in runoff from urban areas

tend to include sediments,

oxygen-demanding substances, nutrients,

heavy metals, pesticides,hydrocarbons,

trash and debris.

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Changes in turbidity,oxygen levels, and

water temperature in a wetland can have

direct impacts on the flora and fauna in the

wetland.

In addition, the assimilation of heavy metals,

pesticides, and hydrocarbons associated with

stormwater runoff by the flora and fauna in a

wetland can result in negative impacts to the

ecological characteristics of the wetland.

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The periods of saturation or dryout in

wetlands have strong implications for the

characteristic structures that develop in

wetlands. This is known as hydroperiod.

Each wetland type exhibits a unique

hydroperiod.

A Hydroperiod is defined as the periodic or

regular occurrence of flooding and/or

saturated soil conditions.

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A hydroperiod is calculated as the ratio of

flood duration divided by flood frequency

over a given period of time.

The hydroperiod for a particular wetland is a

function of the water budget (i.e., inflow and

outflow water balance) and storage capacity.

It is affected by the surface contours of the

landscape and subsurface soil, geology, and

groundwater conditions.

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Since wetlands typically represent a

transition between terrestrial and open-water

ecosystems, the effects of changed

hydrology are extremely variable.

Hydrology of wetlands lead to unique

vegetation composition, but can limit or

enhance the species richness also.

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Hydrology is the most important factor in

the establishment and maintenance of

wetlands and their processes.

Precipitation, surface water inflow and

outflow, groundwater exchange, and

evapotranspiration are the major factors

influencing the hydrology of most wetlands.

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6. BIOLOGICAL FUNCTIONS

Wetlands are often called as “nurseries of

life.”

They provide the habitat for thousands of

species of aquatic and terrestrial plants and

animals.

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The Aquatic plants of wetlands are called

as hydrophytic plants or hydrophytes.

Living on or under the water surface

requires numerous special adaptations and

these plants posses those features.

These hydrophytes have several survival

characteristics:

1. A thin (or no) cuticle. The primary

function of cuticles is to prevent water loss,

thus most hydrophytes have no need for

cuticles.

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2. Stomata that are open most of the time: so

water is (abundant). This means that guard

cells on the stomata are generally inactive.

3. An increased number of stomata, that can

be on either side of leaves.

4. A less rigid structure: water pressure

supports them.

5. Large flat leaves on surface plants for

flotation.

6. Air sacs for flotation.

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7. Smaller roots: water can diffuse directly

into leaves.

8. Feathery roots: no need to support the

plant.

9. Specialized roots designed to take in

oxygen

The notable aquatic vascular plants can be

ferns or angiosperms (from both monocot

and dicot families).

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Good amount of nutrients, and primary

productivity are ideal for the development of

organisms that form the base of the food

web and feed many species of animals.

Wetlands provide unique and critical habitat

for thousands of species of animals ranging

from fish, birds, mollusks, mammals,

amphibians, reptiles and insects.

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There are many types of vegetation in

wetlands.

There are plants such as

Cattails, bulrushes, Sedges, Arrowhead,

Water Lilies, Blue Flag, and Floaters like

common duckweed.

Pondweed is also another type of plant that

grows in wetlands.

Peatland can be dominated by red maple,

silver maple, and Elm trees.

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Swamps can also have white Cedar,

Tamarack, and White Pine.

Coastal wetlands are characterized by the

following types of plant species :

1. Spartina alterniflora: Salt Marsh

Cordgrass (Smooth Cordgrass)

Salt marsh cordgrass is the most common

plant and prime indicator of a coastal

wetland. It forms 1-foot- to 8-feet-tall

meadows that grow just up to the open

water's edge.

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Lush and green in the warmer months, salt

marsh cordgrass becomes golden-brown in

the fall and dies back in the winter. Salt

marsh cordgrass is frequently flooded.

2. Juncus roemerianus:

Black Needlerush

Black needlerush has tall (3 to 5 feet)

needle-like blades in shades of dark green or

gray with sharp blackish tips.

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It grows in the higher areas of the marsh, or

where salt water completely covers the land

only during unusually high tides. In higher

elevations of the marsh, needlerush replaces

cordgrass.

3. Salicornia spp.: Glasswort

Glasswort is found throughout the marsh,

mixed in with cordgrass or on the mud flats.

Glasswort grows low to the ground (rarely

over 2 feet tall) and has short fleshy green

stubby spikes extending from a main stem.

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Glasswort looks like long green pipe

cleaners attached to a long stem. Three

species are found in coastal marshes, and

turns pink colored in the fall.

4. Distichlis spicata: Salt (or Spike) Grass.

Salt grass is a short, green, wiry grass that

lives among the salt meadow grass above

the high tide line.

5. Limonium spp.: Sea Lavender

Sea Lavender grows at the fringe of the

upper intertidal marsh.

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The plant looks delicate, with long, skinny

leaves that sprout small stems as they grow

upward. These stems are covered with tiny

purplish-white flowers in the summer and

fall.

6. Scirpus spp.: Bulrush

With its roots immersed in the mud or water,

the bulrush grows into large, thick colonies.

The plants can reach up to 10 feet tall, and

the tops are crowned with spikelets.

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7.Cladium jamaicense: Saw Grass

Saw grass grows to about 6 or 7 feet tall,

with long, slender, narrow leaves that look

like tall blades of grass. These leaves are

stiff and tough, with tiny saw teeth around

the edges. The top of saw grass has many

branches and branchlets

8. Typha spp.: Cattail

Cattails are easily recognizable by their

flower spikes, or cat tails.

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Cattail spikes can grow up to a foot long and

are densely packed with tiny brown flowers.

The cattail plant can grow to 10 feet tall.

Cattails also commonly grow outside coastal

wetlands along freshwater ponds, lakes,

rivers and ditches.

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9. Spartina patens:

Salt Meadow Grass (or Hay)

Salt meadow hay is a low- to medium-height

perennial wire-like grass, 1-foot- to 3-feet-

tall. It forms dense mats of plants just above

the high tide line.

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10. Spartina cynosuroides: Salt Reed or

Giant Cordgrass

Salt reed is a member of the same family as

salt marsh cordgrass, and they have similar

features. As its name might suggest, this

grass grows taller (up to 10 feet) and thicker

than Spartina alterniflora.

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7. SITE-SPECIFIC CONDITIONS

Changes in the volume or quality of

stormwater runoff resulting from changing

activities in a watershed can affect the

functions and values of a natural wetland by

altering the hydrologic, water quality,

and sediment or soil characteristics of a

wetland.

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Alteration of the physical and chemical

characteristics of a wetland.

This can adversely affect the biological

community and result in negative impacts to

the ecological functions of a wetland.

Wetlands and people:

Only recently have we begun to understand

the importance of the functions that

wetlands perform.

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Far from being useless, disease-ridden

places, wetlands provide values that no other

ecosystem can, including natural water

quality improvement, flood protection,

shoreline erosion control, opportunities for

recreation and aesthetic appreciation, and

natural products for our use at no cost.

Wetlands can provide one or more of these

functions.

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Protecting wetlands in turn can protect our

safety and welfare. Major Causes of Wetland Loss and Degradation are:

Human Actions

Drainage

Dredging and stream channelization

Deposition of fill material

Diking and damming

Tilling for crop production

Levees

Logging

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Mining

Construction

Runoff

Air and water pollutants

Changing nutrient levels

Releasing toxic chemicals

Introducing nonnative species

Grazing by domestic animals

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Natural Threats are:

Erosion

Land Subsidence

Sea level rise

Droughts

Hurricanes and other storms

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Education

In the past, wetlands were regarded as

wastelands.

Education campaigns have helped to change

public perceptions and foster public support

for the wetlands.

Due to their location in the catchment area,

education programs need to teach about total

catchment management programs.

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Educational /awareness programs include

guided tours for the general public, school

visits, media liaison, and information

centers.

Regardless of their name, wetlands are

valuable because they often support diverse

species of plants, wildlife, insects and fish.

Many endangered species inhabit wetlands

during part of their life cycles.

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They are often referred to as “nature’s

kidneys” because they retain and cycle

nutrients from the soil and water.

Amphibians like frogs and salamanders

often rely on wetland areas for mating,

laying eggs and early development of

young.

Wetlands are important for flood reduction

and control.

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Wetlands also help reduce erosion by

trapping soil that is washed off of farm

fields and other open areas.

Many local economies rely on wetland areas

used for wildlife and waterfowl

preservation, and hunting. In addition,

some wetlands help replenish water supplies

for local drinking water sources.

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The common threats to wetlands are:

Area development. Because of their fertile

soil and location, many wetland areas are

desirable for farming, business and housing

developments.

Other threats come from fertilizers,

herbicides and pesticides that are applied to

surrounding areas and washed into wetlands

with storm water.

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Use GIS:

Geographic Information Systems (GIS) is

used to locate potential wetland restoration

and enhancement sites. It also identifies the

type of wetland that could be restored or

enhanced as well as the type of disturbance

that has occurred at each site.

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The Wetlands Conservation Plan has several

components:

a wetlands inventory;

functional assessment;

wetland restoration;

agency coordination;

coastal area wetland policies;

local land-use planning.

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Wetlands are an important part of our

national heritage.

The economic well-being and quality of life

largely depend on a nation's wealth of

natural resources.

Wetlands are the vital link between our land

and water resources.